Nonlinear Incremental Dynamic Analysis Research Articles

Seismic vulnerability assessment of reinforced concrete haunch beam by nonlinear static and incremental dynamic analyses

Seismic vulnerability assessment of reinforced concrete haunch beam by nonlinear static and incremental dynamic analyses

Confinement effects within the seismic design of reinforced concrete frames: reliability assessment and comparison

The current Italian code “NTC2018” and Eurocode “EC8” provide specific design requirements in terms of flexural overstrength factors for reinforced concrete (RC) buildings in seismic areas. This study proposes to improve the design methodology by including explicitly the confinement effects within the seismic design of a new regular RC frame due to their influence on the capacity design principles (at structural and member level). Specifically, the seismic performance of a RC frame designed according to codes is compared, in reliability terms, with the one of the same frame designed including the concrete confinement effects. Moreover, a comparison between three constitutive models for confined concrete is performed. Selecting L’Aquila (Italy) as reference site, the two design methodologies combined with the three confinement models are numerically implemented. Scaling 30 non-frequent natural ground motions to increasing seismic intensity measures, according to the site seismic hazard, non-linear incremental dynamic analyses (IDAs) have been developed. Assuming the interstory drift indices as engineering demand parameters, the peak responses have been fitted through log-normal distributions to define IDA curves. Subsequently, appropriate limit state thresholds have been adopted to define the seismic fragility curves. Finally, through the convolution integral and Poisson model, the seismic reliability curves have been derived showing the importance of the proposed design methodology. In fact, for the frame under investigation, the seismic performance strongly improves in terms of ductility respecting all the reliability objective levels if the confinement effects are explicitly considered in the seismic design. Furthermore, the different confinement models provide similar results when the proposed seismic design is adopted, implying a reduction of the model uncertainty.

Seismic Design Procedure for Low-Rise Cold-Formed Steel–Special Bolted Moment Frames

In 2007, the American Iron and Steel Institute (AISI) established a standard for cold-formed steel–special bolted moment frames (CFS-SBMFs). This structural system is designed to resist seismic forces. The CFS-SBMF system employs double-channel beams and square hollow structural section (HSS) columns that are bolted together to create a sturdy and robust structural frame. However, the CFS-SBMF system is only suitable for constructing one-storey buildings, and ASCE 7 prohibits its use in buildings with a height of over one storey. This study was conducted to expand the use of CFS-SBMFs to the construction of multi-storey low-rise buildings. Firstly, a new moment connection detail is proposed, and a design procedure is proposed to ensure that bolted connections, instead of beams or columns, have the ductility to withstand seismic forces. Secondly, the proposed design procedure for bolted connections was verified through full-scale cyclic testing. Finally, a comprehensive evaluation was undertaken to evaluate the proposed structural system’s performance under seismic excitation. The evaluation included nonlinear dynamic analysis and incremental dynamic analysis (IDA) according to FEMA P695, which provided a detailed understanding of the seismic design factors (SDFs) in multi-storey low-rise CFS-SBMF buildings.

Seismic performance of BRBF with SMA core using incremental dynamic analysis

ABSTRACT In this paper, a new model for Buckling Restrained Braced Frames (BRBF) is proposed that Shape Memory Alloy (SMA) is used for the yielding core instead of steel. The seismic behaviour of a framed structure with chevron type buckling restrained braces is investigated and their seismic performance factors, such as permanent displacements, inter story drifts and response modification factors are evaluated. Nonlinear time history analysis and Incremental Dynamic Analysis (IDA) of two models subjected to 11 ground motion records is performed using OpenSees software. In order to evaluate the efficiency of the proposed model, it is compared to a BRB model with a steel core that the length of yielding core is 1 m for each model. Comparing the proposed bracing systems with conventional BRBFs indicates that buckling restrained braced frames equipped with SMA are better in terms of permanent roof displacement and maximum inter-story drift. However, the response modification factor of BRB models with steel core is higher.

