The load bearing capacity, global ductility and overall stability of steel frame can be improved ... more The load bearing capacity, global ductility and overall stability of steel frame can be improved significantly through the use of buckling-restrained braces (BRBs). Based on the open resource platform OpenSees, finite element models of two types of steel frame buildings, one is nine story steel frame (SF) building and another is buckling-restrained braced steel frames (BRBFs) buildings are developed. The structures were analyzed using both deterministic and probability analysis approach. No component-removal random incremental dynamic analysis (IDA) and component-removal random IDA are used to analyze collapse resistance of the buildings under seismic load. The collapse modes of SF and BRBFs under earthquakes are discovered. The nonlinear dynamic responses of SF and BRBFs are analyzed before and after the removal of certain critical components using the alternative path method (APM) approach stipulated by GSA and vertical IDA method respectively. Correspondently, the probabilistic f...
Earthquake Engineering & Structural Dynamics, 2021
A single intensity measure (IM) is commonly used to develop fragility curves for structures subje... more A single intensity measure (IM) is commonly used to develop fragility curves for structures subjected to mainshock‐aftershock (MS‐AS) scenarios. This study aims to propose a framework to develop MS‐AS fragility surfaces by characterizing the MS‐AS sequences with two IMs. To do this, the well‐known Park & Ang damage index, which increases monotonically with the ground motion duration, is adopted to represent the accumulative structural damage during sequential excitations. The MS‐AS accumulative damage of structures is thus represented by the combination of the initial damage caused by MS and the incremental damage caused by AS. Based on total probability theorem, the process of assessing MS‐AS fragility is consequently divided into two parts, namely the MS fragility assessment and the AS fragility assessment, respectively, where the cases of dynamic instability are considered. The proposed framework is illustrated using a typical four‐story reinforced concrete frame building. The peak ground velocity values of both MS and AS are taken as the representative IMs for the MS‐AS sequences. The fragility results for MS only and MS‐AS sequences are compared to scrutinize the effects of AS on structural damage. It is found that the MS‐AS sequence can cause significantly larger exceedance probabilities of limit states compared to the MS only. The MS‐AS sequence also leads to a reduction of the MS‐AS fragility median conditioned on a given AS intensity. Such reduction increases with the increase of the AS intensity.
Large earthquakes are followed by a sequence of aftershocks. Therefore, a reasonable prediction o... more Large earthquakes are followed by a sequence of aftershocks. Therefore, a reasonable prediction of damage potential caused by mainshock (MS)–aftershock (AS) sequences is important in seismic risk assessment. This paper comprehensively examines the interdependence between earthquake intensity measures (IMs) and structural damage under MS–AS sequences to identify optimal IMs for predicting the MS–AS damage potential. To do this, four categories of IMs are considered to represent the characteristics of a specific MS–AS sequence, including mainshock IMs, aftershock IMs (i.e., IMMS and IMAS, respectively), and two newly proposed IMs through taking an entire MS–AS sequence as one nominal ground motion (i.e., IM1MS–AS), or determining the ratio of IMAS to IMMS (i.e., IM2MS–AS), respectively. The single-degree-of-freedom systems with varying hysteretic behaviors are subjected to 662 real MS–AS sequences to estimate structural damage in terms the Park–Ang damage index. The intensities in ter...
Containment vessels, which contain any radioactive materials that would be released from the prim... more Containment vessels, which contain any radioactive materials that would be released from the primary system in an accident, are the last barrier between the environment and the nuclear steam supply system in nuclear power plants. Assessing the probability of failure for the containment building is essential to level 2 PSA studies of nuclear power plants. Degradation of containment vessels of some nuclear power plants has been observed in many countries, so it is important to study how the corrosion has adverse effects on the capacity of containment vessels. Conventionally, the reliability analysis of containment vessels can be conducted by using Monte Carlo Simulation (MCS) or Latin Hypercube Sampling (LHS) with the deterministic finite element analysis. In this paper, a 3D finite element model of an AP1000 steel containment vessel is constructed using the general-purpose nonlinear finite element analysis program ABAQUS. Then the finite element reliability method (FERM) based on the...
