Hongnan Li

Measurement and Analysis of Wind-Induced Response of Tall Building Based on GPS Technology

The Global Positioning System (GPS) has been used in the health monitoring of large structures in recent years since it is weather independent, capable of autonomous operation, and does not require a line-of-sight between target points. In this paper, a structural health monitoring system based on the GPS is devised for a high-rise building. The field data, such as wind speed, wind direction and displacement responses were simultaneously and continuously measured under strong wind conditions. The relation between velocity components of the atmospheric wind and pressure fluctuations on the roof of the building are analyzed using the wavelet scalogram and wavelet coherence method, and a statistical significance level estimation method based on Monte Carlo simulation is presented to isolate the meaningful coherence from the spurious noise map. Finally, the responses of the high-rise building are investigated using the Periodogram method to conclude that the identified results agree well with the results computed by the Finite Element Method (FEM).

Effects of Strain Rate on Reinforced Concrete Structure under Seismic Loading

The effects of strain rate on the reinforced concrete structure under seismic loading are studied in this paper. Firstly, the strain-rate effects of reinforcing steel with the grades HPB235, HRB335 and HRB400 were investigated using the MTS electro-hydraulic servo-controlled testing system at the strain rate (2.5 × 10−4/s∼0.1/s) that might be experienced during earthquakes. Based on the test results, dynamic increasing factors (DIF) which are functions of strain rate and quasi-static yielding strength of reinforcing steel are gotten. Then, two kinds of expressions on the effects of strain rate on concrete are chosen for these analyses. Finally, considering the strain-rate effects of concrete and steel, the three-dimensional finite element model of reinforced concrete frame structure subjected to three-component earthquake inputs is established based on a practical project, in which three peak levels of ground accelerations are taken into account. Using the nonlinear time history analytical method, the distribution of strain rate and the effects of strain rate on the base shear force, bending moment and top displacement of structure are studied. These results may provide a reference for reinforced concrete frame structure in seismic design.

Seismic response of a steel trussed arch structure to spatially varying earthquake ground motions including site effect

This paper investigates seismic response of a realistic large dimension steel trussed arch structure subjected to the combined spatially varying horizontal and vertical ground motions. The ground motion spatial variations associated with wave passage effect, coherency loss effect and local site effect are considered. In numerical calculations, the simulated spatially varying ground motions are individually compatible with response spectrum defined in Chinese Seismic Design Code, and are compatible with an empirical coherency loss function between each other. Compared with structural responses calculated using uniform and delayed excitations, numerical results show that seismic response is amplified when spatially varying ground motions including local site effect are considered. Each factor of ground motion spatial variations has a significant effect on the dynamic response of the structure. Numerical results also indicate that considering simultaneous vertical and horizontal ground motions will lead to more accurate response predictions of the trussed arch as compared with those obtained by considering horizontal excitations only. Therefore, to have an accurate structural response assessment and a better design of long span steel trussed arch structures, a reliable ground motion spatial variation model is essential.

Cycle Slip Detection and Correction of GPS Carrier Phase Based on Wavelet Transform and Neural Network

In order to attain high precision positioning and navigation results with GPS, cycle slips must be correctly detected and repaired at the data preprocessing stage. Based on the characteristics of cycle slip we analyzed, a novel two-stage method was developed. Firstly, the wavelet multi-resolution analysis (MRA) is carried out and then the location of the cycle slip can be detected by ascertaining the point of modulus maximal value of the wavelet coefficients since the cycle slip can be regarded as the singular point of the signal. Secondly, two prediction models based on artificial neural network (ANN) are established respectively at the both side of the cycle slip. The actual number of cycle slip can be determined through comparing the difference of forecasting data of the two prediction models. Finally, test results are presented to demonstrate the feasibility and validity of the method

Seismic Response Analysis of Transmission Tower-Line System on a Heterogeneous Site to Multi-Component Spatial Ground Motions

This paper studies the nonlinear responses of a coupled transmission towerline system on a heterogeneous site subjected to multi-component spatially varying ground motions. The three-dimensional finite element model of the transmission tower-line system is established with consideration of the geometric nonlinearity of the transmission lines. The spatial variation of ground motions associated with the wave passage, coherency loss and local site effects are considered. The spatial ground motions on ground surface are derived by modelling the base rock motion propagating through the local soil sites. The base rock motions are assumed consisting of out-of-plane and in-plane waves and are simulated stochastically based on an empirical coherency loss function and the filtered Tajimi-Kanai power spectral density function. The effects of multi-component, spatial variations of ground motions and varying site conditions at multiple tower foundations on seismic response of the transmission tower-line system are analysed. The study reveals that for a reliable seismic response analysis and safe and economic seismic resistance design of transmission tower-line systems, the multi-support and multi-component earthquake excitations with consideration of the effects of local site conditions on ground motion spatial variations should be considered.

