Resisting Frame Structures Research Articles

Optimal seismic solution design for underground frame structure of subway station considering uniform damage

Abstract Based on the dynamic finite element theory, this paper establishes a fully coupled Mohr-Coulomb plastic finite element model of the soil ontology with the A metro station structure as the research object, conducts a nonlinear dynamic response analysis of the model structure, studies the variation of the seismic response of the model under different vibrations, soil material parameters and concrete parameters, and analyzes the influence of the station structure form on the displacement. In EL-2 condition, the first pair displacement of the S3 measurement point of the rectangular station is 5.695 mm, and the displacement of the arch-shaped station is 2.5 mm less than that of the rectangular station. The relative displacement of soil shear modulus with Gmax=200 MPa is 2.3 mm less than that of soil shear modulus with Gmax=80 MPa in the case of sidewall height of 3 m, which indicates that both the shape of station and soil stiffness has an effect on the seismic performance of the station. Influence on the seismic performance of the station. The research in this paper has an important reference value for the seismic design of underground frames of subway stations.

The multi-dimensional fragility analysis of the underground large-scale frame structure based on the internal relationships of different seismic performance evaluating indexes

In this paper, the seismic performance of the underground large-scale frame structure (ULSFS) is thoroughly investigated aiming at the drift deformation and rotation deformation of vulnerable positions, and the multi-dimensional fragility analysis of the ULSFS is further developed based on the internal relationship of different seismic performance evaluating indexes. Employing the increment dynamic analysis (IDA) method, the seismic performance of the ULSFS is investigated during diverse earthquakes. The interlayer deformation ratio (IDR) and interlayer rotation angle (IRA) are adopted as Damage measures (DM) to assess the drift deformation and rotation deformation, respectively. The internal relationships of two DMs are revealed, and the correlation coefficients are proposed by the correlation analysis. Assuming the DMs subordinated to the joint lognormal distribution, the generalized equations are established to describe performance states of the ULSFS aiming at different seismic failure modes. Considering the seismic thresholds and correlation coefficients of two DMs in different performance limit states, the 2-D fragility curves of the ULSFS are achieved. The results shows that the correlation of seismic evaluating indexes would decrease with the increase seismic intensities due to the structural inelastic damage; and the 2-D fragility curves with considering the reasonable internal relationships of two DMs would be more accurate and conservative. This paper provides the theoretical basis and technical support for the seismic performance assessment of large underground frame structures with complicate seismic failure modes.

Seismic vulnerability analysis for shallow-buried underground frame structure considering 18 existing subway stations

The variability of structural engineering parameters is not accounted for in available literature on seismic vulnerability of underground frame structures. This study investigates the seismic vulnerability of 18 existing subway stations with different site condition, structural stiffness, reinforcement ratio and buried depth employing two-dimensional (2D) finite element analysis considering soil-structure interaction. The peaks of structure inter-story drift ratio under different earthquake intensity of different ground motion records are obtained from non-linear dynamic time-history analysis. Taking the inter-story drift ratio as the damage measure (DM) and the peak ground acceleration (PGA) as the ground motion intensity measure (IM), the seismic vulnerability curves of 18 subway stations are constructed. The comparison of seismic fragility curves of different subway stations demonstrates that site conditions are critical to the post-earthquake structure probability of failure. Furthermore, representative seismic fragility curves are established based on the data collected form the computed results of 18 subway stations, which can aid in evaluating the seismic performance of existing urban underground frame structures in China. The results of this study can provide reference for the performance-based seismic design of urban underground frame structures.

Study on the seismic control measure of the underground large-scale frame structure

The seismic control measures with isolation bearings (SMIB) on top column joints are widely employed in underground frame structures with small cross-sections. This paper reveals the seismic control mechanism of the SMIB, and verifies the applicability of the SMIB for the underground large-scale frame structure (ULSFS). It is found that: the stresses of middle columns in the ULSFS would be controlled to some extent, but the seismic responses of floor slabs and outside walls would increase due to the smaller lateral horizontal resistance after the SMIB. The SMIB can not aim at the failure mechanism of the ULSFS, and it has been demonstrated to be ineffective for the ULSFS. Therefore, an innovative separation seismic control measure (SSCM) is proposed for the ULSFS based on the structural seismic characteristics and failure mechanisms. The fixed beam-column joints in the frame structure are released to be hinged, and the energy dissipation devices are added between the internal frame structure with outside walls. The analysis results show that the SSCM would cut down the adverse effects of the considerable soil structure interaction and decrease the seismic responses of the whole ULSLS efficiently. The seismic reduction ratio also demonstrates the SSCM has highly reliable seismic control effects on both the entire structure and vulnerable positions.

