The wind velocity spectra at Beijing Meteorological Tower are calculated using Hilbert-Huang transform and Fourier transform,respectively.A innovative model of wind velocity spectrum,which is accordant with the characteristics in both the inertial subrange and the large eddies range,is presented in this paper.The method of least squares is adopted to obtain the parameters in the model.Then the differences between the FFT spectrum and the HHT spectrum are compared.It is indicated that the values of the HHT spectrum in the energy containing range are slightly larger than those of the FFT spectrum while the values of the HHT spectrum in both inertial subrange and dissipation subrange are very close to that of Fourier spectrum.It is concluded that the HHT spectrum describes elaborately and accurately the spectrum values in the low frequencies and the fitted wind velocity model provides a reference for reconstructing the near-ground wind field of Beijing city in wind tunnel test and for numerical simulation.
In order to give the reasonable width of seismic gaps to prevent the structural pounding during ground motions,the maximum relative displacement of adjacent structures is studied in this paper.The factors that may have effects on the maximum relative displacement are discussed.As for multi-degree-of-freedom(MDOF) systems,they can be equivalent to single-degree-of-freedom(SDOF) systems with the influences of high modes neglected.The results show that the period ratio,height ratio and peak ground acceleration are the main factors that have great effects on the maximum relative displacement of adjacent structures.The maximum relative displacement of MDOF systems can be obtained from calculating the maximum relative displacement of the equivalent SDOF systems.
Considering three longitudinal displacement functions and uniform axial displacement functions for shear lag effect and uniform axial deformation of thin-walled box girder with varying depths,a simple and efficient method with high precision to analyze the shear lag effect of thin-walled box girders was proposed.The governing differential equations and boundary conditions of the box girder under lateral loading were derived based on the energy-variational method,and closed-form solutions to stress and deflection corresponding to lateral loading were obtained.Analysis and calculations were carried out with respect to a trapezoidal box girder under concentrated loading or uniform loading and a rectangular box girder under concentrated loading.The analytical results were compared with numerical solutions derived according to the high order finite strip element method and the experimental results.The investigation shows that the closed-form solution is in good agreement with the numerical solutions derived according to the high order finite strip method and the experimental results,and has good stability.Because of the shear lag effect,the stress in cross-section centroid is no longer zero,thus it is not reasonable enough to assume that the strain in cross-section centroid is zero without considering uniform axial deformation.
