An R.C.C. beam of 6 m span is 30 cm wide and has a lever arm of 55 cm. If it carries a U.D.L. of 12 t per m and allowable shear stress is 5 kg/cm², the beam

ANS:D - needs revision of section

To determine the safety of the RCC beam under the given conditions, we need to evaluate if the shear stress experienced by the beam is within the allowable limit and whether the necessary reinforcement (stirrups and inclined bars) is provided adequately. First, let's calculate the maximum shear force (V_max) acting on the beam due to the uniformly distributed load (U.D.L.): Vmax​=w⋅L​/2 Where:

• w= U.D.L. = 12 t/m
• L= Span of the beam = 6 m

Vmax​=212t/m×6m​=36t Now, let's calculate the shear stress (τ) experienced by the beam: τ=Vmax​​/b⋅d Where:

• �=b= Width of the beam = 30 cm = 0.3 m
• �=d= Effective depth of the beam = Lever arm - Clear cover to the longitudinal reinforcement = 55 cm - (2.5 cm + 1.5 cm) = 51 cm = 0.51 m

τ =36 t×9.81 m/s20.3 m×0.51 m ​ τ≈227.294kg/m^2 Now, let's convert this value to kg/cm²: τ≈227.294 kg/m^2/ 10000 kg/cm2  ≈0.0227kg/cm2 Comparing the calculated shear stress (τ) with the allowable shear stress (5 kg/cm²), we find that: τ=0.0227kg/cm^2<5kg/cm^2 Therefore, the beam is safe in shear according to the given condition. However, regarding the necessary reinforcement, it's essential to verify whether the beam is adequately reinforced with stirrups and inclined bars to resist shear forces effectively. Without the details of the reinforcement provided, it's not possible to conclusively determine the adequacy of the reinforcement. Therefore, further information on the reinforcement details would be needed to make a final assessment regarding the necessary revision of the section.