Structville daily questions
From now henceforth, Structville will be publishing daily questions on different aspects of civil engineering. You are expected to enter your response in the comment section. At the end of every week, exceptional participants will stand a chance to win some gifts. This exercise is open to participants all over the world.
Today’s Question What is the degree of static indeterminacy of the frame shown above?
Thank you for participating in exercise today, remember to enter your answer in the comment section. The main aim of this exercise to stimulate knowledge of structural analysis on the internet in a fun and exciting way. We are always happy to hear from you, so kindly let us know how you feel about Structville.
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STRUCTVILLE REINFORCED CONCRETE DESIGN MANUAL
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Fire outbreak is a problem in buildings since it causes loss of human lives, injuries, destruction of properties, and poses serious environmental challenges. Injury and loss of life are caused by heat, inhalation of toxic gases generated by combustion of furnishings/properties, falling debris, etc. Destruction of property and structural damage and failure are caused by heat and burning of combustible material.
Prevention and control of damage due to fire can be achieved through the following means;
(1) Early detection by smoke and heat detectors or manual sighting followed by extinction of the fire by automatic sprinklers, manual application of water, foams, fire extinguishers etc.
Fig 2: Fire Sprinkler System
(2) Containment of the fire by dividing the building into fireproof compartments to prevent fire spread and smoke travels, and provision of fireproof escape routes, fire rated doors and windows, fire rated finishes, etc.
Fig 3: Fire rated doors
(3) Fire protection of load bearing structural members to ensure collapse does not occur before people can escape or the fire be extinguished. This is usually achieved by giving the building a fire rating during the design process.
Fig 4: Beams and Columns Protected By Spraying
The last two control methods form an essential part of the design considerations for steel structures (architectural and structural). All multi-storey commercial and residential buildings require fire protection of structural members, but single-storey and some other industrial buildings might not need protection.
Fire resistance requirements of buildings are usually based on the parameters influencing fire growth and development. These include:
Fire [probability of Fire occurrence, Fire spread, Fire duration, Fire load, Severity of fire…]
Ventilation conditions
Fire compartment (type, size, geometry)
Type of the structural element
Evacuation conditions
Safety of the rescue teams
Risk for the neighbouring buildings
Active fire fighting measures
Structural Considerations in Fire Design
Structural steelworks lose their strength on exposure to fire. Temperatures commonly reach 1200°C at the seat of the fire, while the critical temperature for steel is about 550°C. (see brief calculation below). At this temperature the yield stress of steel has fallen to about 0.7 of its value at ambient temperatures that is to the stress level in steel at working loads.
For instance in the calculation above, the critical temperature (failure temperature) is found to be 603°C (calculation according to EC3). The next step in the calculation is to determine the time at which the bare section reaches the critical temperature. This can offer the right information about the type of protection needed.
To request for a fully solved example of fire design (PDF) in a building, contact the author by clicking HERE.
Types of Fire Protection for Steel Structures
Solid protection for columns, where the concrete assists in carrying the load (this is not so much used in modern construction). Beams can also be cased in concrete. A concrete thickness of 50 mm will give about 2 hours protection.
Brick-clad steel-framed buildings, where brick provides the walling and fire protection, are a popular building system.
Hollow casing can be applied in the form of pre-fabricated casing units or vermiculite gypsum plaster placed on metal lathing.
Profile casing, where vermiculite cement is sprayed on to the surface of the steel member, is the best system to use for large plate and lattice girders and is the cheapest protection method. A thickness of 38 mm of cement lime plaster will give about 2 hours protection.
Intumescent coatings inflate into foam under the action of heat to form the protective layer.
Fire resistant ceilings are used to protect floor steel.
Thank you for visiting Structville today, and God bless you.
Punching shear failure occurs in a slab when the magnitude of a concentrated load (such as that from a column) exceeds the shear strength or resistance of the slab or the column punches through the slab. The failure plane is located at a certain distance from the perimeter of the column and has a funnel-shaped failure pattern. The design for punching shear resistance in flat slabs normally involves controlling the thickness of the slab or providing punching shear reinforcement.
Generically, punching is a three-dimensional, brittle failure mechanism leading to a truncated cone that separates from the slab. The shear crack develops from tangential flexural cracks and propagates into the direction of the compression zone near the column edge constricting the circumferential compression ring with increasing loads. Once the punching shear resistance is reached the shear crack intersects the uncracked compression ring leading to a sudden penetration of the column into the slab.
Typical failure pattern for punching shear
The recommendations found in BS EN 1992 (Eurocode 2) are usually followed when designing punched shear reinforcement. To assess whether punched shear reinforcement is necessary, the shear stress in the concrete is computed at the column face and at the fundamental control perimeter u1 (2d from the column face).
