Horizontal Earthquake Research Articles

Study of Seismic Design Method for Slope Supporting Structure of Soil Nailing

Slope anchorage structure of soil nail is a kind of economic and effective flexible slope supporting structure. This structure at present is widely used in China. The supporting structure belong to permanent slope anchorage structure, so the design must consider earthquake action. Its methods of dynamical analysis and seismic design can not be found for the time being. The seismic design theory and method of traditional rigidity retaining wall have not competent for this new type of flexible supporting structure analysis and design. Because the acceleration along the slope height has amplification effect under horizontal earthquake action, errors should be induced in calculating earthquake earth pressure using the constant acceleration along the slope height. Considering the linear change of the acceleration along the slope height and unstable soil with the fortification intensity the influence of the peak acceleration, the earthquake earth pressure calculation formula is deduced. The soil nailing slope anchorage structure seismic dynamic calculation model is established and the analytical solutions are obtained. The seismic design and calculation method are given. Finally this method is applied to a case record for illustration of its capability. The results show that soil nailing slope anchorage structure has good aseismic performance, the calculation method of soil nailing slope anchorage structure seismic design is simple, practical, effective. The calculation model provides theory basis for the soil nailing slope anchorage structure of seismic design. Key words: soil nailing; slope; earthquake action; seismic design;

The Comparative Analysis on Calculation Methods of Vertical Seismic Response to Suspended-Dome Structure

Based on the vertical seismic information, the vertical seismic response spectrum was calculated by Matlab Lsim function. The seismic effect of Kiewitt-Lamella suspended-dome was measured by dynamic to static ratio. According to the EL-Centro seismic wave, it analyzed and compared the dynamic to static ratios which were calculated by the following four vertical seismic calculation methods respectively: the simplified method of specification, the mode-superposition response spectrum methods based on the horizontal earthquake affecting coefficients and the vertical acceleration response spectrum respectively, and the time history analysis method. Analysis shows that: For the seismic effect, the time history analysis method is larger than the other three methods, and the method based on the vertical acceleration response spectrum is closer to the time history analysis method. Owing to large difference of the four methods for seismic effect, various methods should be adopted to ensure the safety of vertical seismic design.

Analysis on Seismic Behavior of Gravity Dam Based on ANSYS

Dynamic analysis can be carried out quickly and accurately for the seismic performance of dam by using the finite element software. Added massed method is used for the dynamic water. Horizontal earthquake acceleration is 0.2G; vertical earthquake acceleration is two-third of horizontal earthquake acceleration; sub space iteration method is used for the modal analysis of the dam; Finding the maximum response-order mode shape, and then useing a combination of square and square root method to come to the conclusion of overall seismic response. The stress and strain of the dam had been analyzed and the weak link of key parts of the dam had been summarized in this article.It is concluded that seismic design requirement are satified for the dam.

Horizontal pseudo-dynamic experimental study on long-span reticulated structures with multi-dimensional earthquake isolation and mitigation devices

A multi-dimensional earthquake isolation and mitigation device for long-span reticulated structures is a type of newly invented passive control device. In order to acquire the earthquake isolation and mitigation effect of the new devices on long-span reticulated structures under horizontal excitations, the pseudo-dynamic tests for a 1:3 modeled long-span reticulated structure with a size of 3 m × 3 m with and without the devices are carried out. Horizontal dynamic responses of the structure with and without the devices are compared, and the earthquake isolation and mitigation effect of the devices is evaluated under the horizontal excitations. It can be shown from the experimental and finite element numerical results that the proposed new devices have a good effect on earthquake isolation and mitigation on long-span reticulated structures under horizontal earthquake excitations.

A distributed flexibility and damping strategy to control vertical accelerations in base-isolated buildings

SUMMARY Seismic isolation is an effective method for protecting the structural system, nonstructural systems and content from the damaging effects of strong horizontal earthquake ground shaking. However, seismic isolation devices widely used in the USA and elsewhere are not designed to protect nonstructural components and content from strong vertical earthquake ground shaking. Past research efforts aimed at developing three-dimensional isolation have resulted in systems that have limited application or are overly complex, cost prohibitive and unproven. A distributed flexibility and damping concept to control vertical acceleration demands in base-isolated buildings is explored in this study. Unlike past efforts to achieve three-dimensional isolation that concentrate both the horizontal and vertical flexibility at the base of the superstructure, the vertically distributed flexibility and damping concept explored here consists of one or more planes of laterally restrained column bearings distributed at discrete locations up the height of a base-isolated superstructure. The laterally restrained column bearings increase the vertical flexibility and damping in the superstructure without increasing rocking displacements. An analytical study was performed to understand the influence of incorporating vertical flexibility and damping in a base-isolated frame and to evaluate the effectiveness of the concept for controlling vertical acceleration demands. The distributed flexibility and damping concept is shown to significantly reduce vertical acceleration demands and the likelihood of damage to suspended ceiling systems by comparison with an identical conventionally base-isolated frame. Copyright © 2013 John Wiley & Sons, Ltd.

