Elasto-plastic Time-history Analysis Research Articles

Multi-level fortification strategies for double-tower cable-stayed bridges with safe-belt devices

While the current seismic fortification standards for cable-stayed bridges have been established, determining the return periods and fortification objectives remains insufficient. This study introduces a multi-level seismic fortification objective for cable-stayed bridges with safe-belt devices. The safe-belt device protects the primary components and enables transfers to the restraint system based on varying seismic requirements. For this investigation, a double-tower cable-stayed bridge was chosen as the case study. Three finite element models with varying structural configurations were developed. Subsequently, an elastoplastic time-history analysis was performed under four levels of seismic excitation across different site categories. The results indicate that the primary structures of traditional cable-stayed bridges, specifically the towers and lower crossbeams, are vulnerable to severe damage during extremely rare earthquakes. Incorporating safe-belt devices in a double-tower cable-stayed bridge effectively reduces the internal forces exerted on the primary structures by utilizing the combined action of the dual towers, thereby preventing severe damage. Additionally, these devices allow for controlled girder-end displacement until their capacity is reached. This double-tower cable-stayed bridge successfully meets the multi-level seismic fortification objectives and satisfies the performance requirements at each level.

Conservativeness Study on the Seismic Analysis Method for Research Reactor Plant Structure Based on TMSR-LF1

The seismic performance analysis of research reactor plants is crucial for ensuring the safety of the entire reactor system. This paper analyzes the plant structure seismic performance of the 2WMt Thorium Molten Salt Reactor-Liquid Fuel 1 (TMSR-LF1) at the Shanghai Institute of Applied Physics, Chinese Academy of Sciences under the action of frequent earthquakes, fortification earthquakes, and rare earthquakes was analyzed by finite element software PKPM based on the seismic design method of civil code +1°. On this basis, a comparison was made between the seismic responses of structural pushover analysis and elastoplastic time history analysis under the action of rare earthquakes, and the conservatism of these two commonly used methods for elastoplastic analysis was systematically analyzed. The results indicate that the TMSR-LF1 plant structure exhibits well bearing and deformation capacity. It meets the seismic design goal of “no damage under small earthquakes,” “no unrepairable damage under medium earthquakes,” and “no collapse under large earthquakes (using static pushover analysis),” and the critical regions are entirely within the elastic range. Furthermore, the analysis reveals that the elastoplastic time history analysis method produced a significantly higher seismic response than the pushover analysis method, which indicates the conservativeness of the time history method. Therefore, it is recommended to use the elastoplastic time history analysis method to evaluate the seismic performance of research reactor plants under rare earthquake actions. The research in this paper provides important references for the seismic performance analysis of other Class II research reactor plants.

Seismic Performance Assessment of Composite Frame–High-Strength Steel Plate Wall Core Tube Resilient Structural System

Against the backdrop of China’s continuous promotion of green and low-carbon transformation and the development of construction industrialization, high-strength composite structural systems have significant development prospects. However, their research and application in the field of construction are insufficient. In response to this issue, the study proposes a new high-performance structural system, namely the composite frame–high-strength steel plate wall core tube resilient structural system, which includes a core tube composed of double steel plate concrete composite shear walls and replaceable energy dissipation coupling beams, as well as composite frames. The highest strength grades of the steel plate and concrete used in the composite walls of the core tube are Q550 and C100, respectively. Using a 200 m building as an example, this study designs and establishes models for this high-performance structure and a conventional reinforced concrete frame–core tube structure. Subsequently, the dynamic elastoplastic time history analysis and seismic resilience assessment of structures are conducted under design basis earthquakes (DBEs), maximum considered earthquakes (MCEs), and extremely rare earthquakes (EREs). Research has shown that, compared to conventional structures, the thickness of shear walls of new high-performance structures can be effectively reduced, which helps decrease the self-weight of the structure and improve the available space in buildings. Additionally, high-performance structures exhibit a better performance in controlling the story drift ratio, lower plastic damage and overall stiffness degradation of the structure, and better seismic performance. The seismic resilience of the high-performance structure has been significantly enhanced, especially in terms of minimizing casualties, thereby better ensuring the safety of people’s lives and property.

