Structural Modelling using Etabs 2018

Aim:

To design and analyse a G+7 residential building in zone 5 using Etabs.

Introduction:

The architectural plan for the residential building is given and the possible column positions are known. The following factors also considered while designing the model:

i.Typical floor plan – The location and thickness of the brick walls and the use of the
space (for estimating live load) can be obtained from this plan

ii.A building section through the staircase and lift core is provided

iii.Parking layout in the ground floor – the column/shear wall arrangement must not
obstruct entry/exit of vehicles.

Before designing the model, we should aware of loading details. Some of the load details are given below for cosideration:

• Brickwall made of AAC blocks
• Finishes – floor tiles of 75 mm thickness
• Live loads as per IS 875 part 2
• Water tank of 20 KL above the staircase at Mumty level
• Lift Machine room at mumty level above lift core

The structural modelling of the residential building is based on the provision of IS 1983-2016.

Procedure:

i.Initial step is the set the units, provisons codes for steel and concrete to Indian standards and customize the grid lines according to the architectural plan.

ii.Create the storey data according to the paln by keeping base as 4m and the remaining G+7 floors as 3m height including the mumty level.

iii.Once the grid is prepared, create the material propeties for steel as HYSD 500 (Main reinforcement) and HYSD 415 (Confinement bars) and for concrete as M30.

iv.Create the section properties for beam (400mm x 500mm), column (450mm x 600mm), slab (150mm thickness) and shear wall (300mm thickness).

v.Create the load patterns such as dead load, live load, brick load and floor finish load. Earthquake loads in all 6 combinations are to be created. The load combination is also created by selecting the frame and shear wall design.

vi.After the creation of section and load patterns, the beam, column and slab are assigned to the model and load as well. The brick load is applied where the wall exists with reference to the architectural drawings.

vii.The support of the model is assigned as fixed support. The live load reduction factor is also assigned according to the codal provision since it is a high rise building.

viii.Final step is to create the response spectrum of the model. It is created based on the IS 1893-2016 and the function is saved. In load patterns adding response spectrum in both X and Y direction by keeping the scale factor unchanged.

ix.The number of modes also assigned before running the analysis. From the results, base reaction of the member in Earthquake reactions of X and Y is compared with Response spection is X and Y. If the value is lesser than the earth-qauke reaction then it should be made equal to the earthquake reaction by suing the formula given in IS 1893-2016.

x.The number of modes are also checked that in all the three directions the mass participation should reach 90% if not then the number of modes should be increased till it reaches 90%.

xi.After attaining the results, remove the earthquake loads and run the analysis once again and the following results are arrived:

• Modal mass participation for the first 3 modes dominates at least 65% (Achieved for x-axis only)
• Mode 1 and Mode 2 differs by 10% (Achieved)
• Prinicpal modes be greater than torsional mode (Achieved)
• Inter story drift ratio limited to 0.004 (Achieved)
• Axial stress in column and shear wall (Achieved)
• Base shear share between shear wall & columns (Not dual system)

Result:

Thus the design and analysis of G+7 residential building is done in Etabs.