Seismic Design Philosophy and Codes Questions and Answers

Answer: C

Unreinforced masonry has almost no capacity to deform inelastically, so the code allows only a small reduction from the elastic demand and such buildings are accordingly designed for a large force. Adding horizontal bands raises the factor, and adding vertical bars at corners and jambs raises it further.

Answer: D

Raising the demand by half is intended to keep such buildings serviceable after an earthquake, when they are most needed. The factor never drops below unity, so it can only ever add to the design force rather than relieve it.

Answer: A

For a storey three metres high this permits twelve millimetres of relative movement between its floors. The limit protects partitions, cladding and services from damage, and it also keeps second-order effects within bounds.

Answer: B

Correct answer: 12.8 mm

The code limits the storey drift to 0.004 times the storey height under the design lateral force, so \[ 3200 \times 0.004 = 12.8\ \mathrm{mm}. \] The limit exists to protect the non-structural elements - cladding, partitions, glazing, services - and to keep the second-order effects of gravity acting through the displaced geometry within what the frame can carry.

Answer: C

Height stands in for the mass and stiffness that are not yet known when a design begins, and the exponent of three quarters reflects how period grows more slowly than height. The alternative form with the plan dimension applies where brick infill panels stiffen the frame.

Answer: D

Here \( d \) is the base dimension in the direction being considered, and the formula recognises that infill panels act as struts and stiffen the frame considerably. A stiffer building has a shorter period and therefore usually reads a larger acceleration from the spectrum.

Answer: A

Taking \( T = 0.075 \times 20^{0.75} = 0.075 \times 9.46 = 0.71 \) s. Raising the height to the power three quarters rather than to the first power is where slips occur, and the difference is substantial for a tall building.

Answer: B

Taking \( T = 0.09 \times 20/\sqrt{16} = 1.8/4 = 0.45 \) s, appreciably shorter than the 0.71 s the bare frame formula gives for the same height. The infill has stiffened the building, which is exactly what the two formulae are meant to distinguish.

Answer: C

The first expression amplifies the computed eccentricity and adds an accidental allowance, while the second reduces it, and both must be checked because either can govern a particular member. The five per cent term covers construction variability that no calculation can anticipate.

Answer: D

Furniture moves, partitions are altered and construction never matches the drawings exactly, so the real centre of mass wanders from the computed one. Adding five per cent of the plan dimension covers that drift without requiring it to be quantified.