Pushover Curves Research Articles

Improved Modal Pushover Analysis in seismic assessment of asymmetric plan buildings under the influence of one and two horizontal components of ground motions

The Improved Modal Pushover Analysis (IMPA) is a multimode procedure that has the advantage of redefining the lateral load applied, when comparing with the multimode current methods; hence, instead of considering the elastic deformed shape, it is possible to consider the deformed shape of the structure when it is behaving inelastically, as a pattern. The IMPA was proposed in the past and was successfully applied in the seismic assessment of bridges, the main objective of this work being to explore IMPA in buildings. For this purpose the seismic demands of two asymmetric plan buildings are herein estimated by means of IMPA and compared to Nonlinear Dynamic Analyses (NDA) and to current reference Nonlinear Static Procedures (NSPs): Modal Pushover Analysis (MPA) and two other NSPs that are proposed in American and European seismic codes (ASCE/SEI 41-06 NSP and N2 method respectively). In the latter, an extended version (extended N2) is considered, taking into account both the torsional and the higher mode effects.The seismic response of the two buildings herein studied is obtained through two different approaches: the first regarding only one component of ground motion, while the second considers both components of ground motion acting simultaneously. The seismic assessment of both buildings is performed in terms of pushover curves, top displacement ratios, lateral displacements profiles, interstorey drifts, normalized top displacements and shear forces.

Parametric study and computation of seismic performance factors of braced shear panels

By locating a steel shear panel at the intersection point of the X-braces, concentrically or eccentrically braced shear panel (CBFSP and EBFSP) is formed. In this paper, to perform parametric study, 1-story CBFSP and EBFSP models with span length greater or less than height are considered. Using linear static analyses, the effects of size and location of the shear panel on the lateral stiffness of the frame with respect to the moment resisting frame with the same member sections are investigated. Next, for 1- and 3-story models, maximum displacement along with base shear and the ratio between the dissipated energy and input energy are examined under 4 ground motion records. Behavior of the truss elements in cross-strip model for nonlinear dynamic analyses is validated based on a performed experimental program. The findings show that the optimum state is achieved by decreasing size of the shear panel and situating it at the middle of the frame or to some extent upper. Furthermore, in this study, tentative values of the over-strength, deflection amplification and response modification factors, which are estimated by pushover curves, are proposed. Using linear regression, an equation is obtained for estimation of the fundamental period of CBFSP and EBFSP.

An evaluation of the seismic response of symmetric steel space buildings

This paper evaluates the seismic response of three dimensional steel space buildings using the spread plastic hinge approach. A numerical study was carried out in which a sample steel space building was selected for pushover analysis and incremental nonlinear dynamic time history analysis. For the nonlinear analysis, three earthquake acceleration records were selected to ensure compatibility with the design spectrum defined in the Turkish Earthquake Code. The interstorey drift, capacity curve, maximum responses and dynamic pushover curves of the building were obtained. The analysis results were compared and good correlation was obtained between the idealized dynamic analyses envelopes with and static pushover curves for the selected building. As a result to more accurately account response of steel buildings, dynamic pushover envelopes can be obtained and compared with static pushover curve of the building.

Estimating uncertainty in limit state capacities for reinforced concrete frame structures through pushover analysis

In seismic fragility and risk analysis, the definition of structural limit state (LS) capacities is of crucial importance. Traditionally, LS capacities are defined according to design code provisions or using deterministic pushover analysis without considering the inherent randomness of structural parameters. To assess the effects of structural randomness on LS capacities, ten structural parameters that include material strengths and gravity loads are considered as random variables, and a probabilistic pushover method based on a correlation-controlled Latin hypercube sampling technique is used to estimate the uncertainties in LS capacities for four typical reinforced concrete frame buildings. A series of ten LSs are identified from the pushover curves based on the design-code-given thresholds and the available damage-controlled criteria. The obtained LS capacities are further represented by a lognormal model with the median <TEX>$m_C$</TEX> and the dispersion <TEX>${\beta}_C$</TEX>. The results show that structural uncertainties have limited influence on <TEX>$m_C$</TEX> for the LSs other than that near collapse. The commonly used assumption of <TEX>${\beta}_C$</TEX> between 0.25 and 0.30 overestimates the uncertainties in LS capacities for each individual building, but they are suitable for a building group with moderate damages. A low uncertainty as <TEX>${\beta}_C=0.1{\sim}0.15$</TEX> is adequate for the LSs associated with slight damages of structures, while a large uncertainty as <TEX>${\beta}_C=0.40{\sim}0.45$</TEX> is suggested for the LSs near collapse.

