Design Basis Earthquake Research Articles

Seismic performance evaluation of multi-story CBFs equipped with SMA-friction damping braces

Shape memory alloys (SMAs) gained increasing attentions from the perspective of seismic protection, primarily because of their excellent superelasticity, satisfactory damping and high fatigue life. However, the superelastic strain of SMAs has an upper limit, beyond which the material completes the austenite to martensite phase transformation and is followed by noticeable strain hardening. The strain hardening behavior would not only induce high force demand to the protected structures, but also cause unrecoverable deformation. More importantly, the SMAs may fracture if the deformation demand exceeds their capacity under severe earthquakes. In the case of installing SMA braces (SMABs) in the multi-story concentrically braced frames (CBFs), the material failure would lead to the malfunction of SMABs and this further causes building collapse. The friction mechanism could behave as a “fuse” through capping the strength demand at a constant level. Therefore, this paper suggests connecting the SMAB with a friction damper to achieve a novel brace, i.e. the SMA-friction damping brace (SMAFDB). A proof-of-concept test was carried out on a homemade specimen and the test results validated the novel brace behaves in a desirable manner. In addition, to explore the seismic response characteristics of the SMAFDB within structures, a six-story CBF equipped with SMAFDBs was designed and compared against those incorporated with SMABs or friction damping braces (FDBs) at the frequently occurred earthquake (FOE), design basis earthquake (DBE) and maximum considered earthquake (MCE). The comparative results show the SMAFDB is superior to the counterparts. Under the FOE and DBE ground motions, the SMAFDBs successfully eliminated residual deformations as the SMABs do, and achieved identical maximum interstory drift as the FDBs. Under the MCE ground motions, the SMAFDBs not only well addressed the brace failure problem that was possibly encountered in the SMABs, but also better controlled residual deformation than the FDBs.

Performance based assessment of shape memory alloy braces combined with buckling restrained braces in frames subjected to near field earthquakes

Shape memory alloy (SMA) is a relatively new material used in structural engineering. In this paper, responses of braced frames with buckling restrained braces (BRBs) and short-segment SMA braces are investigated. Frame, a six-story structure, is designed according to valid prescriptive codes and then the appropriate nonlinear model is created. Three approaches are examined: The first one is using only BRB in all the stories (BRBF system). The second is using only short-segment SMA braces in all the stories (SMA system). The third approach is combining the BRB and short-segment SMA braces in all stories (COMBINED system). Nonlinear time history analysis (NLTHA) is performed subjected to near field (NF) and far field (FF) record sets at maximum considered earthquake (MCE) and design base earthquake (DBE) levels, and responses of the considered systems are investigated and compared. Results show that none of the three systems is recommended in NF site construction because they exceed the allowable limit state. While, subjected to FF records COMBINED system is a good idea as its responses like maximum inter-story drift ratio, residual drift and brace ductility demand are in an allowable range.

Performance Based Seismic Assessment of Masonry Infilled RCC Building with Diaphragm Discontinuity

In multistoreyed RCC framed buildings, critical damages are due to seismic ground excitations, which cause catastrophic failuresat the weaker locations. Buildings with two types of structural irregularities namely diaphragm discontinuity and open ground story are considered. Assessment of seismic vulnerability of these buildings is done by using Nonlinear Static Pushover Analysis (NSPA). Performance Based Seismic Design of masonry infilled RCC buildings with two different shape of openings in the diaphragm is considered here with Design Basis Earthquake(DBE) and Maximum Considered Earthquake(MCE) where by selecting appropriate performance criteria in terms of Inter-story drift ratio(IDR) and Inelastic displacement demand ratio(IDDR) are critically observed. The Equivalent Linearization Procedure of Pushover analysis presented in FEMA 440, which is a modification of Capacity Spectrum Method based on ATC-40 guidelines, is performed in ETABS-2016 to study the performance of R.C.C. buildings with diaphragm discontinuity, designed as per IS-1893-2016.

