Static Pushover Research Articles

Life-cycle cost (LCC) based design procedure to determine the optimal design parameters and target reliability under nonlinear deformation for marine installations

ABSTRACT This study proposes a procedure to determine the optimal design parameters and target reliability based on Life cycle cost (LCC) based analysis. An iterative design procedure is performed for different levels of reserve strength ratio (RSR), and LCC is calculated. A case study is carried out for installation of the bottom fixed jacket support structure for offshore wind turbines (OWT) system subjected to extreme loading condition. To determine the ultimate capacity of the structure, static pushover analysis is integrated with the proposed design methodology. An evolutionary based particle swarm algorithm is selected for the structural design optimization of offshore jackets. The RSR evaluated from pushover analysis assists to determine the probability of failure based on the first order reliability method (FORM). Based on a set of LCC values, which are the collective sum of capital expenditure (CAPEX), operational cost (OPEX), and risk cost (RISKEX), the optimal design is reached.

Seismic assessments for scoured bridges with pile foundations

To accurately estimate the seismic performances of scoured bridges with pile foundations, an integrated performance-based seismic assessment method is proposed in this paper. Nonlinear deformations of piers and piles are taken into consideration by using the concentrated plastic hinges at the bottoms of piers and the distributed plastic hinges with softened elastic modulus along the piles, respectively. The interaction between soil and pile foundation is modelled through four types of soil springs according to the design code. Seismic assessments of multi-span bridges with pile foundations are performed for different scour depths and soil properties using nonlinear static pushover analyses. Numerical results demonstrate that the seismic demands of bending moments and the locations of maximum moments for piles vary significantly with increasing scour depth. Compared with the fiber element method, the proposed distributed plastic hinges model with a softened elastic modulus can efficiently and accurately estimate the nonlinear deformation of scoured bridges. In addition, in the case of loose sand, the failure mechanism of a scoured bridge is transferred from the piers to the piles as the scour depth increases over a critical value. Finally, seismic assessments demonstrate that the seismic performance indices of scoured bridges increase with increasing scour depth with dense sand, while the seismic performance indices of scoured bridges decrease with increasing scour depth with loose sand when the failure mechanism is transferred. Although scoured bridges have better seismic performances, they may have stability problems.

Seismic investigation of longitudinally aligned shape memory alloy-stainless steel reinforced concrete column

Shape memory alloy (SMA) is a smart material sustain (8∼13%) an enormous amount of strain and having an ability to regain parental shape after the removal of an external load and temperature due to its pseudo-elastic (SE) and shape memory effect (SME) properties. The SE and SME properties, lower modulus of elasticity, and higher elastic straining of SMA compared to conventional steel reinforcement makes it predictable for the design of the reinforced concrete (RC) structure. The present research is focused on the seismic investigation of RC columns reinforced with SMA rebar in the plastic hinge region along with stainless steel (SS) in the remaining portion of the column. A nonlinear static pushover seismic analysis is used for the numerical investigation of SMA-SS RC column. The numerical model is validated having 98% accuracy with existing literature results. The impact of various parameters on SMA-SS RC column is evaluated for SMA in the plastic hinge region. The results reveal that an aspect ratio, the yield strength of reinforcement, the compressive strength of concrete and axial load are significantly affecting the lateral strength and the ductility of the column under seismic loading.

Reliability assessment of RC frames rehabilitated by eccentrically braces having vertical shear link

A considerable number of existing reinforced concrete (RC) structures need to seismic rehabilitation due to several reasons such as being designed just based on gravity loading and/or having an unsatisfactory level of ductility. One of the types of steel bracing can be referred to eccentrically braced frames with a vertical link. This system has some advantages such as an increase in ductility, stiffness and lateral strength, the ability to adapt to the architecture, and also the minimum weight added to the structure. In this study, reliability analysis assessment of two existing 3-, and 9-story RC frames in two cases including original and rehabilitated with an eccentrically braced frame having a vertical link is presented. Two limit states are defined as: maximum roof displacement and maximum inter-story displacement. The seismic behavior of frames was assessed by nonlinear static pushover analysis with finite element program OpenSees in two performance levels, including collapse prevention and life safety. Five random variables represented the variability in resistance of concrete material, bars and steel profiles yield stress, beams height, columns dimension, and also bars cross-section. Sensitivity analysis was carried out to recognize the effect of random variables on the reliability index. The reliability analysis was performed by two different methods: Hasofer–Lind and Monte Carlo with 25, 100, 1000, 10,000 and 100,000 simulated samples by considering two distributions including Normal and Log-Normal. Finally, a comparison between two common reliability methods was carried out in order to select the most appropriate method for performing the best seismic performance reliability analysis of RC frames rehabilitated by the proposed system.