Lateral load response and collapse probability of reinforced concrete shear walls retrofitted for repairability

AbstractThis paper demonstrates the efficacy of a new reinforced concrete shear wall seismic retrofit method through a series of nonlinear static and incremental dynamic analyses. Unlike traditional retrofit methods, the method investigated aims to convert conventional walls into self‐centering walls whose behavior is governed by rocking and flexure. The retrofit involves creating a cold joint at the foundation–wall interface, cutting some reinforcing bars to allow rocking, adding external post‐tensioning to enable self‐centering, and externally confining wall toes to prevent concrete crushing. The retrofit was applied to two building archetypes, each with two different shear wall designs. The four walls were retrofitted by varying retrofit parameters (portion of the vertical reinforcement bars cut, and external post‐tensioning amount). Nonlinear static and nonlinear response history analyses were performed using experimentally validated, computationally efficient models that simulate walls with fiber‐based beam–column elements. Incremental dynamic analysis was used to create collapse fragility functions for pre‐ and post‐retrofit walls. The results show that the retrofit is effective when some vertical reinforcement bars are left uncut across the foundation–wall interface. The retrofit is more effective for walls with vertical reinforcement distributed across cross‐section as compared to walls with reinforcement concentrated near boundary elements and for walls with structurally efficient amounts of reinforcement as compared to walls with higher amounts of reinforcement. This is attributed to the larger amount of reinforcement bars cut in walls with concentrated reinforcement layouts or heavy reinforcement amounts, leading to a larger loss of strength, recovery of which requires larger amounts of post‐tensioning.

Dynamic and uncertainty-based assessment of the progressive collapse probability of prestressed concrete frame structures with infill walls

Since progressive collapse usually has serious consequences, the problem of progressive collapse resistance has gradually become a topical issue in recent years. However, most of the existing studies have been conducted on common reinforced concrete (RC) structures. The methodologies used in the studies are also mostly static and deterministic. There is a lack of research that considers the dynamic effects and uncertainties of pre-stressed structures with infill walls. In this paper, the assessment of progressive collapse probability considering dynamic effect and uncertainties is performed for prestressed concrete frame with infill walls (IW-PC frame) structures. The finite element software OpenSEES is chosen as the analysis platform. By introducing uncertainties in material, geometry and load, five limit states and their quantitative indicators are identified. Based on the nonlinear incremental dynamic analysis (IDA) method, the vulnerability analysis of the IW-PC frame is performed under different working conditions. The vulnerability analysis indicates that the five levels of limit states can visually evaluate the degree of structural damage. Additionally, the resistance relationships of the four structural forms are as follows: IW-PC frame > reinforced concrete frame with infill walls (IW-RC frame) > prestressed concrete frame (PC frame) > RC frame. The load carrying capacity of the frames is significantly increased by the coupling effect of the infill walls and the prestressed strands. Moreover, the prestressed strands can reduce the probability of light and moderate damage, while infill walls have an excellent preventive effect on severe damage. The reliability of the four structures is evaluated using the Zhao-Ono moment method. The results indicate that IW-PC is the safest, followed by IW-RC, PC, and RC.

Seismic performance assessment of post-tensioned CLT shear wall buildings with buckling-restrained axial fuses

Post-tensioned cross-laminated timber (PT-CLT) walls have been demonstrated to be a low-damage seismic force-resisting system (SFRS) due to their self-centering capability. However, there is still a need to examine the seismic performance of such SFRS in high-seismic risk zones. This study evaluates the seismic performance of 6-, 9-, and 12-storey PT-CLT shear wall buildings in Vancouver, Canada, equipped with buckling-restrained axial fuses. The prototype buildings were designed using the displacement-based design method, and the assessment considered the most recent seismic hazard model provided in the 2020 National Building Code of Canada. To conduct nonlinear response history analysis (NLRHA) and incremental dynamic analysis (IDA), numerical models were developed in OpenSeesPy and calibrated based on component- and system-level experimental tests. The NLRHA and IDA results demonstrate that all the studied buildings have adequate collapse margin ratios, with less than a 10% chance of collapsing at the maximum considered earthquakes.