Study of the properties of a multi-dimensional earthquake isolation device for reticulated structures

The earthquake excitation is a kind of complicated multi-dimensional motion. It is not safe and accurate enough if only considering the horizontal earthquake excitation, especially for complex and important engineering structures. Therefore, anti-earthquake measures for engineering structures considering multi-dimensional excitations have become an extremely important research topic. In this paper, a new multi-dimensional earthquake isolation and mitigation device (MEIMD) is developed and tested under different cases at both horizontal and vertical directions. Effects of excitation frequency and displacement amplitude on both horizontal and vertical properties of this device are considered. At the same time, a modified equivalent standard solid model is proposed, which can effectively describe the effects of frequency and displacement on the horizontal and vertical properties of the device. Research indicates that the MEIMD possesses high-energy dissipation capacity at both horizontal and vertical directions and the proposed model can accurately simulate the value of the storage modulus and the loss factor.

The response of a two-degree-of-freedom dynamic sliding system subjected to uni-directional horizontal dynamic and seismic excitations

An investigation is presented that studies the response of a two-degree-of-freedom dynamic sliding system; that is a single-degree-of-freedom oscillator being fi xed on top of a rigid block that can slide on its supporting shaking table along a horizontal axis when subjected to unidirectional dynamic or earthquake excitations along this horizontal axis. This problem appears to be of interest in predicting the dynamic and earthquake response of superstructures supported on a large foundation block capable of horizontal sliding by means of seismic sliding isolators. Special mock-ups are tested at the shaking table of Aristotle University for this purpose utilizing horizontal simulated earthquake excitations based on prototype earthquake ground motion recordings. The numerical results, which were obtained by a computer software developed for this purpose, are compared with the corresponding experimental measurements. The measured acceleration and displacement responses of the mock-ups appear to be, in all the examined cases, in reasonably good agreement with the numerical predictions. However, in certain cases, the numerically predicted sliding displacement of the rigid block appears to have an offset that differs from the sliding response that was observed during the experiments. This is more pronounced when there is no spring linking the rigid block with the shaking table and must be attributed to manufacturing tolerances of the mock-ups. It is demonstrated that the developed software, although it tries to represent such a rather complex problem in a simplifi ed manner, can be useful at the preliminary design stage of structural systems resting on sliding isolators. Results from various experimental and numerical tests demonstrate that the oscillator’s response is generally made smaller by the sliding of the rigid block. This is true for a wide range of frequencies; however, there is a relatively narrow frequency window in which the oscillator’s response is amplifi ed. This frequency window has a peak value that is slightly higher than the oscillator’s eigen-frequency when it is considered to be a single-degree-offreedom system fi xed at its base.

Theoretical model and investigation of concrete filled steel tube columns under axial force–torsion combined action

Concrete filled steel tube (CFST) columns are currently being widely used in the construction of modern buildings and bridges. In practice, the torsion effect will be often created in CFST columns when the horizontal earthquake happened. Based on geometrical, material constitutive and equilibrium equations, a theoretical model called laminated tubes model for analyzing the mechanical behavior of CFST columns under axial force–torsion combined action was proposed. The confined effect provided by the steel tube and the compression softening effect of the concrete could be considered in the proposed concrete material model. Based on the theoretical model, the non-linear analysis program was developed for obtaining the entire loading history of CFST columns under axial force–torsion combined action. The predicted results have good agreement with test results. The torsion behavior of CFST columns was detailed discussed based on the theoretical model, and the simplified formulae for practical design are also proposed based on regression methods.