In seismic fragility and risk analysis, the definition of structural limit state (LS) capacities ... more In seismic fragility and risk analysis, the definition of structural limit state (LS) capacities is of crucial importance. Traditionally, LS capacities are defined according to design code provisions or using deterministic pushover analysis without considering the inherent randomness of structural parameters. To assess the effects of structural randomness on LS capacities, ten structural parameters that include material strengths and gravity loads are considered as random variables, and a probabilistic pushover method based on a correlation-controlled Latin hypercube sampling technique is used to estimate the uncertainties in LS capacities for four typical reinforced concrete frame buildings. A series of ten LSs are identified from the pushover curves based on the design-code-given thresholds and the available damage-controlled criteria. The obtained LS capacities are further represented by a lognormal model with the median mC and the dispersion βC. The results show that structural uncertainties have limited influence on mC for the LSs other than that near collapse. The commonly used assumption of βC between 0.25 and 0.30 overestimates the uncertainties in LS capacities for each individual building, but they are suitable for a building group with moderate damages. A low uncertainty as βC=0.1~0.15 is adequate for the LSs associated with slight damages of structures, while a large uncertainty as βC=0.40~0.45 is suggested for the LSs near collapse.
The hysteretic behavior of four buckling-restrained braces (BRBs) with H cross section unrestrain... more The hysteretic behavior of four buckling-restrained braces (BRBs) with H cross section unrestrained segment was tested under cyclic load. The transformation of the unrestrained segment's section from crisscross shape to H shape can improve the moment-resistance capacity of unrestrained segment significantly and avoid buckling instability of unrestrained segment effectively due to evident stiffness enhancement. BRBs were designed according to Chinese codes, the load-carrying elements of BRBs were fabricated with Chinese Q235 steel. In the process of experiment, BRBs did not buckle, BRBs could undergo fully-reversed axial yielding cycles without loss of stiffness and strength, the ductility and energy absorption capacity of BRBs are large enough to withstand major earthquake. The resilience model can be simplified to a symmetrical bilinear resilience model. The ratio of width to thickness of inner core has a little influence on the mechanical behavior and energy-dissipation capaci...
The load bearing capacity, global ductility and overall stability of steel frame can be improved ... more The load bearing capacity, global ductility and overall stability of steel frame can be improved significantly through the use of buckling-restrained braces (BRBs). Based on the open resource platform OpenSees, finite element models of two types of steel frame buildings, one is nine story steel frame (SF) building and another is buckling-restrained braced steel frames (BRBFs) buildings are developed. The structures were analyzed using both deterministic and probability analysis approach. No component-removal random incremental dynamic analysis (IDA) and component-removal random IDA are used to analyze collapse resistance of the buildings under seismic load. The collapse modes of SF and BRBFs under earthquakes are discovered. The nonlinear dynamic responses of SF and BRBFs are analyzed before and after the removal of certain critical components using the alternative path method (APM) approach stipulated by GSA and vertical IDA method respectively. Correspondently, the probabilistic f...
Earthquake Engineering & Structural Dynamics, 2021
A single intensity measure (IM) is commonly used to develop fragility curves for structures subje... more A single intensity measure (IM) is commonly used to develop fragility curves for structures subjected to mainshock‐aftershock (MS‐AS) scenarios. This study aims to propose a framework to develop MS‐AS fragility surfaces by characterizing the MS‐AS sequences with two IMs. To do this, the well‐known Park & Ang damage index, which increases monotonically with the ground motion duration, is adopted to represent the accumulative structural damage during sequential excitations. The MS‐AS accumulative damage of structures is thus represented by the combination of the initial damage caused by MS and the incremental damage caused by AS. Based on total probability theorem, the process of assessing MS‐AS fragility is consequently divided into two parts, namely the MS fragility assessment and the AS fragility assessment, respectively, where the cases of dynamic instability are considered. The proposed framework is illustrated using a typical four‐story reinforced concrete frame building. The peak ground velocity values of both MS and AS are taken as the representative IMs for the MS‐AS sequences. The fragility results for MS only and MS‐AS sequences are compared to scrutinize the effects of AS on structural damage. It is found that the MS‐AS sequence can cause significantly larger exceedance probabilities of limit states compared to the MS only. The MS‐AS sequence also leads to a reduction of the MS‐AS fragility median conditioned on a given AS intensity. Such reduction increases with the increase of the AS intensity.
