Seismic Deformation Method Research Articles

A BOUNDARY FORCED RESPONSE DISPLACEMENT METHOD FOR SEISMIC ANALYSIS OF SYMMETRICAL UNDERGROUND STRUCTURES

A boundary forced response displacement method is proposed for the seismic analysis of symmetrical underground structures based on the requirement of quasi-static pushover test of soil-underground structure systems. The implementation procedure and special features of the method are introduced in detail. We took the Daikai subway station which was damaged during the Kobe earthquake in Japan as an example for the analysis, and compared the results of boundary forced response displacement method, the FEM seismic deformation method and the dynamic time-history analysis method. The results show that the accuracy of the new method was much higher than the FEM seismic deformation method when the width of the model was reasonable. The errors of the internal forces and the story drift were less than 15%. The new method is an effective simplified method for seismic response analysis of symmetrical underground structures. The attenuation law of lateral boundary forced displacement was analyzed. It provides references for the quasi-static pushover test of soil-underground structure system.

A Study on the Correction Factors of Soil Non-linearity Considering Korean Regional Conditions for Seismic Deformation Method Applied to Multi-Utility Tunnels

A Study on the Correction Factors of Soil Non-linearity Considering Korean Regional Conditions for Seismic Deformation Method Applied to Multi-Utility Tunnels

Integral Seismic Deformation Method: A Pseudo-static Method for Seismic Design of Underground Structures

The traditional seismic deformation method is among the most popular pseudo-static methods for seismic design of underground structures by considering soil-structure interaction through the layout of foundation springs. It can be mechanically proved that the traditional method has a relatively rigorous theory except the discrete foundation springs. A new kind of pseudo-static method, called the integral seismic deformation method, is proposed in this paper by establishing the finite element models of hollow ground and integral soil-and-structure. Equivalent seismic loads of the proposed method are composed of three parts: shear stress of free field, inertia force of underground structure and equivalent nodal forces acquired by the static analysis of the hollow ground model. In order to verify the efficiency of the proposed method, a series of numerical calculations of Daikai subway station are conducted by the two pseudo-static methods and the dynamic time-history analysis, respectively. Comparison of the calculation results shows that the proposed method achieves high precision and extensive applicability. It is also convenient and time-saving to operate. Therefore, the integral seismic deformation method can be widely used for seismic design of underground structures.

Improved longitudinal seismic deformation method of shield tunnels based on the iteration of the nonlinear stiffness of ring joints

Shield tunnels have undergone some prominent damage at joints due to the special structural composition of reinforced concrete segments that are connected by bolts. The generalized longitudinal seismic deformation method can achieve a better balance between the accuracy and efficiency of the calculation than the traditional seismic deformation method by using the time history of ground displacement of free-field as the input for the longitudinal beam-spring model of shield tunnels to determine the seismic responses of shield tunnels. However, the bending and axial stiffness of ring joints in this method simply are assumed to be constant values, which ignores the nonlinearity of the ring joints due to their discrete structures. In this paper, we demonstrate the inherent nonlinearity of ring joints by analytical derivation and obtain the stiffness of the 3D surfaces of ring joints under different loadings. Then, we propose an iterative algorithm for the stiffness of ring joints based on their internal forces, and this algorithm is integrated with generalized longitudinal seismic deformation method to form an improved method. The validity of the proposed method was verified by comparing the results of the longitudinal internal forces, the opening of joints, and the stresses on the joints obtained by generalized method and the improved method based on a Xiamen metro shield tunnel. Compared to the generalized methods, the results of the improved method indicated that the maximum joint opening, the compressive stress on the concrete, and the tensile stress on the bolts increased significantly, and these results demonstrated that the former methods of seismic design is unsafe.

