Challenge

Structural Modelling using Etabs 2018

AAbhishek Surve6 Feb 2023

AIM: 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 THENMODEL 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 MODAL 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 MEET STRUCTURAL CODE RQUIREMENTS WITHOUT COMPROMISING ARCHITECTURAL FUNCTIONS. ALSO, THERE CAN BE MULTIPLE POSSIBLE SOLUTION FOR THIS PROBLEM.

ANS:

GIVEN DATA:

Pinned support, base + 9 story (ground to terrace) + 1 mumty
Column 450mm x 600mm, beam 400mm x 500mm, slab 150mm thick, shear wall 300mm thick
Live load 2.5 kN/m^2, floor finish 1.5 kN/m^2, wall load 5kN/m, water tank 20k litre over mumty equivalent to 200KN overall load

CONCEPTUAL DESIGN CONSIDERATION BEFORE ANALYSIS:

Re-entrant and cut-out check & modification – (compromise)
Vertical irregularity – soft story
Planar irregularity – looks symmetrical
2% shear wall area with respect to building area - 8m^2
Stiffness modifier for column, beam & shear wall- 0.35 for beam 0.7 for vertical

STEPS:

First download and open the ETABS and select new model option from the file menu
Now set the built in setting with option
Now set the grid system data and add 7 storeys with an addition of plinth
Next the plan view are visible in the etabs screen as shown below
Next we need to open the 3d view as shown in the below figure
Next, we need to define option and select material properties as shown below
Now select the material properties from the define menu and add new material as concrete M25 and rebar HYSD 415, 500
Now select the section the section properties and select the frame section now select add new properties select the shape and add beam of required size (250x450)
Now select modify/show rebar option and select M30 design only and select longitudinal bars with HYSD grade 500 and the confinement bars (ties) with HYSD grade 415
Now select the section properties and select the frame section, now select add new property, select the shape and add column of required size (400x400)
Now again select the section properties and select the frame section now select add property select the shape and add column of required size (400x600)
Now from the define menu select section properties and select slab section
Select modify/ show property give a new slab name and mention the thickness as 125 and slab material as M25 and click ok
Now define a new slab for the staircase, with thickness 200mm and slab material as M25
Insert 250mm thickness in the wall property data and click ok with the wall material as M25
Using quick draw columns, draw the column
And now use quick draw beams draw the beams, now draw the secondary beam using quick draw beam option
Now add the shear walls at appropriate location as given in the plan
Now using quick draw floor/wall option draw the slabs
Now select the base joins and select restraints from joint option of assign menu, and fix the joints and click ok
Now from the define menu, define the load patterns as live load dead load, brick wall load, earthquake loads
Now select the frame loads from the assign menu, and select distributed loads, and take a uniform load of 3.5KN/m and close it
Now from the assign option select the shell load and select uniform and apply 3KN/m^2 for staircase life etc
Now from the assign option select the shell load and select uniform and apply 2Kn/M^2 for the rest of the building
Now from the define menu, select mass source and add the load patterns
Now from the select option of the select menu, select object type and select the floors, and click select and then click
Select the shell option and select diaphragms from it, select Di and click on the apply button and close
Now from the assign menu select pier label option from the shell option
Now from the define option select the load combination and select add default design combos
Now select the concrete frame design and concrete shear wall design in the add default design combinations
Now from the define option, select modal cases and give modal case names as modal 1 and give the maximum number of modes as 20
From the analyse menu select check model, and now the warning tab appears
Now from the define option, select response spectrum and choose IS1893-2016.
Now click on modify/ show spectrum option and give an identical function name
From the define menu, select load cases and select load cases and select add new case
Now from the analysis menu, select run analysis
Now select the design menu select the concrete frame design and select start design check
Now select the design menu, select the concrete slab design and select start design check
From the display menu, select show tables and base reactions and click ok
To check if the EQ is closer to RS, we use (EQ/RS)
Now the structure is reanalysed and checked and found that EQ is almost equal to RS
We have to check for both EQx, RSx and EQy, RSy
Now again select the display menu and select storey response plot and select inter storey drift (RSx) and then for (RSy). The storey response for maximum storey drifts at X and Y direction should not be more than 4%
Now again take the display take the display menu and select show table and select modal participating mass ratio and click ok
Now from the display menu select force/shear diagram and select shell stresses/force