• Title/Summary/Keyword: Collapse probability

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Seismic collapse probability of eccentrically braced steel frames

  • Qi, Yongsheng;Li, Weiqing;Feng, Ningning
    • Steel and Composite Structures
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    • v.24 no.1
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    • pp.37-52
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    • 2017
  • To quantitatively assess the safety against seismic collapse of eccentrically braced steel frame (EBSF) system, 24 typical EBSFs with K-shape and V-shape braces with seismic precautionary intensities 8 and 9 were designed complying with China seismic design code and relative codes to constitute archetype space of this structure system. In the archetype space, the collapse probability of the structural system under maximum considered earthquakes (MCE) was researched. The results show that the structures possess necessary safety against seismic collapse when they respectively encounter the maximum considered earthquakes corresponding to their seismic precautionary levels, and their collapse probabilities increase with increasing seismic precautionary intensities. Moreover, the EBSFs with V-shape braces have smaller collapse probability, thus greater capacity against seismic collapse than those with K-shape braces.

Seismic Collapse Risk for Non-Ductile Reinforced Concrete Buildings According to Seismic Design Categories (비연성 철근콘크리트 건물의 내진설계범주에 따른 붕괴 위험성 평가)

  • Kim, Minji;Han, Sang Whan;Kim, Taeo
    • Journal of the Earthquake Engineering Society of Korea
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    • v.25 no.4
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    • pp.161-168
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    • 2021
  • Existing old reinforced concrete buildings could be vulnerable to earthquakes because they were constructed without satisfying seismic design and detail requirements. In current seismic design standards, the target collapse probability for a given Maximum Considered Earthquake (MCE) ground-shaking hazard is defined as 10% for ordinary buildings. This study aims to estimate the collapse probabilities of a three-story, old, reinforced concrete building designed by only considering gravity loads. Four different seismic design categories (SDC), A, B, C, and D, are considered. This study reveals that the RC building located in the SDC A region satisfies the target collapse probability. However, buildings located in SDC B, C, and D regions do not meet the target collapse probability. Since the degree of exceedance of the target probability increases with an increase in the SDC level, it is imminent to retrofit non-ductile RC buildings similar to the model building. It can be confirmed that repair and reinforcement of old reinforced concrete buildings are required.

Seismic Performance Evaluation of Steel Ordinary Moment Resisting Frames with Various Heights (다양한 높이를 갖는 철골 보통모멘트골조의 내진성능평가)

  • Baek, Seong-Jin;Kim, Tae-O;Han, Sang-Whan
    • Journal of the Architectural Institute of Korea Structure & Construction
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    • v.33 no.5
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    • pp.3-10
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    • 2017
  • Steel ordinary moment frame(steel OMF) has been used as a seismic force resisting system in regions of low and moderate seismicity. In this study, the seismic performance of the steel OMFs with various heights in SDC $C_{max}$ was evaluated. For this purpose, nine steel OMFs were designed according to seismic design codes(ASCE/SEI 7-10, ANSI/AISC 341-10), and the collapse probability of these steel OMFs were estimated using FEMA P-695. The collapse probability of steel OMFs became larger with an increase in the height of frames. Some of steel OMFs designed according to current design codes did not satisfy the acceptance criteria specified in FEMA P-695.

Collapse Probability of a Low-rise Piloti-type Building Considering Domestic Seismic Hazard (국내 지진재해도를 고려한 저층 필로티 건물의 붕괴 확률)