The position of the outside control perimeter where shear reinforcement is no longer needed (uout) is then determined if reinforcement is necessary. Shear studs are placed starting at 0.3d or 0.5d from the column face to within 1.5d of the outer control perimeter (uout), with intermediate studs spaced at 0.75d intervals.
The most cost-effective approach will often be a radial arrangement, with rails spaced either 30° or 45° apart. To meet this requirement, extra secondary rails are installed as necessary. The tangential spacing between studs is kept to within 1.5d for studs inside the basic control perimeter (u1) and 2d for studs outside the basic control perimeter.
The suggested values from BS EN 1992 can be used to design shear load VEd for internal, edge, and corner columns where lateral stability does not depend on frame action between slabs and columns and where neighbouring spans differ by less than 25%.
Design for punching shear should take moment transfer into account at the intersection of the column and slab. The design punching shear can be obtained for structures whose lateral stability is not dependent on the frame action between the slab and columns and where adjacent spans do not differ in length by more than 25% by increasing VEd by 1.15 for internal columns, 1.4 for edge columns, and 1.5 for corner columns.
Generally, the following checks should be carried out:
Ensure that maximum punching shear stress is not exceeded, i.e. vEd < vRd,max at the column perimeter
Determine whether punching shear reinforcement is required, i.e. whether vEd > vRd,c at the basic perimeter, u1
Determine whether punching shear reinforcement is required, i.e. whether vEd > vRd,c at at successive perimeters to establish uout= the length of the perimeter where vEd = vRd,c. Perimeters within 1.5 d from uout need to be reinforced.
Where required provide reinforcement such that vEd ≤ vRd,cs.
where
vEd = applied shear stress. The shear force used in the verification should be the effective force taking into account any bending moment transferred into the slab (see above)
vRd,max = design value of the maximum punching shear resistance, expressed as a stress vRd,c = design value of punching shear resistance of a slab without punching shear reinforcement, expressed as a stress vRd,cs = design value of punching shear resistance of a slab with punching shear reinforcement, expressed as a stress.
vRd,cs = 0.75 vRd,c + 1.5 (d/sr)Aswfywd,ef (1/u1d)sin a
where:
Asw = area of shear reinforcement in one perimeter around the column (subject to Asw,min) sr = radial spacing of perimeters of shear reinforcement fywd,ef = effective design strength of reinforcement (250 + 0.25d) ≤ fywd d = mean effective depth in the two orthogonal directions (in mm) u1 = basic control perimeter at 2d from the loaded area sin a = 1.0 for vertical shear reinforcement
Where required each perimeter should have Asw = (vEd – 0.75 vRd,c)sru1/(1.5 fywd,ef)
The punching shear resistance of a slab should be assessed for the basic control section (see Figure 6.12). The design punching shear resistance [MPa] may be calculated as follows:
where: fck is the characteristic compressive strength of concrete, see Table 3.1 k= 1 + √200/d ≤ 2.0 where d is the effective depth, in [mm]ρl= (ρly⋅ρlz)1/2 ≤ 2% ρly, ρlz are longitudinal reinforcement ratios in y- and z- directions respectively. Their values should be calculated as mean values taking into account a slab width equal to column width plus 3d each side σcp= (σcy + σcz)/2, where σcy, σcz are the normal concrete stresses in the critical section in y- and z- directions (in [MPa], positive if compression): σcy = NEd,y / Acy and σcy = NEd,z / Acz NEd,y, NEd,y are the longitudinal forces across the full bay for internal columns and the longitudinal force across the control section for edge columns. The force may be from a load or prestressing action. Acy, Acz are the areas of concrete according to the definition of NEd,y, NEd,y respectively CRd,c is a Nationally Determined Parameter, see § 6.4.4 (1) vminis a Nationally Determined Parameter, see § 6.4.4 (1), or (6.3N) for the calculation of vmin following the Eurocode recommendation k1 is a Nationally Determined Parameter, see § 6.4.4 (1).
Punching Shear Design Example
For the flat slab with the general arrangement as shown below, let us design the punching shear for column B1 given the following design information;
Ultimate axial force on column VEd = 400 kN Thickness of slab = 250 mm Dimension of column = 450 x 230 mm Reinforcement of slab in the longer direction = H16@150mm (As,prov = 1340 mm2) Reinforcement of slab in the shorter direction = H16@175mm (As,prov = 1149 mm2) Grade of concrete = C30 Yield strength of reinforcement = 500 Mpa Concrete cover to slab = 25mm
Solution
Effective depth of slab in y-direction dy = 250 – 25 – (16/2) = 217 mm Effective depth of slab in x-direction dx = 250 – 25 – 16 = 209 mm
Precast piles are designed to withstand stresses caused during their installation, and the load from their service life. Bored piles on the other hand and usually designed to withstand the stresses they are subjected to while supporting the superstructure and other actions as may be anticipated. These could be earthquake forces, other lateral loads, or uplift forces.
