Nonlinear Static Pushover Research Articles

Seismic performance assessment of different fibers reinforced concrete columns using incremental dynamic analysis

Different fiber-reinforced concrete (FRC) has been widely used in the recent decades, which can improve the mechanical behavior and dynamic performance of reinforced concrete (RC) columns remarkably. This paper aims to compare the seismic behavior of columns constructed with different FRC material, namely steel fibers reinforced concrete (SFRC), polypropylene fibers reinforced concrete (PFRC) and steel-polypropylene hybrid fiber reinforced concrete (HySPFRC). 3-D nonlinear finite element models have been built to represent the seismic behavior of different FRC columns, which are calibrated with the available experimental results of quasi-static tests. The seismic capacity of bridge columns with different FRC material are assessed based on four flexural damage states through the nonlinear static pushover analysis, such as a) yielding of longitudinal steels; b) core concrete crushing; c) buckling and d) fracture of longitudinal of steels. Incremental dynamic analyses (IDA) are conducted using the selected suite of 20 near-fault as-recorded ground motions to evaluate the inelastic seismic responses of different bridge columns. IDA curves are generated based on the intensity measure, namely peak ground acceleration (PGA) in this paper and seismic demands (i.e. maximum drift, residual drift, displacement ductility and curvature ductility) through nonlinear dynamic time-history analysis. It can be concluded from the IDA results that the SFRC, PFRC and HySPFRC are all effective to enhance the seismic performance, thus reducing the anticipated damage of the bridge columns. Moreover, SFRC and HySPFRC are more effective to improve the seismic capacity of bridge columns for the slight and moderate damage states, while PFRC and HySPFRC are more effective at the extensive and complete damage states.

Seismic performance of a damage avoidance self-centring brace with collapse prevention mechanism

The Resilient Slip Friction Joint (RSFJ) has recently been developed and introduced to the construction industry. This joint is a friction-based energy dissipation device that owing to its special configuration can provide energy absorption and self-centring behaviour in one package. This device is most applicable when the designers consider a damage avoidance philosophy of design. One of the applications of this device is the RSFJ brace. In this bracing system, the required seismic performance is provided by the RSFJ and the rest of the brace components are aimed to stay elastic. This paper introduces the RSFJ bracing system including the collapse-prevention fuse. This built-in fuse works in a way that when the applied force exceeds the design load, the secondary fuse is activated and the RSFJ brace is still able to provide self-centring up to twice the target deformation with an axial force of up to 1.25 times of the target design force. The performance of this fuse is investigated by experimental tests on the component level and the results are presented. Moreover, a numerical model for a five story steel structure with RSFJ braces is developed and was subjected to non-linear static pushover and nonlinear dynamic time-history simulations in order to investigate the seismic performance of the proposed system. The findings of this research shows that the RSFJ brace system can offer substantial performance benefits and has the merit to be considered as an efficient alternative for the current bracing systems.

Seismic Performance Evaluation of a Fully Integral Concrete Bridge with End‐Restraining Abutments

A fully integral bridge that is restrained at both ends by the abutments has been proposed to form a monolithic rigid frame structure. Thus, the feasible horizontal force effect due to an earthquake or vehicle braking is mainly prevented by the end‐restraining abutments. In a recent study, a fully integral bridge with appropriate end‐restraining abutment stiffness was derived for a multispan continuous railroad bridge based on linear elastic behavior. Therefore, this study aims to investigate the nonlinear behavior and seismic capacity of the fully integral bridge and then to assess the appropriate stiffness of the end‐restraining abutment to sufficiently resist design earthquake loadings through a rigorous parametric study. The finite element modeling and analyses are performed using OpenSees. In order to obtain the force‐deflection curves of the models, nonlinear static pushover analysis is performed. It is confirmed that the fully integral bridge prototype in the study meets the seismic performance criteria specified by Caltrans. The nonlinear static pushover analysis results reveal that, due to the end‐restraining effect of the abutment, the lateral displacement of the fully integral bridge is reduced, and the intermediate piers sustain less lateral force and displacement. Then, the sectional member forces are well controlled in the intermediate piers by a proper application of the end‐restraining abutments.

