Nonlinear Pushover Analysis Research Articles

Post-Earthquake Condition Assessment and Seismic Upgrading Strategies for a Heritage-Protected School in Petrinja, Croatia

Following the Zagreb earthquake in March of 2020, a destructive 6.2 magnitude earthquake struck Croatia again in December of 2020. The Sisak-Moslavina county suffered the most severe consequences; many historical and cultural buildings were badly damaged. In the education sector, 109 buildings were damaged. One such building is the case study of this research. The heritage-protected building of the First Primary School in Petrinja is an unreinforced masonry structure, constructed using traditional materials and building techniques. The historical background of the building and the results of the post-earthquake assessment are presented. A numerical calculation of three strengthening methods was performed in 3Muri software: FRCM, FRP, and shotcrete. Non-linear pushover analysis was performed for each model. Finally, the strengthening methods are compared based on the achieved earthquake capacity, cost, and environmental impact.

Incremental seismic retrofitting for essential facilities using performance objectives: A case study of the 780-PRE school buildings in Peru

This paper presents a methodology to develop incremental seismic retrofitting alternatives for essential buildings through a nonlinear analysis. The retrofitting levels are defined in terms of the performance objectives such as immediate occupancy, life safety, code compliance and collapse prevention. Each of these is associated with a seismic hazard linked to a return period equivalent to a frequent, occasional, rare, and extreme event. The methodological approach conceives the non-linear behavior of the system through the definition of plastic hinges for structural components such as beams and columns. As soon as the model is properly defined, a nonlinear pushover analysis is performed to obtain the seismic response of the buildings. In addition, an incremental dynamic analysis is carried on for the equivalent single degree-of-freedom models of the same buildings, to estimate the critical seismic intensity at which collapse occurs; this allows corroborating the suitability of the proposed retrofitting alternatives. Once the methodology was well explained, a school building typology designated as a 780-PRE was chosen as an interesting case study for validation purposes. A total of 40,000 of its type were designed (under the national building design code RNC-77) and constructed between 1977 and 1997 throughout all the Peruvian territory. Typically, this system is characterized by reinforced concrete moment-resisting frames with unreinforced infill masonry walls. Despite its widespread use, this system typology has shown to be highly vulnerable under previous seismic events, depicting repetitive short-column failure mechanisms and partial collapses. This confirms a fragile failure contrary to the intended original design behavior for the as-built condition. Based on the previous understanding of the problem, several alternatives of incremental seismic retrofitting were considered in this study, supported on a benefit-cost evaluation to come up with feasible seismic vulnerability reduction strategies. After the interventions were selected and implemented, a noticeable improvement of the seismic response was perceived, depicted by a reduction in the expected damage under low and moderate seismic demands. Finally, the analyses were extended to several seismic zones in Peru.

Artificial Neural Network–Based Predictive Tool for Modeling of Self-Centering Endplate Connections with SMA Bolts

Endplate moment connections with shape memory alloy (SMA) bolts provide self-centering for the seismic resilience of structures. Predicting the self-centering response of these new beam–column connections, which have not been codified yet, requires conducting experimental tests or detailed continuum finite-element simulations. Computationally efficient predictive tools are needed to facilitate the analysis, design, and assessment of self-centering connections and moment frames. In this paper, artificial neural networks (ANNs) are used to develop a MATLAB tool for predicting the moment-rotation backbone and self-centering response of extended endplate connections with SMA bolts. As the input for the neural networks, the predictive model development employs a design database of response parameters from 72 finite-element (FE) models and experimental tests of seven beam–column connection specimens. Neural networks are trained for seven response parameters, and the trained networks are used to develop a graphical user interface (GUI). The coefficient of determination for the trained ANNs is in the range of 0.92 to 0.99, indicating acceptable prediction accuracy. Furthermore, optimization studies using a multiobjective genetic algorithm are performed, seeking the minimization of material use (steel and SMA) and improved connection-response characteristics (i.e., stiffness, strength, and ductility). A phenomenological model of SMA connections is also developed in OpenSees. The use of the ANN-based predictive tool for accurate and efficient modeling of SMA-based connections and self-centering moment-resisting frames is illustrated. The computation time for predicting the moment-rotation response of a typical SMA connection is significantly reduced from seven hours in ANSYS to only three minutes in OpenSees while providing the same level of response prediction accuracy. Furthermore, the optimization results are confirmed by performing nonlinear pushover and response history analyses.

