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3D Building Services Systems Integration in Design of Buildings

By
Ivy Ugorji
-

Building service systems (BSS) are important components that makes a building functional and habitable. BSS includes piping network of fresh water and wastewater, electrical installation network, air conditioning systems, fire prevention and protection systems, and communication systems. These are usually sumarised as MEP which stands for Mechanical, Electrical and Plumbing services design.

In the design process, BSS are improtant components which have great impacts on architectural and structural designs. It is generally accepted that integrating the service systems and their components into the architectural and structural designs, and coordinating between these systems help avoid major obstacles during the construction process. In some buildings in Nigeria, it is common to see incoherent arrangement of plumbing systems, chiselling/breaking down of structural members to accommodate mechanical systems and other construction setbacks due to uncoordinated MEP design at an early stage.

unsightly arrangement of MEP services
Unsightly and inefficient arrangement of plumbing system in a building

Usually, after completing the designs, the MEP coordination process begins by holding meetings between the representatives of the general contractor and specialty trades. The MEP systems coordination influences the productivity of all designers of multidisciplinary backgrounds involved in the design process. Any errors or mistakes during designing or constructing the project in the MEP systems would lead to time consuming tasks, budget waste, labour time increment, and project time extension.

clash of HVAC SERVICES IN A BUILDING
Service system, HVAC clashes with both fire system pipes and the suspended ceiling (Wael and Weldy, 2020)

In a research carried out by authors from Applied Science University, and University of Bahrain and published in Journal of Information Technology in Construction, the need to integrated BSS early into preliminary designs (architectural and structural) were reviewed and studied. According to the authors,

The integration BSS inside the building in the early phases of design will save cost and prevent time-consuming modifications. Due to the late integration of the building service systems BSS in the design, negative impact on both the exterior and the interior, may occur. Within the building industry, there has been increasing interest to the building service systems BSS integration, in order to enhance design outcomes, and to detect or even avoid the service systems’ clashes and conflicts.

Problems of 2D drawings

The coordination processes of overlaying two-dimensional drawings of different service systems, each of which is designed by different specialised designers has been identified by the authors as a major cause of clashes and conflicts. The accuracy of this process depends on the experiences of architects and structural engineers in order to avoid the possible conflicts and to include the systems’ components and spatial requirements into the design and its spaces.

Actually, errors may not be fully detected by these traditional processes till the construction stages. Identifying conflicts in the 2D-drawings of service systems is a challenging process, since it depends on designers’ experience. These possible errors or conflicts can negatively affect the projects in many aspects, particularly in the case of being undetected after the construction completion. This can consequentially impact the project’s spaces to accommodate the systems’ components and requirements.

3D to the rescue

Although 2D drawings are still extensively used in every aspect of a building project, there is a strong movement led by the architects to transform to 3D models.

Using 3D digital modelling in the processes of design and coordination not only improves the designers’ raw imagination by representing a 3D model including the components of the service systems, but also eliminates the errors generated from the lack of designers’ experiences by visually presenting all systems’ components. Employing digital modelling eases the processes of coordination and design, and makes them more accurate. Authorities, stakeholders and decision makers will gain many advantages, such as: creating a detailed model of both the design and the service systems which makes their decisions more reliable and accurate.

Building Information Modelling (BIM) is an approach and a process in which the design model potentially includes various building information of different components and spaces, in order for the users to visualise, manage, analyse and/or design in a better way. BIM approach offers an effective assistance represented in making a multidisciplinary model that has BSS in one detailed model, which helps discover and solve any obstacles of overlaps or/and conflicts. Unlike other digital tools that help the imagination capabilities of architects or architecture students, BIM proceeds beyond to unveil and expose possible problems that may appear in the later processes of designing and construction.

Conclusion

Citing previous research works, the authors concluded clash detection has been favoured over the clash avoidance due to cultural practices and lack of technologies to support clash avoidance. From empirical evidence of past research works, MEP-related clashes has been strongly linked to the cultural practices of isolated working among designers, and lack of specialised professional training among designers.

The paper based on the qualitative analysis of both the real projects of construction industry and the student projects of academia, concludes that integrating the MEP systems into the conceptual design phases eliminates the clashes and conflicts that may occur in later stages, and concurrently the possibility of not detecting these conflicts till the construction process.

