Assessment Of Seismic Capacity Research Articles

Assessment of the seismic capacity of existing RC buildings short columns or soft storey, in accordance with the Second-Degree Pre-earthquake Inspection

The seismic capacity assessment of two three-storey reinforced concrete buildings constructed prior to 1984 is being conducted in this paper. Specifically, the case of short columns or soft storey on the ground floor is investigated and a comparison is made regarding the seismic response obtained for each case. The approximate method of the Second-degree pre-earthquake inspection is applied for the case of known and unknown of reinforcement amounts. The obtained results are then compared to the corresponding of a Non-linear static analysis. The primary criterion for the comparison is the failure index of the buildings, as derived from each method. The buildings are categorized into seismic categories according to the Second-degree pre-earthquake inspection, which are compared with the seismic classifications determined by KANEPE. The results of the failure indices and seismic categories according to the Second-degree pre-earthquake inspection were in great convergence with the corresponding results of failure indices in terms of acceleration and the seismic classifications according to KANEPE obtained when the Non-linear static analysis is applied. This convergence is particularly pronounced when known amounts of reinforcement are considered for the vertical elements. Furthermore, the seismic vulnerability of buildings with soft storey or short columns was confirmed in both methods in a similar manner.

Uncertainty effect on seismic capacity assessment in the out-of-plane failure mechanisms of masonry structures by probabilistic and non-probabilistic approaches

The present paper aims to provide a contribution in the study of the seismic analysis of existing masonry structures in presence of uncertain parameters described by following both probabilistic and non-probabilistic models. By posing the attention on the local out-of-plane failure mechanisms, the non-deterministic analysis is conducted on the kinematic chains of masonry portions by first applying the upper bound theorem of the limit analysis providing the expressions of the load multiplier parameter and in turn the acceleration capacity of the local mechanism with an explicit dependence on the uncertainties. Specifically, two particular local failure mechanisms commonly observed in post-earthquake scenarios, namely the vertical bending mechanism and the corner overturning mechanism, are analyzed considering the masonry-specific weight, the position of the cylindrical hinge and the cracks lines inclination as uncertain variables. In the framework of a stochastic approach, the uncertain parameters are described by random variables with assigned probability density functions (PDFs) and the Probability Transformation Method is applied to return the PDFs of the seismic response functions. In a non-probabilistic setting, the same parameters are defined as uncertain-but-bounded variables in terms of lower and upper bounds and a global optimization technique straightforwardly allows to estimate the intervals for the seismic response functions. Taking full advantage of the close link between the two proposed approaches, the numerical investigations allow to better understand whether the interval analysis is adequate for a reliable assessment of the seismic acceleration capacity or a stochastic analysis is preferable and therefore a more in-depth experimental campaign is required to fully describe the uncertain input parameters as random variables. Moreover, results on the separate and combined effect of the uncertain parameters on the seismic response functions provide other useful information to predict the masonry capacity and preserve integrity.

Evaluation of Building Seismic Capacity Based on Improved Naive Bayesian Algorithm

The influencing factors of building seismic capacity are analyzed, the basic cause events of the assessment target based on fault tree analysis (FTA) are determined, the basic cause events in the FTA model are classified and summarized, and a judgment system of building seismic capacity is built. The weight of each index factor in the Gini index calculation system is used, and the importance of the index is analyzed. On the basis of the Spearman correlation coefficient calculation of the index, the improved naive Bayesian algorithm is combined with the importance of the index to build a judgment model for the seismic capacity of housing buildings. The sample set is constructed based on the judgment system with the basic data of some housing buildings in Huoshan County. In order to improve the generalization ability and avoid overfitting, the K-SMOTE algorithm for mixed sampling was modified to improve sample balance, and random k -fold cross validation method was used for sample division and model optimization, achieving the determination of seismic capacity level of building. The research results indicate the following: (1) the accuracy of model evaluation is 93%, with model accuracy and recall rates of 0.913 and 0.93, respectively, indicating strong generalization ability of the model. (2) Selecting some actual examples of a building, the model judgment results are consistent with the actual results, verifying the correctness of the proposed method for building the model, which can be effectively used for determining the seismic capacity of building structures. (3) Applying the proposed method to the seismic capacity assessment of buildings in the Ta-pieh Mountains of Lu’an, it is concluded that the seismic capacity of urban buildings is common, while that of rural buildings is poor.