Comparative seismic fragility assessment of mid-rise steel buildings with non-buckling (BRB and SMA) braced frames and self-centering energy-absorbing dual rocking core system

During the past two decades, many emerging smart lateral force-resisting systems have been proposed for achieving better post-earthquake recoverability than the conventional ones in steel buildings. The Self-centering Energy-absorbing Dual Rocking Core (SEDRC) system has been developed recently by the authors for achieving excellent self-centering behavior with large deformability in steel buildings. This paper intends to investigate the benefit of steel buildings using the SEDRC system compared to that using other emerging smart lateral force-resisting system (e.g., shape memory alloy braced frame (SMABF)) and conventional one (e.g., buckling restrained braced frame (BRBF)). For this purpose, first, three six-story steel buildings with BRBFs, SMABFs, and SEDRC systems, were designed to obtain similar inter-story drifts subjected to the design basis earthquakes. Second, nonlinear static and dynamic analyses were conducted to preliminarily study the seismic performance of the designed buildings. Then, incremental dynamic analyses (IDAs) with far-field and near-fault ground motion inputs were conducted to study the seismic responses of the designed buildings under different seismic hazard levels. Finally, the results from the IDAs were analyzed in a probability framework. The inter-story drifts, residual inter-story drifts, and floor acceleration responses of the considered systems were analyzed to investigate the seismic fragility of the structural and nonstructural components in the designed buildings. The analysis results indicate that the SEDRC system can achieve the best structural collapse-resistant capacity under both far-field and near-fault ground motions because of the excellent deformability. The SMABF and SEDRC system show better seismic resilience performance by controlling the residual inter-story drift responses than BRBF. Moreover, the SEDRC system can obtain a smaller exceedance probability of damage states associated with nonstructural components depending on floor acceleration responses than SMABF because of uniform inter-story drift responses.

The seismic performance of tunnel-form buildings with a non-uniform in-plan mass distribution

The specific operating conditions in concrete box-type (tunnel-form) buildings would lead to the concentration of walls in the interior parts of the plan and lack of structural walls in the perimeter of the plan. In this situation, due to the considerable reduction in torsional stiffness, usually torsional vibration modes prevail over translational vibration modes, therefore the building behaves as a torsionally flexible structure. Torsionally flexible buildings are often more sensitive to the eccentricities of mass and stiffness as well as the intensity of the torsional component of an earthquake, in which, an increase in these parameters results in both increased forces and displacements. In this study, the effect of mass eccentricity in the plan on the behavior of box-type (tunnel-form) concrete buildings with 5 and 10 stories is scrutinized. The performance level of these buildings under the Design Basis Earthquake (475 years return period) for different values of mass eccentricity has been determined. In the framework of reliability studies, fragility curves were extracted based on the IM-Based method. Ratio estimation of the uncoupled frequencies for the studied models is another achievement of this research. The results prove that the studied system has high seismic reliability under torsions due to the asymmetric distribution of mass in the plan. In the studied buildings, while moving the center of mass up to 20% of the plan, there was no drop in performance level in Design Basis Earthquake (DBE) and all of the models stayed in the immediate occupancy performance level.

Seismic performance of a Low-Cost base isolation system for unreinforced brick Masonry buildings in developing countries

Unreinforced masonry (URM) buildings are one of the most common type of constructions in developing countries, due to their reduced cost and ease of fabrication. However, the traditional non-engineered nature of these buildings combined with the poor mechanical performance of their structural materials pose a major threat to their earthquake performance, often resulting in heavy damage and losses. This study investigates the possibility of improving the response of typical URM buildings in developing countries, using a novel low-cost fibre reinforced elastomeric isolators (FREIs) developed with recycled rubber (RR). Detailed three-dimensional finite element analyses were carried out on the fixed-base (FB) and base-isolated (BI) configurations of the prototype building subjected to a set of strong recorded ground motions, considering both the design basis earthquake (DBE) and maximum considered earthquake (MCE). The numerical model of the URM building was developed using non-linear shell elements and bilinear springs that respectively simulated the hysteretic behavior of masonry walls and RR-FREIs. Numerical results show a significant reduction in both the accelerations and inter-story drifts of the BI configuration when compared to the response of the FB building. The global elastic response and corresponding enhanced seismic performance of the BI building under DBE confirm the effectiveness of the proposed base isolation system in protecting non-engineered URM buildings from seismic events with medium-to-high intensity.

