Seismic Design Procedure Research Articles

Ductility Estimation for a Novel Timber–Steel Hybrid System

AbstractIn current force-based seismic design procedures, structures are allowed to behave inelastically during significant seismic events. For this reason, the applied design base shear of a structure is calculated by reducing the elastic strength demand by a ductility factor that represents the ability of a structure or structural system to deform inelastically beyond yielding. Whereas North American building codes provide ductility factors for traditional structural systems, including timber-based or steel-based systems, there are currently no design provisions available for novel hybrid structural systems. Thus research is required to define the force reduction factors, and specifically the ductility factor, Rd, to safely and efficiently design novel systems within the existing seismic design provisions. One such novel system is the so-called finding the forest through the trees (FFTT), proposed in 2012, where mass-timber panels act as shear walls and are connected to each other and to perimeter frame...

New Design Method to Evaluate the Seismic Stress of Single Deck Floating Roof for Storage Tanks

Liquid sloshing causes severe damage to the floating roofs of storage tanks. Liquid–roof interaction imposes a complicated distribution of out-of-plane deformation in a single deck floating roof (SDFR), which is the primary source of high seismic stress. This paper proposes a new seismic design procedure for evaluating the seismic stress of an SDFR. This method revises the relationship between vertical deformation of the deck plate and the radial shrinkage of the pontoon, and estimates the nonlinear behavior of the free surface. Moreover, the attenuation of the sloshing wave height attributable to the presence of an SDFR is analytically evaluated. A design flowchart according to the new method is suggested. This method emphasizes the nonlinear effects of large amplitude wave for smaller capacity tanks, and the seismic stress caused by the second sloshing mode for broad tanks.

An approach to seismic analysis of (engineered) buildings in Sri Lanka

Even though, Sri Lanka was believed to have no seismic threats, it is now realized that Sri Lanka can no longer be considered as a country safe from seismic threats following the recent events that occurred in and around the island. The present study is therefore aimed at providing guidance on suitable analysis procedure for buildings in Sri Lanka where the seismic consideration is explicitly warranted for a structure. The proposed guidelines in this study are based on Euro Code 8 (EN 1998-1: 2004): “Design of Structures for Earthquake Resistance”. Euro Code 8 was selected for this purpose as it allows national choices in defining seismic characteristics such as peak ground accelerations, response spectra, etc. in seismic design procedure. This study mainly focuses on these national choices and suitable values are proposed and discussed, depending on the available seismic data in Sri Lanka. Whenever there is a lack of data, suitable approaches are suggested comparing similar seismic codes such as IS 1893-1: 2002 and AS 1170.4: 2007. Finally, two case studies are carried out in order to illustrate how the developed guidelines can be used in the seismic design procedure of buildings particularly in Sri Lanka. ENGINEER, Vol. 48, No.01, pp. 39-48, 2015

An Optimization Procedure for Seismic Design of Steel Frames for Multi-Performance and Multi-Hazard Levels

This paper describes an optimization procedure for seismic design of steel frames for multi-performance and multi-hazard levels under the different performance objectives. The optimization models and optimization techniques are incorporated in the seismic design procedure. An estimation method is developed to evaluate the residual inter-story drifts of steel frames under multi-hazard levels for the seismic design procedure. The estimation method just needs to perform nonlinear static analysis until all the inter stories yield and all residual inter-story drifts can be achieved. The design procedures of a three-story steel frame for multi-performance and multi-hazard levels under the different performance objectives are demonstrated to elucidate the proposed optimization procedure.

Damage-based optimization of large-scale steel structures

A damage-based seismic design procedure for steel frame structures is formulated as an optimization problem, in which minimization of the initial construction cost is treated as the objective of the problem. The performance constraint of the design procedure is to achieve repairable damage state for earthquake demands that are less severe than the design ground motions. The Park-Ang damage index is selected as the seismic damage measure for the quantification of structural damage. The charged system search (CSS) algorithm is employed as the optimization algorithm to search the optimum solutions. To improve the time efficiency of the solution algorithm, two simplifying strategies are adopted: first, SDOF idealization of multi-story building structures capable of estimating the actual seismic response in a very short time; second, fitness approximation decreasing the number of fitness function evaluations. The results from a numerical application of the proposed framework for designing a twelve-story 3D steel frame structure demonstrate its efficiency in solving the present optimization problem.

Implementation of Database of Masonry Walls Test – Review of Existing Test Data in Peru

Confined masonry walls represent one of the most widely used construction systems for dwellings in Peru and other Latin countries. This study describes the procedure for implementing a database with a web interface of results collected from the experiments conducted over the years by the Japan Center for Earthquake Engineering and Disaster Mitigation. This paper attempts to contribute to the seismic design procedure of this type of structure, and parameters such as stiffness ratios and the deformation (drift) for the characteristic stages of confined masonry walls under different limit states or performance levels are proposed. Also, a semi-empirical equation for estimating the shear capacity using the database is proposed.