Analysis of infilled steel frames subjected to lateral loading

In Recent days Earthquake resistant design of structure has earned a lot of scope as Earthquake has become more common. Lateral loading behaviour and energy absorption capacity of monolithic Steel framed structures is significantly affected by Presence of infill which adds to the bracing of the structure, Researchers developed new methods of seismic analysis to analyse the behaviour of structure during occurrence of an Earthquake. Performance based seismic design gives methodology for accessing the performance of structure occupancy, life safety or Collapse prevention level. A non-linear static pushover analysis can be used to analyse the inelastic response of structure to lateral load or displacement. In the present research a 3D model of G + 8 story steel framed building is considered for seismic design and performance evaluation. The model was analysed using ETABS software by response spectrum method for zone V according to IS 1893–2016. The performance is accessed by Capacity Spectrum Method using non-linear pushover analysis. The result of all models are analysed and compared in terms of base shear, story displacement, pushover curve, spectrum curve, performance point of the structure. Overall performance of the structure is found in safer limits.

Retrofitting of a Precast Reinforced Concrete Industrial Building Using Friction Dampers Without Stopping Functionality

This paper presents a seismic retrofit of an industrial-type precast reinforced concrete building structure using friction dampers. This project consisted of retrofitting two precast reinforced concrete buildings, of which one of them will be presented here. Precast concrete is one of the most preferred methods of construction for industrial structures due to its low cost, fast construction and availability in rural areas. Unfortunately, most structures constructed before “Specification for Buildings to be Built in Seismic Zones(TBDY 2018)” are not sufficiently engineered and are expected to have poor performance when exposed to a major seismic event. Because stopping the production cost can be tolerated by the owners, a retrofitting technique that can be assembled during normal function of the industrial structures is required. As a result of this requirement, friction dampers are selected as the supplemental energy dissipation device. ASCE 41-17 [10] is employed for the damper design and performance evaluation of the building. Before the damper study, some instability and weak connection problems are solved by some traditional measures of strengthening. The most effective damper configuration and capacities are selected after an iterative trial-and-error linear study using the simplified methods developed by PROMER. Nonlinear push-over analysis are conducted after linear prestudies. Finally, a nonlinear time-history analyses is performed for confirmation of the results. , It is shown that the proposed retrofit scheme satisfies the desired performance goals for both DBE and MCE events. Overall, it is considered that proposed retrofit scheme with dampers provides the optimal solution for the stakeholders of the project from a performance, design, constructability, and economical point of view. Some application photos will be presented and methods are explained in detail in the paper. The friction damper behavior is based on the rotational friction hinge concept

Incremental dynamic analysis of steel storage racks subjected to Chilean earthquakes

Steel storage racks are structures commonly used by all industries in Chile; nevertheless, due the seismic hazard in the country and its configurations, these structures are highly vulnerable to earthquakes and no specific regulations exist to design them. In this research, the seismic performance of steel storage racks subjected to Chilean Earthquakes was evaluated using nonlinear pushover and nonlinear dynamic analysis. The studied models consider different heights and global slenderness ratios in both directions and soil types. Racks were evaluated using an Incremental Dynamic Analysis (IDA) according to FEMA P695. Deformation values were exceeded in the down-aisle direction and the use of braces was necessary to control the interstory drift and high deformation levels. Also, the expected level of damage for drift design limits in models unbracing is not enough to keep the operation of the structures and more severe regulations are necessary to achieve a performance in agreement with Chilean design philosophy. Finally, the use of horizontal and lateral bracing improves the seismic performance of steel racks.

