Element 1 - Testing & Analysis
Task 1.4.2 Design Methodology for Diaphragms
PI: J. Daniel Dolan (WSU - formerly with Virginia Polytechnic Institute)
This project is developing information on the performance of wood diaphragms. The project is primarily an experimental study intended to quantify the stiffness of wood diaphragms that are in two conditions (nailed sheathing, and glued and nailed sheathing.) Six specimens will be tested, four with plan dimensions of 16 x 20 feet and two with plan dimensions of 10 x 40 feet.
Each of the diaphragms will be tested under approximately 28 different configurations. These include openings that cause torsional response, with and without chords (ridge vents and truss framing condition), blocked and unblocked, and with and without the walls attached to the floor diaphragm. All of these conditions will be tested with the sheathing nailed only, and then repeated with adhesive attaching the sheathing to the framing.
Each configuration is intended to investigate design parameters and provide data for calibrating numerical models that will be used in the future to conduct parametric studies of wood diaphragms. Two main variables that the project will quantify are the bending and shear stiffness parameters. The goal is to develop a simplified design equation for predicting the deflections of the diaphragm. With the code requirement for determining whether diaphragms are flexible or rigid at the time of design, accurate methods for this prediction, that are easy to implement, are needed by the design community. Current deflection predicting equations require a significant level of understanding of diaphragm behavior by the engineer for accurate use, and much of the data required to use the current equations is not generally available. A simple two-term equation would be much easier to use, and if ranges for the bending and shear stiffness values were readily available to the designer, a more rational design process is possible. Finally, when the effect of variables such as those investigated in the experimental portion of the project are quantified, the deflections and strength of diaphragms will be predicted with acceptable accuracy.