A novel displacement-based seismic design method for framed structures considering P-Delta induced dynamic instability

An innovative displacement-based seismic design procedure for regular planar framed structures considering sidesway collapse prevention is presented. The method proposed, based on the characterization of a multiple degree of freedom system by means of a single degree of freedom system, allows the design of structures with a P-Delta induced negative stiffness to satisfy an interstorey drift threshold and/or prevent dynamic instability. The design procedure relies on the use of elastic analysis of simplified models and collapse or constant ductility spectra, hence, non-linear dynamic analyses are not required. To illustrate the potential of the method proposed, example applications and validation of the results obtained via incremental dynamic analysis are shown.

INFLUENCE OF MOMENT GRADIENT ON ROTATION CAPACITY OF STEEL FLEXURAL MEMBERS

Current seismic design procedures implicitly permit the inelastic structural deformations under strong ground motions for economic reasons. The local ductility is used as a parameter for evaluating the available inelastic performances of structures. Current code provisions take into account the ductility at the level of section, but it is necessary to study member ductility. One of the main factors influencing the value of ductility is moment gradient. This research presents a new method to determine ductility for constant-moment loading of flexural members based on theoretical and numerical studies. A numerical study was carried out on welded I-beams under a monotonic static loading, using nonlinear buckling analysis considering local and overall instabilities. The results illustrate that this new method is more accurate than others, can be used to predict ductility for constant-moment loading, and may be employed for different gradients of moments.

원전 적용을 위한 면진장치의 성능기반 설계 변위 추정

There has been an increasing demand for introducing a base isolation system to secure the seismic safety of a nuclear power plant. However, the design criteria and the safety assessment methodology of a base isolated nuclear facility are still being developed. A performance based design concept for the base isolation system needs to be added to the general seismic design procedures. For the base isolation system, the displacement responses of isolators excited by the extended design basis earthquake are important as well as the design displacement. The possible displacement response by the extended design basis earthquake should be limited less than the failure displacement of the isolator. The failure of isolators were investigated by an experimental test to define the ultimate strain level of rubber bearings. The uncertainty analysis, considering the variations of the mechanical properties of isolators and input ground motions, was performed to estimate the probabilistic distribution of the isolator displacement. The relationship of the displacement response by each ground motion level was compared in view of a period elongation and a reduction of damping. Finally, several examples of isolator parameters are calculated and the considerations for an acceptable isolation design is discussed.

Energy-based seismic strengthening design of non-ductile reinforced concrete frames using buckling-restrained braces

This paper presents the application of an energy-based seismic design procedure to strengthen non-ductile reinforced concrete frames using buckling-restrained braces. An experimental study was conducted to examine the seismic behavior of a large-scale non-ductile RC specimen strengthened with BRBs. For the analytical study, a large number of dynamic analyses of non-ductile systems that were strengthened using ductile elements with varying strength were conducted to investigate the overall response behavior. Finally, a practical strengthening design method was presented. The method was based on the modified performance-based plastic design approach. A design example was presented. Nonlinear pushover and nonlinear time history analyses were conducted to evaluate the performance of a non-ductile RC frame strengthened with BRBs. Both the test and analysis results indicated that BRBs significantly increased the stiffness, lateral force capacity and energy dissipation. The analysis results of the strengthened frame exhibited significant response improvement in terms of structural performance and story drifts. The results were used to verify the effectiveness of the presented design approach.

Proposal of new ground-motion prediction equationsfor elastic input energy spectra

In performance-based seismic design procedures Peak Ground Acceleration (PGA) and pseudo-Spectral acceleration (Sa) are commonly used to predict the response of structures to earthquake. Recently, research has been carried out to evaluate the predictive capability of these standard Intensity Measures (IMs) with respect to different types of structures and Engineering Demand Parameter (EDP) commonly used to measure damage. Efforts have been also spent to propose alternative IMs that are able to improve the results of the response predictions. However, most of these IMs are not usually employed in probabilistic seismic demand analyses because of the lack of reliable Ground Motion Prediction Equations (GMPEs). In order to define seismic hazard and thus to calculate demand hazard curves it is essential, in fact, to establish a GMPE for the earthquake intensity. In the light of this need, new GMPEs are proposed here for the elastic input energy spectra, energy-based intensity measures that have been shown to be good predictors of both structural and non-structural damage for many types of structures. The proposed GMPEs are developed using mixed-effects models by empirical regressions on a large number of strong-motions selected from the NGA database. Parametric analyses are carried out to show the effect of some properties variation, such as fault mechanism, type of soil, earthquake magnitude and distance, on the considered IMs. Results of comparisons between the proposed GMPEs and other from the literature are finally shown.