Damage distribution mechanism of common low-rise steel frame structures

In order to research the damage distribution mechanism of common low-rise steel frame structures under dynamic action, this paper took the column-to-beam strength ratio αi and column base form as the main parameters to research the seismic performance of common low-rise steel frames. To achieve this goal, 24 models of common low-rise steel frame structures were designed and analyzed by elasto-plastic time history analysis method; and the predominant periods of seismic waves are similar to the fundamental periods of these models. This paper focuses on the demand performance of each model such as the distribution of maximum inter-story drift ratio (MIDR), the deformation concentration rate of the first floor dR1, the ductility ratio μ and cumulative plastic ductility ratio η of the beams and columns; and clarifies the relationship between the damage mechanism of common low-rise steel frame structures and column-beam strength ratio αi and column base form in the first place. After that, to investigate the effect of each parameter on the structural energy dissipation, the plastic deformation energy distribution of each model was also studied in this paper. Finally, the mathematical equations of the seismic input energy and plastic deformation energy were studied, which can apply to common low-rise steel frame structures in the resonant state. It can provide a reference for engineers to choose the column-to-beam strength ratio αi and the column base form in the design of low-rise steel frame structures.

Study on the seismic performance of prestressed steel-concrete vierendeel truss transfer story frame

Prestressed steel-reinforced-concrete (PSRC) Vierendeel truss transfer structures significantly increase the span of the transfer story and enhance the seismic performance with prestressing and steel-concrete techniques. A “three lines of defense” seismic design method was adopted in this study to further investigate the seismic performance of this structural system using the finite element software OpenSees to analyze the dynamic response of the PSRC Vierendeel truss transfer story spatial frame structure under an earthquake in the Intensity Region 8 (PGA = 400 Gal). To design four distinct PSRC Vierendeel truss transfer story frame structures, the number of bottom frame spans and the placement of the transfer truss were altered. An elastoplastic time-history analysis under a three-way rare earthquake was conducted by combining the quantitative control indices of the “three lines of defense” design method. The study shows that the PSRC Vierendeel truss transfer story structures designed by the “three lines of defense” seismic design method meet the requirements of the quantitative control indexes, and the structural seismic performance was satisfied.

Probabilistic seismic performance assessment of low-damage self-recovering prefabricated concrete frame subjected to near-field pulse-like earthquakes

The low-damage self-recovering prefabricated concrete (SRPC) frame using modular mild steel dampers is illustrated. Six low-cyclic repeated loading tests adopted 5 types of modular mild steel dampers were performed on the same fabricate joint specimen in turn. Based on the field test results and the displacement-based seismic design (DBSD) approach, a new SRPC deficient frame with four sizes of mild steel dampers are established, and elastoplastic time history analysis are conducted on four scenarios under near-field earthquakes respectively. To evaluate the collapse resistance of the new structure moduli designed in accordance with current design codes without considering the near-field earthquakes in the earthquake-prone regions, the probabilistic seismic performance assessments (i.e., hazard, fragility, risk) are conducted at the DBE and MCE earthquake levels under near-field ground motions. Annual and 50-year probability of exceedance (POE) results reflect that the new framework relieves the failed progression with a lower POE and meets the performance safety criteria under the near-field earthquakes. Furthermore, setting appropriate dimensions of mild steel dampers at the beam-column joints can effectively enhance the collapse resistance and whole safety of the new SRPC frame. This research will further promote the establishment of a reliable earthquake design method for new low-damage SRPC structures under near-field earthquakes.

Performance-Based seismic design and evaluation of out-of-code structure on Nanjing Financial City

The main scope of performance-based seismic design and evaluation study focuses more on the seismic performance of the simple structure or the regular structure, instead of out-of-code structure. The C1 tower in Nanjing Financial City is taken as an engineering case study. Many design indexes of the original design scheme of the structure exceed the requirements of the existing Chinese specifications, such as the height exceed the limits, the torsional irregularity, the partial floor slab discontinuity etc., which are summarized in detail in this paper. Then, several special structural design strategies are adopted to improve the overall seismic performance of this out-of-code structure. For example, multiple lines of seismic defences are set and the outrigger trusses are strengthened to solve the height overrun. For torsion irregularity, the influence of the bidirectional seismic torsion effect is considered in the calculation. Finally, according to the results of dynamic elastoplastic time history analysis under rare earthquakes, the seismic performances of the out-of-code structure are evaluated in detail. The analysis results show that the overall seismic performances of the structure are all within a reasonable range, and the seismic performance of the main components in the structure all meet the specification requirements.

