Design Basis Earthquake Research Articles

Seismic performance evaluation of fiber-reinforced prestressed concrete containments subject to earthquake ground motions

Given the unpredictability of the occurrence of the earthquake and other potential disasters into consideration, the nuclear power plant may be confronted with beyond design-basis earthquake load in the future. The containment structure may be severely damaged under such severe earthquake loading, increasing the risk of containment concrete cracking and potential radioactive materials leaking. Moreover, initial damage caused by the earthquake may significantly alter the pressure performance of the containment under follow-up internal pressure. To compromise the dangers of beyond design-basis earthquake to the containment, an alternative of replacing the conventional concrete with fiber-reinforced concrete (FRC) to upgrade the seismic resistance capacity of the containment is attempted and thoroughly researched. In this study, the influence of various fiber types such as rigid fiber and mixed fiber is regarded to constitute fiber-reinforced PCCVs. The physical properties of traditional and fiber-reinforced PCCVs under earthquake ground motions are scientifically compared and identified by using traditional and proposed evaluation indices. The results indicate that both the traditional evaluation index (i.e. top displacement, stress, strain) and the proposed damage index are greatly reduced by the practice of fiber strengthening under earthquake ground motions.

Parametric Investigation of Self-Centering Prestressed Concrete Frame Structures with Variable Friction Dampers

To enhance the structural stiffness and energy-dissipating capacity after the decompression of beam-to-column connections for self-centering prestressed concrete (SCPC) frames, this study presents the seismic performance of a new type of SCPC frame with variable friction dampers (VFDs). The structure is characterized by a third stiffness and a variable energy-dissipating capacity. A 5-story and an 8-story VFD-SCPC frame were selected as the analytical cases, and their numerical models were built based on OpenSees 3.3.0 finite-element software. Sixteen ground-motion records were selected as excitations for the analyses, and the influence of the second stiffness and the third stiffness for the VFD-SCPC connections, as well as the second activation for VFD, on the seismic performance of the structures, was studied. The results showed that increasing the stiffness (number) of prestressed strands and their distance to the center of the beam section can obviously increase the second stiffness of the structures, thus decreasing their displacement, while the distribution mode of inter-story drift along the building’s height cannot be changed. Increasing the third stiffness of the connections (the angle of slope sliding parts and the stiffness for the combination of disc springs) can effectively reduce the deformation of the structures under MCE (maximum-considered earthquakes) seismic levels and improve the energy-dissipation capacity of structures significantly. The premature secondary activation of VFD can enhance the loading capacity and energy-dissipation capacity of structures under both DBE (design-basis earthquakes) and MCE seismic levels, and reduce the inter-story drift of structures effectively.

Evaluation of slab–wall connections in tunnel form concrete structures: A multi-level approach based on seismic demand and capacity

The seismic performance of an integrated tunnel-form concrete system relies heavily on the performance of walls, considering the safe design of slabs and the substantial length of in-place connections. However, despite ensuring suitable seismic behavior for slabs and walls, the lateral load resistance of the system depends on the capacity of connections between them, which has not received adequate attention in the existing technical literature and prescriptive codes. To address this gap, the present study focuses on the comprehensive evaluation of slab–wall connections in tunnel-form concrete systems. By analyzing 5-story and 10-story models, it was consistently observed that connections at lower levels are more vulnerable. Using the demand approach and considering the design basis earthquake (with a maximum acceleration of 0.35 g and a return period of 475 years) as the input excitation, the system exhibited a reliable immediate occupancy performance level with an estimated reliability of 100%. However, in taller structures, connections were predicted to experience cracking with a maximum demand to capacity ratio of 1.1. Applying the capacity approach and considering the earthquake corresponding to the immediate occupancy performance level in the system as the input excitation, the system achieved a reliable life-safety performance level with an estimated reliability exceeding 79%. However, in more than half of the building height, connections were predicted to experience cracking with a maximum demand to capacity ratio of 2. The results demonstrate that the existing shear-friction capacity adequately meets the demand of cracked connections in both approaches. Nevertheless, an evaluation of the shear-friction capacity demand ratio reveals that connections are undeniably one of the primary weaknesses of the tunnel-form concrete system, especially as the structure’s height, torsional effects, earthquake intensity, or allowable damage level increases. Therefore, special detailing is necessary to address this vulnerability.

