Design of floors for vibration quiz

Please answer the following 10 multiple choice questions, then click 'submit' to check the result. The pass mark for a CPD certificate is 8 out of 10, and you may retake the quiz as many times as you wish, but the questions will vary! Please note that one, two, three or all of the possible answers presented for each question may be right, and to gain a mark for that question all correct answers must be identified.

Good luck

Design of floors for vibration

The frequency of an element or system is inversely proportional to the square root of the deflection. On what loading is the deflection based in the UK?

Dead load + 30% of the imposed load
Dead load + 10% of the imposed load
Dead load only
Dead load + imposed load

The response factor of a floor is:

The peak acceleration of the floor
The peak acceleration of the floor divided by the base value
The root mean square (rms) acceleration of the floor
The rms acceleration of the floor divided by the base value (0.005 for z-axis vibrations)

A designer has conservatively assessed a floor plate for an office of 18m x 30m. The structural grid is 9m x 7.5m and the plans show a central corridor running the length of the building. The target response factor is 8, but initial calculations indicate a response factor of 9. Which of the following strategies could the designer use to potentially reduce the initial response factor calculated?

The source of excitation (the corridor) is close to the column line, and so a µe value less than 1 is possible
Replace normal weight concrete for the composite slab with lightweight concrete
Reduce the walking path and resonance build-up by introducing doors in the corridor
If the axis of vibration is known use the appropriate frequency weighting curve

When assessing vibrations in a floor, appropriate acceptance criteria can be referenced from where (more than one may apply)?

BS 5950: Structural use of steelwork in building
BS 6472: Guide to evaluation of human exposure to vibration in buildings
SCI publication P354 “Design of Floors for Vibration: a New Approach”
BS 6399: Loadings for buildings

In respect of Vibration Dose Values (VDV’s), which statements are correct?

VDV’s provide a mechanism for taking account of the intermittent nature of vibrations
VDV’s can be used for operating theatres in hospitals
VDV’s are generally used when calculated response factors are within the limits of multiplying factors for continuous vibrations
Guidance on the use of VDV’s can be found in BS 6472 and P354

Which of the following statements are true?

The response factors or multiplying factors given in BS 6472 are “for a low probability of adverse comment”
Multiplying factors are for exposure to continuous vibration
Multiplying factors are for a 16 hour exposure period during the day
Multiplying factors are for an 8 hour exposure period during the night

What is a reasonable frequency range caused by walking?

2 Hz to 3 Hz
1 Hz to 2 Hz
2.8 Hz to 3.2 Hz
1.8 Hz to 2.2 Hz

No floor structure, and no single element within that floor structure, should have a fundamental frequency less than what?

8.4hz
5hz
4hz
3hz

Which statement below does NOT describe a characteristic of a low frequency floor?

Has a fundamental frequency greater than 3 Hz but less than 10Hz
Exhibits a near resonant response
Both steady state and transient response must be checked
Has a fundamental frequency greater than 10Hz

Why do we calculate the natural frequency of a floor system? (tick all that apply)

To avoid resonant behaviour of the floor plate
To ensure that any dynamic effects do not induce loads greater than the static loads for which the floor plate has been designed
To ensure that the system frequency is sufficiently greater than the forcing or walking pace frequency
To obtain a qualitative prediction of the serviceability performance of the floor plate