Abstract:

Objective: The bearing performance of Pseudotsuga menziesii and SPF(spruce-pine-fir) parallel chord wood trusses under different web angles was compared to explore the influence of web angles and structural materials on the bearing performance of wood trusses, providing theoretical basis for the structural design of parallel chord wood trusses. Method: Using Smsolver structural mechanics solver, the internal force variation and deformation of each member of parallel chord wooden truss were quantitatively analyzed with bearing capacity and stability as checking indexes, and the upper and lower critical values and optimal web angles values of parallel chord wooden truss were obtained. ABAQUS finite element software was used to analyze and verify the finite element models of Pseudotsuga menziesii and SPF parallel chord wooden trusses with three different web angles. The internal force variation rule of the parallel chord wood trusses with different base materials under different web angles was obtained, and the possible failure mode and stress mechanism were determined. On this basis, with Pseudotsuga menziesii and SPF as base material, respectively, making three web angle parallel chord wood truss, bearing capacity for bending static test, explore parallel chord wood truss of the ultimate load, stress distribution and the main failure mode, and is contrasted with the results of finite element simulation, to verify the exactness of the parallel chord wood truss finite element model analysis and applicability. Result: 1) The optimal web angle of the warren type parallel chord wooden trusses was 47°, the critical value of the lower limit web angle was 34°, and the upper limit web angle was 60°. 2) The ultimate load range of Pseudotsuga menziesii parallel chord wooden trusses was 26.53?40.83 kN and the mid-span deflection range was 30.57?31.01 mm. The ultimate load range of the SPF parallel chord wooden trusses was 23.48?34.16 kN and the mid-span deflection range was 31.85?32.05 mm. 3) The ultimate load of Pseudotsuga menziesii and SPF parallel chord wooden trusses with 34°, 47° and 60° web angle was 26.53 and 23.48 kN, 35.10 and 30.06 kN, 40.83 and 34.16 kN, respectively. The corresponding mid-span deflections were 31.85 and 31.01 mm, 30.72 and 32.05 mm, 30.57 and 31.97 mm, respectively. 4) The failure mode of Pseudotsuga menziesii parallel chord wooden trusses was mainly manifested as the crack in the web member near the truss support and the toothed plate pulling out at the truss end or the load applying point, while the failure mode of SPF parallel chord wooden truss was mainly manifested as the toothed plate pulling out at the truss end and the load applying point. 5) Through ABAQUS finite element simulation and experimental verification, it was found that the chord member axial force at the middle part of the two truss spans is the largest, decreasing gradually on both sides, while the web member force at the middle part of the truss spans is the smallest, increasing gradually on both sides, The chord member axial force was larger than the chord axial force. Conclusion: The bearing capacity of Pseudotsuga menziesii parallel chord wooden trusses is better than SPF parallel chord wooden trusses. The bearing capacity of the parallel chord wood truss increases with the increase of the web angle. Comprehensive analysis shows that the weak points of the two parallel chord wooden trusses are the toothed plate joints at the end of the truss and the loading point. The ABAQUS finite element model can effectively reflect the stress distribution and deformation trend of the whole structure.

Key words: parallel chord wood truss, Pseudotsuga menziesii, spruce-pine-fir (SPF), web angle, bearing performance, ABAQUS finite element simulation