Reinforcement Detailing of Beams from ETABS output

Question:-

Challenge 7 – Detailed design of concrete buildings -1

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.

Answer:-

Aim:-

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.

Introduction:-

• Beams are horizontal structural elements used for the supporting lateral loads.
• In conventional reinforced concrete structure beams usually receive load from the floor slab, but may also be subjected to other loads such as wall loads, finishes services installation etc.
• The design and detailing of RC beams involve the selection of the proper beam size and the quality of longitudinal and shear reinforcement that will satisfy ultimate and serviceability limit state requirements.
• Afterwards, it is very important that the beam reinforcements are placed and arranged properly on site, to avoid construction error.

Procedure:-

Step 1:-

• Download and Open the model file 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 design icon.

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

• After checking it gives the reinforcement requirement for all beams as shown below.

Step 2:-

• We have to provide reinforcement for the Beams alongs Grid A and Grid 3.

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)

Step 3:-

• Refer IS 13920-2016 for beam reinforcement details.

• Draw the Section of Beam and columns at Grid A.
• And mention the reinforcement details of Longitudinal and Shear reinforcement.

Step 4:-

1). For Sway Shear Force Right 2). For Sway Shear Force Left

Design moment values from Etabs for the Beam A2 -A3

Shear Force values for selected beam from Etabs,

As per IS 13920 1.2 loading applied for (DL+LL)

SF value at point A

SF value at point B

M^As = 303 kN-m M^Ah = 321 kN-m

M^Bh =319 kN-m M^Bs =304 kN-m

L_AB = 2.35 m L_AB = 2.35 m

V_u,a^(d+l) = 22.63 kN V_u,b^(d+l) =21 kN

V_u,a = 348 kN V_u,a = 349 kN

V_u,b = 391 kN V_u,b = 393 kN

Grid A_At TOP

Maximum Ast at support = 2045

Maximum Ast at middle = 511

3 # of 25 mm = 1473

3 # of 20 mm = 942

Therefore, to satisfy the support we need to provide 3# of 25 mm bar and additionally in the middle need to provide 3# of 20 mm.

Grid A_At BOTTOM

Maximum Ast at support = 1945

Maximum Ast at middle = 511

3# of 25 mm = 1473

3 # of 20 mm = 942

Therefore, to satisfy the support we need to provide 3# of 25 mm bar and additionally in the middle need to provide 3# of 20 mm.

Step 5:-

• Right-click the grid A beam.
• Click details and switch it into shear details.

Step 6:-

• As per clause 6.3.3 the design force of equivalent Ve = 414.5 KN.
• Shear force under the linear analysis as per the load combination of UD cons67 = 287 KN.

Beam Reinforcement details:

Beam-@ Grid-A

Beam-@ Grid-3

Beam c/s.

Shear capacity in beam as per drawing:

(As per IS 456-2002 clause 40.4)

Fy = 415 N/mm2

Asv = 151 mm2

d = 500 mm

Sv = 100 mm

Vus = 272.6 KN-m

Reason for failure of middle span along gris A, possible way to resolve this issue?

Shear stress = Load / Area

1). Reduse the loading (or)

2). Increase the loading

3). Shear capacity of concrete, it varies w.r.t the grading of concrete

If we use some higher grade for this beam alone, We can increase the shear capacity of the beam, We can make it Pass.

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.