Eccentric steel brace retrofit for seismic upgrading of deficient reinforced concrete frames

The paper presents a simplified static force-based procedure for seismic retrofit design of RC frames using internal eccentric steel braces (ESBs), connected to long beam at distance of L/8 from beam ends, to enhance seismic resistance of the frame. The technique uses the linear static procedure given in ASCE 7-16 for calculation of appropriate design base shear for frame analysis, and the AISC 360-16 seismic provisions for preliminary design of steel braces. Response modification factor R was derived based on simplified kinematics of rigid frame response and flexure hinging of link beam, to reduce the elastic base shear force for lateral load analysis of frame and design of steel braces. This shifts plastic hinges from columns, and reduces joint shear deformation, by means of capacity protected braces and beam shear. The procedure was used for the preliminary design of ESB retrofitting technique for a two-story RC frame, employing hollow box steel sections. Quasi-static cyclic tests were performed on both as-built and ESB retrofitted portal frame panels under multiple-levels of lateral displacements demands. The tests performed on frames were analysed to understand the damage mechanism and retrieve the essential seismic response properties: force–displacement capacity curves, hysteretic cyclic response and hysteretic damping, and to establish performance-based story drift limits. The experimental data was used to calibrate finite element based nonlinear numerical models in SeismoStruct. Nonlinear static pushover analysis of considered two-story ESB retrofitted frame was carried to quantify structure ductility and response modification factors. The preliminary design was verified through nonlinear time history analysis (NLTHA) for both design base earthquakes and maximum considered earthquakes. Proposed seismic design of ESB retrofit for multi-stories RC frames having three to six stories has been presented and verified through NLTHA. It indicates the promising behaviour of ESB retrofit technique as well as the efficiency of the proposed simplified design procedure.

Seismic fragility assessment of the Daikai subway station in layered soil

A numerical method based on nonlinear incremental dynamic analysis is proposed in this paper to develop seismic fragility curves for rectangular subway station buried in layered soil and subjected to transverse seismic excitations. The proposed method primarily consists of four parts, namely, model verification, damage quantification, ground motion processing, and seismic performance assessment. The main section of the Daikai subway station collapsed during the Kobe Earthquake is used as an example to demonstrate the detailed procedure of the proposed method in construction of seismic fragility curves for underground structures. Results from the nonlinear soil-structure interaction model in this paper is firstly verified against the results from existing literature. The threshold values of different damage states of the underground structure are quantified by interstory drift ratio obtained from the nonlinear static pushover analysis of the soil-structure interaction system. Based on the results of the incremental dynamic analysis, it is found that the peak acceleration at the ground surface is an efficient and appropriate intensity measure of the ground motions for shallowly buried underground structure. The proposed method is validated by comparing with the existing empirical and numerical seismic fragility curves of buried rectangular underground structures and can be used as an effective approach in the development of seismic fragility database for underground structures.

Seismic Performance Assessment of Istanbul Airport Viaduct According to Turkish Building Seismic Code 2007 by Pushover Analysis

The goal of this study is to examine and evaluate the structural system and seismic performance of the viaduct which is located the west side of the Istanbul Airport. For this purpose, a three-dimensional structural system of the viaduct is modeled by using SAP2000 (Structural Analysis Program) software. The piers of the viaduct consist of two columns. It connects the terminal building and the parking building to each other, twelve spans and designed according to AASHTO (2002). Earthquake effects are considered in the transverse and longitudinal directions by taking into account the site-specific response spectra. The pre-stressed and precast girders which is used in the deck of the viaduct is designed under bending moment and shear force effects considering service loads, such as self-weight and traffic loads. The pre-stress losses and deflection checks are carried out to satisfy the serviceability conditions of the viaduct deck. The elements of the viaduct, such as pier cap, piers and foundation were designed by considering the vertical and lateral loads, so required cross-sections and reinforcement area are determined. In the present paper earthquake performance evaluation of the viaduct is accomplished according to the Turkish Building Seismic Code 2007 (TBSC 2007). Performance evaluation of the viaduct is carried out by applying static pushover analysis, one of the non-linear analysis methods, is applied to the pier located at the middle axis of the viaduct. Under lateral loading, the plastic hinges are developed at the bottom ends of the piers, as anticipated. In the performance evaluation of viaduct piers, the earthquake effect with 10% probability of exceedance over 50 years is considered adopting the parameters given TBSC 2007, whereas the parameters which define the spectrum compared to the Seismic Code of DLH (2007) code. Numerical results are given in tables and figures, comparatively.

