Equivalent Lateral Force Method Research Articles

A Review on Seismic Analysis of RCC and Steel Structures using Linear and Non-linear Static Analysis

Abstract: An earthquake can cause significant harm to various aspects, including buildings, general life, and particularly multistory structures. In India, structures constructed in earthquake-prone regions, as defined by IS 1893: 2002, must be designed to withstand the loads, stresses, and consequences of earthquakes. Several techniques are available for assessing multi-story structures in this context, such as the Response Spectrum Method, Equivalent Lateral Force Method, Time History Method, and adhering to specific code provisions. Numerous researchers have undertaken studies to analyze multi-story buildings using one or more of these methods. However, there exists still a confusion about an effective and efficient method preferred for seismic design of multi-story buildings. Among the various approaches, the seismic coefficient method and response spectrum method are the most widely used. This comparative investigation aims to review research reports that have employed the Equivalent Lateral Force Method and Response Spectrum Method to analyze multi-story buildings in earthquake-prone areas. The design response spectrum serves as the initial reference point for most established seismic design and assessment procedures. It primarily dictates the inertia forces that buildings and structures must withstand during an earthquake. This paper aims to introduce and discuss contemporary concepts regarding the creation and utilization of earthquake design response spectra. Additionally, the paper highlights the various methods of seismic analysis being investigated in the past literature. It also gives an overview of various investigations being carried out using linear and non-linear static analysis of RCC structures. Many of the ideas presented are specifically aimed at aiding engineers who work in regions with low to moderate seismic activity. The main objective is to inform engineers about modern approaches to developing response spectra. This knowledge can then be applied effectively in both analytical and design contexts when dealing with earthquake-related challenges

Influência de pilares-parede no comportamento estrutural de um edifício de múltiplos pavimentos de concreto de acordo com a norma técnica brasileira ABNT NBR 15421:2006

abstract: This paper presents a comparative study of the influence of shear walls on the behavior of a multi-storey concrete building when subjected to seismic actions. Two structures with different earthquake-resistant systems were evaluated. One is composed of concrete frames with usual detailing in both directions (x and y), and the other one is formed by a dual system, composed of frames and shear walls with usual detailing. The Equivalent Lateral Force procedure and the Modal Response Spectrum analysis presented by the Brazilian Technical Code ABNT NBR 15421:2006 were considered. The dual system building presented a greater stiffness with the shear walls arranged parallel to direction y. In the x direction, the responses are equivalent in both buildings. The horizontal forces obtained by the Equivalent Lateral Force method at the base of the buildings were greater than the Modal Response Spectrum method.

Comparative Study on Overturning Moment and Eccentricity of A I-Shaped Building by Equivalent Lateral Force and Modal Response Spectrum Method Using ETABS Software

Extended Three-Dimensional Analysis of Building System (ETABS) (version19) is a powerful software, used for building analysis and design. This software used for analysis purpose to this study. The study in this paper mainly strengthens on overturning moment and eccentricity of I-shaped fifteen storied building in both equivalent lateral force method and modal response spectrum method. The analyses are carried out as per ASCE7-16 and BNBC 2020 guidelines. It is observed that the overturning moment is approximately 11% greater in equivalent lateral force method than modal response spectrum method while in eccentricity approximately 2% greater in modal response spectrum method than equivalent lateral force method.

A Review on Dynamic Analysis and Design of R.C.C Solids Storage Structure

Aim of research paper is to compare and briefly describe about the advantage and limitations of solid storage structure by using Staad Pro Structural software. Solid storage structures are considered as special structures as its design is based on the properties of materials stored. The pressure exerted by the stored material on the side of a bin varies with the processes and arrangements of filling and emptying operations. Due to this variation, it is extremely difficult to analyze the pressure exerted on the walls of the bins. In our research work, we are designing the RCC solid storage structure located in all seismic zones with the help of structural software Staad Pro. The design concept include, all dimensions of structural component based on trial and error method, using Equivalent lateral force method in term of Comparison of different models of concrete solid storage structure for earthquake such as nodal displacement, stress and vertical or horizontal pressure on walls etc. for volume of 180 m3. All the designs have been based on the recommendations of I.S 4995 -1974 (part 1&2) and I.S 456 – 2000 codes, Based on these designs, that dimension of solid storage structures shows least amount of concrete and steel. Main objective of our research work is to compare of different models of concrete solid storage structure for earthquake in terms of nodal displacement, stress and vertical or horizontal pressure on walls etc.