Reference
Wael Abdelhameed, Weldy Saputra (2020): Integration of building service systems in architectural design. Journal of Information Technology in Construction (ITcon), Vol. 25, pg. 109-122, DOI: 10.36680/j.itcon.2020.007

Disclaimer
The findings of this research has been published on www.structville.com because it is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Restraint and Restraint Factors of Concrete

By
Ubani Obinna Uzodimma
-

If movement (expansion and/or contraction) is restricted within a young concrete element, tensile stresses will develop which will lead to cracking. This restriction to movement is normally referred to as restraint. Restraints may be internal or external to the element. Internal restraint occurs due to differential temperature changes within a mass concrete element and can cause surface and/or internal cracking.  However, it is only significant in very thick sections (1000 mm or more). Internal restraints are not considered in this article.

External restraints are due to the support/casting condition of the concrete. However, external restraints take two basic forms;

(1) End restraints
(2) Edge restraints

End restraint

End restraints occurs when the edges of a young concrete are prevented from movement (see Figure below). This typically occurs in suspended slab cast between rigid cores, walls or columns, in infill bays, ground slab cast on piles, large area ground slabs restrained locally, e.g. by piles, columns or column foundations or by a build up of friction, walls cast against secant, contiguous concrete or steel sheet piled walls etc (CIRIA C660).

End restraint in concrete
Schematic model of end restraint in concrete

Edge restraint

This typically occurs where the young concrete section (say a wall) is cast on a hardened concrete base (see Figure below). This means that restriction is only in one direction, and there is interaction between the old and new concrete in terms of distribution of cracks. Edge restraint is different from end restraint because the crack width is a function of restrained strain rather than the tensile capacity of the concrete.

Edge restraint in concrete
Schematic model of edge restraint in concrete

In some cases also, there can be combination of end restraint and edge restraint.

Restraint Factors

The level of restraint in a young concrete imposed by adjoining element is commonly described using restraint factors. The degree of restraint, R, is generally defined as the ratio between the actual stress in a contracting body and the stress imposed under full restraint.

Degree of restraint R = Actual imposed stress / Imposed stress at full restraint

It is recognised that is difficult to determine the degree of restraint correctly, but it is important to obtain restraint factors that are as accurate as possible.  According to CIRIA C660, the restraint factors given by BS 8110-2 and HA BD 28/87 reflects true restraint values, while the restraint factors from BS 8007 and EN 1992-3 has a modification factor of 0.5 to account for creep under sustained loading.

ACI (1990) (cited by CIRIA C660) developed method for estimating edge restraint based on the relative geometry and stiffness of the old and new concrete. The equation is given by;

Restraint at the joint Rj = 1/(1 + AnEn/AoEo)

Where;

An is Cross-sectional area of the new (restrained) pour
Ao is the cross-sectional area of the old concrete
En is the modulus of elasticity of the new pour concrete
Eo is the modulus of elasticity of the old concrete              

However, CIRIA C660 identified that the relative areas of influence of Ao and An may be difficult to define. Therefore the following simple rules were recommended;

  1. For a wall cast at the edge of a slab (An/Ao) = (hn/ho) (thickness of new concrete/thickness of old concrete)
  2. For wall cast remote from the edge of the slab (An/Ao) = (hn/2ho)
  3. En/Eo ranges from 0.7 to 0.8 (but 0.8 is recommended)

Based on CIRIA C660, the values in Table 1 can be used for edge restraint based on An/Ao or An/2Ao ratio.

Table 1: Values of Edge Restraint Factors (According to CIRIA C660)

Edge restraint factors for concrete

The values of restraint factors for different conditions as given by different codes is summarised in the Table 2.

Table 2: Values of Restraint Factors (BS 8110-2 and EN 1992-3)

Values of restraint factors

Thank you very much for reading.

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TANK SUPPORT TEXTBOOK 1

Cracking in Concrete

By
Peace Ikpotokin
-

Eurocode recognises that cracking is normal in concrete subjected to bending, shear, torsion, and restraint from movement (clause 7.3.1 EN 1992 1-1). Cracking is assumed to occur when the restrained strain exceeds the tensile strain capacity of the concrete. This means that for cracking to occur, some part or the whole of the concrete section must be in tension. Crack width is predicted by multiplying crack inducing strain, (the strain dissipated by the occurrence of cracking) εcr, by crack spacing, sr,max.