  • Kim, Dae-Hwan;Kim, Taewan;Chu, Yurim
    • Journal of the Earthquake Engineering Society of Korea
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    • v.20 no.7_spc
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    • pp.485-494
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    • 2016
  • The risk-based assessment, also called time-based assessment of structure is usually performed to provide seismic risk evaluation of a target structure for its entire life-cycle, e.g. 50 years. The prediction of collapse probability is the estimator in the risk-based assessment. While the risk-based assessment is the key in the performance-based earthquake engineering, its application is very limited because this evaluation method is very expensive in terms of simulation and computational efforts. So the evaluation database for many archetype structures usually serve as representative of the specific system. However, there is no such an assessment performed for building stocks in Korea. Consequently, the performance objective of current building code, KBC is not clear at least in a quantitative way. This shortcoming gives an unresolved issue to insurance industry, socio-economic impact, seismic safety policy in national and local governments. In this study, we evaluate the comprehensive seismic performance of an low-rise residential buildings with discontinuous structural walls, so called piloti-type structure which is commonly found in low-rise domestic building stocks. The collapse probability is obtained using the risk integral of a conditioned collapse capacity function and regression of current hazard curve. Based on this approach it is expected to provide a robust tool to seismic safety policy as well as seismic risk analysis such as Probable Maximum Loss (PML) commonly used in the insurance industry.

Incorporation of collapse safety margin into direct earthquake loss estimate

  • Xian, Lina;He, Zheng;Ou, Xiaoying
    • Earthquakes and Structures
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    • v.10 no.2
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    • pp.429-450
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    • 2016
  • An attempt has been made to incorporate the concept of collapse safety margin into the procedures proposed in the performance-based earthquake engineering (PBEE) framework for direct earthquake loss estimation, in which the collapse probability curve obtained from incremental dynamic analysis (IDA) is mathematically characterized with the S-type fitting model. The regressive collapse probability curve is then used to identify non-collapse cases and collapse cases. With the assumed lognormal probability distribution for non-collapse damage indexes, the expected direct earthquake loss ratio is calculated from the weighted average over several damage states for non-collapse cases. Collapse safety margin is shown to be strongly related with sustained damage endurance of structures. Such endurance exhibits a strong link with expected direct earthquake loss. The results from the case study on three concrete frames indicate that increase in cross section cannot always achieve a more desirable output of collapse safety margin and less direct earthquake loss. It is a more effective way to acquire wider collapse safety margin and less direct earthquake loss through proper enhancement of reinforcement in structural components. Interestingly, total expected direct earthquake loss ratio seems to be insensitive a change in cross section. It has demonstrated a consistent correlation with collapse safety margin. The results also indicates that, if direct economic loss is seriously concerned, it is of much significance to reduce the probability of occurrence of moderate and even severe damage, as well as the probability of structural collapse.

Effect of Analysis Procedures on Seismic Collapse Risk of Steel Special Moment Frames (내진설계에서 사용한 해석방법이 철골 특수모멘트골조의 붕괴위험도에 미치는 영향 평가)

  • Kim, Taeo;Han, Sang Whan
    • Journal of the Earthquake Engineering Society of Korea
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    • v.24 no.6
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    • pp.243-251
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    • 2020
  • In seismic design standards such as KDS 41 17 00 and ASCE 7, three procedures are provided to estimate seismic demands: equivalent lateral force (ELF), response spectrum analysis (RSA), and response history analysis (RHA). In this study, two steel special moment frames (SMFs) were designed with ELF and RSA, which have been commonly used in engineering practice. The collapse probabilities of the SMFs were evaluated according to FEMA P695 methodology. It was observed that collapse probabilities varied significantly in accordance with analysis procedures. SMFs designed with RSA (RSA-SMFs) had a higher probability of collapse than SMFs designed with ELF (ELF-SMFs). Furthermore, RSA-SMFs did not satisfy the target collapse probability specified in ASCE 7-16 whereas ELF-SMFs met the target probability.

Domestic Seismic Design Maps Based on Risk-Targeted Maximum- Considered Earthquakes (위험도기반 최대예상지진에 근거한 국내 내진설계 지도)

  • Shin, Dong Hyeon;Kim, Hyung-Joon
    • Journal of the Earthquake Engineering Society of Korea
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    • v.19 no.3
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    • pp.93-102
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    • 2015
  • This study evaluates collapse probabilities of structures which are designed according to a domestic seismic design code, KBC2009. In evaluating their collapse probabilities, to do this, probabilistic distribution models for seismic hazard and structural capacity are required. In this paper, eight major cities in Korea are selected and the demand probabilistic distribution of each city is obtained from the uniform seismic hazard. The probabilistic distribution for the structural capacity is assumed to follow a underlying design philosophy implicitly defined in ASCE 7-10. With the assumptions, the structural collapse probability in 50 years is evaluated based on the concept of a risk integral. This paper then defines an mean value of the collapse probabilities in 50 years of the selected major cities as the target risk. Risk-targeted spectral accelerations are finally suggested by modifying a current mapped spectral acceleration to meet the target risk.