Seismic strengthening of isolated RC framed structures through orthogonal steel exoskeleton: Bidirectional non-linear analyses

The catastrophic effects of recent earthquakes around the world have highlighted the vulnerability of civil buildings; in Europe, most of the existing buildings were built after World War II and since they have largely exceeded their useful life, are characterized by a high vulnerability linked both to the durability of the materials and to the lack of seismic provisions in design. The current trend in constructional field is to design interventions aimed at the seismic and energy improvement of these structures jointly, in order to achieve a sustainable and integrated retrofit intervention. To this aim, the use of 2D orthogonal steel exoskeletons for the seismic strengthening represents a suitable solution, providing at the same time an enhancement in thermal insulation, through a ‘double-skin’ solution. Due to the growing interest in the design of steel exoskeleton interventions, a detailed dynamic characterization of this external strengthening solution is needed. In this framework, the present work, aims to investigate the effectiveness of the investigated strengthening solution by means of bi-directional non-linear dynamic analyses. Extensive numerical analysis was carried out. The selected case-study is an Italian existing pre-1980 s RC frame building located in Mugnano di Napoli (NA, Italy), which is a medium-high seismic hazard site in Italy (peak ground acceleration equal to 0.156 g). Two alternative strengthening solutions were numerically investigated by means of non-linear time-history and incremental dynamic analyses performed applying fifteen bidirectional ground motions on three-dimensional numerical models. The results of the dynamic non-linear analyses allow to quantify more appropriate performance indicators, both in terms of expected demand and overall collapse capacity, useful for the development of optimization strategy and design of exoskeleton system. The results highlighted that both the investigated strengthening scenarios allow to increase the stiffness of the existing building and allow it to meet the current code safety requirements reducing also the residual inter-storey drift. The obtained results are not strictly related to the investigated case study, but can be extended to all the structures retrofitted that follows the presented design procedure.

Seismic performance factors of quarter-elliptic-braced steel moment frames (QEB-MFs) using FEMA P695 methodology

One of the newest lateral load-resisting systems is quarter-elliptic-braced steel moment frames (QEB-MFs). The elliptical geometry of this bracing system not only resolves the shortcomings of conventional concentrically braced frame systems but also leads to greater energy absorption. The QEB-MF system's seismic performance factors (SPFs) are specified in this paper using the FEMA P695 approach. To this end, a three-dimensional group of 2-, 4-, 6-, and 8-story archetypes in two distinct seismic design categories (SDC Cmax and Cmin) were designed according to presumed SPFs. The adjusted collapse margin ratio (ACMR) for each archetype was calculated utilizing the results of non-linear static (pushover) analysis and incremental dynamic analysis (IDA) under far-field ground motion (FFGM) records. In order to confirm presumed SPFs, ACMRs were compared to FEMA P695's acceptable values. The results indicate that the ACMR values for the QEB-MF systems that were designed with a response modification factor of 6.5 are acceptable. In addition, the deflection amplification factor and the over-strength factor have been acquired to be equal to 6.5 and 2.5, respectively.

Seismic Resilience of Concrete Moment Frames with Fibrous Rubberized Beam-Column Joints

ABSTRACT Ensuring resilience through rapid buildings recovery in seismic zones has been placed at the forefront of recent studies. However, studies that compare the relative resilience of buildings constructed with different materials are lacking. This paper focuses on a comparative resilience analysis of concrete moment frames where beam-column connections are made with varying types of concrete mixtures. The connections are made with normal strength concrete (NSC), rubberized concrete (RbC), steel fiber rubberized concrete (STFRC), synthetic fiber rubberized concrete (SYFRC), and high strength concrete (HSC). Nonlinear static pushover and incremental dynamic analysis (IDA) are utilized to understand system response and the level of damage sustained following an earthquake. Subsequently, seismic fragility functions are constructed for the five considered frame types. The frames are subjected to different seismic scenarios, and the corresponding losses, recovery time, and resilience are quantified. A comparison between the five frame types is carried out to examine the optimal concrete mixture to be used to reduce damage probabilities, total direct losses, and recovery time and subsequently enhance resilience. The results show that rubberized concrete strengthened with steel and synthetic fibers can reduce economic losses by up to 19% and increase building resilience by up to 37% compared with the frames constructed with normal strength concrete.

