Retrofitting a building means
Answer: A
The geometry, the materials and the loads are all given, and the question is what can be added or altered to close the gap between what the building has and what it needs. That constraint is what makes retrofit a different discipline from new design.
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An engineer needs the published acceptance criteria for judging whether an existing reinforced concrete building is seismically adequate. The document to consult is
Answer: B
It sets out the evaluation procedure, the acceptance criteria against which an existing building is judged, and the strengthening options open once it has been found wanting. Repair and seismic strengthening more generally, masonry included, are dealt with in IS 13935 instead.
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The first step in any retrofit project is
Answer: C
Until the geometry, the materials, the reinforcement and the deficiencies are known, no scheme can be chosen sensibly. A retrofit designed on assumptions about hidden reinforcement is the commonest way such projects go wrong.
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A rebound hammer test on existing concrete gives an indication of its
Answer: D
The rebound number correlates loosely with compressive strength but is affected by carbonation, moisture and the aggregate, so it is used for comparison between members rather than as an absolute measure. Cores are taken where a firm figure is needed.
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An ultrasonic pulse velocity test on concrete is used chiefly to
Answer: A
A low or erratic velocity points to honeycombing, cracking or delamination, which matters greatly in a member that is to be relied on. The absolute strength still requires cores, since velocity depends on the mix as much as on its quality.
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A core test on existing concrete is taken in order to
Answer: B
Cutting a cylinder and crushing it is the only direct measurement available on a finished structure, and the result is corrected for the core's proportions and for the reinforcement it contains. Coring damages the member, so the number of cores is kept small.
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A cover meter is used on an existing building to
Answer: C
Correct answer: locate the reinforcement and measure the cover over it
A cover meter detects the steel electromagnetically, so it finds the bars, their spacing and the depth of concrete over them without breaking out. That matters twice over in retrofit work: the reinforcement layout is often undocumented, and the cover governs how long the steel will be protected from corrosion.
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A half-cell potential survey of a reinforced concrete member indicates
Answer: D
Potential readings map the probability of active corrosion across a surface, which tells the engineer where to break out and look. It is a probability rather than a measurement of section loss, so it guides investigation rather than replacing it.
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As-built drawings for an existing building should be
Answer: A
Buildings are altered during construction and afterwards, and drawings are seldom updated, so spot checks on dimensions and reinforcement are essential. Where no drawings exist at all, a full survey with a cover meter and selective breaking out takes their place.
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The most common seismic deficiency found in Indian reinforced concrete buildings of the pre-code era is
Answer: B
Widely spaced hoops with hooks turned outwards, and joints with no transverse steel at all, are the features that most often limit performance. They are also the hardest to correct, because the reinforcement is already cast in.
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