Fan Bai

An improved frequency-domain method for identifying the center of rigidity in multistorey, noncoaxial stiffness-eccentric structures is presented. This approach utilizes successive variational mode decomposition (SVMD) to analyze acceleration responses at the center of mass. By generating power spectral density (PSD) plots for the decomposed acceleration signals, the method allows for the selection of frequency bands that are close to the target spectral peaks. The proposed technique leverages data from these identified frequency bands in a QR decomposition combined with a least-squares algorithm to determine the center of rigidity. This strategy effectively avoids the matrix inversion procedures typically required in time-domain methods, thus enhancing both computational efficiency and robustness. To validate the effectiveness of this method, a four-storey numerical example is employed. Additionally, the technique has been applied to the Yingxian Wooden Pagoda, where it successfully identified the center of rigidity at each storey, demonstrating its practical utility in actual applications.

This paper proposes a time–domain approach to identify eccentricity in three-dimensional multi-storey structures exhibiting nonaxial stiffness eccentricity. Improved lateral–torsional coupled equations of motion are employed to identify the location of the center of rigidity for each storey, using horizontal acceleration measurements in two orthogonal directions obtained from multiple points across each storey. This study mitigates errors typically associated with Fourier transformation by applying a time–domain approach and redefines the dynamic equations for calculating structural eccentricities, with a detailed formulation of the torsional stiffness matrix. Additionally, a novel objective function, based on the root-mean-square of the residual force in the time–domain equations of motion, is proposed to simultaneously identify bidirectional eccentricities of the structure. A numerical example illustrates the implementation and effectiveness of the proposed method. The feasibility of the method is demonstrated using a traditional Chinese timber benchmark structure. This approach overcomes several limitations in current methods and provides a streamlined solution for eccentricity identification in complex asymmetric structures.

Steel sheeting is usually provided at the upper flange of purlin in steel roof with screw connections. The resulting diaphragm effect provided by the sheeting enhances the buckling resistance of the purlin. However, this diaphragm effect will be reduced due to any abnormality in the screw connection caused by wind-induced fatigue particularly from typhoon. This would reduce the buckling resistance of the purlin with sheeting (the purlin-sheeting system), and it would affect subsequent condition evaluation during their service life. This problem is addressed in this paper with a framework of time-dependent reliability evaluation of the buckling limit state of the purlin-sheeting system. The buckling resistance reduction due to the degradation of the diaphragm effect from typhoon is taken into account in the resistance model. The randomness of wind intensity and landfall occurrence of typhoon during the service life of purlin are also accounted for in the wind load effect model. The time-dependent reliability of the purlin at different positions of a roof is studied. Then the variation of reliability of the system due to the effect of climatic changes in the design service life is discussed. The proposed strategy is then applied to the evaluation of a purlin-sheeting system in eleven cities in China with typhoon occurrences with some useful results for future studies in the provisions of the design code.

This study aimed to investigate the moment carrying behavior of typical Tibetan timber beam-column joints under monotonic vertical static load and also evaluate the influence of length ratio of Gongmu to beam (LRGB) and dowels layout on the structural performance of the joint. Six full-scale specimens were fabricated with same construction but different Gongmu length and dowels position. The moment carrying performance of beam-column joints in terms of failure mode, moment resistance, and rotational stiffness of joints were obtained via monotonic loading tests. Test results indicated that all joints are characterized by compressive failure perpendicular to grain of Ludou. Additionally, it was found that greater LRGB leads to greater initial rotational stiffness and maximum moment of the joint by an increase of restraint length for beam end; however, offsetting dowels toward column resulted smaller stiffness and ultimate bending moment of joints, particularly, offsetting Beam-Gongmu dowels toward column changed the moment-rotation curve pattern of the beam-column joint, accompanied by a hardening stiffness at last phase. Furthermore, a simplified trilinear model was proposed to represent the moment-rotation relationship of the typical Tibetan timber beam-column joint.

The damage theory is employed to investigate the mechanical strength deterioration caused by micro defects. Introducing the effective stress, this paper presents a damage-coupled viscoplastic model by applying the Schwartz model with an elastic component. The model is calibrated and validated by asphalt concrete creep test under various stresses. With the help of recursive numerical method, the model parameters include viscoplastic and damage functions for different stresses are determined. The result shows the model not only characterize the three stage creep deformation behaviour at a range of stress, but also can predict the damage evolution during the increased creep strain.