Large earthquakes are followed by a sequence of aftershocks. Therefore, a reasonable prediction o... more Large earthquakes are followed by a sequence of aftershocks. Therefore, a reasonable prediction of damage potential caused by mainshock (MS)–aftershock (AS) sequences is important in seismic risk assessment. This paper comprehensively examines the interdependence between earthquake intensity measures (IMs) and structural damage under MS–AS sequences to identify optimal IMs for predicting the MS–AS damage potential. To do this, four categories of IMs are considered to represent the characteristics of a specific MS–AS sequence, including mainshock IMs, aftershock IMs (i.e., IMMS and IMAS, respectively), and two newly proposed IMs through taking an entire MS–AS sequence as one nominal ground motion (i.e., IM1MS–AS), or determining the ratio of IMAS to IMMS (i.e., IM2MS–AS), respectively. The single-degree-of-freedom systems with varying hysteretic behaviors are subjected to 662 real MS–AS sequences to estimate structural damage in terms the Park–Ang damage index. The intensities in ter...
Containment vessels, which contain any radioactive materials that would be released from the prim... more Containment vessels, which contain any radioactive materials that would be released from the primary system in an accident, are the last barrier between the environment and the nuclear steam supply system in nuclear power plants. Assessing the probability of failure for the containment building is essential to level 2 PSA studies of nuclear power plants. Degradation of containment vessels of some nuclear power plants has been observed in many countries, so it is important to study how the corrosion has adverse effects on the capacity of containment vessels. Conventionally, the reliability analysis of containment vessels can be conducted by using Monte Carlo Simulation (MCS) or Latin Hypercube Sampling (LHS) with the deterministic finite element analysis. In this paper, a 3D finite element model of an AP1000 steel containment vessel is constructed using the general-purpose nonlinear finite element analysis program ABAQUS. Then the finite element reliability method (FERM) based on the...
In seismic fragility and risk analysis, the definition of structural limit state (LS) capacities ... more In seismic fragility and risk analysis, the definition of structural limit state (LS) capacities is of crucial importance. Traditionally, LS capacities are defined according to design code provisions or using deterministic pushover analysis without considering the inherent randomness of structural parameters. To assess the effects of structural randomness on LS capacities, ten structural parameters that include material strengths and gravity loads are considered as random variables, and a probabilistic pushover method based on a correlation-controlled Latin hypercube sampling technique is used to estimate the uncertainties in LS capacities for four typical reinforced concrete frame buildings. A series of ten LSs are identified from the pushover curves based on the design-code-given thresholds and the available damage-controlled criteria. The obtained LS capacities are further represented by a lognormal model with the median mC and the dispersion βC. The results show that structural uncertainties have limited influence on mC for the LSs other than that near collapse. The commonly used assumption of βC between 0.25 and 0.30 overestimates the uncertainties in LS capacities for each individual building, but they are suitable for a building group with moderate damages. A low uncertainty as βC=0.1~0.15 is adequate for the LSs associated with slight damages of structures, while a large uncertainty as βC=0.40~0.45 is suggested for the LSs near collapse.
The hysteretic behavior of four buckling-restrained braces (BRBs) with H cross section unrestrain... more The hysteretic behavior of four buckling-restrained braces (BRBs) with H cross section unrestrained segment was tested under cyclic load. The transformation of the unrestrained segment's section from crisscross shape to H shape can improve the moment-resistance capacity of unrestrained segment significantly and avoid buckling instability of unrestrained segment effectively due to evident stiffness enhancement. BRBs were designed according to Chinese codes, the load-carrying elements of BRBs were fabricated with Chinese Q235 steel. In the process of experiment, BRBs did not buckle, BRBs could undergo fully-reversed axial yielding cycles without loss of stiffness and strength, the ductility and energy absorption capacity of BRBs are large enough to withstand major earthquake. The resilience model can be simplified to a symmetrical bilinear resilience model. The ratio of width to thickness of inner core has a little influence on the mechanical behavior and energy-dissipation capaci...
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