既存壁式プレキャスト鉄筋コンクリート構造集合住宅建物の基礎と地盤を考慮した地震応答解析

Existing wall-type precast reinforced concrete residential buildings maintain high structural quality, although they were constructed widely in Japan more than 40 years ago. A large number of the residential units in these existing buildings are standardized and typically small. Consequently, they do not suit for modern living uses. In order to utilize these buildings, seismic behavior was evaluated by static pushover analyses in past research. It was concluded that the failure mechanisms are rocking of the walls in the transverse direction and beam yielding in the longitudinal direction. In this research behavior of the foundations was not studied. Past large earthquakes such as Hyogoken-Nambu earthquake in 1995 showed that the WPC buildings maintained high structural seismic resisting performance and the foundations including piles were relatively weak. This fact implies need of analytical study of the seismic behavior of the buildings considering their foundation and soil. It is more true on the evaluation of their performance in the transverse direction, where the behavior of the foundation is more influential to the overall structural behavior than the longitudinal direction. In this research, time-history seismic response analyses of the WPC buildings under large earthquakes with 500 year of the recurrence period are conducted. Two cases of combinations of the soil condition and foundation system are studied. One is continuous footing on hard soil and the other is pile in soft soil. 2-D sway-rocking models were created for the two cases with corresponding sway and rocking soil springs. The superstructure is the model which is identical in the cases and composed of inelastic joint springs and elastic precast concrete panels. Pile stresses are evaluated by applying the seismic deformation method. Findings in this research are shown below: (1) In the study case for the building with the continuous foundation, uplift of the building by the overturning moment (OTM) is observed. It is referred that the failure mechanism is rocking of shear walls associated with failure of the vertical joints in past study of pushover analyses with the fixed-base model. In the time-history analyses, the maximum base shear coefficient (CQ1MAX), which is defined as the ratio of lateral force to the building weight, is 0.73. (2) In the study case with the pile foundation, the piles can fail in shear before the collapse of the superstructure. While CQ1MAX reaches 0.81 with the elastic pile model, it would be lower in studies considering inelastic shear failure of piles. (3) In the study case for the building with the continuous foundation, shear stress of shear walls is no more than 1.8N/mm2, which is lower than probable ultimate shear stress (2.0-2.7N/mm2). Although, in the study case with pile foundation, the shear stress is at most 2.1N/mm2, this is the lower limit of ultimate shear stress and would decrease considering shear failure of piles. Therefore, shear walls would not fail under the large earthquakes, while foundation may be damaged. This analytical finding agrees with the past seismic damage of this type of buildings.

Pile Stress Estimation Based on Seismic Deformation Method with Embedment Effects on Pile Caps

A pseudostatic analysis, based on the beam on nonlinear Winkler-spring method considering the seismic earth pressure and side friction acting on embedded pile caps, was developed to estimate pile bending moments and shear forces. To verify the proposed method’s effectiveness, the authors conducted six dynamic centrifuge tests on a superstructure-footing model supported by 2×2 piles in sand deposits comprising a dry sand layer over liquefied soil. The seismic earth pressure, vertical wall friction at the active and passive sides, and friction at the sidewalls of the pile caps were separately measured by two-dimensional load cells during shaking. The seismic total earth thrust and side friction estimated by the proposed method showed good agreement with the experimental results for both the amplitude and phase difference to the superstructure and the pile cap inertia forces. The estimated bending moment and shear force in the piles also showed reasonable agreement with the experimental results; they were able to account for differences in the pile rigidity and soil relative density.

STATUS OF SEISMIC ANALYSIS METHODS FOR TRAFFIC TUNNEL AND THEIR APPLICABILITY SUGGESTIONS IN CHINA

Located between the Eurasia seismic zone and the circum-Pacific seismic belt, China is the largest continent shallow earthquake area around the world by the frequent earthquake activities. And great quantities of tunnels are located in high earthquake intensity area of China. As one of the main structure of the national lifeline, the seismic analysis methods of tunnel must be paid high attention. Based on seismic response characteristics of the traffic tunnel structure, this paper provides a synthesis of the current state of knowledge in the area of seismic analysis for tunnel, including the seismic design criteria, earthquake effects, tunnel seismic behaviors, and the seismic analysis procedure of tunnel. It focuses on analysis methods of tunnel subjected to seismic motion. There are three major seismic analysis methods normally used in tunnel structures; they are seismic coefficient method, seismic deformation method and dynamic response method. The basic principles of the three methods are described in this paper. Based on the different mechanical characteristics between cross-section and axial direction, the proper seismic analysis methods in the two directions are put forward according to the different construction method of tunnel. The research results will provide reference for seismic analysis of traffic tunnel.

