Probability Of Collapse Research Articles

Seismic vulnerability and resilience of steel-reinforced concrete (SRC) composite column buildings with non-seismic details

Prior to the enforcement of seismic details, older-type fully encased steel-reinforced concrete composite (SCR) columns were utilized in many buildings and bridges constructed in active seismic regions worldwide. However, there is serious lack of knowledge in the literature about the seismic behavior of older buildings’ SRC composite columns with non-seismic details. Shear strength expressions, stiffness, backbone curves, nonlinear modeling parameters, and acceptance criteria for these columns are not available. A recent testing campaign (led by the first author) provided more test data to characterize the cyclic performance of SRC columns with non-seismic details. The current study has three primary objectives (1) suggesting some test-based nonlinear modeling parameters for SRC columns; (2) developing fragility, vulnerability and resilience functions for an older-type building with non-seismic details SRC columns; and (3) assessing ASCE 41-17 SRC column modeling recommendations by comparing prototype building performance, fragility, vulnerability and resilience functions obtained using test-based backbone curves and proposed nonlinear modeling parameters with those obtained using ASCE 41-17 SRC column criteria. The methodology used to establish economic vulnerability functions accounts for uncertainties in ground motion, structural response, damages and losses by means of Monte Carlo simulation techniques. The vulnerability functions for the structural, non-structural and content components of the prototype building are established. The results of this study demonstrate that the ASCE 41-17 criteria significantly underestimates the structural capacity and resilience and overestimates the seismic fragility and vulnerability of the system; however, this may not be surprising considering the implicit conservatism included in structural engineering standards. The study shows that the ASCE 41-17 modeling criteria overestimates collapse probability by 30–50% for moderate ground shaking and by 5–15% for intense ground shaking.

Seismic fragility analysis of steel intermediate moment frames with column-tree connections

Steel intermediate moment frames (SIMFs) with column-tree connections have an advantage in that they can ensure quality control and decrease construction cost and time by the factory welding of stub beams to columns and field bolting at the beam splice. Furthermore, the amount of steel can be reduced by distributing the seismic lateral load to the entire frame, for which beam-to-column joints are fully restrained. Despite such merits, concerns about slip at the beam splice and concentrated deformation in the weak panel zone also exist. Therefore, the influence of beam splice slip and weak panel zone deformation on the seismic performance of the SIMF with column-tree connections was examined numerically by seismic fragility assessment. For comparison, the seismic fragility of a SIMF with conventional field-welded connections was also examined. The result showed that the beams and panel zones share energy absorption in the SIMF with column-tree connections, even though the panel zones are weaker than the beams, because the beam splice slip can reduce the concentration of deformation on the weak panel zone. The collapse probability of a SIMF with column-tree connections is expected to be reduced to a value as low as a SIMF with conventional connections if the quality of test data and modeling are improved.

Geological hazard risk assessment based on GIS in Mianchi County

The probability of surface collapse, landslide, collapse and debris flow is very high in hilly and mountainous areas of Mianchi County of western Henan province. The article obtained geological hazard district of Mianchi County though the analytic hierarchy process(AHP) to carry on the geological hazard risk assessment in the study area. Eight disaster-inducing factors were selected the density of disasters, slope gradient, slope height, slope shape, rock-soil body types, vegetation index, rainfall index, and engineering activity intensity based on the GIS platform and combined with the field investigation result of geological disaster points.

Structural score to quantify the vulnerability for quick seismic assessment of RC framed buildings in India

Seismic vulnerability assessment of existing RC frame buildings is important for evaluating their performance to future earthquakes and accordingly plan risk mitigation strategies. Preliminary assessment technique is commonly used to quickly assess the vulnerability based on a sidewalk survey of a building. Majority of existing techniques only provide qualitative results which generally lead to difficulty in classifying building as vulnerable or not. A preliminary assessment method based on HAZUS has been developed for RC frame buildings designed as per Indian standards considering seismicity, soil conditions, frame-type and irregularities as main variables. The proposed technique provides both qualitative and quantitative assessment in a more engineered way by assigning a structural score to a building, which essentially defines its probability of collapse. Nonlinear-static pushover analysis has been performed on certain archetype buildings using open source software (OpenSEES) to develop the structural score of a building. Most commonly observed irregularities such as open ground storey, severe vertical irregularity, short-column and plan irregularity are considered for evaluating the structural score. The proposed structural score helps in taking a step forward to quickly quantify the vulnerability of RC framed buildings in India.

