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Discuss the influence of the Building Regulations on structural design.

Explain the limit state design philosophy and its influence on structural design.

Aim: Understanding Structures – Building Regulations & the Limit State Design Philosophy.

Objectives: At the end of the lesson, the students should be able to:

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Introduction

The Building Act 1984 is the primary piece of legislation that formed the Building Regulations and their Approved Documents.
The Building Act 1984 is an overarching legislation that provides the legal framework for building and construction activities.
Building regulations are minimum standards for design, construction and alterations to virtually every building. The regulations are developed by the UK government and approved by Parliament.
Compliance with Building Regulations is mandatory, and failure to adhere to these standards can result in legal consequences.

Approved Documents set out detailed practical guidance on compliance with the regulations: (Set into a whole range of subsections: Parts A-S).
The Building Act covers some of the following provisions:
Power to make the Building Regulations and any subsequent revisions.
Production of Approved Documents
To allow the passing of submitted plans.
To give powers to inspectors.
Penalties for breaches to the regulations.

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Approved Document
A: Structure	This deals with the structural integrity of a building and its fabric. The supporting structure needs to be safe and secure and free from any movement, settlement or degradation over time.
B: Fire safety	Evacuation and protection of the structure for a minimum time period is essential in saving lives and stopping fire spreading.
C: Site preparation and resistance to contaminates and moisture	This covers the removal of any biological vegetation from beneath a building prior to construction, and includes the provision of drainage and the passage of moisture into a building.
D: Toxic substances	This covers, for example, the provision of insulating materials giving off toxins from cavity walls.
E: Resistance to the passage of sound	Robust details must be employed to prevent the passage of sound between neighbours through walls, ceilings and floors.
F: Ventilation	The provision of natural and forced ventilation to kitchens, bathrooms and toilets.
G: Sanitation, hot water safety and water efficiency	The provision of adequate sanitation facilities, baths and showers and efficient water systems that conserve energy.
H: Drainage and waste disposal	The provision of drainage to carry away foul and surface water.

Approved Documents

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Approved Document.
J: Combustion appliances and fuel storage systems	The safe use of combustion equipment, the discharge of combustion gases to air and all ancillary equipment.
K: Protection from falling, collision and impact	The provision of appropriate stairs, their handrails and balustrade guarding and the provision for ramped access into the buildings.
L: Conservation of fuel and power	The provision of insulation to reduce heat loss and to conserve energy.
M: Access to and use of buildings	The provision of suitable and appropriate disabled access to buildings.
N: Glazing safety (withdrawn)	Part N has been withdrawn and is now incorporated into part K.
O: Overheating	It covers the overheating improvement requirements. It also includes guidance on providing means of removing excess heat from residential buildings.
P: Electrical safety	All electrical works on a property must be carried out by a registered electrician who can provide the correct documentation to sign off on part P.

Approved Documents

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Approved Document
Q: Security in dwellings	This covers the security of new dwellings in preventing ingress (entrance) into a building by unauthorised persons by ensuring a reasonable standard of doors and windows security.
R: High speed electronic communications networks	This covers the provision of data and broadband installations and the provision of the conduits and infrastructure to enable easy installation into a building or structure.
S: Infrastructure for charging electric vehicles	It provides technical guidance regarding the installation and charge point requirements for electric vehicles (EVs)
7: Materials and workmanship	This provides guidance on materials and workmanship, i.e. the use of the appropriate materials for a construction and how those who are working on the building must behave in a workmanlike manner.

Approved Documents

We will only consider Approved Document A in this class

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Structural Stability

Approved documents A provides practical guidance to the following requirements of the Building Regulations 2010 with respect to the structural stability requirements (loading, ground movement, and disproportionate collapse) of dwellings:

A1: The building shall be constructed so that the combined dead, imposed and wind loads are sustained and transmitted by it to the ground: safely; and without causing such deflection or deformation of any part of the building, or such movement of the ground, as will impair the stability of any part of another building
A2: The building shall be constructed so that ground movement caused by: swelling, shrinkage or freezing of the subsoil; or land-slip or subsidence , will not impair the stability of any part of the building
A3: The building shall be constructed so that in the event of an accident the building will not suffer collapse to an extent disproportionate to the cause

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For Stability and Safety of Buildings

The assembly of the structure
Overall size and proportioning of the building need to follow the guidance provided by the Approved document A.
The layout of internal and external walls should form a robust box structure in accordance with the provided guidance.
The internal and external walls are well connected by either masonry bonding or mechanical connections.