Residual storey drift estimation of the MDOF system with the weak storey under seismic excitations using the BP network

This paper focuses on estimating residual storey drifts of multi-degree-of-freedom (MDOF) systems with the weak storey due to seismic excitations. According to the distribution of yield strength coefficients, MDOF systems are categorized into two types: a uniform MDOF system and a non-uniform MDOF system. Through elasto-plastic time history analysis, typical MDOF systems were analyzed considering the P-Δ effect under 60 earthquake records free of near-fault effects. The influences of various structural parameters on distribution characteristics of residual storey drifts along the height of the MDOF systems were investigated in detail. Finally, a back propagation (BP) network model was proposed to estimate residual storey drifts of the MDOF systems with the weak storey under seismic excitations. The results indicate that the maximum residual storey drift usually occurs at the weak storey for a non-uniform MDOF system while at the bottom for a uniform MDOF system. In addition, the larger the overall yield strength coefficient, the yield strength modification factor or the post-yield stiffness coefficient, the smaller the residual storey drift of the MDOF system on the whole. Moreover, the proposed BP model can sufficiently consider the parameters affecting residual storey drifts of the MDOF system with the weak storey, while having a good accuracy and a high efficiency in estimating the residual storey drifts.

Seismic and damping performance of frame-distributed rocking tubes-core tube structure

In order to improve the economical deficiency of the traditional frame-core tube (FCT) structure due to the large tube area proportion, a new high-rise structure of the frame-distributed tubes-core tube (FDCT) is proposed based on the design concept of the distributed tube. Combining the distributed tubes with the rocking system, the frame-distributed rocking tubes-core tube (FDRCT) is further proposed, which aims to solve the problem of insufficient seismic capacity of the FDCT structure due to the decrease of structural stiffness. Simplified dynamic models and equations of FDCT structure and FDRCT structure are established. Frequency domain dynamic analysis and ground motion random analysis are performed based on dynamics principles, which prove that the FDRCT structure can reduce the structural dynamic response. The elastic and elastoplastic time history analysis of the FCT structure, FDCT structure and FDRCT structure are carried out by finite element simulation. FDRCT structure can make the structure deformation uniform and reduce the acceleration response, but the top displacement increases. Compared with the beam ends hinged in the FDRCT structure, the inter-story drift ratio of the structure with the beam ends fixed decreases but the acceleration increases. Increasing the mass of the distributed rocking tubes can effectively improve the seismic and damping capacity of the FDRCT structure. According to the shaking table test and the economic analysis, it is evident that the FDRCT structure can not only improve the economy of the structure, but also have better seismic and damping performance.

Seismic performance of RC frame-shear wall structures with vertical setback

The reinforced concrete (RC) frame-shear wall structure is a typical structural system for modern high-rise buildings. This paper investigates the influence of vertical setback on its seismic performance through elasto-plastic time history analysis on three groups of models under different levels of earthquakes excitation. The studied variables include setback percentage, local lateral stiffness ratio and setback position, which cause vertical irregularity to the structure. It is confirmed that existence of setback increases the inter-storey drift ratio at the setback position due to the sudden change of lateral stiffness thereby. Compared to the structure without setback but having the similar local lateral stiffness, the maximum inter-storey drift ratio is smaller due to the reduced mass associated with the existence of setback. To quantify vertical irregularity, limitation on the local lateral stiffness ratio can be relaxed to some extent for structures with setback. Considering the resulted variation of inter-storey drift ratio, setback percentage and lateral stiffness ratio are equally important. Along the height, setback at the middle height gives larger inter-storey drift ratio and seismic force.

SHAKING TABLE TEST OF OFFSHORE WIND TURBINE SUPPORTING TOWER

At present, the wind power generation technology develops rapidly. As the main supporting structure of the wind turbine, the safety of the tower structure is very important under the action of earthquake. Since the behavior of this kind of tripod structure has not yet been investigated through shaking table test, a 1∶20 scaled model of offshore tripod supporting structure was tested through seismic shaking table. Subjected to a series of seismic ground motions with three peak acceleration levels of 0.3 g, 0.6 g and 0.9 g, the dynamic characteristics of the model structure and the seismic response were studied. Two support condition sceneries of the foundation for the test model were considered: with supports at 1.3 m high of each pile foundation, and removal of the supports (simulated pile foundation failure). Compared with the case with the foundation support, the dynamic acceleration response of the structure after the removal of the support was slightly reduced, and the decrease in the amplitude of peak acceleration in X and Y directions was 9.87% and 5.40%, respectively. In addition, finite element analysis by ABAQUS was performed to analyze the elastoplastic response of the structure, and the simulation results were compared with the test results. Good agreement was observed between the two results, which validates the results of both the finite element analysis and the shaking table test, and provides a reference for the elastoplastic time history analysis of the prototype structure.