Seismic risk assessment of intake tower in Korea using updated fragility by Bayesian inference

This research aims to assess the tight seismic risk curve of the intake tower at Geumgwang reservoir by considering the recorded historical earthquake data in the Korean Peninsula. The seismic fragility, a significant part of risk assessment, is updated by using Bayesian inference to consider the uncertainties and computational efficiency. The reservoir is one of the largest reservoirs in Korea for the supply of agricultural water. The intake tower controls the release of water from the reservoir. The seismic risk assessment of the intake tower plays an important role in the risk management of the reservoir. Site-specific seismic hazard is computed based on the four different seismic source maps of Korea. Probabilistic Seismic Hazard Analysis (PSHA) method is used to estimate the annual exceedance rate of hazard for corresponding Peak Ground Acceleration (PGA). Hazard deaggregation is shown at two customary hazard levels. Multiple dynamic analyses and a nonlinear static pushover analysis are performed for deriving fragility parameters. Thereafter, Bayesian inference with Markov Chain Monte Carlo (MCMC) is used to update the fragility parameters by integrating the results of the analyses. This study proves to reduce the uncertainties associated with fragility and risk curve, and to increase significant statistical and computational efficiency. The range of seismic risk curve of the intake tower is extracted for the reservoir site by considering four different source models and updated fragility function, which can be effectively used for the risk management and mitigation of reservoir.

NATURAL CHARACTERISTICS AND NONLINEAR BEHAVIOR OF A NEW RC FORMWORK SYSTEM

Reinforced concrete (RC) products poured directly at sites or prefabricated are still popular choices in civil engineering field around the world. In the present study, prefabricated RC formwork possibly decreasing project duration remarkably and mostly keeping the monolithic behavior of frames are introduced. A RC prefabricated formwork system not only plays the same role as classical kinds of formwork, particularly wood, plastic or steel but also contributes to the strength of structures. The natural characteristics and the nonlinear performance of a single three-dimensional frame built using a RC formwork system are evaluated by comparing with those of a reference frame constructed traditionally. The natural frequencies are determined experimentally using shaker test and by numerical modeling using finite element method (FEM) whereas the nonlinear performance of the structures is computed by nonlinear static pushover analysis (NSPA) using the software package ABAQUS (2013). Based on the results of the empirical vibration test and numerical modeling, the natural characteristics of both structures are approximately similar to each other. However, in case of nonlinear performance, although the frame built using the RC formwork system performs a lower bending capacity, about 70% of the ultimate flexural strength of the monotonic frame, its ductility ratio is higher, 13.3% in comparison with 8.2% of the classical frame.

Numerical evaluation of the hysteretic behavior of concentrically braced frames and buckling restrained brace frame systems

This paper presents a numerical investigation of buckling restrained brace (BRB) frames (BRBF) and a comparison with concentrically braced frames (CBF). A simplified core-spring finite element model was used to model BRB elements. Four types of CBF (X, V, inverted V, and two-story X) and four types of BRBF (diagonal, V, inverted V, and two-story X) were modeled in ABAQUS. A static nonlinear pushover analysis considering two cyclic loading protocols showed that the buckling restraint allows the BRB elements to undergo significant plasticity without forming plastic hinges, thereby dissipating a proportionally larger amount of energy and delaying yielding in the frame elements. Results indicated dramatic improvements in energy dissipation and ductility in BRBF models as compared to equivalent CBF models. Seismic response modification factors for BRBF models also showed greater values over CBF models. Time-history analysis evaluated the performance of CBF and BRBF under historical earthquake loadings and supported the same conclusions. The best performance was observed for V, inverted V, and two-story X BRBF configurations; the diagonal BRBF configuration performed better than equivalent CBF models, but did not perform nearly as well as the other BRBF models.

