Capacity Spectrum Method Research Articles

Fragility analysis of existing RCC frame structure

This In recent years, number of studies have been carried out for the evaluation of vulnerability of structure during seismic events. Fragility analysis is one of the important probabilistic approach to estimate the damage data at different damage state during seismic events. The G+7 Reinforced Concrete frame structure is considered for analysis. The structure is analyzed in ETABS by Non-linear Pushover Analysis. Fragility curve developed for Non-linear Pushover Analysis from results obtained by capacity spectrum method for different damage states. The fragility curves are derived from analytical method. The fragility points for different damage states are derived from analytical formula. Fragility curve is plotted for probability in Y-axis and spectral displacement in X-axis for 4 different damage states from Non-linear Pushover Analysis. From Incremental Dynamic Analysis fragility curve plotted for probability in Y-axis and peak ground acceleration in X-axis for five different damage state. The behavior of fragility curve after achieving the 100% probability for different damage state is constant.

Estimation of effective damping ratio for cast-in-place tunnel-form system and evaluation of its role in performance point prediction

The extensive time and computational effort are primary challenges in nonlinear dynamic analysis of tunnel-form concrete systems. These challenges lead engineers to resort to simpler, pushover-based analyses, inherently based on estimating the seismic performance point of the system. Technical literature review indicates that no study has yet rigorously evaluated the accuracy of existing methods for estimating the performance point of tunnel-form systems. To eliminate potential ambiguities, in this study, the seismic performance point of the system under design basis earthquake (with a 475-year return period) has been calculated using three different methods (i.e., displacement coefficient, capacity spectrum, and displacement amplification factor), and compared with the results of accurate nonlinear time-history analysis. In the range of 5-, 7-, and 10-story models studied, the results indicate the inefficiency and insufficiency of the mentioned methods. Investigations reveal that while the capacity spectrum method provides better results, but its process is lengthy, and the displacement coefficient method significantly overestimates the performance point (with more than 80 % error). It was also evident that the displacement amplification factor underestimates the performance point and contradicts the direction of confidence. Based on observations, the use of all three methods for the tunnel-form system requires modifications. The calculated values of effective damping ratio for the tunnel-form system explicitly indicate type A behavior according to the ATC-40 classification. By presenting this parameter in a multi-level format, the shortcomings of both capacity spectrum and displacement coefficient methods are easily addressed. Referring to the results, the calculated value of the displacement amplification factor in the system exceeds the recommended value by the seismic design code, and by adjusting it, satisfactory responses can be obtained in the method based on the displacement amplification factor. Finally, introducing the “probable performance interval” parameter, recommending its use instead of the “performance point” parameter in assessments by pushover analysis is suggested. This parameter is applicable with all three mentioned methods and has been introduced in this study as a desirable factor in compensating for inherent uncertainties related to future earthquakes.

A Critical Evaluation of the Coefficient Method, Capacity Spectrum Method and Modal Pushover Analysis for Irregular Steel Buildings in Seismic Zones

A Critical Evaluation of the Coefficient Method, Capacity Spectrum Method and Modal Pushover Analysis for Irregular Steel Buildings in Seismic Zones

A Practice-Oriented Approach for Seismic and Energy Performance Upgrading of Existing Buildings

ABSTRACT Recent studies have focused on identifying the optimal seismic and energy upgrading interventions, among different alternatives, for poorly performing existing buildings. Most of such studies use detailed methodologies to assess the seismic and energy performance of buildings, which are time and computationally demanding, making it nearly unfeasible for practitioners and decision-makers to use them, rendering practice-oriented approaches extremely needed. To overcome the current limitations of more research-oriented methods, this study employs different available simplified approaches, namely SPO2FRAG, cloud-based capacity spectrum method and the Italian seismic risk classification guidelines (Sismabonus), to estimate some of the variables considered when using a multi-criteria decision-making (MCDM) framework to select the optimal combined retrofitting strategy, among a set of different options. To this end, a case-study school building was selected and four seismic retrofitting solutions, combined with three energy-based interventions, were identified. The performance of the building, in its as-built and retrofitted conditions, was analysed considering both simplified and detailed approaches for the estimation of two of the seismic-related variables, namely annual probability of failure and expected annual losses. Such simplified and refined estimates were used as MCDM input, comparing the ranking of retrofitting combined alternatives obtained in both cases, demonstrating the suitability of the proposed simplified methodology for engineering practice.

