Effect of Bottom Chord Extensions on the Static Flexural Stiffness of Open-Web Steel Joists

摘要

Annoying floor vibrations, a growing issue in today's world of lighter structural members and low inherent damping because of modern office fit-outs, may also be significant in open web steel joist supported floor systems. In the presence of these vibrations, sometimes bottom chord extensions are installed in an attempt to stiffen the floor and correct the annoying vibrations problem. This study focuses on the effect of bottom chord extensions on the static flexural stiffness of joists under relatively light loads associated with occupant-induced floor vibrations. Extensive analytical and experimental studies were conducted on single-span and three-span joist-supported laboratory footbridges with different bottom chord extension configurations. Three-dimensional finite-element computer models were created to simulate and compare the results of the stiffness tests. Testing was done with (1) the bottom chord extensions installed prior to concrete placement, (2) all or part of the bottom chord extensions removed, and (3) the bottom chord extensions reinstalled with jacking for the single-span footbridge and without jacking for the three-span footbridge.