Performance-based Seismic Design Procedure Research Articles

Performance-Based Seismic Design for Bridge Bents Retrofitted with BRBs Using the Ductility Demand Spectra of SDOF Oscillators with Bilinear Fuses

ABSTRACT Reinforced concrete bridge bents with double columns in bridge substructures are commonly used, but it has suffered severe damage during strong earthquakes. The seismic retrofit with structural fuses is used to effectively mitigate seismic damage of bridge bents. To obtain the displacement ductility demand for dual systems including the primary structure (PS) and structural fuses (SF), the corresponding ductility demand factor spectra were developed. The interaction between the PS and SF is described by defining two parameters of dual systems: the yield displacement ratio (α) and the initial stiffness ratio (β), and the influence of α, β, and strength reduction factor on the ductility demand factor spectra are also analyzed. For seismic retrofitting in bridge bents, buckling-restrained braces (BRBs) are used as energy dissipation fuses, and the steel core lengath of BRBs with three configurations forms, including diagonal, inverted-V, and toggle systems, are also explored. Then, based on the structural fuses concept and ductility demand factor spectra of dual systems, a performance-based seismic design procedure is proposed for bridge bents retrofitted with BRBs to ensure that the bridge bents maintain the target ductility under design-level earthquakes. Finally, the procedure was utilized to design the bridge bents with BRBs, and the procedure’s feasibility was verified by nonlinear time-history analysis.

Shape memory alloy-reinforced UHPC tube confined bridge piers for enhancing the seismic resistance of highway bridges

Multi-span continuous highway bridges supported with reinforced concrete (RC) bridge piers may experience large permanent deformation after strong earthquakes. To overcome the limitations, an innovative UHPC tube-confined SMA reinforced bridge pier, i.e., shape memory alloy (SMA) replacing the steel rebars at the plastic hinge region and a prefabricated UHPC tube substituting the cover concrete, is proposed. To fully utilize the tensile strength of UHPC, the UHPC tube is embedded into the foundation. A performance-based seismic design procedure considering target residual drift as engineering demand parameter (EDP) is proposed to design this novel UHPC-SMA pier. The seismic responses of novel bridge systems supported by UHPC piers (Bridge II) and UHPC-SMA piers (Bridge III) are investigated and compared with reference bridge (Bridge I) having RC piers. The results indicate that both UHPC piers and UHPC-SMA piers are efficient in improving the seismic resistance of highway bridges. Compared with Bridge I, the prefabricated UHPC tube significantly decreases the residual deformation of Bridge II piers by 22.9 % as a result of the bridging effect of steel fibers. Due to the excellent self-centering property of SMA, the residual deformation of Bridge III piers decreases further by 57.8 % in comparison to reference bridge. The UHPC tube increases the low stiffness of bridge piers caused by SMA rebars at the plastic hinge region. The combination of UHPC tube and SMA can effectively prevent core concrete from severe damage with less dissipated energy of bridge piers.

Machine learning-based design of a seismic retrofit frame with spring-rotational friction dampers

In this study a machine learning-based design procedure for a new seismic retrofit system is presented and its seismic retrofit capability is validated by intensive seismic analyses. The retrofit system consists of a steel frame with rotational friction dampers (RFD) at beam-column joints and linear springs at the corners providing both energy dissipation and self-centering capabilities to existing structures. The performance-based seismic design procedure of the spring-rotational friction damper (SRFD) retrofit system is developed using a genetic algorithm (GA) and an artificial neural network (ANN). The performance of the presented retrofit system and its optimum design procedure is evaluated using case study models for multi-limit states by investigating seismic fragilities, life-cycle cost (LCC), and seismic Resilience Index (RI) before and after the retrofit. According to the analysis results, the SRFD retrofit system proved to be effective in decreasing story drifts, seismic fragility, and LCC of the retrofitted structures significantly. The retrofitted models turn out to be more resilient and recover better than the un-retrofitted models after earthquakes. The developed performance based design procedure is proved to be effective in seismic retrofit of case study structures to satisfy multi-level design objectives.