PUSHOVER ANALYSIS OF EARTHQUAKE RESISTANCE RCC STRUCTURE USING STAAD.PRO SOFTWARE

RCC structure has become crucial to the construction industry in recent decades. A structure must be designed with strong seismic performance in mind. A multi-story reinforced concrete building's seismic performance is planned in compliance with the current Indian code (IS 456 -2000). The study of each structural members performance is conducted using nonlinear static analysis. This paper study about a popular method to ascertain the performance level of a building is through pushover analysis, which yields results that indicate whether collapse occurs at the member or structure level. Performance-based design is used to evaluate the performance level of buildings subjected to earthquakes. Various approaches in nonlinear static analysis were developed to study the performance of a building. This assessment has taken into account a non-existing solid Rcc structure that is assumed to be located in Zone IV, as defined by IS 1893:2000, a classification of seismic zones in India. During the entire inquiry, brick work infills have been considered to be non-structural individuals. Systems for inelastic static static study include the Secant Method, the Displacement Coefficient Method, and the Capacity Spectrum Method. Pushover Analysis, a non-direct static approach, was used to examine the structure's weak points, building on static testing. The structure was recreated in SeismoStruct Version 5.2.2 using M20 cement and Fe415 steel support, as predicted in STAAD Pro v8i. After that, the research is carried out for 150% of the predetermined objective displacing for the structure to track individual yielding and the sufficiency of the core quality. The degree of damage suffered by the structure during the objective displacing is thought to represent the damage the structure would experience under configuration level ground shaking. Key Words: Pushover analysis, RCC structure, Pushover curve, drift velocity, STAAD.PRO, Earthquake structure.

Research on the Seismic Performance-Based Design of Cast Steel Joints Based on the Capacity Spectrum Method

Research on the Seismic Performance-Based Design of Cast Steel Joints Based on the Capacity Spectrum Method

Influence of soil - foundation - tank interaction on buckling strength of liquid storage tanks

Large earthquakes in the last 25 years have caused significant damage to buildings and infrastructure, including the partial or total collapse of storage tanks in various industries. Elephant foot buckling, or local buckling at the base, is one of the main failure modes observed in these structures, and this failure mode can lead to their collapse and/or complete loss of contents. Although hydrostatic and hydrodynamic loads typically affect the seismic response of tanks, the effect of soil type on tank buckling behavior has not been widely studied or recognized. This research aims to evaluate the effect of soil type on seismic fragility of tanks by analyzing typical storage tanks used in the wine industry. The work focuses on elephant foot buckling for tanks with both unanchored and anchored bases and compares the influence of three different types of soil and two different tank geometries. The approach uses the capacity spectrum method, as opposed to the more commonly used incremental dynamic analysis, to determine a critical peak ground acceleration to cause buckling at the tank. The tanks were subjected to 21 Chilean seismic records with three different soil types and a no-soil condition. From the results a lognormal fragility curve, and its median and standard deviation, are calculated. The results indicate that unanchored tanks built softer soils exhibit poorer performance, while tanks in competent soils and rock exhibit good performance. Anchored tanks show less sensitivity to soil types than unanchored tanks. The study demonstrates the importance of considering soil-foundation-structure interaction for wine storage tanks, but the results indicate that many comparable storage structures will be similarly affected.

INFLUENCE OF ANCHORING ON THE SEISMIC FRAGILITY OF BUCKLING IN LIQUID STORAGE TANKS CONSIDERING SOIL-TANK INTERACTION: A CASE STUDY FOR WINE STORAGE TANKS

In the last decades, numerous liquid storage tanks have been affected by strong earthquakes, the damage observed ranges from the partial collapse to the total collapse of the storage tanks. Elephant-foot buckling is one of the most common failures observed in these structures, which can provoke their collapse and complete loss of contents. While hydrostatic and hydrodynamic loads typically impact the seismic response of tanks, the soil type on which they are built plays an important role in influencing their performance during earthquakes. However, the soil-tank interaction has not been considered in the seismic fragility analyses of continuously supported tanks. This research aims to evaluate the seismic fragility of a continuously supported wine storage tank with a particular focus on elephant-foot buckling considering the soil-tank interaction. A specific soil condition and a typical wine storage tank are evaluated utilizing pushover-based seismic analysis and the Capacity Spectrum Method (CSM). 3D nonlinear Finite Element (FE) models are developed considering the tank, foundation, and soil. Seven ground motion records compatible with the soil type are considered. The seismic fragility is estimated using the FE models and the ground motion records. Both unanchored and anchored conditions are evaluated. The obtained results show that for the considered case study, the anchored condition shows better seismic performance when compared to the unanchored condition. Keywords: liquid storage tanks, wine storage tanks, buckling, finite element models

