In bridge design, it is very necessary that bridge decks support both static and moving loads. Every component of a bridge needs to be designed to withstand the worst loading effect that could possibly arise in that part. In effect, traffic live loads should be placed where they will cause the most onerous effect on the structure. ‘Influence lines’ are a helpful tool for assessing the most severe loading condition.
An influence line represents the response of a specific element of a bridge to the effect of a moving load, such as reaction, shear force, bending moment, or axial force. It is a diagram where the value of the response at any point is equal to the effect caused by a unit load applied at that point. Influence lines provide a systematic approach for determining how the force, moment, or shear in a specific part of a structure changes as the applied load moves across the structure.
Influence lines for statically determinate structures consist of straight lines, but for indeterminate structures, they can have more complex shapes. The primary purpose of influence lines is to identify where to place live loads to achieve maximum effect.
Influence Lines for Shear in Simple Beams
Influence lines for shear at two sections of a simply supported beam are shown in Figure 1. When the summation of transverse forces to the left of a section is in the upward direction or when the summation of transverse forces to the right of the section are in the downward direction, positive shear is said to occur. For each position of the unit load, the shear force at sections 1-1 and 2-2 is determined by placing the unit force at various points.
Figure 1: Influence line for shear (Shanmugam and Narayanan, 2008)
The values provide the ordinate of the influence line, which may be used to draw the influence line diagrams for the shear force at sections 1-1 and 2-2. It should be noted that the slope of the influence line for shear on the left of the section is similar to the slope of the line on the right of the section. In other circumstances, this information can be used to draw the influence lines for shear force.
Influence Lines for Bending Moments in Simple Beams
Figure 2 shows the influence lines for the bending moment at the same sections, 1-1 and 2-2, of the simple beam under consideration in Figure 1. For a section, the moment is considered positive when the total of all the moments of the forces to the left is clockwise or when the sum to the right is counterclockwise. For various places of unit load, the values of the bending moment at sections 1-1 and 2-2 are obtained and plotted as shown in Figure 2.
Figure 2: Influence line for bending moment (Shanmugam and Narayanan, 2008)
It should be noted that a shear or bending moment diagram shows how shear or moment values change throughout the entire structure when loads are fixed in a specific position. Conversely, an influence line for shear or moment depicts how that response varies at a specific section of the structure due to the movement of a unit load from one end to the other. Influence lines are helpful in determining the magnitude of a specific response at the section where it is drawn, when the beam is subjected to various types of loading.
For instance, the shear force at section 1-1 is determined by the product of the load intensity, qo, and the net area under the influence line diagram assuming a uniform load of intensity qo per unit length operates throughout the full length of the basic beam depicted in Figure 22.
Since the net area at section 1-1 is 0.3P, the shear force there is 0.3qoP as well. The bending moment at the section is calculated from the area of the appropriate influence line diagram times the intensity of loading, qo. Therefore, the section’s bending moment is 0.08qoP2.
Solved Example
Let us consider the beam loaded as shown below. It is desirous to obtain the influence line for the support reactions, and for the internal stresses with respect to section 1-1.
In all cases, we will be taking P as unity (i.e 1.0)
(1) Influence line for support reactions
Support A Support reaction at point A (FA) = (L – x)/L At x = -L1; FA = (L + L1)/L
At x = 0; FA = 1.0
At x = L + L2; FA = (L – L – L2)/L = – L2/L
Support B Support reaction at point B (FB) = x/L At x = -L1; FB = -L1/L
At x = 0; FB = 0
At x = L; FB = 1.0
At x = L + L2; FB = (L + L2)/L
(2) Influence line for bending moment with respect to section 1-1
(0 ≤ x ≤ a) M1-1 = FA.a – P(a – x) M1-1 = [P(L – x).a]/L – P(a – x) But taking P = 1.0; = [(L – x).a]/L – (a – x)
At x = -L1; M1-1 = [(L + L1).a]/L – (a + L1) = [L1(a – L)/L] = -L1.b/L
At x = 0; M1-1 = [(L – 0).a]/L – (a – 0) = [L1(a – L)/L] = 0
At x = a; M1-1 = [(L – a).a]/L – (a – a) = [L1(a – L)/L] = a.b/L
(a ≤ x ≤ L) M1-1 = [P(L – x)a]/L
At x = a; M1-1 = [(L – a)a]/L = a.b/L
At x = L; M1-1 = [(L – L)a]/L = 0
At x = L + L2; M1-1 = [(L – L – L2)a]/L = – L2a/L
(2) Influence line for shear with respect to section 1-1 (0 ≤ x ≤ a) Q1-1 = P(L – x)/L – P = – FB = –x/L
At x = -L1; Q1-1 = L1/L
At x = 0; Q1-1 = 0
At x = a; Q1-1 = -a/L
(a ≤ x ≤ L) Q1-1 = -(P.x)/L + P = (L – x)/L
At x = a; Q1-1 = b/L
At x = L; Q1-1 = 0
At x = L + L2; Q1-1 = [(L – L – L2)]/L = -L2/L
Influence Lines for Trusses
Influence lines for support reactions and member forces can be constructed using the same approach as influence lines for various beam functions. They provide valuable information for determining the maximum load that can be applied to a truss. By analyzing the movement of a unit load across the truss, we can calculate the responses of interest at each panel point.
However, it is not necessary to calculate the member forces at every panel point, as certain parts of the influence lines can be identified as straight lines for multiple panels. Method of sections can be used to obtain the member forces in any panel of interest.
Figure 3: Influence line for trusses
The truss shown above is used as an example to explain how to construct influence lines for trusses. Passing a section 1-1 and taking into account the equilibrium of the free body diagram of one of the truss segments yields the member forces in BD, CE, and BE.
First, a unit load is applied to node C, and the force in BD is calculated by calculating the moment about node E of all forces acting on the right-hand segment of the truss, then dividing that moment by the lever arm (the distance at which the force in BD is perpendicular to node E).
The resultant value provides the influence diagram’s ordinate at C in the truss. Similar to how the force in BD for a unit load imposed at E is represented by the obtained ordinate at E. Two additional points, one at each of the supports, can be added to the influence line to complete it. The relevant influence line diagram can be finished by obtaining the force in the member CE due to the unit load applied at C and E.
The influence line for force in BE can be obtained by taking into account the horizontal component of force in the diagonal of the panel. The influence diagrams for the member forces in BD, CE, and BE are shown in Figure 3. By running an imaginary vertical section through the panel and taking moments at the junction of the diagonal and the other chord, it is possible to estimate the influence line ordinates for the force in a chord member of a ‘curved-chord’ truss.
One of the most effective methods of obtaining influence lines is by the use of the Müller–Breslau principle, which states that ‘the ordinates of the influence line for any response in a structure are equal to those of the deflection curve obtained by releasing the restraint corresponding to this response and introducing a corresponding unit displacement in the remaining structure’.
In this way, the shape of the influence lines for both statically determinate and indeterminate structures can be easily obtained, especially for beams.
Some methods for drawing influence lines are as follows:
Support reaction Remove the support and introduce a unit displacement in the direction of the corresponding reaction to the remaining structure as shown in Figure 4 for a symmetrical overhang beam.
Figure 4: Influence line for support reaction (Shanmugam and Narayanan, 2008)
Shear Make a cut at the section and introduce a unit relative translation (in the direction of positive shear) without relative rotation of the two ends at the section as shown in Figure 5.
Figure 5: Influence line for mid-span shear force (Shanmugam and Narayanan, 2008)
Bending moment Introduce a hinge at the section (releasing the bending moment) and apply bending (in the direction corresponding to positive moment) to produce a unit relative rotation of the two beam ends at the hinged section as shown in Figure 6.
Figure 6: Influence line for mid-span bending moment (Shanmugam and Narayanan, 2008)
Influence lines for continuous beams
Using the Muller–Breslau principle, the shape of the influence line of any response of a continuous beam can be sketched easily. One of the methods for beam deflection can then be used for determining the ordinates of the influence line at critical points.
Conclusion
In summary, influence lines are valuable tools in structural analysis, providing insights into the behaviour of structures under varying loads. They aid in determining critical locations, optimizing designs, evaluating load effects, and ensuring structural integrity. By utilizing influence lines, engineers can make informed decisions and design structures that are safe, efficient, and capable of withstanding the intended loads.
Reference
Shanmugam N. E. and Narayanan R. (2008). ‘Structural Analysis’ in ICE Manual of Bridge Engineering, Eds by Gerard Parke and Nigel Hewson. Thomas Telford Ltd, UK
Launched single-cell box girders are employed in situations where the bridge alignment is straight or on a constant radius curve, either vertically or horizontally. It is particularly useful for overcoming access issues or avoiding obstructions at ground level.
Typically, this method is used for bridge spans up to 60 meters, but in some cases, it has been utilized for longer spans up to 100 meters by using temporary piers to reduce the effective span length during launching. The depth of the deck must remain constant during the launching process, with a typical ratio to the launched span of 1:16 or less.
The process involves casting segments behind the abutment and pushing or pulling the deck over the piers. A designated casting area is prepared behind the abutment, where the reinforcement is assembled, concrete is poured, and launching takes place. The segments used for the bridge are usually standardized and have lengths of 20-30 meters.
Procedure for Incremental Launching of Box-girder Bridges
The launching process begins with the casting of the first segment, which is then moved forward on temporary bearings. The second segment is cast against the first, and both are incrementally moved forward. This process continues with subsequent segments being cast and the deck being moved until it reaches the opposite abutments and reaches its final position.
