Structural Modelling using Etabs 2018

STRUCTURAL MODELLING USING ETABS 2018

QUESTION:

The architectural drawings for a G+7 residential building in zone 5 has been provided. The floor plan is the same for all 7 floor levels. Possible column positions have also been provided. Conceptualize a framing plan layout and then model the building in ETABS. The following architectural drawings have been provided:

• 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.
• A building section through the staircase and lift core is provided.
• Parking layout in the ground floor – the column/shear wall arrangement must not obstruct entry/exit of vehicles.

The following loadings are to be taken into account:

• Brick wall 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 model must comply with provisions of IS 1893 and IS 13920.

Run a model response spectrum analysis and check analysis results of the ETABS model for inter-storey drift requirements, vertical & planar irregularities, minimum shear wall requirements, maximum axial load ratio for column and shear walls, effective moment of inertia for beams and columns etc.

Please note that the column positions shown in the architectural typical floor plan are only to provide an initial starting point for modelling. Participants will have to change its size, introduce shear walls and add new vertical elements after running the analysis. You will have to run the analysis multiple times until a structural model is obtained that meets structural code requirements without compromising architectural functions. Also, there is no one correct structural system for this challenge. There can be multiple possible solutions for this problem.

ANSWER:

AIM:

To model and analyse the G+7 residential building from the given architectural drawings using the ETABS 2018.

INTRODUCTION:

• ETABS is an engineering software product that caters to multi-storey building analysis and design.
• Modelling 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 modelling is the generalization that multi-storey buildings typically consist of identical or similar floor plans that repeat in the vertical direction.
• Modelling features that streamline analytical-model generation and simulate advanced seismic systems.
• Once modelling is complete, ETABS automatically generates and assigns code-based loading conditions for gravity, seismic, wind and thermal forces.

PROCEDURE:

STEP-1:

• First, we must open the ETABS software.
• Next click on the file option at the left side top corner and select the new model as shown below.

• After selecting the new model, the new tab opens, in that tab we must select ‘use built-in settings with’ option, as shown below.

• After setting the model initialization the template tab will opens and select the grid only and press ok.
• Next, we need to do the settings in grid system data, as shown below.

• Next, we need to add the stories up to 7 story data, as shown below.
• The 7 stories are added in the story data, as shown below.

STEP-2:

• Next the plan views are visible in the ETABS screen, as shown below.
• Next we need to open the 3D view, as shown in the below figure.

STEP-3:

• Next we need to define option and select material properties, as shown below.

• After selecting the material properties, the new tab appears, then we add new materials by selecting the Add new material option, as shown below.

STEP-4:

• Now we need to add material type as concrete and grade as M25.
• Next, we need to check the material property data, as shown below.

STEP-5:

• Now we need to add new material type as rebar and grade as HYSD grade 415.
• Now we need to check the material property data, as shown below.

STEP-6:

• Now we need to add new material type as rebar and grade as HYSD grade 500.
• Next, we need to check the material property data, as shown below.

STEP-7:

• Now we need to select the section properties and click on the frame sections, as shown below.

STEP-8:

• After selecting the frame sections the new tab will be visible, in that we need to select the add new property, as shown below.

• After selecting the add new property, the new tab appears.
• In that new tab we select the rectangular shape type in concrete, as shown below.

• Next the frame section property data will be visible, in that we add beam size as B250x450, as shown below.
• Next, we need to select the modify/show rebar option as shown below.

• 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 with the grade of HYSD500.
• Next, we select confinement bars with the grade of HYSD415.

• Again, we must select rectangular shape type in concrete, as shown below.

• Next the frame section property data will be visible, in that we add column size as B300x500, as shown below.
• Next, we need to select the modify/show rebar option as shown below.

• 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 the longitudinal bars with the grade of HYSD500.
• Next, we select confinement bars with the grade of HYSD415.

STEP-9:

• Next, we must add the column size as 400x400 in the frame section property data, as shown below.

• Again, we must add another column size as 400x600 in the frame section property data, as shown below.

STEP-10:

• Next, we select the slab section option from the section properties, as shown below.

• Next the slab properties tab will be visible, in that we select the modify/show property option, as shown below.

• After selecting the modify/show property option, the new tab appears.
• In that we need to put the slab name as slab125, it means slab with the thickness of 125 mm.
• And we take the concrete grade as M25, as shown below.
• Next, we must click the ok option.

• Now we take the slab thickness separately for staircase with the thickness of 200 mm, as shown below.

STEP-11:

• Next, we must add the wall properties in the wall property data, as shown below.

STEP-12:

• Next we need to add the columns using the quick draw columns option, as shown below.

STEP-13:

• Next, we need to add the beams using the quick draw beams option, as shown below.

STEP-14:

• Next, we need to add the secondary beams using the quick draw beams option, as shown below.

