The influence of internode geometry on the bearing capacity of parallel chord wood trusses

The influence of two factors, web angle and internode spacing, on the bearing capacity of three different configurations of trusses was investigated. The constitutive model of the bearing capacity of trusses was established which are jointly controlled by web angle and internode spacing. With bearing capacity and stability as calculation indexes, the critical web angle and internode spacing values for three different configurations of trusses were obtained quantitatively, the truss structure was designed by combining web angle and internode spacing, the mid-span displacement was further calculated as a theoretical basis for finite element simulation. A bearing capacity test on truss specimens with Spruce-Pine-Fir (SPF) as the base material was conducted using the obtained results. The relationship between the load displacement of the different geometric configurations of trusses and the main failure modes was determined accordingly. Finally, the constitutive model of bearing capacity was established which is jointly controlled by web angle and internode spacing. It was found that the stability of the bearing capacity of the A-type truss (Warren type with vertical bar) increases with an increase in the web angle, but is relatively unaffected by the web angle compared to other truss types. The bearing capacity of the B-type(Warren type) truss increases as the web angle increases and is markedly affected by the web angle. The bearing capacity of the C-type(Pa type) truss decreases as the web angle increases, but this configuration is less affected by the web angle than the B-type. The influence of internode spacing on the load-carrying capacity of the truss weakens with an increase in the web angle, as well. The constitutive model, which was obtained by theoretical calculation and ABAQUS finite element simulation, is valid within the elastic deformation range but is not applicable beyond the elastic deformation range.