Incremental launching of bridge decks (http://en.vsl.cz/incremental-launching-method/)
The area behind the casting bay is used for steel fixing and placing prestressing ducts, which can progress simultaneously with other operations. When the deck is launched, the steel cage is attached to the concrete and pulled into position for concreting. The formwork system is designed to be lowered, leaving the deck on temporary supports ready for launching.
Temporary bearings, consisting of steel plates with stainless steel surfaces and laminated rubber pads, are used on each pier and in the casting area to facilitate the deck launching process. A low-friction sliding surface is created by inserting a Teflon pad between the bearing and concrete deck.
Launching devices, typically fixed to the abutments, are employed to provide the necessary thrust resistance. These devices jack up the deck slightly to grip the structure, push or pull it forward, and then drop down to release the structure and move back for another stroke.
During the launching process, the pushing force needs to increase to overcome the frictional force on the temporary bearings, which can range from 2% to 6% of the vertical load. Greater pushing forces are required when launching a deck up a slope, while a braking device is needed when launching it down a slope. The abutment is primarily responsible for resisting the launching force and must be designed to prevent sliding or overturning.
You can watch the video for the incremental launching of box girder bridges below.
Additional resistance can be achieved by providing the casting area with a ground slab as a working platform and connecting it with the abutment. Guides are fixed to the piers to ensure the deck remains properly aligned during the launching operation. Once the launching is complete, the deck is raised, and the temporary bearings are replaced by permanent bearings.
To reduce cantilever moments occurring as the deck is launched over a pier, a temporary lightweight steel launching nose can be attached to the front of the box. The length and stiffness of the launching nose are critical factors in its effectiveness, and a balance must be struck between its cost and the cost of accommodating additional moments in the deck. Typically, the launching nose length is about 60% of the span length, and its stiffness (EI) is approximately 10-15% of the concrete deck.
Alternatively, a temporary tower and stay-cables can be utilized over the front portion of the deck instead of a launching nose to reduce bending moments. The tension in the stays is adjusted as the deck passes over a pier to control the moments and forces imposed on the structure. As the deck moves over the piers, each section experiences changes in moment and shear, and the prestress design needs to account for the full range of these forces.
During the launching process, the deck needs to be strong enough to resist shear forces and the temporary bearing load under the webs as it passes over the piers. The webs are typically kept at a constant thickness, and the corners where the web meets the bottom slab are reinforced to distribute the local loads from the temporary bearings. Design considerations must also account for unevenness in the concrete surface and differential settlement of the piers and temporary supports, which generate additional moments and shears in the deck during launching.
Launching the deck creates friction in the temporary bearings, resulting in a load being applied to the top of the piers. The temporary bearings are aligned parallel to the deck, inducing a horizontal load on the piers in addition to the vertical loads. Therefore, the piers must be designed to withstand these combined horizontal and vertical loads. Providing stays or guys to the top of the piers can help reduce the effects of these horizontal loads.
Single-cell box girder bridges
Summary of procedure for incremental launching of box girder bridges
The construction methodology for incrementally launched box girder bridges involves a systematic process that can be summarized in the following steps:
Design and Planning: The initial stage involves detailed design and planning of the bridge structure, considering factors such as span lengths, segment sizes, construction sequence, and launching forces. Engineering calculations and structural analysis are performed to ensure the feasibility and integrity of the design.
Fabrication of Segments: The bridge segments, typically box-shaped girders, are prefabricated offsite. This includes the fabrication of individual segments or segments in smaller assemblies, depending on their size and transportation constraints. Quality control measures are implemented to ensure that the segments meet the required specifications and tolerances.
Construction of Piers and Abutments: The piers and abutments that will support the bridge are constructed first. These elements provide the necessary foundation and stability for the bridge structure. Precise alignment and positioning of the piers and abutments are crucial to ensure the accuracy of the bridge alignment during the launching process.
Installation of Bearings and Temporary Supports: Bearings and temporary supports are installed on the piers and abutments. Bearings allow for controlled movement and transfer of loads between the bridge and its supports. Temporary supports, such as launching nose beams and sliding bearings, are positioned to facilitate the launching process.
Incremental Launching: The prefabricated segments are transported to the construction site and assembled in a sequence along the bridge alignment. The launching process involves sliding each segment into its final position using hydraulic jacks, pushing the bridge incrementally forward. The temporary supports facilitate the sliding movement and provide stability during launching.
Post-Launch Adjustments: Once a segment is launched, adjustments may be made to ensure proper alignment, fit, and connection between segments. These adjustments may involve fine-tuning the position and alignment of the segment, as well as making necessary modifications to the temporary supports or sliding mechanisms.
Segment Connection and Completion: Once all segments are in place, they are securely connected and integrated to form a continuous bridge structure. This includes welding or bolting connections, as well as completing any required post-tensioning or grouting activities. Additional construction activities, such as deck placement, barrier installation, and finishing touches, are carried out to finalize the bridge construction.
Throughout the construction process, careful monitoring, quality control, and safety measures are implemented to ensure the structural integrity and safety of the bridge. Engineering expertise and coordination among various stakeholders, including designers, fabricators, contractors, and inspectors, are essential to successfully execute the incremental launching method for box girder bridges.
Advantages of incrementally launched box girder bridges
Access and Obstruction Avoidance: Incrementally launched box girder bridges are beneficial when there are access limitations or obstructions at ground level. By constructing the bridge in segments and launching them over piers, it allows for easier navigation around obstacles or challenging terrain.
Efficient Construction Process: The incremental launching method allows for continuous construction without the need for temporary support in the middle of the span. This can save time and reduce construction costs compared to other bridge construction methods.
Reduced Disruption: Incrementally launched box girder bridges minimize disruption to traffic and water flow during construction. The launching process avoids the need for temporary detours or interruptions in the flow of vehicles or water under the bridge.
Standardized Segments: The use of standardized segments simplifies the construction process, as the same segment lengths can be used for multiple bridge projects. This standardized approach improves efficiency and reduces design and fabrication costs.
Disadvantages of incrementally launched box girder bridges
Limited Span Length: Incrementally launched box girder bridges are typically suitable for shorter to medium spans, up to approximately 100 meters. For longer spans, additional temporary piers may be required to reduce the effective span length during launching, increasing complexity and cost.
Structural Integrity during Launching: The launching process can subject the bridge segments to increased bending moments and shear forces. Proper design and engineering are crucial to ensure the structural integrity of the bridge during the launching phase.
Specialized Equipment and Expertise: Incrementally launched box girder bridges require specialized launching equipment and expertise. The construction process demands careful coordination and precise engineering to ensure safe and successful launches.
Additional Design Considerations: Incrementally launched bridges require specific design considerations, such as accommodating differential settlement of piers and temporary supports, mitigating frictional forces on temporary bearings, and addressing variations in concrete surface. These factors increase the complexity of the design process.
Conclusion
In summary, the incremental launching of bridges involves casting the deck segments behind the abutment and pushing or pulling the deck over the piers.t This method offers a range of advantages, including reduced traffic disruption, enhanced safety, cost-effectiveness, and improved quality control.
By embracing this innovative construction technique, engineers and contractors can achieve efficient and successful outcomes in the construction of box girder bridges. As technology and construction practices continue to evolve, the incremental launching method will likely play a pivotal role in the development of future infrastructure, enabling the efficient and sustainable growth of transportation networks around the world.
An engineer may face significant challenges while designing the foundations for bridges over water, jetties, and offshore marine facilities. In the case of over-water bridges, the environment (water body) can pose more design challenges than the ground conditions (sea bed) at the bridge location. However, for bridges on land, the ground condition is the major deciding factor for the foundation design.
The loading on the foundation for bridges differs greatly from the loading for building foundations. Imposed loads are more prominent in the design of bridges than they are for buildings. They can be as much as half the dead load on highway bridges and two-thirds of the dead load on railway bridges (Tomlinson, 2001).
Traffic-related imposed loads are moving loads that can cause the bridge deck to experience strong longitudinal traction forces. Transverse forces can be induced by wind loadings, as well as by current drag, wave forces, and ship collisions in the case of river or estuary crossings. Longitudinal forces are also induced by shrinkage and temperature changes in the bridge deck.
Earthquake forces can be transmitted by the ground to bridge supports from any direction, especially when it comes to piers in deep water or high-level constructions where the mass of the displaced water must be added to that of the pier body. When whole spans are erected at ground level and hoisted or rolled onto the piers, for example, there might be a quick application of load to the foundations in addition to working loads from traffic.
Continuous-span bridges are particularly susceptible to the effects of differential foundation settlements. The determined total and differential settlements must also be taken into account in relation to the good rideability of the road surface. The intersection of the bridge and embanked approaches, as well as the joints connecting fixed and link spans, are critical places.
Factors affecting the choice of foundation for bridges over water
The following list of environmental factors explains how to choose an appropriate foundation type and construction approach.
Conditions of exposure and water depths
Bridges on open waterways of a vast estuary or bay crossing are in a hostile environment from winds and wave action, which may limit the operational period of floating construction equipment and potentially damage partially completed structures. This encourages the use of massive prefabricated components that can be quickly sunk onto a prepared bed or piled platform after being towed or transported by barges to the bridge site.
When the water level is sufficient for the unit to float, a box caisson is an appropriate design. However, weather conditions are crucial during the initial stages of towing the caisson to the site and sinking it in position. Weather-related delays should be taken into account while planning the overall construction schedule.
