Steel Buildings in Europe

Part 2: Concept Design 2 - 66 A more appropriate approach is an assessment based on a ‘response factor’ that takes into account the amplitude of th e vibration, which is norm ally measured in terms of acceleration. Allowable res ponse factors are also given in national regulations or technical guidance a nd m ay vary between countries. Higher response factors indicate increasingly dynamic floors that are m ore noticeable to the occupants. A response factor of 8 relative to a ba se acceleration of 5 mm/s 2 is generally taken to indicate acceptable performance for an office, but it may be ne cessary to reduce the response factor to (for example) 1 to 2 for a hospital or other specialist rooms. In practice, response factors are reduced (i.e. vibration is less noticeable) by increasing the mass participating in the motion. Long-span beams are generally less of a dynamic problem than shorter sp ans, which is contrary to ideas based on natural frequency alone. Beam layout is often important, as longe r continuous lines of secondary beams in composite construction result in lower response factors than shorter lengths, because m ore m ass participates in the motion with long er lin es of b eams. Figure 6.1 shows two possible arrangements of beams. The response factor for arrangement (b) will be lower (less noticeable to occupants) than arrangem ent (a), as the participating mass is increased in arrangement (b). The dynamic response of bare floors duri ng construction is m ore likely to be perceived than the same floor when furnished and occupied. Further information on the hum an induced vibration if stee l structures can be obtained from the HIVOSS website [9] . Primary beams Secondary beams Secondary beams Primary beams (a) (b) Figure 6.1 Alternative beam layouts