Shaking Table Tests on Seismic Capacity Assessment of Basic Unit of Mineral Wool Ceilings Supported by Iron Sheet-Backed Painted Runners

Mineral wool ceilings supported by iron sheet-backed painted runners are commonly used in public buildings without specific seismic design intensity requirement, which is not good for resilient civil infrastructure. However, standard and fundamental seismic capacity data concerned with the use of mineral wool ceilings are lacking. Accordingly, in this study, nine groups of prototype specimens of basic ceiling units were designed based on construction requirements, and 90 different test scenarios were conducted. The PGAx input increased from 0.10 g to 1.50 g over ten runs for each group of specimens. Two failure processes and six types of damage phenomena as well as their corresponding repair measures were identified. Moreover, the influence of suspension devices, panel specifications, boundary conditions, and other construction features on the seismic response was investigated. When peak floor acceleration (PFA) was low, the hanger rod and hanger rod–diagonal wire effectively reduced the percentage of fallen ceiling panels. However, when the PFA was high, the hanger rod–diagonal wire aggravated the damage. The use of an additional wire hanger on the main runners, a large lightweight ceiling panel, a high suspension height, and a fixed boundary effectively reduced the percentage of panels falling from the basic ceiling unit and improved the seismic capacity. The use of a large panel in which the amount of material was increased by 1.7% effectively reduced the percentage of fallen ceiling panels. Moreover, fixing the boundary joints with adhesive was a convenient method for improving seismic capacity at a low cost. The results contribute to enhancing resilient civil infrastructure and sustainability.

Experimental investigation and numerical modelling of the seismic performance of corroded T-shaped reinforced concrete shear walls

Six T-shaped reinforced concrete (RC) shear wall specimens were subjected to constant-current and drying-wetting cycle accelerated corrosion tests and pseudostatic loading tests in this paper. The corrosion appearance, failure mode, and mechanical properties of each specimen were compared, and the impact of the corrosion degree and axial compression ratio on the seismic performance of the T-shaped RC shear wall was analysed. The experimental outcomes illustrate that the seismic behaviour of the specimens under positive and negative loading was conspicuously different because of the asymmetric section of the specimens. Under positive loading, the bearing capacity of the specimens was higher, and the deformation capacity was poor, while the negative loading was the opposite. As the corrosion degree increased, the bearing capacity, deformability, stiffness degradation degree, cumulative energy dissipation capacity, and proportion of shear deformation in the total deformation of the specimens all showed a downwards trend. With increasing axial compression ratio, the bearing capacity of the specimen increased, the cumulative energy dissipation capacity, ultimate displacement and the proportion of shear deformation in the total deformation decreased, and the degradation rate of stiffness accelerated. Subsequently, considering the correction of corroded materials, a numerical model of the corroded T-shaped RC shear wall based on the ShellMITC4 multilayer shell element was established, and the exactitude of the numerical model was validated based on test data. Finally, based on the established numerical model, the effects of the concrete strength, boundary column longitudinal reinforcement ratio and vertical distribution reinforcement rate on the seismic behaviour of corroded T-shaped RC shear walls were studied. These research outcomes can offer supporting theories for numerical modelling analysis and seismic capacity assessment of existing RC shear wall structures in coastal environments.

