Probability Of Structural Collapse Research Articles

Probabilistic Evaluation of Seismic Performance of Steel Buildings with Torsional Irregularities in Plan and Soft Story under Mainshock-Aftershock Sequence

Due to the tectonic plate movement, numerous aftershocks may occur following an earthquake. There are several real mainshock-aftershock ground motion records in which the peak ground acceleration of aftershock is greater than that of the mainshock. Furthermore, irregularities such as soft story and torsional irregularity may change the structural behavior under the influence of earthquakes. This study investigates the fragility curves associated with the three-, five-, and eight-story models with steel moment-resisting frames under the main earthquake and mainshock-aftershock sequence to probabilistically evaluate the aftershock impacts on the steel structures with irregularities in the plan and height. The seismic fragility curves were calculated for four damage levels by selecting the relative displacement capacity at seismic performance levels of slight, moderate, extensive, and complete damage from the US HAZUS code. The analysis was done using structural reliability relationships and incremental dynamic analysis with the OpenSees software platform. The analytical results showed that the structures with soft-story and torsional irregularity were more vulnerable with an increasing number of stories. Also, aftershocks were found to have a more destructive effect on low-rise models. The probability of structural collapse in a given peak ground acceleration for a damaged state due to the mainshock-aftershock sequence is higher than that of the mainshock sequence.

Seismic probabilistic risk assessment of weir structures considering the earthquake hazard in the Korean Peninsula

Seismic safety evaluation of weir structure is significant considering the catastrophic economical consequence of operational disruption. In recent years, the seismic probabilistic risk assessment (SPRA) has been issued as a key area of research for the hydraulic system to mitigate and manage the risk. The aim of this paper is to assess the seismic probabilistic risk of weir structures employing the seismic hazard and the structural fragility in Korea. At the first stage, probabilistic seismic hazard analysis (PSHA) approach is performed to extract the hazard curve at the weir site using the seismic and geological data. Thereafter, the seismic fragility that defines the probability of structural collapse is evaluated by using the incremental dynamic analysis (IDA) method in accordance with the four different design limit states as failure identification criteria. Consequently, by combining the seismic hazard and fragility results, the seismic risk curves are developed that contain helpful information for risk management of hydraulic structures. The tensile stress of the mass concrete is found to be more vulnerable than other design criteria. The hazard deaggregation illustrates that moderate size and far source earthquakes are the most likely scenario for the site. In addition, the annual loss curves for two different hazard source models corresponding to design limit states are extracted.

Study on the Effect of Extra Pole Support on Seismic Resistance for Low‐Rise RC Structures

There is a common way to enhance the collapse safety of residential houses using extra tilted poles supporting poor structures from the outside before and/or after earthquakes in seismic regions, especially in rural areas. But, almost all of these supporting measures are still weak and lack of scientific design and evaluation. This study takes a poorly designed two‐bay and three‐story RC frame building as an object to explore the effect of this kind of support measures on structural seismic resistance by comparing with a standard‐designed RC frame structure model as a contrastive case. The results obtained by performance‐based methods indicate that extra poles can improve the seismic collapse safety and reduce structural seismic damage of the poorly designed structure (PDS) effectively. The median collapse capacity parameter θ increases from 1.31 g to the range of 1.92∼2.39 g, and Sa(T1; 10%) (spectral acceleration at the first‐mode period which causes 10% probability of structural collapse) also increases from 0.57 g to the range of 0.75∼1.08 g. Study of dynamic structural damage shows a great damage reduction of PDS under seismic loads, especially Sa(T1) = 0.2 g. This study proves that this simple measure can improve the seismic resistance of PDS into an acceptable level by taking our suggested practical and efficient supporting schemes.

Structural reliability assessment of an in-service offshore steel jacket structure using as built data*

This article considers the structural reliability of in-service offshore steel jacket structure with respect to Push Over Plastic Collapse mechanisms. From a structural integrity (SI) perspective, differing methodologies are required when undertaking assessments of these structures in comparison to those applied during the design phase. This difference is explicitly outlined and the associated impacts (and implications) when justifying the continue service under expected loading conditions are demonstrated. An in-service steel jacket is modelled with structural members (comprising cans) initially considered with design parameters (independent and correlated) followed by the as built case. The differing collapse mechanisms and associated probability of structural collapse is highlighted.

Seismic rehabilitation effect in a steel moment frame subjected to tow critical loads