Cracking occurs due to the low tensile strength of concrete, and we normally use reinforcements to assist is controlling cracking. What happens in this case is that the tensile stress in the concrete must be transferred to the steel if cracking must be controlled.

To achieve this, a minimum amount of reinforcement must be provided in order to have small cracks occurring at intervals instead of having one single large crack. However, provision of this minimum reinforcement is not sufficient for controlling crack widths. As a matter of fact, direct crack width calculation must be carried out if the water tightness of the tank must be guaranteed.

Crack widths are normally calculated for;

(1) Restraint to movement (also called imposed deformations)
(2) Loadings

Cracking due to restraints are due to early thermal effects, autogenous shrinkage, and drying shrinkage. Cracking due to loading is usually from flexure or axial tension in the concrete.

Get this publication below for a cheap price by clicking on the image. It goes a long way in supporting what we do here at Structville. To read about the publication, click HERE. Thank you for your kind consideration.

TANK SUPPORT TEXTBOOK 1

Crack Width and Crack Spacing Calculation in Concrete

By
Ivy Ugorji
-

Cracking occurs in concrete when the restrained strain exceeds the tensile strain capacity of the concrete. In critical elements like water retaining structures, crack control is verified by carrying out direct calculation of the crack width. Crack width is calculated by multiplying the crack inducing strain and the crack spacing (i.e. the movement over a length equal to the crack spacing). This also involves limiting the bar size and/or spacing to recommended limits.

According to expression 7.8 of EN 1992-1-1, crack width wk in a concrete element is given by;

wk = sr,max εcr

where;
sr,max = Maximum crack spacing

sr,max= 3.4c + 0.425 (k1k2ϕ /ρp,eff)

Where;
c = nominal cover, cnom in mm in accordance with BS EN 1992-1

k1 = 0.8 for high-bond bars
(Note that for early age cracking calculations CIRIA C660 suggests a value of 1.14 to account for poor bond conditions, see EN 1992-1-1 for poor bond conditions)

k2 = 1.0 for tension (e.g. from restraint)
= 0.5 for bending
= (ε1 + ε2)/2ε1 for combinations of bending and tension where ε1 is the greater tensile strain at one surface of the section under consideration and ε2 is the lesser tensile strain (i.e. = 0 if strain at second surface is compressive).

ϕ = diameter of the bar in mm.

ρp,eff = As/Ac,eff

This is calculated for each face.

Ac,eff  = min[0.5h; 2.5(c + 0.5ϕ); (h – x)/3]

Where;
h = thickness of section
x = depth to neutral axis.

εcr = Crack-inducing strain in concrete

εcr = (εsm – εcm)

Crack-inducing strain is derived according to whether the element is subject to:

(1) edge restraint with

  • (a) early thermal effects or
  • (b) long term effects

(2) end restraint
(3) flexure and/or combinations of flexure and tension from load

Note: It is assumed that the reinforcement will be spaced at reasonably close centres. Where spacing exceeds 5(cnom + ϕ/2), BS EN 1992-1-1 Exp. (7.14) dictates that;

sr,max = 1.3 (h – x)

Thank you very much for reading.

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TANK SUPPORT TEXTBOOK 1

New Textbook: Modelling, Analysis, and Design of Overhead Steel Tank Supports

By
Ubani Obinna
-

This book has been written to address an area of structural design which is usually neglected by clients, architects, and homeowners. During the brief for the structural design of a residential building or a villa, serious attention is not usually paid to the structural design of the overhead tank supports. Overhead tank supports are structural members which are subjected to heavy imposed loads and environmental actions. As a result, they should be treated with much seriousness as other structures.

This publication, therefore, aims to cover the basic requirement or knowledge needed to design steel tank supports. However, it cannot suffice for full structural engineering textbooks on the design of steel structures.

TANK SUPPORT TEXTBOOK

Staad Pro is a popular structural engineering software. It has been utilised in this book to demonstrate, model, analyse, and obtain the internal forces that are induced in a steel tank support. The subsequent structural design of the structure is carried out manually in accordance with Eurocode 3 (BS EN 1993-1-1:2005). The procedure presented in the book is also applicable to the design of steel members in other structures.

STEEL TANK SUPPORT DESIGN TEXTBOOK 2

Chapter one of the book talks about the rationale behind the adoption of overhead tanks, the alternatives, and some engineering principles in water supply and distribution in residential buildings and large-scale municipal water supply.