Considerations on efficient procedural steps for seismic capacity assessment and diagnostics of historic structural glass systems

Structural designers are nowadays supported by standards and guidelines to optimize the mechanical performance and safety level of glass load-bearing elements and assemblies in buildings. Key role is given to deformation and stress check, and post-breakage verification, for newly designed glass systems. Performance limits are provided also for extreme events, such as earthquakes. Besides, major risk for people could derive from existing/historic glass components and systems that have not been conceived to offer minimum structural capacity against operational loads and accidents. No technical recommendations are available to quantify their actual vulnerability and capacity, thus retrofits and mitigations are also hard to plan. In this paper, possible procedural methodology steps towards are addressed. The attention is given to present technical guidelines for structural design, on one side, and on the optimized use of non-destructive methods (like Operational Modal Analysis (OMA)) and numerical methods to facilitate diagnostic steps and the mechanical characterization of components, as well as to realistic description of boundaries and even damage. Practical examples are discussed for a case-study glass-steel envelope built in 60s in Italy, which is analyzed with the support of Finite Element (FE) numerical models against in-plane and out-of-plane seismic actions.

PROS and CONS of linear and nonlinear seismic analyses for existing URM structures: Application to a historical building

Seismic capacity assessment of existing buildings is of paramount importance for mitigating the seismic risk in earthquake-prone areas. In Europe, the next version of Eurocode 8 and the current version of the Italian standards suggest the adoption of both linear and nonlinear approaches to perform seismic analyses of existing masonry buildings.This paper discusses with the main issues concerning linear and nonlinear analyses methodologies provided by the Italian standards for existing unreinforced masonry buildings. An historical building located in Southern Italy, representative of the Mediterranean basin buildings, has been chosen as a case study and modelled through the equivalent frame model. According to the Italian standards, the influence of in-plane stiffness of floors and spandrels on the overall seismic capacity of the structure has been considered in the analyses. Beyond the code prescriptions, the effect of different ultimate drifts values assumed for the spandrels on nonlinear behavior of the structure has been analysed.The results of two types of linear analyses (lateral static force method and modal response spectrum analysis) have been compared among them and with those provided by the nonlinear static method. Conclusions show that either behavior and overstrength factors provided by the Italian standards are conservative than those estimated through the nonlinear static analyses. Moreover, it has been remarked that the value of ultimate drift adopted for the spandrel can affect significantly the nonlinear response of the structures, although this topic still represents an open issue.

Pushover-based probabilistic seismic capacity assessment of RCFs retrofitted with PBSPC BRBF sub-structures

A new external retrofitting sub-structure is introduced in this paper, namely, precast bolt-connected steel-plate reinforced concrete buckling-restrained-brace-frame (PBSPC BRBF). The numerical model is proposed considering the joint mechanical behavior, postcast concrete effects, and interfacial shear performance, and the results are validated via an experimental study. The probabilistic seismic capacity assessments (PSCAs) are performed on the deficient reinforced concrete frames (RCFs) retrofitted with PBSPC BRBFs based on a pushover method. The structural and load uncertainties (e.g., the material parameter and load value) are analyzed, and the Latin hypercube sampling (LHS) method is adopted for the 1-span-3-story, 3-span-6-story and 5-span-8-story frames, respectively. The histograms, probability density functions (PDFs) and PSCA curves for all conditions are provided, and the average median values or logarithmic standard deviations (SDs) are recommended. The sensitivity analysis is also performed, and the tornado diagrams and stack columns are presented. The research provides the thresholds of damage measures for different limit states of the RCFs retrofitted with the external sub-structures, and the corresponding conclusions can be further combined with probabilistic seismic demand analyses to constitute the integrated fragility framework.

Assessment of Seismic Capacity for Reinforced Concrete Frames with Perforated Unreinforced Brick Masonry Infill Wall

Infill walls increase the strength and stiffness of the reinforced concrete frames, but they usually are not considering in design. However, when the infills are considered in the design, the opening for doors/windows necessitates investigation as well. This research work aims to investigate the effect of perforations (openings) in the infill walls on the performance of infilled RC frames, in other words, this research investigates the number of infill walls in infilled RC frames. Based on the current construction practices in Pakistan, two full scales perforated infilled RC frames were constructed in the laboratory. One infilled RC frame has an eccentric door and window (specimen-1) while the other has only window at its centre (specimen-2). Both the specimens were tested against reverse cyclic loading (quasi-static test). From the experimental testing, it was found that infilled RC frame having less amount of opening in infill wall has more resistance to lateral loads, have more stiffness and dissipated higher energy as compared to infilled RC frame having a significant size of the opening in infill wall. Similarly, displacement ductility (µD) and Response modification factor (R) also depend on the quantity of opening in infill wall in infilled RC frame. Doi: 10.28991/cej-2020-03091625 Full Text: PDF

