Structural Modelling using Etabs 2018

1.Aim: To analyse and design the high rise building at a particular seismic zone using the the Etabs for the particular seismic loads.

• To design the buildings for all the seismic actions at the particulat zone based on the givemn architectural inputs.
• To get to know how to check the seismic performance of the building using the Etabs.

Procedure:

• The building model is developed in the e tabs soft ware by using the various tools in the soft ware
• The soft ware is and it displays the home page and after opening the home page we need to click on the new model and after clicking on the model we need to make over the settings, units for the system(metric SI),steel section code(Indian), steel code(IS 800, 2007),Concrete code(IS 456 2000) and click on OK. Then the model will be developed and analysed by using the codes and units.
• After modify the settings of the units and the codes of the materials now the custom grid is to be modified by editting the grid ordinates to the required number in both the X and Y axis of the plot and after the custom storey data is to be modified that the storey description is to be changed to plinth level, base level and the level of the storeys is to be edited that the storey height is to be either 3m mentioned in the description details or some times the storey height is editted.
• After that the required number of the storeys is to be added and they similar to property is to be changed to none if there is no similarity if there is any similarities in the storeys of the building then the reference storey is to be modified in the remaining storey.and click on OK then the grid of the building s layout is displayed in the home page of the model of the building.
• After the modification of the custom grid now click on the define tool bar and select the material properties in the options given and change the material grade, standard ets and then click on the OK, So first we need to ad the material concrete and change the standard to the INDIAN , grade of the concrete to the M30 and concrete code to the IS 456: 2000 and click on OK and now add the material and now change the material in to steel and cahnge the grade to the HYSD bars and the code to the IS 800:2007 and click on the OK option.
• Now the sectional properties of the building units like column and the beam are created. Now the click on the define tool bar and select the section properties and select the add section and select the beam section and edit the name of the property as for the beam B400x500 and click on the property modifiers and change the moment of inertia of the X and Y axis, For the seimic load the moment of inertia is generally taken to the limit of the 35% and this is done to the ultimate loading condition but for the nominal analysis of the building the moment of inertia is to be considered to its full limit and click on OK.
• Now again click on the define and select the section properties and create the column unit of the building and the size of the column is to be about C 450x600 and again change the property modifier also as we done in the case of the building beam.
• Now again select the section property and select the slab section and the property of the slab is changed to Slab 150 and the modelling type is changed to the membrane an click on the OK.
• Now Click on the define tool bar and select the load pattern and add the loads i.e live load, wall as super dead load, seismic load EQX,EQY and the change the zone type and soil factor.
• Now assign the loads live load 2.5kn/m2,wall load 5kn/m2,Floor finish load 1.5kn/m2, the water tank of 20kl to the load of the 200kn
• The shear wall is of 300 mm thick and the shear walls are provided at the stair case and the ift core area based on the architectural plan the shear walls, columns, beams are provided and they can also be changed but it should not affect the parking area in the ground floor.
• Now check the load cases that all the loads is to be included and the load combinations of the various loadings on the building unit.
• Now the modelling of the building is to be done using the options in the left side of the window and now select the quick column option change the property of the column to which we require and the columns is placed in the grid points that the storey stage is selected a all storey in the right side of the window, then only the column is developed in all the storeys.
• The columns may be placed either individually or by using the replicate option in the grid option.
• The beam is also developed in the same way as that of the column, select the quick beam optio nand change the property to the beam which we require the specification.
• THe slab is also placed as that of like the previous, Now select th quick slab option and select the slab property as that of slab150 and based on the boundry of the grids and the column beam position the slab assigned.
• we should be aware that the columns or the shear walls are projected up to mumty level for the water tank and the rest of the shear walls or the columns are ended in the terrace level.
• In the process of the modelling we need to make some considerations

i. No slab and no wall load is to be considered in the ground floor level as the ground floor only used for the parking facility.

ii.Proper end releases in the beams as per the engineer intent that means inthe cantilever beams in the building there will be some sphere heads at the ends that will make the moment zero at the ends and so the beams acts as the secondary beams and the load acting on it wil be divided in to the primary beams attached to it.

iii.At the terrace of the building the load is considered for only for the outer walls and there is no interior wall loads.

iv.Comparision of static and dynamic forces and revising the factor.

After the modeling of the building we need to conduct the analysis and the result should foolow the following checks.

• Modal mass participation for first three modes must achieve 60%: To get to know about these click on the display and select show tables and select the modal participating table and the table is displayed and in the sum of the two modes will form upto the 90%.
• Modal time period will be diffence of 10%.
• Principal modes must be greater than the torsional mode, that is the load deformation modes in the mode 1 and 2 are greater than the mode 3.
• Inter storey drift ratio must be limited to 4% click on display and select the storey response plot and select the RSX and the storey drift ratio differs to up to 2% and the result is achieved.
• Axial stress in column and shear walls, maximum compressive stress is 0.4fck and the load should be with in the limit.
• Base shear share between columns and shear walls: The base shear should be shared by column and shear walls, if the base shear shared by the columns is less then it is not a dual system and the given modal is not a dual system.
• These are the various checks to be followed by the modelling of the building with the shear walls.