Chapter two discusses the structural schemes that can be adopted for overhead steel water tank supports. The members of the frame and their functions are also described.

WATER TANK FRAME

Chapter three talks about the application of wind action to open lattice steel frame structures according to BS EN 1991-1-4. A practical wind action analysis is also presented.

PANEL 2

In chapters four and five, the modelling steps of overhead steel tanks in Staad Pro software, and the results of the analysis are presented.

Chapter six shows the actual structural design and verification of the structural members according to the requirements of Eurocode 3.

PANEL 1

The special benefits of purchasing this textbook are;

(1) Full design manual on modelling, analysis, and design of overhead tanks
(2) FREE video tutorial on modelling and analysis of overhead tanks on Staad Pro Software
(3) FREE AUTOCAD file on detailing of steel tank support members
(4) Knowledge on application of wind load on open lattice structures
(5) Design of structural members subjected to various loading

STEEL TANK PDF BOOK

Get these delivered to your e-mail immediately for NGN 2,550 only by clicking HERE.

The Everyday Engineer

By
Ivy Ugorji
-

What comes to your mind when you hear the word engineering? Does it bring to your imagination skyscrapers, bridges, highways, tech devices as well as every smart and intelligent innovation that are making our lives better? We are in a time where the conventional engineering education will no longer be to teach the engineering students all they need to learn. Modern Engineering education should be geared towards giving students patterns, ideas, and techniques that they need to continue to educate themselves for the future.

Technological advancement has stirred the world to move at a rapid rate and every career field must prepare differently than they have in the past. Engineers of the future must possess skills like innovation, entrepreneurial vision, and teamwork. As history commonly repeats itself, engineers are now shifting into more leadership roles within corporations, similar to engineers’ migration into business in the industrial age.

In the industrial age, engineers like Henry Ford and Nikola Tesla were known for their skills in engineering and business. Now we are approaching our “fourth industrial revolution” as coined by Prof. Klaus Schwab, founder and executive chairman of the World Economic Forum.

The fourth industrial revolution according to Prof. Schwab is characterized by a range of new technologies that are fusing the physical, digital and biological worlds impacting all disciplines, economies, and industries and even challenging ideas about what it means to be human.

However, as much as there are various engineering career majors, there are various techniques to boost learning, career development, and assimilating knowledge. To some engineers, the major focus is on networking, training, and development.

Three (3) major career development considerations are;

  1. Learning Style: Learning style ranges from visual learning by seeing and practicing, auditory learning by hearing and listening, and kinesthetic which is learning by touching and practicing.
  2. Type of Gap: Its no surprise engineers strive to get better by filling some various gaps which includes, knowledge gap, skills or experience gap and leadership gap. These gaps are closed by education and training, exposure to situations so as to learn.
  3. Leadership gaps: Learning and performing at high levels mostly from senior management positions in organizations.
images 1

As the world becomes increasingly interconnected, there is a need for shorter product developments. Sustained technological advancement suggests that engineers would lead projects and engineering professions would take on extra responsibilities. This is an exciting time to be alive and to be an everyday engineer. Check out available civil engineering jobs.

Be passionate for more. Stay curious, stay inspired.

Top Civil Engineering Professional Bodies in the World

By
Ubani Obinna
-

Civil Engineering is the oldest engineering profession in the world, and has been at the forefront of developing infrastructures such as buildings, roads, bridges, towers, sanitary and water supply systems, etc for the benefit of mankind. Different professional bodies have been formed in different countries to foster competence, development, unity, and coherence in the civil engineering profession. This article highlights the biggest civil engineering professional bodies in the world whose members are widely recognised as professionals.

(1) The American Society of Civil Engineers (ASCE)

1200px ASCE logo.svg

The American Society of Civil Engineers was founded in the year 1852, and represents more than 150,000 members of the civil engineering profession in 177 countries. It is the oldest engineering society in the United States of America. ASCE stands at the forefront of a profession that plans, designs, constructs, and operates society’s economic and social engine – the built environment – while protecting and restoring the natural environment.

Through the expertise of its active membership, ASCE is a leading provider of technical and professional conferences and continuing education, the world’s largest publisher of civil engineering content, and an authoritative source for codes and standards that protect the public. ASCE publishes about 35 technical journals to build professional knowledge.