IMPACT EFFECT ON THE EXISTING AND STRENGTHENED REINFORCED CONCRETE COLUMNS

Reinforced concrete (RC) columns are the main vertical elements in the buildings. Superstructure loads are transferred to the foundation by the columns whose design involves sufficient section sizes with longitudinal and transverse reinforcements. However, RC columns are required to be strengthened when low concrete quality and lack of reinforcement is stated. The most common strengthening technique for the RC columns is jacketing. In this method, strength of the existing column is improved by concreting and installing jacketing reinforcements. Although columns are designed according to several vertical and lateral load combinations, impact loads whose effects may reach very high values at short notice are not regarded. In the scope of this study, impact behavior of the existing and strengthened RC columns is numerically investigated. For this purpose, non-linear incremental dynamic analysis is carried out by Abaqus software that is widely utilized by engineers for such solutions. Acceleration, displacement and impact load values as well as crack patterns are obtained after numerical analysis. The results are comparatively presented for the existing and the strengthened columns. Analysis outputs reveal that proposed finite element models give an opinion about the impact responses of the RC columns. Consequently, it is evaluated that this study may make contribution to the researchers generating non-linear analysis without having to perform impact experiments that require high costs and heavy workloads in the laboratory conditions.

Performance assessment of steel frame buildings with hybrid self-centering braces under extremely rare far-field earthquakes

This paper investigates the seismic performance enhancement of steel frame buildings using a novel hybrid self-centering braces (HSBs) under extremely rare earthquake events. The hybrid self-centering brace consists of shape memory alloy (SMA) cables and viscoelastic (VE) dampers. A prototype bracing system is designed and fabricated to explore its basic mechanical behavior and working mechanism under cyclic loading, with a focus on its failure modes under large deformation loading condition. A multi-material mechanical model is developed to capture the mechanical behavior and failure of the HSB. Furthermore, five steel frame buildings with different parameterized HSBs are designed and modeled in OpenSees. Nonlinear dynamic analyses and incremental dynamic analyses are conducted on the five case-study frames using 44 far-field ground motions. The risk-based seismic performances of steel buildings with HSB are evaluated to assess the performance of HSB during extremely rare seismic events. The results show that the hybrid self-centering brace exhibits excellent self-centering and energy dissipation capabilities with the maximum equivalent viscous damping ratio reaching 9.4 %. Even under large deformations, VE dampers continue to work effectively after the failure of SMA cables, demonstrating remarkable redundancy. Numerical simulations further reveal that the redundancy of HSB can improve the structural seismic resilience in terms of inter-story drift ratio, residual drift, and floor absolute acceleration. The higher the redundancy of HSB in the case-study frames, the smaller the seismic response and mean annual frequency of exceedance of the engineering demand parameters, thereby indicating a significant improvement in seismic performance.

Seismic response and performance prediction of steel buckling-restrained braced frames using machine-learning methods

Nowadays, Buckling-Restrained Brace Frames (BRBFs) have been used as lateral force-resisting systems for low-, to mid-rise buildings. Residual Interstory Drift (RID) of BRBFs plays a key role in deciding to retrofit buildings after seismic excitation; however, existing formulas have limitations and cannot effectively help civil engineers, e.g., FEMA P-58, which is a conservative estimation method. Therefore, there is a need to provide a comprehensive tool for estimating seismic responses of Interstory Drift (ID) and RID with novel approaches to fulfill the shortcomings of existing formulas. The Machine Learning (ML) method is an interdisciplinary approach that makes it possible to solve these types of engineering problems. Therefore, the current study proposes ML algorithms to provide a prediction model for determining the seismic response, seismic performance curve, and seismic failure probability curve of BRBFs. To train ML-based prediction models, Nonlinear Time-History Analysis (NTHA) and Incremental Dynamic Analysis (IDA) were performed on the 2-, to 12-Story BRBFs subjected to 78 far-field ground motions, and 606944 data points were prepared for different prediction purposes. The results indicate that the considered approaches are justified. For instance, the proposed ML methods have the ability to predict the maximum ID, maximum RID and maximum roof ID with the accuracy of even 98.7%, 95.2%, and 93.8%, respectively, for the 4-Story BRBF. Moreover, a general preliminary estimation tool is introduced to provide predictions based on the input parameters considered in the study.