Constant Displacement Iteration Algorithm for Non-Linear Static Pushover Analysis

Abstract: The paper presents formulation and implementation of a new static push-over analysis algorithm for the seismic rehabilitation of structure, in accordance with “NEHRP Guidelines for the Seismic Rehabilitation of Buildings”. The concept of non-linear pushover analysis is described and one problem of steel structure with piping racks are examined. Earlier work contributed pushover analysis by controlled node method. Here we go with the different method with new problem statement. The sample structure is steel framed structure with piping racks with the G+10 story building. The final results give us the target displacement.

Fragility-informed seismic design of multi-column bridge bents with post-tensioned concrete columns for accelerated bridge construction

Accelerated Bridge Construction (ABC) is playing an increasingly large role in bridge construction within urban centers due to faster installation, improved quality and lower cost. Concrete columns are prefabricated and connected together with footings and cap beams using either grouted splice sleeves, socket connections, or through post-tensioning. Precast unbonded post-tensioned (PT) concrete columns are protected from damage due to their ability to mitigate seismic demand through rocking. A numerical model is developed for rocking columns which is validated using published data. Seismic assessment of a two-column bridge bent constructed with precast PT concrete columns is carried out; column height-to-width ratio and ratio of initial posttensioning force to axial column capacity are selected as the assessment parameters. Performance limits are defined for the bridge model using non-linear pushover analysis. Probabilistic seismic hazard analysis is carried out using nonlinear time-history analysis for a set of eighty ground motions. The results show that PT concrete columns provide sufficient re-centering to the bridge bent so that it remains serviceable after a large earthquake. An ABC bridge bent with unbonded PT concrete columns is designed using the outcome of seismic fragility analysis. The seismic performance of the fragility-designed PT bridge bent is compared to that of a bent with conventional cast-in-place (CIP) concrete columns using nonlinear time-history analysis. The seismic performance of the ABC PT bridge bent using fragility analysis satisfied performance objectives similar to a monolithic CIP bent designed according to the latest seismic design codes; in addition, the residual drift of the PT bent was practically zero. The fragility-informed approach for designing ABC bridge bents constructed with unbonded PT concrete columns presented is expected to promote post-earthquake serviceability and functional recovery after a large earthquake.

Seismic response of a container crane subjected to ground motions

This study examined the effect of earthquake frequency on the seismic response of a typical modern container crane. A time-history analysis was carried out on the crane using 93 real ground motion records to investigate its behavior. Also, an eigenvalue and a nonlinear pushover analysis were conducted to obtain the dynamic properties and assess the structural performance of the crane, respectively. Three earthquake suites categorized as low-frequency earthquake suite (LFES), intermediate frequency earthquake suite (IFES), and high-frequency earthquake suite (HFES) were considered in this study. The earthquakes were categorized into the three frequency suites based on their peak ground acceleration-to-peak ground velocity ratio (PGA/PGV). By applying the three earthquake suites in the time-history analysis of the crane, drift ratio, internal forces, stresses, and strain were captured to examine its critical seismic response. The results demonstrated the effect of the frequency content on the seismic response of the crane. The LFES was found to cause drift responses averaging 114% and 480% and stress responses averaging 82% and 261%, which were higher than those of IFES and HFES. LFES, IFES, and HFES were found to exact inelastic demands on the crane above the PGA thresholds of 0.34 g, 0.80 g, and 1.99 g, respectively. The LFES was found to cause an uplift response that averaged 468% higher than that of IFES. The uplift caused by the HFES was observed to be inconsequential. Furthermore, it was found that the ground motions with low PGA/PGV ratio values had a larger damage potential on the container crane.

