How much portion of steel that should extend beyond the faces of suppo...
To determine the amount of steel that should extend beyond the faces of support at discontinuous edges of a two-way slab due to negative moments, the effective span of the slab (l) is considered. The correct answer is option 'A', which states that 0.10l should be the portion of steel extending beyond the faces of support.
Here's an explanation of why this is the correct answer:
1. Introduction:
In a two-way slab, negative moments occur at the discontinuous edges of the slab due to the transfer of loads from the slab to the supports. To ensure the stability and strength of the slab, reinforcing steel is provided near the support regions.
2. Extending Steel beyond the Faces of Support:
When negative moments occur at the discontinuous edges, the steel reinforcement is extended beyond the faces of support to resist the bending stresses. This extension of steel helps in providing additional strength and preventing the formation of cracks.
3. Determining the Portion of Steel:
The amount of steel that should extend beyond the faces of support depends on the effective span of the slab (l). The effective span is the distance between the centers of support in a two-way slab.
4. Minimum Extension Requirement:
As per design guidelines, it is recommended that a minimum extension of 0.10 times the effective span (0.10l) should be provided beyond the faces of support. This ensures adequate reinforcement to resist the negative moments and prevents excessive cracking and failure.
5. Other Options:
The other options given in the question (0.15l, 0.25l, and 0.30l) suggest higher extensions of steel beyond the faces of support. However, these options exceed the minimum requirement and may result in unnecessary use of additional steel, which could increase the cost of construction without providing significant benefits.
6. Conclusion:
To provide sufficient reinforcement and resist negative moments at the discontinuous edges of a two-way slab, a minimum extension of 0.10 times the effective span (0.10l) should be provided beyond the faces of support. This extension helps in preventing cracking and ensuring the structural integrity of the slab.
How much portion of steel that should extend beyond the faces of suppo...
The following points should be remembered for reinforcement detailing in the two-way slab as per IS 456-2000:
- Slabs are considered as divided in each direction into middle and end strips. Minimum steel can be provided in the edge strip
- 50% of the tension reinforcement provided at midspan in the middle strip shall extend in the lower part of the slab to within 0.25l of a continuous edge or 0.15l of a discontinuous edge and the remaining 50% shall extend into support.
- 50% of tension reinforcement at top of a continuous edge shall be extended for a distance of 0.15L on each side from the support and at least 50% shall be provided for a distance of 0.3l on each face from the support.
- At the discontinuous edge, the negative moment may arise, so 50% of mid-span steel shall be extended into the span for a distance of 0.1L at the top.
- Tension steel shall be provided at corners in the form of a grid (in two directions) at the top and bottom of the slab where the slab is discontinuous at both the edges. This area of steel in each layer in each direction shall be equal to ¾ the area required for maximum mid-span moment. This steel shall extend from the edges for a distance of L/5.
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