Development of fragility functions of low-rise steel moment frame by artificial neural networks and identifying effective parameters using SHAP theory

Estimating analytical fragility functions requires high computational costs due to numerous incremental non-linear dynamic analyses. This study employs a soft computing approach to reduce this process and increase estimation accuracy. Utilized a fragility database of low-rise steel moment structures designed for different versions of Iranian seismic design code, and six feedforward Artificial Neural Networks (ANN) with various architectures were trained to estimate the fragility function’s parameters to determine the most desired architectures. The neural networks used the design parameters (frames story, code edition of design, ductility, soil type, near- and far-field earthquake, and seismic zone factor and importance factor) as inputs. For each of the fragility function’s parameters (Median PGA and βs of damages: slight, moderate, extensive, and complete) as outputs, an ANN was trained. The best architect of ANN was selected based on the accuracy of the models from different statistical indicators and the most balanced of the inputs’ importance on the outputs using SHapley Additive explanations (SHAP) analysis. To demonstrate the accuracy of the selected architect, the coefficient of determination was estimated for all database values, and the fragility functions of four randomly chosen frames were compared. The high R2 value in most cases and the closeness of the predicted fragility curved with the actual one indicates the reliability of the ANN method for predicting the fragility function.

Impact of asymmetrical corrosion of piers on seismic fragility of ageing irregular concrete bridges

This article investigates the seismic fragility of ageing irregular multi-span reinforced concrete (RC) bridges. Different irregularity sources are considered, including: (i) substructure stiffness irregularity arising from the unequal-height piers, (ii) substructure stiffness irregularity arising from the spatially variable (asymmetrical) corrosion damage of piers and (iii) irregular distribution of effective tributary masses on piers of varying heights. To this end, a three-dimensional nonlinear finite element model is developed for multi-span RC bridges and verified against a large-scale shake table test results of a two-span concrete bridge specimen available in the literature. Nonlinear pushover, incremental dynamic and seismic fragility analyses are performed on three groups of two-span RC bridges with different configurations. Moreover, a time-dependent dimensionless local damage index is employed to evaluate the failure sequence and collapse probability of selected bridge layouts. The analysis results of the three studied irregularity sources show the considerable significance of spatially variable corrosion of bridge piers and substructure irregularity on the failure sequence of piers and seismic fragility of multi-span RC bridges. Furthermore, analysis outcomes show that uneven corrosion of piers triggers an unbalanced distribution of seismic ductility demands and irregular seismic response of equal-height multi-span RC bridges.

Seismic damage analysis of a brick masonry loess cave by a shaking table and FEM

In this paper, a typical brick masonry loess cave (BMLC) is selected, and finite element analysis software is used to establish a model and analyse its seismic performance. The model was verified by the test results of the BMLC on a 3D shaking table, and the damage quantification index was proposed. On this basis, seismic vulnerability analysis was carried out. A method based on nonlinear incremental dynamic analysis (IDA) was proposed to solve the rapid damage assessment of the traditional building of BMLC structures after earthquake action. The proposed method relies on an accurate numerical finite element model and pre-run multidimensional nonlinear IDA simulations with vibration data recorded during earthquakes. The IDA curves were built with different positions of the BMLC structure being considered. Moreover, meaningful local damage parameters were correlated with relevant seismic intensity measures. The results showed that the proposed method immediately and accurately estimated damage after seismic action if the IDA curve set had been previously constructed using a suitable model.

Enhancing seismic performance of buckling-restrained brace frames equipped with innovative bracing systems

Nowadays, to improve the performance of conventional bracing systems, in which, buckling in the pressure loads is the main disadvantage, the buckling-restrained brace (BRB) is introduced as a solution. In this study, the performance of the BRB system was improved with innovative lateral-resisting systems of double-stage yield buckling-restrained brace (DYB), and a combination of DYB improved with shape memory alloy (SMA) materials (DYBSMA). The proposed systems have been verified and implemented in the 2- to 12-story elevation steel buckling-restrained brace frames (BRBFs). To evaluate their effects on the seismic performance, two types of analysis including nonlinear dynamic analysis (NDA) and incremental dynamic analysis (IDA) were performed considering design-based earthquakes (DBE) and maximum considered earthquakes (MCE) levels for far-field ground motions. The results showed that the BRB system in all BRBFs had the highest values of residual drift ratio (RDRMed) demands, while implementing innovative DYBSMA can considerably reduce the values of RDRMed compared to other lateral-resisting systems. In addition, under MCE level, the BRB-DYBSMA system had lower values of the interstory drift ratio (IDRMed) and RDRMed demands (e.g., the IDRMed reduced by 79.67% and 18.5% compared to BRB and DYB systems, respectively), and can be introduced as the best lateral-resisting system. Therefore, the proposed BRB-DYBSMA system can effectively reduce the IDRMed and RDRMed demands, as result, higher performance levels can be achieved, as well as, the collapse probability occurrence over 1 and 50 years impressively decreased.