液状化地盤において杭頭半剛接合構法を採用した杭基礎の耐震性能

The seismic behavior of a pile-supported building with semi-rigid pile head connections in liquefiable soil is investigated using 2D effective stress analysis. The results of the simulations show that the pile damage reducing effect of the semi-rigid pile head connection method is enhanced in liquefiable soil, because the superstructure inertia and external force acting on the embedded footing decrease. And the validity of the seismic deformation method as a seismic design method, which considers the non-linearity and axial force dependency of the pile heads, the varying axial force due to the dynamic interaction, and the total earth pressure acting on the embedded footing, is confirmed.

Behavior of Single Pile in Liquefied Deposits during Earthquakes

AbstractAnalysis of pile foundations for earthquake loads requires the consideration of inertial loads that result from the soil-pile-superstructure interaction, as well as the evaluation of kinematic interactions that result from the movement of the surrounding soil and the pile. Such soil-pile interaction analyses must consider the stiffness degradation that results from earthquake loading. In the current study, the soil-pile interaction analysis considers stiffness degradation effects for a range of earthquakes with different amplitudes [maximum horizontal acceleration (MHA)], mean time periods, and different durations of earthquakes. Effects of both kinematic and inertial interactions are evaluated using a seismic-deformation method. A computer program was developed using MATLAB for the analysis. Results of a ground-response analysis obtained from a separate study were used for the soil-pile interaction analysis. Pile response for kinematic interactions were validated with the available theoretical so...

EVALUATION OF PILE STRESS BASED ON SEISMIC DEFORMATION METHOD WITH EARTH PRESSURE AND SIDEWALL FRICTION ACTING ON EMBEDDED FOOTING

Seismic deformation method with earth pressure and sidewall friction acting on an embedded footing has been developed, to evaluate pile's stress during soil liquefaction. To verify the effectiveness of the proposed method, the dynamic centrifuge tests were conducted. The following conclusions were reached: (1) The bending moment at the pile head, estimated by the proposed method, showed good agreement with the centrifuge tests results; (2) The estimated amplitudes of the resultant force of earth pressure and sidewall friction, and the phase difference between the resultant force and the structure inertia force agreed well with the experimental results.

QUESTIONNAIRE ABOUT PRACTICAL USE OF SEISMIC DEFORMATION METHOD IN LIQUEFIABLE GROUND

In order to investigate the practical use of the seismic deformation method in liquefiable ground, the questionnaire was conducted for structural engineers. The following were concluded. The ground deformation was not considered for the secondary design in the lateral resistance of the pile foundation. There was a difference among structural engineers for the estimation of ground deformation and the reduction of soil reaction spring. A simple design method that is considered of the effect of ground deformation will be needed for aseismic design of the pile foundation.

Effect of local nonlinearity in cohesionless soil on optimal radius minimizing fixed-head pile bending by inertial and kinematic interactions

This study presents the effects of a local nonlinearity in cohesionless soil upon the optimal radius minimizing the bending strains of a vertical, cylindrical fixed-head pile embedded in a layered soil stratum in a soil–pile–structure system where the kinematic interaction dominates. The seismic deformation method (SDM) with discretized numerical models is applied since the SDM is a static numerical method that can easily consider realistic conditions of layered soil strata and the nonlinearity of the soil. In the numerical models, the local nonlinearity of the soil in the vicinity of the pile is represented by subgrade springs having bi-linear skeleton curves with a simple hysteretic loop. Various amplitudes of the lateral displacements of the soil and the lateral forces at the head of the pile are considered as numerical parameters. The results of parametric analyses reveal the presence of an optimal pile radius that locally minimizes the bending strains of the piles under strong nonlinearity of the soil, and the optimal pile radius tends to increase as the degree of nonlinearity increases. Criteria are presented for predicting the increment in the optimal radius of soil–pile–structure systems under strong nonlinearity in the soil.

