Seismic Time History Analysis Research Articles

Research on the multi-shear spring model for circular-section steel piers

The main damage caused by earthquakes to single-column circular-section steel piers is the bulged deformation at the bottom, generated by local instability. The refined shell-based finite element (FE) model can accurately simulate the deformational behavior, but it is still cumbersome and time-consuming to apply to the engineering design currently. Further, the existing simplified methods cannot be used in seismic response analyses under horizontal bidirectional earthquakes. Therefore, this paper uses the multi-shear spring (MSS) mechanical model as the basic model and proposes an MSS calculation model for circular-section steel piers. This model is applicable for horizontal bidirectional seismic response analysis and considers the local instability effect of steel plates. In this study, the load–deformation relationship of the modified Menegotto-Pinto model is employed in all directions as the hysteresis curve equation of the springs. The basic parameters of the corresponding models for different structures are determined according to the calculation results of the refined-shell models. In addition, the Ibarra-Krawinkler degradation rule is employed to simulate the degradation process of structural bearing capacity and stiffness, and the degradation parameters are identified. The pseudostatic and seismic time-history response analyses of steel piers with different width-to-thickness ratios verify that the proposed model has reliable calculation accuracy and greatly improved efficiency. The research in this paper provides a practical calculation method for the seismic response analysis of steel bridge piers.

Effects of axial loads and higher order modes on the seismic response of tall bridge piers

Tall piers are essential components of the earthquake resisting system of bridges. The dynamic behaviour of tall piers differs significantly from that of short piers due to a number of factors, such as their high flexibility and inertia. This paper aims to quantify the influence of axial loads and higher order modes on the seismic response of bridges tall piers and to provide results useful for a more informed design and assessment. For this purpose, an analytical formulation of the dynamic problem, developed and validated in a previous study, is employed to analyse a wide range of piers and bridge configurations. In the first part of the paper, a thorough parametric investigation is carried out to evaluate the influence of axial loads and higher order modes on both the modal properties and the seismic response of tall piers with different geometries and vertical loads. Subsequently, three realistic case studies representing bridges with different geometrical, mechanical and dynamic conditions are analysed and seismic time-history analyses are performed to further investigate the problem. The obtained results provide useful insights into the seismic behaviour of bridges with tall piers, identify the relevant governing parameters and shed light on the accuracy of simplified approaches suggested by the Eurocode 8 to account for the second order effects.

Restoring Force Model Research on Joint of Circular Tubed Steel-Reinforced Concrete Column

In this paper, two joints of circular tubed steel-reinforced concrete (CTSRC) column were designed. The load-displacement hysteretic curve and skeleton curve of this new type of joint are obtained by the pseudostatic test under low cycle cyclic load on the top of the column. The results show that this new type of joint has good seismic energy dissipation performance. On the basis of the test, a three-fold skeleton curve model considering three characteristic points of yield, limit, and failure is proposed, and the expression of skeleton curve model is given. The load and unload stiffness degradation law of specimens under reciprocating load is studied, and the expression of stiffness degradation law is given. The hysteresis law of the new type joint specimens is described in detail. The validity of the model is verified by comparing the experimental curve with the model curve. The model can be used in the elastic-plastic seismic time-history analysis on the joint of circular tubed steel-reinforced concrete (CTSRC) column.

Analysis on the Influence of Increasing Seismic Fortification Intensity on Seismic Performance of Underground Station

China Earthquake Parameter Zoning (2016) has increased the seismic fortification intensity in Chengdu from VII to VIII. It is necessary to conduct in-depth discussion on the impact of the seismic performance of the built underground station structure. In this paper, a stratum-structure finite element model is established with a Chengdu subway station as an example. The model boundary adopts viscoelastic boundary, and the ground motion is input in the form of equivalent nodal force. The equivalent linearization method is used to consider the nonlinearity of soil materials. The time-history analysis of seismic fortification intensity of VII and VIII degrees is carried out, respectively. By comparing the calculation results of the two seismic fortification intensity ground motion conditions, it is concluded that the connection between the side wall and the floor is the weakest position of the station structure under the action of the earthquake; the seismic fortification intensity is increased from VII to VIII to the internal force of the structure. It has a relatively large impact, especially the most obvious impact on the bending moment. The results of the verification of the seismic time-history analysis show that the increase of fortification intensity will have a more obvious impact on the structural deformation, and the structural design of the station can meet the safety performance requirements of VII and VIII degrees of seismic fortification. The research has certain reference significance for the seismic safety evaluation of the built underground station structure in Chengdu area.

