Nonlinear Static Analysis Method Research Articles

The effect of floor slabs in a structure with frame shear walls modeling in pushover analysis

Pushover is a nonlinear static analysis method that provides information on nonlinear structures’ behavior due to earthquakes. Subsequently, it has been recommended as a reliable tool to help know the capacity of structures. Another consideration is its easiness of interpretation than the nonlinear dynamic analysis. Numerical modeling of the structure plays an important role in this analysis since every detail of modeling could give different results. The objective of this study is to analyze the effect of the existence of floor slabs in a structure with frame shear walls modeling, which considers the frequent attempt to simplify structural modeling. The effect of the position of components assignation is going to be analyzed too, especially floor slabs and beams, whether it was assigned with centroid or top center insertion point in pushover analysis. In this study, an existing hospital building with vertical irregularity has been modeled into four various models using SAP2000. As the result of pushover analysis, every model gives its pushover curves which reflect its behavior. Those results show that the models with floor slabs have higher capacities. In addition, the combination of the assignation of floor slabs and the top center insertion point gives the highest capacity compared to the other models.

Effect of alternative load path design method on preventing progressive collapse and reducing the rehabilitation cost using FEMA-P58

The alternative load path (ALP) method is an important modern design approach to prevent progressive collapse of buildings by redesigning adjacent structural elements to provide an alternative load path in case of partial collapse. This may lead to tangible changes in the mass and stiffness of the building, which means a change in the seismic behavior of the building. This shows the fact that choosing and designing an alternative load path is not an easy task. Studying the improvement in the seismic behavior of the building, whether direct or indirect, as a result of using the ALP, is the main objective of this paper. To achieve this goal, this study examined approximately 96 models, including the study of the possibility of progressive collapse occurring, whether there is or isn't an alternative path for the loads using non-linear static and dynamic analysis, as well as evaluating the study models using various seismic evaluation methods, where both the nonlinear static pushover analysis method and the FEMA-P58 method were used and compared. The study models are divided into two sections, with and without (ALP). The study models are also categorized by building height using heights of 6, 9, 12 and 15 floors. The models were also divided based on the locations of weak points in the original design that may be susceptible to damage and lead to progressive collapse, whether they are internal, side, or corner weak columns. The findings from the examined models indicate that the efficiency of (ALP) systems is more prominent in low and mid-height buildings compared to tall buildings. Additionally, the results demonstrate that the FEMA-P58 method yields similar predictions regarding building behavior as traditional seismic assessment methods like pushover analysis, but in a simplified manner that benefits non-engineers by providing clear insights into the financial and temporal aspects of different structural system solutions.

Nonlinear seismic analysis of irregular base isolated structures using a new modified lateral load pattern

Nowadays, seismic isolation systems are increasingly used by engineers for retrofitting existing structures and designing new ones. Nevertheless, limited studies have been conducted on the performance evaluation of the nonlinear static analysis methods for estimating the seismic demands of the base isolated structures. The current study proposes a new modified lateral load pattern for seismic analysis of base isolated structures using modified capacity spectrum method (MCSM). Moreover, this study investigates the applicability of the modal pushover analysis (MPA) and modified capacity spectrum methods for assessing the base isolated structures with setback irregularity. To this end, two types of steel moment resisting structures including 3-story (low-rise) and 9-story (medium-rise) with different irregularities in elevation are considered. All the structures are isolated by three types of lead rubber bearing (LRB) isolators with various stiffnesses. In order to consider the effect of ground motion, two types of near-fault and far-fault ground motions are selected. To evaluate the performance of the MCSM and MPA methods, the structural seismic demands estimated by these methods are compared with their benchmark values obtained by the nonlinear time history analysis method. The obtained results show the superiority of the modified capacity spectrum method and the effectiveness of the new modified lateral load pattern presented for this method.

