Reinforcement Detailing of Beams from ETABS output

Aim: to provide details of longitudnal  and shear reinforcement for the two continous beams using ETABS and also the design recheck for Grid A and 3 RC beam has to be done.

Procedure:

• After downloading the model given on the question,open the ETABS software and open the downloaded model.
• Click on view and revise preferences.Check all the design codes are correct or not.
• Analyze and check the model.

• Analyse and run analysis,
• Using the above toolpath,the given model is checked for its error and warnings.The model found to be ok.
• Analysis is complete.
• Now click on design preferences and click on ok.

• Click on design combinations and click on ok.

• Now click on desgin and verify all members as passed.
• Now click on display design info and select flexural reinforcement.

• Now click on display design info and select shear reinforcement.

• The model is verified for all members satisfying design criteria.
• The design flexural reinforcement and shear reinforcement are noted from the frame design output for the respective RC beams along grid A and grid 3.

Longitudnal sections for two RC beams:

For grid 3:

For grid A:

Reason for the failure of the middle span along grid A:

The central span of grid A RC beam is failing due to higher shear stress.As per the above force value (3.11 Mpa) against maximum allowable shear stress (3.1 Mpa),is failing.This design shear force is arrived in philosophy of capacity design concept.

It can be resolved by:

1. Optimizing provided flexural reinforcement.

2. Reducing the depth of RC beam which in tuen reduce stiffness and flexure requirement.

3. Increasing concrete grade wil increase allowable shear stress limit.

Calculation of shear force in any one of the spans in both continous beams as per clause 6.3.3(b) in IS 13920-2016:

Grid A RC beam:

• With support top flexural moment as 2045 sq.mm.
• With support bottom flexural moment as 1927 sq.mm

Now calculating the hogging and sagging moments of RC beam:

Mu(sagging)= 283KNm   Mu(hogging)=272 KNm

Now the demand shear force from Etabs analysis =22.69 KN.

Clear span is 2.35m.

According to clause 6.3.30 of IS 13920-2016,the sway forces are:

1. Sway shear left= 350.29 KN

2. Sway shear right= 350.29 KN

Required shear reinforcement as per calculation=2260 sq.mm per meter run.

Provided shear reinforcement as per drawing= 4020 sq.mm per meter run.

Grid 3 RC beam:

• With support top flexural moment as 1940 sq.mm.
• With support bottom flexural moment as 970 sq.mm
• We use Annexure G of IS-456 to calculate the moment of RC beams.

Mu(sagging)= 263KNm   Mu(hogging)=161 KNm

Demand shear force from ETABS analysis=174.168 KN

Clear span= 7.365m.

According to clause 6.3.30 of IS 13920-2016,the sway forces are:

1. Sway shear left= 232 KN

2. Sway shear right= 232 KN

Required shear reinforcement as per calculation=1500 sq.mm per meter run.

Provided shear reinforcement as per drawing= 1940 sq.mm per meter run.

Conclusion: Thus the given ETABS moidel is designed and RC beams are detailed as per ductility standards.Also the capacity design of sway shear for the RC beams have been verified.