Assessment of seismic collapse probability of RC shaft supported tank

The present study investigates the response reduction factor and seismic vulnerability of reinforced concrete shaft supported elevated tanks. Twenty-one prototypes of elevated tanks covering wide range of distinct sizes and heights are designed using appropriate Indian codes. The pushover analysis of finite element models is carried out to obtain the response reduction factor from the approximated bilinear pushover curve. The outcome of study shows that the tank capacity and shaft height are critical parameters influencing response reduction factor and its components. Hence, it is advised not to use the code specified unique values of response reduction factor for all tanks, regardless of their size and height for their desired seismic performance. The seismic vulnerability of the shaft stagging corresponding to various damage states has been also evaluated. The increase in the size of the tank reduces its lateral deformation capacity but increases the seismic fragility compared to tanks of smaller size. The probability of undergoing complete damage for seismic hazard corresponding to design basic and maximum considered earthquake level for code-conforming tanks is found to be less than 10%, and 30% respectively. The tanks of large sizes designed in conformity with standards are observed more susceptible to seismic forces compared to tanks of small and medium sizes.

Collapse probability of code-based design of a seismically isolated reinforced concrete building

In this study, the collapse probability of a Reinforced Concrete (RC) seismically isolated building designed according to ASCE 7-16 is given using the Incremental Dynamic Analysis (IDA) and Adaptive Incremental Dynamic Analysis (AIDA) methods. In a region where spectral demands of different intensity levels are known, thirty ground motions are selected and gradually changed from first to last seismic intensity level to match hazard-consistent properties in the extreme events, as given in the AIDA procedure. The collapse probabilities were obtained using FEMA P695 based IDA and AIDA methods by unidirectional analysis results, separately. The fragility curve obtained using bidirectional analysis results of the AIDA method was adjusted to the fragility curve acquired utilizing unidirectional analysis results by a correction factor to consider the accidental torsion effects. It is determined that the collapse probability of isolators is over the ASCE 7-16 acceptable limit, which is 10% for building in Risk Category of I and II at the Risk-Targeted Maximum Considered Earthquake (MCER) level. Also, it is shown that reducing the displacement capacity of isolators according to ASCE 7-16 causes the probability of collapse to exceed the 10% limit considerably. When the displacement capacity was increased to 1.25 times of total maximum displacement, the collapse probability decreases below the acceptable limit at the MCER level. The analysis results reveal that the collapse probability of isolators is sensitive to ground motion suites. Despite the isolator displacement capacity, the fragility curves of the superstructure drift demands, beam plastic rotations, and column tensile strains provide sufficient exceedance probabilities at the MCER level.

Identifying and selecting critical connections for seismic response of steel moment resisting frames

