Inelastic Structural Behavior Research Articles

Numerical examination on seismic response behavior of a piping system considering the plastic deformation of supports

A previous study proposed a passive safety structure to mitigate severe damage to crucial components under the beyond design basis event (BDBE). To examine the applicability of this concept to the piping system, the effect of the elastic-plastic behavior of the piping support structure on the seismic response of the piping system was investigated through elastic-plastic time history response analyses on a piping system model with multiple support structures. The numerical analyses considered the elastic-plastic behavior of supports and/or the inelastic characteristics of pipe material. The analysis results confirmed that the response of the piping system can be suppressed by adequately introducing the inelastic behavior of support structures. The results show the possibility of realizing of passive safety structure in piping systems and addressing some issues, such as changing vibration modes due to the elastic-plastic deformation of the support or the order of generation of inelastic behavior of pipe material and supports.

Inelastic Behavior of Steel and Composite Frame Structure Subjected to Earthquake Loading

Steel construction is used more often these days as an alternative to the R.C.C. when lightweight, high-strength, large-span structures with a faster erection are required. Extensive studies have been conducted by researchers to study the seismic performance of reinforced concrete and steel structures, both in terms of elastic and inelastic behavior. Composite construction is also a recent advancement in the building industry with similar advantages. However, no emphasis has been given to the comparison between the inelastic behavior of steel and composite structures when subjected to lateral loads. This study compares the inelastic behavior of steel and a composite frame designed to have the same plastic moment capacity for structural members. The responses, such as the formation of hinges, story drifts, story displacements, lateral stiffness, ductility, maximum strength, energy dissipated, joint accelerations, and performance points, are compared with the aid of the building analysis and design software ETABS-18. For this, response spectrum analysis, pushover analysis, and nonlinear direct integration time history analysis have been performed on both frames. For design and analysis, international codes, such as IS 800-2007, IS 875 (Part I, II, IV), IS 1893-2002, AISC 360 (16 and 10), and FEMA 440, have been used. Part of this study also aims at comparing the response of these frames when subjected to near-field and far-field earthquakes. It can be concluded from the results that the post-yield performance of the composite frame is superior to that of the steel frame when seismically excited.

Performance Assessment of Different Retrofitting Techniques for Steel-Framed Buildings

The requirement for cost-effective critical infrastructure has made employing nonlinear analysis techniques an appealing choice. Estimating seismic loads on structures necessitates explicit consideration of inelastic structural behavior. Hence, nonlinear approaches such as pushover analyses have become more popular. In this study, the performance of a ten-story steel moment-resisting frame retrofitted with various bracings like diagonal-bracing, chevron bracing, x-bracing and k-bracing is evaluated using linear and nonlinear analysis. The responses, such as base shear, lateral load distribution, displacement, drift, and lateral stiffness, are determined using the ETABS-18 building analysis and design program. The results of the study show that the steel-braced frame systems have substantially greater strength and ductility capabilities than their unbraced or alternate steel-braced moment-resistant steel frame. Further, the unbraced steel frame has a low R-factor as compared to the bracing system due to the increased stiffness at the story level.

Inelastic seismic behavior of asymmetric structures with mass and stiffness eccentricity under bidirectional ground motions

SummaryStructures with an asymmetric plan have proved to be severely vulnerable during the past earthquakes. The vulnerability may arise due to the uneven distribution of stiffness or mass. Most of the research focused on studying the eccentricity arising due to the irregular stiffness distribution. On the other hand, the systems with mass eccentricity arising due to the uneven distribution of mass at floor level are given relatively little attention. Hence, the present paper comprehensively studied the stiffness and mass eccentric systems together. In each case, the structure is subjected to bidirectional components of ground motion, which reflects the real situation more closely. So, for the lateral load‐resisting elements (columns), effect of biaxial interaction due to simultaneous bidirectional movement is included in the hysteresis behavior as explained in the paper to make a reasonably accurate prediction. Primarily idealized single‐story systems were used to study how asymmetric structures are vulnerable if they have stiffness or mass eccentricity. Further, the three‐story asymmetric systems were also included in the scope of the study to observe the effect of higher modes. To simulate a more practical situation, the present paper considers higher eccentricity in the first story of the three‐story system due to functional reasons, while the upper stories have lesser eccentricities compared to the first story. The present study shows that mass eccentric systems are equally vulnerable to earthquakes as stiffness eccentric systems. Further, three‐story systems show a manifold increase in response compared to its single‐story counterparts. Such a study may help to develop more insight into the generic behavior of plan asymmetric systems, leading to the improvement of design guidelines.

Seismic behaviour of structures under bidirectional ground motion: Does the angle of incidence have any influence?