Towing of box caisson (source: https://www.aomi.co.jp/en/tech/cason.html)
The shallow draft bottom part of open-well caissons is floated to the construction site and buried by removing the soil from the open wells while the walls are sunk gradually. These caissons are employed in shallow water. Compared to box caissons, which can be sunk during a very brief window of favourable weather, open-well sinking construction processes are more weather-dependent.
However, it is possible to sink caissons at exposed sites by sinking the caissons from an artificial island or by deploying a jack-up barge to provide a solid working platform. The advent of heavy-lifting cranes capable of lifting a bridge pier caisson as a single item in various regions of the world has significantly reduced delays and dangers caused by weather conditions in recent years.
The use of simple and single-skin cofferdams is only appropriate for sheltered waterways. However, more efficient forms of cofferdams can be employed in conditions of moderate exposure.
Water Currents and Tides
River currents and tidal streams create scour holes when the soil at bed level is vulnerable to erosion, thereby inducing drag forces on the piers or piles. In the vicinity of cofferdams, where eddies are caused by transient factors like partially driven sheet piles, scour can be a very crucial design factor. As a caisson is lowered through the final few meters of water, mattressing can be necessary on an erodible bed to stop erosion under restricted flow circumstances.
Scouring of bridge piers/piles
When pitching bearing piles or sheet piles, the current drag forces can cause problems. Before the piles are held in place at the head by the pile cap or temporary girts, damaging oscillations of the piles may occur at some flow rates.
Rivers in flood pose a major threat to bridges Both from the perspective of lateral pressures on the abutments, piers, and superstructures as well as the potential undermining of the foundations due to the scouring impact of the water. The lateral hydrodynamic forces are calculated in a similar manner to those due to wind. Thus from;
q = ρvc2/2
(where vc is the velocity of flow in m/s), if the density of water is taken as 1000 N/m3 then the water pressure:
q = 500vc2/103[kN/m2] and P = qACD [kN]
Values of CD for various shaped piers in the USA are given in AASHTO LRFD (3rd edition) and in the UK are found in BA 59 (Highways Agency, 1994). The degree of scour depends upon many factors such as the geometry of the pier, the speed of flow and the type of soil.
Ship Collision
The cost of the foundations may increase significantly if measures are taken to reduce the possibility of bridge piers collapsing due to ship collisions. Not just the designated navigation channel is at risk. Collisions are equally likely to happen if a ship drifts outside of the designated channel. In certain large estuaries, the deep-water channel can quickly move from one side of the river to the other. Nearly every pier of a multi-span bridge may be in danger if there is a significant variation in tides.
Ships can collide with bridge piers in water
A ring of skirt piles surrounding a group of large diameter piles to prevent ships from getting wedged between individual units, an independent ring fender, or enclosing the pier by a man-made island can all be used as forms of protection for piers. Impact at any angle to the axis of the pier must be considered. The pier body can experience torsional shear from vessel collision.
Protection of bridge piers using fenders
Artificial islands should only be used in shallow water because the area around the pier needs to be big enough to allow the moving ship to ride up the slope and come to rest before the overhanging bow may hit the pier. The amount of fill material, boulder stone for wave protection, and mattressing for scour protection become unreasonably big in deep water, and the islands may block the navigation channel.
Earthquakes
Because the forces acting at a high level on the bridge superstructure combine with the forces acting on the pier body to produce strong overturning moments at the base level, earthquakes pose serious design challenges for deep-water piles. The mass of the pier itself must be multiplied by the volume of water it displaces.
In deep water, the eccentric loading on the pier base can be very high, favouring once more a long, narrow pier. Because earthquake forces can be oriented in any direction, including vertically, a circular structure may be necessary.
The liquefaction of loose to medium-dense granular soils is a result of ground shaking. With information on the soil deposit’s in-situ density and particle-size distribution, the liquefaction depth can be determined. To support the pier, piled foundations or ground treatment to densify a loose soil deposit may be necessary.
Bridge Pier Construction in Cofferdams
Shallow-water locations with sheltered or moderately exposed conditions are appropriate for the construction of bridge piers within cofferdams. Simple earth bank cofferdams can be used to build the piers in sites with very shallow water or at half-tide.
Although an overall depth of 32 m from high water to the base of the excavation was practical for the Thames Bamer foundations, sheet pile cofferdams can be built in water as deep as 15 m without too much difficulty, but the challenges increase as the depth of the water increases.
Wave action can cause damage to single-skin sheet pile cofferdams, and repeated wave impact can lead to fatigue failure of welded connections. Interconnected cells can be used to create strong cofferdams. To prevent ship collisions, the ring of cells can be left in place.
The locations where sheet piling is most advantageously used are those where there is an impermeable stratum at or below excavation level that serves as a cut-off for groundwater ingress, allowing the excavation to be pumped out and the pier foundation to be built in dry conditions. The excavation and construction of the concrete base are done underwater when a cut-off is not an option.
Bridge Pier Construction with Box Caissons
Box caissons are closed-bottomed hollow constructions that are buoyant when being towed to a bridge site and then buried onto a prepared bed by flooding valves. The top can be left open in sheltered conditions while sinking and ballasting are being done, or a closed top can be provided for towing in turbulent waters. Box caissons should not be used for foundations on weak soils or in locations where erosion might compromise the base.
They are particularly well suited for foundations on compact granular soils resistant to scour erosion or on a rock surface that has been dredged to remove loose material, levelled, and covered in a layer of crushed rock. A cement-sand grout is injected to fill the area between the bottom of the box and the blanket, and skirts are provided to allow the caisson to bed into the blanket. Due to weather conditions at an exposed site, bed preparation of a rock surface in deep water may be prone to lengthy delays.
Typical protection techniques and preparation of seafloor for box caissons (source: https://www.aomi.co.jp/en/tech/cason.html)
A stacked raft can be constructed to support the caisson in situations when the depth of the mud or loose material is too great for dredging. When lowering a huge box caisson, the final few meters are crucial. The structure’s foundation displaces a huge amount of water, and if the caisson is dropped too quickly, it may slide from its desired position. Slack water is preferred during tidal circumstances to reduce the flow velocity producing erosion in the constricting area between the caisson bottom and the bed.
Sinking can be conveniently accomplished by temporarily fastening the caisson to a moored barge and lowering the unit onto the rock blanket during a single tide. After ballasting, grout can be injected through pipes inserted in the exterior and interior walls between the caisson’s base and the blanket. A 300mm deep peripheral skirt can prevent grout from escaping the blanket’s region.
Schematics of sinking of box caisson by flooding with water (source: https://www.aomi.co.jp/en/tech/cason.html)
With the exception of the row of cells next to the shallow-water sides of the piers, where the impact from large ships was not feasible, mass concrete can be utilized to fill the cells up to the level of the capping slab. Sand could be used to fill these cells. The pier can then be constructed from the capping slab.
Bridge Pier Construction with Open-well Caissons
Open caissons (including monoliths) are suitable for foundations in rivers and waterways since soft clays, silts, sands, or gravels are easily excavated by grabbing from open wells and do not present a significant skin friction resistance to the sinking of the caissons. Since men are unable to work under compressed air at pressures higher than 350 kN/m2, open caissons are necessary when the required sinking depth exceeds the pressure of that magnitude.
Foundation for bridges: Open-well Caisson (Tomlinson, 2001)
Open caissons are inappropriate for sinking through soils containing huge rocks, tree trunks, and other obstructions. A great difficulty is encountered when it is sunk to an uneven bedrock surface. Furthermore, when they are buried in steeply sloped bedrock, they are likely to move physically out of the vertical. For bridge foundations, open caissons are useful in rivers where there is a significant seasonal level variation.
Beginning in the low-water period, caisson sinking is finished to the design founding level prior to the annual flood. When no work can be done on the bridge superstructure, the caisson can be permitted to be completely or partially covered by flood water without suffering any damage.
Open caissons are sealed after they reach the founding level by pouring a layer of concrete into the bottom of the wells. After pumping the wells empty and adding more concrete, the caissons can be filled with either clean sand or concrete or, in cases where their dead weight must be maintained low, with clean fresh water.
Support of a bridge using open-well caisson
Open caissons have the drawback that the soil or rock at the foundation level cannot typically be inspected before putting the sealing concrete because the sealing is done underwater. The wells can only occasionally be pumped dry to allow for a bottom inspection.
Another drawback is that the act of grasping loose, soft materials beneath the water causes the material to surge and inflow beneath the cutting edge, leading to significant subsidence of the ground around the caisson. Open caissons are therefore inappropriate for usage on sites where nearby structure sinking could result in damage.
Bridge Pier Construction with Pneumatic Caissons
When dredging from open wells would result in loss of ground surrounding the caisson, causing the settlement of nearby structures, pneumatic caissons are utilized instead of open-well caissons. They are also employed for sinking through uneven ground or obstruction-filled ground, where an open caisson would be more likely to tilt or refuse to continue sinking.
The ‘dry’ working chamber of pneumatic caissons has the benefit that excavation can be done by hand, and obstructions like tree trunks or boulders can be removed from under the cutting edge. Additionally, the soil beneath the foundation can be examined, and if necessary, bearing tests can be conducted in-situ. In contrast to open-well caissons, where the final excavation and sealing concrete are nearly usually completed underwater, the foundation concrete is poured in the dry.
Compared to open-well caissons, pneumatic caissons have the drawback of requiring more equipment and labour during the sinking, and the rate of sinking is often slower. Unless another method of ground-water lowering is utilized externally to the caisson, the depth of sinking is limited to 36 m below the water table due to the important restriction that men cannot work in air pressures much greater than 3.5 bar.