In seismically designed steel moment resisting frames, it is well known that the system-level behavior does not lead to equal rotation demands on all beam-column connections, yet this observation from analysis has rarely been turned into a tool for design. In this regard, this paper examines the differences in seismically induced deformation demands on beam-column connections in steel Moment Resisting Frames (MRFs), with the goal of identifying critical beam-to-column connections for which changes to their local hysteretic behavior result in a significant change in the global probability of collapse of the frame. First, collapse fragility curves are developed for three-, six- and 12-story MRFs using reduced beam section (RBS) connections, representing current practice. The maximum rotation demands on the beam-to-column connections at each level are examined, and connections that exceed a specified mean annual frequency of exceeding the rotation at which their strength begins to degrade are defined as critical to the global performance of the frame. Next, to confirm the definition of these connections as critical, collapse fragility curves are developed for a set of frames that have high-performance low-damage self-centering sliding hinge joint (SCSHJ) connections at only the locations defined as critical, while having low-ductility pre-Northridge (PRENORTH) connections with lower rotational capacity at all other locations. Even with a limited number of connections with high ductility, these mixed connection frames surpass the performance of the frames with only RBS connections and achieve essentially the same system collapse performance as frames with SCSHJ connections at all locations. A simplified pushover analysis method for identifying critical connections is proposed and compared to the results obtained from the non-linear time history dynamic analyses. Finally, a process for selecting these critical connections is introduced, using a Direct Displacement-Based Design (DDBD) procedure to give a designer control over their locations. This paper is useful to both researchers and practitioners who seek to identify or select particular connections where increases in rotation capacity would have the greatest influence on the overall frame performance, whether for retrofit applications or to maximize the benefit of selectively applying emerging connection details that offer enhanced performance.

Textual sentiment of comments and collapse of P2P platforms: Evidence from China's P2P market

Textual sentiment affects the investment activities of investors in traditional financial markets. Peer-to-Peer (P2P) lending market, as one of the emerging and active Internet financial markets, has recently received considerable attention from academia. However, few related studies are available. This work examines the relationship between the textual sentiment derived from investors’ comments on P2P platforms and probability of platform collapse. We collect comments from an authoritative Chinese third-party P2P lending consulting platform and use a weakly supervised convolutional neural network to calculate the textual sentiment of each comment. Empirical results show that the extracted textual sentiment has a significant influence on a P2P platform's collapse. Furthermore, the “agreement” and “disagreement” from other investors of each comment are pivotal in predicting a P2P platform's failure. We find that the textual sentiment of comments regarding P2P platforms from investor communities provide insights into predicting platforms’ collapse in the near future.

Effect of Aftershocks on Seismic Fragilities of Single-Story Masonry Structures

The effect of aftershocks on the fragility of single-story masonry structures is investigated using probabilistic seismic demand analysis Finite element models of an unreinforced masonry (URM) structure and a confined masonry (CM) structure are established and their seismic response characteristics when subjected to mainshock, aftershock, and the mainshock-aftershock sequence are then comparatively investigated. The effects of aftershocks and the use of confining members on the seismic response are studied. Probabilistic seismic demand models of the structures are built, and fragility curves under various conditions are derived to investigate the effect of aftershocks on structural fragility. The maximum roof displacement and maximum inter-story drift ratio are lower in the confined masonry model than in the unreinforced masonry model; additionally, the probability of exceedance (PE) values of each damage limit state reduced, and those of the mainshock-damaged models subjected to aftershock significantly increase compared to those directly subjected to a same-intensity aftershock. The probability of severe damage or collapse compared with the mainshock-damaged CM model is greater than when each is subjected to a same intensity aftershock. The use of confining members benefits aftershock resistance and reduces the failure probability of the mainshock-damaged structure. The PE values significantly increase with the aftershock scaling factor δ. Therefore, the effect of aftershocks should be considered in the seismic design and analysis of masonry structures.

Variability in corrosion damage models and its effect on seismic collapse fragility of aging reinforced concrete frames