Enhanced Seismic Fragility Analysis of Unanchored Steel Storage Tanks Accounting for Uncertain Modeling Parameters

Catastrophic failure of the above ground steel storage tanks was observed during past earthquakes, which caused serious economic and environmental consequences. Many of the existing tanks were designed in the past with outdated analysis methods and with underestimated seismic loads. Therefore, the evaluation of the seismic vulnerability of these tanks, especially ones located in seismic prone areas, is extremely important. Seismic fragility functions are useful tools to quantify the seismic vulnerability of structures in the framework of probabilistic seismic risk assessment. These functions give the probability that a seismic demand on a given structural component meets or exceeds its capacity. The objective of this study is to examine the seismic vulnerability of an unanchored steel storage tank, considering the uncertainty of modeling parameters that are related to material and geometric properties of the tank. The significance of uncertain modeling parameters is first investigated with a screening study, which is based on nonlinear static pushover analyses of the tank using the abaqus software. In this respect, a fractional factorial design and an analysis of variance (ANOVA) have been adopted. The results indicate that the considered modeling parameters have significant effects on the uplift behavior of the tank. The fragility curves of two critical failure modes, i.e., the buckling of the shell plate and the plastic rotation of the shell-to-bottom plate joint, are then developed based on a simplified model of the tank, where the uplift behavior is correctly modeled from the static pushover analysis. The uncertainty associated with the significant parameters previously identified are considered in the fragility analysis using a sampling procedure to generate statistically significant samples of the model. The relative importance of different treatment levels of the uncertainty on the fragility curves of the tank is assessed and discussed in detail.

Seismic capacity estimation of a reinforced concrete containment building considering bidirectional cyclic effect

This study serves to estimate the seismic capacity of the reinforced concrete containment building considering its bidirectional cyclic effect and variations of energy. The implementation of the capacity estimation has been performed by extending two well-known methods: nonlinear static pushover and incremental dynamic analysis. The displacement and dissipated energy demands are obtained from the static pushover analysis considering bidirectional cyclic effect. In total, 18 bidirectional earthquake intensity parameters are developed to perform the incremental dynamic analysis for the reinforced concrete containment building. Results show that the bidirectional static pushover analysis tends to decrease the capacity of the reinforced concrete containment building in comparison with unidirectional static pushover analysis. The 5% damped first-mode geometric mean spectral acceleration strongly correlates with the maximum top displacement of the containment building. The comparison of the incremental dynamic analysis and static pushover curves is employed to determine the seismic capacity of the reinforced concrete containment building. It is concluded that bidirectional static pushover and incremental dynamic analysis studies can be used in performance evaluation and capacity estimation of reinforced concrete containment buildings under bidirectional earthquake excitations.

Probability-based practice-oriented seismic behaviour assessment of simply supported RC bridges considering the variation and correlation in pier performance

Abstract Probability-based seismic performance assessment of in-service bridges has gained much attention in the scientific community during the past decades. The nonlinear static pushover analysis is critical for describing the seismic behaviour of bridges subjected to moderate to high seismicity due to its simplicity. However, in existing analysis methods, the generation of pushover curve needs tremendous amount of computational costs and requires skills, which may halter its application in practice, implying the importance of developing practice-oriented analysis method with improved efficiency. Moreover, the bridge pier performance has been modelled as deterministic, indicating that the variation associated with the pier material and mechanical properties remains unaddressed. The correlation in the performance of different piers also exists due to the common design provisions and construction conditions but has neither been taken into account. This paper develops a simplified pushover analysis procedure for the seismic assessment of simply supported RC bridges. With the proposed method, the pushover curve of the bridge can be obtained explicitly without complex finite element modelling. A random factor is introduced to reflect the uncertainty in relation to the pushover curve. The correlation in the pier performance is considered by employing the Gaussian copula function to construct the joint probability distribution. Illustrative examples are presented to demonstrate the applicability of the method and to investigate the impact of variation and correlation in bridge pier behaviour on the seismic performance assessment.