Seismic performance-based design optimization considering direct economic loss and direct social loss

Seismic performance-based design of a steel structure is performed using a multi-objective optimization that considers both direct economic and social losses. Specified performance objectives are considered as constraints and their variance over the obtained Pareto front is investigated. Optimization objectives are selected as the lifetime cost calculated from the initial construction cost and expected annual loss associated with seismic direct economic losses, and direct social loss parameter defined as expected annual social loss. Inelastic time history analysis is used to evaluate structural response under different levels of earthquake hazard to obtain engineering demand parameters. To illustrate the seismic performance-based design procedure, calculations are presented and compared for a sample steel structure located in Los Angeles, CA and Memphis, TN.

Response Modification Factor for Y-Eccentric-Braced Steel Frame Structures Designed Based on Chinese Code

In current seismic design procedure, structure base shear is calculated according to the linear elastic response spectra divided by the response modification factor, which accounts for ductility and overstrength of a structural system. In this paper, the response modification factors of Y-eccentric braced steel frames (YECBF) designed based on Chinese Code were evaluated by an improved pushover analysis on 12 examples with various stories and spans lengths. According to the analysis results, the effects of fundamental periods, storey numbers, and spans of frames on the behavior factor were studied. In the end, an appropriate response modification factor was proposed for YECBF designed base on Chinese Code.

Efficient and accurate procedure for selecting ground motions matching target response spectrum

Linear and nonlinear response history analyses have become popular in seismic design and seismic performance evaluation procedures. The accuracy of analysis results depends not only on the accurate analytic models for structures but also on the proper selection of input ground motions. The purpose of this study is to develop a computationally efficient and accurate procedure for selecting ground motions considering the target response spectrum mean and variance, and the correlations between response spectra of different periods. In this procedure, a number of response spectra are simulated equal to the number of ground motions to be selected, using a Monte Carlo simulation. Subsequently, ground motions are selected from a ground motion library to individually match the simulated response spectra, using the proposed selection procedure. This procedure is computationally efficient and accurate in selecting a ground motion that best matches a simulated response spectrum and in determining a scaling factor for the selected ground motion. In order to further improve the selection result, multiple sets of simulated response spectra are considered. The accuracy and efficiency of the proposed procedure are verified with numerical examples.

Effects of Earthquake Ground Motion Selection and Scaling Method on Performance-Based Engineering of Wood-Frame Structures

AbstractThis paper examines the effects of procedures for both ground motion record selection and scaling on performance-based engineering tools underlying emerging seismic design procedures for en...

Assessment of spectrum matching procedure for nonlinear analysis of symmetric- and asymmetric-plan buildings

Current performance-based seismic design procedures rely on response history analysis (RHA) for estimating engineering demand parameters (EDPs) of base-isolated structures, high-rise buildings and irregular structural systems. Ground motion records for RHAs should be appositely selected in compliance with site-specific hazard conditions, and properly modified either by amplitude-scaling or spectrum matching (SM) to ensure that the modified records provide accurate and efficient estimates of “expected” median demands. While amplitude-scaling techniques change intensity of the ground motion record, SM methods also alter the record’s waveform (in frequency or time domain) to match its response spectrum to a target (or design) spectrum. The research on adequacy of spectrum-matched records for nonlinear RHAs of buildings is not only limited to symmetric-plan buildings subjected to one component of ground motion but also lacks consensus. This study comprehensively examines the accuracy and efficiency of a SM method for nonlinear RHAs under bi-directional earthquake excitations by covering single- and multi-story buildings having symmetric- and asymmetric-plans. For this evaluation, three-dimensional computer models of 48 single-story and nine multi-story buildings were created. Their structural responses were obtained from subsets of seven records modified by SM and separately by amplitude-scaling according to the regulatory ASCE/SEI 7-10 scaling procedure. The accuracy and efficiency of both procedures are examined by comparing their median EDP estimates from subset of records against the median values of EDPs due to a larger set of unscaled records, and by comparing record-to-record variability of the response. It is shown that the time-domain SM procedure provides more accurate median EDP estimates as compared to the ASCE/SEI 7-10 amplitude scaling procedure; however, it critically vanishes the variability of EDPs associated with aleatoric uncertainty in ground motion records. Retaining a certain level of aleatoric variability in EDPs can be an important parameter to be considered for certain projects.