Seismic margin assessment of the real dynamic response of nuclear engineering structures based on the response envelope method

The accuracy of response calculations for nuclear structures is directly related to the reliability of margin assessment results. The seismic response envelope (SRE) method, which is more effective than the traditional mode decomposition response spectrum method, has received increasing attention in studies on structural dynamic responses in nuclear engineering. It is able to consider the characteristics of multiple seismic responses occurring simultaneously, but applying it to the seismic margin assessment of structures beyond design-basis earthquakes becomes a challenge and some practical issues remain unaddressed. Focusing on the characteristics of the seismic response spectrum and regularization of the coordinate system, this study derived an SRE concentric circle equation in the regular coordinate system and defined the seismic safety margin level. A seismic margin assessment strategy for nuclear shear wall structures was developed based on the relationship between the bearing capacity surface controlled by the reinforcement ratio and the concentric circle of the SRE. A comparison between the SRE method and other seismic analysis methods for multiple seismic response calculations verified the effectiveness of the proposed method. Moreover, in particular, the emphasis was on the variation characteristics of the seismic safety margin level considering discrete points under the new and old strategies, and the solution accuracy and efficiency of the proposed strategy were discussed. Finally, the SRE method was used to evaluate the seismic margin of a real nuclear engineering structure, providing reliable data support for the solution strategy in practice.

Numerical simulation and seismic performance analysis of sacrificial-energy dissipation beam-column joint

To enable secondary energy-dissipating components to actively attract and dissipate seismic energy, a new type of sacrificial-energy dissipation beam-column joint (SEDJ) was proposed for frame structures. During strong earthquakes, the post-yield strength of the SEDJ was actively weakened by the shear failure of the bolts, and the friction between the friction plates and metal plate ensured that the SEDJ could fully dissipate the seismic energy. Meanwhile, the adjacent column and beam components remained elastic after the earthquake, so as to achieve the purpose of protecting the main beam and column components. Based on finite element analysis of the SEDJ using a solid element model, the expected seismic performance of the SEDJ was verified through displacement-controlled monotonic and cyclic loading tests. The peak strength Fu and post-yield strength Fr of the SEDJ could be controlled by adjusting the shear strength of the bolts and the preload of the friction plate and metal plate connecting bolts. Furthermore, the effectiveness of the SEDJ was evaluated by applying it to a three-story steel frame structure, and a parametric analysis was conducted. The results indicate that appropriately and actively reducing the post-yield strength of the SEDJ, with Fr/Fu equal to 0.3, provides the most favorable effect on improving the plastic dissipation energy distribution of the beam and column components and reducing the damage to the bottom column under strong earthquakes. Meanwhile, the structure meets the requirements of inter-story drift under design basis earthquakes and the collapse resistance under maximal considered earthquakes. The SEDJ only requires the replacement of the bolts and friction plates after the earthquake. Therefore, this study can provide new ideas for designing seismic-resilient structures.

Design-condition-informed shear wall layout design based on graph neural networks

The construction industry, traditionally labor-intensive, has now been evolving towards automation and the incorporation of intelligence. Notably, the shear wall layout has been a critical component in structural construction, where neural networks have promoted the emergence of sophisticated design methods. These methods integrate graph neural networks (GNNs), successfully mitigating the computational resource demands and challenges in capturing the topological features, which are the impediments in pixel image-based methods. However, the existing GNN-based methods marginally accommodate structural design conditions and underperform in fulfilling practical engineering requirements. Specifically, these methods overlook influential factors such as the peak ground acceleration (PGA) of the design basis earthquake (DBE), characteristic ground period, and building height, all of which are crucial to the shear wall layout design. To address this research gap, this study proposes an innovative GNN-based design method that duly incorporates design conditions—including the PGA of the DBE, characteristic ground period, and building height—and rigorously evaluates its advantages over previous approaches. The findings confirm the efficiency and reliability of the proposed design-condition-informed method and highlight its capability to accurately correlate shear wall layouts with design conditions.

