Accurate loading of buildings is necessary if accurate analysis and design would be carried out for the building. In the loading of structures, two types of load are encountered, dead load (BS 8110) or permanent action (EC 2) and live load (BS 8110) or temporary action/imposed loads (EC 2). For all types of structures, these two loads are encountered.
Permanent actions chiefly consist of the self-weight of the structures or construction works. Self-weight is usually represented as single characteristic value or estimated as the product of the nominal dimensions as shown on the drawings of the structural elements, non-structural elements, or fixed services and the mean characteristic values of weight/density of the constituent materials. In the determination of the permanent action, the following shall be taken into consideration:
- The total self-weight of structural and non-structural members.
- The critical load cases in areas where it is expected to add and remove structural and non-structural members.
- The self-weight of new coatings and distribution conduits.
- The moisture content of stored materials in case of buildings used for storage.
Examples of Elements in Buildings
Structural elements include: beams; columns; slabs; stairs; pad bases; raft foundation etc.
Non-structural elements include: roofing; surfacing and coverings; partitions and linings (except movable partitions that are treated as imposed loads); hand rails, safety barriers, parapets and kerbs; wall cladding; suspended ceilings thermal insulation; bridge furniture; fixed services.
Fixed services include: equipment for lifts and moving stairways; heating, ventilating and air conditioning equipment; electrical equipment; pipes without their contents; cable trunking and conduits.
The self-weight of elements such as flooring systems, facades and ceilings, lifts and equipment for buildings may be provided by the manufacturer.
The self-weight of movable partitions may be determined as its equivalent UDL which is then added to the imposed loads.
Imposed loads on buildings are those arising from occupancy. By occupancy may include: normal use by persons; furniture and moveable objects (e.g. moveable partitions, storage, the contents of containers); vehicles; anticipating rare events, such as concentrations of persons or of furniture, or the moving or stacking of objects which may occur during reorganization or redecoration. Imposed loads which are classified as free actions are usually modeled as uniformly distributed loads, line loads or concentrated loads or combinations of these loads. Imposed loads on Table 2 below are valid for all structures except in the following cases:
- Imposed loads on bridges (EN 1991-2).
- Imposed loads due to accidental actions such as impact from vehicle or accidental loads from machines (EN 1991-1-7).
- Imposed loads associated with resonance effects from synchronized rhythmical movement of people or dancing or jumping. In this case, dynamic effect should be factored in the analysis.
- Imposed loads with additional loads such as in forklifts and helicopters due to masses and inertial forces caused by fluctuating effects. Here, dynamic magnification factor, ϕ is applied to the static loads to take care of the effects.
- Imposed loads due to actions that cause acceleration of the structure or structural members shall be considered as dynamic actions and analysed using dynamic analysis.
- The total imposed loads in a situation where imposed loads act simultaneously with other actions such wind, snow, cranes and machinery.
- The fatigue load where it is expected that a number of load variations or effect of variations would cause fatigue.
- Dynamic loads or dynamic models of imposed loads for structures susceptible to vibration.
For the design of floor in one storey building, roof, column and walls, imposed loads should be placed at the most unfavourable location or part of the influence area. Imposed load from a single storey may be reduced by the factor, αA but where imposed loads from several storeys act on columns and walls, the total imposed loads may be reduced by a factor αn.
Table 1: Values of ψ in Buildings based Table A 1.1, Annex A1 of EN 1990
|Category of imposed loads in buildings||ψ1||ψ2||ψ3|
|Category A: domestic, residential||0,7||0,5||0,3|
|Category B: office areas||0,7||0,5||0,3|
|Category C: congregation areas||0,7||0,7||0,6|
|Category D: shopping areas||0,7||0,7||0,6|
|Category F: storage areas||1,0||0,9||0,8|
Categories of Loads and their Values
Whether the purpose of the structure is for residential, commercial, social or administrative, imposed loads on buildings are classified into 4 categories
Table 2: Categories of use (Table 6.1 of BS EN 1991-1-1:2002)
|A||Areas for domestic and residential activities||Rooms in residential buildings and houses; bedrooms and wards in hospitals; bedrooms in hotels and hostels kitchens and toilets.|
|C||Areas where people may congregate (with the exception of areas defined under category A, B, and D1)||C1: Areas with tables, etc. e.g. areas in schools, cafes, restaurants, dining halls, reading rooms, receptions.
