At a joint the beams framing in have a total moment capacity of 500 kNm. The columns must provide a total capacity of at least
Answer: C
Applying the factor gives \( 1.4 \times 500 = 700 \) kNm about the axis considered. Providing only the equal capacity would leave the columns liable to hinge first once the beams strain harden past their nominal strength.
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The minimum thickness of a reinforced concrete shear wall under IS 13920 is
Answer: D
Below that thickness the wall cannot accommodate two layers of reinforcement with cover, and it becomes prone to out-of-plane instability of its compression edge under cyclic loading. Walls carrying large shear are commonly much thicker than the minimum.
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The minimum reinforcement ratio required in each direction of a shear wall is
Answer: A
Steel in both directions distributes cracking and holds the wall together through reversing diagonal tension. The requirement applies horizontally as well as vertically, since the diagonal cracking that shear produces runs across both.
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Two curtains of reinforcement are required in a shear wall when its thickness exceeds
Answer: B
A single central curtain in a thick wall leaves the two faces unreinforced against the cracking that reverses across them. Two curtains are also required where the factored shear stress is high, irrespective of the thickness.
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Boundary elements at the ends of a shear wall are provided to
Answer: C
A wall bending in its plane develops large forces at its extreme fibres, and thickened confined zones with concentrated vertical steel are what resist them. Confining those zones is essential because they are where crushing would otherwise begin.
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Coupling beams between two shear walls are detailed with diagonal reinforcement when
Answer: D
A short deep coupling beam is dominated by shear, and diagonal bars aligned with the strut and tie action carry that force far more reliably than conventional stirrups. Slender coupling beams are detailed as ordinary flexural members instead.
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The purpose of confining the concrete core of a column with closely spaced hoops is to
Answer: A
Hoops restrain the lateral expansion that accompanies compression, putting the core into triaxial compression so that it can keep its strength to much larger strains. The cover, being outside the hoops, spalls away and is not counted on once that stage is reached.
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Cross ties are provided in a wide column in addition to the perimeter hoop in order to
Answer: B
A perimeter hoop alone bows outward between its corners and leaves the bars along the middle of a wide face unsupported. Cross ties engaging those bars keep the confinement effective across the whole section rather than only at the corners.
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The purpose of ductile detailing is to give a member the ability to
Answer: C
Earthquake demand comes in cycles, and a member that loses strength after the first excursion cannot see the event out. Detailing that confines the concrete, restrains the bars and anchors them properly is what makes repeated large deformation survivable.
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A brittle failure in a reinforced concrete member is characterised by
Answer: D
Shear failure, bond failure and concrete crushing in an over-reinforced section are all of this kind, and none of them gives warning. Ductile detailing exists to ensure that flexural yielding happens first, since it is gradual and can be seen.
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