The roof and intermediate floors are well connected to the walls to provide adequate support and transfer of wind loads to the foundation/buttressing elements.

Figure 1. Size and proportion of residential buildings ≤ three storeys (The Welsh Government, 2010).

Figure 2. Size and proportion of non-residential buildings and annexes (The Welsh Government, 2010).

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For Stability and Safety of Buildings

The quality of the workmanship
Attention to detail.
Properly executed connections and joints.
Adherence to industry standards and building codes.
Thorough inspections and rigorous testing.
Continuous monitoring and quality control measures are implemented to identify and rectify potential issues.
Effective collaboration and communication among all stakeholders.

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For Structural Stability of Buildings:

The different loadings on the structure: dead load, imposed load, wind load, etc.

Elements	Loading
Roof	Distributed loads. 1.0 kN/m² for spans not exceeding 12 m. 1.5 kN/m² for spans not exceeding 6 m.
Floors	Distributed load: 2.00 kN/m²
Ceilings	Distributed load: 0.25 kN/m² Together with concentrated load: 0.9 kN

Table 1. Imposed load on structural elements of residential buildings of traditional masonry construction (The Welsh Government, 2010)

BS 6399 : Part 1 : 1996: Code of practice for dead and imposed loads

BS 6399-2:1997 Loading for buildings. Code of practice for wind loads BRE digest 436 Parts 1, 2 and 3.

BS 6399-3:1998 Loading for buildings. Code of practice for imposed roof loads.

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Assignment

Discuss the statutory requirements to ensure safety in structural designs.

Hint:

Make reference to at least ANY THREE of the following:
Building Regulations.
Eurocodes/British Standards.
Construction (Design and Management) Regulations 2015.
Planning Permission.
Building control Authorities.
Etc.�

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Limit State Design Method

The only design method/philosophy we will consider in this class is the limit state method since we will be working with Eurocodes. This method considers the safety at the ultimate load and serviceability at the working load.
“Limit state is the state of impending failure, beyond which a structure ceases to perform its intended function satisfactorily, in terms of either safety or serviceability.”

Eurocodes

BS EN 1990 Eurocode 0: Basis of structural design
BS EN 1991 Eurocode 1: Actions on structures
BS EN 1992 Eurocode 2: Design of concrete structures
BS EN 1993 Eurocode 3: Design of steel structures
BS EN 1994 Eurocode 4: Design of composite steel and concrete structures
BS EN 1995 Eurocode 5: Design of timber structures
BS EN 1996 Eurocode 6: Design of masonry structures
BS EN 1997 Eurocode 7: Geotechnical design (foundations)
BS EN 1998 Eurocode 8: Design of structures for earthquake resistance (seismic design)
BS EN 1999 Eurocode 9: Design of aluminium structures

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Limit State Design Method

Ultimate Limit State (ULS)
This state is associated with collapse or similar structural failure. It considers strength, overturning, fatigue, sliding etc.
The categories of ULS are: EQU Loss of equilibrium of the structure. E.g. overturning, sliding of retaining wall. STR Internal failure or excessive deformation of the structure or structural member. E.g. buckling, bending, shear failures. GEO Failure due to excessive deformation of the ground. E.g. settlement, liquefaction, slope failure. FAT Fatigue failure of the structure or structural members E.g. cracking, deterioration. UPL Uplift failure. E.g. buoyancy-induced uplift, wind-induced uplift. HYD – Seepage failure E.g. internal erosion/piping of dams, external erosion of foundation.
Design situations: Persistent: design situation that is relevant during a period of the same order as the design working life of the structure. E.g. cyclic loads, normal conditions of use for a building. Transient: design situation that is relevant during a period much shorter than the design working life of the structure and which has a high probability of occurrence. E.g. Maintenance/repair activities, wind. Accidental: design situation involving exceptional conditions of the structure or its exposure, including fire, explosion, impact or local failure. Seismic: design situation involving exceptional conditions of the structure when subjected to a seismic event.

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Limit State Design Method

Serviceability Limit State (SLS)
This is the state such that the structure remains functional for its intended use subject to routine loading.
It does not relate to the building strength but other factors that make the structure functional. For example, vibration of floors or other building components causing discomfort while the building/floor has not collapsed.
It considers durability, fire resistance, deflection, excessive vibration, etc.

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Partial Factor

Partial Factors on Action (A) - dead load and variable loads.