Fiber-Element Modeling for Seismic Performance of Square RC Bridge Columns Retrofitted with NSM BFRP Bars and/or BFRP Sheet Confinement

This paper presents an analysis of the seismic performance of square RC bridge columns retrofitted with near-surface-mounted (NSM) basalt fiber-reinforced polymer (BFRP) bars and/or BFRP sheet confinement based on fiber element modeling. An axial stress versus loaded-end displacement model of NSM FRP bars, including both elastic elongation and bond-slip effects, is proposed to account for the significant slippage of FRP bars in the plastic hinge region of strengthened columns. The simplified FRP bar model is then converted into the equivalent stress-strain relationship for easy implementation in fiber-based analysis. Moment-curvature analysis is performed based on the proposed FRP bar model, and the analytical moment versus fixed-end rotation relationship of a strengthened column is calculated and assigned to the rotational spring in the fiber element model. The proposed method avoids the nested iterations in sectional analysis that require force equilibrium and deformation compatibility. Comparisons between the numerical simulations and experimental results indicate that the proposed method is appropriate for predicting pushover curves and the hysteretic response of strengthened columns. Furthermore, the mechanism of the hybrid effect of combining NSM FRP bars with externally bonded FRP sheets can be interpreted after the analytical study; that is, confining the column with FRP sheets improves the bond conditions for NSM FRP bars, while the bond-slip effect mitigates the premature fracturing of the FRP bars, leading to more effective utilization of the NSM reinforcement and a more ductile column behavior.

Performance Based Seismic Design of Reinforced Concrete Building

In past two decades earthquake disasters in the world have shown that significant damage occurred even when the buildings were designed as per the conventional earthquake-resistant design philosophy (force-based approach) exposing the inability of the codes to ensure minimum performance of the structures under design earthquake. The performance based seismic design (PBSD), evaluates how the buildings are likely to perform under a design earthquake. As compared to force-based approach, PBSD provides a methodology for assessing the seismic performance of a building, ensuring life safety and minimum economic losses. The non-linear static procedures also known as pushover analysis are used to analyze the performance of structure under lateral loads. Pushover analysis gives pattern of the plastic hinge formations in structural members along with other structural parameters which directly show the performance of member after an earthquake event. In this paper, a four-storey RC building is modelled and designed as per IS 456:2000 and analyzed for life safety performance level in SAP2000 v17. Analysis is carried out as per ATC 40 to find out storey drift, pushover curve, capacity spectrum curve, performance point and plastic hinges as per FEMA 273 in SAP2000 v17. From the analysis, it is checked that the performance level of the building is as per the assumption.

Piecewise linear fitting of softening static pushover curves

Piecewise linear fitting of softening static pushover curves

Evaluation of Regular Multistory Buildings Using IBC2009 Code and ESEE Regulations by Pushover Analysis Method

For structural design and assessment of reinforced concrete members, the nonlinear analysis has become an important tool. The purpose of the pushover analysis is to assess the structural performance by estimating the strength and deformation capacities using static, nonlinear analysis and comparing these capacities with the demands at the corresponding performance levels. This paper aims to compare the results given by IBC2009 code and ESEE regulations. In this paper, four RC frames having 5, 15, 20 and 30 storeys were designed for seismicity according to both the recently adopted seismic code in Abu Dhabi (IBC2009) and the ESEE regulations. A pushover analysis is carried out for these buildings using SAP2000 (Ver. 15) and the ultimate capacities of the buildings are established. The obtained pushover curves and plastic hinges distributions are used to compare between the IBC2009 code and ESEE regulations. The comparison showed that there was variation in the obtained results by the two codes and the buildings designed by IBC2009 code were more vulnerable.

Preparing the Fragility Curve of Semi-Rigid Beam-to-Steel Column Connection

Background/Objectives: Examination of the connections in a steel structure is of paramount importance and lack of precision in design and implementation of connections in steel structures will cause not only failure in the connection itself but also devastating effects on structural members and thereby entire the structure. Methods/Statistical Analysis: In present study, structural safety is assessed through probabilistic methods and the work mainly tries to make a suitable platform for its performance within the useful life of structure. To this end, the experimental setup for testing these connections - which are proper agents of their performance in a building frame (connection place and a half of joint beam and column) - was modeled in the software ABAQUS and acceleration time history of the frame it is embedded in is included under a set of certain records of the desired site. Results: Connection in a structure with a special frame and moderate height was studied and initially it was determined to join levels of performance with a suitable criteria based on connection failure. Thereafter, the corresponding fragility curves were drawn and then compared with moment-rotation curve and cyclic loading based on joining models which are influenced by nonlinear static analysis and cyclic loading. Conclusion/Application: Pushover and cyclic loading curves of this connection were determined in order to specify level of performance of the connection as per the connection failure.