A Story-Based Random Structure Modeling Method for Regional Buildings Earthquake Loss Estimation

To estimate earthquake losses for regional buildings, it is important to consider the varying seismic performances of different types of buildings. To achieve this, a dynamic elastic–plastic analysis based on detailed structural modeling is more accurate than the capacity spectrum method based on a single degree of freedom to obtain the response and damage of various structures under seismic activity and provide a more precise estimate of earthquake losses for buildings. Detailed information about the building facilities is necessary to create a fine structural model. However, obtaining precise actual structural details can be challenging with existing methods, especially when there are a large number of buildings to consider. This paper proposes a new method called story-based random structure (SBRS) modeling to address this issue, which is based on the common and reasonable layout of the structure. The process involves choosing design parameters that can represent the structural arrangement of a building as variables. These parameters include the materials’ type and strength, proportions, the components’ size, and other relevant factors. The values for these variables are determined based on engineering experience and design specifications. The range of values for these variables is also determined to ensure that all design requirements are met. Finally, the Latin Hypercubic Sampling (LHS) method is used to randomly sample and combine the variables, establishing a detailed structural model of the building with structural uncertainty. According to the results of the analysis, this method can simulate the structure and component information of a building by using a probabilistic approach, even without knowing the specific structural design. This method can be based on a small amount of readily available building information and solves the problem of the rapid and refined modeling of a large number of buildings at the regional scale. It also makes it possible to estimate the earthquake loss of regional buildings based on their seismic capacity.

Structural performance‐based anomaly detection for velocity pulse

AbstractPulse‐like ground motion can cause extreme damage to long‐period structures. An automatic algorithm is proposed to identify pulse‐like ground motions, in which improved anomaly detection is applied and the structural performance is considered. To characterize the intrinsic pulse‐like features, the distance‐based anomaly detection algorithm is improved, and the relative cumulative energy is added to the Manhattan distance. The first application of the anomaly detection algorithm performs well in pulse‐like motion identification. The pulse‐like ground motions are identified according to the performance of typical long‐period engineering structures in Hazus by the improved capacity spectrum method. The method is applied to 214 strong ground motions in the Next Generation Attenuation West 2 database. Comprehensive comparisons of the proposed approach with the wavelet analysis and the energy method are presented to illustrate the significance of the structural performance on the pulse‐like identification method.

A non-linear static analysis for the seismic design of single-span integral abutment bridges

Integral abutment bridges are characterised by a monolithic connection between the deck and the abutments. Because of this connection, the seismic behaviour of the entire structure tends to be controlled by its interaction with the surrounding soil, and especially with the approach embankments. To date, methods for the seismic design of this type of bridges are still characterised by substantial uncertainties, mostly because of insufficient understanding of the dynamic response of the soil–structure system. This paper provides a contribution to the interpretation of the seismic behaviour of integral abutment bridges, focusing on a single-span structural scheme that has been receiving significant attention in recent years. The dynamic interaction between the bridge and the soil is studied with global numerical models of the soil–bridge system developed in OpenSees and subjected to a variety of ground motions. The results of the dynamic simulations, interpreted also with the aid of a modal analysis of the system, are used to develop and finally validate a simplified design procedure. This procedure is based on the capacity spectrum method, aimed at evaluating the maximum deformation and internal forces in the structure produced by the longitudinal component of the seismic motion that typically dominates the design of integral bridges.

Exploratory study on the applicability of the capacity spectrum method on bridge pile groups

Exploratory study on the applicability of the capacity spectrum method on bridge pile groups

Seismic fragility of circular piers in simply supported RC bridges: A proposal for capacity assessment

Bridges are crucial structures of a roadway system, always exposed to both natural and anthropic hazards. Several approaches have been investigated in the past two decades to evaluate the seismic vulnerability of bridges; the development of fragility curves represents a sound tool to evaluate their performances at a large scale. This study aims at the estimation of seismic fragility curves for a structural element of a very common bridge typology in Italy, that is the single circular cross-section pier of a simply supported Reinforced Concrete (RC) bridge. Two analytical methodologies for deriving fragility curves are applied to a case study model. The first one is the Capacity Spectrum Method (CSM). This method accounts for the non-linearities and the seismic energy dissipation, in fact it is based on a non-linear static analysis and the definition of Damage States (DSs) on the capacity curve of the piers. By contrast, the second one is the Response Spectrum Analysis (RSA), that is a methodology based on a linear method. By using both methods, a parametric study is carried out, varying the bridge’s geometrical and mechanical properties within standard ranges, to evaluate their effect on the seismic vulnerability of the pier. This study refers to four DSs and proposes a multilinear regression model to directly evaluate the pier’s seismic performances based on the geometrical and mechanical properties of the bridge to which it belongs.