C2: Areas with fixed seats, e.g. areas in churches, theatres or cinemas, conference rooms, lecture halls, assembly halls, waiting rooms, railway waiting rooms.
C3: Areas without obstacles for moving people, areas in museums, exhibition rooms, etc. and access areas in public and administration buildings, hotels, hospitals, railway station forecourts.
C4: Areas with possible physical activities, e.g. dance halls, gymnastic rooms, stages.
C5: Areas susceptible to large crowds, e.g. in buildings for public events like concert halls, sports halls including stands, terraces and access areas and railway platforms.
|D||Shopping areas||D1: Areas in general retail shops
D2: Areas in department stores
Table 3: Imposed loads on the floors as per categories (Table 6.2 of BS EN 1991-1-1:2002)
|Categories of loaded areas||qk (kN/m2)||Qk (kN/m2)|
1,5 – 2,0
2,0 – 4,0
2,5 – 4,0
2,0 – 3,0
2,0 – 4,0
2,0 – 3,0
|Category B||2,0 – 3,0||1,5 – 4,5|
2,0 – 3,0
3,0 – 4,0
3,0 – 5,0
4,5 – 5,0
5,0 – 7,5
3,0 – 4,0
2,5 – 7,0 (4,0)
4,0 – 7,0
3,5 – 7,0
3,5 – 4,5
4,0 – 5,0
4,0 – 5,0
3,5 – 7,0 (4,0)
3,5 – 7,0
(1) qk represents uniformly distributed loads and it intended for the determination of general effects while Qk represents concentrated loads and it intended for the determination of local effects.
(2) Where necessary qk and Qk should be increased in the design (e.g for stairs and balconies depending on the occupancy and on dimensions).
(3) For local verifications a concentrated load Qk acting alone should be taken into account.
(4) For concentrated loads from storage racks or from lifting equipment, Qk should be determined for the individual case.
(5) The concentrated load shall be considered to act at any point on the floor, balcony or stairs over an area with a shape which is appropriate to the use and form of the floor. The shape may normally be assumed as a square with a width of 50 mm.
(6) The vertical loads on floors due to traffic of forklifts shall be assessed differently
(7) Where floors are subjected to multiple uses, they shall be designed for the most unfavourable category of loading which produces the highest effects of actions (e.g forces or deflection) in the member under consideration.
(8) Provided that a floor allows a lateral distribution of loads, the self-weight of movable partitions may be taken into account by a uniformly distributed load qk which should be added to the imposed loads of floors obtained from Table 2. This defined uniformly distributed load is dependent on the self-weight of the partitions as follows:
– for movable partitions with a self-weight ≤ 1,0 kN/m wall length: qk =0,5 kN/m2;
– for movable partitions with a self-weight > 1≤2,0 kN/m wall length: qk =0,8 kN/m2
– for movable partitions with a self-weight > 2 ≤ 3,0 kN/m wall length: qk = 1,2 kN/m2
(9) Heavier partitions should be considered in the design taking account of:
– the locations and directions of the partitions;
– the structural form of the floors.
Areas for Industrial and Storage Activities
These are divided into two categories as shown below (Table 4).
Table 4: Categories and imposed loads on floors due to storage (Table 6.3 of BS EN 1991-1-1:2002)
|Category||Specific Use||Example||qk (kN/m2)||Qk (kN/m2)|
|E1||Areas susceptible to accumulation of goods, including access areas||Areas for storage use including storage of books and other documents.||7,5||7,0|
(1) The values of qk and Qk above may be changed if necessary according to the usage for the particular project or by the National annex.
(2) The characteristic value of the imposed load shall be the maximum value taking account of the dynamic effects if appropriate. The loading arrangement shall be defined so that it produces the most unfavourable conditions allowed in use.
(3) The characteristic values of vertical loads in storage areas should be derived by taking into account the density and the upper design values for stacking heights. When stored material exerts horizontal forces on walls etc., the horizontal force should be determined in accordance with EN 1991-4.
(4) Any effects of filling and emptying should be taken into account.
(5) Loads for storage areas for books and other documents should be determined from the loaded area and the height of the book cases using the appropriate values for density.
(6) Loads in industrial areas should be assessed considering the intended use and the equipment which is to be installed. Where equipment such as cranes, moving machinery etc, is to be installed the effects on the structure should be determined in accordance with EN 1991-3.
Eurocode 1: Actions on structures – Part 1-1: General actions – Densities, self-weight, imposed loads for buildings.