STEP-15:

• Next, we add the shear walls in required locations in the residential building, as shown below.

STEP-16:

• Next we need to add the slabs using the quick draw floor/wall option, as shown below.

STEP-17:

• Now we go to the base plan and select all base joints.
• Next, we select the restraints from joint option, as shown below.

• Now we need to select the fixed joint and click on apply and then click on close button, as shown below.

STEP-18:

• Next, we need to select the load patterns from the define option, as shown below.

• Now we should add dead load, live load, brick wall load and earthquake load, as shown below.

STEP-19:

• Next we need to select the distributed load from the frame loads, as shown below.

• Then after the new tab will appear, in that we select load pattern as brick wall and we take uniform load as 3.5 KN/M and then click on the apply button and close.

STEP-20:

• Next we have to click on the assign option and then select shell loads from the shell loads we select the uniform option, as shown below.

• Here we apply the 3KN/m^2 live load for the staircase portion, veranda and lift core area.

• Next, we apply the 2KN/m^2 live load for the remaining portions in the residential building, as shown below.

STEP-21:

• Next we have to select live load reduction factors from the design option, as shown below.

• Now we add the reduction factor by decreasing 10% from 1^st floor to 7^th floor, as shown below.

STEP-22:

• Next, from the define option we select the mass source, as shown below.

• Next, we add the load patterns in the mass source data, as shown below.

STEP-23:

• In the select option we select object type option, as shown below.

• After selecting the object type option, the new tab will be visible, in that select the floors and click on the select button and close.

• Next, we must select the diaphragms from the shell option, as shown below.

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

STEP-24:

• Next, we must select the pier label from the shell option, as shown below.

• Before going to the shear wall design, we must assign the names for the shear walls (P1, P2, P3, P4, P5, P6, P7, P8), as shown below.

STEP-25:

• Next, from the define option we select the load combinations, as shown below.

• 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’ & ‘concrete shear wall design’ in the ‘add default design combinations’, as shown below.

• Now we can see here that the load combinations are visible, as shown below.

STEP-26:

• Next, we select the modal cases from the define option, as shown below.
• After selecting the modal cases the new tab is visible, in that we give modal case name as modal 1 & we give the maximum number of modes as 20, as shown below.

STEP-27:

• Next we have to check the model by clicking the check model option, as shown below.

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

STEP-28:

• Now we select the response spectrum from the functions from define option, as shown below:

• After selecting the response spectrum, the new tab is visible, in that we choose IS 1893 2016 from the choose function type and click on the modify/shear spectrum option, as shown below.

• After selecting the modify/show spectrum option the new tab will be visible, in that we give the function name as ‘IS FUNCTION’ and remaining details will be set by the software itself, we don’t need to change any of the details in that response spectrum function tab, as shown below.

STEP-29:

• Next we have to select the load cases from the define option, as shown below.

• Next the load cases tab will be visible, in that we select the ‘add new case’, as shown below.

• Now we must enter the details of load case in the ‘load case data’, as shown below.

• Now we must do the run analysis, as shown below.

STEP-30:

• Next, from the display option we select the show tables option, as shown below.

• After selecting the show tables option the new tab will be visible.
• Now we select the base reactions and click on the ok button, as shown below.

• Next the base reactions table will be visible, as shown below.
• Here, we must check that EQ should be closer to the RS, to get the closer to each other we should calculate that, (EQ/RS) X scale factor of response spectrum.
• Now substituting the values from the table, at X-direction (2844.6348/900.7656) x 9806.65 at Y-direction (2844.6348/1002.1982) x 9806.65.

• At X-direction we get, 30969.6
• At Y-direction we get, 27835.15
• We put the above values as scale factor for response spectrum at X and Y directions in the load case data.
• After we enter these values for response spectrum as scale factors at X and Y directions in load case data, then the EQ is closer to the RS from the base reaction tables, as shown below.

STEP-31:

• Next, from the display option we select the show tables option.
• After selecting the show tables option the new tab will be visible.
• Now we select the modal participating mass ratios and click on the ok button, as shown below.

• Now the modal participating mass ratios table will be visible, as shown below.

STEP-32:

• Next we select the story response plots from the display option, as shown below.

• The story response for maximum story drifts at X & Y directions, should not be made than 4%.

STEP-33:

• Next we open the select plan view tab and select the base floor, as shown below.

• Next, we must open the reactions tab, then we select the earthquake load towards X-direction (EQX) in the load case, then click on the ok button as shown below.
• Now the base shear reactions will appear, as shown below.
• When we divide the base shear taken up by the shear wall divide by the total base shear of building will get the % of the shear forces taken up by the shear wall
• And if that is less than 80% then the move shear walls, we need to add to the structure.

RESULT:

The G+7 residential building has been modelled and analysed successfully using the ETABS 2018.