The second system effect is deflection compatibility. For example, in the complex assembly model, the total applied load assumed by the CDP was 155,000 pounds (assuming 2-ft spacing on center for every truss in theĪssembly) while the total load for the SDP was only 142,000 pounds (based on the actual overall roof loading area in the assembly). In most cases, the CDP overestimated the applied loads. This effect occurs because the CDP assumes a 2-ft spacing for every truss in an assembly, whereas the SDP assumes the actual tributary area, with normally a lower total applied load. The first is the reduced applied load effect.
These effects were observed in all three assemblies.
From this investigation, there are three system effects observed by the SDP, but not accounted for by CDP. The structural responses including CSI, truss deflections, and reactions from both CDP and SDP were compared and the system effects were evaluated. A commercially available structural analysis program, SAP2000, was then utilized to model 3D truss assemblies with a system design procedure (SDP). Uses a conventional design procedure (CDP) by analyzing one truss at a time in two-dimensions. The VIEW (Visually Integrated Engineering Window) program, used by a truss plate manufacturer to design truss assemblies, was used to layout assemblies and to design individual trusses. T-shaped, L-shaped, and complex assemblies were composed of 4 (total of 37 trusses), 17 (total of 56 trusses), and 27 (total of 123 trusses) different types of individual trusses, respectively. Three types of 3D truss assemblies (i.e., T-shaped, L-shaped, and a complex assembly) were investigated. The objective of this research was to use a three-dimensional (3D) analysis method to include system effects directly in the design of light-frame roof truss assemblies. Two technical publications from this work have been prepared and submitted to two peer-reviewed journals for publication consideration. A brief paper was also prepared and presented at the 8th World Conference on Timber Engineering in Lahti, Finland in August.