Inelastic seismic behaviour of structures is needed to be predicted as accurately as possible. As during the seismic design, structures are allowed to undergo a stipulated amount of inelastic deformation in the dual design philosophy and its further extension of performance-based design. To obtain reasonably accurate behaviour in post-elastic ranges has manifold issues to be addressed together. The simultaneous effect of bidirectional ground motion is one of the major factors that need to be considered, and many studies also did the same. However, hardly any of them did consider the interaction between the deformations along two principal orthogonal directions on the yield criteria, post-elastic range excursion and the criteria of unloading. The present study makes an attempt to address these issues. Further, a few more studies mentioned that the angle of incidence of such orthogonal components of ground motion might influence the response of the structure. Hence, along with incorporating the effect of bidirectional interaction in the post elastic range, the issue of incidence angle is also studied extensively to reach a conclusive end. The detailed results presented in the study not only help to develop the physical insight but also maybe help in fine-tuning the design provisions.

Evaluation of seismic forces under modified structural schemes in the process of vibrations

The aim of the work - development of one of the possible methods for seismic analysis that considers the inelastic behavior of structures under seismic loads. This requires the development of seismic analysis methods that take into account the change (decrease) in the bearing capacity or the destruction of individual elements until the final loss of the bearing capacity of the structure. Methods. The dependences and algorithms include determining seismic forces using the method of normal forms, which until now is the main one in solving problems of the seismic resistance theory in seismic regions, calculation formulas to calculate seismic forces at each time step are presented in the form of expansions into natural vibration modes, which regard the changes in the design scheme. The calculation is repeated at each time step as a static calculation for the action of seismic forces determined at the previous stage, before the building collapses. Results. The developed dependencies and algorithms allow to consider changes in the design scheme during vibrations at each time step, changes in the dynamic properties of the building and, as a result, the values of seismic forces. The value of the coefficient of inelastic work of structures K 1, which are given in regulatory documents, do not give fully correspond to the actual behavior of the structure under seismic influences. The proposed calculation method allows to determine the estimated values of seismic forces and their distribution taking into account the influence of damage of elements and the appearance of inelastic zones in the design process of fluctuations at each time step and to assess the dynamic behavior of the building.

EVALUASI KINERJA STRUKTUR BANGUNAN DENGAN METODE PUSHOVER ANALYSIS PADA GEDUNG RUMAH SAKIT STROKE NASIONAL BUKITTINGGI

Earthquake phenomena are natural phenomena that greatly affect buildings, especially high-rise buildings. Planning of earthquake-resistant building structures is very important in Indonesia, considering that most of the area is located in earthquake areas with moderate to high intensity. Buildings in earthquake-prone areas must be designed to be able to withstand earthquakes. The latest planning trend is performance based seismic design, which utilizes computer-based non- linear analysis techniques to analyze the inelastic behavior of structures from various ground motion intensities (earthquakes), so that their performance can be known in critical conditions. Further action can be taken if it does not meet the required requirements. The purpose of this study was to determine the pushover analysis procedure to evaluate the performance of the building structure and to determine the pattern of the collapse of the building structure after being analyzed by pushover. This study uses the Static Pushover Analysis method with reference to the displacement coefficient method (FEMA 356, 2000). The lateral load used is the result of an equivalent static analysis which is carried out monotonically in one direction. Research shows that there are several conclusions. First, the displacement of the maximum pushover result (δmax) in the XZ direction, which is in step-7, is greater than the displacement target (δt), with a figure of 61541.4681 mm > 58.212 mm. Second, the displacement of the maximum pushover result (δmax) in the YZ direction, namely in step-5, is greater than the displacement target (δt), with a figure of 10450.54 mm > 58.212 mm. Third, the evaluation in the XZ direction is still safe even though max > t, because all beam elements in the portal appear plastic hinges with levels A-B which are still elastic, all marked in pink. The distribution of plastic hinges that occur at all steps shows that no structural member exceeds the performance limit so that it can be said that the performance of the structural component is in a safe condition. Fourth, the structural members in the YZ direction are also safe because max > t and the plastic hinge distribution scheme shows the structural members marked in pink with levels A-B. Keywords: pushover, non-linear, plastic hinge

Energy-balance based plastic design and analysis of hybrid coupled wall system

The hybrid coupled wall (HCW) system consists of steel coupling beams that connect adjacent reinforced concrete (RC) wall piers. In order to minimize or even eliminate the lengthy design iterations of conventional performance-based seismic design method and directly account for inelastic structural behavior, the modified energy-balance based plastic design (EBPD) method is proposed and developed for the seismic design of HCW systems with the consideration of influences of the degradation of hysteretic behavior and pinching effects. The design base shear can be obtained by solving the modified energy balance equation analytically. Twelve HCW prototype structures with different structural heights and coupling ratio (CR) were designed and evaluated by conducting a series of push-over analyses and nonlinear dynamic time-history analyses with the proved-reliable program of PERFORM-3D. The analysis results indicate that all HCW prototype structures exhibit the favorable yield mechanism and satisfactory seismic performance. Particularly, the influences of CR on the deformation characteristics, bending moment distribution among wall piers and vertical distribution of overturning moment are revealed. Suggestions are made in terms of the appropriate selection of CR for different structural heights.

