VIBRATION SUSCEPTIBILITY OF MULTI-SPAN LVL-CONCRETE COMPOSITE FLOORS

摘要

Vibrations within floor system are caused by rotating machinery, human activity, traffic, etc. Human activities such as walking or jumping can produce discomfort which mainly comes from resonant accelerations rather than the amplitude of the vibration.This issue was studied more than 30 years ago and many approaches were published to provide remedies to decrease the effects of vibration in a floor system. Floor vibrations have recently become a significant design consideration for engineers due to the light weight and slenderness of modern floor systems.Various factors have been investigated experimentally, including the structural mass, flexibility, type of material and boundary conditions. The boundary condition is shown to be one of the most important parameters that affect the dynamic performance of timber-concrete composite floor systems. Unfortunately, the influence of the boundary conditions is very difficult to investigate numerically and analytically.The dynamic behaviour of multi-span LVL-concrete composite floor systems was partially investigated using four one-third scale simply supported beam specimens. These had 2870 mm long 250 x 45 mm LVL joists hung from 300 * 65 mm timber blocks at each end using standard joist hangers. Six 100 x 45 mm rectangular notches were cut from the top surface of the LVL joist to create a shear connection to the concrete topping. Two 6 mm diameter coach screws were installed in each notch to improve the performance of the connection system. Permanent formwork for the 500 mm wide, 25 mm thick concrete topping was provided with 7 mm plywood sheathing nailed to the LVL joist.The four simply supported LVL specimens were connected together by screwing the adjacent end blocks together to create a continuous 4-span beam (Figure 1). The continuous concrete topping was then poured across the tops of the simply-supported LVL beams. To investigate the vibration behaviour for different numbers of spans, the four-span continuous LVL-concrete composite beam was separated in a three- and then a two-span beam by cutting the concrete slab above the inner supports after the tests.