Seismic reliability analysis of steel moment-resisting frames retrofitted by vertical link elements using combined series\u2013parallel system approach

The eccentric bracing system equipped with vertical links is capable of providing high levels of stiffness, strength and ductility, and therefore, can be efficiently used for seismic retrofit of existing structures. This study aims to investigate the seismic reliability of steel moment-resisting frames retrofitted by this system using a novel combined series–parallel system approach. The seismic response of 4, 8 and 12-storey steel moment-resisting frames (MRFs) are evaluated under a set of design basis earthquakes (DBE) before and after retrofitting intervention. Adopting an engineering demand parameter approach (EDP-Based) for reliability assessment and development of analytical models for the frames using systems consisting of the series–parallel elements are the major distinctions between the present study and the other similar works. To estimate the global reliability of the frames, first, the reliability of each storey is individually derived based on various probable damage levels for the lateral-load resisting members. Then, the seismic reliability of the frame is globally obtained by combining the reliability of each storey for different damage levels in the lateral load-resisting subsystems. The results indicate significant impact of this type of bracing system on improvement of the performance level and load-carrying capacity of the frames along with reduction of the lateral displacements. It is shown that application of the vertical links can reduce the maximum inter-storey drifts by at least 60%, while it leads to at most 17% increase in the base shear. All retrofitted frames exhibited a performance level higher than the Life Safety (LS) when subjected to the DBE hazard level records (earthquakes with return period of 475 years). At the same level of earthquake intensity, in the cases when the drift corresponding to the LS performance level is used as the target, the reliability of the retrofitted frames was improved by more than 90% compared to the original frames for all damage states developed in the vertical links.

Evaluation of Clearance to Stop Requirements in A Seismically Isolated Nuclear Power Plant

Seismically isolated nuclear power plants (NPPs) can provide substantial benefits towards reducing the failure probability of NPPs, especially for beyond design basis earthquake shaking. One risk posed by seismic isolation is the potential for pounding to a stop or moat wall, with currently little guidance provided by design standards on how to address this concern. In this paper, a structural model of an isolated NPP based on the Advanced Power Reactor 1400 MW is enveloped with moat walls and advanced bearing models. The bearing models account for large strain behavior through failure based on full-scale experiments with lead rubber bearings (LRBs). Using these analytical models and a measured ultimate property diagram from LRB failure tests, the range of clearance to the stop considering the performance criteria for the NPP is investigated. Although the analysis results are dependent on the particular models, ground motions, and criteria employed, this research provides an overview of the seismic response and performance criteria of an isolated NPP considering the clearance to the stop.

Seismic microzonation of Sarpol-e-zahab after Mw 7.3 2017 Iran earthquake: 1D-equivalent linear approach

The impacts of Iran’s recent and destructive earthquake of Mw 7.3 November 12 2017, and its important subsequent events are investigated at Sarpol-e-zahab by means of 1D-equivalent linear site response analyses. Local damages at Sarpol-e-zahab highlighted the role of seismic microzonation in seismic risk reduction and damage prevention plans for future events. Hence, the main goals of this study are set to provide maps for amplification factors and shaking levels of the city as well as validating design-basis earthquake loads for buildings and structures of the national code of IRSt2800. This is achieved by deconvolution of the strong motions recorded by ISMN-SPZ as the closest station to the epicenter of Mw 7.3 earthquake and finding the two horizontal bedrock motions and subsequently, convolution of the horizontal bedrock motions to find the ground motions at 38 points across the city. The results of seismic site response analyses have provided very instructive information for rehabilitation of the existing buildings and future constructions as well as seismic vulnerability assessment of buildings during earthquakes. Furthermore, it provides an unprecedented research in Iran of a complete seismic microzonation at urban scale after an earthquake and a successful application of seismic microzonation at urban area with inadequate number of strong motion recording stations.