A simplified method in comparison with comprehensive interaction incremental dynamic analysis to assess seismic performance of jacket-type offshore platforms

The primary goal of seismic reassessment procedures in oil platform codes is to determine the relia- bility of a platform under extreme earthquake loading. Therefore, in this paper, a simplified method is proposed to assess seismic performance of existing jacket-type offshore platforms (JTOP) in regions ranging from near-elastic to global collapse. The simplified method curve exploits well agreement between static pushover (SPO) curve and the entire summarized interaction incremental dynamic anal- ysis (CI-IDA) curve of the platform. Although the CI-IDA method offers better understanding and better modelling of the phenomenon, it is a time-consuming and challenging task. To overcome the challenges, the simplified procedure, a fast and accurate approach, is introduced based on SPO analysis. Then, an existing JTOP in the Persian Gulf is presented to illustrate the procedure, and finally a com- parison is made between the simplified method and CI-IDA results. The simplified method is very informative and practical for current engineering purposes. It is able to predict seismic performance elasticity to global dynamic instability with reasonable accuracy and little computa- tional effort.

Experimental and numerical analysis of RC structure with two leaf cavity wall subjected to shake table

This paper presents finite element (FE) based pushover analysis of a reinforced concrete structure with a two-leaf cavity wall (TLCW) to estimate the performance level of this structure. In addition to this, an unreinforced masonry (URM) model was selected for comparison. Simulations and analyses of these structures were performed using the DIANA FE program. The mentioned structures were selected as two storeys and two bays. The dimensions of the structures were scaled 1:1.5 according to the Cauchy Froude similitude law. A shake table experiment was implemented on the reinforced concrete structure with the two-leaf cavity wall (TLCW) at the National Civil Engineering Laboratory (LNEC) in Lisbon, Portugal. The model that simulates URM was not experimentally studied. This structure was modelled in the same manner as the TLCW. The purpose of this virtual model is to compare the respective performances. Two nonlinear analyses were performed and compared with the experimental test results. These analyses were carried out in two phases. The research addresses first the analysis of a structure with only reinforced concrete elements, and secondly the analysis of the same structure with reinforced concrete elements and infill walls. Both researches consider static loading and pushover analysis. The experimental pushover curve was plotted by the envelope of the experimental curve obtained on the basis of the shake table records. Crack patterns, failure modes and performance curves were plotted for both models. Finally, results were evaluated on the basis of the current regulation ASCE/SEI 41-06.

Effect of types of reinforcement on plastic hinge rotation parameters of RC beams under pushover and cyclic loading

Experimental evaluation of reinforced concrete beam specimens with different characteristics of reinforcement subjected to pushover and cyclic loading is presented. Plastic hinge rotation parameters are determined based on the idealization of pushover and hysteresis curves of reinforced concrete beam specimens constructed in two percentage of reinforcement (0.471% and 0.71%) with different ductile characteristics. The experimental test results provide a clear demarcation of the effect of types of loading and the types of reinforcement on the nonlinear performance characteristics of beam specimens. These results are helpful to update the nonlinear modeling parameters of beam components for the specific type of reinforcement used in the construction of a structure. The updated non-linear modeling parameters of beam components in lumped plasticity model are compared with the values of ASCE/SEI 41-06 (2007) used for the performance based design of structures.

Assessment of a rolling isolation system using reduced order structural models

This paper examines the performances of lightly- and heavily-damped rolling isolation systems (RISs) located within earthquake-excited structures. Six steel structures of varying height and stiffness are selected so as to represent a range of potential RIS installations. Computation models of representative frames from each of the six structures are reduced through dynamic condensation and assembled with models for biaxial isotropic hysteretic behavior within each floor. A novel reduced order modeling approach is presented in this paper. The method combines a dynamic condensation of a linear-elastic frame with the inelastic-push over curve for a detailed elastic–plastic frame model and a novel bi-axial hysteretic model for the net inter-story inelastic behavior. The reduced inelastic model combines stiffness and mass matrices from the reduced linear model with the bi-axial inelastic floor model, and is subsequently fit to push-over curves from the detailed hysteretic model. The resulting reduced order model has three coordinates per floor and provides a much simpler model for simulating the floor responses of inelastic structures. The resulting inelastic structural models are isotropic in plan and uniform along the height. Suites of recorded ground motions representative of near-fault and far-field hazards are scaled and inputted into these hysteretic reduced models. The bidirectional floor responses at varying heights are then applied to experimentally-validated models of lightly- and heavily-damped RISs. Empirical cumulative distribution functions of peak isolator responses (relative displacement and total acceleration) for the two systems are compared, from which installation guidelines are presented.

