How many types of load should calculate in construction?

There are three main types of load,

Vertical Loads Horizontal Loads Diagonal Loads

Here are they with examples,

Dead loads are the vertical stationary loads acting on the structure throughout its lifespan . The self weight of the structure us primarily considered as dead load, whereas it may include some other loads like weight of permanent partition walls, weight of permanent equipment etc. The dead loads for the structure is calculated by multiplying volume of structure with the unit weight of structure.

E.g. A PCC of size 1.2 × 1.2 × 0.15 will have self weight (Dead load) of

1.2 × 1.2 × 0.15 m3 (volume) × 24 KN/m3 (unit weight of pcc) = 5.18 KN

Live loads are movable or moving vertical loads which doesn’t causes any acceleration or impact on structure. This loads are particularly caused due to use of structure by their occupants. Live load might differ considering different time and conditions, thus the live loads for the particular structure are defined by the engineer considering site conditions. Whereas the code (IS 875-1987) also specifies the minimum values of live loads to be assumed depending upon occupancy of building (e.g. Residential building, hotel, educational building, godown etc.) . In the code the minimum live loads can be found in both terms uniformly distributed load as well as the concentrated loads. The structure can be designed either considering the uniformly distributed loads or concentrated loads, the final design will be done by considering greatest stresses from both conditions.

Snow Load

Construction Loads :

• Weight of Temporary Structures : This includes load due to shoring, scaffolding & other construction related to temporary structures which will be gone after the completion of construction.

• Material Loads : This includes load of the material required to be stored for the execution of construction work. Most of the time these load is transform as a permanent dead on structure after it become part of structure.

• Construction Procedure Loads : This includes Personal or equipment loads, erection or fitting forces, equipment reactions, other pressure loads

Despite of being categorized as vertical load, the construction loads might act horizontally or diagonally on the structure depending upon the site conditions

Creep

Creep in a structure can be defined as: deformation of structure under sustained load (i.e. long term pressure or stress) . This phenomenon causes similar effect as the compression of the member like a concrete column getting more compressed, or a beam getting more bended. Despite, the Creep doesn’t necessarily cause concrete to fail still we should consider the creep load while designing the structure.

Horizontal Loads

Earthquake forces can act both vertically or horizontally on the building. The earthquake causes the building to vibrate, this vibrations are resolved into three directions, i.e. one vertical & two horizontal (mutually perpendicular directions). But, generally we ignore, the forces/moments in vertical direction as they doesn’t affect the superstructure to significant extent. Whereas the horizontal movement of building due to earthquake is significant one to consider while designing.

The response of structure to the vibration caused by earthquake is depends on the various factors like nature of foundation soil, mode of construction, size of building ,the duration & intensity of ground motion. The code (IS1893:2014) provides the calculations details for earthquake-zones structures. In the calculation of seismic accelerations for the design, we consider the seismic coefficient, which is the ratio of acceleration due to earthquake with acceleration due to gravity.

Wind load is the load caused due to the movement of air relative to earth. Wind load is especially considered for high rise building (i.e. buildings in which height of the building exceeds two times the dimension transverse to the exposed wind surface). Whereas for low rise building(i.e. up to four to five stories) the wind load is not critical, hence it can be ignored. Further in LSM(limit state method) the factor for the design load is reduced to 1.2 (DL+LL+WL). The wind load on building depends upon two factors, velocity of wind & size of the building. The code(IS 875(part 3):1987) provides details of wind load calculations on structures.

Up to the height of 30 m, the wind pressure is assumed to be act uniformly. Above 30m height, the wind pressure increases.

How to select Correct Loads For Building:Load Combination

Many structure, if not all will be subjected to all type of the loads listed above at sometime in their life. But direct combination of all thus loads at their maximum can’t be considered as probable, for example it would not be probable to expect a full live load to occur simultaneously with a full snow load during a design level wind storm.Thus proper load combination is important to design economical as well as safe structure.

ASCE 7-05 or IS475 provides load combination equations for both service & factored loads. whereas the final choice of loads will be based on the design philosophy of individual.Yet the final load combination decided by Individual should satisfy various conditions given in respective codes. .