Decoupling criterion for elastic-plastic seismic analysis of large-scale complex piping systems in nuclear power plants

This paper proposes an elastic-plastic-based decoupling criterion that can be applied to the seismic analysis of large-scale complex piping systems in nuclear power plants under beyond design basis earthquakes. First, the existing elastic-based decoupling criteria for seismic analyses were critically reviewed. Next, the effect of plasticity on the decoupling criteria was investigated by considering the equivalent damping and stiffness reduction. Finally, the decoupling criterion considering plasticity was developed based on the changes resulting from existing decoupling criteria. The validity of the proposed decoupling criterion was confirmed through its application to an analysis of a real piping system.

Seismic design of a curved bridge as per performance based criteria

In the present study, seismic design of a bridge curved in plan has been done for various response reduction factors (R) and the performance has been investigated as per FEMA-356 performance based criteria. Both uni-directional and bi-directional nonlinear dynamic time history analyses have been performed for the bridge. The performance of the bridge in terms of pier ductility demand has been determined for Kobe earthquake ground motion, compatible for Design Basis Earthquake (DBE) and Maximum Considered Earthquake (MCE) response spectrums. For different values of R-factors, suitable value of safe pier diameter of the bridge has been determined. The strength reduction factor and over strength factor have also been determined for various cases considered. It has been obtained that the bi-directional effect increases the performance state and ductility demand of the bridge. The maximum R-factor of 2.5 can be recommended for the studied bridge.

Seismic Behavior of a Bridge with New Composite Tall Piers under Near-Fault Ground Motion Conditions

Currently, the seismic designs of reinforced concrete (RC) bridges with tall piers are often accomplished following the ductility-based seismic design method. Though the collapses of the RC bridges with tall piers can be avoided, they are likely to experience major damage and loss of functionality when subjected to strong near-fault ground motions. The objectives of this study are to put forward an innovative design concept of a tall-pier system and its application in tall-pier bridges. The concept of the innovative tall-pier system is derived from the principle of earthquake-resilient structures, and is to improve the seismic performances of the tall-pier bridges under strong near-fault ground motions. The proposed tall-pier system has a box section and is composed of four concrete-filled steel tubular (CFST) columns and energy dissipating mild steel plates (EDMSPs). Trial design of a bridge with the new composite tall-pier system is performed based on a typical continuous rigid frame highway bridge with conventional RC box section tall piers. Both static analysis and nonlinear time history analysis of both the bridges with the new composite tall piers and conventional RC tall piers under the near-fault velocity pulse-type ground motions were conducted in Midas Civil2019 and ABAQUS. The results show that: under the design-based earthquake (DBE), the CFST columns and connecting steel beams remain elastic in the bridge with the new composite tall piers, while the damage is found in the replaceable EDMSPs which help dissipate the seismic input energy. The displacement responses of the new bridge are significantly smaller than those of the conventional bridge under DBE. It is concluded that the bridge with the new composite tall piers is seismic resilient under near-fault ground motions.

Static and dynamic analysis on slope stability using a DFN-DEM approach on the right abutment of the Karun 4 dam

Uncertainty in input fracture geometric parameters during analysis of the stability of jointed rock slopes is inevitable and therefore the stochastic discrete fracture network (DFN) — distinct element method (DEM) is an efficient modeling tool. In this research, potentially unstable conditions are detected in the right abutment of the Karun 4 dam and downstream of the dam body as a case study. Two extreme states with small and relatively large block sizes are selected and a series of numerical DEM models are generated using a number of validated DFN models. Stability of the rock slope is assessed in both static and dynamic loading states. Based on the design basis earthquake (DBE) and maximum credible earthquake (MCE) expected in the dam site, histories of seismic waves are applied to analyze the stability of the slope in dynamic earthquake conditions. The results indicate that a MCE is likely to trigger sliding of rock blocks on the rock slope major joint. Furthermore, the dynamic analysis also shows a local block failure by the DBE, which can consequently lead to slope instability over the long term. According to the seismic behavior of the two models, larger blocks are prone to greater instability and are less safe against earthquakes.