Design and analysis of LRB base-isolated building structure for multilevel performance targets

According to China's current code for the seismic design of buildings (GB50011-2010), in the course of designing base-isolated building structures, the isolation system and superstructure are designed separately. Hence, the horizontal seismic isolation coefficient in terms of the design-based earthquake (DBE) and horizontal deformation of the isolation system under the maximum considerable earthquake (MCE) cannot be considered simultaneously. Consequently, the optimum mechanical parameters for isolation bearing and the corresponding horizontal seismic isolation coefficient used in the seismic design of the superstructure cannot be obtained. To address these shortcomings, we propose an optimum seismic design procedure for LRB base-isolated building structures to meet multilevel performance fortification criteria, where explicit mathematical formulations for horizontal seismic isolation coefficients and the horizontal deformation of isolation systems in terms of the mechanical parameters of the LRB isolation system are established by combining equivalent linearization and modal decomposition response spectrum methods. Through a parametric study, we find the critical yield strength ratio, i.e., the ratio of the yielding shear of lead core to the total weight of the LRB base-isolated structure, which leads to the minimal value of the horizontal seismic isolation coefficient. Beyond this critical yield strength ratio, an optimum solution is unavailable, as the horizontal seismic isolation coefficient and horizontal displacement of the isolation system are of a conflicting nature. By converting the multi-criterion formulation into an auxiliary problem with a scalar objective, the optimum design method of an LRB base-isolated building structure oriented to multilevel performance fortification criteria is proposed, so as to obtain the optimum yield strength ratio and the optimum second shape coefficient for the seismic design of the superstructure. A numerical example demonstrates that the seismic horizontal seismic isolation coefficient and maximum horizontal displacement of the isolation system calculated from the optimum yield strength ratio and the optimum second shape coefficient agree well with the results from the time-history method. In a comparative study, LRB base-isolated building structures designed by the critical yield strength ratio, the optimum yield strength ratio and the optimum second shape coefficient, the optimum yield strength ratio and the corresponding fixed-base superstructure are subjected to MCE and mega earthquakes, where the LRB base-isolated structure shows good seismic performance in terms of the optimum yield strength ratio, even when subjected to mega earthquakes.

Modelling of non-structural components of an industrial multi-storey frame for seismic risk assessment

Seismic risk assessment of industrial facilities is complex due to the presence of different types of equipment. It represents a research issue that requires further investigation. To this end, some analytical approaches have been developed in the framework of performance-based earthquake engineering. Nonetheless, their accuracy in the case of complex critical facilities, such as nuclear and non-nuclear industrial plants, is still under investigation. Thus, the proposed study intends to research in depth, in a risk assessment framework, some critical aspects related to: (1) modelling of industrial facilities and their secondary equipment with different degrees of accuracy, also taking into account their dynamic interaction; (2) selection of seismic records for fragility analysis, due to the narrow distribution of frequency values for non-structural components; (3) effectiveness of performance-based earthquake engineering applied to this particular class of coupled structure-equipment for risk assessment. In this context, the proper selection of seismic records becomes relevant, and SCoRes, an innovative algorithm for accelerograms selection is worthy of investigation. On these premises, two different configurations of a primary industrial structure, i.e. a moment resisting frame and a braced frame, equipped with non-structural components and subjected to shake table test campaigns are selected as case studies. For the two configurations, a vulnerability assessment of two vertical tanks installed on the first floor was carried out. Along these lines, to establish the effectiveness of the proposed method for both the moment resisting frame and braced frame configurations, the mean annual frequency of exceedance of the bottom-wall strain of the above-mentioned tanks, both at the design basis and safe shutdown earthquake has been evaluated.