Simplified frame model for capacity assessment of masonry buildings

Masonry buildings comprise a major fraction of the total buildings globally. Analysis of masonry buildings is challenging due to underlying uncertainties in material properties, variation in construction system, workmanship discrepancies, and analysis schemes. At present, several finite element approaches are available for masonry modeling; however, most of such methods are sophisticated as they require huge computational efforts, time, and realistic allocation of material properties. Thus, there is a need for a simple yet representative method to capture the complex behavior of masonry buildings. To this end, we propose a displacement-based Simplified Frame Model (SFM) to analyze masonry structures. Details of the methodology including the analysis results are presented in this paper. Nonlinear static pushover analysis is adopted for finite element modeling of the prototype building. A comparison between the analytical and experimental results highlights that the SFM can be effectively used for masonry analysis assuring less computational efforts.

Experimental investigation and seismic vulnerability assessment of low flexural strength rectangular bridge piers retrofitted with ultrahigh-performance concrete jackets

Effectiveness of an innovative retrofitting technique using ultrahigh-performance concrete (UHPC) jackets was investigated, for “as-built” bridge piers with low flexural strength. Cyclic loading test was performed on the pier specimens, two of which were retrofitted with a mono-wide-strip UHPC (W-UHPC) jacket, and the other two were with a multi-narrow-strip UHPC (N-UHPC) jacket. Their seismic responses were compared, regarding damage evolution, hysteretic behavior, skeleton curve, ductility and energy dissipation. The piers with the W-UHPC jacket exhibited a higher lateral strength, but were prone to plastic hinge relocation. Comparatively, N-UHPC jacket improved the piers’ ductility and smeared concrete damage. Nevertheless, guaranteeing the tight contact between the N-UHPC jacket and the shaft was crucial. Both W- and N- UHPC jackets mitigated residual drift and concrete damage, and thereby enhancing the piers’ seismic resilience. Four enhancing mechanisms from the UHPC jackets are discussed, namely passive confinement effect, cross-section enlargement effect, gap-opening effect, and interface-opening effect. Alongside, 3D solid and 1D fiber-based finite element (FE) models are constructed to represent the piers’ nonlinear static push-over (SPO) and cyclic responses, respectively. Finally, seismic vulnerability of the retrofitted piers was evaluated by generating structure-specific fragility curves.

Seismic Performance Evaluation of RC Frame Designed Using Ethiopian and Chinese Seismic Codes

This study presents the seismic performance evaluation of the reinforced concrete (RC) frame designed as per Ethiopian (based on EN1998‐1) and Chinese seismic codes to realize best practices within them. In the study, three‐model RC frames with 4‐, 8‐, and 12‐story are designed with the respective codes. Then, their seismic performances are evaluated using the nonlinear static (pushover) procedures of FEMA 356 and ATC 40 provisions. To validate the analysis result, dynamic nonlinear time history analysis is also made. The comparison parameters include elastic stiffness, peak strength, target displacement, and plastic hinge formation patterns in the structures. The results display many similarities in the global and local performances of the structures. Despite these, some noteworthy discrepancies are also noted. Besides, the performance point analysis revealed a significant difference in target displacement that reflects the two codes’ demand spectrum essential disagreements, particularly for the period of vibration greater than 2.0’s. In conclusion, the study highlighted the beneficial aspects of both codes, which will be useful for the future studies.

Seismic performance evaluation of regular and irregular composite moment resisting frames

Abstract In this study, the seismic behavior of regular and irregular composite moment resisting frame (CMRF) buildings was investigated. To this aim, 5, 8, 10, 13 and 15-story CMRFs having concrete filled steel tube columns and composite beams were designed at high ductility level and their performances were evaluated comparatively. The case study CMRF structures were categorized into two groups as regular and irregular in elevation. Examined irregular structures have setbacks in different story levels. During the design and performance analysis, SeismoStruct software was employed. Nonlinear static pushover and incremental dynamic analyses were used in the seismic performance assessment. The uniform and triangular load distributions were considered in the pushover analysis while a total of 22 earthquake acceleration records were utilized in the dynamic analysis. The variation in the lateral response, global yielding value, interstory drift, behavior factor, inherent strength factor, overstrength factor, and ductility factor were examined for the regular and irregular CMRF structures. It was observed that the regular CMRFs were more consistent with the design assumptions as compared to the irregular ones. Moreover, the former exhibited more uniform non-elastic demands over the building height according to the results of the incremental dynamic analysis. Under the seismic scenario adopted, all the building types yielded higher values of the behavior factor complied with the limits available in the code.