LATERAL RESISTANCE OF PILE FOUNDATION DURING SOIL LIQUEFACTION ESTIMATED BY CENTRIFUGE AND BLIND TESTS

Blind tests by seismic deformation method, dynamic analysis using 2D-finite element method, and dynamic one using Penzien model were performed to centrifuge test of lateral resistance of pile foundation during soil liquefaction. The test results showed that 1) the pile stresses estimated by seismic deformation method were larger than the observed ones, 2) the pile stresses estimated by 2D-finite element method and Penzien model were different from each other, because of differences between the deformation characteristics of the liquefiable soil models, 3) it was effective in improvement of analysis precision, to take into consideration fixation degree of the pile head.

LATERAL RESISTANCE OF PILE FOUNDATION ESTIMATED BY CENTRIFUGE AND BLIND TESTS ON SOFT GROUND

The centrifugal model test with the soil-pile-structure system was performed for the dry Toyoura sand layer. In order to investigate the applicability of the seismic deformation method and the Chang equation as the prediction method, the pile response was estimated before the test. The time history response analysis was also carried out. The analysis result was compared with the test. It was found that it may be better to take into consideration the ground displacement caused to an earthquake for evaluation of pile response on the non-liquefying ground.

EVALUATION OF THE RESPONSE OF A PILE FOR SEISMIC DESIGN CONSIDERING SOIL-STRUCTURE INTERACTION

An evaluation method of the response of a pile due to an earthquake for the seismic design of medium-rise buildings is investigated based on the analysis with a three dimensional frame model considering soil-structure interaction. The effect of embedment of a structure on a story shear forces, the seismic coefficient for the foundation and the pile response are examined first. The effect of inertial and kinematic interactions on the pile stresses is then evaluated by the so-called seismic deformation method that is frequently used to estimate the response of piles in the practical design. Finally, the effective method for superposing pile response due to inertial and kinematic interaction are discussed.

Introduction to Dr. Okubo's Paper Entitled "Aseismic Considerations of Transportation Systems"

Damage to underground water pipes can be traced back to the 1923 Kanto earthquake, and it was well recognized from the early days that seismic effect was important in the construction of underground structures. It was not known, however, how seismic effect could be included in the design and construction of underground structures. In the late 1960s, field measurements and shaking table experiments gradually showed that ground deformation developed during an earthquake induced deformation in underground structures. This finding led to the development of new seismic design for underground structures embedded in subsurface ground. This was first designated as the “seismic deformation method” when the “new seismic design method” was developed as the final accomplishment in a five-year research project by the Ministry of Construction in 1977. In the 1960s and 1970s, Dr. Okubo took the leadership in developing seismic design methods for underground tunnels, pipelines, and bridges. Transportation of aviation petroleum was a critical requirement for the new Narita International Airport. Because no alternatives for transporting aviation petroleum other than pipeline embedded under national roads were possible in congested urban areas, it was important to protect pipelines and roads against seismic effects. When the law for petroleum pipelines went into effect, a seismic design method for petroleum pipelines was included in the notice on technical detailing on petroleum pipelines in 1973. This was the first mandated requirement for underground structures in seismic effects. Subsequently, seismic design based on the seismic deformation method has been extensively used for underground structures. Dr. Toshio Iwasaki, head of the Ground Vibration Division of the Public Works Research Institute of the Ministry of Construction at that time named this method the “seismic deformation method.” The author, a researcher of the Ground Vibration Division at the time, proposed calling it the “deformation method.” Because “deformation method” was widely used in computational structural analysis, Dr. Iwasaki suggested adding “seismic” to “deformation method.” As shown in his paper, Dr. Okubo contributed greatly to clarifying the failure mechanism of seismic damage, and compiled technical knowledge on seismic effect in various design codes. His interest extended beyond underground structures to bridges, roads, and dams. He expanded the foundation of seismic design of civil infrastructures in the early days of earthquake engineering.