Shape-memory alloy-friction isolator enhanced with inertia pendulum for seismic mitigation of bridges

Research has demonstrated that shape-memory alloy-based friction bearings (SMAFBIs) can obtain significant seismic response reduction and self-centering performance of isolated bridges. However, SMAFBIs, similar to conventional isolation techniques, reduce seismic forces at the cost of increasing deck drift. Excessive deck drift will increase the probability of the deck unseating, while large seismic forces such as base shear of piers will increase the risk of damage to piers. To limit the deck drift and the pier base shear of bridges isolated with SMAFBIs at the same time, an inertia pendulum (IP), which can amplify the inertia of a pendulum mass by a lever to effectively tune the natural period of structures, is proposed to enhance the bridge isolated with SMAFBIs. The seismic design spectrum of the linearized SDOF system with IP is proposed and examined by direct integration method. Based on this seismic design spectrum, the performance-based seismic design procedure for bridges isolated with IP-SMAFBIs is proposed. The two bridges isolated, respectively, with SMAFBIs and IP-SMAFBIs are designed according to this procedure, and their seismic responses obtained by elastic–plastic time history analysis are examined and compared. The research results show that IP-SMAFBIs have significant advantages in terms of reducing maximum deck drift not at the cost of increasing the pier base shear. In addition, the effects of the mass ratio and leverage ratio of the IP on seismic performance of the isolated bridge are investigated in detail, and the optimal parameters are suggested.

Performance-based optimum seismic design of cable tray system

This study aims to develop a simple yet efficient performance-based design optimization methodology for cable tray systems in building structures. In the paper, the drift ratio between adjacent supports is proposed as a performance index and the acceptable threshold values are specified based on experimental results of shaking table tests for cable tray systems. The seismic performance levels of cable tray systems are presented according to current seismic design codes. A performance-based optimum seismic design procedure for cable tray systems is given and verified by three studied cases. The results show that the proposed performance index (drift ratio between adjacent supports) for cable tray systems is a reasonable criterion for performance-based seismic design and is much more practical and rational than the typical criterion recommended in seismic design codes. The cable tray systems designed according to the proposed procedures can derive the cost-efficient solution and meet the expected seismic performance objectives for cable tray systems as well as control the damage development of the cable tray.

Performance-based seismic design of full and partial self-centering steel braced frames using modified lateral force distribution

Design base shear and lateral force distribution are two important aspects of the seismic design process. Different design methods have been proposed to obtain the design base shear of different types of structures. However, the study related to the lateral force distribution is limited, especially for self-centering (SC) structures. The primary objective of this research is to develop a performance-based seismic design (PBSD) procedure for steel braced frames considering the modified lateral force distribution. Six-story steel braced steel frames are designed to explore the influence of the energy dissipation factor on the lateral force distribution of the frames. Results of nonlinear time-history analyses indicated that the lateral force acting on the roof increases with the decrease in energy dissipation factor. Following the parametric analyses of single-degree-of-freedom (SDOF) systems, the energy factor design spectra are established and the corresponding PBSD procedure for the steel braced frames is proposed. Finally, the four six-story braced steel frames are redesigned using the PBSD procedure with the modified lateral force distribution to illustrate the efficiency of the proposed design method. Analyses results indicate that the steel braced frames designed by the proposed design can satisfy the expected inter-story drift limit with a reasonably uniform distribution of peak inter-story drifts. Furthermore, the ‘partial’ SC system appears to be a desirable option that effectively controls the residual displacement and peak acceleration responses at the same time, and could achieve a manageable cost control compared to the full SC systems.

Performance-based seismic design methodology for tall buildings with outrigger and ladder systems

