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DEPARTMENT OF ARCHITECTURE

ABUBAKAR TAFAWA BALEWA UNIVERSITY, BAUCHI

ARC 615: ADVANCED BUILDING STRUCTURES

LESSON 1: LOADS ACTING ON STRUCTURAL SYSTEMS

1.1 Introduction

1.2 Types of Loads

1.2.1 Dead loads

1.2.2 Live loads

1.2.3 Wind loads

1.2.4 Snow loads

1.2.5 Stress created by temperature differences (temperature

loads)

1.2.6 Stress created by ground movement (seismic loads)

1.2.7 Accidental loads

1.2.8 Dynamic loads

1.3 Load combinations

1.4 Codes used for estimating loads

1.5 Examples of loading estimates

1.1 Introduction

This lesson covers loads acting on structural systems. These loads are dead loads, imposed

or live loads, wind loads, snow loads, stress created by temperature differences, stress

created by ground movement, accidental loads, and dynamic loads. These loads are

combined in various configurations to determine the most onerous load combination for

structural analysis. The codes used for estimating loads for buildings are BS 6399 parts 1, 2

and 3. Examples of loading estimates are given.

1.2 Types of Loads

The loads found in building structures are:

1. Dead loads.

2. Imposed loads (live loads).

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3. Wind loads.

4. Snow loads.

5. Temperature loads.

6. Seismic loads.

7. Accidental loads.

8. Dynamic loads.

Dead loads

These are loads due to the weight of all walls, permanent partitions, floors, roofs, finishes

and all other permanent construction including services of a permanent nature. The loads

are permanent and stationary.

Imposed loads

This is the load assumed to be produced by the intended occupancy or use, including the

weight of movable partitions, distributed, concentrated, impact and inertia, loads, but

excluding wind loads. These loads are often called live loads due to their changing nature.

Wind loads

The load due to the effect of wind pressure or suction on walls and roofs both internally

and externally.

Snow loads

These loads are due to the accumulation of snow on building components, especially roofs.

The accumulation of water on membrane covering of tent structures produces a similar

effect.

Temperature loads

These loads result from diurnal and seasonal temperature variations. Building components

made from varying materials will expand and contract at different rates, leading to stress.

Seismic loads

These loads are caused by ground movement.

Accidental loads

These are loads resulting from an accidental occurrence, such as an explosion, fire, or

impact by an external force such as a vehicle.

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Dynamic loads

These loads are caused by moving loads, such as vehicles moving on a bridge, a column of

soldiers marching, or a large group of people walking in a building.

1.2.1 Dead Loads

Dead loads are calculated from the unit weights given in BS 648 or from the actual known

weights of the materials used. Where there is doubt as to the permanency of dead loads,

such loads should be treated as imposed loads. Where permanent partitions are indicated,

their actual weights are included in the dead load.

Unit weights of basic roofing elements and components.

Basic roofing (sheet) materials Unit weight (psf) Unit weight (kN/m2)

Aluminium roofing sheet 0.84 0.04

Asphalt (19 mm) 9.40 0.45

Asphalt (approx. 6 mm) 2 0.10

Glass (single glazing) 2.09 0.1

Rafters battens roofing felt 2.92 0.14

Slates 12.53 0.6

Slate (6 mm) 10 0.48

Heating and cooling ductwork 4.0 0.19

Steel suspended ceiling 2.0 0.10

Channel suspended ceiling

system 1.0 0.05

20 ga metal deck 2.5 0.12

Cement asbestos (9.5 mm) 4.0 0.19

Timber floorboards 3.13 0.15

Source: Adapted from E-bookspdf.org (2014) and Internet search. The coloured figures are

conversions.

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1.2.2 Imposed floor and ceiling loads

The loads appropriate to the type of activity/occupancy for which the floor area will be

used in service are given in the codes. The loads in the codes should be treated as the

unfactored or characteristic loads for design purposes. They should be considered as the

minimum values to be adopted. Where higher values are considered more appropriate,

based on knowledge of the proposed use of the structure or proposed installation of

equipment, machinery, stacking systems, etc., they should be used instead.

All floors should be designed to carry the uniformly distributed or concentrated load,

whichever produces the greatest stresses (or where critical, deflection) in the part of the

floor under consideration.

The categories adopted for types of activity/occupancy are:

Category Activity / Occupancy

A Domestic and residential activities

B Office and work areas not covered elsewhere

C Areas where people may congregate

D Shopping areas

E Areas susceptible to the accumulation of goods

F/G Vehicle and traffic areas

Typical Floor Loads

Typical floor loads are shown in the table below.

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Typical floor loads.

Function Typical floor load (kN/m2)

Classrooms 3.0

Computer labs 3.5

Dance halls 5.0

Offices (general) 2.5

Offices (filing) 5.0

Theatres (fixed seats) 4.0

Shops 4.0

Art galleries 4.0

1.2.3 Wind loads

The Steel Construction Institute (2002) recommends four stages in the calculation of wind

loads.

1. Dynamic classification of the structure,

2. Calculation of wind speeds,

3. Calculation of the dynamic pressure, and

4. Calculation of the loads on the building.

This procedure was streamlined in a flowchart by Mahfouz (1999) after British Standards

Institute (2002b) as shown in the figure below.

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Flow chart illustrating outline procedure for the determination of the wind loads according

to BS 6399: Part 2. Source: Mahfouz (1999, p.8) after British Standards Institute (2002b).