Modelling of probability liquefaction based on standard penetration tests using the jointly distributed random variables method

Soil liquefaction during an earthquake can be a major cause of damage to structures. The inherent variability of the soil parameters which affect liquefaction potential dictates that the problem is of a probabilistic nature rather than being deterministic. Probabilistic assessment of liquefaction potential has received considerable attention in the past few years. In this research, the Jointly Distributed Random Variables (JDRV) method is used as an analytical method to develop a model for probability of liquefaction potential based on standard penetration tests. The selected stochastic parameters are corrected SPT blow count and stress reduction factor, which are modeled using a truncated normal probability density function and the peak horizontal earthquake acceleration ratio and earthquake magnitude, which are considered to have a truncated exponential probability density function. The depth of water table and fines content are regarded as constant parameters. The results of JDRV method are verified with those of the Monte Carlo simulation. It is shown that the moment magnitude is the most effective parameter in soil liquefaction potential. Comparison of the model results indicates reasonable performance of the proposed approach in assessment of probability of liquefaction and empirical data.

Study on Seismic Behavior of Evacuated Square Pyramid Space Grids in a Project

With an actual project example, a parametric model of the evacuated square pyramid space grid was established. The natural vibration characteristics and seismic response analyses were carried out by ANSYS, and the results were compared with the square pyramid space grid. The distributions of dynamic internal force of bar members were summarized under vertical earthquake action and horizontal earthquake action. The research shows that evacuated square pyramid space grids is a reasonable structural style for the large-span roofs due to good mechanical properties and low steel consumption. The results provide an important guiding significance for engineering design and development of this structure.

Providing a Model for Assessment of Horizontal and Vertical Earthquake Effects on the Double-layer Barrel Vaults in Space Structures

In this study, the effect of place soil and seismic vulnerability has not been considered in determining the earthquake force, although all results have been based on scale accelerographs. Moreover, the importance of structures has not been rated based on small or large spans, decorative or structural structure and the effect of these cases is not considered. In this regard, double-layer barrel vaults have been studied and effect of horizontal and vertical seismic force on it reviewed and equations are presented in order to evaluate the equivalent static force of horizontal and vertical earthquake. Presented equations facilitate determining the equivalent static force due to earthquake for space structures, but they also have deficiencies which solving them can be useful for researchers who want to continue the way.

Fluid-Structure-Soil Interaction Effects on Seismic Behaviour of Elevated Water Tanks

Abstract The multiple base motion effect on hydrodynamic pressure, acceleration of tank and fluid surface elevation problem in Elevated water tank is understood as a Fluid-Structure-Soil Interaction problem. Where, Soil-Structure interaction causes rocking motion and Fluid Structure interaction causes the hydrodynamic behaviour of water tank. According to the available literature, substantial amount of study has been done on behaviour of elevated steel water tank under pure rocking, but no study is done on water tanks with horizontal and vertical earthquake excitation, along with rocking motion. An experimental investigation for a 1:4 scale model of cylindrical steel elevated water tank has been carried out on shake table facility at CSIR-SERC, Chennai. Test program on elevated steel water tank consisted of combined horizontal, vertical and rocking motions, for a synthetic earthquake excitation for 0.1 g and 0.2 g accelerations, with increasing angle of rocking motion. The impulsive base shear and impulsive base moment values increase with increase in earthquake acceleration. Whereas, the convective base shear and base moment values increase for increase in earthquake acceleration, but decrease with increasing angular motion. Hence, there is no considerable effect of rocking motion on sloshing of water. The non-linearity in structure is observed, when the impulsive pressure of tank decreases with increase in tank acceleration. The pressure variation along tank height due to vertical excitation increased with increasing acceleration, and increased furthermore with added rocking. Using various codes available on water tanks, the recorded experimental results were used to calculate and compare the base shear, base moment, pressure variation in the tank.

Shake-Table Studies of a Four-Span Reinforced Concrete Bridge

Shake-table response of a 33.6-m-long (110-ft-long), four-span, RC bridge model with a continuous posttensioned superstructure supported on three, two-column bents was studied under horizontal bidirectional coherent simulated earthquakes. The pier heights varied, introducing a slight asymmetry about the centerline of the bridge model. The superstructure ends were supported on seat-type abutments that were connected to hydraulic actuators simulating abutment movements. The skew angle was zero. The bridge model was subjected to successive motions simulating a modified version of a record from the 1994 Northridge Earthquake. Results showed that damage was concentrated in plastic hinge regions of the columns and that the pier caps and the superstructure remained essentially elastic. The shortest pier failed, but this pier continued to carry vertical loads, and the bridge did not collapse. Despite the lack of skew, the superstructure-abutment interaction led to large in-plane rotations that caused significant residual displacements in the piers.

