Analysis & Design of RCC shear walls in the model using ETABS

Aim-

The etabs file for a G+6 building is provided. Run the analysis and design the RCC shear walls (show in the etabs model). The following challenge deals specifically with the shear wall of size 300x1500 at grid A-11 in the structural model.

• Extract values of longitudinal steel ratio, boundary element length and shear reinforcing ratio from the design results.
• Provide cross sectional steel arrangement of the shear wall from its base up to terrace, in compliance with provisions of IS 13920 – 2016. AutoCAD application can be used for this exercise. Alternatively, it can be drawn by hand as well.
• Provide elevation drawings of the reinforcement details of the shear wall from base up to terrace.

Answer-

Step 1- Open Etabs with the attachment given

Step 2- Select the A- 11 Shear wall and view selected shear wall only

Step 3- Selecting elevation view of 11 grid

Step 4- To check the shear wall is assigned any Pier assignment from display option and labels

Step 5- Run the analysis

Step 6- Select the shear wall design option

Step 7- Select shear reinforcement details

Step 8- Also select the boundary elements

Step 9- Keep a note of the elevations and floor heights

Step 10- Shear wall detailing calculations:

Here, the total height of the wall is 21000mm and the width of the wall is 1500mm.

Hence, the ratio is obtained as 21000/ 1500= 14 which is greater than 2 hence, it can be considered as a slender wall.

Maximum diameter of the bar that can be used from IS code = 1/10th of thickness of that part = 30mm. Hence, we take the dia of bar as 25mm.

Maximum spacing between the bars should not exceed the minimum of the following:

1. a) 1/5 x 1500 = 300mm
2. b) 3x300 = 900mm
3. c) 450mm

Hence, the maximum spacing is limited to 300mm.

- Longitudinal reinforcement:

From ETABS results the maximum longitudinal reinforcement obtained is 13128mm²

Since we are using 25mm dia bars, the no. of bars required will be 13128/ 490= 28 bars. But we are providing two additional bars in the boundary element for proper confinement. i.e total 30 longitudinal bars.

Hence the total area of reinforcement provided is 13720mm². Hence, it is safe.

Now, from the code the minimum vertical reinforcement required is 0.0025+0.01375(tw/Lw)= 0.00525, i.e 0.00525x300x1500 = 2362.5mm2 which is less than actually provided hence safe.

Now, minimum vertical reinforcement to be provided in the boundary region = 0.008 x 1500 x 300 = 3600mm2.

The reinforcement provided for boundary element in right side = 4410mm2 and At left side = 5390mm2 Both are greater than the required value i.e 3600mm2. Hence safe.

In the web area the minimum reinforcement provided is 0.0025x1500x300=1125mm2 and the provided amount of reinforcement in web area is 3920mm2..Hence it is safe.

- Horizontal reinforcement:

From Etabs results the shear reinforcement amount is obtained as 750mm2.

So let us provide 8mm dia bars @ 100 mm c/c, then the provided area of reinforcement will be 1000mm2. hence it is safe.

This shear reinforcement can be provided for the entire shear wall.

-Now, we need to check for boundary element

From clause 10.4.4, the shear reinforcement required in the boundary element can be obtained from the equation

A_sh is the area of shear reinforcement required per link.

S_v - spacing between the shear reinforcement = 100mm

h - spacing between the extreme longitudinal reinforcement in the boundary element i.e 600-80=520mm

f_ck = 25N/mm2 and fy = 500N/mm2.

Hence it is obtained as Ash =0.05x 100x 520x 25/415= 156mm2 for this one link

One link has 2 legs hence area of each leg = 156/2=78mm2

Hence, we can choose 10mm dia bars for shear reinforcement in the boundary element width whose area is around 78.5mm2. This can be provided at the left side of the wall.

Now, in the right side the boundary element width is 450mm2 so, h=450-80=370mm. Hence, Ash requirement will be

A_sh = 0.05x 100x 370x 25/ 415= 111mm2 for each link. Hence, for one leg = 55mm2

Hence, we can provide 8mm dia bars for shear reinforcement in the boundary element width whose area is around 50mm2. This can be provided at the right side of the wall.

That is, for boundary element width special confining reinforcement to be provided is 10mm dia bars @ 100mm c/c at left side BE and 8mm dia bars @100mm c/c BE.