The Society advances civil engineering technical specialties through nine dynamic Institutes and leads with its many professional- and public-focused programs. Members have special benefits of free PDHS, mentorship, discounts on journal and articles, free and paid webinars and conferences with discounts, career enhancements, etc.

ASCE has different membership cadres such as:

  • Student member
  • Member
  • Affiliate member
  • Associate member
  • Fellow
  • Life member
  • Distinguished member

(2) Institution of Civil Engineers (ICE)

ice logo black 002 e1587200955266

The Institution of Civil Engineers UK was formed in the year 1818 and boasts of about 95,000 civil engineer members in more than 150 countries. ICE can be regarded as the oldest civil engineering professional body in the world. The Institution aims to support the civil engineering profession by offering professional qualification, promoting education, maintaining professional ethics, and liaising with industry, academia and government. Under its commercial arm, it delivers training, recruitment, publishing and contract services.

ICE is a licensed body of the Engineering Council and can award the Chartered Engineer (CEng), Incorporated Engineer (IEng) and Engineering Technician (EngTech) professional qualifications. ICE publishes hundreds of civil engineering journals.

The membership grades of the Institution are;

  • Student
  • Graduate (GMICE)
  • Associate (AMICE)
  • Technician (MICE)
  • Member (MICE)
  • Fellow (FICE)

(3) International Association for Bridge and Structural Engineering (IABSE)

IABSE

The International Association for Bridge and Structural Engineering (IABSE) was founded in the year 1929, and has its seat in Zurich, Switzerland. It is a scientific / technical Association comprising members in 100 countries and counting 55 National Groups worldwide.

The aim of the Association is to exchange knowledge and to advance the practice of structural engineering worldwide in the service of the profession and society.

The objectives of the association are;

  • to promote cooperation and understanding among all those concerned with structural engineering and related fields by worldwide exchange of knowledge and experience
  • to encourage awareness and responsibility of structural engineers towards the needs of society
  • to encourage actions necessary for progress in structural engineering
  • to improve and foster cooperation and understanding between organisations having similar objectives.

Different membership cadres are available and they are;

  • Student member
  • Individual member
  • Collective member (for organisations)
  • Fellows

(4) The Institution of Structural Engineers (IStructE)

The institution of structural engineers logo

The Institution of Structural Engineers is the largest professional body dedicated to the practice of Structural Engineering. It was founded in the year 1908 as the Concrete Institute, and have been known since the year 1922 as the Institution of Structural Engineers. The Institution has over 27,000 members in 105 countries. They are the publishers of The Structural Engineer magazine, and the journal Structures by Elsevier.

The Institution strives towards a structural engineering profession that is built on competence, accessibility, and community. Members are offered a wide range of opportunities to develop, refresh and extend personal competencies. The Institution also help members specialise by offering tailored courses, resources and specialist qualifications.

Membership cadres;

  • Student member
  • Graduate member
  • Member (MIStructE)
  • Fellow (FIStructE)
  • Technician member (TIStructE)
  • Associate-Member (AMIStructE)
  • Associate (AIStructE)

(5) International Society for Soil Mechanics and Geotechnical Engineering (ISSMGE)

ISSMGE logo

The ISSMGE is the pre-eminent professional body representing the interests and activities of Engineers, Academics and Contractors all over the world that actively participate in geotechnical engineering. ISSMGE provides a focus for professional leadership to some 90 Member Societies and around 20,000 individual members the world. 

The ISSMGE originated in the International Conference on Soil Mechanics and Foundation Engineering, held in June 1936 at Harvard University as one of many events held to mark the university’s 300th anniversary.

The aim of the International Society is the promotion of international co-operation amongst engineers and scientists for the advancement and dissemination of knowledge in the field of geotechnics, and its engineering and environmental applications. Benefits of membership include:

• possibility to submit papers to many conferences and symposia 
• lower conference registration fees 
• possibility of membership of one the many technical committees working on specific topics 
• access to work of ISSMGE in various fields of activity, including Education, Communications,
   Technology Transfer
• opportunities to demonstrate leadership in Technical Committee, conference and other activities 
• opportunities to build lasting world-wide relationships 
• a clear demonstration of interest and professionalism in the field of Geotechnics 

Application of Courbon’s Theory in the Analysis of T-Beam Bridge Decks

By
Ubani Obinna
-

Courbon’s theory is one of the popular classical methods of analysing slab and beam girder (T-beam) bridges. However, the results obtained from the method are usually very uneconomical when compared with other numerical methods like grillage analogy. It is one of the easiest manual calculation methods that can be adopted in evaluating the effect of traffic actions in bridge deck girders.

