Structural Loads

A structure stands by resisting its own load of beams, columns, foundations etc. The occupancy of the structure, soil pressure, temperature variation, rain or snow fall, earthquake, wind force also provide loads. So a structure has to resist all the loads to stand strongly. A structural designer designs considering all the above loads. The acting loads on a structure are classified into three main categories according to their types.
  1. Live Loads
  2. Dead Loads
  3. Environmental Loads


Live Load vs Dead Load

Live Loads

Live loads are consists of occupancy loads in buildings and traffic loads on bridges. They may be fully or partially in place or not present at all and may change its location. Human, chair, table, computer, bed, furniture etc are live loads. Live loads may change its present location as they are not lifetime part of a structure. So, in structural design live loads are provided a larger safety factor than the others. All the structural loads are expressed in psf (per square feet). The minimum uniformly distributed live loads for a residential building is 40 psf and for a office 50 psf.

Dead Loads

Dead loads are those that are constant in magnitude and fixed in location through out the lifetime of the structure. Usually the major part of the dead load is the self weight of the structure. The dead load can be calculated accurately from the design configuration, dimension of the structure and density of the material. The loads of the beams, columns, foundations, slabs etc are the dead loads of a structure.

The major difference between live loads and dead loads is:
  • Dead loads can be calculated accurately as they are constant but the live loads can not be calculated exactly.
  • So, live loads require a greater value of safety factor than dead loads. Live loads are given a safety factor of 1.6 and dead loads are given 1.2 in structural design. Basic equation of total live load and dead load calculation is:
    U = 1.2 D + 1.6 L

Environmental Loads

The environmental load mainly consist of snow loads, wind pressure and suction, earthquake loads, soil pressures on subsurface portion of structures, forces caused by temperature variation. The total lateral force is distributed to floors over the entire height of the structure in such a way as to approximate the distribution of the force obtained from a dynamic analysis.

Structural Safety

The structural safety requires that the strength of the structure be adequate for all load that may foresee-ably act on it. The strength of a structure could be predicted accurately if the loads and their internal effects (moment, shear, axial force) were known accurately. Safety could be ensured by providing a carrying capacity just over the known loads. What a general civil engineer does is providing safety factor to a minimum extend as these loads can't be predicted accurately.
 


Comments

seng lok
04/02/2013 05:02

formular of dead load and live load of RC and Steel structure

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10/02/2013 14:25

what is the formula to calculate the size of a spread footing?

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TMI
14/02/2013 04:43

Can you give more information on lists of live and dead loads and not TO MUCH INFORMATION on other loads?

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06/06/2013 19:53

plz dont judge me but idk wat a live load wat is it??

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lala
06/02/2014 00:56

a live load is a load that is active, ex humans, animal etc.

dead load is a load anything that is stationary. ex sofa, desks etc.

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papo
13/02/2014 13:22

you're wrong!!! a dead load is describe to be the self weight.sofa desk are all liveloads!!you suck

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13/02/2014 13:50

everything stationary like sofa, desk etc are not dead loads. these are live loads as sofa or desk can be changed and their load also can be changed if we buy another sofa or desk! So dead loads are only those which are mostly constant in load and generally a part of the structure. as given example; slab, columns,beams etc.

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    Author

    Md. Shahe Asekeen

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