Furthermore, piles of all types may be subjected to bending stresses caused by eccentric loading, either as a designed loading condition or as a result of the pile heads deviating from their intended positions. This post is aimed at exploring the methods of providing longitudinal reinforcement for bored piles, and the minimum reinforcement acceptable.
Buckling of piles that are embedded in a firm soil cannot occur unless they are loaded beyond their capacity, hence there is no need to design such piles as slender columns. However, when the piles are projecting above the ground level, then there is a need to consider such behaviour.
Also, when a pile passes through a very weak stratum of clay with low lateral stiffness, and is founded on a hard stratum, then buckling becomes a problem. If the undrained shear strength of the soil cu is less than 10 kN/m2, then there is a need to check for buckling.
Reinforcement Requirement and Detailing of Bored Piles Section 9.8.5 of EN 1992-1-1:2004 deals with the detailing requirements of bored piles. Clause 9.8.5(3) said that bored piles with a diameter not exceeding 600mm should be provided with a minimum longitudinal reinforcement of As,bpmin. The recommended minimum longitudinal reinforcement of cast-in-place bored piles is given in Table 9.6N of EN 1992-1-1:2004 and reproduced below;
The requirement further states that the minimum diameter for the longitudinal bars should not be less than 16 mm. Piles should have at least 6 longitudinal bars and the clear distance between bars should not exceed 200 mm measured along the periphery of the pile.
However, these rules differ from the requirements of BS EN 1536:2010 + A1(2015) which states that for reinforced piles, the minimum longitudinal reinforcement shall be 4 bars of 12 mm diameter, and the spacing should be maximised to allow proper flow of concrete but should not exceed 400 mm.
According to clause 6.9.2.1 of BS 8004:2015, the design compressive resistance (Rc,d) of the reinforced length of a cast-in-place pile is given by;
Rc,d = fcdAc,d + fydAs,d
Where; fcd = design compressive strength of the concrete = (αcc × fck)/(kf × γc) αcc = factor taking into account the long-term reduction in strength of concrete (take as 0.85) fck = characteristic compressive strength of concrete kf = A multiplier to the partial factor of concrete for concrete piles cast-in-place without permanent casing (value is 1.1) γc = partial factor for concrete Ac,d = cross-sectional area of pile
fyd = design yield strength of steel = (fyk / γs) fyk = characteristic yield strength of steel γc = partial factor for steel As,d = Area of steel required
The links, hoops, or helical reinforcements are required to be designed in accordance with EC2, but the diameter of the bar should not be less than 6 mm, or one-quarter of the maximum diameter of the longitudinal bars. The maximum reinforcement should be taken as 4% of the cross-sectional area.
According to clause 6.9.2.6, of BS 8004:2015, depending on the magnitude of loading, a cast-in-situ pile may be reinforced over its whole length, over part of its length, or merely provided with short splice bars at the top for bonding into the pile cap. If the concrete pile is expected to resist tensile forces, the reinforcement should be extended down to the full length.
Solved Example
A 500 mm diameter pile has a safe working load of 540 kN and the actual load it is being subjected to is 485 kN. Provide suitable reinforcement for the pile if it is a frictional pile embedded in dense sand and the characteristic strength of concrete and steel are 30 MPa and 500 MPa respectively.
540000 = (196349.54 × 15.45) + 434.782 As,d A little consideration will show that solving for As,d will give us a negative value, therefore provide minimum reinforcement
Since Ac < 0.5 m2; As,bpmin = 0.005 × Ac,d = 0.005 × 196349.54 = 982 mm2 Provide 6H16mm (As,prov = 1206 mm2)
Following strictly the detailing requirements of EC 2, a clear distance of 200 mm has not been exceeded.
Structville daily questions
From now henceforth, Structville will be publishing daily questions on different aspects of civil engineering. You are expected to enter your response in the comment section. At the end of every week, exceptional participants will stand a chance to win some gifts. This exercise is open to participants all over the world. Happy new month to you all.
Today’s Question What is the vertical support reaction at point B of the frame?
Thank you for participating in exercise today, remember to enter your answer in the comment section. The main aim of this exercise to stimulate knowledge of structural analysis on the internet in a fun and exciting way. We are always happy to hear from you, so kindly let us know how you feel about Structville.
