Concrete Technology (121-140)

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

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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

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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

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

given by

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

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

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

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

ii) passage of time

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

only at bottom tends to deflect downward

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

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

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

distributed load, the meridional force is always compressive

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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

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

wR/2d

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

tensile everywhere

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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

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137. In prestressed concrete forces of tension and compressions

remain unchanged but lever arm changes with the moment

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138. The purpose of reinforcement in prestressed concrete is

to impart initial compressive stress in concrete

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

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