Probabilistic seismic demand assessment accounting for finite element model class uncertainty: Application to a code‐designed URM infilled reinforced concrete frame building

SummaryReliable and robust probabilistic assessment of structures requires explicit consideration of all relevant sources of uncertainty, both aleatory and epistemic. This paper proposes a formulation to incorporate model class uncertainty in probabilistic seismic demand assessment (PSDA) of structures, where model class uncertainty relates to the use of different structural analysis models used to predict the physical response of structural systems. The application of the proposed formulation is illustrated through the assessment of a recent code‐designed reinforced concrete (RC) frame building with unreinforced masonry (URM) infills, which is a prevalent form of construction worldwide. The model class uncertainty analyzed in this paper is related to the potential selection of one of three state‐of‐the‐art masonry infill strut models. In the application example, nonlinear static pushover (NSP) analyses and tornado sensitivity analyses are performed to identify the important parameters of infill strut models affecting the seismic response of the infilled RC frame. A hybrid stripe analysis (HSA) approach is adopted to perform nonlinear response history analyses (NRHAs) of the example RC frame. To account for relevant sources of uncertainty, latin hypercube sampling (LHS) is used to quantify the minimum number of realizations of model parameters necessary to achieve convergence of the coefficient of variation (COV) of the engineering response parameters assessed. Results of the NRHAs indicate that incorporating model class uncertainty significantly affects the estimation of uncertainties of the drift hazard demand.

Elastic-displacement-based multi-modal pushover analysis in high-rise core wall buildings

Higher mode effects play a major role in the seismic demands of high-rise buildings. Several recent studies have shown that seismic design demands such as design shear and bending moment in high-rise buildings cannot be predicted by the conventional code-based response spectrum analysis procedure. These can be determined by the more rigorous and accurate non-linear response history analysis procedure, but this procedure is computationally very extensive and time consuming. Yet a non-linear static pushover analysis cannot account for higher mode effects. Therefore, the applicability of a multi-modal pushover analysis (MMPA) procedure using elastic target displacement to cases of 20- 30- and 40-storey high-rise reinforced concrete core wall buildings is investigated in this study. The results obtained by the elastic displacement MMPA (EDMMPA) procedure are compared with those obtained from non-linear analysis. The comparison shows that EDMMPA can satisfactorily estimate the design shear force, bending moment and deformation demands with a variation of 10–20%. Thus, this computationally less demanding analysis can serve as a base line for preliminary design of high-rise reinforced concrete core wall buildings.

Role of masonry infill wall on the seismic behavior of typical four-storey building in Pakistan

Masonry infill walls are used as partition in reinforced concrete frames and are considered as a non-engineering structure for design and analysis purposes. The goal of this study is to compare different response parameters such as displacement, storey drift, base shear and ground overturning moment of a multi-storey RC frame structure with and without infill walls. For this purpose, a four-storey building is selected, which is supposed to be situated on stiff soil type (SD) and seismic zone 2B according to the Building Codes of Pakistan. Openings are neglected in the building. Non-linear static pushover analysis method is used to check the behavior of building during earthquake using SAP-2000. To find the width of compression struts, FEMA-356 is used. The results are compared and shown in the form of graphs. It is concluded that the masonry infill walls may have significant effects on the seismic response of the reinforced concrete frame structures, therefore, infill walls need to be considered during the design and analysis of the building.

