Seismic Design Philosophy and Codes Questions and Answers

Answer: A

The objective has three levels: minor shaking should leave the structure undamaged, moderate shaking may cause repairable damage to non-structural elements, and severe shaking may damage the structure heavily provided it does not collapse. Designing for no damage at all under the severest shaking would be prohibitively expensive and is not what the code asks for.

Answer: B

The code accepts that partitions may crack and finishes may spall in moderate shaking, so long as the structural frame remains sound and the building can be repaired and reoccupied. Expecting nothing at all to crack would require a far stiffer and more expensive structure than the risk justifies.

Answer: C

Such an event is rare, and paying for the full elastic strength at every site would be extravagant. The accepted alternative is to design for a fraction of the elastic demand and to detail the structure so that it can dissipate the balance by yielding, which is what the response reduction factor represents.

Answer: D

A ductile structure absorbs energy over many cycles of large deformation, which is how it survives an earthquake that exceeds its elastic strength. Brittle behaviour, by contrast, means failure follows very soon after the elastic limit is passed, leaving no reserve.

Answer: A

The designer nominates ductile locations, typically beam ends, proportions them for the code force, and then designs columns, joints and foundations for the force those locations can actually deliver when they yield. That hierarchy is what stops a brittle element from failing first and turning a ductile mechanism into a collapse.

Answer: B

Hinges in beams produce a distributed mechanism that can absorb a great deal of energy, while hinges in columns produce a storey mechanism that can collapse the building. Making the columns stronger than the beams framing into them is how the desirable mechanism is forced.

Answer: C

With every column of a storey hinged, that level must accommodate the entire drift while the storeys above ride along as a rigid block. The demand on those few columns quickly exceeds what they can sustain, which is why capacity design goes to such lengths to avoid the mechanism.

Answer: D

Many hinges, each rotating moderately, absorb far more energy in total than a few hinges rotating severely, and no single failure brings the frame down. This is why codes reward frames detailed to yield in their beams with the highest response reduction factors.

Answer: A

R is a credit against the elastic demand that the structure must earn through detailing. Claiming it without providing confinement, anchorage and joint reinforcement leaves a structure with neither the strength for an elastic response nor the capacity for an inelastic one, which is the most dangerous shortcut available in seismic design.

Answer: B

A special frame is detailed to IS 13920 so that it can yield reliably at its beam ends, and it earns the highest factor available to reinforced concrete frames. An ordinary frame takes 3.0 and unreinforced masonry only 1.5, reflecting how little inelastic capacity each of them has.