Dewatering wells must be situated far enough away from the caisson to be unaffected by ground movement brought on by the caisson sinking if such measures are employed to lower air pressures in the working chamber.
Pneumatic caisson (Tomlinson, 2001)
Bridge piers supported by piling
Bridge piers that are situated in water can also be supported by using precast piles that have been driven into the ocean floor. The typical approach is to position the pile heads at or above the level of the high water mark, and then to employ standard pile caps to provide support for the piers.
Typically, barges are used to transport the piles and pile drivers to the desired location in the water. The diameter and embedment length of the piles must be obtained from the geotechnical and structural design using the sea bed soil information and the anticipated loading condition. When the barge floats the piles to the required location, they are placed on the underwater surface and then driven down by the pile driver.
To ensure stability and resistance against water currents, the piles are inclined outward (battered piles), enabling them to support the lateral load of the bridge structure and withstand the forces of the water. The piles are installed in groups, with wider spacing at the bottom and closer spacing at the top, (similar to a triangular shape).
Following the pile installation, the next step involves placing pile caps on the top of the grouped piles. Pile caps serve to create a stable foundation and provide a larger surface area for the distribution of the load onto the piles. Once this is completed, the construction of the bridge pier structure can commence from the pile cap.
An additional possibility is to erect the pile caps inside of a cofferdam. Either the combined mass and bending resistance of the pile group and cap, or a separate fender structure, can provide protection against the possibility of a ship colliding with the structure.
Conclusion
Bridge foundations constructed in water require specialized techniques to ensure stability and structural integrity. These foundations are typically built using one of the following methods: cofferdams, caissons, or drilled shafts/piles.
Cofferdams are temporary structures built in the water to create a dry work area. They are often constructed using sheet piles driven into the riverbed or seabed. Once the cofferdam is in place, the water is pumped out, allowing workers to excavate the foundation and pour concrete. After the foundation is complete, the cofferdam can be removed.
Caissons are large watertight structures that are built on land and then floated into position. They are then sunk to the riverbed or seabed, creating a dry workspace. Caissons are commonly used for building bridge piers or abutments. The caisson is filled with heavy material such as concrete or stone to provide stability. Once the caisson is in place, the foundation is constructed within it.
Precast piles or drilled shafts are another method used for constructing bridge foundations in water. This technique involves drilling deep holes into the riverbed or seabed and then filling them with concrete or reinforcing steel. Alternatively, precast piles can be driven into the seabed and then joined using pile caps.
Regardless of the method used, bridge foundations in water must be designed to withstand the forces exerted by water currents, waves, and changing water levels. They often require additional measures such as scour protection to prevent erosion around the foundation.
Overall, constructing bridge foundations in water is a complex and challenging task that requires careful planning, specialized equipment, and experienced professionals. By employing the appropriate construction techniques and accounting for environmental factors, engineers can ensure the stability and longevity of the bridge structure.
References Tomlinson M. J. (2001). Foundation Design and Construction (7th Edition). Pearson Education Ltd.
Soil nailing is an in-situ technique for reinforcing, stabilizing, and retaining excavations and deep cuttings by introducing relatively small, closely spaced inclusions (typically steel bars) into a soil mass, whose face is then stabilized locally.
The result of soil nailing is a zone of reinforced ground that serves as a soil retention system. Soil nailing is utilized for temporary or permanent excavation support, tunnel portal stabilization, slope stabilization, and repair of retaining walls.
Soil nailing procedure
Applicable Soil Types
Prior to the installation of a series of nails and facing, the procedure requires the soil to be able to temporarily stand on its own on a near-vertical face. Consequently, cohesive soil or weathered limestone is best suited for soil nailing. The installation of soil nails is difficult in cohesionless granular soils, soft plastic clays, and organics/peats.
In order to successfully employ soil nailing on weathered rock, the weathering must be uniform across the rock and free of any planes of weakness. A high groundwater table, cohesionless soils, soft fine-grained soils, extremely corrosive soils, loess, loose granular soils, and land that is subjected to recurrent freeze-thaw action are all examples of soils that are not suitable for soil nailing.
Equipment
Soil nailing typically requires the use of earth-moving equipment (such as a dozer or backhoe) to excavate the soil, a drill rig to install the nails, a grout mixer and pump (for grouted nails), and a shotcrete mixer and pump (to stabilize the face with shotcrete).
Spraying shotcrete on the surface of soil nailing stabilisation
Procedure
The top-down method is usually employed in the construction of a soil nail excavation support wall. Typically, earth-moving machinery (such as a dozer or excavator) excavates the soil in increments of 3 to 6 feet (1 to 1.8 meters). Then, a drill rig is utilized to drill and grout the nails into position, typically on 3 to 6-foot (1 to 2-meter) centres. Following the installation of each row of nails, the excavated face is typically stabilized by affixing a welded wire mesh to the nails and then applying shotcrete.
Drilling for soil nailing
Materials
Typically, soil nails are steel reinforcing bars, but they can also be steel tubing, steel angles, or high-strength fibre rods. Typically, grouted fasteners are installed with a Portland cement grout slurry. The facing can be prefabricated concrete or steel panels but is typically reinforced shotcrete with welded wire mesh, rebar, or steel or polyester fibres.
Design
Soil nails are designed to increase the apparent cohesion of a soil mass by transmitting the tensile forces generated by the inclusions into the ground. The frictional interaction between the soil and steel inclusions restrains the movement of the soil. The primary engineering concern is to ensure that the ground–inclusion interaction can effectively restrain ground displacements and secure structural stability with an adequate safety factor.
There are two primary types of design techniques:
Limit equilibrium design methods
Working stress design approaches
The following factors will influence the design of soil nailing:
Strength limit: The point at which probable failure or collapse occurs is known as the limit state.
Service limit: The limit state at which excessive wall deformation results in the loss of service function.
Length and height of the retained earth.
The vertical and horizontal spacing of the soil nails.
The inclination of the soil nails
Geotechnical properties of the soil.
Length, diameter, and maximum force of the nail.
Drainage, frost penetration, wind- and hydrostatic-induced external loads.
Generally, the walls of soil nails are not designed to withstand water pore pressures. Therefore, drainage systems, such as geotextile facing or drilled-in-place relief wells and perforated plastic collection piping, are incorporated into the wall. Also crucial is surface drainage control above and behind the retaining wall.
When an existing structure is adjacent to the top of a soil nail wall, extreme caution is required. As the soil nail-reinforced mass stabilizes under strain, it tends to deflect slightly. This movement may result in structural damage to the adjacent building.
Construction of soil nailing
Quality Assurance and Quality Control
The locations and lengths of the nails must be monitored and recorded. Additionally, the grout used in the installation of grouted nails can be sampled and tested to ensure that it exceeds the specified strength. Test nails can also be subjected to tension tests to corroborate that the design bond has been achieved.
Advantages and Disadvantages of soil nailing
The following are a few benefits of employing soil nails:
They are very useful in constrained sites with limited access.
Less damage is done to the environment.
They may be installed quickly and easily.
Fewer materials and shoring are used.
They can be applied to new buildings, temporary structures, or remodelling projects because they are adaptable enough.
There are no restrictions on height.
A few drawbacks of employing soil nails are as follows:
For places with a high water table, they are unsuitable.
High soil nail density may be necessary for soils with poor shear strength.
They are unsuitable for long-term use in delicate and large-scale soils.
Detailed design in the context of buildings and structures refers to the phase of the design process where the overall design concept is developed further and translated into precise, detailed specifications and drawings. This stage follows the schematic/conceptual design phase and precedes the preparation of construction documents and drawings.
In a global sense, the “building design” process is a long-term activity that begins with the decision of the client/owner to construct a building. Interestingly, the process continues until all those requirements are met, the building serves its purpose and is eventually demolished or recycled for a different purpose.
There are a lot of stakeholders involved in this process, ranging from users to engineers. The majority of these actors typically participate in one of the sub-processes. A process cannot be concluded successfully, however, if all subprocesses are not coordinated and combined by an actor.
In the building construction process, the “architect” is primarily responsible for coordination. In addition, the architect creates a concept for the specified requirements, designs and communicates his design concept to the contractor, and oversees the construction process to ensure that the building is constructed according to his design.
The typical processes involved in the design of a building are;
Project Definition and Programming: This initial step involves establishing the project goals, requirements, and constraints. It includes understanding the purpose of the building, the intended users, functional needs, site conditions, budget, and any legal or regulatory considerations.
Site Analysis/Feasibility Study: A thorough analysis of the building site is conducted to understand its context, topography, climate, utilities, environmental factors, and any potential limitations or opportunities presented by the site.
Conceptual Design: During this stage, the architect or design team develops the initial design concepts. They explore various ideas, spatial arrangements, and forms that respond to the project requirements and site analysis. Sketches, diagrams, and 3D models may be used to communicate and refine these design concepts.
Schematic Design: Building upon the conceptual design, the schematic design phase involves further development and refinement of the chosen design direction. Floor plans, elevations, sections, and other drawings are created to illustrate the overall design intent. Materials, systems, and basic spatial relationships are considered.
Design Development/Detailed Design: In this stage, the design is fleshed out in more detail. The architect works on refining the layout and design of various building components, including structural systems, mechanical and electrical systems, interior finishes, and exterior materials. Coordination with engineers and other consultants must take place during this phase.
Construction Documentation: The design intent is translated into a comprehensive set of drawings and specifications known as construction documents or blueprints. These documents provide the necessary information for contractors to accurately price, permit, and construct the building. They include detailed plans, sections, elevations, schedules, specifications, and other technical details.