On the seismic response of rack structures affected by pinching

The nonlinear static and dynamic behavior of rack structures affected by joint pinching are studied using a simplified single-degree-of-freedom system. Since the joints of steel rack structures play a crucial role in the capacity design methodology, as they are the main source of energy dissipation, their behavior is widely studied in the literature, highlighting their reduced hysteresis loop. However, no systematic study investigates and associates these characteristics with a possible increase in displacement demand. Using a single-degree-of-freedom system focuses attention on the type of cyclic behavior and allows a comparison of linear and nonlinear responses, the latter evaluated using both elastic-plastic and pinching laws. At prescribed ductility, the elastic-plastic and pinching responses can be compared with the prescriptions of Italian and European building codes. This simplified method was also applied to case studies of experimental pushover tests on racks found in the literature. Results showed that neglecting the joint pinching behavior for a rack structure can lead to an underestimation of the displacement demand in the case of the application of the nonlinear static seismic analysis method and hence to the overestimation of the q-factor for the application of linear seismic analysis methods.

Nonlinear Seismic Analysis of Perforated cold-formed steel shear wall with Upright Section

During the last few decades, cold-formed steel (CFS) is extensively used in mid- and low-rise housing due to the increasing demand of rapid constructions along with its various advantages in comparison with other structural material. Cold-formed steel framed shear walls (CFSFSW) are most common and primary lateral load resisting system. However, adopting it in the seismic zone is difficult, especially because many design components remain open. In this research an effort has been made to design the shear wall system with both unperforated and perforated upright sections using nonlinear static analysis method. In ABAQUS, a general-purpose finite element analysis software, three-dimensional models using shell elements are used to simulate a shear wall system. A comparative study regarding the lateral load capacities with respect to maximum allowable lateral deflection including different parameters like column sections, thickness and perforation arrangements are presented here. It was found that increasing thickness and including Chanel stiffeners improves the lateral strength of original upright section. The developed modelling protocol helps to estimate its lateral performance under earthquake with reasonable accuracy.

Modal Pushover Analysis for Seismic Performance Assessment of Underground Structures

ABSTRACT Pushover analysis as an efficient nonlinear static analysis method has been widely applied to the seismic inelastic performance evaluation of above-ground structures. Although it has the main advantage of high computational efficiency compared to nonlinear dynamic time-history analysis (THA), the assumption that the fundamental mode dominates structural response limits its application to long-period structures. Improved pushover analysis has been developed to consider the higher mode effect, named modal pushover analysis (MPA), but all research mainly focused on buildings and bridges. Since the mechanical behaviors of the underground structures and above-ground structures under seismic exaction are not exactly the same, so far, MPA suitable for seismic performance assessment of underground structures still has not been developed. Therefore, the aim of this investigation is to develop MPA for the seismic performance assessment of underground structures. A prototype subway station structure and a soft site are used to study the applicability of the developed MPA and compare it with the traditional pushover analysis procedure and nonlinear THA. Numerical analysis results of the subway station illustrate the applicability and potential of the developed MPA for underground structures.

COMPARISON OF MRF AND CBF STRUCTURAL RESPONSE TO EARTQUAKE IN OFFICE BUILDING SURABAYA

Indonesia is a country that prone earthquakes. Therefore, knowledge of earthquake-resistant building construction is needed in reducing the risk of damage caused by earthquakes. There are several methods of earthquake-resistant construction planning, one of which is the pushover analysis method. Pushover is a nonlinear static analysis method in which the structure is subjected to gravity loading and displacement-controlled lateral loads which continue to increase through elastic and inelastic behavior until the final condition. One of the popular construction materials in structural planning is steel construction, which has a uniform structure, lightweight, strong, and easy to work with. In modeling earthquake-resistant structures, several popular models are the MRF and CBF models. MRF is a structural configuration model configured on beams that are firmly connected to columns. Based on a rigid beam-column connection, the moment frame cannot be moved laterally without bending the beam or column depending on the connection geometry. Results The case study on the comparison of the two structural models concluded that in the design of earthquake-resistant steel structures using the pushover method, it was found that the MRF structure had higher ductility than the CBF, namely 2.1:1.6.

Earthquake Performance Analysis of Steel Structures with A3 Plan Irregularities

In earthquake engineering, a performance-based design method is used to determine the level of the expected performance of the structures under the earthquake effect. The level of performance is related to the damage situation that could be occurred in the structure after the earthquake. In the performance-based structural design, it is predicted that more than one damage levels emerge under one certain earthquake effect. In this study, the seismic behavior of steel structures with plan irregularities in the Turkey Building Earthquake Code in the 2018 (TBEC-2018) is investigated by the nonlinear static analysis methods. The selected steel structures are located in İzmir, Turkey. The Turkey Earthquake Code in 2018 is considered for assessing seismic performance evaluation of the selected moment-resisting frame steel building. Four different A3 type irregularity was investigated. The steel building with no irregularity in its plan. was selected as the structure of the reference. The performance goals of the five different steel structures are evaluated by applying the pushover and procedures of the TBEC-2018. The steel structures were compared by obtaining pushover curves for both the X and Y directions. The results show that the effects of A3 type irregularity should be not considered in design and buildings without irregularities are safer.