Life cycle cost analysis of seismic retrofit policy at the city scale

Many early-developed cities are grappling with aging building environments, characterized by chronic deterioration of structures. The consequent rise in seismic risk and loss has spurred governments to promote relevant disaster mitigation plans. In the process of urban renewal or the retrofit of dilapidated buildings, it is crucial to consider economic feasibility and the impact of policies. To support decision-making, this study aims to develop a framework for evaluating different seismic reinforcement strategies at a city level using a life cycle cost-benefit analysis. The reduction of seismic loss by a certain reinforcement strategy was assessed through the capacity spectrum method, fragility curves, and probabilistic seismic hazard analysis. Construction costs and reinforcement costs were adapted from historical data. The Equivalent Uniform Annual Cost Method was also adopted to analyze the overall life cycle cost of the target buildings based on the chosen reinforcement strategy. The researchers of this study analyzed the private buildings in Taipei City, Taiwan, to demonstrate the proposed method. The priority for reinforcement was determined based on various vulnerability measures of the buildings. Six different reinforcement strategies were compared in the case study. The results revealed that the strategies that can properly exploit soft story reinforcement are more economically attractive in terms of life cycle cost. However, a decline in marginal utility was detected. The results also showed that the proposed method could provide an objective reference for determining the priority of reinforcement plans and effectively mitigate the impact of earthquakes on the community. The findings of this research can assist stakeholders in earthquake disaster preparedness and mitigation.

Seismic Behavior of an Inter-story Hinged Lateral Resistance Braced Frame

Based on the deflection behavior of structural components occurring at the lateral deformation of moment frames, a new lateral force-resisting system, the R-BRACE Frame (RBF) system, was proposed. This system is capable of effectively limiting the inter-story drift response of tall buildings. An evaluation was conducted using the finite element method program SAP2000 to simulate the internal force distribution and deformation of the system. The equivalent lateral force procedure (ELFP), the capacity spectrum method (CSM), a linear time-history analysis and the pushover method were applied to assess the yielding mechanism of the structure under different earthquake intensity levels. The findings revealed that the sub-unit, referred to as an R-BRACE, had a major impact on improving a structure's lateral stiffness. The placement of R-BRACE units could guarantee controllable stiffness degradation and enhanced seismic ductility, but would not alter the vertical load transfer path of the initial structure, which makes the RBF system an ideal option for seismic retrofitting. KEYWORDS: Lateral force-resisting system, R-BRACE frame, Enhanced lateral stiffness resistance, Seismic ductility

Application of Capacity Spectrum Method (CSM) for non-symmetrical reinforced concrete high-rise buildings as a tool for seismic design

The development of earthquake resistance design of structures in the last decade has been critically changing from strength and ductility to performance criteria, where the structure is decided for various levels of structural performance. To understand the structural performance because, at time, a large earthquake load on the structure will experience structural yielding, non-linear analysis with the capacity spectrum method will be performed. The relationship between roof displacement and base shear force is described by a curve that describes the structural capacity is a capacity curve. To determine the behavior of the structures under review for a given earthquake intensity, the capacity curve is then compared with the performance demand based on various earthquake intensities. The results of the case studies for reinforced concrete portals non-symmetrical 3D concluded that the convergence obtained at the point of the structure performance is and . The displacement results for the actual structure () were 286.71 mm and building base shear coefficient was 15.46 %.