Typical conceptual development of a building by an architect
Detailed Design
Through the provision of detailed drawings, sections, and general arrangement drawings, the detailed design phase specifies the actual geometry/dimensions of members, foundation details, structural details, roofing details, spatial arrangement, material specifications, and tolerances of each and every element of the building or structure. The procedure of refining and expanding the conceptual design phase of a building to the point where it is ready for construction is called ‘detailed design’.
During the detailed design phase, the focus is on refining and expanding upon the initial design ideas and decisions made in the earlier stages. The goal is to ensure that all aspects of the building or structure are thoroughly considered and addressed, including architectural, structural, mechanical, electrical, plumbing, and other systems.
As the design team learns more about the impact of design decisions on the building’s performance, reliability, and cost, design compromises are made. In addition, the design team learns more about the availability of materials and expertise, cultural differences, etc enabling it to modify and refine the designs and, if necessary, the building design requirements.
Furthermore, during detailed design, designers delve deeply into each element of the building to define its features and arrangement, resulting in a design that facilitates the efficient construction of the structure. It also contains the specifications for all purchased components, including preferable suppliers and material specifications. This phase produces a comprehensive and accurate physical description of every element of the building.
A typical detailed design drawing of a steel roof framing
Key aspects of detailed design for a building project
Here are some key aspects typically covered in the detailed design of buildings/structures:
Architectural Design: Detailed floor plans, elevations, and sections are created to accurately represent the layout and appearance of the building. The design of each space, including rooms, circulation areas, entrances, and exits, is refined. Material selections, finishes, and interior details are specified.
Structural Design: The structural system of the building is designed in detail, including the foundations, columns, beams, slabs, and other structural elements. Load calculations, structural analysis, and the selection of appropriate materials are carried out. The design ensures that the structure is safe, stable, and capable of withstanding anticipated loads and environmental conditions.
Mechanical, Electrical, and Plumbing (MEP) Systems: Detailed designs for mechanical, electrical, and plumbing systems are developed. This includes HVAC (heating, ventilation, and air conditioning), electrical power and lighting systems, plumbing and sanitary systems, fire protection systems, and other related systems. The design considers energy efficiency, code compliance, equipment selection, and coordination with other building systems.
Sustainability and Energy Efficiency: Detailed design may include incorporating sustainable design principles and energy-efficient strategies into the building’s systems and materials. This could involve optimizing insulation, selecting efficient equipment, incorporating renewable energy sources, designing for natural daylighting and ventilation, and considering water conservation measures.
Accessibility and Universal Design: Detailed design addresses accessibility requirements to ensure that the building is inclusive and accessible to all users. This involves considering features such as ramps, elevators, accessible restrooms, handrails, signage, and other elements that comply with applicable accessibility standards and codes.
Coordination and Integration: Detailed design involves close coordination and integration among various design disciplines. Architects, structural engineers, MEP engineers, and other consultants work together to ensure that their respective designs align and that potential clashes or conflicts are resolved. This coordination is crucial for the efficient and effective construction of the building.
The output of the detailed design phase typically includes detailed drawings, specifications, calculations, and other technical documentation that form the basis for the construction documents. These detailed designs provide the necessary instructions for contractors and builders to accurately execute the construction of the building or structure according to the intended design.
Requirements of a Detailed Design
The detailed design of a structure requires a necessary condition in order to be draftable. Excellent understanding of the construction process and technical methodologies based on architectural and scientific principles. Designers with actual site/construction experience usually produce better designs.
For detailed design, it is important to know that the theoretical knowledge of Civil Engineering/Architecture, which are prerequisites for design drawings proposals to comply with the regulations and building codes, is insufficient. Without construction experience, a detailed design will be practically impossible to implement.
A well-detailed design should ensure the following in a building project;
(1) Avoidance of exceeding the initial budget estimate. (2) Ability to control the quality of the entire project undertakings (3) Avoidance of misunderstandings in the agreement and work scope. (4) Effective workflow. (5) A clear and sufficient level of project supervision. (6) The building results precisely as the Owner had envisioned. (7) Effectiveness, dependability, and on-time delivery of the project. (8) Due to the fact that Purchase Orders are well-known from the beginning of the project, on-time delivery is ensured. (9) Seamless collaboration between all the stakeholders in the project.
Conclusion
Detailed design is the refined development of conceptual ideas for a building project, leading to the provision of adequate construction details, material specifications, and construction procedures depicted in drawings. Without detailed design, problems will arise during construction that may require immediate resolution.
This frequently results in malfunctions, cost increases, and detuning. The detailed design ensures that the proposed budget for the proposed building is founded on facts instead of assumptions. This ensures that the owner has a “locked” total price by the conclusion of the project and that there are no disagreements or misunderstandings with the contractor.
The aesthetics and architecture of every building project should meet the owner’s precise specifications. Elegant architecture is comprised of the textures, materials, thicknesses, and cross-sections of every building component. Detail design ensures that the final result is consistent with your own aesthetics, ergonomics, functionality, and usability, as everyone’s aesthetic preferences differ.
Construction estimation services are professional services that provide accurate and detailed cost estimates for construction projects. These services are essential in the construction industry as they play a paramount role in assuring the conquest of any construction project.
Construction estimation services typically involve a team of specialists who use their expertise and knowledge to assess the expenses associated with a construction project. They consider various factors, such as the cost of materials, labour, equipment, permits, and other fees related to the project. Based on this evaluation, they provide a detailed cost estimate that gives the project owner an exact picture of its cost.
One of the main reasons why construction estimation services are essential is that they help project owners make informed decisions about their construction projects. With an accurate cost estimate, project owners can determine whether a project is feasible and whether it fits within their budget. This, in turn, helps avoid cost overruns and delays, which can harm the project’s success.
Choosing the Right Construction Estimation Service for Your Project
Choosing the exemplary construction estimation service for your project is a crucial decision that can impact the success of your project. A construction estimator is responsible for evaluating the cost of a construction project and providing an accurate estimate for the client. When choosing the exemplary construction estimation service for your project, there are several aspects to weigh.
Firstly, it is essential to consider the experience and expertise of the construction estimator. A construction estimator with extensive experience in the field will better understand the project requirements and potential challenges, which can result in a more accurate cost estimate. Additionally, an experienced estimator can provide valuable insights and suggestions to help optimize the project and reduce costs.
Secondly, ensuring that the construction estimation service has a proven path record of supplying accurate estimates is essential. Ask for contacts and testimonials from prior clients to verify the estimates’ accuracy. A reputable construction estimation service will be transparent about its estimating process and provide a detailed breakdown of costs.
Thirdly, it is crucial to consider the communication skills of the construction estimator. A good estimator should be capable of communicating virtually with consumers and other stakeholders concerned with the project. They should be competent in clarifying problematic concepts concisely and be responsive to any questions or concerns the client raises.
Fourthly, it is crucial to consider the technology and tools used by the construction estimation service. A modern estimator should use advanced software and tools to ensure accuracy and efficiency in the estimating process. They must also be up-to-date with the most delinquent initiative trends and developments.
The Benefits of Outsourcing Estimation Services
Outsourcing construction estimation services can offer numerous benefits to companies in the construction industry. Corporations in the building industry can aid in outsourcing construction estimation services in multiple ways.
First and foremost, outsourcing allows companies to access specialized expertise without hiring additional staff. Estimation involves complex calculations and requires specific knowledge and skills. By outsourcing, companies can access the expertise of professionals specializing in construction estimation and with years of experience in the field. This can result in more accurate estimates and better project outcomes.
Secondly, outsourcing can help companies save time and money. Creating accurate construction estimates is a time-consuming process that requires a significant amount of resources. By outsourcing, companies can free up their staff’s time to focus on other essential tasks. Additionally, outsourcing can help companies save money by reducing overhead costs associated with maintaining an in-house estimation team.
Thirdly, outsourcing can provide companies with flexibility. Construction projects are often unpredictable, and the demand for estimation services can vary greatly depending on project requirements. It permits corporations to climb up or down their estimation services as needed without worrying about hiring or firing staff.
Finally, outsourcing can help companies stay up-to-date with industry trends and technologies. Estimation services providers invest heavily in research and development to stay ahead of the competition. By outsourcing, companies can benefit from the latest tools and technologies used in construction estimation without investing in them.
Understanding the Different Types of Construction Estimation Services
Several construction estimation services are available, each with a unique approach. Let’s assume a nearer eye on these services.
Conceptual Estimating Conceptual estimating is the first step in the estimation process, which provides a rough estimate of the project cost before any detailed design work is done. This estimation is based on the task dimensions, site conditions, and the client’s requirements. Conceptual estimates are often used to evaluate the feasibility of a project before proceeding with detailed design work.
Preliminary Estimating Preliminary estimating involves a more detailed project analysis and is often used to determine the feasibility of various design options. Preliminary estimates include a breakdown of costs by major systems, such as structural, mechanical, electrical, and plumbing. This type of estimation helps to identify potential cost savings and to establish the project’s budget.
Detailed Estimating Detailed estimating is the most comprehensive type of estimation, providing a detailed breakdown of all costs associated with the project. This type of estimation is often used to prepare bids or negotiate contracts with subcontractors. Detailed estimates include thoroughly analyzing materials, labour, equipment, and overhead costs.
Design-Build Estimating Design-build estimating is a method that integrates the format and construction phases of a project into a single entity. In this approach, the design and construction teams work together to develop a cost-effective design meeting project requirements. This type of estimation typically provides a more accurate estimate of the project cost and helps to avoid potential design conflicts.