Seismic Risk Assessment of a Novel Self-Centering Precast Concrete Frame under Near-Fault Ground Motions

The damage to structures caused by the velocity pulse effect of near-fault earthquake waves cannot be ignored, yet there are few studies on the risk assessment of seismic performance for precast concrete frame under near-fault earthquake waves. A novel self-centering precast concrete (SCPC) frame with hysteretic dampers is proposed to obtain great self-recovering and energy consumption characteristics. To accurately assess the seismic behaviors of the novel SCPC frame under the near-fault earthquake waves, a prototype structure is modelled and elastoplastic dynamic analysis is conducted at the design basis earthquake (DBE) and the maximum considered earthquake (MCE) seismic levels. Incremental dynamic analysis and the vulnerability analysis are performed. Annual and 50-year exceeding probabilities of the novel SCPC frame are calculated afterwards. In addition, the reinforced concrete (RC)frame and the traditional SCPC frame are also modelled, whose section sizes, reinforcements arrangement and seismic intensity are consistent with the novel SCPC frame. The dynamic time-history analysis at the two seismic levels are also carried out for two types of frames. The analysis results demonstrate that the novel SCPC frame has great seismic performance and low seismic risk possibility under the near-fault earthquakes loading.

A novel double slip loads friction damper to control the seismic response of structures

In this study, the performance of a proposed friction damper with two slip loads in controlling the seismic response of steel moment resisting buildings structures under moderate and intense earthquake excitations is investigated. The proposed friction damper initially operates with a smaller slip load and could shift to the higher slip load after a certain amount of slippage when subjected to intense ground motions. In this regard, the hysteresis behavior of the proposed double slip loads (DSL) friction damper is modeled and after necessary verifications is imported to the material library of OpenSees software to be used for parametric study. To evaluate the performance of the proposed DSL damper, three steel moment resisting frame (SMRF) models with 4, 8 and 14 stories are considered that are designed according to the AISC-LRFD and ASCE7-16 codes. Using a suite of earthquake records, nonlinear time history analyses (N-THA) are carried out to determine the optimal slip loads as well as the optimal amount of the slippage in between to minimize the seismic response of the considered models. The smaller slip load is optimally determined by performing N-THA on the structural models equipped with a single slip load friction damper using the earthquake records that are scaled to the design basis earthquake (DBE) level. Then, utilizing the obtained first slip load, N-THA are repeated for the models equipped with DSL friction dampers using the same earthquake records that are now scaled to the maximum credible earthquake (MCE) level to optimally determine the second slip load as well as the amount of the slippage between two slip loads. The genetic algorithm is employed to find the optimal slip loads and the amount of slippage in between. Two scenarios for height-wise variation of the DSL parameters, i.e, the slip loads and the extent of slippage, of the SMRF models are considered. In the first scenario as a practical approach, an upward decreasing pattern of slip loads along the height of the buildings is considered. In second scenario a simple search is performed to optimally identify those parameters for all floors. Furthermore, the performance of the structural models with DSL dampers are compared with those equipped with conventional single slip load systems. The results clearly demonstrate the efficiency of the proposed DSL dampers in effectively reducing the seismic response of the structures in terms of story drifts, residual drifts, absolute floor accelerations, and base shear forces in comparison to the conventional single slip load friction dampers.