SEISMIC FRAGILITY EVALUATION OF SOIL-PILE-STRUCTURE INTERACTION EFFECTS SUBJECTED TO MAINSHOCK-AFTERSHOCK RECORDS

In most current seismic design on bridges, only mainshock actions are considered without incorporating the effect of mainshock-aftershock (MA) sequences and interaction soil-pile.However, a large mainshock usually triggers numerous aftershocks in a short period. This paperstudy the effect of mainshock-aftershock sequences on the behavior of interaction Soil-pile-structure system (ISPS). abeam on nonlinearWinkler foundation (BNWF) model is usingand subjected to non-linear static analysis and incremental dynamic analysis (IDA) leading finally to the fragility curves which are developed. These analyses aim to capture the collapse state of structures under aftershock events preceded by various mainshock levels. Results obtained from capacity curve, incremental dynamic and fragility curves of ISSP system.The analytical results show that in the MA sequences,for dense soil the vulnerable of mainshock-aftershock (MS-AS) loading are more damage due to mainshock loading for all diameter of the pile and the mass. For soft soil are more vulnerable to damage due to mainshock-aftershock (MS-AS) loading. But in the stiff clay the effect of mainshock-aftershock (MS-AS) loading for all the diameter of pile and for masse are neglected.
 Keywords:bridge,interaction soil-pile-structure, Winkler foundation, dynamic analysis, fragility curves,mainshock-aftershock.

Seismic performance assessment of self‐centering hybrid coupled walls: an 8‐story case study structure

AbstractIn response to the demand for resilient structures, a variety of innovative structural solutions have been recently introduced to reduce residual deformations and expedite the repair of structures subjected to earthquakes. This paper discusses the seismic performance of a self‐centering lateral load‐resisting system developed with the intent of diminishing earthquake‐induced damage and residual deformations. The proposed solution is composed of a reinforced concrete (RC) shear wall coupled to two steel side columns with coupling beams featuring a friction‐damped self‐centering mechanism. The intended system is referred as Self‐Centering Hybrid Coupled Wall (SC‐HCW). The applied self‐centering mechanism is aimed at reducing earthquake‐induced residual deformations. Limited residual deformations facilitate the repair of SC‐HWs after severe earthquakes, which improves the seismic resilience of the structure. The seismic performance of a SC‐HCW is examined and compared with that of a conventional hybrid coupled wall (HCW). Nonlinear static and Incremental Dynamic Analyses (IDAs) are conducted on these archetypes. The outcomes elaborate the efficiency of the SC‐HCW in minimizing earthquake‐induced residual deformations.

Seismic Fragility Analysis of a High-Pier Bridge under Pulse-like Ground Motion, Based on a PCA and K-Means Approach

The objective of this study is to present a novel fragility analysis method that combines principal component analysis (PCA) and the K-means clustering algorithm for a probability assessment of seismic damage in high-pier bridges undergoing pulse-like ground motions. Firstly, the method uses the correlation coefficient and the condition number as judgment indices to eliminate those seismic intensity measures (IMs) with weak correlation and multicollinearity from all 29 of the initial candidate seismic IMs, the optimal combination of IMs that satisfies the requirements for the PCA method is determined. Secondly, the method utilizes PCA to reduce the dimensionality of the optimal combination of IMs to obtain the principal components, after which the K-means algorithm is applied to classify the original group of selected pulse-like ground motions into four classes. Thirdly, a 3D finite element model of the exemplary high-pier bridge is developed via OpenSees, while incremental nonlinear dynamic time-history analyses are conducted to record the maximum cross-section curvatures of high piers under the influence of various categories of ground motions. Finally, based on the analytical procedures used in the increment dynamic analysis (IDA) method, this study develops and compares the fragility curves for the various classes of pulse-like ground motions. The results indicate the necessity of utilizing the PCA and K-means approach for classifying pulse-like ground motions in the seismic fragility analysis of high-pier bridges. This approach also significantly improves the precision and accuracy of damage probability analysis.