An open ground storey in an existing building is a deficiency because
Answer: C
The flexible storey must accommodate almost the whole of the building's drift while the storeys above ride as a rigid block. Correcting it means stiffening that level, or designing its columns for the magnified forces it attracts.
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A floating column found in an existing building should be treated as a deficiency because
Answer: D
The load has to travel sideways through a beam before continuing down, and under reversing seismic load that beam is doing something it suits badly. Providing a new column or a strengthened transfer member is the usual remedy.
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Short lap splices in the columns of an existing building are a concern because
Answer: A
A lap shorter than the development length relies on bond that cyclic loading progressively destroys, and the column then loses flexural capacity. Confining the splice region with a jacket or a wrap is the usual correction.
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Beam-column joints in older buildings are frequently deficient because
Answer: B
Detailing practice before ductile codes simply stopped the column hoops at the beam soffit, leaving the joint unconfined. Because the joint carries the full capacity of the members framing into it, that omission is often the governing deficiency.
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Strong beams and weak columns in an existing frame indicate
Answer: C
Hinges will form in the columns rather than the beams, and hinges at the top and bottom of one storey's columns leave nothing holding the building up. Reversing the hierarchy by strengthening the columns is a standard retrofit objective.
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Plan irregularity in an existing building leads to
Answer: D
Separation between the centres of mass and stiffness twists the building about a vertical axis, and the elements furthest from the centre of rotation take far more than their nominal share. Adding stiffness on the flexible side is the usual correction.
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Corrosion of reinforcement in an existing building affects its seismic performance by
Answer: A
Section loss reduces capacity, and the expansion of the corrosion products cracks and spalls the cover that provides bond and confinement. Repair has to arrest the corrosion as well as restore the section, or the problem simply returns.
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Heavy roofs on older masonry buildings are a deficiency because they
Answer: B
Thick mud or stone roofs generate a large inertia force at the top of walls that have very little capacity to resist it out of plane. Replacing them with a light roof, well tied to the walls, is one of the most effective retrofits available.
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A global retrofit strategy is one that
Answer: C
Adding shear walls or bracing, isolating the base or installing dampers all change the periods, the force distribution and the drift of the entire structure. Local measures raise the capacity of particular members without altering how the building responds.
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Adding new shear walls to an existing frame will
Answer: D
Stiffening shortens the period and usually moves the building towards the plateau of the spectrum where the ordinate is largest. The walls take most of the increased force, so the existing frame may still be relieved, but the foundations under the new walls must be checked carefully.
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