Keywords: wood floors, I-joists, vibrations, experimental data, finite element analysis.

With the advent of engineered wood products, structural members can now be produced with greater lengths and lower weights than previously attainable from solid sawn wooden structural members. The longer lengths and lower weights that make these engineered products attractive also make them more prone to human-induced vibrations. One area of concern is the possible detrimental effect of having the engineered I-joists inadvertently installed in a slightly "out of plumb" condition. In the past, preliminary research was conducted on the narrow floor strips with rotated I-joists using finite element software, but no experimental data has been available. The first objective of this project was to perform the necessary experiments of wood I-joists oriented in a rotated condition for the purpose of building a database that can be used for validation of finite element modelling [1]. Secondly, finite element models were developed specifically for wood floors with slightly rotated joists [2].

Static and dynamic experiments were performed on the single I-joist, the single I-joist with sheathing (floor strip), and the experimental floor system. A laboratory experimental system was designed and constructed in which the I-joists were easily rotated to any angle or any combination of angles. An electric oscillator was designed and fabricated that provided unidirectional excitation and accurate speed control. A test fixture was developed for experimentally determining the stiffness values of deck screw connections. Finally, a mechanical impactor was designed and fabricated to simulate a human heel-drop test with a high degree of repeatability.

The I-joist was modelled with three-dimensional continuum elements. Two different material properties were used; one for the web and one for the flanges, as determined in the experimental tests. The tongue and groove joints between the floor sheathings were modelled using spring elements that transfer shear, have some horizontal resistance (friction), but do not transfer bending moment.

Results from the experiments and finite element simulations revealed that there is a very small detrimental effect of having the I-joists in a rotated orientation on either natural frequency or the acceleration value. The computer simulation shows that bridging reduces the acceleration root mean square values, especially for small joist rotations. The computer model developed in this study allows for alternate configurations and new insights into the behaviour of engineered wood floor systems.

1

J.D. Wolfe, "Development of Experimental Data Base for Finite Element Vibration Analysis of Floor Systems with Rotated Engineered Wood I-joists", MS thesis, Idaho State University, Pocatello, Idaho, 296 p, December 2007.

2

K.B. Shrestha, "Finite Element Modeling of Vibrations in Wood Floors with Rotated Joists", MS thesis, Idaho State University, Pocatello, Idaho, 179 p, May 2008.

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