The plethora of efforts needed for conducting the Performance-Based Seismic Design (PBSD) to investigate the tall buildings' performance requires sustainability in developing this approach and facilitating its implementation to obtain an effective final design. To tackle this issue, novel performance-based design procedures are proposed in this study. The novel PBSD procedures commence with integrating the optimization and simplification techniques into the preliminary design stage to rapidly obtain an optimal initial amount of materials required to establish outrigger and ladder systems models. Then, conducting a nonlinear time history analysis with the aid of ETABS and Peforme-3D software to scrutinize the extent to which the initial design approaches the final design and the superiority of each system under frequent or rare earthquake events. The global and component responses are examined for each system under three performance levels: immediate occupancy IO, life safety LS, and collapse prevention CP. The optimization and simplification techniques in the preliminary design stage have reduced the overwhelming efforts required to generate and prepare an optimized preliminary design for both systems. Furthermore, the results of the nonlinear time history analysis found that the ladder system reduced the structure's global response by 27.2% for the lateral displacement and 30.4% for the base shear than the outrigger system. However, the evaluation of the components acceptance criteria confirmed that the ladder system increased the plastic damage distribution in the external structural system's components and reduced it in the internal one. Generally, the preliminary design approached the final design by varied ratios, 60–80% in the ladder system and 60–95% in the outrigger system for different components. Therefore, it is recommended to apply this approach to the outrigger system and improve the ladder system's efficiency. Finally, this study is limited to an optimized preliminary design that approaches the final design and reduces the iteration number of the PBSD procedures. Thus further researches are required to improve and extend the applicably of these procedures.

Performance-based seismic design and optimization of damper devices for cable-stayed bridge

The seismic vulnerability of cable-stayed bridges located in seismically active regions can be of great concern to the regional safety and resilience. A promising design practice for cable-stayed bridges lies in decoupling the deck from deck-pylon connection and incorporating energy dissipation devices to reduce the dynamic responses. In this study, the performance-based seismic design (PBSD) procedure is adapted to the optimal design of damper devices at the deck-pylon connections in a benchmark cable-stayed bridge. The benchmark cable-stayed bridge was modeled in the OpenSees platform, which was calibrated against the previous finite element models. Then it was seismically designed with viscous and metallic dampers in the longitudinal and transverse direction, respectively. The component-level fragility functions of the cable-stayed bridge were first derived based upon the multiple stripe analysis (MSA) method, and then the system-level repair cost ratio (RCR) surfaces were built under the PBSD framework. Finally, the genetic algorithm based on parallel computation was utilized to identify the optimal parameters of the damper devices. The analysis results illustrate that the optimal design parameters can be effectively obtained through the proposed method, and the damper devices with optimal parameters lead to a significant reduction of the overall repair cost. The study also demonstrates that if the device parameters are not selected appropriately, the dampers can have negative effects on bridge responses. The design framework and the findings could provide the guidance for the designing and retrofitting of cable-stayed bridges in practice.

Self-centering steel slotted friction device for seismic retrofit of beam-column joints

A new self-centering slotted friction device (SC-SFD) is introduced for seismic retrofit and upgrading of beam-column joints. The device can be used for existing or new structures. A framework utilizing a performance-based seismic design procedure combined with a genetic algorithm (GA) optimization is used to obtain the optimum design variables of the device. A 5-story building and one-story industrial structure are used as case studies. The effectiveness of the proposed retrofit is assessed through conducting non-linear time-history response analysis (NLTHA), incremental dynamic analysis (IDA), fragility analysis, and seismic life cycle cost (LCC) evaluation. The obtained results demonstrate that the proposed retrofit is effective in reducing the maximum inter-story drift ratio (MIDR) significantly and in eliminating the residual drift. Additional engineering demand parameters, such as the floor acceleration and the base shear have been investigated to prove the superiority of the proposed retrofit technique compared to the fully rigid joint alternative. A finite element method (FEM) is used to ensure that concrete stresses after retrofit are within the acceptable limits. The retrofitted models show high energy dissipating potential compared to the bare cases. The IDA and fragility analyses show significant improvement in the retrofitted structures in terms of the median collapse capacity and seismic fragility. The probabilities of exceeding different limit states and the LCC of the retrofitted structures have been reduced significantly compared to the bare cases. Based on these findings, the proposed retrofit is recommended for similar structures to improve their resilience against earthquakes and to reduce the total seismic LCC.