Feasibility Study on Strain-Based Seismic Design Criteria for Nuclear Components

In this paper, the feasibility study to develop strain-based seismic design criteria applicable for the components of nuclear power plants are carried out as an alternative rule to the current stress-based criteria. To do this, two acceptance criteria are investigated through the detailed example of an application for the surge line nozzles in a nuclear steam supply system, which are known as one of the seismic fragile components in nuclear power plants. These strain-based seismic design criteria are primarily to prevent two types of failure modes, such as a ductile fracture and a cyclic fatigue-induced damage due to continuous large amplitude cyclic loads during seismic event. Through the example problem, the required procedures are described step-by-step with calculations of an accumulated plastic strain, triaxiality factor by the elasto-plastic seismic analysis using the finite element method. For a precise inelastic seismic analysis, the Chaboche kinematic and Voce isotropic hardening material parameters are identified by the test data and used for an inelastic material model. The results by the strain-based criteria are compared with those by the ASME (American Society of Mechanical Engineers) stress-based design criteria for a service level D limits. From the study, it is expected that the strain-based seismic design method investigated in this paper will be beneficial for the nuclear components, especially when the design basis earthquakes are large enough to cause severe plastic strains at a critical location.

Seismic reliability assessment of RC tunnel-form structures with geometric irregularities using a combined system approach

Tunnel-form structures represent a new type of structural systems with enhanced earthquake resistance and considerably reduced construction times, if compared to conventional reinforced concrete frames and dual systems. Due to the limited information about the seismic performance of tunnel-form buildings in the presence of vertical and horizontal irregularities, seismic design standards generally prevent such irregularities and therefore impose significant architectural limitations. To address this issue, a liability assessment is here conducted on irregular 5- and 10-storey tunnel-form buildings subjected to 12 different earthquakes, representing a design spectrum. The structural response of these buildings is obtained under both Design Basis Earthquake (DBE) and Maximum Considered Earthquake (MCE) hazard levels by using time-history and nonlinear static (pushover) analyses. The reliability of the buildings is then assessed by using a novel combined system approach, in which the structural effects of walls and coupling beams at each storey are modeled as series and parallel sub-systems. The results of this study show that, despite the geometric irregularities, all the structural elements could satisfy the Immediate Occupancy (IO) performance level under both DBE and MCE scenarios with over 95% reliability. Therefore, enforcing the regularity for tunnel-form structures in current seismic design guidelines appears to be too conservative; the results of this study can then prove useful for a more efficient design of irregular tunnel-form structures in seismic regions.

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.

Performance-Based Seismic Design of RC Moment Resisting Frames with Friction-Damped Self-Centering Tension Braces

ABSTRACT This paper presents a performance-based seismic design method of RC moment resisting frame with friction damped self-centering tension braces (FSTB-Frame). The structural configuration and theoretical model of FSTB is introduced, and the numerical model of FSTB is established and validated through cyclic loading tests of a FSTB specimen. Based on the equivalent linear method, the seismic design procedure is developed and verified through 3-, 6-, 9-, and 12-story structures with different design performance objectives. Numerical models of FSTB-frames are established and used to verify whether the design performance targets are achieved through nonlinear dynamic analyses using the design-basis earthquake (DBE) ground motions. The research results show FSTB-frames can achieve the intended performance levels in terms of story drift, residual story drift and base shear, and the maximum and residual story drift of RC frames can be significantly decreased after equipping FSTBs.

Seismic fragility curves using pulse-like and spectrally equivalent ground-motion records

4- and 8-storey reinforced-concrete frame buildings are analyzed under the suites of the near-fault pulse-like, and the corresponding spectrally equivalent far-fault ground-motion records. Seismic fragility curves for the slight, moderate, extensive, and complete damage states are developed, and the damage probability matrices, and the mean loss ratios corresponding to the Design Basis Earthquake and the Maximum Considered Earthquake hazard levels are compared, for the investigated buildings and sets of ground-motion records. It is observed that the spectrally equivalent far-fault ground-motion records result in comparable estimates of the fragility curve parameters, as that of the near-fault pulse-like ground-motion records. As a result, the derived damage probability matrices and mean loss ratios using two suites of ground-motion records differ only marginally (of the order of ~10%) for the investigated levels of seismic hazard, thus, implying the potential for application of the spectrally equivalent ground-motion records, for seismic fragility and risk assessment at the near-fault sites.