Construction Management Estimating Construction management estimating involves a professional construction manager overseeing the entire project, including the design, procurement, and construction phases. This type of estimation provides a comprehensive analysis of all project costs and aids in confirming that the project remains on plan and within budget.
Conclusion
In conclusion, estimation services are crucial in the construction industry by providing accurate and reliable project cost estimates. These services are essential for project planning, budgeting, and decision-making processes.
By utilizing estimation services, construction companies can assess the financial feasibility of their projects, identify potential risks and challenges, and make informed decisions regarding resource allocation and project scheduling. Estimation services help in ensuring that projects are completed within the allocated budget and timeline, minimizing the chances of cost overruns and delays.
Fibre-reinforced polymer (FRP), commonly known as fibre-reinforced plastic, is a composite material comprised of a polymer matrix reinforced with fibres. Due to its simplicity of use and unique physical properties, fibre-reinforced polymer (FRP) has emerged as one of the most widely used techniques for repairing and renovating concrete infrastructure.
The fibres in the composite provide the required strength and stiffness and typically carry the majority of applied loads, while the polymer matrix functions to bind and protect the fibres as well as to enable the transfer of shear stresses from fibre to fibre.
Although other fibres like paper, wood, or asbestos have occasionally been utilized, glass, carbon, aramid and synthetic fibres are the most common types of fibre. The polymer is typically epoxy, vinylester, or polyester thermosetting plastic. FRP composites are nonconductive, noncorrosive, and lightweight materials with exceptionally high strength qualities. FRPs are frequently used in the construction, automotive, marine, and aerospace industries.
Composite Materials
Composite materials typically consist of two or more constituent materials that have very different physical or chemical properties yet continue to exist separately and independently inside the final structure. More often than not, the complimentary behaviour/action of the different materials defines the properties of the composite. Composite materials can be engineered or naturally occurring. Most composites have strong, stiff fibres in a softer, less rigid matrix.
Usually, the aim of engineered composite materials is to produce a component that is stiff and strong, and often times, with a low density. Glass or carbon fibres are frequently found in thermosetting polymer matrices used in commercial materials like epoxy or polyester resins. Since they can be moulded after initial production, thermoplastic polymers may occasionally be preferable.
There are further categories of composites where the matrix is made of metal or ceramic. Furthermore, the reasons for adding the fibres (or, in some cases, particles) to these composites are frequently quite complex; for instance, improvement in resistance to creep, wear, thermal stability, fracture toughness etc. may be desired.
Fibre-reinforced Polymers
Fibre-reinforced polymer composite materials are used in almost every type of advanced engineering structure, including aeroplanes, helicopters, spacecraft, boats, ships, and offshore platforms, as well as cars, sporting goods, machinery for processing chemicals, and civil infrastructure like bridges and buildings.
As these materials are employed more often in their present industries and start to dominate relatively new areas like those for biomedical devices and civil structures, their use is expanding at a remarkable pace. The construction industry accounts for about 26% of the FRP market share by application.
Figure 1:Market share of Fibre-Reinforced Polymer (FRP) by application
The creation of new cutting-edge forms of fibre-reinforced polymer materials has been a major element in the growth of composite applications in recent years. This includes innovative reinforcing techniques using carbon nanotubes and nanoparticles as well as advancements in high-performance resin systems.
The fibre-reinforced polymer composites (FRPs), which are made of classic civil engineering materials like concrete and steel, are increasingly being evaluated as an improvement to and/or replacement for infrastructure components or systems. In the structural engineering and building construction industry, three FRP types are typically used:
Fibre-reinforced polymer profiles for new construction
Fibre-reinforced polymer rebars, and
Fibre-reinforced polymer strengthening systems
FRP composites are easy to produce, lightweight, non-corrosive, have high specific strength and stiffness, and may be customized to meet performance needs. FRP composites have been used in new construction and structure rehabilitation due to their beneficial properties. They are used as reinforcement in concrete, bridge decks, modular structures, formwork, and external reinforcement for strengthening and seismic upgrades.
FRP Reinforcements
Numerous research studies worldwide by professional associations and laboratories worldwide have actively investigated the use of fibre-reinforced polymer (FRP) reinforcements in concrete structures as an alternative to steel bars or prestressing tendons.
The benefits of FRP reinforcements are their resistance to corrosion, non-magnetic qualities, high tensile strength, lightweight, and simplicity of handling. However, they typically have a weak transverse or shear resistance and a linear elastic response in tension up to failure (referred to as a brittle failure).
Additionally, they have poor resistance when exposed to fire and extreme temperatures and are susceptible to the effects of stress-rupture and lose a significant amount of strength when bent. Furthermore, their price is expensive compared to traditional steel reinforcing bars or prestressing tendons, whether measured in terms of weight per unit or load-carrying ability.
The lack of plastic behaviour and the extremely low transverse shear strength of FRP reinforcements pose the most critical structural engineering issues. These properties, especially where coupled effects are present, like at shear-cracking planes in reinforced concrete beams where dowel action exists, may cause premature tendon rupture.
The dowel action lessens the tendon’s residual tensile and shear resistance. Solutions and usage restrictions have been provided, and future advancements are anticipated to continue. With rising market share and demand, it is anticipated that the unit cost of FRP reinforcements will drop dramatically. FRP reinforcements are still appropriate and cost-effective in several applications today.
FRP in Strengthening Applications
Existing structures deteriorate due to environmental factors, poor design, lack of maintenance, or unintentional occurrences. By strengthening these structures with FRP systems, they are not only restored but also strengthened. FRP is offered as strips, sheets, and textiles for strengthening.
Research, design, and practice have evolved significantly in the application of FRP as a strengthening material. Existing structures can be strengthened and repaired with FRP. Reinforcements that are externally bonded can be used to strengthen masonry, steel, concrete, and timber structures. Both Europe (CEB-FIP fib bulletin 14) and America (ACI 440.2R-17) have design guidelines for concrete structures strengthened using externally bonded FRP systems.
FRP strengthening can be prefabricated in a factory or applied on-site utilizing hand layup. Epoxy resin is applied by hand or in a wet layup process to woven fabric or flexible fibre sheets to create FRP sheets that are attached to concrete members.
These instances include the repair and strengthening of concrete structures using bonded FRP sheets or plates as well as the usage of FRP meshes, textiles, or fabrics in thin cement products. In relative terms, the cost of repairing and renovating a structure is invariably far more than the cost of the original structure.
Repair typically demands a considerable labour commitment but only a little amount of repair materials. Furthermore, the cost of labour is so high in developed nations that it overshadows the cost of materials. Therefore, the more cost-effective the repair, the higher the performance and durability of the repair material. This suggests that material cost is not actually a problem in repair and that the high cost of FRP repair materials is not an impediment.
FRP in New Building Construction
Pultruded fibre-reinforced forms are mostly used in all-FRP new-build constructions. Automatic pultrusion is a method for mass-producing constant section profiles. Although the FRP shapes behave like timber, they resemble structural steel components. As shown in Figure 2, the conventional profiles are created as I, H, C, leg-angle, and tubular sections.
Furthermore, building systems, bridges, cooling towers, chemical and food processing factories, railroad platforms, and maritime structures have all incorporated FRP components. At the 1999 Swiss Building Fair, the first movable five-story FRP building, called Eyecatcher (Figure 3), was displayed. It was afterwards moved to another Basel location, where it is now used as an office building. Three parallel wooden frames with adhesive bonds made up the structure. The only places where bolted joints were employed were for disassembly.
Figure 3: Five-storey FRP building in Switzerland
Sustainability of FRP in Construction
When it comes to FRP composites, environmental issues seem to be a hurdle to its viability as a sustainable material, particularly when taking into account the use of fossil fuels, air pollution, smog, and acidification during its manufacture. Additionally, it is difficult to recycle FRP composites, and unlike steel and wood, structural elements cannot be used again to serve the same purpose in another structure. However, a life cycle study of FRP composites used in infrastructure applications may reveal direct and indirect advantages that are more cost-effective than those of conventional materials.
On the surface, it would seem that the case for FRP composites in a sustainable built environment is questionable when merely looking at energy and material resources. However, this conclusion needs to be weighed against the potential benefits of using FRP composites, including those linked to factors like:
Higher strength
Lighter weight
Higher performance
Longer lasting
Defence systems
Space systems
Ocean environments
Seismic upgrades
Existing structure rehabilitation and life extension.
Conclusion
Since their debut, composite materials have seen significant development. However, a number of requirements still need to be met before composite materials may be used as an alternative to conventional materials as part of a sustainable environment.
The accessibility of standardized data on the durability characterization of FRP composite materials.
Using FRP composites to anticipate the service life of structural members by integrating durability data and techniques.
Creation of methodologies and methods for material selection based on analyses of the life cycles of structural parts and systems.
Composites must ultimately be structurally and economically practical in order to be taken seriously as an alternative. There are much research into the structural viability of composite materials in the literature. Since only recent data is available or only economic expenses are taken into account in the comparison, there are few studies on the viability of these materials from an economic and environmental standpoint from the perspective of a life cycle approach. Determining the long-term effects of employing composite materials is also necessary.
To determine if composite materials can be a component of a sustainable environment, the production byproducts, the sustainability of the constituent materials, and the potential for recycling composite materials must be evaluated.
Average daily temperatures could reach 40°C in some parts of the world, especially in the tropics. The most recent forecast indicates that the weather will be so hot in most of the UK and other countries, which has caused concern among individuals and especially among construction workers who carry out their work in open spaces.