Performance-based seismic design and assessment of low-rise steel special moment resisting frames with block slit dampers using endurance time method

Block Slit Dampers (BSDs) are recently developed metallic yielding dampers for passive structural control. This type of damping devices can provide designers with an option of using highly ductile systems, such as steel special moment resisting frames (steel SMRFs), in important structures located in regions of high seismicity. The aim of this study is to obtain a performance-based seismic design (PBSD) procedure for these devices, and to assess the seismic performance levels of low-rise steel SMRF equipped with BSDs using the endurance time (ET) dynamic analysis method. For this purpose, first, the simplified behavioral model of these devices was established based on the analysis of available experimental data. Afterwards, the effects of the geometric dimensions of the damper on its hysteresis behavior were investigated through a parametric study conducted using ABAQUS software. Next, based on the results of the parametric study, the design formulations were developed. In the next step, a step-wise guideline was developed for the PBSD of BSD devices used in a low-rise steel SMRFs. In this guideline, ET dynamic analysis method was used to reduce the calculation costs and complexities of PBSD. Then, a six-story steel SMRF equipped with BSD devices was designed using the developed guideline, and the seismic response of this structure was compared to that of a companion conventional SMRF without BSD devices. The results show that through the use of BSD devices, which have a unique secondary hardening portion in their hysteresis behavior, it becomes possible to satisfy performance objectives of flexible steel SMRFs in regions of high seismicity. In addition, like stiff lateral resisting systems, BSD devices can reduce the inter-story drift ratios (ISDRs) of steel SMRFs. Controlling the absolute floor accelerations (AFAs) and non-structural element damages also become easier with the use of BSD devices. These results indicate that BSD devices are hysteretic devices that are well suited for design and retrofit of flexible steel SMRFs. In the final part of the study, the ET analysis results were compared to the results obtained from a response history analysis (RHA) method conducted using a set of 22 scaled FEMA P695 far-field earthquake records. This comparison shows the suitability of ET method in PBSD of steel SMRFs equipped with BSD devices.

Quantitative assessment of nonlinear macro-models for global behavior and design of planar RC walls

Performance-Based Seismic Design (PBSD) procedures require adequate estimation of the global cyclic force–displacement (F-D) behaviors of the primary lateral load-resisting elements. As reinforced concrete (RC) walls constitute one of the most widely used lateral load elements in building construction, several nonlinear analytical modeling approaches have been developed over the past several decades to numerically simulate the hysteretic behavior of these structures. However, comparisons between these models have often provided few details on the model input parameters, have not used consistent model discretization, and have assessed hysteretic predictions more qualitatively than quantitatively. Accordingly, the objectives of this paper are to: 1) provide detailed information on the modeling parameters used to simulate the cyclic lateral F-D behavior of a set of planar RC walls with flexure-dominant as well as shear-dominant behaviors, 2) evaluate the sensitivity of the F-D curves to different wall model discretizations applied consistently between different models, and 3) propose and use a new quantitative approach to assess the hysteretic behaviors predicted by the numerical models. The considered models are PERFORM 3D, MVLEM, SFI-MVLEM, and BTM. To represent the information that is typically known during the design of a structure, the nonlinear modeling parameters were limited to the wall geometry, reinforcing layout, concrete compression strength, and reinforcing steel yield strength, with no calibration of the material behaviors to the reported test results. A total of 2,300 analyses were performed to simulate four slender and four squat previously-tested RC walls. Results of the cyclic lateral F-D predictions were evaluated based on commonly used measures of effective stiffness, maximum strength, and ultimate displacement. Additionally, the hysteretic response of the numerical simulations was assessed by proposing, validating, and using the Modified Nash-Sutcliffe Efficiency (NSEm) metric. Comparisons between the computing times for the models were also made, as well as comparisons of the local nonlinear behavior of a slender wall. Results show that the discretization used in the PERFORM 3D, MVLEM, and SFI-MVLEM simulations did not significantly affect the predicted global response, whereas the discretization did affect the F-D curves from the BTM model. The values of NSEm agreed with qualitative evaluations of the F-D curves and were able to properly evaluate complex cyclic behaviors of RC walls including pinching and stiffness deterioration. The results of this investigation are expected to be used as modeling guidelines of RC walls when conducting PBSD.

Performance Based Seismic Analysis of Steel Frames

The Civil Engineering profession has been changing the structural engineering design paradigm from life safety (LS) to Performance Based Seismic Design (PBSD) to tackle catastrophic damage caused by recent earthquakes worldwide. This paper is about the PBSD analysis of steel frame subjected to earthquake loading. Steel is by far the most versatile building material in the world and steel structure has played a major role in construction industry in the last decades. In this a multistoried bare and braced steel frames are analyzed by PBSD procedure in STAAD Pro Advanced following nonlinear static analysis. Frame components (beam, columns, etc.) are progressively adjusted to account for nonlinear elastic–plastic behavior under constant gravity loads and incrementally increasing lateral loads. Capacity curve is obtained for each frame and comparatively studied to decide which type of frame can meet the desired performance level during earthquake. The results of the analysis performed to meet required performance are presented in terms of displacement, shear forces, plastic hinges and capacity curve.