Courbon’s theory was originally developed for bridge girders with series of cross beams (diaphragm) in which the cross beams are stiff enough to provide adequate lateral stiffness. By implication, the application of the method requires that the cross beams will have a depth not less than 75% of the main longitudinal girders. It also requires that the span to width ratio of the bridge will be greater than 2 but less than 4.  

T beam bridge deck arrangement

Let us consider the application of Courbon’s theory on the bridge deck arrangement shown above. When the beams are equally spaced and geometrically equal, the reaction factor for each beam is given by equation (1);

Ri = P{(1/n) + 6ei/[nS(n + 1)]} ——- (1)

Where;
Ri = Reaction factor
P = Applied load
n = Number of longitudinal beams
S = Spacing of longitudinal beams
ei = Eccentricity of load with respect to the centroidal axis of the bridge deck

If we set P = 1.0, we can obtain the influence line pertaining to each beam.

Solved Example

A T-beam bridge deck with 3 girders is loaded according to Load Model 1 of EN 1991-2 as shown below. Using Courbon’s method, calculate the bending moment and shear force on girder number 1.

Loaded bridge deck

Setting P= 1.0 at girder number 1 as shown below, we can obtain the influence diagram using equation (1).

K

Ri = P{(1/n) + 6ei/[nS(n + 1)]}

R1 = 1.0{(1/3) + (6 x 3.6)/[3 x 3.6(3 + 1)]} = 0.833
R2 = 1.0{(1/3) + (6 x 0)/[3 x 3.6(3 + 1)]} = 0.333
R3 = 1.0{(1/3) + (6 x -3.6)/[3 x 3.6(3 + 1)]} = -0.167

The influence diagram for the girder is therefore given below. The values at the two cantilever portions of the bridge deck can be obtained using similar triangles.

Influence diagram for bridge deck

We can therefore apply the Load Model 1 on the influence line diagram. You will need careful calculation of the ordinates of the influence line diagram using similar triangle.

influence line of a loaded bridge

For the tandem wheel loads (concentrated wheel actions), we will multiply the wheel load by the ordinate that the influence line makes with the centreline of each tandem wheel load;
QT = (600 x 0.625) + (400 x 0.209) = 458.6 kN

For the uniformly distributed loads, we will multiply the load (udl) by the width and by the centroid the load makes with the ordinate of the influence line. We normally neglect the beneficial effect of the negative part of the influence line.
wT = (3 x 1.45 x 0.934) + (9 x 3 x 0.625) + (2.5 x 3 x 0.209) = 22.51 kN/m

Let us assume that we are dealing with 20m span bridge, the preliminary effect of the vehicle action on the girder can be taken as given below;

Loaded beam with internal stresses diagram

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Design of Timber Beams

By
Ubani Obinna
-

Design of flexural members such as timber beams principally involves consideration of the effects of actions such as bending, deflection, vibration, lateral buckling, shear, and bearing. The process of design of such structures is described in Eurocode 5 (EN 1995-1-1:2004), and a design example is shown in this article.

Design Example

Loaded Timber beam

A 75 mm by 200 mm deep sawn timber beam in a domestic residence supports the characteristic loading shown above. The beam has a clear span of 2.75 m, the bearing length has been restricted to 100 mm at each end, is of strength class C24 to BS EN 338:2003, and functions in service class 2 conditions. The beam is laterally restrained against lateral buckling along its length.

Given that;

Gk.udl  = 1.3 kN/m (characteristic uniformly distributed permanent action)
Qk.udl = 1.5 kN/m (characteristic uniformly distributed medium-term action)
Gk.p = 1.00 kN characteristic point load at mid-span

1. Beam geometric properties
Breadth of the beam b = 75 mm
Depth of the beam h = 200 mm
Clear span of the beam, lc = 2750 mm
Bearing length of the beam at each end, bl  = 100 mm
Design span of the beam l = (lc + lb) = 2750 + 100 = 2850 = 2.85 m
Section modulus of the beam about the y–y axis, Wy = bh2/6 = (75 × 2002)/6 = 5 × 105 mm3