Study of inelastic behaviour steel structure of special moment frame (SMF) and eccentrically braced frame (EBF) with pushover analysis

High rise buildings should be made as sufficient seismic performance, so it won’t immediately collapse when an earthquake occurs. Therefore, lateral strengthened stories are required in high rise buildings to enhance the lateral rigidity of structure. The use of lateral strengthening has a great effect on the entire seismic performance. A 20-stories high rise steel structure building was evaluated on this research comparing the structures’ inelastic behaviour using two seismic force-resisting system, i.e., special moment frame and eccentrically braced frame. The analysis of inelastic behaviour in this research using static non-linear analysis, i.e., pushover analysis. By using pushover analysis, the inelastic behaviour of structures, including story drift, shear story, displacement, plastic joint formation, and ductility, were obtained. In the elastic condition, the shear story of the eccentrically braced frame system is smaller than the special moment frame system. While in plastic condition, the shear story of the eccentrically braced frame system is larger than the special moment frame system. The story drift and the displacement of the special moment frame system are indicated to be larger than the eccentrically braced frame system. These results show that the eccentrically braced frame system has better rigidity than the special moment frame system.

Consideration of strength-stiffness dependency in the determination of lateral load pattern

The lateral load pattern used in design can significantly influence the distribution of strength and stiffness and consequently the distribution of damage along the height of the structure. The distribution patterns provided in seismic design codes are primarily derived from the fundamental elastic mode of vibration without considering the inelastic behavior of structures. This code-based load pattern causes concentrated damage in some stories, while leading to inefficient use of materials in other stories. Therefore, recent studies have employed optimization algorithms to develop lateral load patterns that achieve a uniform distribution of damage over all stories. These algorithms usually determine the distribution of strength along the height to achieve a particular ductility, while the stiffness is assumed to be constant. This assumption is contrary to the strength-stiffness dependency in steel or RC elements, hence causing some errors in the proposed load patterns. This paper presents an innovative algorithm to consider strength-stiffness dependency in the development of a lateral load pattern used for the design of moment frames. The proposed algorithm is implemented in MATLAB with supplementary OpenSees codes called in for nonlinear dynamic analysis. To reduce the computational cost of the nonlinear dynamic analysis during the optimization process, original n-bay frames are represented by simplified single-bay frames. The algorithm is implemented 800 times for 5 multi-story building models, 4 target ductility level, and 40 earthquake ground motions, with each implementation requiring a large number of trial and error iterations. The analysis results are processed to achieve two new lateral load patterns, which are evaluated using three original frames subjected to different ground motions. The results demonstrate that the moment frames designed by the proposed load patterns exhibit a more uniform distribution of ductility along the building height compared to the structures designed by the previously proposed lateral load patterns.

Reliability-based design optimization of steel frames using direct design

This paper presents an effective method for reliability-based design optimization (RBDO) of steel frames by combining direct design using nonlinear inelastic analysis, an improved importance sampling technique for structural failure probability analysis, and an improved differential evolution (DE) algorithm for optimization. The nonlinear inelastic analysis using the beam-column approach is used to capture the second-order effects and the inelastic behavior of structures. An improved importance sampling technique based on nonlinear inelastic analysis of the structure is employed that significantly reduces the number of structural analyses required for calculating the structural failure probability. An improved DE algorithm, which can effectively eliminate the redundant structural analyses for objective function evaluation, is utilized. A six-story space frame is studied to demonstrate the computational efficiency of the proposed method.

Evaluating alternative approaches for the seismic design of structures

The current design approach recommended by seismic codes is often based on the use of uniform-hazard response spectra, reduced to account for inelastic structural behaviour. This approach has some strong limitations that have been highlighted in many studies, including not allowing a direct control of the seismic risk and losses. This study aims at quantifying the levels of safety and the costs associated with this design approach, and to investigate alternative design approaches that have been developed in the last decades. In particular, a risk-targeting approach and a minimum-cost approach are considered. The first one, allowed by US codes, aims at designing structures with the same risk of collapse throughout regions of different seismicity. The second one aims to minimize the sum of the initial construction cost and the cost of expected losses due to future earthquakes. The comparison of the three approaches is performed by considering, as an example structure, a four-storey reinforced concrete frame building located in different areas in Europe, and by looking at the implications in terms of achieved safety levels, initial costs, and future losses. The study’s results provide useful information on how the design criteria and the different hazard levels throughout Europe affect the cost and safety levels of seismic design.