Corrosion of embedded reinforcement is an important form of degradation of reinforced concrete (RC) structures. The corrosion damage can degrade the mechanical behaviors of the corroded reinforcement, the surrounding concrete, and the interaction between them. These deterioration mechanisms can be simulated by different corrosion damage models. Different corrosion damage models could result in difference in the structural collapse capacity under earthquake excitations. However, the variability in these corrosion damage models and its effect on seismic collapse fragility of corroded RC structures are not well examined in the past studies. This study conducts an investigation of the variability in the available corrosion damage models. To do this, a total of 29 empirical models are collected to represent the corrosion-induced deterioration mechanisms. The results show that different corrosion damage models lead to significant variability. The changing range of the prediction by different corrosion damage models for the bond strength is even beyond three times wider than the minimum prediction value. As a further step, two typical RC frame structures are designed as the study cases. Then a suite of 19 corroded frame cases are modeled with their material parameters deteriorated according to the collected corrosion damage models. Their seismic collapse fragility curves are then generated and compared. It is found that, at a high corrosion rate of 0.2, the variability in the corrosion damage models can cause a significant difference in the collapse probability as high as 8.4% and 6.54% for the case frames designed with a low and high earthquake hazard levels, respectively. However, this effect due to the variability in the corrosion damage models is limited to the collapse probability when the structure is slightly or moderately corroded. Among the considered deterioration mechanism due to corrosion damage, the maximum difference of collapse probability are caused by the variability in the corrosion damage models for the yield strength and ultimate deformation of the corroded reinforcement, which are as high as 6.18% and 5.32%, respectively. While for the other deterioration mechanisms, the variability in their corresponding damage models leads to a limited effect on the collapse probability of structures.

Challenges in Evaluating Seismic Collapse Risk for RC Buildings

The development of fragility functions that express the probability of collapse of a building as a function of some ground motion intensity measure is an effective tool to assess seismic vulnerability of structures. However, a number of factors ranging from ground motion selection to modeling decisions can influence the quantification of collapse probability. A methodical investigation was carried out to examine the effects of component modeling and ground motion selection in establishing demand and collapse risk of a typical reinforced concrete frame building. The primary system considered in this study is a modern 6-story RC moment frame building that was designed to current code provisions in a seismically active region. Both concentrated and distributed plasticity beam–column elements were used to model the building frame and several options were considered in constitutive modeling for both options. Incremental dynamic analyses (IDA) were carried out using two suites of ground motions—the first set comprised site-dependent ground motions, while the second set was a compilation of hazard-consistent motions using the conditional scenario spectra approach. Findings from the study highlight the influence of modeling decisions and ground motion selection in the development of seismic collapse fragility functions and the characterization of risk for various demand levels.

Characterization of local and global capacity criteria for collapse assessment of code-conforming RC buildings

The paper investigates both local and global capacity criteria for collapse assessment of RC frame buildings. Both literature and regulations criteria are considered, also including the formulation recommended in the draft of the new Eurocode 8 (part 3) and other collapse criteria never investigated. The case studies consist of low-rise bare and infilled frame buildings, which are designed according to the Italian code provisions considering low-to-high seismicity sites in Italy. The seismic demand is estimated by performing multiple-stripe analysis based on inelastic modeling, also including the presence of the infills. The capacity assessment and the performance evaluation associated with the (building) collapse are carried out according to the latest approaches and methodologies of performance-based earthquake engineering. The investigated capacity criteria are characterized as a result of the collapse assessment in terms of (a) collapse demand to capacity ratios, (b) collapse fragility curves, (c) collapse margin ratios and probabilities, and (d) inter-capacity margin ratios. The findings provide novel information and technical insights into the influence of the collapse capacity criteria selection on the collapse features of the investigated buildings. In particular, the capacity criteria are quantitatively correlated to the building collapse performance, also outlining safety and economic considerations.

Failure mechanism and seismic performance evaluation of steel frame using rocking truss

To mitigate the deficiency of the conventional steel frames, a novel steel frame system using rocking truss (SFWRT) and self-centering energy dissipative devices (SCED) was developed. The SCED consists of structural members, pre-tension tendons, abutting element and friction dissipation devices, which exhibits excellent self-centering and energy dissipation capacity. This new structural system is analyzed using Incremental Dynamic Analysis method (IDA). A scaled earthquake acceleration response spectrum from a specified ground motion was used in this analysis. It is found that the formation of the plastic hinges of the structural components includes four stages: emergence, developing, degradation and completely bearing capacity loss. A comparative study is also made to investigate the development of these plastic hinges under different ground motions in both traditional steel frame and SFWRT. The results for evaluating the lateral collapse resistance capacity indicate that the rocking truss can significantly decrease the structural dynamic response and improve the seismic performance of buildings. The collapse probability curves of the steel frame and SFWRT based on three limit states are compared. It is found that the rocking truss is helpful to reduce the collapse probability under earthquakes. The damage of the steel frame as well as the expected loss of the main structure after an earthquake can be significantly reduced with the help of rocking truss, which would also reduce the repair cost and improve the structural resilience under earthquakes significantly.