Seismic Capacity Assessment of Unreinforced Brick Masonry Building Performed According To Eurocode

Brick Masonry Building with cement sand mortar is a common type of building typology in Nepal. Regardless of being one of the eldest construction technology, the behavior of masonry building is still a matter of study. The uncertainty in the behavior of masonry structures is due to material heterogeneity, complex behavior under different loading conditions and may be due to less research in this arena. Different modeling strategies are used and proposed worldwide to design and to identify the seismic performance of Masonry Building. The analysis strategy ranges from the simple linear method, equivalent frame method, static nonlinear method to dynamic nonlinear, which may be chosen according to engineering design aims and research purpose. In this attempt, authors choose two degrees of freedom 3D model of Unreinforced Brick Masonry Structures which catches both overturning and hysteresis mechanisms due to the shear response implemented by the TREMURI program with static nonlinear procedures. This verified method of modeling and analysis is applied to assess the performance of three different Unreinforced Brick Masonry buildings of the same plans with different numbers of storey.

Seismic capacity and vulnerability assessment considering ageing effects: case study—three local Portuguese RC buildings

A high percentage of reinforced concrete (RC) buildings in Portugal were designed and built before the introduction of modern seismic codes. This research aims to assess the seismic capacity and vulnerability of RC buildings in the city of Lisbon. For that purpose, nonlinear static procedures have been used and fragility curves have been developed. These buildings are reaching the end of their nominal life. Therefore, ageing effects have been taken into account, as well as the presence of smooth rebar. To do so, a sensitivity analysis has been performed by considering the chloride-induced corrosion of the reinforcement steel rebar and the degradation of the concrete cover. To illustrate the effects of ageing and the procedure adopted for the seismic fragility assessment of old RC structures, three RC buildings with masonry infills have been selected as case studies. They were all built between 1960 and 1980, and they are representative of the current building stock in Lisbon. The seismic capacity of the buildings has been determined by means of nonlinear static analyses of three-dimensional numerical models. The N2 method and its extended version have been considered to determine the target displacement. The seismic safety of the buildings has been estimated in terms of the demand/capacity ratio for each vertical structural element (columns and walls) according to the bending and the shear failures. Then, a set of fragility curves has been developed for all buildings to represent the probability of RC elements reaching or exceeding the significant damage limit state. Results have shown that the concrete strength degradation has had more influence than reduction of the rebar diameter in the seismic capacity. When considering steel corrosion, it has been demonstrated that the corrosion rate has reduced the capacity more than the time of exposure. It can be concluded that ageing affects the seismic behaviour of RC structures, increasing the vulnerability of these buildings.

Deteriorated seismic capacity assessment of reinforced concrete bridge piers in corrosive environment

AbstractThe coupled effects of corrosion and earthquake action on bridges piers are investigated in this study. Starting from a literature review to collect existing corrosion models, a bridge overpass is selected to perform seismic analyses. It allows to assess the degrading seismic capacity of the bridge pier at different periods due to general and pitting corrosion. The selected bridge structure belongs to the class of motorway overpass, that is a frequently used structural system all around the world. Consequently, the development of a suitable and effective tool for an in‐depth degradation analysis of this type of system, with the identification of the most appropriate time for restoration, is of paramount importance to guarantee continuous serviceability and safety.

