Reinforcement Detailing of Beams from ETABS output

Reinforcement Detailing of Beams from ETABS output

Detail design of beams in Etabs 2018.
The ETABS file for a G+4 building is provided. Run the analysis and design the RCC Moment ResistingFrame. The following challenge deals specifically with two continuous beams in the 1st floor.

1) 3 span continuous beam along grid A
2) 7 span continuous beam along grid 3

Address the following issues thereafter.
• Provide details of longitudinal and shear reinforcement for the two continuous beams. Sketch the beam elevation details or draft it using autocad software. A sample of how beam elevation details is prepared in consultancy firms is provided below. Participants can prepare it as per their preference:

• Provide reasons for failure of the middle span along grid A. What are the possible ways this issue can be resolved?

• Calculate value of the maximum shear force in any one of the spans in both the continuous beams, as per clause 6.3.3 (b) in IS 13920 – 2016. Also, confirm these values from shear force demand calculated by ETABS.Please note that if longitudinal reinforcement provided is more than required (as per ETABS results), the shear force demand will vary from what is provided by ETABS.

Aim: to know how the quantity of steel required in given section, or details of given two RC beam

Introduction: work on the check satisfaction, its satify the IS with analys values, to ensure the load capacity of member over the load demand

Procedure:

step 1)

open the plan provided in challenge

in etabs 2018

open first floor plan

step 2)

Analys the structure

by clicking on run anlyasis tab

we get the maximum and minimum deflection

step 3) concrete frame design

click on concrete frame design button to know the longitudinal and axial reinforcement of all the frames

like column and beams

step 4) also check the shear reinforcement

by drop down the icon side of concrete frame design

then click on apply button

Step-5)

As per the noted rebar outputs, the Longitudinal sections for those two RC beams are drawn using AutoCAD software and detailing is done complying IS 13920-2016 requirements.

Note: Drawing is attached as PDF format.

The scope of failure in midspan of Grid-A RC beam:

It is noted that central span of Grid-A RC beam is nearly failing due to higher shear stress. As per the above shear force value (3.08 MPa) against the maximum allowable shear stress (3.1 MPa), is almost failing but passes numerically. This design shear force is arrived in philosophy of Capacity design concept. This can be resolved in any of the following process.

1. a) Optimizing provided flexural reinforcement
2. b) reducing depth of RC beam which in turn reduce stiffness and flexure requirement
3. c) increasing concrete grade will increase allowable shear stress limit.

Calculation of Design shear force of RC beams complying clause 6.3.3 (b) of IS 1920-2016:

Grid-A RC beam:

Support top flexural reinforcement as per Drawing- 2098 sq.mm

Support bottom flexural reinforcement as per Drawing- 1960 sq.mm

Using Annexure-G of IS-456 indian standard, the moment capacity of RC beams are calculated as follow.

Hogging Moment capacity of RC beam (MsuMus)- 283 KNm

Sagging Moment capacity of RC beam (MhuMuh)- 272 KNm

The demand Shear force for 1.2(DL+LL) combination is derived from ETABS model as follow.

Demand shear force from ETABS analysis (VD+Lu,aVu,aD+L= VD+Lu,bVu,bD+L = 22.65 KN

Clear span (LABLAB= 2.35 meter

Using clause 6.3.30 of IS13920-2016 indian standard, the sway shear force is calculated as follow.

1. Sway shear at Left as per IS 13920-2016 = 353.29 kN

2. Sway shear at Right as per IS 13920-2016 = 353.29 kN

Required shear reinforcement as per calculation = 2174 sq.mm per meter run

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

Hence OK.

Grid-3 RC beam:

Support top flexural reinforcement as per Drawing- 2098 sq.mm

Support bottom flexural reinforcement as per Drawing- 1030 sq.mm

Using Annexure-G of IS-456 indian standard, the moment capacity of RC beams are calculated as follow.

Hogging Moment capacity of RC beam (MsuMus)- 283 KNm

Sagging Moment capacity of RC beam (MhuMuh)- 171 KNm

The demand Shear force for 1.2(DL+LL) combination is derived from ETABS model as follow.

Demand shear force from ETABS analysis (VD+Lu,aVu,aD+L= VD+Lu,bVu,bD+L = 150.65 KN

Clear span (LABLAB= 7.365 meter

Using clause 6.3.30 of IS13920-2016 indian standard, the sway shear force is calculated as follow.

1. Sway shear at Left as per IS 13920-2016 = 237 kN

2. Sway shear at Right as per IS 13920-2016 = 237 kN

Required shear reinforcement as per calculation = 1459 sq.mm per meter run

Provided shear reinforcement as per drawing = 1570 sq.mm per meter run

Hence OK.

Result:

Thus the given ETABS model 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.