PERFORMANCE BASED SEISMIC ANALYSIS OF RC BUILDING CONSIDERING THE EFFECT OF DUAL SYSTEMS

Due to the present increase in world population, people in this world tend to occupy available locations present in any zone which also include zones falling in the high seismic zone categories. The buildings to be built in these seismic zones are more susceptible to earthquakes for obvious reasons, and the buildings constructed in such zones must be analysed and designed for the unpredictable earthquakes with unpredictable magnitudes by various lateral load resisting systems such as shear walls, bracings, tubular systems, coupled shear walls and even a combination of two load resisting systems called as dual systems. Present study includes linear-static and non-linear static analysis with different shear wall arrangements on dual systems such as flat slabs and shear walls & moment resisting frames and shear walls for different irregular plans using ETABS 9.7.4 software. Parameters such as point displacements, base shears, pushover curves are studied.

COMPARISON OF SYMMETRIC AND ASYMMETRIC STEEL DIAGRID STRUCTURES BY NON-LINEAR STATIC ANALYSIS

Diagonalized grid structures – “diagrids” - have emerged as one of the most innovative and adaptable approaches to structuring buildings in this millennium. Diagrid is a particular form of space truss, it consists of perimeter grid made up of a series of triangulated truss system. Diagrid is formed by intersecting the diagonal and horizontal components. Construction of multi‐storey building is rapidly increasing throughout the world. Advance in construction technology, materials, structural systems, various analysis and design software have facilitated the growth of various kinds of buildings. Diagrid buildings are emerging as structurally efficient as well as architecturally and aesthetically significant assemblies for tall buildings. Recently these diagrid structural systems have been widely used for tall buildings due to the structural efficiency and aesthetic potential provided by the unique geometric configuration of the system. This paper presents a 12 storey steel diagrid structure which is 36m in height. Symmetric and asymmetric structural configurations of diagrid structures were modelled and analyzed using SAP 2000 by considering Dead load, Live load and Seismic Loads (IS 1893-Part-1, 2002). Then FEMA 356 hinges (auto hinges) are assigned to the same structure and Nonlinear Static (Pushover) analysis is carried out by using seismic load as the pushover load case to find out the performance points that is Immediate Occupancy, Life Safety, and Collapse Prevention of diagrid elements using static pushover curve. At the same time spectral displacement demand & spectral displacement capacity as well as spectral acceleration demand and spectral acceleration capacity is compared to know the adequacy of the design by using ATC capacity spectrum method.

Sensitivity of Pushover Curve to Material and Geometric Modelling—An Analytical Investigation

Nonlinear static analysis or pushover analysis developed over the last two decades and became the preferred procedure for design and seismic performance evaluation, as this procedure is relatively simple and considers post-elastic behaviour. It provides information on seismic demands imposed by the design ground motion on the structural system and its components. Generation of pushover curve from analysis for reinforced concrete structure involves tremendous amount of computational efforts as the input data for analysis itself is quite exhaustive. The analysis results are very sensitive to the techniques employed in geometric and material modelling. This paper envisages presenting the sensitivity of pushover analysis results to geometric and material modelling parameters by comparing the analysis results with that of experimental investigations. Attempt has been made to understand the sensitivity of parameters like variation in material properties, inaccuracies in placement of reinforcement, effect of confinement of concrete and modelling techniques for elements and plastic hinges. SAP-2000 has been utilised in the current investigation and results have been highlighted suggesting strategies to enhance pushover analysis capabilities.

Seismic design or retrofit of buildings with metallic structural fuses by the damage-reduction spectrum

Recently, the structural fuse has become an important issue in the field of earthquake engineering. Due to the trilinearity of the pushover curve of buildings with metallic structural fuses, the mechanism of the structural fuse is investigated through the ductility equation of a single-degree-of-freedom system, and the corresponding damage-reduction spectrum is proposed to design and retrofit buildings. Furthermore, the controlling parameters, the stiffness ratio between the main frame and structural fuse and the ductility factor of the main frame, are parametrically studied, and it is shown that the structural fuse concept can be achieved by specific combinations of the controlling parameters based on the proposed damage-reduction spectrum. Finally, a design example and a retrofit example, variations of real engineering projects after the 2008 Wenchuan earthquake, are provided to demonstrate the effectiveness of the proposed design procedures using buckling restrained braces as the structural fuses.