Quasi-Static Cyclic Tests of Precast Two-Column Bent Connected with Both Grouted Splice Sleeves and Grouted Central Tenon

Owing to the advantages of accelerated construction, reduced traffic disturbance, and enhanced quality control, precast segmental two-column bents are extensively utilized in urban and highway bridges, particularly in areas of low-to-medium seismicity. However, the application of this technique in high-seismicity regions is limited owing to insufficient knowledge about the seismic performance of such precast bents. To address this, the present study investigates the seismic performance of precast segmental two-column bents, focusing on the connection of “grouted splice sleeves and grouted central tenon”, namely the proposed GSS-GCT connection. For this purpose, three large-scale two-column bent specimens were fabricated and subjected to quasi-static cyclic tests: one cast-in-place bent, one precast two-column bent with conventional grouted splice sleeves, and another with the GSS-GCT connection. The benefits of the GSS-GCT connection under high seismic activities were demonstrated regarding lateral load-carrying capacity, displacement ductility, energy dissipation capacity, and residual displacement. Moreover, five levels of damage states were qualitatively and quantitatively divided based on experimental observation, which can be evaluated with lateral displacements. Furthermore, seismic assessments of the two-column bents were obtained using the capacity spectrum method. The proposed GSS-GCT connection could significantly improve the seismic performance of precast segmental two-column bents under high-level earthquakes.

Development of a pseudostatic method for seismic performance evaluation of rocking bridge foundations

AbstractPseudostatic analysis can be an efficient approach to evaluating the dynamic response of structures for a preliminary design. In this paper, we present a pseudostatic method based on a pushover analysis to assess the seismic performance of bridge piers supported by rocking‐governed shallow foundations. The method has two stages. In the first stage, the capacity spectrum method (CSM) is applied to evaluate the maximum acceleration and displacement response of the bridge system. To have an appropriate system damping ratio in the CSM, we propose a method to consider various earthquake energy dissipation mechanisms for the pier and foundation. In the second stage, the footing settlement is evaluated based on the maximum footing rotation; an incrementally cyclic pushover analysis with a fixed footing rotation increment is performed to estimate the footing settlement. Examples are presented to demonstrate the applicability of the proposed method and the results of the proposed method are compared with the dynamic analysis results. Compared with the conventional CSM, the proposed method improves the estimation of system damping and can estimate the settlement after earthquakes.

Nonlinear seismic analysis of irregular base isolated structures using a new modified lateral load pattern

Nowadays, seismic isolation systems are increasingly used by engineers for retrofitting existing structures and designing new ones. Nevertheless, limited studies have been conducted on the performance evaluation of the nonlinear static analysis methods for estimating the seismic demands of the base isolated structures. The current study proposes a new modified lateral load pattern for seismic analysis of base isolated structures using modified capacity spectrum method (MCSM). Moreover, this study investigates the applicability of the modal pushover analysis (MPA) and modified capacity spectrum methods for assessing the base isolated structures with setback irregularity. To this end, two types of steel moment resisting structures including 3-story (low-rise) and 9-story (medium-rise) with different irregularities in elevation are considered. All the structures are isolated by three types of lead rubber bearing (LRB) isolators with various stiffnesses. In order to consider the effect of ground motion, two types of near-fault and far-fault ground motions are selected. To evaluate the performance of the MCSM and MPA methods, the structural seismic demands estimated by these methods are compared with their benchmark values obtained by the nonlinear time history analysis method. The obtained results show the superiority of the modified capacity spectrum method and the effectiveness of the new modified lateral load pattern presented for this method.

A stochastic CSM-based displacement-oriented design strategy for the novel precast SRC-UHPC composite braced-frame in the externally attached seismic retrofitting

With the development of performance based earthquake engineering, the recognition of performance based seismic design (PBSD) is continuously growing in academia and industry. Meanwhile, with the gradual awareness of earthquake threat to the existing aged buildings, researchers are focusing more on the novel retrofitting technologies to enhance the structural capacity. Based on this background, a novel precast steel-reinforced-concrete and ultra-high-performance-concrete composite braced-frame is developed for the externally attached seismic retrofitting, and a stochastic capacity spectrum method (CSM) based displacement-oriented design strategy is proposed and well validated via a case study. In general, the novel external composite substructure combines the superiority of substructure technology, precast technology, energy-dissipation technology and high-performance material technology, and is a promising structural form in the seismic retrofitting. The proposed design strategy derives from the classic CSM, and its procedure is in alignment with the PBSD to make the designed building to satisfy various predetermined functional requirements during use. The incorporation of probability factors makes evaluation results more comprehensive and objective, and the control of displacement targets makes structural systems more performant under different demand levels. The case study indicates that the stochastic CSM-based design strategy can be well coupled with the novel external composite substructure during the whole retrofitting process (i.e., three design parts), which demonstrates the superior applicability and stupendous potentials of the proposed design strategy for the subsequent in-depth research.