Reinforcement Detailing of Beams from ETABS output

CHALLENGE 7

Aim: The main aim of this challenge is to gain the knowledge about the concept of design of RC beam using ETABS Software and also to know the basics of beam reinforcement detailing with respect to primary standards. The concept of ductility reinforcement by IS – 13920 – 2016 as to be satisfied in ETABS software.

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.

Ans:

• 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.
• 
• 
• 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.

1). For Sway Shear Force Right

i) VuD+L= 92 Kn

ii) Mas= 176 kn-m

iii) Mbh= 295 kn

iv) Lab = 4.725 m

Vu,a= 48 Kn

Vu,b = 230 Kn

2). For Sway Shear Force Left

i) VD+Lu= 74 Kn

ii) Mah= 236 kn

iii) Mbs= 150 kn

iv) Lab = 4.725 m

`V_(u,a)`= 190 Kn

Vu,b = 50 Kn

i) fy = 415 N/mm2

ii) Asv = 151 mm2

iii) Spacing = 100 mm

iv) d = 450 mm

Put this value in above eqn we get

Vus = 246 kn> 230 kn (Shear sway) (Hence Safe)

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

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

Shear stress = Load / Area

1). Reduce 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

Conclusion:

From the challenge carried out it can be concluded that the concept of design of RC beam using ETABS Software and also to know the basics of beam reinforcement detailing with respect to primary standards. The concept of ductility reinforcement by IS – 13920 – 2016 as to be satisfied in ETABS software.

Vijayalakshmi S H