Three-Dimensional Equivalent Parameterized Beam Element for Nail Connections in Wood Residential Buildings

Abstract

Nail connections, serving as critical nodes in the loading path of wood residential buildings, could play a crucial role in structural analysis and damage prediction when the structures are subjected to winds and floodings from natural hazards, such as hurricanes or tsunamis. To simulate the nonlinear behavior of the nail connections, nonoriented nonlinear spring elements usually are used for three translation degrees of freedom (DOFs). However, because the three DOFs are decoupled as three independent springs, their coupled effects can not be included in the modeling scheme, which leads to inconsistency for displacement trajectories. The equivalent parametrized beam element (EPBC) was proposed to avoid this inconsistency. However, the EPBC assumes the same response in two transverse directions, inducing inaccurate nail connection response predictions for three-dimensional (3D) problems. To include material nonlinearity and the coupled effects between different DOFs of the nail connections, this study proposes a three-dimensional equivalent parametrized beam element (3DEPBC). An algorithm of importance sampling for shear stiffness (ISSS) was developed to determine the optimal parameters for the 3DEPBC. Data from experimental tests were used to validate the accuracy of the proposed connector modeling scheme. The capability of loading coupling of the 3DEPBC was demonstrated by comparing the result with that of the equivalent nonlinear spring connector (ENSC), which uses nonlinear spring elements, and the EPBC with combined loadings. A case study was presented for the application of the nail model in a real roof. The investigation of shear stress suggested that shear stress has a limited influence on the total stress, indicating that ignoring the shear stress in the ISSS algorithm is reasonable, which also makes the algorithm more applicable. The proposed new connector significantly reduces the number of elements in the building model, and real nonlinear behavior of the building under complicated loadings can be captured carefully.