Three-dimensional seismic performance analysis of large and complex underground pipe trench structure

The existed 1D (dimensional) and 2D seismic analysis methods couldn't met the seismic research requirements of large and complex underground pipe trench structure (LCUP). In order to solve the problem that the seismic performance analysis of LCUP requires high 3D modeling ability and calculation equipment, an integrated seismic analysis method of "overall structure + key nodes" was proposed in this paper. Firstly, according to the research purpose, the seismic analysis strategy of LCUP was proposed, and the main factors influencing the seismic time history analysis of LCUP were analyzed one by one, and a series of accurate analysis parameters and simplified assumptions were obtained. Secondly, the 3D seismic analysis model of LCUP was established, including the overall pipe trench model and the local key nodes model, and the material parameters, boundary conditions, ground motion and calculation conditions of the model were determined. Finally, 3D seismic time history analysis was carried out for the whole structure and key joints, and the seismic performance evaluation based on mechanics and deformation was carried out. The seismic performance of the LCUP met the design requirements. The results showed that the method didn't only meet the requirements of seismic analysis accuracy and depth for complex underground space structure, but also significantly reduced the time of seismic analysis and improves the research efficiency. This research method will provide a useful reference for the seismic research of similar large complex underground structures.

Application of the Newmark Analysis Method in Stability Evaluation of Submarine Slope

The Newmark seismic time-history analysis method can take into account the effects of natural seismic peak ground acceleration (PGA), duration, and seismic frequency; seismic wave can be input into the method for simulation. This study calculates the dynamic response of the typical seabed slope of Caofeidian in the event of a similar Tangshan earthquake, and the displacement value can be used to quantitatively reflect the influence of the earthquake on the slope of the site. The allowable displacement value of the top of buildings or submarine slope can be used as a marker of security and stability analysis, which can further provide important reference for similar slope stability evaluation and offshore engineering construction.

Influence of the excitation frequency content on the efficiency of a tuned liquid column damper

The current study addresses the influence of the excitation frequency content on the efficiency of a tuned liquid column damper (TLCD) to control the displacement response in structures subjected to seismic excitations. A time-domain stochastic stationary analysis is performed, and an equivalent statistical linearization for the TLCD is obtained. The results show that the TLCD is more efficient in structures subjected to broadband processes. In narrowband processes, the maximum performance of the TLCD occurs when the linear equivalent period of the system TLCD-structure tunes the TLCD period, and the frequency of the structure matches the predominant frequency of the input motion. Results derived from this analysis are validated through two time-history seismic analyses.

The Effect of Long Duration Earthquakes on the Overall Seismic Behavior of Steel Structures Designed According to Eurocode 8 Provisions

Premature and simultaneous buckling of several steel braces in steel structures due to the prolonged duration of a seismic motion is one of the issues that must be addressed in the next version of Eurocode 8. In an effort to contribute towards the improvement of the seismic design provisions of Eurocode 8, an evaluation of the overall behavior of some steel building-foundation systems under the action of long duration seismic motions is performed herein by means of nonlinear time-history seismic analyses, taking into account soil–structure interaction (SSI) effects. In particular, the maximum seismic response results—in terms of permanent interstorey drifts, overturning moments and base shears of the steel buildings as well as of the permanent settlement and tilting of their foundations—are computed. It is found that the seismic performance of steel buildings when subjected to long duration seismic motions is: (i) acceptable for the two and five-storey fixed base steel buildings and for the two-storey steel buildings with SSI effects included; (ii) unacceptable for the eight-storey fixed base steel buildings and for the five and eight-storey steel buildings with SSI effects included. In all cases of steel buildings with SSI effects included, the seismic performance of the mat foundation, as expressed by the computed values of residual settlement and tilting, is always acceptable.