Hybrid experimental and numerical approach for assessment of non-linear dynamic behavior of soil-nailed retaining walls

Seismic Performance-based design demands reliable means for profound understanding of inelastic and non-linear dynamic behavior of civil structures. In this study, a hybrid experimental and numerical approach for seismic assessment of soil-nailed structures is introduced which incorporates simple static loading of a small-scale physical model and non-linear dynamic analysis of a two degree-of-freedom (2 DOF) system. A vertical loading pattern was applied on a small-scale modeling test behind a soil-reinforced block at the surface to mobilize extra lateral pressure on the reinforced soil zone. Two non-linear force–displacement relations obtained from the lateral pressure and facing displacement values of the physical test have been denoted as capacity curves and employed as the non-linear stiffness of the 2 DOF springs. The capacity curves obtained from this approach inherently take into account the complexities of soil, nail, soil-nail-facing interactions and geometrical nonlinearities. The results of dynamic analysis from the 2 DOF model are presented in terms of bottom and top displacements as the direct performance of the structure under seismic excitation. A soil-nailed wall was tested under different input motions on a shaking table and the results were compared to assess the accuracy of the approach and identify the performance levels of soil-nailed structures.

Inelastic seismic behavior of asymmetric structures under bidirectional ground motion: An effort to incorporate the effect of bidirectional interaction in load resisting elements

Seismically driven asymmetric structures are more vulnerable than their symmetric counterparts because of the coupling of lateral and torsional vibration. Though the research effort has been made to study the behavior of asymmetric structures, however, studies under the bidirectional ground motion of such structures are extremely terse. Further, in the inelastic range, the interaction between seismic forces under bidirectional ground motion may influence the yield criteria, inelastic excursion, and displacement demand considerably. In this context, the present paper is an effort to study the influence of bidirectional interaction, which occurs in reality under two orthogonal components of ground motion in real seismic events for asymmetric structures. A recently developed, adequate bidirectional hysteresis model that is capable of capturing the effects of bidirectional interaction is used. The governing equation of motion is solved by step by step integration following Newmark’s β-γ method. For improving the accuracy, iterations are carried out in each time step applying the Newton-Raphson technique. The spring force updates at the end of each time step to account for material nonlinearity with reasonable accuracy. Further, the present study not only helps to develop physical insights into the behavior of asymmetric systems but also shows that inelastic response may be grossly underestimated if the interaction between seismic forces along two principal directions is not incorporated. The broad conclusions developed in the study may be a help to fine-tune the provision for asymmetric structures in seismic code.

Vibration control of structure by top base isolated storey as tuned mass damper

Presently, earthquake-resistant design provisions are based on the assumption of inelastic behaviour of structures in major earthquake occurrences. It is generally possible to achieve ductile behaviour with significant damage in steel and reinforced concrete structures. The passive control system is generally used to protect a building from the damaging effect of an earthquake. In the present work, the study of building with Base Isolated top floor as a tuned mass damper (TMD) is considered. The top storey is used as TMD for this purpose, the isolation system is provided at the base of the top storey of a building. This TMD being made up of concrete has the same damping ratio as that of the main building. Effectiveness of Base Isolated TMD is ascertained by comparing the results of the considered building of analysis by using Time History Analysis. By comparing the results, it is observed that Base Isolated TMD is quite effective as compared to building without TMD.

Performance of Outrigger System by Non-Linear Static Method

High rise building structures are highly affected by lateral loads and wind forces. To enhance lateral force outrigger systems are developed, which are one of the most popular and efficient, because they are easier to build and they provides good lateral stiffness. With the rise of building height, deep beam become concrete walls at least of one story height. Axial shortening effect between core and perimeter structure has to be considered.In the present work 20 story reinforced concrete structure has taken with outrigger walls attached from core to the outer perimeter column. By changing the different position of outrigger level are kept for analysis.The building without and with outrigger are compared with bareframe. These are different building models analysed (a) Bare frame of twenty story building (b) Bare frame with core shear wall building (c) Outrigger system at top of building (d) Outrigger system at top & 0.75 Height of building (e) Outrigger system at top & 0.50 Height of building (f) Outrigger system at top & 0.25 Height of building. Non-linear static analysis results were compared. The analytical methods used in the work are pushover method. In this work, various parameters like pushover curve, displacement vs base force, story displacement, hinges formation are obtained for all the models.Outrigger at optimum level at 0.5 Height gives better results in both displacements and base force. To sustain peak lateral loads these systems are provided half of the height. These study gives has inelastic behaviour of structure.