A methodology for evaluating seismic capacity and seismic risk assessment of reinforced concrete buildings in Korea

ABSTRACTThe purpose of this study was to propose a method for evaluating the seismic capacity of existing RC buildings in Korea by reviewing the applicability of the Japanese Standard. Based on the seismic capacity of Korean buildings evaluated by this standard, we modified the basic structural index, which is calculated in terms of the ultimate horizontal strength and ductility. We compared our experiment results to the values calculated using the strength equations for columns and walls from the Japanese Standard. The flexural strength equations could be applied without modification, while the shear strength equations required modification. We evaluated these modified strength equations and proposed unit average shear stresses of columns and walls based on statistical data relating to the structural characteristics of Korean buildings. The values of the ductility indices, which are primarily calculated based on the shear-to-flexural capacity ratio, of Korean buildings with hoop spacing wider than 300 mm, as computed by the proposed method, were more reasonable than those calculated by the Japanese Standard. We believe that the proposed method provides a useful strategy for identifying Korean buildings that are vulnerable to seismic activity, and recommend urgent earthquake preparedness measures.

Seismic capacity assessment of postmainshock damaged containment structures using nonlinear incremental dynamic analysis

SummaryThis paper investigates the structural performance and seismic capacity of the postmainshock damaged containment structure through the incremental dynamic analysis (IDA). To evaluate the seismic capacity with minimum uncertainty, the damage measure (DM) and intensity measure (IM) for IDA curves are selected in term of the coefficient of variation. The IDA using mainshock records is implemented to examine the seismic damage process of a containment structure and determine key damage states. The static cyclic loading analysis and aftershock IDA are also conducted on mainshock‐damaged containment structures to investigate the effect of initial damage states on the dynamic characteristics of structures. Finally, based on IDA results, limit states of a containment structure are defined using a generalized multidimensional limit‐state function that allows considering the dependence between the mainshock‐damaged level and residual seismic capacity. These proposed bidimensional limit‐state functions can be used in the fragility analysis and risk assessment of containment structures under mainshock–aftershock, which can improve the accuracy of seismic assessment.

Seismic capacity assessment of cracked lining tunnel based on the pseudo-static method

Crack is one of the most common lining deteriorations, which is generally regarded as an indicator of tunnel safety. The present study investigated the lining cracks of 11 tunnels which are 200 km away from the Longmenshan fault zone. In order to evaluate the seismic capacity of these tunnels with longitudinal cracks in the permanent lining, a modified deformation-based pseudo-static assessment method was developed. The propagation of lining cracks was simulated by a reconstructed damaged plasticity constitutive model of reinforced concrete. The analyses adopted a two-dimensional finite element model and took tunnel depth, initial crack position, and the interaction between soil and lining structures into account. The analysis results showed that the modified evaluation method could simulate the damage process of lining structures under the action of seismic shear wave well. The results also showed that the failure modes of tunnels with cracked permanent lining were different with different burial depth in an earthquake. The cracks in the spandrel had the greatest impact on the seismic capacity of tunnels and should be reinforced in time before the earthquake. In addition, the interaction between the temporary support and permanent lining had little effect on the damage process of linings but had an impact on the damage speed. This study can provide a reference for the safety assessment of cracked lining tunnels in seismically active areas and help to determine the reinforcement measures and time more reasonably.

A study on the selection of ground motion measures for seismic capacity assessments of urban building complexes in Weinan

Selecting reasonable ground motion intensity measures (GMIMs) can facilitate more accurate seismic capacity assessments of urban building complexes (UBCs). In this study, basic structural classes (BSCs) were proposed to be used as analysis models for selecting GMIMs for UBCs in Weinan, China. A total of 171 BSCs for typical buildings were established under certain assumptions. In addition, 41 GMIMs were extracted from each of 273 ground motion records selected for analysis in this study and used to build a set of candidate optimal GMIMs. Moreover, each BSC was subjected to an elastic–plastic time-history analysis to determine its maximum inter-story drift ratio (MIDR). Furthermore, the corresponding relationships between the GMIMs and the MIDR of each BSC were established. The applicability of each GMIM for UBCs was evaluated using four metrics, i.e., correlation coefficient, effectiveness, practicability and sufficiency. Four GMIMs, namely, peak ground acceleration (PGA), root mean square of acceleration (aRMS), average spectral acceleration (Saavg) and velocity response intensity (VSI), were selected as optimal input GMIMs for seismic capacity assessment of UBCs in Weinan. This study provides a reference for selecting GMIMs for seismic capacity assessment of UBCs in Weinan.

