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.

Answer

1)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:

Aim:

• To design the beams in detail from the Etabs 2018.       
• To provide the detailing of longitudinal and shear reinforcement for two continuous beams .
• To calculate the value of maximum shear force in any one of the spans in the continuous beams
• To provide the reasons of failure of middle span along grid A.

Introduction:

• Beams are horizontal structural elements used for the supporting lateral loads.
• 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.
• 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.
• Afterwards, It is very important that the beam reinforcements are placed and arranged properly on site to avoid construction error.

Procedure: 

Step 1

• Open the challange 7 attachment which are provided to us and download it .
• After downloading open the Challenge open it in the Etabs software .

Step 2

• Now check the load combinations which are already created in given modeling file .

Step 3

• Before run analysis we have to check the model 
• Click on analyze 
• Click on check model 
• A structure is verified without any error and Model has been checked . 

Step 4

• Now we have to start the beam design by selecting the 'Start Design/Check' option .
• Once you click on Start / Design check you will see Display concrete frame Design results box .
• Where you can select whatever design output you want 
• So Click on Longitudinal Reinforcement .

Step 5

• Once you click on , Longitudinal reinforcement details will appear .

 Step 6

1) Reinforcement details along Grid A 

1. Max $A_{st}$ at bottom support = 1026 
2. Max → $A_{st}$ at bottom middle = 757 
3. Max ${\mathrm{\to \; A}}_{st}$ at Top support = 1896 
4. Max $A_{st}$ at Top middle = 474 

Reinforcement Calculation 

1) For Top 

Total Ast required at top is = 1896 mm²

So,we can provide 3 bars of diameter 20 mm and 5 bars of 16 mm satisfies the overall  Ast 

• 3 x T20 = 942  mm²
• 5 x T16 = 804  mm²
• 3 X T20 + 5 x T16  = 1946mm²

Hence Satisfy. 

2) For Bottom

Total Ast required at top is = 1026mm².

So,we can provide 2 bars of diameter 20 mm and 2 bars of 16 mm satisfies the overall  Ast 

• 2 x T20 = 628  mm2
• 2 x T16 = 402 mm2
• 2X T20 + 2 x T16  = 1030 mm2  

Hence Satisfy. 

3) For Shear details

• Right click on and click on details 
• Click on shear details 
• Fig. As per Clause 6.3.3 we have to provide Spacing till 2d from the face of the column is 100 . 

• 2)Provide reasons for the failure of the middle span along grid A. What are the possible ways this issue can be resolved?
  • As we see mid span is indicate bema O/S -Overstressed

3)Calculate the maximum shear force value in any spans in both continuous beams, as per clause 6.3.3 (b) in IS 13920 – 2016. Also, confirm these values from the 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.

Sway shear force to Right 

• Mas = 174 km 
• Mbh = 293 km
• Lab=4.725 m
• V.d+l = 92 kN

After substituting the values, we get,

• V u,a= 46 kN 
• V u,b = 230 kN

Sway shear force to the left

• Mah = 234 km 
• Mbs = 155 km
• Lab=4.725 m
• V.d+l = 70 kN

After substituting the values, we get,

• V u,a= 185 kN 
• V u,b = 45 kN

Result:

• The longitudinal and shear reinforcement details for the two continuous beams are Provided. The beam elevation details were Sketched or drafted it using AutoCAD software.
• Reasons and the possible ways this issue can be resolved of failure of the middle span along grid A id provided 
• The 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.I also confirmed these values from the shear force demand calculated by ETABS.