Large‐scale real‐time hybrid simulation of a three‐story steel frame building with magneto‐rheological dampers

SUMMARYA series of large‐scale real‐time hybrid simulations (RTHSs) are conducted on a 0.6‐scale 3‐story steel frame building with magneto‐rheological (MR) dampers. The lateral force resisting system of the prototype building for the study consists of moment resisting frames and damped brace frames (DBFs). The experimental substructure for the RTHS is the DBF with the MR dampers, whereas the remaining structural components of the building including the moment resisting frame and gravity frames are modeled via a nonlinear analytical substructure. Performing RTHS with an experimental substructure that consists of the complete DBF enables the effects of member and connection component deformations on system and damper performance to be accurately accounted for. Data from these tests enable numerical simulation models to be calibrated, provide an understanding and validation of the in‐situ performance of MR dampers, and a means of experimentally validating performance‐based seismic design procedures for real structures. The details of the RTHS procedure are given, including the test setup, the integration algorithm, and actuator control. The results from a series of RTHS are presented that includes actuator control, damper behavior, and the structural response for different MR control laws. The use of the MR dampers is experimentally demonstrated to reduce the response of the structure to strong ground motions. Comparisons of the RTHS results are made with numerical simulations. Based on the results of the study, it is concluded that RTHS can be conducted on realistic structural systems with dampers to enable advancements in resilient earthquake resistant design to be achieved. Copyright © 2014 John Wiley & Sons, Ltd.

LNG 저장탱크의 면진시스템 적용을 위한 내진설계

The demand of natural gas is gradually increasing as a clean fuel in the world. Therefore, LNG storage tanks and related facilities of the importance of leading a community-based facility have emerged. The seismic design of LNG storage tank including seismic analysis have been developed steadily. But, the seismic analysis and design techniques for LNG storage tanks are lacking, in Korea. Consequently, it is necessary to develop an analysis model that LNG storage tanks in isolation system can describe the behavior. Further, LNG storage tank capable of ensuring safety and economy, it is necessary to develop design techniques. The studies have suggested seismic design procedures of LNG storage tanks with isolation system including triple-FPB and idealized complex hysteresis model of triple-FPB.

Optimal integrated seismic design of structural and viscoelastic bracing‐damper systems

SUMMARYPassive structural control techniques are generally used as seismic rehabilitation and retrofit methodologies for existing structures. A poorly explored and exciting opportunity within structural seismic control research is represented by the possibility to design new structural forms and configurations, such as slender buildings, without compromising the structural performance through an integrated design approach. In this paper, with reference to viscous dampers, an integrated seismic design procedure of the elastic stiffness resources and viscoelastic properties of a dissipative bracing‐damper system is proposed and developed to ensure a seismic design performance, within the displacement‐based seismic design, explicitly taking into account the dynamic behaviour both of the structural and control systems. The optimal integrated seismic design is defined as the combination of the variables that minimizes a suitable index, representing an optimized objective function. Numerical examples of the proposed integrated cost‐effectiveness seismic design approach both on an equivalent SDOF system and a proportionally damped MDOF integrated system are developed defining the design variables, which minimize the cost index. Validation of the effectiveness of the proposed integrated design procedure is carried out by evaluating the average displacement of the time‐history responses to seven unscaled acceleration records selected according to EC8 provisions. Copyright © 2014 John Wiley & Sons, Ltd.

State-of-the-Art Report on Partially-prestressed Concrete Earthquake-resistant Building Structures for Highly-seismic Region

Prestressed concrete has long been accepted in statically loaded structures. Thus, for many years now we have seen the construction of prestresed concrete bridges, dams, pipelines, reservoirs and various structures including more recently atomic reactor pressure vessels. These stand as irrefutable proof of engineers’ confidence as to the integrity of this new material. In recent years prestressed concrete has been used in seismic resistant structures. Just like any other new material, it will attract criticism and comment, sometimes by people who may not have had the opportunity of full investigation of the material in question. Furthermore, today engineers are more critical of any new material or technique and will seldom accept them unless conclusive evidence of their performance can be produced. This is as it should be. The purpose of this paper is to observe the application of prestressed concrete to seismic resistant multi-storey structures. However, this paper should be read bearing in mind the fact that the widest application of prestressed concrete (to bridge and kindred structures) has been in the countries subject to earthquake and with operative seismic codes. In the paper, the latest seismic design procedure for prestressed concrete buildings in Indonesia is introduced. The current design method is based on the latest Indonesian Building Code for Structural Concrete and Seismic Code, namely SNI 2847:2013 and SNI 1726:2012, respectively. The design method itself is not a novelty to those who are familiar with the capacity design developed for years. This paper is also intended to bring the attention of structural designers and other engineers to the option of using partially-prestressed concrete in buildings. The results of an investigation into the seismic resistance of partially-prestressed concrete frames are described. The experimental part of the project involved the testing of six near full scale beam-interior column assemblies under static cyclic loading to obtain information for seismic design.