Study on the Development of Seismic Fragility of Steel SMRF

Abstract: Vulnerability assessment of the structure is the most important and wide area of research which requires more input from the engineers and seismologist. The seismic vulnerability assessment of the structure can be evaluated by developing Fragility curves. Fragility curves shows the conditional probability of the structure exceeding the particular performance limit of the given damage state during strong ground motions. Fragility curves can be developed for different parameters like spectral displacement (Sd), spectral acceleration (Sa) Peak ground acceleration (PGA) , Inter storey drift ratio (IDR) etc. This paper describes about the different methods used in deriving the Fragility curves like conventional methods, Nonlinear Dynamic analysis methods and Nonlinear Static analysis methods. Also the fragility analysis of 5 Storied Steel Moment Resisting Frame (SMRF) has been carried out based on the parameters suggested by HAZUS M.H 2.1. Nonlinear static pushover analysis of the frame has been carried out in ETABS2016. Fragility curves are developed based on the pushover analysis results. The damage states defined as per HAZUS are Slight damage (SD), Moderate damage (MD) Extensive damage (ED) and Complete damage (CD). After carrying out the fragility analysis for the steel SMRF, it has been found out that, as the spectral displacement increases probability of failure for the slight damage of the structure is very high and the probability of failure for the complete damage is very low. Hence the probability of failure of the structure reduces from slight damage to complete damage. Keywords: Fragility curves, vulnerability assessment, Nonlinear static pushover analysis, HAZUS M.H 2.1.

Assessment of wind-induced fragility of transmission towersunder quasi-static wind load

Overhead power transmission line systems consisting of long-span conductors and high-rise towers are wind-sensitive structures featured with significant structural nonlinearity and fragility under wind hazards. To assess wind-induced structural fragility of a transmission tower, a novel efficient quasi-static approach, which is based on the analytical probability distribution of extreme wind effect in frequency domain and the probabilistic wind-resistant capacity, is developed in the present study. The 90-degree wind direction (perpendicular to conductors), which is always the worst scenario, is considered in this paper. The structural nonlinearity and failure modes are captured using a nonlinear static push-over analysis method, which simulates the failure process of the tower structure with random initial geometric defects. Wind-resistance performance of the tower is quantified based on the principle of energy equivalence. Damage of the tower is classified into three levels including slight damage, severe damage, and collapse. The tower fragility curve, which predicts damage of the tower as a function of wind speed, is presented and discussed.

Research on determining the aseismic performance level of reinforced concrete building

In seismic design based on performance, seismic performance level is determined based on failure state of the building and seismic design objective is set according to the importance of the buildings. In many countries, they calculate the seismic reaction of the buildings with the use of structural design programs to check the aseismic performance through the nonlinear static analysis method. In this paper, we established seismic performance levels and aseismic design objective to design on the basis of design objective according to the three levels in Seismic Design Code of Building, DPR Korea, 2010.

Nonbearing Wall infill Under Seismic Impacts In Terms Of Non-Linear Static Analysis

The presence of wall infill during seismic impacts is one of the key factors that significantly affect the seismic stability of buildings. Also, irregularity of configuration in plan and height can often lead to more serious damage comparing to regular buildings, due to torsional oscillations and stress concentration on individual elements. The purpose of this article is to study the behavior of various irregularities in the shape of buildings under seismic impacts in terms of non-linear static analysis, taking into account the non-bearing wall infill. For this purpose, five typical geometric shapes of the building plan used in Ukraine and abroad (rectangular, + shape, L-shaped, T-shaped and 4-shaped) were adopted.The calculations were performed using the Pushover Analysis (nonlinear static analysis) method in CAD Lira-SAPR 2019. The main parameter that forms the basis for seismic stability analysis is the story drift under seismic impacts. Obtained results indicate the need to take into account the effect of wall infill, as this can lead to an increase in the seismic stability of the building and stress concentration on individual elements, which can lead to their collapse.

