A doubly reinforced beam is considered less economical than a singly reinforced beam because
Since the maximum compressive stress is not reached in doubly reinforced beam compressive steel. This is because the we need to find the compressive stress depending on the strain in beam and thus, the stress obtained for all the practical case is less than fy.
The maximum percentage of moment redistribution allowed in RCC beams is
As per clause 37.1.1 of IS: 456-2000 the ultimate moment of resistance at any section should not be less than 70% of the factored moment at that section as obtained from the elastic moment envelope (considering all loading combinations).
Partial safety factor for concrete and steel are 1.5 and 1.15 respectively, because
Steel Is produced in factory in which controlled environment is possible. However, concrete is produced at site itself leading to more chances of carelessness. Thus, higher factor of safety for concrete in comparison to steel.
In the design of two-way slab restrained at all edges, torsional reinforcement required is
A reinforced concrete slab is 75 mm thick. The maximum size of reinforcement bar that can be used is of
The diameter of the bars shall not exceed one eight of the total thickness of the slab.
∴ Maximum size = 75/8= 9.375 mm
So the diameter will be 8 mm.
In the limit state method, balanced design of a reinforced concrete beam gives
Balanced Design means both concrete and steel will fail at the same time. Thus, it gives optimum smallest concrete section for a given reinforcement and maximum reinforcement for a given concrete section.
In case of simply supported beam , the clear distance between lateral restraints shall not exceed
As per IS 456:2000 for lateral stability, the clear span of
Simply supported beam should be less than 60b or 250(b2)/d
Cantilever Beam should be less than 25b or 100(b2)/d
When shear reinforcement is not provided in flat slab, the calculated shear stress at the critical section shall not exceed Ks ζc, where Ks is
Where βc is ratio of short side to long side of column capital.
In case of 2-way slab, the limiting deflection of the slab is
The strip of a two way slab may be checked against shorter span to effective depth ratios.
The main reinforcement of a RC slab consists of 10 mm bars at 10 cm spacing. If it is desired to replace 10 mm bars by 12 mm bars, then the spacing of 12 mm bars should be
The horizontal distance between parallel main reinforcement bars shall not be more than three times the effective depth of solid slab or 300 mm whichever is smaller. The total reinforcement in the slab should remain same. By replacing 10 mm bars by 12 mm bars, the spacing will increase as