Vibration characteristics of joist and joist-girder members

With the development of lightweight steel beam and steel joist-concrete slab floor systems, floor vibration problems are becoming more and more prevalent. This paper presents the experimental and analytical study of the vibration characteristics of steel joist and joist-girder members. Three aspects were studied to prevent and correct vibration problems. Long span-joists and joists-girders, with a span greater than forty feet, have not been considered for Murray's criterion and the Modified Reiher-Meister scale. This study shows that these two methods can be used to predict the acceptability of a long span floor system to the occupants. Modifying existing floors so that they will be considered acceptable to the occupants is a concern for existing vibrations problems. This study has shown that by adding additional steel to the bottom chord of the joists and/or joist-girders the floor system frequency can be modified so that the floor will be considered acceptable to the occupants.

Predicting the effective moment of inertia of joists and joist-girders is essential to accurately predict the frequency and displacement of a floor system due to human occupancy. This paper presents two new equations that can be use to predict the effective moment of inertia of round web joist and angle web joist and joist-girders based on their span-to depth ratio.