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shivam_sharan_lall SEFI Member
Joined: 14 May 2023 Posts: 1

Posted: Sun May 14, 2023 2:30 pm Post subject: Boundary condition according to Table 26 (IS 456:2000). 


Hi
My question is:
If we want to design a slab and there is a downslab and a duct adjacent to it, so what will be the boundary condition considered for it according to table 26 of IS 456:2000?
Case 1: The downslab or duct takes about 1/3rd of edge length. the rest of the edge length is taken by another adjacent slab. How should the reinforcement be provided at the top of the slab and the adjacent slab?(What will be the value of the negative moment produced there?) If such is the case present on all the four edges, what will be the span to the effective depth ratio to be chosen for the slab?(simplysupported or continuous)
Case 2: If the downslab and duct covers more than half the edge length of the slab. So, what should be the boundary condition according to table 26 and span to depth ratio to be chosen for deflection control?
Thanks and Regards
shivam Sharan Lall
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rajagopalan_kameswaran SEFI Member
Joined: 05 Dec 2013 Posts: 1

Posted: Mon May 15, 2023 1:30 am Post subject: Boundary condition according to Table 26 (IS 456:2000). 


The best way to design such slab panel is as follows:
Consider that edge as discontinuous and use the corresponding moment coefficient for midspan moment in that direction. Provide midspan reinforcement based on that moment.
Consider that edge as continuous for determining the support moment for that edge and provide the corresponding reinforcement over the continuous portion of that edge.
Follow the same procedure if this condition occurs along all edges too.
However, if the discontinuity occurs only for a short length of the edge, the edge can be considered as continuous.
Regards
B K Rajagopalan
On Mon, 15 May, 2023, 02:09 shivam_sharan_lall, <forum@sefindia.org (forum@sefindia.org)> wrote:
Quote:  Hi
My question is:
If we want to design a slab and there is a downslab and a duct adjacent to it, so what will be the boundary condition considered for it according to table 26 of IS 456:2000?
Case 1: The downslab or duct takes about 1/3rd of edge length. the rest of the edge length is taken by another adjacent slab. How should the reinforcement be provided at the top of the slab and the adjacent slab?(What will be the value of the negative moment produced there?) If such is the case present on all the four edges, what will be the span to the effective depth ratio to be chosen for the slab?(simplysupported or continuous)
Case 2: If the downslab and duct covers more than half the edge length of the slab. So, what should be the boundary condition according to table 26 and span to depth ratio to be chosen for deflection control?
Thanks and Regards
shivam Sharan Lall

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akuc007 SEFI Member
Joined: 25 Aug 2015 Posts: 15

Posted: Mon May 15, 2023 11:41 am Post subject: Re: Boundary condition according to Table 26 (IS 456:2000). 


As a structural engineer, you could assume any edge condition and detail the rebar and anchorage length accordingly.
In my personal experience, the down slab (sunken slab) to up slab connection beam/wall portion concrete is always compromised. That to manual batch mix, will cause honeycombs. This will lead to the leakage after yrs or so.
So it is always better to release the moment at the edge and design the slab accordingly. Important thing is detail the rebar accordingly.
If you have could sketch the requirement may be helpful to explain further.
shivam_sharan_lall wrote:  Hi
My question is:
If we want to design a slab and there is a downslab and a duct adjacent to it, so what will be the boundary condition considered for it according to table 26 of IS 456:2000?
Case 1: The downslab or duct takes about 1/3rd of edge length. the rest of the edge length is taken by another adjacent slab. How should the reinforcement be provided at the top of the slab and the adjacent slab?(What will be the value of the negative moment produced there?) If such is the case present on all the four edges, what will be the span to the effective depth ratio to be chosen for the slab?(simplysupported or continuous)
Case 2: If the downslab and duct covers more than half the edge length of the slab. So, what should be the boundary condition according to table 26 and span to depth ratio to be chosen for deflection control?
Thanks and Regards
shivam Sharan Lall
Posted via Email 


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