Gravity framing and composite action effects on residual drifts of steel SMFs

In this study, the effects of gravity framing and composite action on the residual drift performance of steel special moment frames (SMFs) are investigated. Four steel structures including 4-, 8-, 12-, and 20-story SMFs are selected, and nonlinear models are created by considering the effects of gravity framing and composite action and neglecting these effects. Nonlinear dynamic analyses are performed on the structures subjected to the design basis earthquake (DBE) level ground motions. Under the DBE hazard level, accounting for the effects of gravity framing and composite action can reduce the maximum of median residual interstory drift ratios between 32% and 74%, when compared with that obtained by neglecting these effects. Incremental dynamic analyses are performed on the structures assuming the maximum residual interstory drift ratio (MRD) as the engineering demand parameter and four MRD limit states of 0.2%, 0.5%, 1.0%, and 2.0% to assess the residual drift performance of the structures in a probabilistic framework. The results show that considering the effects of gravity framing and composite action leads to significant decreases in the mean annual frequencies of exceeding different MRD limit states (i.e., λMRD values). These effects have the lowest impact on the λMRD values when the MRD is 0.2%. However, they have the highest impact on the λMRD values when the MRD is 1.0%.

A seismic resilient design method for structures equipped with two-level yielding dampers, accounting for extremely rare earthquakes

Current design methods for achieving seismic resilience of structures are limited to hazard levels of service level earthquake, design-based earthquake and maximum considered earthquake, but they do not account for the risk of extremely rare earthquake (ERE) that poses a significant challenge to structural and human safety. To address this issue, this paper proposes a new seismic resilient design method that considers ERE by incorporating two-level yielding dampers as the primary structural fuse while satisfying the performance objectives of all four seismic hazard levels. The paper presents a detailed derivation of the proposed design method and outlines a step-by-step design procedure. The proposed design method is applied to a seismic resilient system called the two-level yielding beam linked steel frame system (TYBLSFS), and two TYBLSFSs with three and six stories are designed and numerically modeled. Nonlinear dynamic analyses are then conducted to validate the effectiveness of the proposed design method. The results show that the two TYBLSFSs achieve the designed targets of roof drift ratio (RDR) and inter-story drift ratio (ISDR) and that the RDR-base shear curves obtained from the dynamic analyses match the design curves. The predetermined yielding mechanism and anticipated performance goals for all four seismic levels have been achieved. And the presented TYBLSFS can be effectively utilized as a seismic resilient system against very strong earthquakes.

Global method for nonlinear seismic analysis of embedded base-isolated nuclear island buildings in layered sites

Owing to the increasing scarcity of high-quality sites, the seismic analysis of base-isolated nuclear power plants (NPPs) under complex non-lithology sites has gained important engineering significance. In this study, a global method for nonlinear numerical analysis was developed for the seismic evaluation of base-isolated NPPs in complex layered sites. The seismic analysis of layered sites is realised using the equivalent linear method and one-dimensional wave propagation theory, the radiation damping of the infinite domain is modelled with a visco-elastic artificial boundary, and the nonlinear behaviour of the isolators is fully considered using a bilinear hysteretic model. Using this method, the influence of soil–structure interaction (SSI) and soil nonlinearity on the behaviour of base-isolated NPPs under the design basis earthquake and beyond design basis earthquake was analysed and compared, in terms of the floor response spectra (FRS) and inter-story displacement angle. In addition, the influence of embedment is also studied. The results show that in layered sites, the SSI significantly amplifies the response values for base-isolated NPPs, and as the ground motion input increases, the soil nonlinearity more effectively inhibits the response of base-isolated NPPs. In addition, embedding can significantly reduce the response, but it increases the FRS at some frequency domains. The isolation effect of base-isolated NPPs decreases significantly when SSI effects are considered, and the soil nonlinearity and embedment have little impact on the base isolation capacity. The method proposed in this study can be easily applied to study base-isolated NPPs in layered sites.

3D nelinearna seizmička analiza i projektiranje izoliranih zgrada pri gibanjima tla s plitkim žarištem

The structural performance of base-isolated buildings during past earthquakes confirmed the suitability of Lead Rubber Bearing (LRB) isolators. To assess the effectiveness of such isolators, 3D base-fixed and associated base-isolated models of a multi-story building are performed for three components recorded at each of the three stations with the closest distances to the seismic fault of approximately 5.54, 11.39, and 17.82 km during the 6.7 Mw Northridge earthquake in 1994. In this study, we discuss important issues regarding the analysis and design of base-isolated buildings under near-field ground motions at both the Design Basis Earthquake (DBE) and Maximum Capable Earthquake (MCE) levels. The results demonstrate that although the shear strain and stability conditions are fulfilled, it is crucial to satisfy the rollout condition requirements because of the large isolator displacement at MCE level while utilising supplemental viscous dampers to improve the desired efficiency of isolation.