Seismic vulnerability and retrofitting scheme for low-to-medium rise reinforced concrete buildings in Nepal

In this paper, seismic capacity assessment is presented for representative low-to-medium rise reinforced concrete (RC) buildings in Nepal. The structural behavior of buildings was studied with different analysis techniques and loading considerations. The non-linear behaviors of nine residential building structures were studied with finite element analysis. Structural performance is presented in terms of strength, stiffness, capacity curves, and inter-story drifts. The building models were analyzed as bare frames, and the drift profiles were compared with some standard drift limits to depict the vulnerability. Buildings noted as vulnerable after the analyses were modified as retrofitted using column jacketing technique, and finite element analyses were carried out again. Comparisons were made in terms of seismic performance of as-built and retrofitted buildings. The sum of observations depicts that column size directly affects the vulnerability of buildings. Moreover, column jacketing significantly ameliorates the seismic performance of low-to-medium rise RC buildings as depicted by the comparison between as-built and retrofitted structures in terms of inter-story drift and fundamental period.

Seismic Vulnerability for RC Infilled Frames: Simplified Evaluation for As-Built and Retrofitted Building Typologies

Several studies investigated the influence of infills on the response of reinforced concrete (RC) frames. However, possible shear brittle failures are generally neglected. The interaction between the infill panels and the surrounding frames can lead to anticipated brittle-type failures that should be considered in code-based assessment of lateral seismic capacity. This paper investigates, by means of simplified pushover analyses, on the effect of infills on the lateral seismic capacity explicitly considering possible brittle failures in unconfined beam-column joints or in columns. Archetype buildings representative of existing gravity load designed (GLD) RC frames of three different height ranges are obtained with a simulated design process and a sensitivity analysis is performed to investigate on the effect of infill consistency on the capacity. Moreover, possible alternative local retrofit interventions devoted to avoiding brittle failures are considered, evaluating their relative efficacy in case of different infill typologies. It is seen that for the considered existing GLD buildings, the attainment of life safety limit state is premature and happens before the damage limitation limit state. The capacity can be increased with application of local retrofit interventions. However, the retrofit efficacy varies depending on the infills consistency if the horizontal action transferred from the infills to the surrounding frame is not absorbed by the retrofit solution.

Seismic Capacity Assessment of Existing RC Building by Using Pushover Analysis

The infrastructure, existing in Sudan, is mostly not structured or designed to resist seismic forces accordingly. The study investigated the seismic damage of a 5 storey existing reinforced concrete building in Khartoum, Sudan. Three performance levels were considered in the study, which included immediate occupancy, life safety, and collapse prevention. The gravity push was carried out using force control method and lateral push with displacement control, using SAP2000. Pushover analysis produces push curve, consisting of capacity spectrum, demand spectrum, and performance point. It showed the performance level of building components along with maximum base shear carrying capacity. It has been observed that demand curve intersected the capacity curve between the points B and C at the X direction that is life safety level; and between the points B and C at the Y direction that is life safety and collapse prevention level. Therefore, some building elements are needed to be strengthened.

Seismic Capacity Assessment of Confined Brick Masonry Building: An Experimental Approach

Brick masonry is widely used for building construction throughout the world. However, unreinforced brick masonry buildings performed poorly in the 2005 Kashmir earthquake, in Pakistan, resulting in a decline in the use of brick masonry. In order to investigate and quantify the performance of brick masonry against the seismic forces by confining it through typical stiffer, line elements (column and beams), a full‐scaled room model of an area 3048 × 3658 mm (10 × 12 ft) and height of 3353 mm (11 ft) was constructed using confined brick masonry. The model was tested under quasistatic loading system. Crack pattern was noted at the end of each loading cycle. The response of the model was interpreted through a hysteresis curve, which was then idealized by a bilinear curve. A comparison of the results has been made with four different studies done on the similar model made of unreinforced brick masonry before and after retrofitting and unreinforced concrete block masonry before and after retrofitting previously tested at the same testing facility.