Concrete Technology (121-140)

Updated: Apr 30, 2020

121.According to IS: 456-1978, the maximum strain in concrete at the outermost

compression fibre in the limit state design of flexural member is 0.0035


 

122.The minimum eccentricity for design of columns as per IS : 456-1978 is

1/500 +D/30

subjected to a maximum of 20 mm. where l = unsupported length of the

column and

 

123. For the deflection of simply supported beam to be within permissible limits, the ratio of its span to effective depth as per IS : 456-1978 should not exceed

20


 

124. The development length of bars of diameter Φ, as per IS : 456-1978 is

given by



 

125.For bars in tension, a standard hook has an anchorage value equivalent to a straight length of 16Φ

 

126.The creep strains are caused due to dead loads only


 

127. The effect of creep on modular ratio is to increase it

 

128. Shrinkage of concrete depends upon i) humidity of atmosphere

ii) passage of time

 

129. Due to shrinkage stresses, a simply supported beam having reinforcement

only at bottom tends to deflect downward

 

130. In symmetrically reinforced sections, shrinkage stresses in concrete and steel are respectively tensile and compressive

 

131. A beam curved in plan is designed for bending moment, shear and torsion

 

132. In a spherical dome subjected to concentrated load at crown or uniformly

distributed load, the meridional force is always compressive

 

133. Sinking of an intermediate support of a continuous beam

i) reduces the negative moment at support

ii) increases the positive moment at centre of span


 

134. The maximum value of hoop compression in a dome is given by

wR/2d

 

135. In a spherical dome the hoop stress due to a concentrated load at crown is

tensile everywhere

 

136. In a ring beam subjected to uniformly distributed load

i) shear force at mid span is zero

ii) torsion at mid span is zero

 

137. In prestressed concrete forces of tension and compressions

remain unchanged but lever arm changes with the moment

 

138. The purpose of reinforcement in prestressed concrete is

to impart initial compressive stress in concrete

 

139. Normally prestressing wires are arranged in the lower part of the beam


 

140. Most common method of prestressing used for factory production is Long line method

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