Edinburgh Napier University

  Metal web engineered timber joists have been largely used nowadays to replace traditional solid timber joists for constructing intermediate-span timber floors in low-rise houses and long-span floors in commercial buildings. Vibrational criteria become crucial for serviceability design of timber floors and often control the design. This paper presents the study on the dynamic performance of the floors constructed with metal-web joists with focus on modal frequencies, modal shapes and damping. The studied parameters included spacing of joists, type, size, number and location of strongback, ceiling, etc. In general, joist spacing, strongback bracings and ceiling did not significantly influence the fundamental frequency and damping ratio for Mode 1-1, both required for the design of timber floors, but they did influence those of higher modes. The measured damping ratio for the fundamental mode was 0.87% on average, which is below the 1% recommended in Eurocode 5 and much smaller than the 2% recommended in the UK National Annex. The use of strongback, however, could considerably reduce the number of first-order modes below 40 Hz, which, used to determine the unit impulse velocity response, can thus be decreased notably.