Elastoplastic analysis of Kunshan Xintiandi super high-rise office building under earthquake

Kunshan Xintiandi Super Tall Building is 142 meters high, with 3 floors underground and 31 floors above ground. Its structural system is composed of concrete-filled steel tube frame and core tube. The elastoplastic time-history analysis of the building was carried out by using PKPM-SAWS to analyze the overall overall index of the whole structure under large earthquake, and the mechanical performance of the key components under large earthquake was analyzed, and the loss mechanism of the key components under large earthquake was obtained, so as to ensure the mechanical performance target of the super high-rise building under large earthquake are not bad.

Seismic Performance Analysis of Self-Centering Concentrically Braced Steel Frame Structures

To study the seismic performance of self-centering concentrically braced frame (SC-CBF) structure, the static elastoplastic analysis, low-cycle repeated loading analysis, and elastoplastic time-history analysis were conducted for a four-story SC-CBF structure, compared with the traditionally concentrically braced frame (CBF) structure. The influences of different GAP stiffnesses and cross-sectional areas of prestressed tendon were investigated on the self-centering and seismic performance of the SC-CBF structure. The results show that the SC-CBF structure has a strong lateral resistance, a small base shear under earthquake action, and a slight residual drift after unloading. The SC-CBF structure has a better ductility than the CBF structure. The displacement of the SC-CBF structure under the action of rare and extremely rare earthquakes is large, and the structure can dissipate more energy; the interstory drift is large, but the residual drift is small, exhibiting its ideal seismic and self-centering performance. However, the mechanical behavior of prestressed tendons is significantly affected by the stiffness of the GAP. The mechanical and seismic performances of the overall structure are slightly affected by the stiffness of the GAP, but the cross-sectional area of the prestressed tendons has a remarkable influence on the overall performance of the structure.

Investigation of seismic responses of reactor vessel and internals for beyond-design basis earthquake using elasto-plastic time history analysis

Existing elastic analysis methods cannot be adhered to in order to assess the structural integrity of a reactor vessel and internals for a beyond design basis earthquake. Elasto-plastic analysis methods are required, and the factors that affect the elasto-plastic behavior of reactor materials should be taken into account. In this study, a material behavior model was developed that considers the irradiation embrittlement effect, which affects the elasto-plastic behavior of the reactor material. This was used to perform the elasto-plastic time history analyses of the reactor vessel and its internals for beyond design basis earthquake. For this investigation, appropriate beyond design basis earthquakes and reliable finite element models were used. Based on the analysis results, consideration was given to the load reduction effect and the margin change. These were transferred to the internals due to the plastic deformation of the reactor vessel.

Research on Torsional Effect of Friction Pendulum Isolation Structure Based on Nonlinear Time History Analysis

A multi-layer irregular reinforced concrete frame structure in the 8-degree area is taken as the research object, and the working principle and hysteretic model of the friction pendulum bearing (FPB) are explained in detail. With the help of SAP2000 finite element software, a friction pendulum isolation model and its corresponding non-isolation model were established. Plastic hinge constitutive models were defined at both ends of the beams and columns of the RC frame structure, and 100 sets of two-way elastoplastic time history analysis of ground motion are carried out by using dynamic time history method. The results show that: under rare earthquakes, the seismic response of interlayer displacement, interlayer shear, interlayer torque and interlayer torsion angle of the structure after friction pendulum isolation is significantly reduced. Among them, the maximum torsional angle of the base-isolated structure is reduced by nearly 60% compared to the maximum inter-layer torsional angle of the non-isolated structure, and the torque of the first-layer base-isolated structure is reduced by nearly 74.1% compared to the torque of the non-isolated structure, which can prevent serious torsional damage under rare earthquakes and ensure the safety of the structure.

Structural selection and design analysis of a super high-rise office building

A super high-rise building, with a height of 238 meters, 4 floors underground and 50 floors above the ground, exceeds the Class B height limit of the specification, and belongs to an ultra-high over-limit structure. Through the selection of different structural systems, its structural system is determined as the frame core tube structure. This structure uses YJK, SATWE, PKPM-SAUSAGE for structural analysis, uses performance-based methods for seismic design, and the weak parts of the structure are strengthened accordingly. Structural analysis mainly includes elasticity analysis of small earthquakes, elastic time history analysis of small earthquakes, elastic and inflexion analysis of moderate earthquakes, inflexibility analysis of large earthquakes and elastoplastic time history analysis of large earthquakes.