Seismic retrofit of RC buildings using self-centering PC frames with friction-dampers

This paper presents the seismic upgrade of existing reinforced concrete (RC) structures by using a self-centering post-tensioned pre-cast concrete frame with friction dampers (SC-PC-FD). The effectiveness of the retrofit is investigated through conducting cyclic loading tests on a single story RC frame before and after the retrofit. The experimental results are used to validate the numerical modeling of the test specimens. A performance-based seismic design procedure is proposed based on a genetic algorithm (GA) to determine the story-wise distribution of the damper friction capacity and the area of post-tensioning steel. Three-, five-, and eight-story RC framed structures are used as case study models for evaluating the effectiveness of the retrofit technique. Non-linear time-history response analysis (NLTHA), incremental dynamic analysis (IDA), and fragility analysis are conducted to investigate the seismic performance of the retrofitted structures. Results of the nonlinear time-history analyses show that the retrofit reduces the maximum inter-story drift ratio (MIDR) and the residual drift of the model structures. IDA and fragility curves show that the collapse capacities of the model structures are increased after the retrofit and the retrofitted buildings have lower probabilities of reaching the design limit states compared to the un-retrofitted ones.

Ground motion input for nonlinear response history analysis

Nonlinear response history analysis (NLRHA), or so-called “nonlinear time history analysis”, is adopted by practicing structural engineers who implement performance-based seismic design and/or assessment procedures. One important aspect in obtaining reliable output from the NLRHA procedure is the input ground motion records. The underlying intention of ground motion selection and amplitude-scaling procedures is to ensure the input for NLRHA is representative of the ground shaking hazard level, for a given site and structure.
 The purpose of this paper is to highlight the salient limitations of the ground motion selection and scaling requirements in Sections 5.5 and 6.4 of the New Zealand (NZ) loading standard NZS 1170.5 (2004). From a NZ regulatory perspective; there is no specific framework for seismic hazard analysis and ground motion selection (thus self-regulation is the current norm). In contrast, NZS 1170.5 contains many prescriptive requirements for scaling and applying records which are challenging to satisfy in practice. Also discussed within, there are implications for more modern guidance documents in NZ, such as the 2017 “Assessment Guidelines” for existing buildings, which cite NZS 1170.5, a standard which is at least 16 years old (draft issued in 2002). To emphasize the above issues with NZS 1170.5, this paper presents a summary of the more contemporary approaches in the US standards ASCE 7-16 (new buildings) and ASCE 41-17 (existing buildings), along with some examples of the more stringent US requirements for Tall Buildings.

SEISMIC DESIGN OF FRAME STRUCTURES EQUIPPED WITH INNOVATIVE HYSTERETIC DISSIPATIVE DEVICES

In the present work, a Performance-Based Seismic Design procedure applied to multi-storey frame structures with innovative hysteretic diagonal steel devices (called Crescent Shaped Braces or CSB) is introduced. CSBs are steel elements of peculiar geometrical shapes that can be adopted in frame buildings as enhanced hysteretic diagonal braces. Based on their "boomerang" configuration and placement inside the frame structure, they are characterized by a lateral stiffness uncoupled from the yield strength and, if properly inserted, by an overall symmetric hysteretic behavior with hardening response at large drifts, thus preventing from global structural instability due to second-order effects. The procedure here presented is intended to guide the structural engineer through all the steps of the design process, from the selection of the performance objectives to the preliminary sizing of the CSB devices, up to the final design configuration. The steps are described in detail through the development of an applicative example.

Performance-Based Seismic Design of Steel Buildings Using Rigidities of Connections

AbstractThis paper develops a performance-based seismic design (PBSD) procedure specifically for steel structures. Several improved steel connections were proposed to eliminate brittle fractures in...