2. Timber properties
Strength class C24 (BS EN 338:2003, Table 1):
Characteristic bending strength,  fm.k = 24 N/mm2
Characteristic shear strength,  fv.k = 2.5 N/mm2
Characteristic bearing strength,  fc,90,k = 2.5 N/mm2
Fifth-percentile modulus of elasticity parallel to the grain, E0.05 = 7.4 kN/mm2
Mean modulus of elasticity parallel to the grain, E0,mean = 11 kN/mm2
Mean shear modulus, G0,mean = 0.69 kN/mm2
Mean density of the beam timber, ρm = 420 kg/m3

3. Partial safety factors
(UKNA to BS EN 1990:2002, Table NA.A1.2(B))) for the ULS
Permanent actions, γG.ULS = 1.35
Variable actions, γQ.ULS = 1.5

(UKNA to BS EN 1990:2002, Table NA.A1.1 – Category A)
Factor for the quasi-permanent value of the variable action, ψ2 = 0.3

(UKNA to EC5, Table NA.3)
Material factor for solid timber at the ULS, γM = 1.3

4. Actions

(i) ULS
(a) Characteristic self-weight of the beam, Gk,swt
Gk,swt = b · h · g · ρm = (0.075 × 0.2 × 9.81 × 420)/1000 = 0.062 kN/m
Design action from the selfweight of the beam, Fd,swt
Fd,swt = γG.ULS · Gk.swt  = 1.35 × 0.062 = 0.0837 kN/m

(b) Characteristic permanent action due to the point load, Gk,p
Gk,p = 1.00 kN
Design permanent action due to the point load, Fd.p
Fd,p = γG.ULS · Gk.p =  1.35 ×  1.0 = 1.35 kN

(c) Characteristic permanent action due to the UDL, Gk,udl
Gk,udl = 1.3 kN/m
Design action due to the permanent action UDL, Fd,p,udl
Fd,p,udl = γG.ULS · Gk.udl  =1.35 x 1.3 = 1.755 kN/m

(d) Characteristic medium-term action due to the UDL, Qk,udl
Qk,udl = 1.5 kN/m
Design action due to the variable action UDL, Fd,q,udl
Fd,q,udl = γQ.ULS · Qk.udl = 1.5 × 1.5 =  2.25 kN/m

Total UDL @ ULS = 0.0837 + 1.755 + 2.25 = 4.1 kN/m
Total concentrated action @ ULS = 1.35 kN

5. Modification factors
Factor for medium-duration loading and service class 2, kmod.med = 0.8 (EC5, Table 3.1)
Size factor for depth greater than 150 mm, kh = 1.0 (EC5, equation (3.1))
Lateral stability of the beam: kcrit = 1 (EC5, 6.3.3))
Bearing factor kc,90 = (taken as 1.0) (EC5, clause 6.1.5(2) )
Deformation factor for service class 2, kdef = 0.8 (EC5, Table 3.2)
Load sharing factor, ksys is not relevant ksys = 1.0

(6) Bending strength
The design bending moment;

Md =ql2/8 + PL/4= (4.1 × 2.852)/8 + (1.35 × 2.85)/4 = 4.162 + 0.96 = 5.122 kNm

Design bending stress, σm,y,d = Md/Wy = (5.122 × 106)/( 5 × 105) = 10.244 N/mm2

Design bending strength, fm,y,d = (kmod.med·ksys·kh· fm.k)/γM = (0.8 × 1.0 × 1.0 × 24)/1.3 = 14.77 N/mm2

σm,y,d < fm,y,d   Section is okay in bending

(7) Shear Strength
Design shear force Vd = ql/2 + P/2 = (4.1 × 2.85)/2 + (1.35/2) = 6.52 kN

Design shear stress, τv.d (EC5, equation (6.60))
τv.d = 1.5Vd/bhef = (1.5 × 6.52 × 1000)/(75 × 200) = 0.652 N/mm2

Design shear strength,  fv,d = (kmod.med·ksys· fv.k)/γM = (0.8 × 1.0 × 2.5)/1.3 = 1.54 N/mm2

τv.d < fv,d  Section is okay in shear

(8) Bearing Strength
The design bearing force will equal the design shear force in the beam, Vd

Design bearing stress, σc,90,d  = Vd/b·lb = (6.52 × 1000)/(75 x 100) = 0.833 N/mm2

