Reinforcement Detailing of Beams from ETABS output

QUESTION:- 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

ANS:-

Introduction -

1) Beams are horizontal structural elements used for the supporting lateral loads.

2) In conventional reinforced concrete structures, beams usually receive load from the floor slab, but may also

be subjected to other loads such as wall loads, finishes, services installation, etc.

3) The design and detailing of RC beams involves the selection of the proper beam size and the quantity of longitudinal

and shear reinforcement that will satisfy ultimate and serviceability limit state requirements.

4) Afterwards, It is very important that the beam reinforcements are placed and arranged properly on site,

to avoid construction error.

AIM:-

A.

To Provide details of longitudinal and shear reinforcement for the two continuous beams. Sketch the beam elevation details or draft it using autocad software. To Calculate value of the maximum shear force

After downloading the model given in the question, click the concrete frame design tool in the ribbon tab.

Choose select design combinations.

Select the appropriate combination from the dialogue box. & Click ok.

Run analysis for the given structure.

Once the analysis is done, click concrete frame icon.

After clicking the icon, it starts checking the concrete design.

After the checking is done, go to the plan view.

On the plan view we have a column and beam detailing.

For this, grid 3 & grid A need to provide reinforcement details.

Longitudinal Reinforcement of Beam at grid -A from Etabs (mm2)

Shear Reinforcement of Beam at grid -A from Etabs (cm2/1000mm)

Longitudinal Reinforcement of Beam at grid -3 from Etabs (mm2)

Shear Reinforcement of Beam at grid -3 from Etabs (cm2/1000mm)

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:

Next we need to draw the Reinforcement diagram of 3 span continuous beam along Grid-A, and also need to provide the reinforcement details.

The maximum Ast for the bottom support is 1766mm2 and bottom middle is 702 mm2.

The maximum Ast for the top support is 1889mm2 and top middle is 453mm2.

Now we provide 3-28Φ at the top and bottom, as shown in the below figure.

Next we provide 1-8Φ at the top supports for the continuous beam, as shown below.

Next we need to draw the Reinforcement diagram of 7 span continuous beam along Grid-3, and also need to provide the reinforcement details.

The maximum Ast for the bottom support is 1061mm2 and bottom middle is 1493mm2.

The maximum Ast for the top support is 1915mm2 and top middle is 479mm2

Now we provide 3-22Φ at the top and bottom, as shown in the below figure.

Next we provide 1-10Φ and 1-12Φ at the top supports and we provide 2-16Φ at the bottom middle for the continuous beam, as shown below.

B.

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

Reason of failure:-Here from the above shear details we can see that the limiting value of shear stress 3.1 MPa and the devoloped shear stress is 3.11 Mpa which is clearly shows that the it exceeds the limiting value of shear of the beam.

Possibilities for resolving:-

1. Using higher grade of concrete
2. reducing effective depth.
3. By providing diagonal reinforcement bars.

C.

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.

Grid A(Beam )

1.Sway to right

Mu(Sagging )= 164.52 KN-m

Mu(Hogging )= 293.53 KN-m

2.Sway to left=

Mu(Sagging )= 177.83 KN-m

Mu(Hogging )= 296.42 KN-m

Factored shear force Vu(D+L)= 39.2802 kN

Clear span, LAB= 5.375-(2*0.65/)= 4.725m

Now according to IS 13920

Vub= 174.99 KN (right sway)

Similarly left sway also computed.

Vub= 179.799 KN (Left sway)

Result:-

• The beams are designed successfully in detail from the ETABS software.
• Provided the details of longitudinal and shear reinforcement for the two continuous beams.
• And also calculated the value of maximum shear force in the continuous beams using the ETABS.