A comparison of structural analyses procedures for earthquake-resistant design of buildings

Several seismic analysis procedures in the latest standards have been developed for structural design and assessment. Since these methods have different advantages and limitations, a comprehensive comparison of these procedures is required to select the most effective one. The three most common methods are the Equivalent Lateral Force (ELF) method, Modal Response Spectrum (MRS) analysis, and Linear Response History (LRH) analysis. This research intends to present a comparative study of these methods, according to ASCE 7-16 standard by utilizing ETABSR software. They were examined in terms of base shear and distribution of story shear forces for a sixth-story reinforced concrete (RC) building, designed according to ACI 318-19 standard. Building code requirements for RC structures with the dual lateral force-resisting system in a high seismic zone are discussed. The results show that the ELF procedure's base shear for the building under consideration is conservative compared to the MRS or LRH analysis. The vertical distribution of the ELF procedure is just a function of the structure's fundamental period; however, the advantage of the MRS and LRH analysis is that they provide information as to how the distribution of mass and stiffness of a structure influences the member forces and displacements.

Study of Seismic Response Demands of Different L-shaped Buildings

The present study evaluates the effect of plan configuration irregularity of different L shaped models. For this, one regular and six different L-shaped RC building frames were modeled for numerical analysis. The analysis was done through an equivalent static lateral force method and response spectrum analysis (dynamic analysis). The seismic response demands were measured in terms of story displacement, inter-story drift ratio, torsional irregularity ratio, and torsional diaphragm rotation. In addition, fundamental time period of structure, vibration mode shapes and modal participating mass ratios were also studied. The study shows that the fundamental time period of structure based on standard code shows a lower value as compared to a finite element approach. It is concluded that to account for the irregularities present within the buildings, current code provisions are insufficient and should be amended.

Seismic collapse performance of steel special moment frames designed using different analysis methods

Building structures designed according to current seismic design codes should satisfy the seismic performance objectives specified in codes during big earthquake events. ASCE 7-16 specifies that risk category I and II structures should have a probability of collapse less than 10% against the maximum considered earthquake (MCE) shaking hazard. ASCE 7-16 provides four analysis methods to calculate the seismic demands on structures. In this study, 4-, 8-, 12-, and 16-story steel special moment frames (SMFs) are designed using the two most popular elastic analysis methods: the equivalent lateral force (ELF) method and the modal response spectrum analysis (RSA) method. The collapse probabilities of these structures are estimated against MCE shaking hazards according to FEMA P695. It is observed that the collapse probabilities of these structures vary according to analysis methods used for design. To improve the seismic collapse performance of SMFs, a modified method is proposed.

Effects of opening dimension in shear wall on the behavior of high-rise building structure due to earthquake load

The aim of this study is to analyze the effects of opening dimension in shear wall on the behavior of high-rise building structure due to earthquake load. The 20-story building prototype with shear wall placement as core wall with various sizes of opening are analyzed with the help of software MIDAS GEN, using equivalent lateral force and response spectrum method in X and Y direction. The shape of opening is square with width vary from 0.8 m – 1.3 m and height set at 2.2 m. This analysis will discuss structure’s natural time period, core wall distribution between shear wall and frame, lateral deflection, and story drift. The results show that the greater the opening will increase the natural time period by 1.72% and 1.67%, increase lateral deflection by 21.7932% and 23.5964%, and increase story drift by 24.6910% and 29.077% in each direction.

