Test: RCC- 2 - SSC JE MCQ

Taking Moment of area of tension and compression zone for a singly reinforced beam:

Where,

X_c = critical depth or economic depth of neutral axis

m = modular ratio

A_st = area of steel required for balanced section

m = 18

c = 50 kg/cm2

t = 1400 kg/cm²

For all cases, Effective depth of the beam cross-section is to be taken as:

According to IS 456: 2000, minimum nominal cover to all bars in the slab is 20mm. According to new code, nominal cover does not depend upon the diameter of bar used.

Working stress method: working stress method is based on elastic theory. Concrete and steel are assumed to act together elastically and follow hook’s law. This method follows a deterministic approach as it assumes that the loads, factor of safety and permissible stresses are accurately known. In this method material strengths are not fully utilised in designing the member.

Limit state method: This method follows a non-deterministic approach as it adopts probable loads and probable strengths of materials as per actual or based on experience or observations depending upon the situations. Material strengths are fully utilised in designing the member.

As per Bureau of Indian standards,

Period of structural adequacy under fire: The time (t), in minutes, for the member to reach the limit state of structural inadequacy in a standard fire test.

As per IS 456:2000, slenderness limit for lateral stability of beam shall be:

As per IS 456 : 2000 In the Design of compression members the ultimate load on the short axially loaded column is:

P_u = 0.4f_ck A_c + 0.67f_y A_sc

where,

f_ck = Characterstics strength of concrete

f_y = characterstic strength of steel

A_c = Area of concrete in column cross-section

A_sc = Area of steel in column in compression

Counterforts are firmly attached to the face slab as well as the base slab. The earth pressure acting on the face slab is transferred to the counterfort which deflects as vertical cantilever. The back of rear counterfort comes under tension and the front face is under compression. So the inclined (back) face of the rear counterfort should be provided with main reinforcement.

Deep beams are structural elements loaded as simple beams in which a significant amount of the load is carried to the supports by a compression force combining the load and the reaction. As a result, the strain distribution is no longer considered linear, and the shear deformations become significant when compared to pure flexure.

In view of ample shear strength, deep beams are primarily recommended as transfer girders. These members transfer loads through-loading face to supports in the transverse direction. The deep horizontal members predominantly fail in shear rather than flexure. These beams are characterized with small span-to-depth ratio. Pile caps, corbel, brackets, foundation walls and off-shore structures are few examples of RC deep beams.

According to IS 456-2000 a beam shall be deemed to be a deep beam when the ratio of effective span-to-overall depth, l/D is less than:

1) 2.0, for simply supported beam; and

2) 2.5, for a continuous beam.

Though different codes define deep beams in different clear span-to-depth ratios, as a general rule deep beams are recognized by their relatively small span-to-depth ratio.

Hence, Deep beams are designed for bending moment and checked for shear.

IS 456:2000 limits the maximum diameter of reinforcing bars to 1/8^th of the total thickness of the slab.

D_max = 128/8 = 16 mm; Hence use 16 mm diameter bars.