A Structural Configuration with Separate Substructures towards Reducing the Seismic Damage of Spatial Structures with Rectangular Plan

Seismic damage of spatial structures of rectangular plan with RC substructures was observed in several earthquakes, especially in the RC substructures. In order to reduce the seismic damage potential, a new structural configuration of spatial structure of rectangular plan is proposed, the substructures of which are composed of the steel substructure and the RC substructure. The latter only bears the vertical load of roof by the arrangement of horizontal sliding bearings between the roof and the RC substructure. The pushover analyses are performed on a steel braced frame and an RC frame with similar lateral stiffness, and the results show that the lateral capacity of the steel structure is much larger than those of the RC structures. A spatial structure of rectangular plan with two different substructures is designed according to Chinese structural designing codes. Seismic time history analyses are carried out for the spatial structure under five ground motions. The results show that the damage mainly concentrates on the substructures, and the seismic performance of the structure with steel and RC substructures is much better than that of the structure with RC substructures.

Seismic analysis of the CFETR CS Model Coil

The China Fusion Engineering Test Reactor (CFETR) Central Solenoid (CS) Model Coil is being fabricated by the Institute of Plasma Physics Chinese Academy of Sciences, and will be cryogenically tested in 2021. In order to validate the structural integrity of the CS Model Coil under seismic loads, response spectrum (RS) and time history analyses have been carried out. This paper first introduces the manufacturing progress of the CS Model Coil and the structure of the CS Model Coil. Then, the RS analysis is perfomed with the complete-quadratic-combination (CQC) modal combination rule. Finally, time history analyses under the artificial Hefei wave and the modified El Centro wave are conducted. The seismic response of the CS Model Coil is described and the obtained maximum von-Mises stresses are respectively 30.9 MPa and 34.0 MPa for the RS and time history analysis. These stresses are mainly caused by the horizontal excitations, and are lower than the allowable stress limit.

내부 유체에 의한 고유진동수 분리 효과를 고려한 배관계의 적절한 시간이력 해석 방법론

In this study, the natural frequency separation phenomena found in the dynamic analysis of piping systems with internal fluids were identified, and methods for efficient seismic time history analysis were studied. We conducted a dynamic analysis of a piping system with consideration for the effect of its internal fluids using the coupled model, which incorporates the fluid-structure interaction effect. Owing to the mode separation effect, modes were divided into the fluid mass added (FMA) mode, generated by the added mass effect of the fluid, and coupled mode, which is created by the resonance of the internal fluid. The response contribution of the FMA and coupled modes was confirmed to be effective for efficient seismic time history analysis.

Seismic Performance of Steel Structure-Foundation Systems Designed According to Eurocode 8 Provisions: The Case of Near-Fault Seismic Motions

The seismic performance of steel structure-foundation systems subjected to near-fault earthquakes was assessed on the basis of response results from nonlinear time-history seismic analyses. The structural results included the maximum values for residual interstory drift ratios, base shears, and overturning moments of the steel structures, as well as the maximum values for residual settlement and tilting of the foundations. In order to reveal the influence of soil-building-interaction on the aforementioned response results, the steel building-foundation systems were designed according to Eurocode 8 provisions, assuming initially fixed and then compliant base conditions. It was concluded that for the case of near-fault seismic motions, good seismic performance of steel building-foundation hybrid systems designed according to European Codes was not guaranteed. A particular thing to note for these systems under near-fault seismic motions was that the seismic performance of the steel structure was most likely unacceptable, while one of the foundations was always acceptable.

Application In Communication Equipments Antiseismic Time History Analysis Based on Advanced Mass Scaling

RADIOSS is a powerful and stable explicit non-linear finite element analysis (FEA) solver in Altair HyperWorks. In this paper, the seismic time history analysis of communication equipment based on RADIOSS solver was taken as the research object. In the numerical simulation, three methods were applied in the computational efficiency enhancement: the non-timestep control method, the traditional mass scaling technology, and the advanced mass scaling technology (AMS). Calculations prove that the AMS technology in RADIOSS can not only improve the solution efficiency, but also guarante the calculation accuracy in antiseismic time history analysis.

