Multi-dimensional Earthquake Excitations Research Articles

Study on the performance of lead rubber bearing considering vertical force correlation

To study the vertical force correlation of the lead rubber bearing, the pseudo static test of the bearing has been carried out, and the test shows that when the vertical force is small, the pre-yield stiffness and the yield shearing force of the bearing are increased with the increase of vertical force, while the post-yield stiffness is decreased with the increase of vertical force. When the vertical force is increased to a certain extent, the bearing parameters may be stable. The bearing parameter has been identified by the least square method, and then, the quantitative relation between the bearing parameter and the vertical force could be obtained. The calculation model and the motion equation of the isolation structure under the multi-dimensional earthquake excitation have been established, and the parameter iteration of bearing obtained from the test has been used for solving the motion equation, from which the seismic response of an isolation structure has been made available when the vertical force of the bearing is considered. The calculation of engineering examples shows that the displacement of the isolation layer will increase after the consideration of the vertical force correlation of the bearing, and the displacement of the upper structure will have a larger overall shifting.

Multidimensional Seismic Control by Tuned Mass Damper with Poles and Torsional Pendulums

Due to the eccentric characteristics and the torsional excitation of multidimensional earthquakes, the dynamic response of asymmetry structure involves the translation-torsion coupling vibration and it is adverse to structural performance. Although the traditional tuned mass damper (TMD) is effective for decreasing the translational vibration when the structure is subjected to earthquake, its translation-torsion coupled damping capacity is still deficient. In order to simultaneously control the translational responses and the torsional angle of asymmetry structures, a new type of tuned mass damper with tuned mass blocks, orthogonal poles, and torsional pendulums (TMDPP) is proposed. The translation-torsion coupled vibration is tuned by the movement of the mass blocks and the torsional pendulums. According to the composition and the motion mechanism of the TMDPP, the dynamic equation for the total system considering eccentric torsion effect is established. The damping capacity of the TMDPP is verified by the time history analysis of an eccentric structure, and multidimensional earthquake excitations are considered. The damping effect of the traditional TMD and the TMDPP is compared, and the results show that the performance of TMDPP is superior to the traditional TMD. Moreover, the occasional amplitude amplification in TMD control does not appear in the TMDPP control. The main design parameters which affect the damping performance of TMDPP are analyzed.

The Simplified Model and the Critical Angle of the Curved Bridges with Multi-Dimensional Earthquake Excitation

The existing methods of curve beam bridge is the finite element method, the modeling and analysis of complex, heavy workload, not suitable for the proposed design method of regularity. According to the character of curved bridge, the bridge superstructure and piers is simplified as packing quality model that have two levels of degrees of freedom and a surrounding mass center shaft torsion degree of freedom, then the analysis model of double mass simplified 6 degrees of freedom is established, studying the dynamic characteristics and the structure vibration behavior through the dynamics equation of curved bridges. Example show that,the results of double mass model with the traditional of finite element model is consistent, double mass model has simple calculation method and can consider the influence of sensitive factors, with the help of programming is more suitable for the proposed design method of regularity. At last, Application MATLAB programming discussed the critical angle of the curved bridges under multi-dimensional earthquake based on double mass model, after change the curve bridge related parameters only one operation can achieve the most disadvantaged angle.

Seismic performance of circular RC bridge columns with flexure–torsion interaction

Reinforced concrete (RC) bridge columns for skewed, curved bridges and other kinds of irregular bridges can be subjected to combined loadings with axial load, shear force, flexure and torsion under multi-dimensional earthquake excitations. Combined loadings including torsion probably affect the seismic performance of these bridge columns. The experimental investigation on the seismic performance of circular RC bridge columns under combined cyclic bending and torsional loading is conducted in this paper. Twelve circular RC bridge column specimens are tested under various loading conditions: cyclic bending, cyclic torsion, and combined cyclic torsion and cyclic bending. Several combinations of cyclic bending and cyclic torsion are applied to evaluate the interaction between torsion and flexural capacity of bridge columns. The experimental results showed that the flexural capacity decreases and the damage tends to occur upward outside the flexural plastic hinge region as the level of applied cyclic torsion increases, and the torsional capacity decreases as the level of applied cyclic bending increases. The failure mode and deformation characteristics of RC bridge columns will be changed due to the effect of combined flexural and torsional loadings. The locking and unlocking effect of the spiral reinforcement on torsional and flexural envelopes of columns under pure torsion and combined cyclic bending and torsion is found. The influence of aspect ratio, longitudinal reinforcement ratio and type of spiral reinforcement on the seismic performance of columns under combined action with the same rotation-drift ratio is also discussed. An empirical flexural and torsional hysteretic model for circular RC columns with single spiral stirrup under combined cyclic bending and torsion is proposed based on the experimental results.