A novel reliability technique for implementation of Performance-Based Seismic Design of structures

A unified Performance-Based Seismic Design (PBSD) procedure is proposed and successfully implemented. It provides an alternative to the currently used life safety design requirement. To successfully develop the concept, structures are represented by finite elements and excited by the seismic loading in time domain. A novel reliability evaluation procedure is proposed for such representation. An improved response surface based procedure is proposed by combining it with the First-Order Reliability Method (FORM) and the appropriate response surfaces are constructed by combining the saturated design and the central composite design sampling schemes. Performances are defined in terms of Collapse Prevention (CP), Life Safety (LS), and Immediate Occupancy (IO), as commonly used in the profession. The corresponding risks are evaluated by exciting a 9-story steel frame designed by experts satisfying all post-Northridge seismic design requirements. It was excited by 20 earthquake time histories for each performance level and the corresponding probabilities of failure were estimated. It took around 300 deterministic evaluations. The accuracy of the method was established using 600,000 cycles of Monte Carlo simulations. The probabilities of failure estimated using the proposed algorithm are very similar to that of simulations indicating that it is accurate. The probability of failure for two serviceability limit states (overall and inter-story drifts) are very similar, indicating that the procedure will satisfy the basic intent of PBSD. They are also similar to the values used in developing the Load and Resistance Factor Design (LRFD) guidelines used in many current design codes. Designing a structure using multiple time histories, as suggested in recent design guidelines, is a step in the right direction. From the results and the observations made in this study, the authors believe that they proposed a robust, efficient, and accurate unified PBSD procedure and documented its implementation potential.

Performance-based seismic design of staggered truss frames with friction dampers

In this study performance-based seismic design procedure for staggered truss frames with friction dampers in the vierendeel panels was developed and their seismic performance was evaluated. To this end 6- and 12-story analysis model structures with friction dampers were designed using the capacity design procedure. For comparison the same structures without dampers were designed following the strength based approach specified in the ASCE 7–13, and the seismic performances of all model structures were compared. Fragility analyses were carried out to evaluate the seismic safety of the model structures and to validate the response modification factor used for seismic design. Analysis results showed that the capacity design method leaded to the formation of plastic hinges concentrated at vierendeel panels. It was also observed that the substitution of rotational friction dampers at the location of plastic hinges resulted in enhanced ductility and reduced probability of failure when the structures were subjected to design level seismic load.

Pushover Analysis of Buildings Considering Soil-Structure Interaction

Structural vulnerability of buildings to damage needs to be identified during the time of earthquake for reliable seismic design. Conventional linear elastic design methods cease to predict seismic damages in buildings. Pushover analysis is a popular displacement-based nonlinear structural analysis procedure employed to predict the seismic behaviour of structures. Generally, buildings are designed based on the assumption that they are fixed at their base, without considering the foundation as well as soil. But in reality, when a structure is subjected to an earthquake excitation, it interacts with the soil, influencing the structural response. In this study, a multi-bay building with different heights are modelled and analysed, duly considering Soil-Structure Interaction (SSI). The study can form foundation for rigorous performance-based seismic design procedure, considering the effect of soil beneath the structure.

Cost-benefit analysis of seismic-isolated structures with viscous damper based on loss estimation

This paper presents a methodology to utilise performance-based seismic design procedure for evaluating isolated structures with or without viscous dampers (VD) considering cost-benefit analysis. A non-linear four-story archetype of conventional steel structure, a lead-rubber-bearing isolated structure and a natural rubber-bearing isolated structure with the linear VD are compared with each other under far-field (FF) and near-field (NF) ground motions. Also, loss parameters, such as expected annualised loss, expected annualised repair time, expected annualised fatalities and expected annualised injuries based on loss estimation process, are utilised for evaluating the structures. Sensitivity analysis is used to study the effect of modelling uncertainty variations in the loss estimation process. It has been found that the effectivity of supplemental damping for low damping isolated structures increases in the NF comparing with the FF ground motions. Finally, the cost-benefit analysis is done to calculate payback period of investment for additional cost of the isolation system with or without the supplemental damping. The advantage of loss estimation is an improved method to evaluate the effectiveness of the isolation system in terms of loss parameters that are useful in the cost-benefit studies and for determining rational insurance premiums.