Seismic Performance Evaluation Method of Underground Frame Structures Considering the Vertical Seismic Capacity of Structural Components

The seismic performance of large underground structures can be evaluated from two perspectives, namely the horizontal interlaminar deformation and the vertical loading-carrying capacity. The current seismic analysis methods focus on the horizontal seismic performance with the interlaminar drift ratio as the evaluation index. It is difficult to fully reflect the vertical failure characteristics of the overall structure. This paper aims to develop an evaluation method to comprehensively evaluate the seismic performance of underground frame structures. The quantitative evaluation indexes, i.e. the vertical loading-carrying risk factor of columns and the vertical deflection risk factor of slabs, were defined to evaluate the seismic performance of underground frame structures. Then, the seismic performance evaluation method was established and the evaluation processes were described. Seismic response analysis of an underground frame structure with different spans on the upper and lower stories was conducted, and the seismic performance of the structural components and overall structure was quantitatively evaluated by using the proposed evaluation method. The seismic response laws of columns and slabs were analyzed and the potential failure mode of the structure was clarified. Furthermore, the failure mechanism of the structure was explained in detail. Numerical results presented that the proposed evaluation method can effectively identify the seismic-induced weak components and failure modes of underground frame structures, and thus has guiding significance for the seismic design of the underground frame structures.

Upgrading seismic performance of underground frame structures based on potential failure modes

Most subway stations in China have been constructed recently and their seismic performance and potential failure modes are not well characterized. This paper is dedicated to identifying potential failure modes of underground frame structures through numerical simulations, and developing an optimized method for upgrading the seismic performance of deficient structures via controlling the potential failure modes. The dynamic response of an unequal-span subway station structure was calculated considering different ground motions with increasing peak horizontal acceleration, and the structural seismic performance characteristics were evaluated. Seismic performance evaluation indexes, including interlaminar deformation risk factor of columns and sidewalls and deflection risk factor of slabs, were established to identify the most critical structural component under strong earthquake excitations. The structure failure mechanism was analyzed, and consequently, the corresponding retrofitting scheme for upgrading its seismic performance was proposed. Finally, the structural responses before and after retrofit were calculated and compared to demonstrate the effectiveness of the retrofitting scheme. The results can improve the understanding of the failure modes of underground frame structures and provide references for their seismic design.

Seismic mitigation performance analysis of underground subway station with arc grooved roller bearings

A seismic mitigation control technology involving arc groove roller bearings (AGRB) for shallow buried underground frame structures is proposed for reducing the horizontal deformation of the central column. Firstly, the working mechanism of AGRB component is described and its mechanical properties are analyzed through pseudo-static analysis. The results show that AGRB offers good vertical bearing capacity and horizontal deformation performance. Secondly, the finite element models of the soil-structure system for subway stations with and without AGRB are established for implementing the nonlinear dynamic time-history analysis. Compared with the observed response of the structures without AGRB, the horizontal deformation, shear force and bending moment of the central column fitted with AGRB are greatly reduced and the maximum seismic mitigation rate is above 80%. In addition, the results demonstrated that utilizing AGRB could greatly reduce the plastic damage area and damage degree of the supporting column, and avoid the occurrence of plastic hinges and shear failure due to insufficient lateral deformation resistance of the central column under high axial compression. Thus the AGRB can be used as an effective design scheme to achieve seismic mitigation control for underground structures.

Study on seismic failure mechanism of shallow buried underground frame structures based on dynamic centrifuge tests

During the Kobe earthquake in 1995, Daikai subway station suffered the severe collapse, which aroused people's more attention to the earthquake damage response of underground structures. In order to investigate the seismic failure mechanism of underground frame structures, a series of 1/50-scaled dynamic centrifuge tests were conducted. To make the underground structures produce a reasonable seismic failure mode in tests, an experimental scheme was designed in detail based on the author's previous numerical studies. With the purpose of simulating the vertical inertial effect of the overburden soil in the dynamic centrifuge tests, a certain proportion of steel grits were mixed into the overlying soil. A model structure finally occurred the overall collapse mode, which was similar to that of Daikai subway station. Based dynamic centrifuge tests, the seismic failure mechanism of shallow buried underground frame structure was analyzed and summarized in the paper. It could offer a reference for the cause of collapse of Daikai subway station. The series of tests provided valuable experimental data for further studies of the earthquake damage response of underground frame structures, and also enriched the testing technique for destructive model tests.

