__Loads In Buildings:__

__Loads In Buildings:__

In the design of any RCC structure, calculation of the upcoming load is the first and foremost step. The design load is considered for its design life. In this post, I will illustrate the basics of the design loads considered while designing of structures & the basic mathematics involved in their calculation.

__Types of building loads:__

__Types of building loads:__

The following given loads are present In a typical residential building as discussed below-

**Dead Load**– All the load of the dead or non-moving/stationary/fixed elements of the building fall in this category. Some examples of dead load are the weight of walls, the weight of roof/floor finishes etc. Self-weight of structural members such as beams, columns, Footings & RCC slabs etc are also taken as dead-load. The calculation of live loads has to be done by taking properties of the material & the dimensions of the element considered.**Live Load**– ll the moving loads due to human use or furniture or any other mechanical equipment. For all general categories live loads are defined in Indian Code IS 875 Part-3. Rest if any shall be calculated as per the requirement.**Dynamic Load**– Apart from dead & live loads a building structure is also subjected to the application of dynamic load. Dynamic loads are the loads in which the value & nature of the application of force is not constant throughout & is subjected to changes as per the conditions governing the forces. Forces due to wind, earthquake, traffic or heavy machinery (such as blowers or pumps) fall under this category.

(Also Read: Different Types of Failure of Foundation)

__Dead Loads:__

__Dead Loads:__

**Self-weight**– It is the weight of the frame or the individual weight of the structural elements such as Beams, Columns & Slabs. In computer programs such as STAAD Pro inbuilt capability is there which allows the program to calculate the self-weight of the elements automatically in accordance with the shape, size & member dimensions.

#### Example: Below given are the examples for manual calculation of self-weight of the structural elements.

Let it be of any shape Rectangular/square/tee/trapezoid anything, for calculation of weight, use the given formula-__Beam:__

Weight of member = cross-section area of member x length of member x RCC density

For a 0.3 m wide 0.45 m deep beam section of 5 m clear length & material density = 25 kN/m^{3} (for RCC), the weight will be-

Weight of beam = (0.3 x 0.45) x 5 x 25 = **16.875 kN**

The above calculated weight of **16.875 kN** is the total weight which can be further converted into Uniformly Distributed Load (UDL) by dividing the total weight by member length.

U.D.L in the beam = 16.875/5 = **3.375** **kN/m**

Same as explained above the self-weight of a column can be calculated only the terminology of member length will be changed to member height & the weight of column will be calculated as point load only its conversion in UDL is not required.__Column:__RCC slabs, the weight of roof slabs is applied as uniform pressure in kN/m__Slab:__^{2}. For analysis purpose, it is we consider a 1 m x 1 m square section & calculate the volume of the RCC & then the same is multiplied with the density for the derivation of pressure in kN/m^{2}.

Weight of slab = (1 x 1 x slab thickness) x RCC density

In the above formula as (1 x 1) doesn’t affect the calculation thus, it can be further simplified as-

Weight of slab = slab thickness x RCC density

For 0.15 m thick slab the calculation will be as follows-

Weight of slab = 0.15 x 25 = **3.75** **kN/m ^{2}**

In the above calculation of RCC slab weight, further additional load due to floor finishes are included generally for stone/cement floorings 0.75 kN/m^{2} to 1.5 kN/m^{2} is considered.

__Distribution of slab load on supporting beams:__

__Distribution of slab load on supporting beams:__

Depending upon the arrangement of beams (square or rectangular) triangular or trapezoidal shape distribution is carried out. For example (refer fig below) in case of a rectangular slab of 6 m x 4 m, the longer side beams spanning between A-B & D-C will carry a load of the corresponding trapezoidal portion. Whereas the shorter span beams spanning between A-D & B-C will support the weight of roof slab coming from the corresponding triangular region.

Load on 6 m span = area of trapezoid x thickness of slab x density

Load on 6 m span = 8 x 0.15 x 25 = **30** **kN.**

Thus, U.D.L = 30 / member length = 30/6 = **5 kN/m.**

Load on 4 m span = area of triangle x thickness of slab x density

Load on 4 m span = 4 x 0.15 x 25 = **15 kN** = 15 / member length = 15/4 = **3.75 kN/m**

Above discussed was the case of a rectangular slab. In the case of the square slab, the slab plan is divided into 4 number of equal triangles. Then the load for the same is transferred to the corresponding beam members.

Generally in building construction brick walls of single brick (0.115 m thick) & double brick (0.230 m thick) is used, a load of brick walls is calculated as follows-__Walls:__

Weight of wall (In kN/m) = Height of wall x thickness of wall x density of brick/stone masonry

For 0.23 m thick wall of 3.2 m clear height, the load will be-

Weight of wall (In kN/m) = 3.2 x 0.230 x 22 = **16.192** **kN/m**

The load of 16.192 kN/m is applicable in the form of UDL on the beam supporting the brick wall. In the above calculation, brick wall density considered is 22 kN/m^{3}.

__Live Loads:__

__Live Loads:__

Live loads or imposed loads as per building type & occupancy classification shall be provided as per Indian Code IS 875 Part-2 in table-1.

__Dynamic Loads:__

__Dynamic Loads:__

Mainly, the following dynamic forces are subjected to RCC buildings-

Wind load is calculated in line with the provisions of IS : 875 (Part-3).__Wind Force__:Seismic load is calculated in line with the provisions of IS 1893: 2016.__Seismic/Earthquake Force:__

Methodology for calculation of wind forces & earthquake forces will be discussed in a separate post, keep following.

Hope above given explanation helps in understanding the fundamentals for determination of dead & live loads as per Indian Code.

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