Comparative Capacity Assessment of CFRP Retrofit Techniques for RC Frames with Masonry Infills Using Pushover Analysis

In this study, nonlinear static pushover analysis was performed to compare the effectiveness of different carbon fibre-reinforced polymers (CFRP) rehabilitation schemes for existing masonry-infilled RC frames. A three-bay five-storey reinforced concrete (RC) frame with masonry infill walls designed according to previous building codes was modelled as a representative of existing low-rise RC frames. The earthquake retrofitting effects of twelve CFRP strengthening schemes were compared in terms of the global pushover curve, maximum load capacity, maximum interstorey drift ratio (IDR), plastification in the frames, and maximum energy dissipation capacity. The results indicate that the improper selection of a retrofitting scheme is likely to result in the change of the soft storey location, which would cause unexpected damage to structures. The CFRP rehabilitation of both columns and infills for the bottom three floors or more leads to a significant increase in maximum load, maximum IDR, maximum energy, and maximum number of plastic hinges in the frames.

Performance-based assessment of response reduction factor of RC-elevated water tank considering soil flexibility: a case study

The seismic design codes/standards of most countries include the nonlinear response of a structure implicitly through a response reduction/modification factor (R). It is the factor by which the actual base shear should be reduced to find the design base shear during design basic earthquake considering nonlinear behavior and deformation limits of structures. In the present study, attempts are made to determine the ‘R’ factors of four existing RC staging elevated water tanks, which are designed as per draft Indian standards for seismic design of liquid and RC designs and having a ductile detailing considering the effects of soil flexibility. The elevated RC water tanks are analyzed using displacement controlled non-linear static pushover analysis to evaluate the base shear capacity and ductility of tank considering soil flexibility. The ‘R’ factor is obtained for four realistic designs of elevated RC water tanks having different capacities at two performance levels. The evaluated values of ‘R’ factor are compared with the values suggested in the design code. The results of the study show that the flexibility of supporting soil has considerable effect on response reduction factor, period and overall performance of water tank, indicating that idealization of fixity at base may be seriously mistaken for soft soils. All the studied water tanks were designed with higher safety margin than that of specified in Indian Standards.

ANALYTICAL FRAGILITY CURVES FOR REINFORCED CONCRETE BUILDING USING SINGLE POINT SCALED SPECTRUM MATCHED GROUND MOTION ANALYSES

Seismic performance is obtained for a five-storied reinforced concrete frame building performing non-linear dynamic time history analyses. Performance of the building was obtained as a mean of fragility function of spectral acceleration. Earthquake ground motion records are selected from online source considering local earthquake faults scenario proposed in Comprehensive Disaster Management Program (CDMP) and then scaled to fit with Bangladesh National Building Code (BNBC) 1993 design response spectra. Since the structure is considered as typical reinforced concrete ordinary moment resisting frame located in Bangladesh, mechanical properties and other associated parameters are chosen according to Bangladeshi perspective. Each ground motion spectrum is matched with design code spectrum at fundamental time period of the building. Non-linear static pushover analysis is performed to determine damage states from pushover curve. Four damage states (from slight to collapse) are defined based on simplified assumptions. A set of dynamic time history analyses are carried out in order to obtain probability density function of the displacement demand correspond to different level of ground motions. Cumulative distribution of each associated damage states allows deriving fragility curves. Finally four fragility curves are obtained for four damge grades (slight, moderate, severe and collapse).

Seismic collapse assessment of bridge piers constructed with steel fibers reinforced concrete.

Steel fiber is one of the most widely used reinforcements to improve the performance of concrete members. However, few studies have been proposed to study the seismic performance of bridge piers constructed with steel fiber reinforced concrete. This paper presents the collapse vulnerability assessment of typical single bridge piers constructed with steel fibers. Fiber element models of RC bridge piers with and without steel fibers are firstly built by selecting suitable cyclic constitutive laws of steel fiber reinforced concrete, and then calibrated using the experimental results. The seismic capacity and inelastic demand of RC piers with steel fibers are quantified using both nonlinear static pushover analyses and nonlinear incremental dynamic analyses (IDA). In order to conduct the IDA, a suite of 20 earthquake ground motions are selected and scaled to different levels of peak ground acceleration (PGA). Collapse fragility curves are then generated using the maximum drift ratio of piers as the engineering demand parameter (EDP). In order to investigate the impact of various parameters on the collapse fragility curves, six parameters are considered in the parametric study: peak compressive strength of concrete, yield strength of steel, longitudinal reinforcement ratio, axial load ratio, transverse hoops ratio and steel fiber content. It was observed that the concrete strength, longitudinal reinforcement ratio and steel fiber content could significantly affect the collapse fragility curve of the bridge piers with steel fibers.