Seismic Fragility Assessment of Ordinary RC Shear Walls Designed with a Nonlinear Dynamic Analysis (비선형 동적해석에 의해 내진설계된 철근콘크리트 보통 전단벽의 지진취약도 분석)

  • Jeon, Seong-Ha;Park, Ji-Hun
    • Journal of the Earthquake Engineering Society of Korea
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    • v.23 no.3
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    • pp.169-181
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    • 2019
  • Seismic performance of ordinary reinforced concrete shear wall systems commonly used in high-rise residential buildings is evaluated. Three types of shear walls exceeding 60m in height are designed by performance-based seismic design. Then, incremental dynamic analysis is performed collapse probability is assessed in accordance with the procedure of FEMA P695. As a result, story drift, plastic rotation, and compressive strain are observed to be major failure modes, but shear failure occur little. Collapse probability and collapse margin ratio of performance groups do not meet requirement of FEMA P695. It is observed that critical wall elements fail due to excessive compressive strain. Therefore, the compressive strain of concrete at the boundary area of the shear wall needs to be evaluated with more conservative acceptance criteria.

The effect of finite element modeling assumptions on collapse capacity of an RC frame building

  • Ghaemian, Saeed;Muderrisoglu, Ziya;Yazgan, Ufuk
    • Earthquakes and Structures
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    • v.18 no.5
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    • pp.555-565
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    • 2020
  • The main objective of seismic codes is to prevent structural collapse and ensure life safety. Collapse probability of a structure is usually assessed by making a series of analytical model assumptions. This paper investigates the effect of finite element modeling (FEM) assumptions on the estimated collapse capacity of a reinforced concrete (RC) frame building and points out the modeling limitations. Widely used element formulations and hysteresis models are considered in the analysis. A full-scale, three-story RC frame building was utilized as the experimental model. Alternative finite element models are established by adopting a range of different modeling strategies. Using each model, the collapse capacity of the structure is evaluated via Incremental Dynamic Analysis (IDA). Results indicate that the analytically estimated collapse capacities are significantly sensitive to the utilized modeling approaches. Furthermore, results also show that models that represent stiffness degradation lead to a better correlation between the actual and analytical responses. Results of this study are expected to be useful for in developing proper models for assessing the collapse probability of RC frame structures.

Seismic performance analysis of steel-brace RC frame using topology optimization

  • Qiao, Shengfang;Liang, Huqing;Tang, Mengxiong;Wang, Wanying;Hu, Hesong
    • Structural Engineering and Mechanics
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    • v.71 no.4
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    • pp.417-432
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    • 2019
  • Seismic performance analysis of steel-brace reinforced concrete (RC) frame using topology optimization in highly seismic region was discussed in this research. Topology optimization based on truss-like material model was used, which was to minimum volume in full-stress method. Optimized bracing systems of low-rise, mid-rise and high-rise RC frames were established, and optimized bracing systems of substructure were also gained under different constraint conditions. Thereafter, different structure models based on optimized bracing systems were proposed and applied. Last, structural strength, structural stiffness, structural ductility, collapse resistant capacity, collapse probability and demolition probability were studied. Moreover, the brace buckling was discussed. The results show that bracing system of RC frame could be derived using topology optimization, and bracing system based on truss-like model could help to resolve numerical instabilities. Bracing system of topology optimization was more effective to enhance structural stiffness and strength, especially in mid-rise and high-rise frames. Moreover, bracing system of topology optimization contributes to increase collapse resistant capacity, as well as reduces collapse probability and accumulated demolition probability. However, brace buckling might weaken beneficial effects.