Different Types of Loads in Buildings

 Different Types of Loads in Buildings  

 General 

 In structural design, account shall be taken of the dead, imposed and wind loads and forces such as those caused by earthquake, and effects due to shrinkage, creep, temperature, etc, where applicable.

The loads on buildings and structures can be classified as vertical loads, horizontal loads and longitudinal loads. 

The vertical loads consist of dead load, live load and impact load. 

The horizontal loads consist of wind load and earthquake load. 

The longitudinal loads i.e. tractive and braking forces are considered in special cases of design. The estimation of various loads acting is to be calculated precisely. Indian standard code IS: 875–1987 

 1 Dead Loads-  Dead loads shall be calculated on the basis of unit weights which shall be established taking into consideration the materials specified for construction.

Alternatively, the dead loads may be calculated on the basis of unit weights of materials given in IS 875 (Part I). Unless more accurate calculations are warranted, the unit weights of plain concrete and reinforced concrete made with sand and gravel or crushed natural stone aggregate may be taken as 24 kN/m” and 25 kN/m” respectively. 

2 Imposed Loads-Definition- As per IS 875(II) The load assumed to be produced by the intended use or occupancy of a building, including the weight of movable partitions, distributed, concentrated loads, load due to impact and vibration, and dust load but excluding wind, seismic, snow and other loads due to temperature changes,

Imposed loads  shall be assumed in accordance with IS 875 (Part II) Anything in a building that is not fixed to the structure can result in a live load since it can be moved around.

e.g for Residential bungalow live load considered as 2kN/m. 

As per IS 875( Part II) The use of the term ‘live load’ has been modified to ‘imposed load’ to cover not only the physical contribution due to persons but also due to nature of occupancy, the furniture and other equipment's which are a part of the character of the occupancy. 

 The imposed loads on floors and roofs have been rationalized based on the codified data available in large number of latest foreign national standards, and other literature. Further, these values have been spelt out for the major occupancies as classified in the National Building Code of India as well as the various service areas appended to the major occupancies.

3 Wind Loads shall be assumed in accordance with IS 875 (Part III).Wind loads can be applied by the movement of air relative to a structure, and analysis draws upon an understanding of meteorology and aerodynamics as well as structures. Wind load may not be a significant concern for small, massive, low-level buildings, but it gains importance with height, the use of lighter materials and the use of shapes that may affect the flow of air, typically roof forms.

In IS 875(III) briefly given wind forces and their effects ( static and dynamic ) that should be taken into account when designing buildings, structures and their components .

4 Snow Loads shall be assumed in accordance with  IS 875 (Part IV). 

5 Earthquake Forces The earthquake forces shall be calculated in accordance with IS 1893. Earthquake load takes place due to the inertia force produced in the building because of seismic excitations. Inertia force varies with the mass. The higher mass of the structure will imply that the earthquake loading will also be high.

6 Shrinkage, Creep and Temperature Effects-  If the effects of shrinkage, creep and temperature are liable to affect materially the safety and serviceability of the structure, these shall be taken into account in the calculations in accordance with IS 875 (Part V). 

In ordinary buildings, such as low rise dwellings whose lateral dimension do not exceed 45 m, the effects due to temperature fluctuations and shrinkage and creep can be ignored in &sign calculations.

 7 Other Forces and Effects-  In addition, account shall ‘be taken of the following forces and effects if they are liable to affect materially the safety and serviceability of the structure: 

a)  Foundation movement (see IS 1904), 

b) Elastic axial shortening, Soil and fluid pressures [see IS 875 (Part S)], 

c) Vibration, Fatigue, Impact [see IS 875 (Part 5)], 

d) Erection loads [see IS 875 (Part 2)], and Stress concentration effect due to point load and the like.

Load Combinations - IS 875(V)-1987

 In the absence of such load combination guidelines, the following loading combinations, whichever combination produces the most unfavorable effect in the building, foundation or structural member concerned may be adopted as a general guidance. It should also be recognized in load combinations that the simultaneous occurrence of maximum values of wind, earthquake, imposed and snow loads is not likely, 

 a) DL 

 b) DL+IL 

 c) DL+WL 

 d) DL+EL 

 e) DL+TL 

 f) DL+IL+ W

g) DL+IL+EL

h) DL+ IL+ TL

i) DL+WL+TL 

j) DL+WL+TL

k) DL+EL+TL

m) DL+IL+WL+TL 

 n) DL+IL+EL+TL 

Where DL = dead load, IL = imposed load, WL = wind load, EL = earthquake load, IL = temperature load.

References

 IS 456 (2000): Plain and Reinforced Concrete - Code of Practice [CED 2: Cement and Concrete] July 2000 IS. 456 : 2000 (R••fflrmed2005) Indian Standard PLAIN AND REINFORCED CONCRETE ­ CODE OF PRACTICE (Fourth Revision) 
Explanatory Handbook on Earthquake Resistant Design and Construction (IS : 1893 .
 Loading Code-CODE OF PRACTICE FOR DESIGN LOADS IS 875 Part (1to5)

RCC Columns Prof. P. R. Thorat