E-mail:info@structville.com WhatsApp: +2347053638996 You can also visit Structville Research for downloads of civil engineering materials.
STRUCTVILLE REINFORCED CONCRETE DESIGN MANUAL
We have this very affordable design manual available…
Do you want to preview the book, click PREVIEW To download full textbook, click HERE
Structville Integrated Services in our commitment to human capacity development, has decided to launch series of online lectures and webinars for civil engineering professionals and students. We wish to specify that this program is by choice, and there must be interest to participate before you can embark on this journey. We called it a journey because the whole program will be carried out online, and you should have enough data to download the videos, PowerPoint presentations, and papers that would circulated during the program. This is the only way you can maximize your benefits.
The program will last for 3 weeks (Friday 15/06/2018 to Friday 06/07/2018), and the arrangement is prepared in such a way that you will be able to download the resource materials and follow the discussions even if you are not online at a period that a particular session will be held. A time table would be published for the program, and it is advisable that you plan ahead and make yourself available so as to enable you ask questions. The promise is that all questions would be adequately attended to. We have mobilised distinguished resource persons from civil engineering profession all over the world to participate in the different sessions and give us the best ideas/interactions.
The online training has been divided into two categories;
– Category 1 – ₦5,000
– Category 2 – ₦10,000
The topics to be treated are as follows;
Category 1 (₦5,000 / $15.00) (1) Basis of Structural Design(PowerPoint Presentations, Papers, Case Studies, Discussions)
(2) Structural Analysis and Design of Office Complex Using Staad Pro Software (Video Tutorials, PowerPoint Presentations, Lecture notes)
(3) Structural Analysis and Design of Industrial Steel Structure Using Staad Pro Software(Video Tutorials, Powerpoint Presentations, Lecture Notes)
(4) Structural Analysis and Design of Beam and Raft Foundation Using Orion Software (Video Tutorials, Powerpoint Presentations, Lecture Notes)
(5) Matrix Methods of Structural Analysis – Force Method, Stiffness Method, and Finite Element Analysis(Lecture notes, Video Tutorials, Solved Examples)
(6) Life as a Civil Engineer and Challenges of the Industry(Power Point Presentations, Discussions, and Case Studies)
Category 2 (₦10,000 / $30.00) (1) Leadership, Intelligence, Investment, and Capacity Building in Civil Engineering Profession (Papers, PowerPoint, Case Studies, Videos, Foreign Interactions) (2) Basis of Structural Design(PowerPoint Presentations, Papers, Case Studies, Discussions) (3) Limit State and Structural Reliability Theory (Papers, Lecture notes, and discussions) (4) Structural Analysis and Design of Office Complex Using Staad Pro Software (Video Tutorials, PowerPoint Presentations, Lecture notes)
(5) Structural Analysis and Design of Industrial Steel Structure Using Staad Pro Software(Video Tutorials, Powerpoint Presentations, Lecture Notes)
(6) Structural Analysis and Design of Beam and Raft Foundation Using Orion Software (Video Tutorials, Powerpoint Presentations, Lecture Notes)
(7) Advanced Modelling and Analysis on Staad Pro – Bridges, Box Culverts, and Staircases (Video tutorials, PowerPoints, and Lectures)
(8) Advances in Civil Engineering Materials (Videos, PowerPoint, Case studies, and Papers)
Followers of Structville blog can testify on our commitment to quality and excellence, and this webinar and online training will be another testimony. Just like I stated earlier, the idea is for you to have adequate data bundle beacause there will be excess downloads to make (especially for the videos). If you cannot afford it, do not bother yourself so much, but you would really miss. Structville’s vision and mission is very accommodating.
REGISTRATION WOULD RUN FROM MONDAY 04/06/2018 TO THURSDAY 14/06/2018
To participate in this program, and for further inquiries, all you need is to send an e-mail and/or whatsapp message to;
From the rules of the competition, the winners for the week are as follows;
Ogungbire Adedolapo
Giuseppe Martino Erbi
Romel Sevilla Batongbakal
Ovie Agbaga
We say a big congratulations to you all, and we sincerely appreciate your valuable contributions. Kindly forward your e-mail addresses for some special gifts. Our sincere appreciation also goes out to those who participated on various social media platforms. God bless you all.
Cracking is the partial or complete separation of a section into two or more parts as a result of fracture. In concrete sections, cracking occurs when the tensile stress exceeds the tensile strength of the concrete. Due to the inherent weakness of concrete in tension, it is bound to crack easily and more often than not, steel reinforcements are used for crack control.
