Design Basis Earthquake Research Articles

Seismic dynamic analysis and structural integrity assessment of the PWR spent fuel pool under beyond design basis earthquake

A series of numerical analyses were carried out to assess the safety of spent fuel pool (SFP) of a pressurized water reactor (PWR) power plant in Taiwan. These analyses performed seismic force evaluation and 3D nonlinear finite element analysis (FEA) for the SFP under beyond design basis earthquake (BDBE). In addition, this study considered various in-structural response spectra (ISRS) with various damping ratios and the reduced factors to account for the partial cracking effects from BDBE. In the seismic force evaluation, the results show that the pool base takes the greatest uniform equivalent loading resulted from the cooling water, racks, and spent fuel components. For the walls, the south wall suffers the greatest equivalent force. The results of 3D FEA indicated that the largest values of stress and strain appear at the bottom corner near south wall of the channel between the main pool and cask loading pit for the overall SFP structure. It is also found that the influences of cracking effects on the seismic force calculation and structural analysis are significant. But comparing the results of numerical analysis by 5% damping ratio with 0.7 reduced factor and 10% damping ratio with 0.5 reduced factor, the impacts on the liner of the SFP are insignificant. Because the cooling water leakage depends on the liner failure, the influence on the leakage is small.

Seismic vibration control of novel prefabricated industrial equipment suspension structures with tuned mass damper

This paper presents a full-scale shaking table test on a novel prefabricated steel moment resisting frame (MRF) with tuned mass damper (TMD) for the purpose of seismic vibration control. The seismic performance of three structural models, i.e., uncontrolled MRF (UCMRF), MRF with undamped TMD (MRF-UDTMD), and MRF with damped TMD (MRF-DTMD), is examined under different seismic intensities. Numerical models for the three systems are developed and validated through the shaking table test. An important finding from the study is that resonance and violent vibrations occurred in the UCMRF and MRF-UDTMD due to the low damping ratio and lack of energy dissipation sources, whereas the damped TMD was found to more effectively control the excessive responses of the structures. The acceleration responses of structural and non-structural elements in MRF-DTMD can be effectively controlled, and the structural members remain elastic under the design-based earthquake (DBE). Compared with the UCMRF, the peak acceleration reduction coefficients (PARCs) of the MRF-DTMD range between 50.23% and 58.69% in the two considered directions. Parametric studies towards the optimum design of the TMD are finally carried out, where the theoretical peak acceleration reduction coefficients are particularly discussed.

Experimental investigation on the connection performance of defect detectable and repairable half-grouted sleeve under cyclic loads

A defect-detectable and repairable half-grouted sleeve (DDRHGS) was developed to address the detection and repair of insufficient grouting of grouted sleeve connections (GSCs). This research focused on quantitatively evaluating the influence of insufficient grouting on the connection performance of GSCs and validating the feasibility and reliability of DDRHGS under cyclic loads. To achieve these, a total of 52 DDRHGS specimens were tested under two cyclic loading protocols. The influences of two rebar diameters, four defect ratios, two repair materials, and two loading protocols were analyzed, with emphasis on the failure mode, load-bearing capacity, and deformation capacity of the tested specimens. The test results indicated the following: 1) for the specimens with grouting defects, when the defect ratio reached a certain threshold, the bar-slip failure mode, rather than the expected bar-fracture failure mode, was observed. The load-bearing capacity and deformation capacity were significantly lower than those of the specimens without defects. 2) For the specimens with a diameter of 12 mm and a defect ratio of 60% as well as a diameter of 20 mm and a defect ratio of 45%, the connection performance did not meet the requirements of the design basis earthquake (DBE) and maximum considered earthquake (MCE). Specimens with a diameter of 20 mm and a defect ratio of 60% could not perform well under service level earthquake (SLE), DBE, MCE, and wind load. 3) The repaired specimens exhibited the expected bar-fracture failure mode, and the load-bearing capacity and deformation capacity were approximately identical to those of the specimens without defects. The feasibility and reliability of DDRHGS and its repair method were validated, and the research outcome can serve as a reference for the quality control of precast concrete structures using GSCs.