An improved multidimensional MPA procedure for bidirectional earthquake excitations.

Presently, the modal pushover analysis procedure is extended to multidimensional analysis of structures subjected to multidimensional earthquake excitations. an improved multidimensional modal pushover analysis (IMMPA) method is presented in the paper in order to estimate the response demands of structures subjected to bidirectional earthquake excitations, in which the unidirectional earthquake excitation applied on equivalent SDOF system is replaced by the direct superposition of two components earthquake excitations, and independent analysis in each direction is not required and the application of simplified superposition formulas is avoided. The strength reduction factor spectra based on superposition of earthquake excitations are discussed and compared with the traditional strength reduction factor spectra. The step-by-step procedure is proposed to estimate seismic demands of structures. Two examples are implemented to verify the accuracy of the method, and the results of the examples show that (1) the IMMPA method can be used to estimate the responses of structure subjected to bidirectional earthquake excitations. (2) Along with increase of peak of earthquake acceleration, structural response deviation estimated with the IMMPA method may also increase. (3) Along with increase of the number of total floors of structures, structural response deviation estimated with the IMMPA method may also increase.

Seismic Behavior of Long-Span Connected Structures under Multi-Supported and Multi-Dimensional Earthquake Excitations

Seismic behaviors of long-span connected structures under multi-dimensional and earthquake excitation while considering wave passage effect are investigated through both numerical simulation and a shaking table test on a scaled model. It is found that seismic responses will be increased significantly if multi-dimensional earthquake excitation is considered; and wave-passage effect has diverse influence on different elements. Also special attentions should be paid to those elements near connections between the main tower and the corridor which inertial forces may change a lot when subjected to Traveling wave excitation with different apparent velocities. Moreover, the vertical acceleration responses of the corridor can be increased significantly due to wave passage effect. Therefore, it is necessary for aseismic design of long-span connected structure to take into account multi-dimensional earthquake components and multi-support earthquake excitations with different apparent velocities.

Nonlinear analysis of pounding between decks of multi-span bridge subjected to multi-support and multi-dimensional earthquake excitation

The nonlinear analysis of pounding between bridge deck segments subjected to multi-support excitations and multi-dimensional earthquake motion was performed. A novel bottom rigid element (BRE) method of the current displacement input model for structural seismic analysis under the multi-support excitations was used to calculate structural dynamic response. In the analysis, pounding between adjacent deck segments was considered. The seismic response of a multi-span bridge subjected to the multi-support excitation, considering not only the traveling-wave effect and partial coherence effect, but also the seismic non-stationary characteristics of multi-support earthquake motion, was simulated using finite element method (FEM). Meanwhile, the seismic response of the bridge under uniform earthquake was also analyzed. Finally, comparative analysis was conducted and some calculation results were shown for pounding effect, under multi-dimensional and multi-support earthquake motion, when performing seismic response analysis of multi-span bridge. Compared with the case of uniform/multi-support/multi-support and multi-dimensional earthquake input, the maximum values of pounding force in the case of multi-support and multi-dimensional earthquake input increase by about 5–8 times; the absolute value of bottom moment and shear force of piers increase by about 50%–600% and 23.1%–900%, respectively. A conclusion can be given that it is very necessary to consider the pounding effect under multi-dimensional and multi-support earthquake motion while performing seismic response analysis of multi-span bridge.