Seismic performance improvement of underground frame structures by changing connection type between sidewalls and slab

Seismic failure mechanism of underground frame structures presents that the collapse of underground structures attributes to the insufficient seismic resistance of central columns. Therefore, researches have been conducted to improve the seismic performance of underground structures by enhancing the loading-carrying capacity of the central columns or decreasing the seismic loads transmitted to central columns. For this purpose, this study proposed a new approach by changing the connection type between sidewalls and slab: setting shock absorbing gap (SAG) between sidewalls and ceiling slab, which aims to decrease seismic loads transmitted to central columns. The proposal and working mechanism of SAG were illustrated detailedly. Afterwards, nonlinear finite element models, in which a developed elastoplastic constitutive model was used to simulate the 3D strength and softening behaviour of surrounding soils, were built for simulating the static and dynamic responses of underground structures. Based on the numerical results, SAG affecting the internal forces of structural components before earthquakes were discussed firstly. Then the seismic efficiency of SAG updating the seismic performance of underground frame structures was analyzed by discussing earthquake-induced damage mode of overall structures, soil pressure on structures, earthquake-induced deformations and internal forces of structural components. Finally, the seismic performance of underground frame structures influenced by the width of SAG and frictional coefficient of the sliding surface was investigated, and advice for reasonably using SAG was suggested.

Seismic response and failure mechanism of underground frame structures based on dynamic centrifuge tests

AbstractDuring the 1995 Kobe earthquake in Japan, the Daikai subway station suffered total collapse, which made the research on the seismic failure mechanism of underground frame structures become a hot topic. The author has carried out a lot of research on earthquake failure mechanism of underground frame structures based on numerical method. To validate and further study the seismic failure response and mechanism of underground frame structures, a series of comparative dynamic centrifuge tests were carried out. The research conclusions are as follows. The vertical earthquake action significantly increased the axial pressure on the columns of an underground frame structure, reducing their horizontal deformation capacity. The columns subjected to high axial compression were prone to brittle damage under a relatively strong horizontal earthquake, which led to the overall collapse of an underground frame structure. The areas near the intersection of the ceiling slab and the sidewalls were the weak part of the underground frame structure and were vulnerable to tensile cracks under earthquake. The columns' top and bottom were the fragile parts and were prone to concrete cracking or even shear failure under an earthquake. If the columns could remain intact and effectively provided vertical support under a strong earthquake, it was beneficial to reduce the risk of the overall collapse of an underground frame structure.

Validation of a numerical model based on dynamic centrifuge tests and studies on the earthquake damage mechanism of underground frame structures

A series of dynamic centrifuge tests were performed to analyse the seismic response and failure mechanism of the underground frame structures. In the model test, the model structure experienced complete collapse, which has rarely been reported in previous studies. This study aimed to obtain an effective numerical model based on physical tests that could properly simulate large deformations or even the collapse of soil-structure systems under earthquake loads. The tests were numerically analysed via a full dynamic time history analysis considering the non-linear properties of the material and contact. The process of establishing numerical model and the method of determining material parameters were elaborated. The numerical results were compared to experimental data to validate the effectiveness of the numerical model. Finally, the calibrated numerical model was used to carry out further research on the seismic damage response and failure mechanism (i.e., collapse damage) of underground structures. Some of most important insights based on the model test and numerical results are as follows. The top and bottom of the column of underground frame structure were determined to be the weakest positions under earthquake loading conditions and were vulnerable to bending-shearing failure. The vertical earthquake load could significantly increase the axial forces on the columns and then reduce their horizontal deformation capacity. The columns subjected to high axial compression were prone to complete brittle failure under a relatively strong horizontal earthquake load and caused the overall collapse of the underground frame structure. Therefore, the underground frame structure could avoid complete collapse under a strong earthquake load as long as the column was free from damage and provided sufficient vertical support.

A novel segmental cored column for upgrading the seismic performance of underground frame structures

A novel segmental cored column (SCC) is proposed to enhance the seismic performance of underground frame structures, especially the interlaminar deformability of the intermediate columns. The basic composition and behaviour mechanism of the SCC are introduced. An analytical model for calculating the horizontal load-displacement curve and the interlaminar deformability of the SCC is established, and pushover simulations are conducted to verify its efficacy. The developed model is then employed to investigate the critical factors that may affect the interlaminar deformability envelope of the SCC. To further demonstrate the feasibility of the SCC in upgrading the seismic performance of underground frame structures, the seismic responses of the same structure are analysed considering alternative column design, i.e., conventional rectangular or circular columns, or the SCC. The obtained results demonstrate that the structure retrofitted with the SCC experiences less damage and exhibits better seismic performance compared to those designed with conventional rectangular or circular columns.