Computation of the repairability index of short buildings with rocking connections

Recently developed steel self-centring moment-resisting frames have been analytically and experimentally validated as having the potential to eliminate structural damage under a design basis earthquake and restore their original vertical position following a major earthquake. In this study, the repairability index of post-tensioned self-centring frame for near-field earthquake has been developed. According to the six models of the studied building, a building that can be repaired, the maximum rotation in its connection after the earthquake does not exceed the rotation of the immediate occupancy performance. Based on this, the output data of incremental dynamic analysis analyses were drawn according to the connection of relative rotation and spectral acceleration. According to the predicted performance levels for each acceleration level, the value of the connection opening is divided by the opening of the design-basis earthquake level. The resulting curve shows the repairability index according to spectral acceleration, which if less than one, the repairability target is achieved. To evaluate the damage, the angle failure probability of post-tensioned self-centring frame for near-field earthquake has been developed. This index equation is determined according to the fragility curve and the intensity of damage in each building.

Seismic reliability evaluation of steel gabled frames consisting of web-tapered members using joint analysis of hazard and fragility

Despite the wide application of steel gabled frame (SGF) systems in large industrial projects, the current literature lacks accurate information on their seismic performance to ensure satisfactory performance at different levels of earthquake intensity. Also, given the scant information on the structural performance and their seismic design parameters in most of the available guidelines, the use of joint analysis of hazard and fragility can be very important, since both the reference hazard on site and the structural performance are considered. To address this issue, in the present paper, incremental dynamic analysis (IDA) was performed using 20 ground motions on four SGFs and their results were collected in the form of fragility curves. Then to obtain the annual rate of exceedance, hazard curves of the study region were generated and combined with the fragility curves, and finally, the seismic reliability of SGFs was evaluated at design basis earthquake (DBE) and maximum considered earthquake (MCE) hazard levels. Seismic reliability results indicated that the available seismic design guidelines lead to a too conservative design for SGFs, especially when they have long periods, where at the MCE hazard level, long-period SGFs with about 58% safety margin do not even experience LS performance level. The results of this study can prove useful for a more efficient design of SGFs in seismic regions.

Deterministic and Probabilistic Evaluations of Structures and Components Credited for Seismic Design Extension Conditions

Abstract There is “high confidence” in the ability of the structures, systems, and components (SSCs) of nuclear power plants (NPPs) to perform as designed for design basis accidents (DBAs). For design extension conditions (DECs), the SSCs are required to perform as designed with “reasonably high confidence.” DECs represent scenarios or accidents that are more severe than DBAs. Typically, a spectrum of initiating events including random failure of systems or components, internal and external hazards is used in defining scenarios leading to the DECs. Seismic events that exceed the design basis earthquake (DBE) of a station could be considered seismic DECs. A deterministic design method is proposed to address higher demands of seismic DECs in the new and existing Canada Deuterium Uranium (CANDU) NPPs. The deterministic method builds on the current requirements of applicable codes and standards and recommends more relaxed acceptance criteria. Nevertheless, a means to probabilistically evaluate built-in margin exceeding the demand induced by a seismic DEC would provide a measure of the confidence in a DEC-assigned structure or component performing its function. Therefore, a probabilistic method that estimates the probability of survivability for a structure or component when subjected to the demand induced by a seismic DEC is proposed. The probabilistic method could be used to indicate whether there is a need for applying design modification to existing design features to address demands of seismic DEC. The mean, 5th-percentile, and 95th-percentile fragility functions of these SSCs are used. These fragility functions are typically developed to determine the high-confidence-low-probability-of-failure (HCLPF) value associated with the contribution of a structure or component to the overall plant seismic risk. Sample cases for design features that were implemented in existing CANDU NPPs to address seismic DECs are presented. Both the deterministic and probabilistic methods are applied to cases of civil structures, passive mechanical and electrical components, as well as active control and instrumentation components.