Investigation the Sidesway Collapse and Seismic Fragility Analysis of Frames with BRB Equipped with SMAs

Although Buckling-Restrained Braces (BRBs) can dissipate a large amount of the seismic input energy. However, they need to be repaired or replaced due to large permanent deformation after a severe earthquake. To overcome this issue, the use of Shape Memory Alloys (SMAs) in the braces has recently received attention. These alloys are able to return to their original state after loading. The present study aims to analyze the fragility curves and to investigate the sidesway collapse of the BRB frames equipped with SMA during near-field earthquakes in comparison with those given for the case without SMA. For the purposes, two 5 and 15-story BRB and BRB-SMA frames subjected to 7-pair of near-fault earthquake records are studied. Nonlinear Incremental Dynamic Analyses (IDAs) are carried out using OpenSees software. On average, the simulation results showed that collapse capacity and collapse duration of the BRB-SMA frames are about 30% and 35% more than those given for the BRB frames, respectively. For an instance, a collapse probability of 38% for the 5-story BRB-SMA frame and a collapse probability of 60% for the BRB frame is given for 3g spectral acceleration. Furthermore, at the performance level of 50% for the 15-story frame, the collapse duration of the BRB-SMA frame is obtained 25.6 seconds, while it is given about 10 seconds for the BRB frame. In addition, the use of a memory alloy for spectral accelerations of 1 to 4 g resulted in a reduction of 50% to reach the collapse performance level of the frames.

Probabilistic economic seismic loss estimation of steel braced frames incorporating emerging self-centering technologies

This paper presents a comprehensive economic seismic loss assessment of emerging steel frames incorporating different types of self-centering braces. Particular focus is on failure mechanism of the braces and accurate modelling of the possible failure modes, especially fracture of the PT tendons and failure of energy dissipation devices. Moreover, the damage state, component fragility, and repair cost of the considered braces are developed in a more rigorous manner, aided by professional judgment and market research with reduced subjective decision. System-level analysis shows that tendon fracture indeed happens in the braces with FRP tendons under the maximum considered earthquake (MCE), which compromises the self-centering capability of the structures. Shape memory alloy (SMA)-viscoelastic hybrid braces are shown to effectively reduce the deformation and floor acceleration demands, and leads to the lowest probability of collapse. By examining the vulnerability functions and expected losses of the structures, a single-core SCB configuration with FRP tendons leads to the worst economic performance due to the limited brace ductility. A dual-core configuration can significantly improve the brace ductility and hence reduce the economic loss. The SMA-viscoelastic hybrid brace results in the best economic performance with the lowest expected loss. A subsequent sensitivity analysis shows that the vulnerability curves of the structures exhibit mild sensitivity to the residual inter-story drift threshold, but the modelling assumption has a more remarkable influence on the economic loss estimation results. Employing idealized numerical models without considering brace failure in the analysis could underestimate the seismic loss of self-centering braced frames by more than 30%.

Erratum for “Variability in Seismic Collapse Probabilities of Solid- and Coupled-Wall Buildings” by Nasser A. Marafi, Kamal A. Ahmed, Dawn E. Lehman, and Laura N. Lowes

Erratum for “Variability in Seismic Collapse Probabilities of Solid- and Coupled-Wall Buildings” by Nasser A. Marafi, Kamal A. Ahmed, Dawn E. Lehman, and Laura N. Lowes