Seismic design parameters (R, Cd, and Ω0) for uncoupled composite plate shear walls−concrete filled (C‐PSW/CF)

AbstractComposite Plate Shear Walls−Concrete Filled (C‐PSW/CF) are an innovative seismic force resisting system recently adapted for building applications. The walls consist of parallel steel faceplates connected with tie bars and filled with concrete. This paper summarizes the results of a recent FEMA P695 study completed to verify seismic design parameters for uncoupled C‐PSW/CFs with rectangular flange plate boundary elements. Seven archetype structures were: (i) designed, (ii) modeled using a benchmarked fiber‐based finite element analysis approach, (iii) subjected to nonlinear pushover analysis, (iv) and to incremental nonlinear dynamic analysis to failure for 22‐sets of scaled ground motions, and (v) the results were statistically analyzed to assess performance. These structures ranged from three (3) to twenty‐two (22) stories and included both planar and C‐shaped configurations. As part of this design process, recommendations for stiffness approximations for linear analysis of C‐PSW/CFs were developed. Additionally, these nonlinear incremental dynamic analysis results were post‐processed to determine the rotation and strain demands at the base of these structures at the design basis, maximum considered, and failure level earthquakes. These results showed that the rotation and strain demand at failure level earthquakes were comparable regardless of the ground motion. Ultimately, this FEMA P695 approach verified the R factor of 6.5, Cd factor of 5.5, and Ω0 of 2.5 for C‐PSW/CFs with boundary elements.

Life‐cycle benefits estimation for hybrid seismic‐resistant self‐centering braced frames

AbstractThe hybrid self‐centering braced frames (HSBFs) with shape memory alloy‐based braces (SMABs) and viscous dampers (VDs) are an emerging structural system developed for improving the seismic resilience of traditional braced frames (e.g., buckling restrained braced frames [BRBFs]) and self‐centering braced frames (SCBFs) by reducing residual inter‐story drifts (RIDs) and floor acceleration responses simultaneously. Nevertheless, the excellent performance of HSBFs is captured by introducing high initial construction costs. This paper aims to highlight the benefits of HSBFs compared with BRBFs and SCBFs by investigating the earthquake‐induced life‐cycle costs. To this end, 6‐story BRBF, SCBF, and HSBF are designed separately to achieve the same maximum inter‐story drifts under design basis earthquakes (DBE) for a fair comparison. The advanced numerical models of the considered systems were developed, and nonlinear dynamic analyses were conducted to obtain the structural seismic responses under various intensities. Monte Carlo simulation (MCS) was adopted for considering the modeling uncertainty. The life‐cycle costs were subsequently estimated based on the revised HAZUS loss estimation method. The influence of RIDs, initial construction costs of SMABs and VDs, and values of contents inside buildings were comprehensively investigated. It has been found that HSBF can achieve better performance in reducing seismic loss than BRBF and SCBF due to its excellent capability of controlling structural and nonstructural damage. SCBF may show higher seismic loss than BRBFs, given high RID limits for demolition or high building contents’ value, highlighting the importance of controlling floor acceleration responses of SCBFs. The life‐cycle benefits of BRBFs, SCBFs, and HSBFs are highly influenced by the RIDs, initial construction costs of SMABs and VDs, building contents’ values, and building's lifetime. HSBFs show better life‐cycle benefits than SCBFs when the building's lifetime is not lower than 50 years. Compared to BRBF, the life‐cycle cost effectiveness of SCBF can be only achieved when the initial cost of SMABs is lower than 1.21 times that of BRBs for the building with 50 years’ lifetime; the life‐cycle cost effectiveness of HSBF6 can be only achieved when the initial cost of SMABs or VDs is lower than 1.84 times that of BRBs for the building with 50 years’ lifetime. It has been concluded that reducing the initial costs of SMABs and VDs is critical and essential for increasing the life‐cycle economic benefits of SCBFs and HSBFs and promoting their real‐world applications.