Heat poses a major risk to the health and safety of workers conducting their duties because a sizable portion of the construction crew works outside. A recent tool station poll found that over half of the tradespeople are concerned about getting burned while working outside, and more than a fifth admit to forgoing sun protection when working on a project. There have been discussions about the legal obligations employers have to protect their workers from the effects of excessive heat.
What is the Maximum Temperature in the Workplace?
The Health and Safety Executive (HSE) states that there are no set regulatory requirements for the minimum or maximum temperature in the workplace. However, in order to safeguard workers, the Workplace (Health, Safety and Welfare) Regulations of 1992 mandate that firms maintain a “reasonable temperature.” However, the type of job being done and the surrounding factors at the workplace will determine whether the temperature is “appropriate.”
Minimum Workplace Temperature
According to the Approved Code of Practice, a workplace’s minimum temperature should typically be at least 16 degrees Celsius. When physically demanding labour is being done, the temperature should be at least 13 degrees Celsius. The employer has a responsibility to establish what will be an acceptable level of comfort in the specific circumstances; these temperatures are not absolute legal requirements.
Higher Temperatures at Work
Due to the high temperatures present in places like glass factories and foundries, for example, an accurate figure cannot be provided at the higher end of the scale. As long as the proper safeguards are in place, it is still possible to work safely in these conditions. Other factors, such as radiant temperature, humidity, and air velocity, become more important, and the relationship between them becomes more complex with rising temperatures.
What is Thermal Comfort and how is it Measured?
To determine whether the temperature that people are working in is appropriate, thermal comfort can be employed. It relates to a worker’s mental state, including whether they feel overheated, and takes into account a variety of environmental, occupational, and psychological aspects.
Thermal comfort is influenced by six environmental and individual factors. The thermal comfort of an employee is influenced by a number of factors, some of which may be independent of one another.
The environmental factors are:
Air temperature
Radiant temperature
Air velocity
Humidity
The Personal factors include:
Clothing Insulation
Metabolic heat
Factors affecting thermal comfort
According to the HSE, “Thermal comfort is measured by the number of employees reporting of thermal discomfort, not by the temperature of the room.” According to the regulator, heat discomfort can have an impact on morale and productivity and put people’s health and safety in danger. For instance, persons who are working in uncomfortable heat are more likely to act unsafely since it impairs their judgment. The capacity of an individual to perform manual work can also decline.
How can Employers Safeguard Employees who are Outside?
Although companies have little control over the outdoor temperature, the HSE offers numerous suggestions for how they can safeguard workers. These consist of:
Bringing shade to rest spots and scheduling more regular breaks.
The addition of shade in areas where people are working.
Providing free access to chilled water for drinking.
Encouraging workers to remove personal protective equipment (PPE) while they are resting to aid in heat loss; and
Instructing them on how to spot the early signs of heat exhaustion.
What is the Recommended PPE Usage in Scorching Heat?
Because of discomfort, workers may not properly use PPE in high temperatures, according to the HSE. Employers are urged to take this danger into account because it makes working on a construction site risky. In order to make employees more comfortable, managers can ensure that they are not wearing any more PPE than is necessary for their jobs.
Alternative uniform designs made of lighter materials can also be taken into account. Workers may find it useful to modify their work attire according to their personal comfort if it has numerous layers. The HSE advises using high-factor sunscreen with at least SPF 15 on exposed skin.
How should Workers Express Concerns?
According to the HSE, employees can discuss concerns with their manager, supervisor, or union representative. It states that companies should conduct a risk assessment and take appropriate action if a considerable number of workers express complaints about thermal discomfort.
According to the regulation, in addition to Workplace Regulations, employers must analyze the risks to their employees’ health and safety and take appropriate measures when necessary and when reasonably practical. One of the potential dangers that firms should address to comply with legal requirements is the temperature of the workplace. Employers should speak with staff members or their representatives to build practical coping mechanisms.
The employees are also free to do a variety of activities that will enhance their workplace’s thermal comfort. They comprise;
Depending on how hot or chilly it is, add or remove layers of clothing.
Utilize a desk or pedestal fan to improve airflow.
If window coverings are available, use them to block the sun’s heating influence.
Drink a lot of water in hot weather (avoid caffeinated or carbonated drinks)
Work away from sources of radiant heat or direct sunshine if at all possible.
Periodically pause to cool off in hot settings and warm up in cold ones.
If possible, bring up the matter with your managers, your union, or other workplace officials.
Drink a lot of water in hot weather
Even though any of the aforementioned measures might help in some small way to lessen your thermal discomfort, there are a number of additional things that your manager or company could do to assist. Discuss the following with your manager, supervisor, union official, or employee representative:
Introduce work systems to limit exposure, such as flexible hours or early/late starts to help avoid the worst effects of working in high Temperatures, by, whenever possible, ensuring windows are open, fans that promote local cooling, radiators that can be switched off or air conditioning units that are maintained.
Easing up on formal attire
Insulating hot equipment or pipes, relocating workstations out of direct sunlight or away from hot equipment, and include thermal Risk assessments in workplace risk assessments.
Given that thermal stress can have a detrimental effect on an employee’s health, employers should consider and pay attention to their employees’ worries and provide the necessary support.
Jacketing of reinforced concrete columns is normally done to reduce the lateral deformation of columns, and ultimately increase the strength and load-carrying capacity of the column. This activity is usually carried out on columns that are failing as a result of overload, material deterioration, poor maintenance, inadequate construction practices, etc. Furthermore, when the load-carrying capacity of a column is to be increased as a result of construction modification or change of usage of the building, jacketing of the column can also be done.
Materials such as concrete, steel, or laminates made of a fibre-reinforced polymer may be used for column jacketing, and as the stiffness of the jacket in the transverse direction increases, the resistance to lateral deformation of the column increases.
A column member is in a state of uniaxial deformation if the lateral expansion is totally restrained, i.e., if no lateral deformation is permitted to occur. Columns subjected to uniaxial compression fail as a result of lateral tensile strains caused by the Poisson effect, which causes lateral expansion (Abdelrahman, 2023).
Figure 1: Concrete columns under uniaxial load (Abdelrahman, 2023)
The Poisson effect is the term used to describe a material’s expansion or contraction in directions perpendicular to the direction of loading. If lateral expansion occurs freely, the member is under uniaxial stress, and tensile-splitting cracks parallel to the direction of loadings are the resultant cracks. Typically, uniaxially loaded columns with low or normal compressive strengths exhibit this form of failure.
However, since the stiffness of jackets can never be infinite, it is impractical to achieve a uniaxial stress state in jacketed columns. As a result, the triaxial stress state and deformation are always present in jacketed columns.
High tensile stresses are induced in the jacket as its stiffness increases, and vice versa, the original column section experiences high confining pressure and hence experiences less lateral displacement. It should be noted that as the cracking of concrete increases, the concrete Poisson ratio increases as well, allowing for greater confinement before failure.
The Behaviour of Jacketed Square Columns
When a square column is jacketed, the jacket is subjected to high internal pressure, causing tensile stresses in the transverse direction of the column jacket. Different deformations are seen along the jacket wall, as illustrated in Figure 2b, indicating that the distribution of confining stresses is not uniform (Abdelrahman, 2023).
The tensile stress causes elongation of the jacket at the corners; however, extra flexural deformation is also seen at the mid-wall width (δsquare in Fig. 2b); as a result, the confining effect is diminished in the mid-wall zones. As the dimensions of the square column increase, less confinement is developed at the mid-wall width and the overall confinement of the column decreases.
Figure 2: Confinement of the columns induced by the jacket (Abdelrahman, 2023)
However, as seen in Figure 2d, jacketing does not properly confine rectangular columns, especially those with a large aspect ratio. This is mostly caused by the initial column section expanding, which causes a significant outward distortion of the long side of the column (the δrectangle in Figure 2d).
The behaviour of Jacketed Circular Columns
When jacketing is applied to circular columns, uniform internal pressure develops in the jacket, producing uniform tension and equal lateral displacement in the jacket wall. In this instance, the original concrete section is confined as shown in Figure 2c, and the maximum benefit of the jacket is achieved since it undergoes minimal deformation (see the δcircle in Figure 2c).
Figure 3: Jacketing of circular columns
Jacketing with Reinforced Concrete
Reinforced conncrete jacketing can be applied to columns by increasing the size of the column and adding more longitudinal and transverse steel reinforcement. The essential factor in determining whether the concrete strengthening operation is successful is the composite action between the old and new concrete.
Concrete jackets are used to increase the axial-moment capacity, shear capacity, or stiffness of columns. The lateral deformation of a building can be improved by making the columns stiffer, but this will also result in higher straining actions because of the increased lateral load demand. Concrete jackets can also be used to fix the buckling issues of slender columns.
The use of concrete jacketing in the strengthening of RC columns has its drawbacks, despite being a very popular alternative. For instance, it is adverse to architects and building owners since the size of the finished concrete section after restoration increases and the amount of open space in the building decreases.
Care should be used when applying the jacket because it necessitates extensive drilling into the original column section, which may already be weak, as well as in the slabs/beams and footings. The procedure of applying concrete jackets takes time, and accuracy is necessary when casting the concrete monolithically, especially for the upper portions of the jackets.
The strength of the repaired column member following the addition of the concrete jacket mostly depends on the strength of the jacket as well as the increased strength of the original member following the jacket’s confinement (Abdelrahman, 2023). As a result, it is ideal to have the jacket on all four sides of the column; however, this is not always possible, especially for the columns that are located at the edge or corners of structures.