Analiza oštetljivosti i robusnosti višekatne armiranobetonske zgrade

The robustness of a reinforced concrete (RC) five-storey building (frame system stiffened by walls) is analysed in the paper. A high ductility class structure is designed in accordance with structural Eurocodes. The response of the structure to eight different scenarios of the ground floor vertical element loss is analysed. Nonlinear Static Analysis (NSA) and Nonlinear Dynamic Analysis (NDA) methods are used for the robustness analysis. Fragility curves of the building are derived from statistical analysis of these results. The values obtained through NSA and NDA, damage limit states of the system, and fragility curves, are compared. The influence of the position of the removed element on robustness of the structure is also analysed.

FEMA P695 methodology for safety margin evaluation of steel moment resisting frames subjected to near-field and far-field records

This study presents the impact of near-field and far-field earthquakes on the seismic design of Intermediate Moment Resisting Frame (IMRF) and Special Moment Resisting Frame (SMRF) structures through FEMA (Federal Emergency Management Agency) P695 methodology to highlight the importance of probabilistic collapse as well as seismic performance factors of these structures. The purpose of this study is to investigate the collapse performance of steel intermediate and special moment resisting frame systems as the most common structural systems in urban areas in order to assess the seismic performance factors used for the design using nonlinear static and dynamic analysis methods. In this regard, as the representatives of low-rise to high-rise buildings, archetypes with 5-, 10- and 15- story of intermediate and special moment resisting frames are designed and then the nonlinear models are developed in OpenSees software. Nonlinear static analyses are performed to assess the overstrength and ductility of these systems. The effects of near-field and far-field ground motions on these frames are investigated through incremental dynamic analysis. These analyses are performed with 22 far-field and 20 near-field ground motion records using FEMA P695 methodology. The results show that near-field earthquakes have serious impacts on the collapse probability of structures. The superiority of special moment resisting frame over intermediate moment resisting frame is quantified in terms of safety margin and median collapse capacity under both near-field and far-field earthquakes. Finally, the results indicate that the response modification factors introduced in seismic design code are acceptable for intermediate moment resisting frame and special moment resisting frame under far-field ground motions. However, in the near-field sites while SMRF system meets the requirements of FEMA P695 methodology, the IMRF system does not satisfy these criteria.

Evaluation of seismic demands of reinforced concrete frames with steel plate shear wall

To assess the seismic demands of structures at different performance levels, the non-linear static analysis method (pushover) has always been of interest to researchers. However, the most important shortcoming of this analysis method pertains to the pattern of lateral load distribution, which has to be carefully selected, especially when buildings of great height enter the plastic range of behaviour, otherwise inaccurate results will be obtained. To tackle this issue, the researchers have proposed advanced approaches to modify the conventional non-linear static method accounting for the effects of higher modes. In this respect, a displacement-based adaptive pushover algorithm (DAPA) and an adaptive pushover analysis method (APAM), taking account of the effects of mode interaction, have recently come to light.

CFRP strengthening of steel beam curved in plan

Nowadays, one of the practical, fast and easy ways to strengthen steel elements is the use of Carbon Fiber Reinforced Polymer (CFRP). Most previous research in the CFRP strengthening of steel members has carried out on straight steel members. The main difference between horizontal curved beams and straight beams under vertical load is the presence of torsional moment in the horizontal curved beams. In the other words, the horizontal curved beams are analyzed and designed for simultaneous internal forces included bending moment, torsional moment, and shear force. The horizontal curved steel beams are usually used in buildings, bridges, trusses, and others. This study explored the effect of the CFRP strengthening on the behavior of the horizontal curved square hollow section (SHS) steel beams. Four specimens were analyzed, one non-strengthened curved steel beam as a control column and three horizontal curved steel beams strengthened using CFRP sheets (under concentrated load and uniform distributed load). To analyze the horizontal curved steel beams, three dimensional (3D) modeling and nonlinear static analysis methods using ANSYS software were applied. The results indicated that application of CFRP sheets in some specific locations of the horizontal curved steel beams could increase the ultimate capacity of these beams, significantly. Also, the results indicated when the horizontal curved steel beams were under distributed load, the increase rate in the ultimate capacity was more than in the case when these beams were under concentrated load.

