Research On Combination Method Of Multi- Dimension Random Loads And Wind-wave Coupled Structural Load Effects

Contrary to the deficiency in the research on combination methods of multi-dimension random loads and extreme load effects, the following studies on correlationship of multi-dimension random processes, combination method of multi-dimension random loads and wind-wave coupled structural load effects, which were based on the basic properties of Copula funcitons and demonstrated on typical civil engineering structures, were carried out in this paper:1. A Copula-based combination method of three-dimension random processes was proposed based on the basic properties of Copula functions and the related theories in probability and statistics. This method, which made up the difficiency of the current combination rules and methods, could be used to estimate the combination coefficients of three-dimension random processes associated with a certan exceedance probability. In this method, both the Joint Probability Density Function (JPDF) and correlationship of multi-dimension random processes were expressed by Copula function. Without any assumption of random processes, this method could be applied to both Gaussian and non-Gaussian processes.2. Applying the Copula-based combination method of three-dimension random processes to the reseach of design wind load of high-rise building, three Dimension Realizable Equivalent Static Wind Loads (3D R-ESWLs) were put forward by considering the characteristic of the extreme values of three dimension realistic wind-induced effects.3D R-ESWLs was the linear combination of three Single Equivalent Static Wind Loads (S-ESWL) and made up the difficiency that without considering the correlationship of three-dimensional wind-induced response in S-ESWL. Because the combination coefficients reflected the correlationship and relative magnitude of three-dimensional wind-induced responses,3D R-ESWLs could realize the full equivalence of major extreme response and probabilistic equivalence of other two extreme responses, and relect the real physical mechanism that the extreme responses with same probability of three wind-induced responses would not appear at the same time. The analysis processes and results of 3D R-ESWLs were illustrated by use of the wind tunnel test data of a high-rise building, the non-Gaussian characteristic of three-dimensional wind-induced background and resonant responses were also investigated.3. A synchronous simulation scheme of random wind field and random wave was poposed. The wind-wave synchronous simulation was realized though the reasonable set of frequency interval, dispersion of frequency interval and correction of spectrum matrix in this scheme. Frequency interval and its division were set according to the frequency distribution of fluctuating wind speed spectrum and wave spectrum, repectively. In order to improve the computational efficiency and stability of the scheme, the joint spectral matrix at each representative frequency should be transformed to a positive and definite matrix, which can be decomposed by Cholesky decomposition, by a certain algorithm.4. Taking the foundation of a cross-sea bridge as object, this paper studied the design rules of hydro-elastic and rigid model of a structure under the coupled action of wind, wave and current in a flume experiment. Thougth a series of flume experiments, the properties of structural load effects under wind-wave, wave-current and wind-wave-current were investigated. The test results of rigid and hydro-elastic model of the high pile piers showed that the couple effect of wind-wave, wave-current and wind-wave-current were quite weak under the test conditions in this paper. The test results of rigid model of circular caisson showed that the pressure history of each measuring point was not synchronized and retardation existed because of size effect of the caisson.5. Contrary to the fact that difficulties will appear in the construction of limit state curve based on Rosenblatt transformation when EC (Environmental Contour) method is adopted in the extreme load effects estimation, a simplified approach to limite state curve construction based on the basic properties of Copula functions was proposed, thougth which the direct calculation of conditional function and its inverse function of an environmental variable was avoided, and the feasibility of EC method was improved greatly. Taking the tower-fundation system of a cross-sea bridge as an engineering example and the wind wave synchronous observation data of the ocean station at Weizhou Island as statistical data of environmental variables, the extreme load effect of base shear force of the tower-fundation system based on EC method was estimated. It was found that the correlationship of mean wind speed and significant wave height made a significant influence on extreme load effects, and the extreme load effects with a certern exceedance probability PE could be caused by different mean wind speed and significant wave height.