Reinforcement Detailing of Beams from ETABS output

AIM & INTRODUCTION :

AIM :

• To create a detailed design of concrete building by Running the analysis and designing the RCC Moment ResistingFrame specifically with two continuous beams in the 1st floor.

INTRODUCTION :

• In E-TABS the stuctural members such as beams, columns and slabs can be created and analysed its bending moment and shear force.

• We can Run the Concrete Frame Design fo the created structure to provide required both Longitudinal and shear reinforcement bars automatically.

• The values for the created structures can be automatically calculated by E-TABS.

• Here in E-TABS we can know the number of Reinforcement bars should be provided for the concrete structures.

• From Frame design analysis we can see both Top and Bottom reinforcement figures for each beam sections.

• Also we can display concrete frame design result for Shear reinforcement.

• Moreover we can view the concrete beam design information as per IS 456:2000.

• The Design details of the overall structures can also be viewed as Summary, Flexural Details, Shear Details, Envelope.

PROCEDURE :

• Open the Delivered E-Tabs file from the attachment with Base, ground, first, second, third, terrace and mumty level.

• After opening of the file click the plan tool and from select plan view tab click and select First floor level and click OK.

• Then we can see the beam size of 300x500 in all the grids from 1 to 4 and A to F with varying span length.

• Now click Run Analysis tool to start analyse the opened file.

• After the Analysis of the E-Tabs file we need to create a concrete frame design for all the beams.

• For that click the option present in the Tool bar above the E-Tabs workspace to create a Concrete Frame Design.

• Then we can see the concrete Design check Tab opened while creating Concrete frame and asking for the cancellation

• After the completion of the frame designing, we can see the reinforcement requirement for the every span of the beams.

• These required reinforcement is provided for End top, End Bottom, Mid top, Mid bottom of the beams.

• Here, we can see the Shear reinforcement of the beams as well as Longitudinal reinforcement of the beam.

• For that click the downward arrow present near the concrete frame design tool and Select Display Design Information.

• After the selection of the Display design Information, the Display concrete frame design Result Tab will be opened.

• From the Design Output select the Downward arrow and then select the shear reinforcement.

• Then click Apply to see the reinforcement requirement for the shear demand of the beams.

• Now, after applying the design output as Shear reinforcement we can see the Mid,Top's end and bottom required reinforcements.

• To see the Design details of any one of the beams created in Shear reinforcement.

• Right click on any beam and we can see the Concrete beam design information Tab is opened.

• From there click Details to check the Designs of the shear details.

• The Design check tab will be opened, then click the Shear Details menu present at the Menu bar.

• There we can see all the shear details of the beams created.

RESULT :

1) 3 span continuous beam along grid A :

2) 7 span continuous beam along grid 3 :

Addressed the following issues below :

A ) Provided the details of longitudinal and shear reinforcement for the two continuous beams :

B ) Provided the reasons for failure of the middle span along grid A and the possible ways to resolve this issue :

MID SPAN ALONG GRID A :

• The mid span along Grid A is failed due to it is Over stressed.

• It means it is violated the code values for shear reinforcement for shorter span beams.

• Now right click on the Over stressed mid span to open the new tab named the concrete beam design information (IS 456 2000).

• In this opened tab we can see the shear steel was not calculated for 3 combinations .

• Then select and click the over stressed beam and click Details button to view the Details it.

• From the Design Details tab we can see that it shows 'O/S #45 Shear stress due to shear force and torsion together exceeds maximum allowed '

• Shear stress is nothing but Load/Area.

• So we have to Reduce the loading or Increase the Area to get rid of these over stresses.

• The shear capacity of the concrete it varies with respect to the grade of concrete.

• Instead of the default M25 graded concrete used for the entire model we can use some higher grade for this beam alone like M30, M35, M40 etc.

• By this we can increase the shear capacity for the beam and therefore we can make it pass in the shear stress design

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 :

a. SWAY SHEAR FORCE TO RIGHT :

i. `V_u,_a = V_u,_aD^+L` - 1.4 `frac{M_u ^As + M_u^Bh} {L_AB}`

Given :

`M_as = 174 kNm`

`M_bh = 293 kNm`

`L_ab = 4.725 m`

`V_d +_l = 92 kN`

Solution :

or

`V_u,_a = 92` - 1.4 `frac{174 + 293} {4.725}`

`V_u,_a = 46 kN`

ii. `V_u,_ab = V_u,_bD^+L` + 1.4 `frac{M_u ^As + M_u^Bh} {L_AB}`

Given :

`M_as = 174 kNm`

`M_bh = 293 kNm`

`L_ab = 4.725 m`

`V_d +_l = 92 kN`

Solution :

`V_u,_a = 92` + 1.4 `frac{174 + 293} {4.725}`

`V_u,_a = 230 kN`

b. SWAY SHEAR FORCE TO LEFT :

i. `V_u,_a = V_u,_aD^+L` - 1.4 `frac{M_u ^Ah + M_u^Bs} {L_AB}`

Given :

`M_ah = 234 kNm`

`M_bs = 155 kNm`

`L_ab = 4.725 m`

`V_d +_l = 70 kN`

Solution :

`V_u,_a = 70` - 1.4 `frac{234 + 155} {4.725}`

`V_u,_a = 185 kN`

ii. `V_u,_b = V_u,_bD^+L` + 1.4 `frac{M_u ^Ah + M_u^Bs} {L_AB}`

Given :

`M_ah = 234 kNm`

`M_bs = 155 kNm`

`L_ab = 4.725 m`

`V_d +_l = 70 kN`

Solution :

`V_u,_a = 70` + 1.4 `frac{234 + 155} {4.725}`

`V_u,_a = 45 kN`

THE SWAY - SHEAR RESULT :

Open Load Combination by clicking Define < Load Combination.

• Then Click existing load combination and select 'Add copy of combo'.

• Here we can see the opened Load Combination Data Tab.

• In this opened tab, change 'Load combination Name = Sway'.

• Now make scale factor for all the Loads as 1.2 and click OK.

• After providing the Load combination Data, we can see the created Load combination at the Load Combination List.

• Atlast to see the E-tabs calculation of shear force demand through Shear force Diagram.

• For that Click 'Display Frame' tool present at the Tool bar to open the 'Member Force Diagram Tab'.

• After the opening of the Tab click Combo < Shear 2-2 and select OK to see the E-tabs calculated sway values as shear diagram.

EXISTING SHEAR CAPACITY IN BEAM AS PER DRAWING (AS PER IS-456 2000 CLAUSE 40.4) :

iii. `V_us = frac{0.87 fy A_sv d}{S_v}`

Given :

`Fy = 415 Nmm^2`

`A_sv = 151 mm^2`

`d = 450mm`

`Sv = 100mm`

Solution :

`V_us = frac{0.87 (415 x 151 x 450)}{100}`

`V_us = 245 kN`

Hence shear rebar in drawing is okay as per IS - 13920 code guideline.