The effects of steel X-brace retrofitting of RC frames on the seismic performance of frames and their elements

Steel X braces are used extensively to retrofit RC frames. When steel braces are added to an existing RC frame, the load paths through which the lateral forces are transferred change considerably, resulting in changes in demand on the frame and its elements. The present study attempts to examine the possible side effects of retrofitting RC frames with steel X braces, regarding their overall seismic performance such as global displacements, drifts and base shears, as well as, their individual members, including beams and joints. To this end, a large number of nonlinear time history seismic analyses are performed on retrofitted 2D, RC frames, being 4, 8 and 12 storeys high. It is found that, retrofitting an RC frame with steel X braces improves its global seismic response by reducing the maximum displacement, inter-storey drifts and demand base shear. However, the effectiveness of the bracing system in improving global responses is generally reduced as the height of the frame increases. Regarding the local effects on beams and joints, it is noted that although retrofitting, in general, reduces ductility demand in beams, and shear demand in joints, the reductions are not substantial in taller frames and in some beams and joints retrofitting may even have an adverse effect. Also, the connections between the steel X brace system and the RC frame cause the plastic hinges in beams and columns to relocate further away from the joint, resulting in a reduction in the effective length and possible increase in the level of plastic shear in these members. The local adverse effects of retrofitting an RC frame by steel X-braces may necessitate prior local strengthening of some members.

Effect of soil properties on the seismic damage assessment of historical masonry minaret–soil interaction systems

SummaryThe interaction between soil and structure plays a crucial role on accurate determination of structures' seismic behavior. The assumption of fixed base structure has been commonly used in traditional design works, and the interaction between soil and structure is thus often neglected. In addition, historical masonry structures particularly built on elastic soil media may be significantly affected seismic behavior of the structure under earthquakes. In this research, the damage distribution on a historical masonry minaret is numerically investigated under horizontal earthquake ground motion. Alaca Mosque minaret was built in 1271 in Bolvadin district of Afyon province. The historical masonry minaret was chosen as the subject of the study. Nonlinear seismic time history analyses were conducted for fixed‐based and different soil properties under horizontal earthquake ground motion. The horizontal (East–West) component acceleration records of Dinar earthquake (Mw = 6.1) that took place on October 10, 1995, were used during the analyses. Maximum displacement, maximum/minimum principal stresses, and damage ratios were determined by nonlinear analyses performed considering fixed base and soil–structure interaction. The analysis results showed that soil–structure interaction had significant effect on the structural behavior of the minaret, such that, the minaret that was expected to get damage in the case of fixed base did not get any damage when soil–structure interaction was considered.

Seismic drift response of seesaw-braced and buckling-restrained braced steel structures: A comparison study

A numerical comparison study of the interstorey and the residual interstorey seismic drifts of steel structures equipped with the seesaw system and buckling-restrained braces is carried out. This investigation involves inelastic time-history seismic analyses of 2-, 5- and 8-storey 3-D steel structures, with specific orientation of columns and configuration of braces, for the design basis earthquake. The effects of soil-structure interaction and seismic incident angle are also considered in these analyses. Comparison of the seismic drift responses experienced by the seesaw-braced and the buckling-restrained braced steel structures, reveals different peak interstorey drift values but in many cases similar drift concentration along the height of the structures. Furthermore, the seesaw-braced steel structures exhibit, in general, larger peak residual drifts than buckling-restrained braced steel structures.