PurposeThe purpose of this paper is to present a probabilistic assessment and verify the effectiveness of seismic improvement schemes against earthquake, blast and progressive collapse. The probabilistic analysis is performed by taking into account the uncertainties in loading such as planar configuration and amplitude of the blast loading. A standard Monte Carlo (MC) simulation method is employed to generate various concepts of the uncertain parameters within the problem. For a given concept, various local dynamic analyses are performed within a certain range of distance, in order to quantify and locate the damage induced by impact wave on structural elements. In the next step, a limit state analysis is performed in order to investigate whether a progressive collapse mechanism forms under the acting loads or not.Design/methodology/approach( | ) and ( | ) are blast fragility and seismic fragility, respectively; ( ) and ( ) are annual occurrence rate of earthquake and blast, respectively. The purpose of the current study is to calculate for the primary structure as well as the retrofitted structure. Annual occurrence rate of earthquake can be calculated by using probability seismic hazard analysis for the site of interest, where the structure is located. In this paper, blast fragility and seismic fragility are defined rather differently; in other words, seismic fragility is defined as the probability of structural collapse given a specified level of seismic intensity whereas blast fragility is defined as the probability of collapse given that a significant blast event takes place. Both blast and earthquake loading conditions involve the activation of energy dissipation mechanism and, as a consequence, both can be resisted employing ductility enhancing techniques, such as column wrapping or jacketing and steel bracing.FindingsThe current paper aims to present a probabilistic assessment of progressive collapse under blast and earthquake loads. Non-dependent and incompatible events are considered to obtain a general rate of collapse. Finally, probabilistic collapse rate was obtained for a moment frame before and after modifying with convergent steel brace (CBF). The purpose of doing so is to investigate whether seismic improvement schemes can reduce collapse risk of different critical events or not.Originality/valueObjective of the present work is to present a methodology for calculating the annual risk of collapse for a civil structure subjected to both seismic and blast loads, using a bi-hazard approach. Given that a blast event takes place, the probability of progressive collapse is calculated using a MC simulation procedure. The simulation procedure implements an efficient non-linear limit state analysis, formulated and solved as a linear programming problem. The probability of collapse caused by an earthquake event can be calculated by integrating the seismic fragility of the structure and the seismic hazard for the site.

Prediction of spatially distributed seismic demands in specific structures: Structural response to loss estimation

AbstractA companion paper has investigated the effects of intensity measure (IM) selection in the prediction of spatially distributed response in a multi‐degree‐of‐freedom structure. This paper extends from structural response prediction to performance assessment metrics such as probability of structural collapse; probability of exceeding a specified level of demand or direct repair cost; and the distribution of direct repair loss for a given level of ground motion. In addition, a method is proposed to account for the effect of varying seismological properties of ground motions on seismic demand that does not require different ground motion records to be used for each intensity level. Results illustrate that the conventional IM, spectral displacement at the first mode, Sde(T1), produces higher risk estimates than alternative velocity‐based IM's, namely spectrum intensity, SI, and peak ground velocity, PGV, because of its high uncertainty in ground motion prediction and poor efficiency in predicting peak acceleration demands. Copyright © 2009 John Wiley & Sons, Ltd.

Probabilistic evaluation of global seismic capacity of degrading structures

AbstractThe present study addresses the probabilistic seismic capacity evaluation of the existing non‐ductile reinforced concrete structures that are vulnerable to shear, and thus axial, failures of their columns. The probability of structural collapse at a target lateral displacement imposed by seismic hazard is estimated by reliability analysis. For this purpose, the prevalent nonlinear static procedure is extended with finite element reliability analysis. The global structural model is enhanced by incorporating probabilistic capacity and post‐failure response models of individual columns. The challenges in the detection of collapse and the potential problems and remedies in the reliability analysis due to ‘gradient discontinuities’ are presented. In particular, ‘smoothing’ of the post‐failure response models is implemented to represent realistic member behaviour and to avoid non‐convergence in the reliability analysis. Finally, parameter importance measures are employed to identify the parameters with the highest contribution to the uncertainty in the structural performance. Copyright © 2007 John Wiley & Sons, Ltd.

New Appoaches to Inspection Planning of Fatigue Damaged Offshore Platforms

The present paper summarizes the results of research and development efforts over the last approximately five years to develop simplified and practically applicable approaches for reliability and risk based inspection planning. These efforts have led to the development of a generic inspection planning approach. Following the approach the fatigue sensitive details are categorized and described generically according to standard design parameters such as the Fatigue Design Factor (FDF) and the SN curve. When a measure of the structural consequences of fatigue failure e.g. the RSR and the corresponding probability of structural collapse given fatigue failure of the considered detail are known, generic inspection plans may derived as a function of the generic parameters together with the relative cost of inspections, repairs and failures. Due to the simplicity of the format of the developed inspection plans, the proposed approach has a high potential to be used in codes for the design and maintenance of steel structures. The validity of the proposed approach is illustrated through a study regarding inspection planning of a tri-pod offshore structure where generic inspection plans are obtained using two approximations, namely assuming equidistant inspection intervals and using constant thresholds for the annual probability of failure.

Codified Risk-Based Inspection Planning

Simplified methods are described for reliability- and risk-based inspection planning of steel structures. The methods simplify the practical aspects of identifying inspection plans complying both with specific requirements to the maximum acceptable annual probability of structural collapse and member failure and at the same time minimizing overall total service life costs. Generic inspections plans can then be established for representative fatigue sensitive details in terms of characteristics such as FDF (Fatigue Design Factor), detail type, RSR (Reserve Strength Ratio) given fatigue failure and inspection/repair techniques. Generic inspection plans can be used for design of new structures as well as for requalification of existing structures. In this paper it is described how generic inspection plans can be used for codification purposes in connection with inspection planning of steel structures.