Structural Isolation and Mitigation Technology under Multi-Dimensional Earthquake Excitations

Researches on structural isolation and mitigation under multi-dimensional earthquake excitations are overviewed in terms of the analysis methods, devices and developing trend. The analysis methods for dynamic responses of building structures, long-span reticulated structures and bridges under multi-dimensional earthquake excitations, are systemically introduced. Several types of multi-dimensional earthquake isolation and mitigation devices are presented, and experimental results of a new type of device are discussed, it shows that the new device has good ability of multi-dimensional earthquake isolation and mitigation. Finally, suggestions for further study in this area are presented.

Experimental Study of CFRP Confined RC Rectangular Hollow Section Bridge Piers

To investigate the seismic performance of FRP strengthened RC hollow section bridge piers under multi-dimensional earthquake excitation, the pseudo-static test was carried out to RC rectangular hollow section as-built and CFRP confined bridge piers under constant axial compression force and bidirectional horizontal repeated load. The failure characteristics, lateral force-deformation curves and ductility of specimens were analyzed. The experimental result shows that CFRP constraining may change the failure mode of hollow section bridge piers, and significantly improve the deformation ductility, plastic deformation, however, it is less contribution to horizontal force of specimens with less wall-thickness.

Semi-active control on long-span reticulated steel structures using MR dampers under multi-dimensional earthquake excitations

This paper focuses on the vibration control of long-span reticulated steel structures under multidimensional earthquake excitation. The control system and strategy are constructed based on Magneto- Rheological (MR) dampers. The LQR and Hrovat controlling algorithm is adopted to determine optimal MR damping force, while the modified Bingham model (MBM) and inverse neural network (INN) is proposed to solve the real-time controlling current. Three typical long-span reticulated structural systems are detailedly analyzed, including the double-layer cylindrical reticulated shell, single-layer spherical reticulated shell, and cable suspended arch-truss structure. Results show that the proposed control strategy can reduce the displacement and acceleration effectively for three typical structural systems. The displacement control effect under the earthquake excitation with different PGA is similar, while for the cable suspended arch-truss, the acceleration control effect increase distinctly with the earthquake excitation intensity. Moreover, for the cable suspended arch-truss, the strand stress variation can also be effectively reduced by the MR dampers, which is very important for this kind of structure to ensure that the cable would not be destroyed or relaxed.

Experimental study on horizontal performance of multi-dimensional earthquake isolation and mitigation devices for long-span reticulated structures

Earthquake excitation is a kind of complicated multi-dimensional ground motion. Therefore, anti-earthquake measuresfor complex and important engineering structures, such as long-span structures and high rise buildings under multi-dimensional earthquake excitations, have become an extremely important research topic. In this paper, a new multi-dimensional earthquake isolation and mitigation device (MEIMD) is proposed for protecting long-span reticulated structures due to strong earthquake motions. It consists of a viscoelastic bearing and several viscoelastic dampers. Property tests on the MEIMD under different excitation frequencies, excitation amplitudes and vertical pressure forces are carried out. Then, a mathematical simulation is carried out for the equivalent stiffness and the equivalent damping of the device, and the numerical results agree reasonably well with the experimental data. Experimental and numerical results show that the MEIMD has a fine energy dissipation capacity, and can be used for anti-earthquake purposes for long-span reticulated structures.

Multi-Dimensional Pseudo Excitation Method for Nonstationary Random Seismic Analysis of Spatial Lattice Shells

Lattice shell is a type of spatial structure whose vibrations are dominated by both horizontal and vertical motion. In this paper, a multidimensional pseudo excitation method is developed for nonstationary random seismic analysis of structures under multi-support and multi-dimensional earthquake excitations, in which the phase lags between the excitations have been involved. Mathematical formulations are derived. A method of evaluating peak responses is recommended. Multi-dimensional seismic random models are discussed. A random vibration analysis is performed for a double-layer cylindrical lattice shell to investigate its seismic performance. It is shown that the developed method is a highly efficient algorithm, which can easily solve the nonstationary problem of large structures under multi-support and multidimensional earthquake excitations.