Probabilistic evaluation of post-earthquake functional recovery for a tall RC core wall building using F-Rec framework

This paper presents a detailed evaluation of the functional recovery of a 42-story reinforced concrete core wall building located at a site of high seismicity using a newly developed, fully probabilistic, and comprehensive analytical framework for the assessment of post-earthquake functional recovery of buildings. This innovative framework allows complete and detailed evaluation of the seismic performance of tall buildings considering all structural and nonstructural building components/systems, and the calculation of performance metrics relevant for the assessment of functional recovery, including building’s post-earthquake functionality along with the duration and path of functional recovery. A nonlinear model of the building is created in OpenSees using a recently developed three-dimensional macro model for RC walls. Building seismic response is obtained for three seismic hazard levels corresponding to Service-Level Earthquake (SLE), Design-Based Earthquake (DBE), and Maximum Considered Earthquake (MCE). Based on the results of nonlinear analyses, damage-impaired losses are calculated using FEMA P-58 tools, while the building recovery process is evaluated using a novel framework for functional recovery (F-Rec framework). Building seismic performance obtained using new, advanced structural and recovery models suggest that the post-earthquake functionality of the tall building is primarily governed by the structural subsystem. In particular, for SLE, the functionality of the building is compromised mostly due to the damage to shear walls resulting in 3 to 6 months of functional recovery time (FRT); for DBE, the building’s functionality is fully impaired due to significant damage to slab-column connections and shear walls (FRT = 8 to 13 months); and for MCE, the building’s functionality is fully impaired due to significant damage to slab-column connections, shear walls, coupling beams, and partition walls (FRT = 12 to 16 months). Given the great contribution of tall buildings to community resilience, this study reveals a need for the development of design requirements for improving the post-earthquake functionality of tall buildings.

Evaluation of Damage Limit State for RC Frame Based on FE Modeling

Many damage limit states have been defined to characterize the extent of damages occurred in RC frame. Some of the damage limit states are defined by models that relate the limit states with the control points. Both control points and the limit state are expressed in term of response quantities. This research aims to evaluate the validity of such models by identifying the defined damage limit state with the corresponding damage based on FE modeling. The FE modeling provides a direct link between the damage and the response quantities. This link can be exploited as a basis for the evaluation. Based on the evaluation, this study proposed modified damage limit states. The response quantities with its corresponding progressive damage from FE simulation will also be used to inspect whether damage that can be expected to occur in the model structure is within the range estimated by the code based approach (CBA) damage limit state. Finally, fragility curves are constructed to assess the probability of the expected damage in the model structure under Design Basis Earthquake (DBE) and Maximum Considered Earthquake (MCE) scenarios. Utilizing the proposed damage limit states, the most probable damage in the structure falls in the category of slight if an earthquake at a level of DBE or MCE strikes the structure. However, at MCE level the probability of moderate damage attains 35%, or an increase by 23% compared to the DBE level.

Experimental Approach for the Failure Mode of Small Laminated Rubber Bearings for Seismic Isolation of Nuclear Components

Response characteristics of small-sized laminated rubber bearings (LRBs) with partial damage and total failure were investigated. For nuclear component seismic isolation, ultimate response characteristics are mainly reviewed using a beyond design basis earthquake (BDBE). Static tests, 3D shaking table tests, and verification analyses were performed using optional LRB design prototypes. During the static test, the hysteresis curve behavior from buckling to potential damage was observed by applying excessive shear deformation. The damaged rubber surface of the laminated section inside the LRB was checked through water jet cutting. A stress review by response spectrum analysis was performed to simulate the dynamic tests and predict seismic inputs’ intensity level that triggers LRB damage. Shaking table tests were executed to determine seismic response characteristics with partial damage and to confirm the stability of the superstructure when the supporting LRBs completely fail. Shear buckling in LRBs by high levels of BDBE may be quickly initiated via partial damage or total failure by the addition of torsional or rotational behavior caused by a change in the dynamic characteristics. Furthermore, the maximum seismic displacement can be limited within the range of the design interface due to the successive slip behavior, even during total LRB failure.