Limit state	Load effect
A-EQU	Unfavourable	1.10	1.50
A-EQU	Favourable	0.90	0.00
B-STR/GEO (Set A1)	Unfavourable	1.35	1.50
B-STR/GEO (Set A1)	Favourable	1.00	0.00
C-STR/GEO (Set A2)	Unfavourable	1.00	1.30
C-STR/GEO (Set A2)	Favourable	1.00	0.00

In Eurocode, a "favourable" load effect refers to the load effect that produces the most favourable conditions for the structure. Favourable action are forces that prevents failure.

On the other hand, an "unfavourable" load effect refers to the load effect that produces the most adverse conditions for the structure. It is the load effect that leads to the most critical response in terms of safety and stability. Unfavourable actions are forces that causes failure.

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Partial Factor

This is a coefficient applied to the design loads or structural capacities to account for uncertainties and variabilities in the loadings, materials, and construction processes.
Characteristic Value: The characteristic value of a material refers to the statistical measure of strength that is representative of the material. It is denoted as fck (e.g., fck of concrete = 25 MPa), where "f" stands for characteristic and "ck" represents the cylinder compressive strength of concrete.
The characteristic value of a material property is normally defined as the value below which not more than 5% of test results may be expected to fail. For example, for 100 concrete cubes, this would mean approximately 95 of the samples would be stronger than the characteristic value of the material strength.

28-day Cube compressive strength (higher) used in UK.
28-day Cylinder compressive strength (lower) used in Europe.

Concrete grades to BS 8500 and BS EN 206

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Partial Factor

Partial safety factors for material properties
Combination
Fundamental	1.5	1.15
Accidental (not earthquakes)	1.3	1.0

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Worked Example 1

Determine the values of the reactions at the supports. Draw the shear force diagram and determine the maximum bending moment in the simply supported beam shown in fig. 1.

Figure 1.

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Worked Example 1; Solution

Draw free body diagram.

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Worked Example 1; Solution

Drawing the Shear Force Diagram (SFD)

@ A, Shear Force, SF = 21.75 kN

@ 1.5 m from A, Shear Force, SF = 21.75 – 20.25 = 1.5 kN

Then, adjust for the 3 kN point load:

1.5 – 3 = - 1.5 kN

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Worked Example 1; Solution

Drawing the Shear Force Diagram (SFD)

@ 3 m from A, Shear Force, SF = 21.75 – 40.5 - 3 = - 21.75 kN

Then, adjust for reaction R_bV21.75 kN:

- 21.75 + 21.75 = 0 kN

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Worked Example 1; Solution

Maximum Bending Moment

Any points where the shear force diagram cross the x-axis will be a maximum or minimum Bending Moment.
Since the diagram crosses at 1.5 m, we will determine the bending moment value at that point along the beam.

@ 1.5 m from A, maximum bending Moment =

(21.75 X 1.5) – (13.5 X 1.5 X 0.75) – (3 X 0) = 17.4375 kNm

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Worked Example 1; Solution

Maximum Bending Moment- Alternative Method

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Self-assessment Task

Determine the values of the reactions at the supports. Draw the shear force diagram and calculate the maximum bending moment in the simply supported beams shown in figs. 2 and 3.
Finally, check your answers using the standard formulas shown in fig. 4.

Figure 2.

Figure 3.

Figure 4.

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References/Bibliography

Emmitt, S. and Gorse, C. (2006) Barry’s advanced construction of buildings. Oxford: Blackwell publishing.

Minimising Energy in Construction (n.d.) Characteristic values – why “95%”?. Available at: https://www.meicon.net/95-values#:~:text=Characteristic%20material%20properties%20are%20divided,properties%20of%20materials%20in%20buildings. (Accessed: 30 September 2023).

Pearson (2017) BTEC national construction student book. London: Pearson.

Planning portal (2023) Approved documents. Available at: https://www.planningportal.co.uk/applications/building-control-applications/building-control/approved-documents (Accessed: 9 October 2023)

Smith, P. S. (2001) An introduction to structural mechanics. Basingstoke: Palgrave.

The Concrete Centre (2017) Practical design to eurocode 2. Available at: https://concretecentre.com/TCC/media/TCCMediaLibrary/PDF%20attachments/Lecture-1-Intro-and-background.pdf (Accessed: 9 October 2024)

The Welsh Government (2010) Approved document A: structure. Available at: https://www.gov.wales/sites/default/files/publications/2019-04/170403building-regs-approved-document-a-structure-en.pdf (Accessed: 19 August 2023)

Virdi, S. (2012) Construction science and materials. West Sussex: John Wiley & Sons, Ltd.