Design and Theoretical Studies of Pulsatile Hydraulic Vertical Isolation Device

Vertical seism has the same damage to the structure as the horizontal earthquake did. But vertical seism has not been taken seriously as it should be because its acceleration is smaller than that of horizontal earthquake. This paper describes the characteristics of vertical seism and a kind of vertical isolation device is designed based on the application of pulsating hydraulic theory. Moreover, it also states theoretical analysis and experimental study about properties of the device.

The Analysis of a Frame Structure with Additional Shear-Bending Bars under Horizontal Earthquake Action

The analytical result of the model under horizontal earthquake action is discussed in this paper, According to the analysis, this structure can effectively reduce stress and deformation. The structural potential behavior and failure principle are presented. Some advices are given in this paper for deeply studying such frame structures.

Analysis of Brick Wall’s Failure Modes under Earthquake Effect

Brick wall has large lateral sidesway stiffness and shear failure often occurs under horizontal earthquake effect, but the scourge surveys indicate that flexural failure can also occurs sometimes. Given that there are still few researches about masonry’s failure modes in China, Finite Element Models of non-reinforced brick masonry with different Depth-width Ratios and reinforced brick masonry whose Depth-width Ratio is 1.444 are established with the help of MSC.MARC to analyze its failure mode under horizontal action. The researching results indicate that: The larger the Depth-width Ratio of non-reinforced brick masonry is, the more flexural components it has and the better its ductility is; the smaller its Depth-width Ratio is, the larger the D-value of Bottom Shear and Ultimate Shear Bearing Capacity according to formulas from code before damage, and thereby the more easily the shear failure takes place; however, the ductility of brick wall’s flexural failure is improved evidently through making reasonable reinforcement schemes.

Study on a Roller-Footing Isolated Single-Pier System

As to improve bridges’ seismic performance, horizontal earthquake was isolated at the bottom of piers. With one pier system as the object of study, adopting nonlinear time history analysis analyzed the un-isolation system, the traditional isolation system and the new isolation system’s seismic performance especially when the actual earthquake was different from the design earthquake, in which the new isolation system was based on rolling balls. Results shows, as for the new isolation system, the internal force is independent of earthquake accelerations and earthquake periods, therefore, sympathetic vibration will not exist, and the internal force is always too small to destroy the system.

Seismic Response Analysis on Two-Tower Isolated Structure with Enlarged Base

In this paper, the three-dimensional finite element method has been adopted to respectively establish the base isolation of the two-tower structure with enlarged base and the story-isolated vibration analysis model. Each model has been conducted the elastic-plastic time-history analysis under the horizontal earthquakes. The results show that the dynamic characteristics of the structure have been significantly changed through the arrangement of isolation layer; the seismic responses, such as the story drift, the seismic shear and the acceleration of the structure, have been also greatly affected and the damping effect of the structure is obvious.

Analysis on Seismic Response of Portal Segment of Highway Tunnel in High-Intensity Earthquake Areas

The use of underground structures such as tunnel for subways, highways, material storage, and sewage and water transport is increasing in the West of China. As the strongest earthquake recent years，the Wenchuan Earthquake (M8.0) on May 12nd, 2008，has caused very severe casualties and property losses. Relying on the left line tunnel portal segment of the Xiaoshicun Tunnel, the dynamic response analysis were conducted by FEM. The response patterns of stressand displacement of the tunnel structure were respectively studied both under the single horizontal earthquake action and the interaction of horizontal and vertical earthquake actions. The results indicated that the difference of seismic response in diffrent parts of tunnel linging was obvious, the response under both horizontal and vertical earthquake action was bigger than that under single horizontal motion.

Pseudo-dynamic evaluation of passive response on the back of a retaining wall supporting c-Φ backfill

The study presents a rational analytical approach to obtain the seismic passive response of an inclined retaining wall backfilled with horizontal c-Φ soil. Pseudo-dynamic analysis is carried out to obtain the seismic passive response. Here in this analysis, the critical wedge angle is a single one irrespective of weight, surcharge and cohesion and this fact satisfies the field situation in a more realistic manner. A planer failure surface is considered in the analysis. The effect of soil and wall friction angle, wall inclination, horizontal and vertical earthquake acceleration on the passive resistance and the variation of passive earth pressure along the height of the wall have been explored. A comparison to pseudo-static and other available methods have been made to highlight the non-linearity of seismic passive earth pressure distribution.