Nonlinear seismic performance study of D‐type self‐centering eccentric braced frames with sliding rocking link beams

AbstractThis paper presents a nonlinear numerical simulation study of the D‐type self‐centering eccentric braced frame system with a sliding rocking link beam (SCEBF‐SRL) to overcome the beam‐growth problem. The re‐centering capability of such SCEBF‐SRLs is enabled by post‐tensioned (PT) steel‐stranded cables. Replaceable hysteretic dampers termed RHD are used as seismic fuse devices for energy dissipation, while the friction force due to the relative movement of the sliding rocking link beam inside the column corbels would also contribute to the energy dissipation capacity of the system. Analytical load versus displacement relationships of an SCEBF‐SRL module frame were formulated and cross‐validated with nonlinear finite element (FE) analysis results. The seismic performance of the proposed system was studied through nonlinear static and dynamic analysis of three‐ and six‐story prototype SCEBF‐SRL buildings. A set of twenty‐two far‐field ground motions from the FEMA P695 database was adopted for nonlinear dynamic analysis (NDA). NDA results revealed that the ensemble median of the maximum inter‐story drift ratios (IDRs) of both SCEBF‐SRL prototypes were less than 1.4% and 2.0% at the design basis earthquake (DBE) and the risk‐targeted maximum considered earthquake (MCER) levels, respectively. Additionally, both SCEBF‐SRL buildings fully re‐centered themselves at MCER with negligibly small residual drift (<0.01%). The parametric study results suggest that with an energy dissipation ratio, between 25% and 60% and a minimum stiffness ratio of 5%, the ensemble median of the maximum IDR of the considered prototype building could be made less than 1.5% and 2.3% at DBE and MCER levels, respectively.

Structural performance of buildings during the 30 November 2018 M7.1 Anchorage, Alaska earthquake

Southcentral Alaska, the most populous region in Alaska, was violently shaken by a Mw 7.1 earthquake on 30 November 2018 at 8:29 am Alaska Standard Time. This was the largest magnitude earthquake in the United States close to a population center in over 50 years. The earthquake was 46 km deep, and the epicenter was 12 km north of Anchorage and 19 km west of Eagle River. The event affected some 400,000 residents, causing widespread damage in highways, nonstructural components, non-engineered and older buildings, and structures on poorly compacted fills. A few isolated serious injuries and partial collapses took place. Minor structural damage to code-conforming buildings was observed. A significant percentage of the structural damage was due to geotechnical failures. Building stock diversity allows use of the region as a large test bed to observe how local building practices affected earthquake damage levels. The prevailing peak ground acceleration (PGA) was 0.2–0.32 g, causing shaking intensity at most sites of 50%–60% of the ASCE 7-16 design basis earthquake acceleration. Thus, the seismic vulnerability of building stock in the region was not truly tested. Reinforced concrete buildings had minor structural damage, except in a few cases of shear wall and transfer girder shear cracking. Fiber-reinforced polymer (FRP)-retrofitted buildings performed satisfactorily. Concrete-masonry-unit (CMU) masonry buildings experienced serious structural damage in many cases, including relatively newer buildings. The earthquake caused widespread structural damage in non-engineered buildings (primarily wood and CMU masonry) that exist widely in the region, especially in Eagle River. Of these, non-engineered single-family wood buildings had the heaviest structural damage. No structural damage could be observed in steel buildings. The aftershock sequence, which included 7 M5+ and 50 M4+ events, exacerbated structural damage in all types of buildings. The present study is based on the EERI field reconnaissance mission conducted by the authors following the earthquake. Based on the observed damage and structural performance, seismic risk mitigation recommendations are suggested.

Seismic Performance of a Full-Scale Two-Story Bolt-Connected Precast Concrete Composite Wall Panel Building Tested on a Shake Table

A novel bolt-connected precast concrete wall panel structural system has recently been proposed for low-rise buildings in rural areas. The system features replaceable distributed bolt-connections adjoining walls, floors, and connecting columns fixed in base, enabling the whole system to be demountable and remountable. Previous quasi-static cyclic push-over test results showed an unfavorable punching shear failure of bolted joints without fully mobilizing the strength of the wall panels. Therefore, the connections were strengthened by using high-strength bolts and adjusting the positions of bolts. In order to evaluate the seismic performance of the precast system with the improved connections, incremental dynamic shake table tests were performed on a full-scale two-story building. Seismic demands and capacities of the precast building with connecting columns fixed in base (Model I) and without fixed-base constraints (Model II) were compared. The experimental results highlighted the high capacity of the improved precast system against beyond design-basis earthquakes with a peak ground acceleration of up to 0.8 g. Only slight to moderate damage was observed in terms of cracks at the edges of the door/window openings, similar to those on a cast-in-place structure, followed by cracks on concrete at connections. Although Model I showed higher lateral stiffness and lower seismic fragility, seismic energy was dissipated more evenly throughout the whole structure of Model II, which was proven well suited for low-rise buildings. Insight was given to explain the improvements on the bolt connections and the reinforcing effects of the connecting columns to provide references for the potential application of the proposed precast system.