Numerical Analysis of Masonry Assemblages through Simplified Micro-Modeling

Recently, research focused on preventing the aging of masonry structures, and minimization of damage caused by earthquakes to these structures has gained significant attention. To improve the performance of these structures, an appropriate method is required for their performance evaluation. Generally, the equivalent strut model is employed for the performance evaluation of a masonry wall. However, this method is known to have limitations in implementing reinforced masonry and in reflecting the actual reinforcement effect. Appropriate evaluation techniques should be developed to implement the performance improvement methods developed in the future. Therefore, in this study, analysis methods were developed considering the nonlinear static analysis method for masonry elements. In addition, using these methods, the analysis considering the various reinforced thicknesses and shapes was performed, and the appropriate reinforcement methods were presented for these structures.

Analytical Investigation of the Differences between Cast-In-Situ and Precast Beam-Column Connections under Seismic Actions

At present, the engineering designers generally design and analyze the precast structural models according to the equivalent cast-in-situ principle, and have a vague understanding of non-identical problems. However, these issues cannot be ignored, especially for high-intensity areas. This paper considers the differences of the hysteretic relationship between two typical precast joints and cast-in-situ (RC) joints, and researches the influence of these differences on the seismic response of frame structures. For the monolithic precast joint, the force mechanism was analyzed based on its assembly form, and the differences with the RC joint in the testing phenomena were explained accordingly. The dimensionless hysteresis models of two types of joints were proposed, and the rationality of the monolithic precast joint model was verified according to the existing experimental results. Different performances of joints were realized by assigning the constitutive models calculated from sectional reinforcement to the spring elements of analysis models. Considering two possible performance deficiencies of each type of precast joint separately, a total of seven structural analysis models were formed. Nonlinear static analysis and dynamic time-history analysis methods were adopted to reveal the differences between precast frames and the RC frame in terms of structural capacity curve, displacement response, ductility demands of components and structural residual deformation. The results showed that under strong seismic excitation, the response differences between precast frames and the RC frame were significant, so it is worthwhile to establish nonlinear models suitable for precast frames in seismic analysis. This study is valuable for understanding and distinguishing the nonlinear response of precast frames and traditional RC frames.

Seismic performance assessment of multi-story RC buildings with soft-story collapse mechanism equipped with gapped inclined bracing (GIB)

Gapped inclined bracing (GIB) is an innovative retrofit system for buildings with soft-story collapse mechanism. The system consists of a brace with gap element that activates before the structure approaches post-capping negative stiffness and collapse, providing supplemental plastic deformation and enhancing ductility of the system. This technique is also a resilient solution as the damage is controlled at the retrofitted soft-story, reducing the cost and time of repair. The paper presents a numerical study to verify the application of GIB systems for modern RC buildings, where masonry infill panels may be removed from lower stories due to functional requirements for more open spaces. Based on nonlinear static analysis, a novel and efficient design method is proposed to determine the GIB design parameters. To verify the performance of the retrofitting methodology, 12 configurations of RC moment frames with 4 and 8 stories are designed according to modern seismic codes and subjected to nonlinear static and incremental dynamic analyses. The results are then used to conduct fragility analysis to assess classical performance levels including immediate occupancy, life-safety, and collapse prevention. The results show that using the proposed design of GIB elements, the ultimate drift capacity corresponding to the collapse of soft-structures are increased by a factor of two. Also, the probability of collapse is reduced by 50% increase in the median collapse hazard intensity. These highlight significant improvements in the safety and resilience of buildings with soft-stories.

Research on RC Frame Structure’s Resistance to Continuous Collapse

A typical 8-story RC frame structure model with floor is established by using ABAQUS finite element software. The nonlinear static analysis method and the incremental dynamic analysis method are used to explore the influence of the floor slabs after the demolition on the continuous collapse resistance of the RC frame structure at the same time. Determine the most reasonable amount of reinforcement that meets the requirements for continuous collapse resistance of the frame beams of each layer, and the layer height that is most beneficial to the structure’s continuous collapse resistance.It is concluded that the floor can greatly improve the continuous collapse resistance of the overall structure, and the nonlinear static analysis is conservative; the amount of longitudinal reinforcement in each frame beam should be increased by 1.9% ~ 2.9% to meet the most reasonable requirements for continuous collapse of the frame beam; the floor height is between 4.3 and 4.8 meters, which is the most ideal state for the structure to resist continuous collapse.