PRIMENA “PUSHOVER“ ANALIZE NA VIŠESPRATNE ARMIRANOBETONSKE RAMOVE

The subject of this paper is the result of the analysis of a multistorey reinforced concrete frame, using nonlinear static pushover analysis. The analysis was performed on a structure calculated according to the current regulations for the design of earthquake resistant structures. The results were obtained using two software suites Radimpex Tower and Abaqus. Curves of the nonlinear response of the structure were formed in order to compare the results obtained by applying these two software suites.

Optimal design algorithm for seismic retrofitting of RC columns with steel jacketing technique

Steel jacketing (SJ) of beams and columns is widely employed as retrofitting technique to provide additional deformation and strength capacity to existing reinforced concrete (RC) frame structures. The latter are many times designed without considering seismic loads, or present inadequate seismic detailing. The use of SJ is generally associated with non-negligible costs depending on the amount of structural work and non-structural manufacturing and materials. Moreover, this kind of intervention results in noticeable downtime for the building. This paper presents a new optimization framework which is aimed at obtaining minimization of retrofitting costs by optimizing the position and the amount of steel jacketing retrofitting. The proposed methodology is applied to the case study of a 3D RC frame realized in OpenSEES and handled within the framework of a genetic algorithm. The algorithm iterates geometric and mechanical parameters configurations, based on the outcomes of static pushover analysis, in order to match the optimal retrofitting solution, intended as the one minimizing the costs and, at the same time, maintaining a specified safety level. Results of the proposed framework will provide optimized location and amount of steel-jacketing reinforcement. It is finally shown that the use of engineering optimization methods can be effectively used to limit retrofitting costs without a substantial modification of structural safety.

Non-Linear Performance of Strong Column Weak Beam RC Frame Building

Buildings are designed in different methods for resisting the lateral loads, in which strong column weak beam concept is one of the methods of designing, this method is used to avoiding the global failure of the structure In this work 3bay 5 story RC frame building is consider for the analysis, the structures are design strong column weak beam with the help of static non-linear pushover analysis of RC frame building with increasing the percentage of column sizes 20%, 40%, 60%, 80% and 100%. By varying with percentage of columns resistances of structure is increased. The parameters base shear, story displacement, and hinge formations in the structure is obtained from this analysis. The base shear and displacement are increased by increasing the column sizes, these parameters are discussed the results in detail. Comparing the all six model results the base shear in increased by 266.64% when the column size is increased by 100%. From this analysis we can reduce the failure in the structure during the earthquake. Formation of plastic hinges in column changes to beam by increasing the column size, so increase the capacity of structure. The building is analyzed by using SAP2000.

Response Reduction Factor For Different Heights of RC Structure

Seismic analysis is considered as an important parameter for any structural design. The strength and ductility of frame members in seismic design depends on the response reduction factor. In this paper four symmetrically framed structures are considered of different heights under the critical zone condition. The primary emphases of this work is regarding calculation of response reduction factor values attained from designing RC framed structures. The results are computed by applying non-linear static pushover analysis. SAP-2000 software is used for analyzing the non-linear behaviour of the structure.

The Effect of Different Braced Configurations on the Nonlinear Seismic Behavior of Steel Structure

Improvements in construction technologies have allowed steel structural elements to become more frequently used today in order to enable different architectural designs and to meet structural performance more effectively and efficiently. Structural steel has been used for more than a hundred years and has been tested under real earthquakes, which provide the basis of many earthquake-resistant steel construction standards. The major advantage of steel construction material is that it allows for large plastic deformations. Structural deformations vary depending on the deformation capacity of the structural components in addition to the configuration of the structural components. In this study, moment resisting frames (MRF), X braced frame (XBF), Inverse V braced frame (IVBF), K braced frame (KBF), and eccentric inverse V braced frames (EIVBF) were used to examine the effect of different steel braced systems on the plastic deformation capacity of steel structure with the help of nonlinear static pushover analysis. Bilinear material model was utilized to represent nonlinear steel material behavior and inelastic displacement-based frame element were used to represent column and beam element. The analyses' results demonstrated that the braced frame configuration had a significant effect on the lateral response of steel frame structures.