Design bearing strength, (EC5,equation (6.3)))

fc.90.d = (kmod.med · ksys · kc.90 · fc.90.k)/ γM = (0.8 × 1.0 × 2.5)/1.3 = 1.54 N/mm2

σc,90,d  < fc.90.d  Section is okay in bearing

(9) Deflection

Instantaneous deflection due to permanent actions

Deflection in timber structures

uinst,point,G = (1/4) × [1/(11 × 75 × 2003)] × 28503 × [1 + 1.2 × (11/0.69) × (200/2850)2] = 0.959 mm

Uinst,udl,G = (5/32) × [(1.3 × 10-3 + 0.062 × 10-3)/(11 × 75 × 2003)] × 28504 × [1 + 0.96 × (11/0.69) × (200/2850)2] = 2.287 mm

Uinst.G = uinst,point,G + Uinst,udl,G =  0.959 + 2.287 = 3.246 mm

Instantaneous deflection due to variable action

Deflection in timber due to variable action

Uinst,Q = (5/32) × [(1.5 × 10-3)/(11 × 75 × 2003)] × 28504 × [1 + 0.96 × (11/0.69) × (200/2850)2] = 2.519 mm

Combined permanent and variable instantaneous deflection = uinst = uinst,G + uinst,Q = 3.246 + 2.519 = 5.765 mm

Eurocode 5 limit on deflection (Table 7.2, EC5) winst = l/300 = 2850/300 = 9.5 mm (uinst < winst Instantaneous deflection is okay)

Final deflection
Final deflection due to permanent actions ufin,G = uinst,G (1 + kdef) (Equation 2.3, EC5)
ufin,G = 3.246  (1 + 0.8) = 5.843 mm

Final deflection due to the variable and quasi-permanent actions,  ufin,Q = uinst,Q (1 + ψ2kdef) (Equation 2.4, EC5)
ufin,Q = uinst,Q (1 + ψ2kdef) = 2.519 (1 + 0.3 × 0.8 ) = 3.12 mm

Final deflection due to the permanent and quasi-permanent actions actions
unet,fin = ufin,G + ufin,Q = 5.843 + 3.12 = 8.963 mm

Deflection limit wnet,fin = l/150 = 2850/150 = 19 mm

The deflection of the beam is satisfactory

To download this design article in PDF format, click HERE.

IABSE Postpones 2020 Congress due to COVID-19

By
Ivy Ugorji
-

The International Association for Bridge and Structural Engineering (IABSE) has postponed the IABSE 2020 Congress ChristChurch New Zealand, initially scheduled to hold from 2 – 4 September 2020 to 3 – 5 February 2021 due to the COVID-19 global pandemic.

IABSE is a fellowship of structural engineers operating on a worldwide basis, with interests in all type of structures, in all materials. It acts to improve our knowledge and understanding of the performance of structures. Its members represent structural engineers of all ages, employed in design, academia, construction, regulation and renewal. Many of its members occupy senior roles based on a history of personal achievement.

In a statement released by the IABSE 2020 Congress Organising Committee on their website;

The IABSE 2020 Congress which was supposed to take place on 2 – 4 September 2020 is now rescheduled to take place on February 3-5, 2021. We sincerely hope that this date is far enough in the future that will allow us to have a successful and productive event.

This decision has been taken in consideration of the safety and comfort of all our participants especially those coming from abroad. February is a beautiful time of year to visit New Zealand, with it being summer we encourage you to make a plan to have an extended trip to this side of the world once international travel bookings can commence again.

The registration platform remains open and we encourage you to register as soon as you are in a position to do so. We will extend the early registration deadline out to 2 October 2020 to ensure you don’t miss out on the opportunity to get a discounted rate.

We are currently undertaking the paper review process and this will continue as normal, however authors will receive feedback at a slightly later date than previously advertised. Please refer to www.iabse.org/christchurch2020 for revised dates.

We are looking forward to welcoming you to New Zealand when we’re all in a position to meet again!

In another related event, the IABSE Symposium Wroclaw 2020 which was supposed to take place on 20-22 May 2020 has also been rescheduled to take place on 7-9 October 2020. The Registration Platform has been re-opened, and authors, registered participants will automatically receive updates through mails, newsletters and on their official symposium website at www.iabse.org/Wroclaw2020.

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