With rapid development of physical testing technology,structural model testing can more correctly obtain dynamic response of structure under action of environmental load.However,in studying model testing problems of soil-structure interaction,regional group structures as well as wind tunnel,pseudo static and dynamic tests of large and complex structures,simple,practical,and correct structural test simplified models are still the study focus.Here,aiming at problems of complex calibration of nonlinear mechanical parameters and insufficient test feasibility in existing model simplification methods,a simplified design method for dynamic test model of high-rise structure was proposed.High-rise structure's bending and shear recovery force models were decomposed into a combination of linear and nonlinear behaviors,structural nonlinear behavior was simulated using Coulomb friction model,because of its parameters being simple and having certain physical meanings,it could be directly applied in dynamic test study for scaled models.Based on the above theoretical methods,effectively combining bending-shear coupled model and translational and torsional friction devices,physical model design method and calculation methods for parameters of equivalent stiffness,post yield stiffness and load-bearing capacity applies in scaled dynamic tests were proposed.The corresponding mechanical calculation model of"interlayer double-shear and double-bending spring"was established.It was shown that the proposed methods can effectively predict dynamic responses of prototype structure in elastic and nonlinear stages with model test results.Taking a certain high-rise structure as an example,the correctness and feasibility of the proposed methods were verified with numerical simulation and shaking table tests.
Blast loading is characterized as an impact loading with exponential attenuation, while damping serves as an intrinsic parameter that affects the vibration effect of beam members. The linear attenuation for simplified blast loading and undamped situation for beam members is often adopted by most scholars or codes for the calculation of dynamic factors. These assumptions that do not conform to the actual situation can lead to deviations in the results of the dynamic factor. In this study, the implicit solutions for the dynamic factors of both flexible and rigid beam members were derived by the exponential attenuation loading and damping of beam members. The dynamic response verification of an H-shaped steel beam blast test was completed using LS-DYNA software. The comparison calculation of the theoretical solutions of dynamic factors in this paper with the Chinese blast-resistant design code and finite element simulation was carried out. The results show that the dynamic factor will be higher when the blast loading is simplified to linear attenuation loading for undamped beams. The shape parameter of the exponential attenuation loading and the damping ratio of beam members both reduce the effect of the dynamic factor, with the damping ratio having a more significant effect.
Ship-mounted cranes are becoming increasingly essential to modern ocean shipping. However, due to the continuous influence of waves, currents, and winds, achieving accurate and fast lifting is difficult because of the large payload swing during the lifting operation. Therefore, this study proposes a Four Anti-swing Cable System (FASCS) for ship-mounted cranes. Firstly, a dynamic model of the FASCS was established by using Robotics and Newton method, and a tension control method (TCM) is designed to reduce the swing angle of the payload. Concurrently, a sliding mode variable structure controller with improved reaching law (SMVSC-IRL) is designed to control the cooperative movement of the anti-swing cables and prevent the occurrence of snap. The dynamic characteristic analysis by MATLAB/Simulink shows that the swing angle suppression effect reaches 89.3% on average, and the projected area of the payload trajectory was reduced by 60%, which can significantly improve the efficiency of ship-mounted cranes lifting operations. In addition, the length and speed of cables in errors can approach 0 within 7 s, and the strong robustness of the designed SMVSC to control the cooperative motion of the anti-swing cables is proved. The results of this study contribute to the in-depth optimization and engineering verification of the FASCS for ship-mounted cranes.
Earthquake damage to engineering structures often occur in near-fault areas. Near-fault ground motion is characterized by high-energy velocity pulses, long action period, and strong destructiveness. This paper forces on the seismic analysis of a multi-tower super high-rise building that subjected to near-fault ground motions. The interactions between each tower makes the internal forces and dynamic responses much complex and totally different from single-tower super high-rise buildings. However, currently, multi-tower buildings in China are usually regarded as multiple single-tower buildings, and then separately designed based on the relevant provisions in seismic code for single-tower buildings. The mutual influence between the towers is almost not taken into account. Seismic response history analysis was carried on a three-tower super high-rise building using finite element method. Various near-fault and far-fault ground motions and high-energy velocity pulses were used as inputs. Through calculation of inter-story drift ratio and maximum displacement, the quantitative seismic fragility analysis was conducted for the main tower and sub-tower structures. The results show that the responses from near-fault ground motions to the structure are much greater than those from far-fault ground motions. The damage probabilities of various damage levels for near-fault ground motions are 12.5% higher than far-fault ground motions averagely. A further analysis reveals that the velocity pulses are the main factor causing structural damage in near-fault ground motions.
Due to friction vibration dampers’ inability to effectively dampen low loads during high-frequency dewatering, drum washing machines vibrated intensively. In order to address this problem, in this paper, a novel type of low-cost non-Newtonian fluid damper is proposed and investigated based on the non-Newtonian fluid shear thinning properties’ effect on vibration suppression during the high-frequency dewatering process of the washing machine. In contrast to other commonly used dampers, the homemade non-Newtonian fluid damper significantly suppresses the growth trend of the apparent elastic coefficient at high frequencies. A systematic investigation of damper structural parameters reveals that smaller gap height, higher piston head number, and more viscous fluid viscosity are adequate for vibration suppression and noise reduction. These results demonstrate that the non-Newtonian fluid damper can produce an excellent vibration-damping effect for the entire washing process of the washing machine, especially for the high-frequency dewatering process. The acceleration attenuation ratio can reach up to 83.49%, the energy attenuation is up to 98.44%, and the noise reduction is up to 10.38 dB.