Seismic Analysis of Underground Structures

A review on the seismic behavior and design of underground structures in soft ground is described focusing on the development of equivalent static seismic design called the seismic deformation method. Seismic isolation of underground structures is also presented.

A STUDY ON SEISMIC ANALYSIS METHODS IN THE CROSS SECTION OF UNDERGROUND STRUCTURES USING STATIC FINITE ELEMENT METHOD

Based on the dynamic substructure technique, the author proposes a static seismic analysis method, the Ground Response Method, for underground structures modeled on the structure and surrounding soil that is expressed using finite elements. By comparing existing static seismic analysis methods, it is verified that the Ground Response Acceleration Method for Buried Structures provides results almost equivalent to those obtained from the Ground Response Method. However, the FEM Seismic Deformation Method yields different results. Thus, the author proposes a new seismic load that is equivalent to seismic ground strains and modifies the FEM Seismic Deformation Method.

LIQUEFACTION AND PILED FOUNDATIONS: SOME ISSUES

Selected case histories recording the behaviour of piled foundations in lateral-spreading fields are reviewed. From these observations and from laboratory experiments in the centrifuge and on the shaking table, it is clear that the resistance of liquefied soil is very small and that the critical points for a pile are at the bottom as well as near the top of the liquefied layer. It is also apparent that liquefaction does not-occur until a significant threshold level of shaking is exceeded, and that even then it does not occur instantaneously. Thus damaging motions can be felt by the pile and transmitted to the superstructure before liquefaction and lateral spreading occurs. There is a critical period early in the shaking when the soil has softened enough for ground motion to be amplified but is still stiff enough to induce large bending moments in the pile, near the top of the liquefiable layer. Liquefaction is certainly not a dependable base-isolation mechanism. A controversial issue concerns the continuity or localisation of displacement within the liquefied layer. There is evidence that, in the majority of cases, displacement within the liquefied layer is continuous with depth; although when a sufficiently impermeable layer overlies the liquefiable one, a layer of free water can accumulate and localise displacement. Another old controversy, which now seems to be resolved, concerns the generation of passive earth pressures in non-liquefiable surface layers. There is clear field and laboratory evidence for the development of the passive state in superficial layers. For use in everyrday design, two simple methods of analysis have recently emerged. They are the earth pressure method and the seismic deformation method. They have been calibrated against the Kobe data and appear to work well in the few cases where they have been checked on other soils. It remains for them to be verified against a broader range of soils and for further soil-spring models.

Verifying adequacy of the seismic deformation method by using real examples of earthquake damage

In a seismic design, the dynamic loads are generally dependent on the inertial interaction caused by earthquake. But for the foundations embedded in soil, the dynamic loads are influenced by both the inertial and kinematic interactions among superstructure, foundation and soil. Especially, when a foundation is embedded in soft surface ground, the effects due to the kinematic interaction increase and should be considered in seismic design. For this reason, a method called seismic deformation method (SDM), which is suitable for an intensive earthquake motion (level 2 earthquake motion), has been stipulated recently in a new design code called Seismic Design Code for railway structures (the Railway Code, drawn up by Railway Technical Research Institute, Japan, 1999) [Railway Technical Research Institute. Seismic Design Code for railway structures. Tokyo: Maruzen; 1999]. In order to grasp the suitability of the SDM to actual structures, pile foundations, which experienced the Hyogoken-Nanbu earthquake, were taken as the objects for investigations. Comparison studies between the SDM analysis and reconnaissance were conducted. As a result, the adequacy of the SDM to actual foundations was confirmed to prove good agreement between the two results from the viewpoint of engineering practice. In addition, determination of indices for seismic-performance evaluation and speculation of damage mechanism of the foundations are also discussed in this paper.