An Integral Approach to Probabilistic Seismic Hazard Analysis and Fragility Assessment for Reinforced Concrete Frame Buildings

Fragility curves are useful tools for presenting the risk of structural damage from earthquakes as a function of a ground-motion parameter. Seismic hazard analysis for an area precedes the fragility analysis for structures built in that area. Many studies are available in the literature regarding probabilistic seismic hazard analysis (PSHA) and fragility estimation. However, a practical approach to integrate the hazard curve from PSHA and using the ground motion of that level to estimate fragility can be an area to explore further. In this study, an effort has been made to obtain peak ground acceleration (PGA) level at design-based earthquake (DBE) from PSHA. Based on this PGA value obtained, a fragility assessment has been performed. This study aims to obtain a fragility curve for a midrise RC frame building for DBE hazard level using PSHA. Three 6-story RC frame buildings are considered in this study for a seismically active zone in India. The buildings have been designed with the following performance objectives: (1) immediate occupancy (IO) with 1% drift, (2) life safety (LS) with 2% drift, and (3) collapse prevention (CP) with 3% drift. Incremental dynamic analysis (IDA) is performed using 22 numbers of far-field ground motions as prescribed by a strong ground-motion database to obtain the capacity of exceeding the respective drift limit states. Fragility curves for the three buildings are generated based on those capacities. The present study is a practical approach to capture the consequence of seismic hazard for an area and predicting the seismic risk.

Seismic performance of suspended‐floor structures with viscous dampers considering acceptable interstory drift

SummaryNumerical studies of suspended‐floor structures were conducted, and viscous dampers were applied to improve their seismic performances. The following issues were analyzed under 20 earthquake records: seismic responses of the primary structure and suspended floors, the distributions of the damping coefficient c0, and the interstory stiffness of the suspended floors. There was a significant reduction in the roof drift and the base shear force of the cores after replacing the steel bars with viscous dampers. The suspended‐floor structures with viscous dampers exhibited an optimal c0. The suspended‐floor structure with a triangular distribution of c0 showed a smaller seismic response than the one with a uniform distribution of c0. Under the design‐based earthquake, there was complete damage of nonstructural components in the y‐direction. Hence, applications of diagonal steel braces within the 1st to 10th floors were suggested to increase the lateral stiffness of the suspended floors in the y‐direction. The application of diagonal steel braces reduced the story drift Sd of the suspended floors, resulting in slight damage to nonstructural components under the design basis earthquake (DBE) hazard level. However, the roof floor, which contains electrical and mechanical components, exhibited an increase in Sd after the application of the diagonal steel braces. With increasing stiffness of the diagonal brace, the story drift profile of the suspended floors tended to be uniform, and the suspended‐floor structures with the uniform distribution of c0 exhibited seismic performances closer to those of the suspended‐floor structures with the triangular distribution of c0.

Efficient seismic risk assessment of irregular steel‐framed buildings through endurance time analysis of consistent fish‐bone model

