Dynamic Behaviour of LVL-Concrete Composite Flooring Systems

Abstract

An LVL-concrete composite floor (LCC) is a hybrid flooring system, which was adapted from a timber-concrete composite (TCC) floor system. By replacing the timber or glulam joists with LVL joists, the strength of the floor was increased. However, the demand nowadays is to build longer spans and this may reduce the stiffness and lead to the floor being more susceptible to vibration problems. While the vibration problem may not be as critical as other structural issues, people could feel sick and not comfortable if the floor vibrates at the resonant frequency of the human body. Hence, this research focuses on the dynamic behaviour of long span LCC flooring systems. Experimental testing and finite element modelling was used to determine the dynamic behaviour, with particular regard to the natural frequency, fn and mode shape of an LCC floor. Initially, a representative series of LVL-concrete composite specimen types were built starting from (1) full-scale T-joists specimens, (2) reduced-scale (one-third) multi-span T-joists specimens and (3) reduced-scale (one-third) 3m x 3m floor. The specimens were tested using an electrodynamic shaker. The SAP 2000 finite element modelling package was used to model and evaluate the full- and reduced-scale LVL-concrete composite T-joist experimental results. Additionally, a 8m x 7.8m LCC floor was modelled and analysed using SAP 2000. The behaviour of the 8m LCC floor was investigated through the changing of (1) concrete topping thickness, (2) depth of LVL joists, (3) different types of boundary conditions, and (4) the stiffness of the connectors. Both the experimental results and the finite element analyses agreed and showed that increased stiffness increased the natural frequency of the floor, and the boundary conditions influenced the dynamic behaviour of the LCC floor. Providing more restraint increased the stiffness of the floor system. The connectors' stiffness did not influence the dynamic performance of the floor. The study outcomes were based on a 8 Hz natural frequency limitation where the fundamental natural frequency of the LCC floor must exceed 8 Hz in order to prevent vibration problems. The research showed that a 8m LCC long span floor can be constructed using LVL joists of between 300 mm to 400 mm depth with a concrete thickness of 65 mm for the longer spans, and joists of between 150 mm to 240 mm depth in conjunction with a concrete topping thickness of 100 mm for the shorter spans.