Influence of Vertical Inertia Force of Covering Soil on Seismic Damage Response of Shallow Buried Underground Frame Structure Shaking Table Model Test of Centrifuge

Influence of Vertical Inertia Force of Covering Soil on Seismic Damage Response of Shallow Buried Underground Frame Structure Shaking Table Model Test of Centrifuge

Comparative numerical analysis on dynamic effects of underground large scale frame structures under seismic waves

In this paper, dynamic effects of the underground large scale frame structure (ULSFS) with large scales along both two horizontal directions are investigated by 3-D numerical analyses. To guarantee the accuracy of seismic inputs, seismic waves are transformed into equivalent forces adding on the truncated boundary nodes based on the viscous-spring artificial boundary. 3-D finite element models of 4-span, 8-span, and 20-span underground frame structures with surrounding foundation are proposed to simulate small, middle and large scale underground structures. For a comprehensive study of results, another two analyses of the ULSFS are proposed to evaluate the two dynamic effects of structures: structural inertial effects on inner structures, and effects of structural vibration on the whole soil-structure system, respectively. Furthermore, several soil conditions are employed to study influences of the relative stiffness between the structure and soil on the two mentioned dynamic effects of the ULSFS. The results demonstrate that dynamic effects of the ULSFS are much more significant compared with small scale underground structures which make the structural deformations and internal forces to be larger; and dynamic effects of the ULSFS would decrease with increasing elastic moduli of surrounding soils due to great soil constraints.

A pseudo-static method for seismic responses of underground frame structures subjected to increasing excitations

The determinant factor for the seismic response of underground structures is the deformation of surrounding soil, which is different from above-ground structures. Considering that the existing deformation-based seismic design methods for underground structures are based on elastic hypotheses, this study proposes an improved Finite Element method called New Pseudo-Static Analysis (NewPSA) to predict the nonlinear behavior of underground frame structures subjected to increasing horizontal seismic excitations. A new method for one-dimensional(1-D) seismic analysis of soil layers is proposed to calculate the distributions of displacements and shear stresses along the depth in the free-field with increasing bedrock motions. Pseudo-static Finite Element analysis is then carried out by imposing the distributions of body forces derived from the 1-D analysis. A series of comparisons were made to validate the applicability of the proposed method. Its prediction capacity was also compared with that of a well-known method. The proposed method is able to predict the nonlinear performances of underground structures under horizontal earthquake loadings. Particularly, similar to the push-over analysis of above-ground structures, the method has the potential to predict the seismic capacity of underground frame structures subjected to design seismic loadings.

Surface Overpressure Distribution and Dynamic Response of the Retaining Wall of the Underground Structure Subjected to Inner Explosion

An underground structure has been in a state of static equilibrium under the combined effect of gravity and the surrounding soils confining pressure before internal explosion occurred, and the blast wave can experience multiple reflections and diffractions in closed space, so the overpressure on the surface of structural members was more complex than that when explosion happened in the open space. In this paper, a finite element model of a closed underground frame structure was established by using the finite element software ANSYS/LS-DYNA. Based on the model, numerical simulation by stages was done to study the overpressure distribution on the surface of the retaining wall. This paper main analyzed the effect of the initial balance stress on the blast overpressure distribution rule and the retaining walls dynamic response.

Numerical Simulation of Shield Tunnel Passing Through Underground Structure

Shield tunneling is often adopted in underground engineering such as civil tunnel construction and mine excavation. The program FLAC3D is used to simulate the process of the tunnel excavation through underground structure in Shenyang in this paper. The analysis results show that,(1) the soil below the end wall suffers great displacement, when the shield approaches the end wall of underground framework from different directions, so the soil under the end wall needs to be reinforced. (2) Increasing pressure and volume of grouting can’t significantly reduce the amount of surface subsidence when the drilling of the shield acrosses through the independent foundation. (3) The influences of shielding to the construction are limited because of the constraint function to the surrounding rock above the tunnel by the great entire rigidity of under-ground framework. The results of numerical simulation exactly matches the monitoring data when the stiffness of under-ground frame structure is considered, and it can provide guidance for engineering practice.