Structural analysis of a Concrete supertall buildings

A high-rise building, with a height of 146 meters, 4 floors underground and 32 floors above the ground, is a Class B limit of the specification, and belongs to an ultra-high over-limit structure. Through the selection of different structural systems, its structural system is determined as the frame core tube structure. This structure uses YJK, SATWE, PKPM-SAUSAGE for structural analysis, uses performance-based methods for seismic design, and the weak parts of the structure are strengthened accordingly. Structural analysis mainly includes elasticity analysis of small earthquakes, elastic time history analysis of small earthquakes, elastic and inflexion analysis of moderate earthquakes, inflexibility analysis of large earthquakes and elastoplastic time history analysis of large earthquakes.

Study on seismic performance of steel frame with archaized-style under pseudo-dynamic loading

This paper presents an experimental study on a 1/2 scale steel frame with archaized-style under the pseudo-dynamic loading. Four seismic waves, including El Centro wave, Taft wave, Lanzhou wave and Wenchuan wave, were input during the test. The hysteresis characteristic, energy dissipation acceleration response, displacement response, strength, stiffness and strain were analyzed. Based on the experiment, the elastoplastic dynamic time-history analysis was carried out with the software ABAQUS. The stress distribution and failure mode were obtained. The results indicate that the steel frame with archaized-style was in elastic stage when the peak acceleration of input wave was no more than 400 gal. Under Wenchuan wave with peak acceleration of 620 gal, the steel frame enters into the elastoplastic stage, the maximum inter-story drift was 1/203 and the bearing capacity still tended to increase. During the loading process, Dou-Gong yielded first and played the role of the first seismic fortification line, and then beam ends and column bottom ends yielded in turn. The steel frame with archaized-style has good seismic performance and meets the seismic design requirement of Chinese code.

Hysteretic Behavior of Steel Reinforced Concrete Columns Based on Damage Analysis

With the aim to model the seismic behavior of steel reinforced concrete (SRC) frame columns, in this research, hysteresis and skeleton curves were obtained based on the damage test results of SRC frame columns under low cyclic repeat loading and the hysteretic behavior of the frame columns was further analyzed. Then, the skeleton curve and hysteresis loops were further simplified. The simplified skeleton curve model was obtained through the corresponding feature points obtained by mechanical and regression analysis. The nonlinear combination seismic damage index, which was developed by the test results and can well reflect the effect of the loading path and the number of loading cycle of SRC frame columns, was used to establish the cyclic degradation index. The strength and stiffness degradation rule of the SRC frame columns was analyzed further by considering the effect of the accumulated damage caused by an earthquake. Finally, the hysteresis model of the SRC frame columns was established, and the specific hysteresis rules were given. The validity of the developed hysteresis model was verified by e comparison between the calculated results and the test results. The results showed that the model could describe the hysteresis characteristics of the SRC frame columns under cyclic loading and provide guidance for the elastoplastic time-history analysis of these structures.

Seismic Analysis of Steel Solid Web Girder-RC Tubular Column Hybrid Structure

This paper aims to investigate the seismic performance of a novel type of steel–concrete hybrid supporting structure consisting of reinforced concrete (RC) tubular columns, steel solid web girder platform, and A-shaped steel frames. It is typically used to house air-cooled condensers (ACC) in thermal power plants (TPPs). First, the finite-element (FE) model was implemented in ABAQUS and the simulation approaches were validated by pseudo-dynamic test results of a scaled steel-concrete hybrid supporting structure. Then, the elasto-plastic time-history analysis of the steel solid web girder-RC tubular column hybrid structure was conducted. The El Centro (NS) record was scaled to peak ground acceleration (PGA) of 0.07, 0.20, 0.40 and 0.62 g to reflect the frequent, basic, rare, and very rare earthquakes. The dynamic characteristics, base shear force, lateral deformation performance, stiffness deterioration, and damage evolution characteristics were analyzed. The numerical results showed that the first vibration mode of this hybrid structure is torsion, due to its small torsional stiffness and the nonuniform distribution characteristics of stiffness and mass in the vertical direction; the lateral deformation shape is shear mode; and the damage mainly occurred on the RC tubular columns, while the steel components did not yield under severe earthquakes. In general, the overall seismic performance of the steel solid web girder-RC tubular column hybrid structural system could meet the seismic design requirements with respect to the high-intensity earthquakes.