Deciding between retrofit and demolition turns principally on
Answer: C
Where strengthening approaches the cost of rebuilding, and where no heritage or occupancy value argues otherwise, replacement wins. Heritage fabric, a functioning tenancy or a difficult site all shift the balance towards retrofit.
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Retrofit work carried out while a building remains occupied requires
Answer: D
Exoskeletons, external buttresses and bay-by-bay bracing all suit occupied buildings, whereas jacketing every column does not. Temporary propping and the sequence in which capacity is removed and restored have to be designed as carefully as the permanent work.
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Temporary propping during retrofit work is required when
Answer: A
Breaking out cover, cutting a column to insert a bearing, or removing a wall all leave the structure weaker until the new work is complete and has gained strength. The propping scheme is part of the design rather than a matter for the contractor alone.
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Verification after a retrofit normally involves
Answer: B
Cores, pull-out tests on anchors and inspection of the new reinforcement confirm that what was designed has been built, and the analysis is updated with the properties achieved. Ambient vibration measurement before and after gives a useful check on the stiffness gained.
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Consider the following statements about retrofitting.
1. Assessment precedes the choice of scheme.
2. Adding stiffness on one side only can create torsion.
3. Reducing mass reduces demand.
Which of the statements are correct?
Answer: C
All three are sound. The second and third between them capture the two levers available: change the distribution of stiffness carefully, and reduce the mass wherever it can be spared, since demand follows mass directly.
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Consider the following statements about jacketing.
1. A concrete jacket adds confinement and flexural strength.
2. A steel jacket adds confinement with little flexural strength.
3. Fibre wrapping adds a great deal of mass.
Which are correct?
Answer: D
The first two describe the two methods correctly, and the distinction matters because adding flexural strength to a column can disturb the capacity hierarchy. Fibre wrapping is a few millimetres thick and adds essentially no mass.
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Match the technique with the deficiency it addresses.
1. Seismic bands 2. Column jacketing 3. Added shear walls
P. Insufficient overall lateral strength Q. Walls acting independently R. Inadequate confinement in a member
Answer: A
Correct answer: 1-Q, 2-R, 3-P
Three deficiencies and three remedies. Bands tie walls that would otherwise act independently. Jacketing wraps a column that lacks confinement, giving it the ductility to survive large deformations. And new shear walls supply lateral strength the building as a whole does not have.
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Match the test with what it measures on an existing building.
1. Rebound hammer 2. Cover meter 3. Half-cell potential
P. Position of reinforcement Q. Likelihood of corrosion R. Surface hardness
Answer: B
The three instruments answer quite separate questions, and a survey normally uses all of them together. None of them measures compressive strength directly, which is why cores are still taken where a firm figure matters.
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Arrange the stages of a retrofit project in order.
1. Select and design the scheme 2. Assess the existing structure 3. Verify the completed work 4. Agree the performance objective
Answer: C
The assessment establishes what the building is, the objective says how well it must perform, and only then can a scheme be chosen and designed. Verification closes the loop by confirming that what was designed is what was built.
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Assertion (A): Adding shear walls to a frame can increase the force it attracts.
Reason (R): Stiffening shortens the period towards the plateau of the spectrum.
Select the correct option.
Answer: D
A stiffer building reads a larger ordinate over most of the period range, so the total force rises even as the drift falls. The new walls carry most of that increase, but the foundations beneath them have to be designed for it.
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