STUDY OF A STRUCTURE SUSPENDED FROM A SYSTEM OF STEEL COLUMNS AND TRUSSES (SYSTEM AND STABILITY)

Throughout history, men always wanted to build structures that are each more impressive than the next, while rising higher in the air. In this process, men were not satisfied with making sure that these structures were beautiful, impressive and majestic, but that they could also be very useful, that they fulfilled a function, and that they were able to resist the various structural constraints that will be imposed on it, or that could be imposed on it. With this in mind, we thought of creating a structure that could both inspire this side of wonder and structural beauty, while being useful and resistant to the loads imposed on it. In this work, we are going to talk about a building suspended to its foundation, in the sense that the building does not rest directly on the ground, but is suspended nearly eight meters from the ground by each of the three columns which support the said building by a system of trusses. The structure is made of steel with reinforced concrete slabs, which gives it a significant advantage in terms of weight. Another advantage is that it reacts quite well to earthquakes, showing only very small deflections using the equivalent lateral force method. In this work we will focus on the stability of the members of the system that carries the building and the stability of the building in general.

Assessment of Accidental Torsion in Building Structures Using Static and Dynamic Analysis Procedures

This article presents the findings of a study on assessment of the increase in building’s response due to accidental torsion when subjected to seismic forces. Critical stiffness and geometrical parameters that define buildings torsional response are examined including: (1) the ratio, Ω, between uncoupled torsional frequency ωθ to uncoupled translation frequencies in the direction of ground motion ωx or ωy, (2) floor plan aspect ratio, b/r, which is a function of the floor dimension and radius of gyration. The increased response is assessed on symmetric multi-storey buildings using both static and dynamic analysis methods specified by ASCE-7 and considering parameters affecting the torsional response. It was concluded that static and dynamic analysis procedures predict different accidental torsion responses. Static analysis based on the Equivalent Lateral Force (ELF) method predicts more conservative accidental torsions responses for flexible structures with Ω < 0.7~0.80, while the responses are less conservative for stiffer buildings. The conservativism in static analysis method is attributed to the response amplification factor, Ax. Floor plans and their lateral support system having frequency ratio Ω = 1 will also have a torsional radius equal to radius of gyration, and will experience drop in torsional response relative to more torsionally flexible buildings. This article presents a procedure to overcome the shortcomings of static and dynamic analysis procedures in terms of estimating accidental torsion response of symmetric building structures.

Seismic elastic performance of L-shaped building frames through plan irregularities

The trends of irregular building construction have rapidly increased due to aesthetic and limited availability of land. Past studies have shown that the structures with configuration irregularity are damaged under strong ground motion. Structural irregularities are important factors which decrease the seismic performance of the structures. Buildings having structural irregularities result in the uneven distribution of the story drift, excessive torsion, etc. according to the irregularity type and may fail during an earthquake. One such form of irregularity is the presence of re-entrant corners and torsional irregularity that causes stress concentration due to sudden changes in stiffness and torsion amplification in buildings. In this context, the present study evaluates the effect of plan configuration irregularity when subjected to the varying angle of the input response spectrum. For this, one regular and six different L-shaped RC building frames were modeled for numerical analysis. The analysis was done through an equivalent static lateral force method and response spectrum analysis (dynamic analysis). The structural responses were measured in terms of story displacement, inter-story drift ratio, torsional irregularity ratio, torsional diaphragm rotation, normalized base shear force, and overturning moment. The results indicate that buildings with plan configuration irregularity are more sensitive to the varying angle of the input response spectrum as compared to the symmetrical building model. The significant increase in seismic response demand was observed when the finite element models were subjected to a 135-degree angle as compared to the zero-degree angle of seismic incidence. In addition, the study shows that the fundamental time period of structure based on standard code shows a lower value as compared to a finite element approach. It is concluded that to account for the irregularities present within the buildings, current code provisions are insufficient and should be amended.

Earthquake lateral force analysis of reactor building, experimental power reactor

Indonesia is considering to construct its first experimental power reactor. Similar to other conventional nuclear power plants, this type of reactor is designed and built to withstand external hazards such as an earthquake. The seismic resistance design standard for building (SNI 03-1726-2012) as basic guidance should be implemented and used for earthquake-resistant building design. In this paper, a reactor building is considered for earthquake lateral force analysis to determine the design base shear force. In general, this analysis performed statically and dynamically. For static analysis, the equivalent lateral force method were used, while for dynamic analysis, the response spectrum method is used. The results of this study have shown that the value of displacement by using static analysis is more significant than the value of displacement by using dynamic analysis. It can be concluded that although the dynamic analysis is more accurate, the static analysis would lead to a more conservative result.