Cracking can occur in concrete in a plastic or hardened state. Autogenous shrinkage, differential settlement, drying shrinkage, thermal stresses, chemical reactions, imposed restraints, corrosion of reinforcement, poor construction techniques, construction overloads, errors in design and detailing, and externally applied loads are all potential causes of cracking in concrete.
Cracking is considered a serviceability limit state problem in reinforced concrete design. Reinforced concrete slabs are prone to cracking because they are predominantly subjected to flexural stresses. Therefore, crack control using reinforcements is very important in the design of reinforced concrete slabs. The serviceability limit states covered by Eurocode 2 are;
– Stress limitation (section 7.2) – crack control (section 7.3) and – deflection control (section 7.4)
According to clause 7.3.1 of EN 1992-1-1:2004, the general considerations in the control of cracking in a building are as follows;
(1)P Cracking shall be limited to an extent that will not impair the proper functioning or durability of the structure or cause its appearance to be unacceptable.
(2) Cracking is normal in reinforced concrete structures subject to bending, shear, torsion or tension resulting from either direct loading or restraint or imposed deformations.
(3) Cracks may also arise from other causes such as plastic shrinkage or expansive chemical reactions within the hardened concrete. Such cracks may be unacceptably large but their avoidance and control lie outside the scope of this Section.
(4) Cracks may be permitted to form without any attempt to control their width, provided they do not impair the functioning of the structure.
(5) A limiting calculated crack width, wmax, taking into account the proposed function and nature of the structure and the costs of limiting cracking, should be established.
In Eurocode 2 cracking is controlled in the following ways:
wkmax is determined from Table 7.1N (in the UK from Table NA.4)
These limits can be met by either: – ‘deemed to satisfy’ rules (Cl. 7.3.3) – direct calculation (Cl. 7.3.4) – design crack width is wk Note: slabs ≤ 200 mm depth are okay if As,min is provided.
A little consideration will however show that the deemed to satisfy rules are more handy and applicable for all design purposes. A solved example on application of deemed to satisfy rules is presented in this post.
Worked Exampleon the Crack Control of RC Slab
Let us consider a simply supported slab in a proposed office building. The thickness of the slab is 150 mm, and the dead load on the slab gk = 5.6 kN/m2, and the live load qk is 3 kN/m2. The area of steel required is 698 mm2/m, and the area of steel provided is 753 mm2/m. (T12@150mm). Verify if the slab meets the cracking requirement according to Eurocode 2 limiting the crack width to 0.3mm.
Solution
In order to use Tables 7.2N or 7.3N of EC2, we need to determine the service stress in the bars by;
Service stress/Ultimate stress = [(Gk + ψ2Qk,1)/(γGGk + γQQk,1)] × (1/δ) ψ2 = 0.3 (see the table below for combination factors)
Structville daily questions From now henceforth, Structville will be publishing daily questions on different aspects of civil engineering. You are expected to enter your response in the comment section. At the end of every week, exceptional participants will stand a chance to win some gifts. This exercise is open to participants all over the world. Happy new month to you all.
Today’s Question What is the deflection at point 2 of a structure if diagram (a) is the bending moment due to externally applied load, and (b) is the bending moment due to vertically applied virtual load at point 2? (The main bending moment diagram is obtained from equation of the form, wl2/2)
Thank you for participating in exercise today, remember to enter your answer in the comment section. The main aim of this exercise to stimulate knowledge of structural analysis on the internet in a fun and exciting way. We are always happy to hear from you, so kindly let us know how you feel about Structville.
E-mail:info@structville.com WhatsApp: +2347053638996 You can also visit Structville Research for downloads of civil engineering materials.
STRUCTVILLE REINFORCED CONCRETE DESIGN MANUAL We have this very affordable design manual available…
Do you want to preview the book, click PREVIEW To download full textbook, click HERE
Structville daily questions From now henceforth, Structville will be publishing daily questions on different aspects of civil engineering. You are expected to enter your response in the comment section. At the end of every week, exceptional participants will stand a chance to win some gifts. This exercise is open to participants all over the world.
Today’s Question For the frame loaded as shown above, which of the options is the most likely bending moment diagram considering linear elastic response.
Thank you for participating in exercise today, remember to enter your answer in the comment section. The main aim of this exercise to stimulate knowledge of structural analysis on the internet in a fun and exciting way. We are always happy to hear from you, so kindly let us know how you feel about Structville.
E-mail:info@structville.com WhatsApp: +2347053638996 You can also visit Structville Research for downloads of civil engineering materials.
STRUCTVILLE REINFORCED CONCRETE DESIGN MANUAL We have this very affordable design manual available…
Do you want to preview the book, click PREVIEW To download full textbook, click HERE