Theory for nonlinear section model tests in the wind tunnel for cable-supported bridges

Wind tunnel tests for cable-supported bridges have been utilized extensively to achieve stable and wind resistant bridge designs over the past decades. Section model tests are by far the most common tests carried out. This is mainly due to their simplicity and their cost effectiveness. However, in order to reach this level of simplicity, some generalizations are required. One of them is the assumption that the bridge structure behaves linearly. For most bridges, this seems reasonable, but for very long spans, the cable system plays a dominant role in providing the vertical and torsional stiffnesses. Hence, as the cable system behaves nonlinearly, very long spans show a stronger nonlinear behavior, especially for suspension bridges. Furthermore, the theoretical demonstrations that have been made with regard to structural dynamic instabilities associated with geometric nonlinearities in suspension bridges confirm the need for a better understanding of the possible interaction between nonlinear structural effects and aeroelastic effects. Therefore, this paper presents the theoretical developments for a new type of section model test for bridges that accounts for geometric nonlinearities of the bridge structure. This theory for nonlinear section model tests starts from two-mode nonlinear generalized stiffness parameters obtained using nonlinear pushover analysis, which need to be scaled using a specifically developed procedure. Using eleven numerical models of cable-supported bridges, the assumptions made in the theory for nonlinear tests are then validated. The proposed scaling procedure is also tested.

An energy-based method to calculate the vulnerability scores of RC buildings for rapid structural assessment methods

In this study, the some of the vulnerability scores commonly used in rapid structural assessments methods are obtained by an energy based method. For this purpose, non-linear time history and non-linear pushover analyses of several 2D frames with different structural and dynamic properties are performed. Both of the material and geometric nonlinearity are considered in the structural models. The non-linear time history analyses are performed with response spectra compatible far fault ground motion records. The analyses results revealed that the vulnerability score of soft story formation may be improved by considering it in a parametric manner instead of using a constant vulnerability score. The presence of brick masonry infill walls reduces the negative effect of soft story formation. The presence of weak story formation (for the considered case) also affects the earthquake performance of structure but this negative effect is not considerable as that of soft story formation. The combined effect of structural deficiencies can be more significant than the values of vulnerability scores calculated by summing the vulnerability score of each structural deficiency.

Steel moment resisting frames with energy-dissipation rocking columns under near-fault earthquakes: Probabilistic performance-based-plastic-design for the ultimate stage

In this paper, a probabilistic performance-based-plastic-design methodology for steel moment resisting frames with energy-dissipation rocking columns (MRF-EDRCs) was developed, and the emphasis was given to the ultimate stage of the structure subjected to near-fault earthquakes. Firstly, based on the energy balance notion and an equivalent nonlinear single-degree-of-freedom (SDOF) system representing a low-to-medium steel MRF-EDRC, nonlinear spectral analyses were carried out considering various combinations of hysteretic parameters and a wide range of structural periods. More than 55 million energy modification factors quantifying the seismic demand of the system subjected to near-fault earthquake motions were obtained. Then, a probabilistic spectral model of the energy modification factor was established, which can be utilised as the basis of the design methodology. To promote engineering applications, a stepwise design framework for the steel MRF-EDRC with target drift and a prescribed probabilistic performance target was proposed. To verify the effectiveness of the proposition, a prototype structure with two target drifts was designed and modelled by finite element approach. The rationale of the modelling strategies was confirmed by previous test data. Subsequently, the seismic performance of the designed structure was evaluated by nonlinear pushover and dynamic analyses. The results showed that the designed structure conforming to the proposed method can limit the maximum inter-storey drift to a preselected threshold with a prescribed probabilistic performance target.

Numerical Analysis to Evaluate the Structural Performance of NFRCM (Natural Fabric-Reinforced Cementitious) Strengthened Masonry

The innovative sustainable technology based on natural fabric-reinforced cementitious matrix (NFRCM) is analyzed for strengthening masonry. A new frontier for composite materials is proposed as an alternative to well-known traditional technologies used to improve the seismic behavior of buildings, such as the portuguese technique ‘gaiola pombalina’, the Italian ‘baraccata house’ and the turkish ‘himis house’. Preliminary sensitivity analysis is performed on NFRCM and ‘baraccata’ numerical models. Both technologies are numerically compared. From the experimental results of in-plane incremental load test carried out by CNR-Ivalsa a numerical model is calibrated by non-linear pushover analysis to evaluate the behavior of masonry wall strengthened with natural fibers. This paper demonstrates the effectiveness of NFRCM systems for strengthening masonry as: i) a non-invasive solution without significant thickness; ii) a sustainable technology; iii) an intervention involving the whole wall surface avoiding failure local mechanisms.