Experimental Investigation of Structural Response of Corrugated Steel Sheet Subjected to Repeated Impact Loading: Performance of LNG Cargo Containment System

The primary barrier in contact with LNG (Liquefied natural gas) cargo is manufactured from stainless steel, and has a corrugated membrane structure due to thermal deformation caused by extreme temperature differences. Because the primary barrier is tailored to be LNG watertight, the structural integrity of the primary barrier must be maintained despite the increase in LNG sloshing load. Among the various types of fluid impacts in a cargo hold, jet flow runs up along the wall of the cargo hold and extreme impact load is exerted on the side of the corrugation of the primary barrier. However, the impact behavior of the primary barrier under the prevailing environment has not been investigated due to the limitation of test methods. Thus, in the present study, the inelastic structural behavior of thin-walled and curved-shaped structures for liquefied natural gas cargo containment systems under repeated impact loading was investigated experimentally. Custom-built structural impact test equipment with large-scale weight drop test facilities was fabricated, and a series of structural impact tests were carried out. The impact energy and the number of repetitions were taken into account in order to investigate the characteristics of the inelastic structural behavior, such as plastic deformation and reaction force time history according to impact energy.

Co-rotating rigid beam with generalized plastic hinges for the nonlinear dynamic analysis of planar framed structures subjected to impact loading

The purpose of this paper is to model the nonlinear dynamical response of steel frame structures subjected to impact loading. A 2D co-rotational rigid beam element with generalized elasto-plastic hinges is presented. The main idea is to integrate the concept of the generalized elasto-plastic hinge into the standard co-rotational framework by performing a static condensation procedure in order to remove extra internal nodes and their corresponding degrees of freedom. In addition, impact loading is applied through a contact model that is described in the rigorous framework of non-smooth dynamics. In this framework, equations of motion are derived using a set of differential measures and convex analysis tools, whereas Newton's impact law is imposed by means of a restitution coefficient in order to accommodate energy losses. An energy and momentum conserving scheme is adopted to solve the dynamical equations. The main interest of the current model is the ability to evaluate the geometrically nonlinear inelastic behaviour of steel structures with semi-rigid connections subjected to impact in a simple and efficient way, using only a few number of elements. The accuracy of the proposed formulation is assessed in three numerical applications.

Intervention cost optimization of bracing systems with multiperformance criteria

In this paper a multiperformance optimization procedure to design dissipative bracing systems controlling the structural performance while minimizing the intervention cost is proposed. The procedure allows dimensional and topological optimization of bracing, considering inelastic behaviour of braced structures through properly developed visco-elastic equivalent linearization schemes. The structural behaviour is controlled through constraint functions on interstory drift ratio (IDR) while the intervention cost is explicitly encountered by considering real costs that mainly influence it. The procedure is suitable for both new and existing structures, however the objective function is specialized on typical costs of retrofit interventions. A numerical example on a multistory frame has been developed in order to show the effectiveness of the procedure to provide the optimal characteristics and arrangement for the braces, while the suitability of linear equivalent schemes to predict the structural response is investigated through Nonlinear dynamic analyses. Further, a comparison of the estimated intervention costs by asking for different performance levels is performed, showing how the proposed objective function is able to help the designers to identify the ideal performance levels and acceptance criteria to reduce the cost-benefit ratio.

Evaluation of the Equivalent Ductility of Buildings with Dynamic Soil-Structure Interaction Effects Using Capacity Curves

The analysis of buildings under seismic motion with a exible base must consider two principal aspects of structural displacement: the rst being structural deformation, the second rigid body behavior. This effect produces a modi cation of the inelastic behavior of structures. In addition, a consideration of the exible base may change the distri - bution of internal forces along the structure that could generate vari - ations in the ductility demands on different structural elements. This article summarizes the results of previous studies on variations in the inelastic behavior of steel and reinforced concrete structures, taking dynamic soil structure interaction into consideration. The response of buildings with a exible base is compared and contrasted with those with rigid bases. The inelastic behavior of buildings is set out in terms of ductility capacity and demands. Pushover analysis is used to estab lish inelastic capacity parameters by comparing the capacity curves of buildings with rigid ( xed) and exible bases. Some comments and general guidelines are made about how base exibility in uences the inelastic behavior of structures.