Seismic Performance of Steel Frames with Inverted V-Braces for North Cyprus

Cyprus Island is located in a high-risk zone, in which the buildings should have lateral load-resistance systems to resist the lateral imposed loads. Bracings play a vital role in the structural behavior of buildings during an earthquake. There are many bracing systems that can be found thorough searching in the literature. However, there are insufficient studies regarding the inverted-V bracing system in accordance with the Northern Cyprus seismic code of NCSC-2015. In this study, the seismic performance of steel structures equipped with various types of inverted-V bracing systems is investigated for mid-rise and high-rise buildings in accordance with NCSC-2015 code. Several steel structure buildings having different lateral load-resistance systems are analyzed under different loading patterns applying ETABS2016 software. For this purpose, linear static equivalent lateral force method (ELFM), nonlinear static (Pushover) and nonlinear dynamic time-history (TH) analyses were adopted. The obtained results in this research indicate that the inverted-V bracing systems dramatically enhance the performance of the steel structures more particularly when the earthquake is applied perpendicular to the weak axis of the columns. This indicates that the inverted-V bracing system is an effective solution to resist the applied lateral loads while maintaining the functionality of the building. By applying the regression analysis some practical equations were submitted for the stiffness factor to be employed in similar cases as a guideline.

On the vulnerability of the Shrine of Prophet Daniel through field observation and numerical simulation

The Shrine of Prophet Daniel, located in the south-western part of Iran, represents one of the great examples of the pure brick cultural heritage buildings. This study summarizes the historical background of the shrine building. The structural parts of the building are covered in detail. The existing damages to different parts of the building are classified and the cause of each damage type is elaborated. Several in-situ and laboratory standard tests were carried out to determine the most important material characteristics of the building. Field observations and tests results prove that the building has mostly suffered from the ascending moisture which caused foundation settlement and material deterioration in some parts. In order to evaluate the effects of these imperfections on the response of the structure, the second phase of study including the numerical modeling is performed. Through performing nonlinear finite-element simulations and equivalent lateral static force method, having used the limited available data from the previous phase of assessment, it is concluded that the Shrine of Prophet Daniel is vulnerable against the design level earthquake and proper retrofit measures should be considered to improve its seismic performance.

Evaluation of Seismic Analysis Procedures for Concrete Moment-Resistant Frames with Horizontal Re-entrant Corners Irregularity

Seismic design codes and standards such as the IBC 2012 and ASCE/SEI 7-10 allow using different seismic analysis procedures for buildings having horizontal re-entrant corner irregularity. However, such codes allow using Equivalent Lateral Force (ELF) procedure for buildings having re-entrant corner irregularity but not exceeding 50 m in height. The aim of this study is to quantify the limits on building height and on the percentage of re-entrant corner of building, where ELF procedure may not produce a reasonable results when compared to Response Spectrum (RS) and Response Time History (TH) procedures. Usually, these limits in seismic design standards are based on judgments and experience rather than quantification studies. Based on the results of this study, it is observed that using ELF method mostly overestimates maximum displacements and drift ratio. However, this method can be used safely up to 12-storey buildings, because the maximum underestimation of column shear forces for buildings with higher stories gives 30% less compared to other procedures. Moreover, it has been found that the maximum underestimation of column shear forces for buildings without re-entrant corner is 0% less than those with re-entrant corners. Furthermore, buildings analysed by ELF method are also exposed to have a higher percentage value of underestimation of column shear forces as the case of 12-story buildings with 40% less when compared to TH Procedure. In addition, the column at the re-entrant corner is not effectively affected until a re-entrant corner of 25% exists in buildings. Thus the ASCE/SEI 7-10’s limit for using ELF procedure for buildings with re-entrant corner irregularity may be increased from 15% to 25% with less conservative results.

