Steel Buildings in Europe

Part 4: Detailed Design 4 – 24 The dynamic response of floor systems to human excitation is complex, for three reasons:  The nature of the excitation is uncertain in magnitude, duration and frequency of occurrence.  The structural response is substantially influenced by the magnitude of the damping in the structure and the damping effect of non-structural components of the building and its fittings, furnishings and furniture.  Human perception of vibration and the definition of appropriate acceptance criteria are both very imprecise, varying between individuals and for a single individual over time. It must be emphasised that a floor that has a ‘lively’ response to human excitation is most unlikely to have inadequate or impaired strength. Traditional timber floors have always exhibited such behaviour yet have performed satisfactorily. However, both the increasing use of longer span steel floor systems and the move to lighter construction increase the probability that performance may cause discomfort to some users. Designers therefore need to pay attention to this aspect of serviceability. Historically, designers have used the natural frequency of the floor as the sole measure of acceptable performance. A sufficiently high natural frequency means that a floor is effectively ‘tuned’ out of the frequency range of the first harmonic component of walking. However, resonance might still occur with higher harmonics. As a guideline, a fundamental frequency above 4 Hz is usually appropriate, but no requirements are given in EN 1994 [2] and the designer should seek guidance in the national regulations. Much more effective, though more complex, methods of assessing dynamic serviceability have emerged recently:  Vibration design of floors RF32-CT-2007-00033 : This is freely available from RWTH Aachen. It provides a single mode analysis on the floor.  Design of floors for vibration : A new Approach [10] presents a more comprehensive, multi-mode approach to the same methods of assessment. Design software is becoming available that takes full account of the method presented in Reference 10. 4.7 Design summary  Verify the horizontal deflections defined in Section 4.3 against the criteria defined in the relevant National Annex  Verify the relevant vertical deflection, defined in Section 4.4 against the criteria defined in the relevant National Annex  Consider pre-cambering for beams greater than 10 m in length  Verify the dynamic response of the floor against one of the references given in Section 4.6.