Experimental and numerical analyses on nonlinear behaviour of wooden parallel chord trusses composed of self-tapping screws

Five different wooden parallel chord trusses were made of Canadian spruce 2 by 4 lumbers. Chord–web nodal points were composed of self-tapping-screws (STS) whose numbers per nodal point and allocations in nodal point were considered as the main experimental parameters which were varied from 2rows-2lines till 2rows-4lines. Load–slip relationships at nodal point were evaluated using the joint specimens made of similar materials. These parallel chord trusses were modeled using a finite element method (FEM) program by taking not only nonlinearity of nodal point joints but also material nonlinearity of chord members using fiber model into consideration. Strength properties of the chord members were deduced via specific gravity of chord member based on the regression equations given by a literature. Static monotonic central point loading tests were conducted on five specimens to investigate nonlinear behaviors of wooden parallel chord trusses. Comparisons between observed results by experiments and computed ones by FEM calculations showed a tendency that material nonlinearity gave less effect on the total nonlinear behaviour of the specimens when joint performance was inferior, on the other hand, as the joint performance increased material nonlinearity gave dominant effect on the total nonlinear behaviour of the specimens.