SummaryThe seismic risk framework of building structures has been presented to reduce earthquake‐induced adverse consequences. In this context, probabilistic analysis of engineering demand parameters (EDPs) is always associated with many uncertainties and high computational demand for use in practical applications. This study has been presented to efficiently estimate the distribution of EDPs in probabilistic seismic risk assessment of irregular steel moment‐resisting frames (SMRFs). For this purpose, the incorporation of the consistent fish‐bone (CFB) model and the endurance time (ET) analysis method has been used. The proposed method (i.e., CFB‐ET) has a substantial impact on reducing the complexities of the new generation of performance‐based earthquake engineering (PBEE) by significantly reducing the degrees of freedom (DOFs) of the original building and the number of required nonlinear time history analyses (NLTHAs). The efficiency of the proposed method has been evaluated using three 3‐, 9‐, and 20‐story SMRFs irregular in bay lengths and three other SMRFs with the same number of stories but irregular in height. In this evaluation, the maximum structural response at all seismic intensity levels up to the collapse stage and also the structural response profile along the building height at service‐level earthquake (SLE), design‐based earthquake (DBE), and maximum credible earthquake (MCE) seismic intensity levels have been investigated. Next, the efficiency of the proposed method in seismic risk assessment is investigated by using seismic fragility and vulnerability curves. The results of these evaluations have been compared with the full incremental dynamic analysis (IDA) of the full DOF model of the building (i.e., SMRF‐IDA) under 44 far‐field ground motions of FEMA P‐695 in terms of computational accuracy and effort. Furthermore, a new approach to estimating the dispersion of the structural response in the ET method has been proposed, whose efficiency has been investigated in the above‐mentioned evaluations. The results show that the proposed method allows for using the new generation of PBEE in engineering applications by significantly reducing computational demand and having sufficient accuracy in the seismic assessment process.

The role of site effects on elevated seismic demands and corollary structural damage during the October 30, 2020, M7.0 Samos Island (Aegean Sea) Earthquake

On October 30, 2020 14:51 (UTC), a moment magnitude (M) 7.0 (USGS, EMSC) earthquake occurred in the Aegean Sea. This paper presents the reconnaissance findings regarding the site effects on recorded strong ground motion intensities and duration, along with the resulting induced-structural damage in Izmir Bay and Samos Island, respectively. In all rock records, relatively high intensity long period rock spectral accelerations were observed in the mid to long period range of 0.5–1.5 s, which are attributed to the source, more specifically, to the slower rupture-mechanism of the event. These rich spectral intensities were further amplified by soil site effects and soil-superstructure resonance, leading to two to six times amplified overall responses and prolonged seismic shaking durations, more pronounced in Bayrakli and other Izmir Bay sites in Turkey. However, these amplified and prolonged excitations are still below design basis earthquake levels, which addresses the lack of proper structural design and construction deficiencies, as the underlying causes for the collapse to heavy damage performance of 795 buildings. On the other hand, although located only about 10 km from the rupture (22 km from the epicenter) and within the near fault zone, the town of Vathy on Samos Island (Greece) was rather lightly affected by the earthquake, with relatively few collapsed or heavily damaged buildings, partially attributed to the low height/low weight of structures in the area. However, a concentration of damage in low-rise buildings in Ano Vathy hill is considered indicative of a combination of coupled valley and topography effects on the strong motion. This event once again addressed the need to develop region-specific zonation and provisions, when more general code practices are proven to be inadequate to assess these extreme site effects.

Performance-based seismic design method for retrofitting steel moment-resisting frames with self-centering energy-absorbing dual rocking core system

This research intends to propose an upgraded strategy for steel moment-resisting frames (SMRFs) by implementing Self-Centering Energy-absorbing Dual Rocking Core (SEDRC) systems to achieve enhanced seismic performance, improved seismic resilience, and avoid inter-story drift concentration. A performance-based method is developed to design the SEDRC system for upgrading the existing SMRF. The maximum inter-story drift and drift concentration factor are adopted as the design performance objectives. Two prototype SMRFs with three and nine stories are introduced to validate the proposed performance-based design procedure. Nonlinear static analyses were first performed for the original SMRFs and the updated ones (denoted as SEDRC-MRFs) to investigate the efficiency of the proposed retrofit strategy. The pushover curves of the analytical structures confirm that the SEDRC systems can increase the stiffness and strength of SMRFs, and SEDRC-MRFs upgraded through the proposed design procedure show no strength deterioration before the fracture of the brace in the SEDRC system. A set of 18 ground motions were chosen to study the seismic performance of the designed SEDRC-MRFs. The analysis results indicate that SEDRC-MRFs can obtain the desired performance objectives. The SEDRC system could reduce the maximum and residual inter-story drifts of SMRFs and promote uniform inter-story drift distribution. Moreover, the designed SEDRC-MRFs can be used immediately without the need for repairing structural members after the design basis earthquakes and can be repaired economically after the maximum considered earthquakes.

