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

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

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

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

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

An engineer has designed a floor plate to a response factor of 7. The floor comprises secondary beams at 3m centres acting compositely with a 140mm composite deck. The secondary beam has a frequency of 4.5Hz. The main contractor is having difficulty in getting materials into what is a congested site, and has asked if it would be acceptable to replace the composite deck with a lightweight timber joist floor. He submits calculations that demonstrate that the same beam acting non-compositely is perfectly adequate in terms of strength, and achieves the same frequency of 4.5Hz due to a reduction in dead load of 75%. How should the engineer respond?

As long as the beam is satisfactory in terms of strength and the beam frequency remains the same or higher, then that proposal is perfectly acceptable.
Whilst your calculations demonstrate that the beam can support the change in loads, and that both the beam and system frequency are satisfactory, I have concerns about the vibration performance of the floor. The dead load of the floor construction has been reduced by 75%. Newton’s second law (acceleration = Force/Mass) suggests a four fold increase in the accelerations due to this significant reduction in dead load. The response factor has gone up from 7 to 28, which is well in excess of current practice.
No, the drawings clearly state the form of construction required.
Your proposal is acceptable provided you can offer a saving to the Client and accept design liability for your proposals.

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

Human perception to vibration depends on the direction of incidence of the acceleration relative to the human body. In the basicentric coordinate system, the z-axis corresponds to the direction of the human spine. In which of the situations below is the human body more sensitive to vibration?

Walking (z-axis perpendicular to the floor)
Lying down (z-axis parallel to the floor)
Sitting
Standing

According to SCI’s P354, “Design of Floors for Vibration: A New Approach”, the recommended response factor or multiplying factor for an office is?

2
4
6
8

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

8.4hz
5hz
4hz
3hz

When assessing the frequency of a floor, which elements of the floor must the designer check?

The slab
The secondary beam
The primary beam
All of the above, both individually and collectively