Seismic response factors of reinforced concrete pedestal in elevated water tanks

Reinforced concrete (RC) elevated water tanks are critical structures that are expected to remain functional after severe earthquakes in order to serve the water system networks. Despite this significant role, the number of research studies which investigated the nonlinear seismic response of RC pedestals in elevated water tanks is very limited. In the current codes and standards, the seismic response factors are mainly based on engineering judgement. In this paper, a systematic approach is employed to establish the seismic response factors for a wide range of elevate water tank sizes and RC pedestal dimensions commonly built in industry. In total, forty-eight model configurations (prototypes) are selected and designed based on current codes and standards. The finite element (FE) method is then used for nonlinear static (pushover) analysis of the prototypes. The pushover curve of each prototype is developed and the seismic response factors are determined accordingly. The effect of various parameters such as fundamental period, height to diameter ratio, seismic design category, and tank size on the seismic response factors of elevated water tanks is evaluated. Furthermore, the cracking propagation pattern in RC pedestal is studied. The result of the study shows that the tank size is a critical parameter affecting the seismic response of elevated water tanks. It is recommended not to use the same seismic response factors for all RC elevated water tanks regardless of the tank size. In addition, two different patterns of cracking depending on the height to diameter ratio of the pedestal are detected and discussed.

IARJSET - Science, Engineering and Technology

2 Abstract: This paper deals with the non-linear analysis of frame for various positions of shear wall in a building frame. In this present study, the focus is to identify effective location of shear wall in multi-storey building. Considering model one is bare frame structural system and other three models are dual type structural system. An earthquake load is applied to a building of eight storey is located in zone II, zone III, zone IV and zone V as per Code Provision IS1893- 2002. The analysis has been carried out using ETABS software. Pushover curves have been developed and compared for various models. It has been observed that structure with shear wall at appropriate location is more significant in case of displacement and base shear. Shear wall is one of the excellent means of providing earthquake resistance to multi-storeyed reinforced concrete building. Behavior of structure during earthquake motion depends on distribution of weight, stiffness and strength in both horizontal and vertical planes of building. To reduce the effect of earthquake reinforced concrete shear walls are used in the building. These can be used for improving seismic response of buildings. Structural design of buildings for seismic loading is primarily concerned with structural safety during major Earthquakes, in tall buildings, it is very important to ensure lateral stiffness to resist lateral load. The provision of shear wall in building to achieve rigidity has been found effective and economical. Shear walls are usually used in tall building to avoid collapse of buildings. When shear wall are situated in advantageous positions, they can form an efficient lateral force resisting system. The major criteria now-a-days in designing RCC structures in seismic zones is control of lateral displacement resulting from lateral forces. The effort has been made for investigate the effective location of shear wall for lateral displacement and Base Shear in RCC Frames. For this study four types of structures, with G+7 are considered which one of the frame without shear wall and other three with shear wall in various position. Non-linear static analysis (pushover analysis) was carried out four types of frames and the frames were compared with the push over curves. Displacement and Base shear is calculated from the curves and compared. The nonlinear analysis of a frame has become an important tool for the study of the concrete behavior including its load-deflection pattern and cracks pattern. It helps in the study of various characteristics of concrete member under different load conditions.

Seismic Capacity Assessment of Existing RC Buildings in The Sudan by Using Pushover Analysis

Recently, the evaluation of seismic performance of existing buildings has received a great attention. Current research works and observations indicate that The Sudan have low-to-moderate seismic regions. Most of existing buildings are designed only for gravity load. The objective of this paper is to assess the seismic performance of existing RC buildings in The Sudan. Four typical buildings were investigated using pushover analysis according to ATC-40. They were designed according to the Regulations for earthquake-resistant design of buildings in Egypt (ESEE) and International Building Code (IBC2012). Results showed that the buildings designed considering by ESEE and IBC2012 loads were found adequate and satisfied the Immediate Occupancy (IO) acceptance criteria according to ATC-40. The comparison of the pushover curve shows that the stiffness of frames is larger when using ESEE Regulations compared to the IBC2012 design. This means that ESEE design procedure provides a greater capability to resist seismic load than the IBC2012 design.