Capacity Design of Coupled Composite Plate Shear Wall–Concrete-Filled System

Composite plate shear walls–concrete-filled (C-PSW/CF) are a new and innovative lateral force–resisting system intended for high-rise buildings. High-rise building applications of this system are particularly efficient in the coupled wall configuration, in which the walls are C-PSW/CF and the coupling beams are concrete filled steel box sections. This paper presents a capacity design principle for the seismic design of coupled composite plate shear wall–concrete filled (CC-PSW/CF) systems. The capacity design principle implements a strong wall–weak coupling beam approach, in which flexural yielding occurs in the coupling beams before flexural yielding at the base of walls. The coupling beams are sized to resist the calculated seismic lateral force level. The composite walls are sized to resist an amplified seismic lateral force corresponding to the overall plastic mechanism for the structure, while accounting for the capacity-limited forces from the coupling beams and the coupling action between the walls. The paper summarizes the recommendations and requirements for appropriate sizing of the composite coupling beams and walls. These recommendations were used along with the capacity design principle to design four example (8–22-story) structures and evaluate their seismic behavior. The structures were modeled using benchmarked finite-element models and fiber-based models that accounted for the various limit states, including steel yielding, local buckling, fracture, concrete crushing, confinement, and tension cracking. The numerical models were analyzed for monotonic pushover loading and scaled seismic ground motions. The structural responses from the nonlinear pushover analysis and the nonlinear time history analyses were in accordance with the capacity limited design philosophy, thus confirming its efficacy.

Seismic Risk Assessment of Urban Areas by a Hybrid Empirical-Analytical Procedure Based on Peak Ground Acceleration

The seismic risk assessment of existing urban areas provides important information for the process of seismic risk reduction in different phases of planning and emergency management. Between different large-scale assessment approaches, a vulnerability index method is often used for the first screening of the buildings and vulnerability classification. However, this method cannot fully predict the effects of a specific seismic action on buildings. This paper fully extends the scale of the settlement and properly upgrades a methodology previously proposed by authors to predict seismic damage and the risk to a restricted number of masonry buildings in the Croatian settlement Kaštel Kambelovac located along the Adriatic coast. The proposed approach is based on a hybrid empirical-analytical procedure that combines seismic vulnerability indices with critical peak ground accelerations for different limit states computed through a non-linear pushover analysis. The procedure’s outcomes are the computation of a relationship linking vulnerability indices to peak ground acceleration for a series of states, corresponding to damage limitation, significant damage, and near collapse. The described methodology is used to estimate seismic risk in terms of damage and the index of seismic risk for selected return periods. The general methodology has allowed a full seismic vulnerability assessment of the whole Croatian settlement of Kaštel Kambelovac.

Experimental and numerical investigation on reserve strength of jackets with single diagonal and X brace configurations

ABSTRACT Jacket framing arrangement X, K, V and single bracing systems used in jackets influence the ultimate strength and redundancy in the system. Experimental investigation was conducted on a 2D frame (1:20) with two different bracing patterns (2D-1 and 2D-2) the results are compared with that obtained from nonlinear pushover analysis. Parametric assessment of Reserve Strength Ratio has been carried out on three bracing patterns, namely 3D-A, 3D-B and 3D-C using non-linear pushover analysis including pile-soil interaction. It is observed that RSR increases by 15% for X brace configuration (2D-2) compared to single brace configuration (2D-1). The RSR for 3D-B is found to be higher by be 35 % and 12% compared to bracing patterns 3D-A and 3D-C respectively. The brace pattern 3D-C exhibits similar strength to 3D-B, illustrating the insignificance of the brace at the top bay and this leads to reduction in wave loads on the system.