Seismic Performance Assessment of Existing RC Frames with Different Ultimate Concrete Strains

In recent years, because of the older version code, inadequate design, lacks of construction supervision, change in loading pattern, damages and casualties of earthquakes or environmental degradation, buildings at risk need to be investigated frequently for safety purpose. To increase the strength and ductility capacities of deficient reinforced concrete (RC) beams, columns and beam-column joints, retrofitting may require. In this paper, a numerical investigation using nonlinear static pushover analysis is conducted to assess the seismic behavior of existing moment resisting RC frames. In numerical modeling, different plastic hinge lengths as well as different concrete ultimate strain conditions of RC members are considered. Pushover analysis has been carried out with the commercial software ETABS v.9.6.0 to evaluate structural behavior of RC frames located in a seismic region. Hinge properties simulating moment-rotation behavior of frame members considering different plastic hinge lengths as well as concrete ultimate strains are evaluated. Pushover curves are compared with each other to determine the plastic hinge length and strain values which provide better agreement with that of the default properties. Seismic performance criteria in terms of ductility, overstrength as well as response modification factor for frames are determined from pushover curves. From the analyses in general, the load carrying capacity as well as displacement at maximum lateral load and interstory drift index at any floor level of RC frames is assessed.

“SEISMIC RESPONSE OF INFILL FRAME G+20 BUILDING WITH SHEAR WALL FOR LIFT USING SAP 2000 SOFTWARE”

This paper presents an analysis on performance-based seismic evaluation of G+20 RC frame Building with masonry infill (MI) and shear wall (SW) for lift using Non-linear Static Pushover Analysis with SAP2000v14 software for two different models i.e., Model-1: RC bare frame and Model-2: RC frame with MI wall and SW for lift (Soft storey). Result indicates, maximum Displacement for Model-1 i.e., 0.3346m, Model-2 gave displacement of 0.0718m respectively. These results clearly show, the stiffening in Model-2 is increased to 78.54% compared to Bare Frame. 

Seismic Performance of Partially Dismantled Buildings

This study carries out the comparative study of Seismic Performance of residential buildings after partial dismantling for road widening works in Kathmandu city. Two types of buildings were taken for the study, i.e. 4 storey building and 6 storey building. The Buildings were assessed for bare frames. The detail level of the seismic evaluation was carried out by preparing 3-D modeling of the buildings in SAP2000 software by nonlinear static pushover analysis. The capacity of the buildings has been found significantly decreased after the partial dismantling of the building due to the road widening works. The behavior of buildings has been found like a strong beam and weak column mechanism.Journal of the Institute of Engineering, 2017, 13(1): 69-77

Pushover analysis of the reinforced concrete frames with soft first storey using a fiber hinge model

In seismic zones, the problem with the soft storey is amongst the factors that causes the formation of the rupture mechanism in reinforced concrete structures due to variation in the lateral stiffness between levels. Most seismic codes have addressed this phenomenon in realizing the admissible lateral stiffness ratio between levels, without specifying the method to be used in determining this stiffness. The current study is aiming at determining the secant stiffness of each level by using the level capacity curve obtained by nonlinear static pushover analysis, based on a fiber hinge model. The results obtained made it possible to plot a curve that represents the variation of the elastic or secant stiffness ratio between the first level and the second level of a construction as a function of a displacement at the top of the structure. This curve examines the possibility of occurrence of a first soft storey for different points of performance.