Modelling of 25 storey building with the specified properties using ETABS

Model a 25 storey building on ETABS with structural properties as specified below. Ground floor or plinth floor level can be taken at a height of 1.5 metres from the base. Each of the successive 25 storeys has a storey height of 3 metres.

Structural Element Sizes

• Beams : 300 × 400 mm
• Columns : 800 × 800 mm
• Slab : 150 mm thick

Material Properties

• Grade of Concrete : M30
• Grade of Steel Reinforcement Bars : Fe 415

Loading

• Dead Load on beams from infill wall : 10 kN/m (Let us assume the same for roof floor in view of parapet)
• Live load on floor : 3 kN/m2 (Let us assume the same for roof floor)

a) Buildings are assumed to be pinned at the base

b) All columns in all storey are of the same size

c) All beams in all storeys are of the same size

d) Building is located on Soil type-II and in Zone-III. Assume other factors if required.

Carry out the following exercises:

• Check if the translational fundamental natural period of vibration in both the x and y direction is approximately: Tx1Tx1= 4.4 second Ty1Ty1= 4.2 second

This check will help confirm if modelling is done correctly. Some deviations from the above values is possible (± 2%). But any major deviation will suggest an error in modelling.

• Check if the following provision in Table 5 of IS 1893 (part 1) – 2016, on torsional irregularity satisfied:

The natural period corresponding to the torsional mode of oscillation must be less than the two fundamental translational modes of oscillation along each principal plan directions.

• Check if the two provisions of clause 7 in Table 6 (shown below) of IS 1893 (part 1) – 2016, regarding vertical irregularity is satisfied

• Check if provision on inter-storey drift limitations in clause 7.11.1.1 satisfied. Please note that this check is for Serviceability Limit State and hence is for situation when stucture is subjected to unfactored seismic base shear

Ans.

AIM - To model a 25 storey building with the given structural properties using Etabs.

INTRODUCTION -

- ETABS is an engineering software product that caters to multi-story building analysis and design.

- Modeling tools and templates, code-based load prescriptions, analysis methods and solution techniques, all coordinate with the grid-like geometry unique to this class of structure.

- Basic or advanced systems under static or dynamic conditions may be evaluated using ETABS

- ETABS modeling is the generalization that multi-story buildings typically consist of identical or similar floor plans that repeat in the vertical direction.

- Modeling features that streamline analytical-model generation, and simulate advanced seismic systems.

- Once modeling is complete, ETABS automatically generates and assigns code-based loading conditions for gravity, seismic, wind, and thermal forces.

- Users may specify an unlimited number of load cases and combinations.

PROCEDURE -

Step:-1

- First we have to open the etabs software.

- Next click on the new model at the left side top corner.

- After selecting the new model the new tab opens, in that tab we have to select 'Use Built-in Settings with' option.

- After setting the model Initialization the templates tab opens and, select the Grid only and press ok.

- Next we need to do the settings in Grid system data

- Next we need to add the stories upto 25 story in the Story Data

- The 25 stories are added in the Story Data.

Step:-2

- Next the plan views are visible in the etabs screen.

- Next we can see the 3d-view on the right hand side.

Step:-3

- Next we need to go to the define option and select material properties.

- After selecting the material properties the new tab appears, then we add new materials by selecting the Add new material option.

Step:-4

- Now we need to add material type as concrete and grade as M30.

- Next we need to check the material property data.

Step:-5

- Now we need to add material type as rebar and grade as HYSD Grade 415.

- Next we need to check the material property data.

Step:-6

- Now we need to select the section properties from define tab and click on the frame sections.

- After selecting the frame sections the new tab will be visible, in that we need to select the Add New Property.

Step:-7

- After selecting the Add New Property, the new tab appears.

- In that new tab we select the Rectangular shape type in concrete.

- Next the frame section property data will be visible, In that we add beam size as B300x400.

- Next we need to select the Modify/Show Rebar option.