Seismic design and performance study of self‐centering moment‐resisting frames with sliding rocking beams and preloaded disc springs

AbstractThis paper focuses on the seismic analysis and performance assessment of the self‐centering moment‐resisting frames with sliding rocking beams (SCMRF‐SRB) through a nonlinear numerical simulation study. In the SCMRF‐SRB systems, the beam is comprised of three segments with the rocking beam placed in the middle segment. The beam growth (expansion) problem due to the gap‐opening in the rocking joint is counteracted by the sliding movement of the rocking beam inside the beam brackets. The restoring force of such SCMRF‐SRBs is generated by two sets of preloaded disc springs mounted on each side of the web of the beam and the energy dissipation is provided by replaceable hysteretic dampers (RHD). The relative movement of the rocking beam inside the brackets generates a friction force that contributes to the energy dissipation capacity and strength of the system based on prior experimental observations. Load vs. displacement relationships of an SCMRF‐SRB modular structure were formulated and verified with nonlinear finite element analysis results. A three‐story building located in downtown Seattle was designed and its seismic performance was studied through nonlinear static and dynamic analyses. According to the results of the nonlinear dynamic analyses, the prototype structure met the expected performance criteria in terms of inter‐story drift ratio (IDR), re‐centering behavior, and responses of the frame member at design basis earthquake (DBE). In different parametric studies, the effect of the length and location of the rocking beam on the seismic performance of the prototype structure was investigated. Moreover, the effects of the energy dissipation capacity and post‐yielding stiffness on the structural responses of the prototype buildings were studied. It was also shown that an SCMRF‐SRB structure with a large energy dissipation ratio of up to 90% can be utilized without adversely affecting the self‐centering performance of the system.

Experimental study on low-damage performance of Sliding Hinge Joint

The Sliding Hinge Joint (SHJ) is a low damage beam-to-column joint primarily for moment resisting steel frames (MRSFs). It is intended to remain rigid during frequent earthquake events, while rotation occurs between the column and beam under design basis earthquake events. At the end of earthquake events, the joint is expected to seize up and become rigid again. However, residual strength and stiffness of the SHJ are considerably reduced even within design-level sliding. The objective of this study is to evaluate resilience and repairability of the SHJ by carrying out cyclic loading on a full-scale beam-to-column assembly considering both design-level sliding and post design-level sliding. Overall, the SHJ exhibited a predictable and stable hysteretic response. It was concluded that the SHJ experienced a 79.5% decrease in average moment resistance and a 59.4% decrease in elastic rotational stiffness with no repair actions taken. Resilience of the joint could be achieved by replacing and retightening the asymmetric friction connection (AFC) bolts to bring the joint back to an as-built condition. Moreover, a detailed finite element model was developed to further investigate the plastic strain distribution, frictional sliding and energy dissipation behaviours of the joint, and the low-damage performance was verified. Finally, a simplified analytical model based on the component method was proposed to predict the joint behaviour.

Probability-Based City-Scale Risk Assessment of Passengers Trapped in Elevators under Earthquakes

An accurate prediction of the number of passengers trapped in elevators under earthquakes in urban areas is essential for promoting earthquake emergencies. A probability-based city-scale method for assessing the earthquake-induced risk of passenger entrapment in elevators was proposed, in which city-scale time history analysis was performed to simulate the seismic response of building clusters, and the Monte Carlo simulation was conducted to consider the uncertainty of multiple factors, including the mechanical properties of buildings and elevators, the elevator story position, and the spatiotemporal nature of elevator traffics. A case study of the Tsinghua University campus was performed to demonstrate the practicability of the method. The results show that the number of trapped passengers when an earthquake occurs during the off-peak hours of elevator traffic is approximately a quarter of that when the earthquake occurs at 8:00. The maximum number of trapped passengers under the maximum considered earthquake reaches 195, approximately five times that under the design basis earthquake. This study fills a gap in the research on city-scale earthquake-induced passenger entrapment risk. The proposed method can be used to perform both scenario- and intensity-based assessments, thereby having the potential to facilitate virtual rescuer drills and earthquake emergency plans.