Modeling and Simulation of Spatially Correlated Ground Motions at Multiple Onshore and Offshore Sites

A simulation method of spatially correlated seafloor motions is proposed by considering the influences of seawater on the seafloor motions and their spatial variations at different subsea sites. The offshore site transfer functions are theoretically derived using the fundamental hydrodynamics and one-dimensional wave propagation theory. Three-dimensional spatially varying ground motions on the surfaces of multiple onshore and offshore sites are synthesized based on the spectral representation method and the calculated site transfer functions. A pair of onshore and seafloor recordings from the same earthquake event is employed to examine the basic characteristics of simulated onshore and seafloor motions.

Simplified Calculation Approach of Torsionally Coupled Seismic Response for Base-Isolated Eccentric Structures

More and more applications exist of base-isolated buildings. So far much attention has been paid to the improvement of design approaches. In this paper, the equation of motion is derived for a torsionally coupled base-isolated structure under the action of seismic ground motion. Based on numerical analyses of the structure, torsional responses and influencing parameters have been investigated and some rules obtained for sites with different soils, in which the superstructure is idealized as a series-rigid floor model, while the isolation system adopts the Bi-linear resilience curve. Applying the method of least squares to the numerical results, three simplified formulae have been produced to approximately calculate the torsional seismic accelerations of base-isolated structures. The results calculated by the practical method proposed in this paper approximate to those obtained by time history analyses. It is shown that the method is of good accuracy in comparative terms and suffices for the needs of engineering designs for base-isolated eccentric structures with rubber bearings under earthquake action.

Energy Spectra of Constant Ductility Factors for Orthogonal Bidirectional Earthquake Excitations

Current research findings about energy spectra are almost entirely based on the single-degree of freedom system that is only fit for two dimensional analyses. Therefore, it is necessary to establish energy spectra of multidimensional systems subjected to multidirectional earthquake excitations. The bidirectional energy balance equation is established based on the single-mass bi-degrees of freedom system. The equation of normalized energy spectra is presented with earthquake motions, periods, and strength reduction factors as variables. The approximate relation of strength reduction factors between the x and y directions are derived from the seismic influence coefficient spectra. The 89 pairs of bidirectional earthquake motion records are selected as earthquake excitations to establish mean normalized input energy spectra and hysteretic energy spectra. The spectral values of normalized energy are compared between the single-mass bi-degrees of freedom system and single degree of freedom system, which shows that in some cases traditional energy spectra may underestimate the energy responses. The influence factors of mean spectra such as period, ductility factor, period ratio, and soil site are analyzed. Analytic results show that the coupling influences of nonlinear responses of structural two lateral components are considered in normalized energy spectra and are theoretically more rational than traditional spectra. In addition, two kinds of energy spectra have the typical spectral pattern features of the soil site, while the pattern and values of the two kinds of spectra are affected by the ductility factor, period ratio and the soil site.

Simplified Method for Pushover Curves of Asymmetric Structure with Displacement-Dependent Passive Energy Dissipation Devices

This paper presents a simplified method to calculate pushover curves for an asymmetric structure with displacement-dependent passive energy dissipation devices (DDPEDDs). The deformations of a symmetric structure are analyzed in translation and torsion, respectively. These results are then combined in order to calculate the pushover curve for an asymmetric structure with DDPEDDs. The numerical results obtained by using the simplified analytical method are then compared to those obtained from the analysis of the models using the software SAP2000. The results show that the simplified analytical method can be an effective tool for engineering analysis of an asymmetric structure.

Seismic Responses Prediction of Nonlinear Building Structures Based on Multi-Branch BP Neural Network

In this paper, a multi-branch back propagation neural network (BPNN) is adopted to predict the nonlinear seismic responses of an eccentric three-story reinforced concrete building. First of all, the network is trained in batch by the vibration table test data of the structure with the maximum acceleration of ground motion in 0.4g. Then, the trained network is used for structural responses prediction. The nonlinear structural acceleration responses of the each story are evaluated by the trained network for the maximum acceleration of ground motion in different amplitudes. Compared with the experimental results, it turns out that the trained network can accurately predict structural future dynamic responses.