Procedure for the Construction of Concrete Jacket
The following steps can be adopted in the construction of column jacketing;
(1) Since the column capacity is greatly reduced during the application of the jacket, propping of the slabs surrounding the column and the slabs at other floors must be provided to establish an alternative load path to the foundations.
Figure 4: Propping of slab and beams is important before the commencement of column jacketing
(2) If there is no steel corrosion, the concrete cover is removed until sound concrete is reached in the original section. Since pneumatic hammering may cause the substrate to micro-crack, sandblasting is advised to roughen the concrete surface. If the original section’s reinforcement has corroded, the concrete cover should be completely removed so that the longitudinal steel bars are visible. If the level of corrosion is severe, the steel bars are cleaned, painted with anticorrosion paint, or replaced with new steel bars.
Figure 5: Removal of concrete cover prior to jacketing
(3) To mechanically join the new concrete portion to the old concrete section, steel dowels are placed along the column all around the cross-section. The foundation must receive the longitudinal steel bars of the jacket, and holes in the slabs must be constructed to allow the longitudinal bars to pass the floor slabs.
Figure 6: Profile of dowels anchored to original column and reinforced concrete jacket
(4) The specified longitudinal and transverse steel reinforcement for the jacket is set in place, and it is advised that the steel dowels that were planted be fastened to the longitudinal bars. The hooks will stop the longitudinal steel bars from early buckling and improve the confinement level of the column cross-section.
Figure 7: Installation of longitudinal and transverse steel reinforcement
(5) The jacket should be cast using a material that is compatible with the original concrete section’s properties. In order to reduce the strain on the steel dowels and the likelihood of fresh concrete cracking, the shrinkage of the jacket material should be kept to a minimum. If the original column has been provided with both dowels and surface roughening, monolithic behaviour—where there is no separation at the joint between the old and new concrete—can be anticipated.
Figure 8: Summary of steps for the construction of column jacket (Abdelrahman, 2023)
Material Specifications for Concrete Jacketing
The design mix used to cast the concrete jacket should have physical properties that are comparable to or compatible with those of the concrete used in the original section. Compressive strength, elastic modulus, coefficient of thermal expansion, and creep are some of these properties. Unless it can be demonstrated through testing that similar physical properties are attainable, the type of aggregate used in the mix should be comparable to that of the original concrete.
If the properties of the two materials differ, a vertical separation between the original section and the jacket can be anticipated over time. In this regard, grout or mortar used in the jacket shouldn’t have long-term behaviour that differs from that of concrete. The tensile properties of the jacket may be improved by adding fibres or shrinkage-compensating material to the mixture.
Prior to casting, a bonding agent may be applied to the old concrete as long as the manufacturer’s material specifications are rigorously followed. In order to prevent honeycombs or voids from appearing in the jacket, it is recommended to utilize the form-and-pump approach during concreting.
Reference Abdelrahman A. (2023): Strengthening of Concrete Structures, Springer https://doi.org/10.1007/978-981-19-8076-3_1
Planning is the key to the successful execution of any construction project. A project take-off plan can be categorized under project initiation and planning management. This is a deliberate and measurable plan set up to strategize, manage and ensure the efficient delivery of the project.
A project take-off plan is set up to review and analyse the ten (10) project management body of knowledge (PMBOK) areas as it relates to the project being undertaken. The project take-off committee are required to evaluate and oversee all the phases of the project end-to-end from initiation to execution and close out of the project.
Portfolio contractors, new companies, or site engineers with no prior experience on how to set up or mobilize to the site after the awarding of a contract always find it challenging, thereby wasting useful project time. The aim of this article is to give some inputs, tips and tools needed to set up or mobilize to site.
Tips for Initiating a Project Take-off Plan
The initial useful steps that are required in the preparation of a project take-off plan are provided below;
Project feasibility study Many projects fail to achieve proper success because of a lack of feasibility study and not being able to forecast ahead as to why and how a project might succeed or fail. This study includes but is not limited to awareness of the project team to the following important indicators;
Socio-economic factors or conditions
Demography
Labour rate and material rate in the construction area
Availability of materials within the construction area
Environmental conditions in the dry and rainy season
Topography of the site,
The security situation in the area
Behavioural characteristics of the locals
Availability of important machines, tools, personnel,
Availability and rate of rent for personnel during the project, etc
At the end of these studies, the contractor will be equipped with many intelligence data gathering to position the project for success.
Appointment of a project team This includes Engineers, Quantity surveyors, architects, Project Managers, etc. The team are appointed and their roles and responsibilities are defined as well as the organograms to be used on the project site.
Sourcing of Artisans and Craftsmen: It is also important to source artisans and craftsmen like iron benders, carpenters, masons, and labourers who are very key to the success of any project.
Review and analysis of the Bill of Engineering Measurement and Evaluation (BEME), Bill of Quantity (BOQ), drawings, notes and schedule: This activity should be carried out in order to come up with different documents like Project deliverables, labour and material bills, the scope of work, work breakdown, work plan, and programme of work of different items of work towards achieving a fast track and value engineering approach to the project.
Setting out details and bar bending schedule: For clarity in the arrangement of the elements of the construction, and not to waste time during the substructure stage or at any setting out stages, setting out details in the form of a drawing should be done. Also, before reinforcement cutting, bending, fixing, and placement, a bar bending schedule should be prepared. It is important that the bending schedule take into account offcuts and wastes so that procurement will not be done twice.
Design of program of work with respect to contract duration: Project time starts counting immediately after taking possession of the site. Many projects encounter difficulties because no timelines were established that guide the construction operations. This can be avoided by creating a program of work at the planning stage of the project. A program of work assigns a timeline to all project activities/tasks to ensure project deadlines are met.
Informing the consultant/client of award and mobilization to site: This activity falls under project stakeholder management. All stakeholders should be informed prior to taking possession of the site to avoid any conflict from the stakeholders. All required contract documents and approvals should be obtained. Thereafter, official possession of the site by the contractor is established.
Site safety planning: The site layout, convenience points, muster points, safety signs and symbols, and personal protective equipment (PPE) should be procured and commissioned where necessary.
Procurement of Project Vehicle: A project vehicle always comes in handy to help project logistics and procurement management.
Appointment of guards and a storekeeper: The issue of project site security is a very important aspect that must be on all project manager’s watch lists. Inventories and materials must be properly safeguarded. How and when materials come into the site, the quantity delivered, and how they are utilised should be properly recorded by the storekeeper.
Site clearing: Depending on site condition, site clearing is done manually or by mechanical means using machines. E.g. JCB backhoe or Bulldozer.
Construction of site office, store, cafeteria and temporary perimeter fencing: Depending on the anticipated duration of the project, site offices, store, and cafeteria can be constructed using different materials. Some of the popular materials are timber, roofing zinc; sandcrete blocks; polystyrene; or steel. There are also portable cabins and containers that can be refurbished and converted to a site office.
Delivery of a container site office to site
Project billboard: Project billboards give more branding and visibility to the project site. It contains important information like the project title, project address, project number (contract number), project approval details, name of the contractor, name of consultants, name of client, etc.
Borehole construction and water storage tank: The availability of potable water is essential for all sites. The project team should make concerted efforts to ensure that potable water is available for running the site. Water is required for construction works, cleaning, and human consumption. Essentially, all wet works require water at one stage or the other.
Office and store administration: Provision for tools to be used in the administrative aspect of the project site includes- pen; pencil; masking tape; chairs; tables; generator; fan; board (for pasting pictures, drawings, schedules, instructions and program of work); laptop; calendar; notepad; keys; chains; coffee; refrigerator; stapler; pin; calculator; envelopes; instruction booklet; weather booklet; visitors’ booklet; requisition/purchase order booklets, etc.
Procurement: At this stage, the major stockpiling of site inventories starts in earnest. This procurement is done at different stages of the project depending on the scale and scope of the projects.
For a building project, some of the necessary materials include but are not limited to materials and equipment like;
cement
sand
gravel
reinforcement bars
binding wire
marine board
planks
1″ x 3″, 2″ x 3″ and 2″ x 4″ timber
Nails of different sizes and types
A toolbox of pliers, screwdrivers, spanners, cutters, wrenches, etc
buckets and head pans
water hose
chisels and hammers
paint and brush
concrete mixer
shovel and spade
poker vibrator
wheelbarrow
pumping machine
generator and fuel can
acrow props or bamboo
perry beam
spirit and water levels
lines
Digger
plumb bob
rammer
mechanical and electrical materials (e.g extension cables and boxes)
slump cone and mould for concrete test
caution tape
blocks
a blue line and blue
dumpy level
laser light equipment for horizontal and vertical control
crane
Damp-proof membrane (DPM)
hardcore
fabrics (BRC wire mesh)
setting out materials and tools (builders rope, measuring tape (10m and 50m iron tape), 2×3 wooden and 12mm iron peg, 1 x 2 profile board, builder square, spirit level, markers, masking tape, 2’’ and 3’’ nail, hammer etc.)
camera for taking site pics for project progress and presentation
safety gadgets (first aid box, safety boots, jacket, helmets and signboard).
Note that some of these items must be tested and approved before any bulk purchases.
Conclusion
From the foregoing, the contractor or site engineer will increase in confidence and knowledge of some of the things requires during a project take-off plan. This plan is not a one size fit all approach and it is to be used where it is applicable. It is intended to familiarize the project team with the preparation of a basic take-off plan for a building site in Nigeria and also, to serve as a checklists before mobilization to the site. The plan should be documented in a report-like format for proper review and reference in the future.