- After selecting the Modify/Show Rebar option the new tab appears, In that we select the design type as M3 Design only (Beam).

- Next we select longitudinal bars and confinement bars with the grade of HYSD415.

Step:-8

- Again we have to select Rectangular shape type in concrete

- Next the frame section property data will be visible, In that we add column size as C800x800.

- Next we need to select the Modify/Show Rebar option.

- After selecting the Modify/Show Rebar option the new tab appears, In that we select the design type as P-M2-M3 Design (Column).

- Next we select longitudinal bars and confinement bars with the grade of HYSD415.

Step:-9

- Next we select the slab section option from the section properties from define tab.

- Next the slab properties tab will be visible, In that we select the Modify/Show Property option.

- After selecting the Modify/Show Property option, the new tab appears.

- In that we need to put the slab name as Slab 150, it means slab with the thickness of 150mm.

- And we take the concrete grade as M30.

- Next we have to click the ok option.

Step:-10

- Next we need to add the columns using the Quick draw columns option.

Step:-11

- Next we need to add the beams using the Quick draw beams option.

Step:-12

- Next we need to add the slabs using the Quick draw floor/wall option.

Step:-13

- Next we need to select the load patterns from the define option

- Now we add Dead load, live load, Brickwall load, and earthquake load.

- Next we need to select eqx and click on the Modify Lateral Load, then the new tab appears.

- In this tab select X Dir and take seismic zone factor as per code is 0.16.

- And we need to select site type as ll.

- Next click on the ok button.

- Similarly, do this for all the seismic loads such as eqx+, eqx-, eqy, eqy+, eqy-

Step:-14

- Now we select the object type option

- After selecting the object type option, the new tab will be visible, In that select the beams and click on the select button and close.

- Next we select the distributed load from the frame loads

- Then after the new tab will appear, In that we select load pattern as Brickwall and give uniform load as 10 KN/m, and then click on the apply button and close.

Step:-15

- Next, from the define option we select the mass source

- In the mass source tab, we select Modify/Show Mass Source option.

- Next we add the load patterns in the Mass Source Data.

Step:-16

- Next, from the define option we select the load combinations

- After selecting the load combinations the new tab is visible, In that we select 'Add Default Design Combos' option.

- Next we select concrete frame design in the Add Default Design Combinations.

- Now we can see here that the load combinations are visible.

Step:-17

- In the select option we select object type option

- After selecting the object type option, the new tab will be visible, In that select the Slab150 and click on the select button and close.

- Next select uniform from the shell loads. In that select load pattern as live and apply the load as 3 KN/m^2 and then click OK.

- Next we have to select the Diaphragms from the shell option

- After selecting the diaphragms the new tab will appear, in that select D1 and click on the apply button and close.

Step:-18

- Next we have to check the model by clicking the check model option

- Next the check model tab will appears, in that we select the all options and click on the ok button.

- After the model is checked, then the warning tab will be visible and it tells that there is no warning messages.

Step:-19

- Next we select the 'show deformed shape' option, then the new tab appears.

- In the deformed shape tab, we select Dead load in the load case

- Next we see the deformed shape of the structure with the dead loads.

- Next we see the deformed shape of the structure with the Live loads.

- Next we see the deformed shape of the structure with the Brickwall loads.

Step:-20

- Next, from in the model explorer expand modal information and right click on Modal periods and frequencies option and select show table.

- Here we can see the results are 4.4 and 4.2 for mode 1 and mode 2 respectively.

- Now we select the Modal Participating Mass Ratios and click on the ok button

- Next the Modal Participating Mass Ratios table will be visible.

- In the table we can see that the natural period corresponding to the torsional mode of oscillation is less than the two fundamental translational modes of oscillation along each principal plan directions.

Step:-21

- Select the display tab and select story response plots.

- Next select max story drifts from the display type.

- Select Eqx and Eqy as case/combo and see the drifts.

RESULT -

The 25 storey building has been modelled successfully in the ETABS.