Optimization of shape memory alloy braces for concentrically braced steel braced frames

Abstract Expanding the use of smart braced frames to govern the seismic response of structures by providing ductility and elasticity has been hampered and delayed by cost indexes. The braces in frames comprise two segments of expensive shape memory alloys (SMAs) and high-strength steel with high stiffness. These smart materials can reduce seismic damage by providing stiffness, yielding, and phase shifting. In this study, the length of the SMA segments in three- and six-story frames (applied either at all floors or as part of a dual system) was increased to determine the optimal length at a constant period. Performance levels and fragility curves were obtained to evaluate the seismic behavior of the optimized frame. The response modification factor determined based on the static pushover, incremental nonlinear dynamic analysis, and linear dynamic analysis suggests the ductility and over-strength of the optimized frame. The probability of being in or exceeding each damage state was determined with a Monte Carlo analysis and was acceptable and in accordance with previous deterministic analysis results.

Advanced Seismic Assessment of Four Masonry Bell Towers in Italy after Operational Modal Analysis (OMA) Identification

ABSTRACT The paper presents an advanced seismic assessment of four masonry bell towers located in Northern Italy based on detailed 3D FE models on which elastic parameters were previously identified by operational modal analysis. The numerical assessment includes a preliminary identification of the elastic moduli of the different volumes of each tower made by means of a fast-micro-GA approach. After proper identification of the main four eigenfrequencies, non-linear static (pushover) and full non-linear dynamic analyses are performed adopting a material model for masonry which is characterized by softening and two distinct damage parameters in both tension and compression. The results obtained with non-linear static and non-linear dynamic analyses in all the simulations performed exhibit a satisfactory match, suggesting similar conclusions in terms of general dynamic response and seismic vulnerability of the towers.

Comparison of Static Pushover Analysis and IDA-Based Probabilistic Methods in Assessing the Seismic Performance Factors of Diagrid Structures

This study attempts to reliably quantify the seismic response parameters of the steel diagrid structural systems. In that regard, in addition to the conventional static pushover analysis (SPA), the dynamic pushover analysis (DPA) based on the incremental dynamic analysis (IDA) technique is also considered. FEMA P-695 recommends a methodology for establishing seismic performance factors (SPFs). The present study tries to propose a simpler framework for estimating and validating SPFs while applying the concepts of FEMA P-695 guideline. The results show that the R-factors obtained with the SPA procedure for steel diagrid systems are conservative and the IDA-based probabilistic method gives a more rational value for the R coefficient. Furthermore, the proposed simplified method has good agreement with FEMA P-695 in predicting the collapse capacity of diagrid models.

Simplified seismic assessment of infilled RC frame structures

Earthquake-induced structural damage, characterised by the exceedance of different damage states during ground shaking, is typically quantified using fragility curves generated through non-linear dynamic analyses often requiring a large computational effort. This level of effort has led to the necessity of simplified methods and approximate analysis tools. In this regard, SPO2IDA has emerged as a convenient tool for the assessment of structures. It relates a structure’s backbone characteristics to a set of incremental dynamic analysis (IDA) curves using static pushover analysis (SPO) results and a library of empirical fitting coefficients for the different branches of the idealised SPO backbone. It permits the quantification of structural performance up to structural collapse as a function of seismic intensity in a simple and efficient manner. It has been developed mainly for ductile structures that can be sufficiently represented via a SPO backbone with a certain ductile post-yield hardening followed by a post-peak degradation. This behaviour is quite representative of ductile RC and steel moment-resisting frames and has resulted in the tool being widely adopted. However, the same may not be observed when dealing with reinforced concrete (RC) frames with masonry infill, a structural typology that still requires significant addressing in the earthquake engineering field. The present study describes an extension to this methodology for structural typologies with a more particular backbone behaviour, typical of RC frames with masonry infill panels, since differences in backbone behaviour compared to typical structures render the extension of the original tool inappropriate and at times unconservative. Extensive analyses were conducted to investigate the behaviour and trends when pushing infilled RC frames up to complete structural collapse. A new library of empirical coefficients was then fitted and proposed by considering a large database of representative backbones to result in an extended SPO2IDA proposal for infilled RC frames. It is then shown how these coefficients provide a much-improved matching, when compared to the original tool for this specific case, both in terms of the produced IDA traces and also the drift-based mean annual rates of exceedance.