Seismic Performance Comparison of Hybrid, Isolation, and Damping Control Structures through 1/2-Scale Shaking Table Tests Based on Chinese Standard

A hybrid control structure (HCS) using seismic isolation at the base and energy dissipating cladding panel system (EDCPS) in the superstructure was proposed to realize enhanced seismic performance objectives of the main structure and nonstructural walls. To verify the feasibility of the HCS and validate its advantages in controlling the damage of structures compared with a seismic isolation structure (SIS) and a damping structure (DS), 1/2-scale shaking table tests were conducted on a HCS, an SIS, and a DS designed based on Chinese Standard. The seismic performance of the three damage control structures under different earthquake levels and ground motions (i.e., normal and velocity pulse-type ground motions) were investigated, including the damage characteristic, global responses, and isolator and damper behaviors. The test results indicated that the HCS provided the best control effect and remained elastic under the maximum considered earthquake (MCE). In contrast, slight and moderate damage were observed in the main structures of the SIS and DS under the MCE, respectively. Under the service level earthquake, the seismic response of the HCS was similar to or even greater than that of the SIS. While under the design basis earthquake and MCE, the U-shaped steel dampers in the HCS yielded and partially dissipated the earthquake energy; thus, this resulted in an obvious reduction in the drift ratio compared with that of the SIS. No damage to the cladding panels was observed in the HCS and DS, which indicated that the EDCPS was effective in controlling damage to the panels. In addition, a velocity-pulse type ground motion and the peak ground velocity significantly influenced the seismic responses of the HCS, SIS, and DS, particularly under the MCE.

Hybrid Test of Precast Concrete Frame with Energy-Dissipation Cladding Panel System

To investigate the influence of an energy-dissipation cladding panel system (EDCPS) on the dynamic responses of a precast concrete (PC) frame structure, a six-story, three-span planar frame structure with an EDCPS (called “damping structure”) and a counterpart planar bare frame structure (called “bare frame structure”) were designed. The middle span and bottom two stories of the frame were selected as the test substructures, whereas the rest were considered using the numerical substructure. Hybrid tests were conducted on the two structures under four earthquake levels. The test results indicated that the damage evolution characteristics of the PC frame were not affected by the introduction of EDCPS. The dampers in the EDCPS successfully yielded and dissipated seismic energy under the four earthquake levels. Moreover, the maximum inter-story drift ratio of the damping structure was reduced by 12.59%, 17.68%, and 10.34% under the design-basis earthquake, maximum considered earthquake, and very rare earthquake, respectively, exhibiting a satisfactory damage-control effect. The cladding panels remained intact under the four earthquake levels, indicating that this structure effectively prevents damage to the cladding panels. Finally, a numerical simulation method is recommended according to the damage characteristics of the damping structure and is validated against the test data.

Evaluation of seismic margins for nuclear power plant piping systems using ratcheting criterion

In the wake of recent beyond design basis earthquakes, it is very essential to evaluate seismic margins of nuclear power plant piping systems. Better seismic margins will ensure the safety in the event of less probable bigger seismic event beyond consideration of design level. At present, permissible codal stress limits are used to evaluate these margins and it has been experimentally demonstrated that ratcheting is the significant failure mode for piping systems subjected to reversing dynamic load. Hence, it is more prudent to use actual failure criterion for evaluation of seismic margins. In this paper, a detailed framework is provided for evaluation of seismic margins of piping systems using ratcheting criterion. As ratcheting is the potential mode of failure for piping systems under earthquake load, two strain-based performance levels based on code practice and experience gained with experiments carried out by Bhabha Atomic Research Centre, are used for margin assessment. It is usual practice to carry out stress-based response spectrum analysis for design and qualification of piping systems under earthquake load. In order to offer a practical, simpler and feasible solution for ratcheting evaluation, the same response spectrum analysis in iterative way, can be used to evaluate ratcheting in the piping systems. Experimentally validated numerical procedure is used for ratcheting evaluation. This procedure is demonstrated for a piping system of a typical nuclear power plant. Seismic margins for the piping system are evaluated using codal provision and two ratcheting based performance levels for deterministic and probabilistic methods.