DYNAMIC RESPONSE AND STABILITY ANALYSES OF AKOSOMBO DAM USING NUMERICAL ANALYSIS

Dams are very important in Ghanas economic development and environmental improvement. Although Ghana dams are seismically far from the active zone, accurately analysed dams should be evaluated since failure could severely impact the people in the flood environment and the regions economy on a large scale. This paper proposes a numerical procedure for the static, slope stability, and dynamic analysis of the Akosombo embankment dam. Nineteen horizontal acceleration time histories recorded data was used based on Maximum Design Earthquake (MDE), Maximum Credible Earthquake (MCE), Design Basis Earthquake (DBE) and Operating Basis Earthquake (OBE) data. The numerical results estimated showed that the Akosombo embankment dam is likely to experience moderate deformations during the different design earthquakes. The result also indicated that non-linear analysis capable of capturing dominant non-linear mechanisms could be used to assess the stability of embankment dams. The factor of safety (FS) calculated was greater than 1.5 for high reservoir, rapid drawdown condition and low reservoir condition whereas, the FS values were found to be 1.42 for slow drawdown condition.

Shaking Table Tests to Validate Inelastic Seismic Analysis Method Applicable to Nuclear Metal Components

The main purpose of this study is to perform shaking table tests to validate the inelastic seismic analysis method applicable to pressure-retaining metal components in nuclear power plants (NPPs). To do this, the test mockup was designed and fabricated to be able to describe the hot leg surge line nozzle with a piping system, which is known to be one of the seismically fragile components in nuclear steam supply systems (NSSS). The used input motions are the displacement time histories corresponding to the design floor response spectrum at an elevation of 136 ft in the in-structure building in NPPs. Two earthquake levels are used in this study. One is the design-basis safe shutdown earthquake level (SSE, PGA = 0.3 g) and the other is the beyond-design-basis earthquake level (BDBE, PGA = 0.6 g), which is linearly scaled from the SSE level. To measure the inelastic strain responses, five strain gauges were attached at the expected critical locations in the target nozzle, and three accelerometers were installed at the shaking table and piping system to measure the dynamic responses. From the results of the shaking table tests, it was found that the plastic strain response at the target nozzle and the acceleration response at the piping system were not amplified by as much as two times the input earthquake level because the plastic behavior in the piping system significantly contributed to energy dissipation during the seismic events. To simulate the test results, elastoplastic seismic analyses with the well-known Chaboche kinematic hardening model and the Voce isotropic hardening model for Type 316 stainless steel were carried out, and the results of the principal strain and the acceleration responses were compared with the test results. From the comparison, it was found that the inelastic seismic analysis method can give very reasonable results when the earthquake level is large enough to invoke plastic behavior in nuclear metal components.

Effects of cyclic strain hardening on performance of eccentrically braced frames

Performance based seismic design (PBSD) procedures have been developed in recent years. Studies conducted in the past revealed that strain hardening ratio (SHR) used in numerical modeling can be influential on the performance of steel structural systems. In this paper, the effects of SHR on the performance assessment of eccentrically braced frame (EBF) buildings were studied by using FEMA P-58 methodology. The numerical model was validated using the pseudo-dynamic test results of the DUAREM structure. Seismic performance of six archetype EBFs with different number of stories and link length to bay width (e/L) ratios were evaluated under design basis earthquake (DBE), maximum considered earthquake (MCE), and collapse level earthquake (CLE). Irreparable residual drift, repair cost and unsafe placards were calculated for SHR ranging between 0 and 0.01. The results showed that the residual interstory drift ratio is more influenced by the SHR when compared with the interstory drift ratio, link rotation angle and story acceleration. The replacement decision was found to depend on the SHR, the number of stories, the e/L ratio, and the seismic hazard. Under MCE and CLE level events, almost all of the archetypes with SHR ≤ 0.003 required replacement while replacement can be avoided for some of the archetypes with SHR > 0.003. Under DBE level events, 3-story archetypes and 6-story archetypes with SHR ≥ 0.002 did not require replacement. Nine-story archetype with e/L = 0.08 required replacement for SHR = 0 only, while archetypes with e/L = 0.12 required replacement for SHR ≤ 0.003. The study demonstrated the strong influence and sensitivity of the repair cost to the SHR.