How can I model boundary elements for concrete shear walls in ETABS?
Some people say that there are two main ways to model boundary elements in a shear wall using ETABS:
Boundary elements could be modeled as columns. In other words, in this way, at first two columns should be created, then a wall should be created between them. With this method, is the stiffness analysis and period calculation right? Because there we have columns and walls at the same node?
Draw the wall and its boundary elements in section designer when defining the shear wall. With this method, if we create the extended boundary element, is the extended area calculated in analysis? Because I've tried to create an extended boundary element using section designer and the cumulative mass of the structure has not changed.
Method (1) uses Frame and Shell elements together. Hence, the best modelling practices concern: a) the description of the exact geometry, i.e. relative distances from the center of Frame elements to the edges of Shell element, b) rigid connection between Frame and (edge of) Shell elements at floor levels.
Method (2) is about equivalent Frame modelling of Walls. This is an efficient method for modelling low Length/Height Walls due to plane-section hypothesis. SD always produce Frame sections and calculates the physical properties of the drawing section geometry as a whole.
Im assuming u know how to draw shear walls in ETABS :P,
Make sure u have defined a wall as shell thin.
Step 1 : Define Pier labels for every wall in the plan,for instance name a wall as pier 1.
Step 2: Select the wall defined as pier 1 and mesh it as required.
Step 3: Now after meshing the pier go to base plan and select the nodes of Pier 1 and assign the supports as fixed
Step 4: Analyse the structure once.
Step 5: unlock model again.
Step 6: Add Shear wall load combinations.
Step 6:Now select the wall that has to be designed,say Pier 1
Step 7:Go to Shear wall Design Select view revise pier overwrites and select C & T method if u are designing the Shear wall to take Axial Forces & Moments. If u designing Shear wall of uniform thickness no need of defining Boundary elements in ETABS 2013 onwards as it calculates itself, provides reinforcement for entire shear wall considering Axial load and moment.
Step 8: Now design the wall to get reinforcement, Etabs displays 2 reinforcements one is for compression Zone and another for tension Zone.
Step 9: After getting Reinforcement say u got 4000 Sqmm for Compression and 4500 Sqmm for Tension zone. on safet side i consider 4500asmm as my reinforcement to be provided.
Now provide obtained reinforcement in 2 boundary elements,lenght of boundary elements can be obtained in the calculation report generated for the pier.
Divide obtained reinforcement to provide in boundary elements.say wall length is 4m & Boundary element length is 1m ie 4500/2=2250 provide 12 bars of 16 dia in both boundary elements and minimum reinforcement in the middle.
If you want to design a wall just as a reinforced wall design the wall as uniform reinforcing.
for detailing go through IS 13920 latest version,codes specifies a min thickness of 150mm for shear walls.