Linkage structure of China’s housing market and its risk-defusing capability

There have been many recent fears of severe house-price decreases in some provinces in China causing a nationwide collapse of the housing market. Therefore, this paper aims to clarify the linkage structure of China’s housing market and its risk contagion routes. Given monthly data of provincial housing and stock-market capital returns from 2001M01 to 2019M12, on the basis of graph theory, this paper first explores the linkage structure of provincial housing markets. Relying on the linkage structure, this paper then simulates the effect of unexpected negative shocks from the stock market on the probabilities of a housing-market collapse based on the epidemic model. The results show that (i) consistently with practical evidence, the probability of housing-market collapse is relatively high in the southwest of China and (ii) reducing housing-market linkage, such as through a blocking mechanism, to prevent collapse is helpful.

Seismic loss assessment of steel structures equipped with rotational friction dampers subjected to intensifying dynamic excitations

The expected seismic losses of structures with Rotational Friction Dampers (RFDs) are assessed by the Endurance Time (ET) method considering the optimal frictional moment of the devices. A practical method is proposed to obtain the optimal frictional moment of the dampers in multi-story structures at multiple seismic hazard levels. The ET method is used as the analytical tool in this research due to its ability to reduce the number of required analyses and providing good estimations of structural responses at various hazard levels. In order to investigate the effectiveness of the dampers, the life cycle costs of a weak steel structure equipped with optimal RFDs are compared with a standard structure with optimal RFDs and without RFDs. To this end, a comprehensive performance evaluation is performed on the structures based on FEMA P-58 methodology. The ET method is also used as a tool to assess the structural responses in the framework of this methodology. The probability of collapse, fatalities, and expected damage costs are estimated utilizing a Monte Carlo procedure considering uncertainties. Also, a cost-benefit analysis is performed to determine the payback period of investment for the additional cost of the rotational friction damping systems.

Seismic performance assessment of steel frame structures equipped with buckling-restrained slotted steel plate shear walls

The near-fault ground motion records may impose high seismic energy input to the building structures. The steel plate shear walls (SPSW) are one of the robust and efficient lateral-force resisting and energy-dissipating components and SPSWs are increasingly equipped in steel moment frame to form a dual structural system. A modified type of buckling-restrained SPSW with inclined slots has been proposed and applied in the steel frame. This paper presents the seismic performance of steel frame-SPSW system subjected to near-fault ground motions. Four multi-story (5-, 10-, 15- and 20-story) steel frame-SPSW structures were selected and designed. The accuracy of the SPSW models' predictions was assessed using previous experimental results. Nonlinear time-history analysis assuming two groups of 15 near-fault ground motions and 15 far-fault ground motions was used to predict the structures' interstory drift ratios, floor accelerations, residual interstory drift ratios and drift concentration factor. Incremental dynamic analysis was used to predict collapse probabilities using the same groups of ground motions. The analytical results can provide significant insights to the seismic behavior of steel frame-SPSW structures when subjected to near-fault ground motions.

Effect of the arc-surfaced dampers on the collapse probability induced by pulse-like earthquakes

Since the friction dampers possess constant friction forces, they cannot play a significant role in mitigating the strong earthquakes' demands. The application of the variable-force friction dampers is one way of circumventing this problem. In this paper, the design parameters of a specific force-variable friction damper namely Arc-Surfaced Friction Dampers (ASFD) have been investigated and their effect on the efficiency of their performance has been assessed. To this end, a 4-story structure designed according to Iranian Building Code Standard-2800 equipped with an ordinary frictional damper (LSB) and an ASFD has been excited by an ensemble of near- and far-field ground motions. To determine the optimal ASFD parameters, which in here reflected as the initial sliding force and the radius of curvature of the ASFD, the response of the structure due to 44 FEMA-p695 ground motions scaled to the elastic design spectra corresponding to 10% of exceedance in 50 years are estimated. The nonlinear dynamic analysis has provided a basis to define the optimal parameters concerning the life-safety and collapse-prevention performance. The results showed that implementing the ASFD as a control device has significantly reduced the median spectral acceleration corresponding to the onset of collapse compared to the uncontrolled structures.