Behavior of columns of steel plate shear walls with beam-connected web plates

Steel plate shear walls with beam-connected web plates (B-SPSWs) are an alternative configuration of steel plate shear walls (SPSWs) where web plates are connected to the beams only. Detaching web plates from columns and introducing simple beam-column connections in B-SPSWs eliminate flexural demands in the columns resulting from web plate tension field action; consequently, the columns of B-SPSWs are designed primarily for axial loads. A recent study, however, showed that the columns of B-SPSWs resist significant flexural demands during earthquake shaking due to differential interstory drifts that result in significant column rotations at floor levels. Typical design methods (i.e., the Equivalent Lateral Force method and Modal Response Spectrum analysis) do not capture these rotations associated with differential drifts that might lead to column instability. A two-phase numerical study is conducted to evaluate the behavior and stability of B-SPSW columns. In the first phase, three-dimensional nonlinear response-history analyses are conducted to investigate the column stability for eighteen B-SPSWs with different geometric characteristics designed following two design approaches. The results suggest that column buckling is a possible mode of failure for one of the design approaches. In the second phase, a parametric study is undertaken to further investigate potential column buckling failure modes in B-SPSW columns and to establish an upper-bound estimate for the column buckling strength reduction due to column rotations at floor levels that are not considered in traditional design approaches.

Dual Equivalent Lateral Force Method for Low‐Rise Wooden Horizontal Hybrid Structure with Rigid Core

Hybrid structure has shown some great features in the earthquake‐resistant design. However, due to the different properties between the combined building systems, the distributions of structural mass and stiffness are prevalently irregular in breadth or height, which makes the widely used equivalent lateral force (ELF) method powerless to predict the seismic shear force of such hybrid structure. This study proposed a simple design procedure for determining the concerned seismic shear force of low‐rise wooden horizontal hybrid structure in the preliminary linear design. The dual equivalent lateral force (DELF) method is presented that permits the extension of the ELF method by separating the hybrid structure into two independent substructures. It is shown that the proposed DELF method is sufficient to provide a reasonable estimation of the seismic shear force with satisfied accuracy.

Analyses of the Base Isolated Buildings; Nonlinear Model Time History Versus Codes' Methods

Multi-story hypothetical reinforced concrete buildings of variable geometric configurations (symmetrical, vertically irregular, horizontally irregular, with and without shear walls); with the isolated bases via high damping rubber bearing and friction pendulum systems, are analyzed using finite element method under seismic load function (North-South component of the ground motion that recorded at a site in El Centro, California in 1940) via SAP2000-V16 software. Four methods of analysis are adopted. The accuracy of the nonlinear model time history is compared with that recommended by the international codes, namely; nonlinear direct integration, equivalent lateral force, and response spectrum methods. The bilinear hysteretic model of base isolation system and the Rayleigh damping framework for superstructure are adopted. The results support the powerful nonlinear model time history analysis, due to the negligible deviations from those predicted by the robust nonlinear direct integration method. The response spectrum method is proved to be more reliable than the equivalent lateral force method which over predicts the displacement and rotation profiles for the isolated buildings.

A Simplified Review on the Seismic Performance of Nonstructural Components

For the reason of rising proportion of the nonstructural components in engineering cost, and its main function can’t interrupt after the earthquake and its damage is easy to cause the secondary disasters, the researchers gradually brought the attention to the seismic performance of nonstructural components, and the study of its seismic performance has been gradually deepening. This paper will discuss the research status of the seismic performance of nonstructural components from the three aspects of classification of nonstructural components, seismic calculation method and details of seismic design. The seismic calculation method will introduce the research progress of equivalent lateral force method and the floor response spectrum method, details of seismic design are expounded in several design principles and specific methods, and some suggestions for further researches are put forward.

Effect of vertical ground motion on the response of structures isolated with friction pendulum isolators

Structures isolated with friction pendulum isolators have their instantaneous stiffness and friction force dependent on vertical load. As such they are affected by vertical ground motion. This paper presents a study to investigate the vertical earthquake effects on the base shear force and isolator displacement in structures equipped with friction pendulum isolators and with or without added viscous damping devices in the isolation system. Analyses are carried out for a simple rigid structure and results are presented for values of the ratio of the base shear and isolator displacement calculated with the effect of the vertical ground motion and divided by the same quantity when the vertical ground motion effect is disregarded. The effects of two-component horizontal ground motion are also studied. The results may be used to modify the equivalent lateral force method of ASCE 7 for seismic isolated structures in order to account for the vertical earthquake effects.