1.2.4 Snow loads

This is required is areas where snowfall or frost is experienced.

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1.2.5 Temperature loads

This is required where there are large diurnal (daily) and seasonal temperature variations.

1.2.6 Seismic loads

This is required in areas prone to earthquakes and ground tremors.

1.2.7 Accidental loads

The maximum loading resulting from a single accidental loading is estimated and applied

to structural elements essential to the residual stability of the building.

1.2.8 Dynamic loads

The most common source of dynamic loading in buildings is wind. This is however treated

as a separate loading from other common dynamic loads resulting from moving loads such

as vehicles, equipment and people.

1.3 Load combinations

Loads on structural members are combined to determine the most onerous loading for

each member and this loading combination is then used to design the structural member.

This is to ensure that the member does not exceed the ultimate and serviceability limit

states.

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Load cases and load combinations

Case Label Case name Nature Analysis type

1 DL1 Self-weight Dead Static - linear

2 LL1 Live roof access & maintenance Live Static - linear

3 DL2 Roof covering, ceiling and services Dead Static - linear

4 PURLIN Dead load from purlins Dead Static - linear

5 JOIST Dead load from joists Dead Static - linear

9 WIND1 Wind load Wind Static - linear

11 TEMP1 TEMP1 Temperature Static - linear

12 SEIS1 SEIS1 Seismic Static - linear

13 ACC1 ACC1 Accidental Static - linear

21 COMB1 Self-weight + roofing + access +

services Combination

Linear combination

22 COMB2 All loads except wind loads Combination Linear

combination

23 COMB3 All loads Combination Linear

combination

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Sample load case combination matrix.

Load Combination

Case Label Case name

Case 21 (COMB1) Self-weight +

roofing + access + services

Case 22 (COMB2)

All loads except wind loads

Case 23 (COMB3) All loads

1 DL1 Self-weight ● ● ●

2 LL1 Live roof access &

maintenance ● ● ●

3 DL2 Roof covering,

ceiling and services

● ● ●

4 PURLI

N Dead load from

purlins ● ● ●

5 JOIST Dead load from

joists ● ● ●

9 WIND1 Wind load

●

11 TEMP1 TEMP1

● ●

12 SEIS1 SEIS1

● ●

13 ACC1 ACC1

● ●

1.4 Codes used for estimating loads

Loading estimates for buildings in Nigeria are usually made according to BS 6399 Parts 1, 2

and 3 (British Standards Institute, 2002a; 2002b and 2002c). These codes provide for

loading of buildings in various scenarios:

5. Part 1: Dead and imposed loads, excluding wind loads, imposed roof loads, snow

loads, et cetera.

6. Part 2: Wind loads (gust peak wind loads on buildings and components). Does not

apply to buildings susceptible to dynamic excitation.

7. Part 3: Imposed roof loads produced by environmental effects on the roof,

excluding wind loads, and by use of the roof either as a floor or for access for

cleaning and maintenance.

Examples of other codes used for estimating loads in structures other than buildings are

found in the table below

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Examples of British codes used for estimating loads in structures other than buildings

Code Used for

BS 5400 Road and rail bridges

BS 2655 Lifts

BS 2573 Crane gantry girders

1.5 Examples of loading estimates

An example of loading estimate is shown below.

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Load Case Load Description Load type Node list FX (kN) FY (kN) FZ (kN)

1 DL1 self-weight 2875 to 2912 Whole structure

Factor=1.00

9 Wind load nodal force 1 0 0 -0.79






9 Wind load nodal force 2 0 0 2.34

9 Wind load nodal force 35 141 to 143 0 0 3.89

9 Wind load nodal force 5 to 31 By 2 144 to 148 150 to 171 0 0 2.87

2 Live Roof Access & Maintenance Load nodal force 1 0 0 -8.06



2 Live Roof Access & Maintenance Load nodal force 37 0 0 -18



2 Live Roof Access & Maintenance Load nodal force 5 to 35 By 2 141 to 148 150 to 173 0 0 -20.25


3 Roof covering, ceiling & services nodal force 1 0 0 -1.94






3 Roof covering, ceiling & services nodal force 5 to 35 By 2 141 to 148 150 to 173 0 0 -4.86


28 Dead Load from Purlins nodal force 1 0 0 0

28 Dead Load from Purlins nodal force 177 0 0 -0.05





28 Dead Load from Purlins nodal force 5 to 35 By 2 141 to 148 150 to 173 0 0 -0.3


29 Dead Load from Joists nodal force 1 0 0 -3.83






29 Dead Load from Joists nodal force 5 to 35 By 2 141 to 148 150 to 173 0 0 -3.83


9 Wind load nodal force 33 172 173 0 0 -1.99

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References

British Standards Institute (2002a). BS 6399-1:1996. Loading for Building Part 1. Code of

practice for dead and imposed loads. British Standards Institute.

British Standards Institute (2002b). BS 6399-2:1997 - Loading of Buildings – Part 2: Code of

practice for wind loads. Incorporating amendment number 1 corrected and reprinted

June 2002. British Standards Institute.

British Standards Institute (2002c). BS 6399-3:1988 - Loading of Buildings – Part 3: Code of

practice for imposed roof loads. Incorporating amendments numbers 1 and 3, and

implementing amendment number 2. British Standards Institute.

E-bookspdf.org (2014). Loads Dead Loads Imposed Loads – Dalhousie University.

Retrieved from http://e-bookspdf.org.

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