Effect of the Presence of Basements on the Vibration Period and Other Seismic Responses of R.C. Frames

The soil-structure interaction (SSI) of R. C. building frames including basements below ground level has been the subject of extended research, mostly in the form of theoretical dynamic analysis. There are different issues concerned with this type of work, as e.g. the location of the base of the structure. Usually, the base of the structure in dynamic analysis or according to the codes is the level at which the lateral displacement is zero. According to this definition, and with the presence of basement floors and the soil mass below, the ground level may not be the base of the structure. The soil stiffness around basement walls has a great effect on the lateral displacement of the basement floor. Another issue is the effect of the presence of the basement floors on the dynamic behavior of the structure. A third issue is the effect of the soil around the basement walls and the soil mass below the foundation in general, which is known as the SSI. In this paper, 3-dimensional regular building frames subjected to seismic loading are analyzed using SAP2000 software. The first frame is a 5-floor, 3-D frame without including the soil mass below the raft foundation and without a basement floor. The second frame is the same frame with a basement floor and with consideration of the soil mass below the raft foundation and around the walls of the basement floor. The third frame is the same frame with consideration of the soil mass below the raft foundation but without the basement floor. Results of the seismic time history analysis and UBC97 response spectrum analysis are presented and discussed.

Seismic response of low-rise 3-D steel structures equipped with the seesaw system

The efficiency of the seesaw system when applied to low-rise 3-D steel structures is presented in this paper. This efficiency is judged by several seismic response results coming from inelastic seismic time-history analyses of 2-, 5- and 8-storey steel structures. These response results involve height wise distributions for peak interstorey drift ratios (IDR), peak residual interstorey drift ratios (RIDR) and plastic hinge formations in frame elements as well as peak forces to spiral strand ropes and viscous dampers of the seesaw system. For the foundation of the steel structures, different soil types are considered in order to assess the effects of soil-structure interaction (SSI). The seismic incident angle is also taken into account. From the results presented it is concluded that the seesaw system, essentially working always in tension, constitutes a bracing solution that can be potentially proposed by seismic codes as an alternative seismic force resisting system for low-rise steel structures.

Seismic performance evaluation of a fire-exposed historical structure using an updated finite element model

This paper presents a seismic performance evaluation of a historical masonry structure. The process involves geometrical checking and seismic performance controls and also requires consideration of relevant codes and guidelines. Geometric checking was carried out in accordance with previous and newly-introduced Turkish Earthquake Codes. In order to obtain reliable results for seismic evaluation, the numerical model of the building was updated by means of non-destructive experimental measurement methods. The experimental measurement process was carried out using the Operational Modal Analysis method. The maximum error between the numerical and experimental natural frequencies, calculated as 37.11%, was reduced to 2.39% through the use of updating procedure. Time history seismic analysis was conducted on the updated finite element model using the Kocaeli 1999 earthquake record. Evaluation of the seismic performance of the structure was carried out with reference to a new guideline published specifically for assessment of historical structures. At the end of the analyses, maximum displacements and principal stresses were obtained and presented in detail using contour diagrams. In terms of displacement control, the structure showed only limited damage during the applied earthquake record: 0.0001 < 0.003. In other words, in terms of the new guideline, the structure behaved in a linear way when exposed to the selected earthquake.

Seismic effects on leaning slender structures and tall buildings

A problem of joint effects of a structural leaning and seismic excitations can be particularly important for tall buildings and slender towers. Present paper addresses problems of loss of seismic resistance of leaning tall structures on examples of two selected typical structures: a 160 m high industrial chimney and a slender 30-storey high building. The problem is discussed first for strong seismic rockburst excitations (induced seismicity – where structural leaning often occurs) and also for strong natural earthquakes. Dynamic, non-linear time-history seismic response analyses of the 160 m high, reinforced concrete industrial chimney and the 30-storey shear wall building are carried out. Detailed parametric analyses of non-linear interaction of the effect of initial leaning and simultaneous seismic action, in form of inelastic time-history analyses, are performed. Unique changes in seismic responses of the leaning structures depending on combinations of various initial foundation tilts and seismic intensities are observed and studied in detail. It is demonstrated that the limitations on structural leaning described in an actual industrial mining code of practice are enough conservative. Various mechanisms driving seismic response at base and in the upper part of a leaning structure are recognized and carefully analysed for various combinations of initial ground tilts and seismic intensities.