Lateral behavior of trapezoidally corrugated wall plates in steel plate shear walls, Part 2: Shear strength and post-peak behavior

This research focuses on the shear strength and post-peak behavior of trapezoidally corrugated wall plates in vertically or horizontally Corrugated Steel Plate Shear Walls (CoSPSWs) through nonlinear pushover analyses. Results showed that different from flat wall plates, corrugated wall plates could develop a shear strength close to the shear yield strength at relatively low lateral drifts, and the lateral load-drift curves usually experienced a descending stage, which was closely related to the elastic shear buckling stress, the dominant shear buckling mode, and the shear yield strength. Corrugated wall plates with higher elastic shear buckling stress, dominant global shear bucking mode, or lower shear yield strength would generally have slightly higher peak nominal shear stress ratio and much higher ductility than wall plates with lower elastic shear buckling stress, dominant interactive or local shear bucking mode, or higher shear yield strength. A shear slenderness ratio λs was then introduced as the square root of the ratio between the shear yield strength and the elastic shear buckling stress, and simplified lateral load-drift curves were proposed for corrugated wall plates with different dominant shear buckling modes and range of λs values. The proposed curves could accurately predict the initial lateral stiffness, the shear strength as well as the post-peak descending behavior of corrugated wall plates.

A Procedure for Performing Nonlinear Pushover Analysis for Tsunami Loading to ASCE 7

A Procedure for Performing Nonlinear Pushover Analysis for Tsunami Loading to ASCE 7

A methodological approach for seismic performance of existing single-storey industrial RC precast facilities

In critical earthquake-prone regions, many kinds of old-dated industrial facilities having structural deficiencies exist. Evaluation of seismic performance of these buildings to reach a sufficient level is quite vital. This paper scopes seismic performance assessment of an existing industrial structure. In the study, a comprehensive methodology is presented to carry out the seismic evaluation process of the buildings. The entire process is illustrated using a case study from an existing industrial precast facility. In this scope, initially, construction system, geometry, layout and material properties of the examined structure were determined through lab studies and site surveys to assess the performance level. Secondly, the current status of the structure was modeled using Midas Gen finite element software and a series of analyses were performed to reveal the seismic performance. In the analyses of seismic performance, the non-linear pushover analyses method was employed in seismic code. In the model the fiber and lumped hinges were assigned to the columns and beams, respectively. The strains occurring in the column cross-sections were calculated using the curvature values obtained from the corresponding members assigned hinges. These values were compared with the limit values which were specified in the code. It is concluded that this case study presents a practical approach for engineering applications regarding the seismic evaluation of industrial structures from the perspective of update codes.

Effect of Masonry Infill Panels on the Seismic Response of Reinforced Concrete Frame Structures

The present work concerns the numerical investigation of reinforced concrete frame buildings containing masonry infill panel under seismic loading that are widely used even in high seismicity areas. In seismic zones, these frames with masonry infill panels are generally considered as higher earthquake risk buildings. As a result there is a growing need to evaluate their level of seismic performance. The numerical modelling of infilled frames structures is a complex task, as they exhibit highly nonlinear inelastic behaviour, due to the interaction of the masonry infill panel and the surrounding frame. The available modelling approaches for masonry infill can be grouped into two principal types; Micro models and Macro models. A two dimensional model of the structure is used to carry out non-linear static analysis. Beams and columns are modelled as non-linear with lumped plasticity where the hinges are concentrated at both ends of the beams and the columns. This study is based on structures with design and detailing characteristics typical of Algerian construction model. In this regard, a non-linear pushover analysis has been conducted on three considered structures, of two, four and eight stories. Each structure is analysed as a bare frame and with two different infill configurations (totally infilled, and partially infilled). The main results that can be obtained from a pushover analysis are the capacity curves and the distribution of plastic hinges in structures. The addition of infill walls results in an increase in both the rigidity and strength of the structures. The results indicate that the presence of non-structural masonry infills can significantly modify the seismic response of reinforced concrete "frames". The initial rigidity and strength of the fully filled frame are considerably improved and the patterns of the hinges are influenced by structural elements type depending on the dynamic characteristics of the structures. Doi: 10.28991/cej-2021-03091764 Full Text: PDF