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- Publisher
- Taylor & Francis
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- © 2023 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group on behalf of the Architectural Institute of Japan, Architectural Institute of Korea and Architectural Society of China.
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- 1347-2852
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- 1346-7581
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- 10.1080/13467581.2023.2193616
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Abstract
JOURNAL OF ASIAN ARCHITECTURE AND BUILDING ENGINEERING https://doi.org/10.1080/13467581.2023.2193616 BUILDING STRUCTURES AND MATERIALS Comparative benefit-cost analysis for a resilient industrial power plant building with isolation system and energy dissipating devices a,b a a,c d a,b e Kaoshan Dai , Abba Mas’ud Alfanda , Jianze Wang , Solomon Tesfamariam , Tao Li and Reza Sharbati Department of Civil Engineering and MOE Key Laboratory of Deep Earth Science and Engineering, Sichuan University, Chengdu, China; Failure Mechanics & Engineering Disaster Prevention and Mitigation, Key Laboratory of Sichuan Province, Sichuan University, Chengdu, c d China; State Key Lab of Subtropical Building Science, South China University of Technology, Guangzhou, China; School of Engineering, University of British Columbia, Kelowna, Canada; Department of Civil and Environmental Engineering, Amirkabir Uinversity of Technology, Tehran, Iran ABSTRACT ARTICLE HISTORY Received 3 September 2022 While the use of innovative seismic control strategies has become widespread in industrial Accepted 17 March 2023 plants, assessment of benefits derived from these measures in a quantifiable form can sig- nificantly contribute to a more rational risk-informed decision-making of essential infrastruc- KEYWORDS tures. In this paper, a benefit–cost analysis is used to examine three retrofit design schemes of Benefit-cost analysis; an actual thermal power plant building equipped with different seismic control systems, i.e. industrial power plant; buckling-restrained brace (BRB), the hybrid shape memory alloy-buckling restrained brace seismic resilience; seismic (SMA-BRB), and the partial mass isolation of heavy industrial equipment. The original design retrofit; loss estimation scheme having concentrically braced frames as lateral resisting systems is considered as a benchmark model for comparison purposes. For each mitigation alternative, the benefits against seismic effects were quantified in terms of repair cost and recovery time. The results showed that the retrofit system using SMA-BRB leads to the best performance achieving average reduction in residual drift, peak story drift, resilience index, repair time, and average annual loss by 71%, 27%, 48%, 83%, and 89% compared to the original system, respectively. The proposed benefit–cost analysis framework for industrial power plant buildings can be considered as a practical approach of supporting decision-making for non-technical stake- holders and motivating practicing engineers. 1. Introduction due to inadequate electrical power supply and Natech With the rapid development and integration of car- disasters (Caputo et al. 2019). Resilience is usually bon-capture technology in fossil fuel power plant (IEA regarded as the ability of a system to quickly recover 2018), power plant now plays a significant role in the from the disaster disruption to the initial state and energy production for sustainable economic growth regain its functionality (Fang and Wang 2020). Thus, (Figure 1). Great attentions have been devoted to the minimizing the loss of resilience is essential for indus- evaluation of seismic performance of energy infra- trial structures. To facilitate operational recovery, the structures. However, major earthquakes such as the performance-based earthquake engineering (PBEE) 2011 Christchurch earthquake in New Zealand (Uckan framework developed by the Pacific Earthquake et al. 2015), the 2011 Great Sendai and the 1995 Kobe Engineering Research (PEER) has been receiving earthquakes in Japan (Fujisaki et al. 2014), the 1999 increasing attention (FEMA 2012) and the design Kocaeli and the 2011 Van earthquakes in Turkey objective for such critical structures is not only to (Uckan et al. 2015), and the 2008 Wenchuan earth- protect the structural system but also to limit the quake in China (Aida et al. 2014) have raised a great non-structural damage to be repairable within a rea- concern for the need of incorporating resilience con- sonable shutdown period. cept into the seismic design of infrastructural systems. As a result of technological advancements in geo- Post-earthquake surveys of recent earthquakes graphic information systems (GIS), and the availability revealed that the damages and subsequent opera- of computational GIS-oriented and multifunctional tional interruption of electric power facilities would applications, researchers are now able to perform lead to severe, unexpected social and financial conse- more accurate and timely assessments of residential, quences (Fujita et al. 2012; Rahnama and Morrow sensible, and strategic structures. For example, 2000). The resulting consequence includes direct loss Leggieri, Mastrodonato, and Uva (2022) proposed GIS due to repair and replacement costs for building func- model for estimating the seismic fragility of residential tional recovery (Fujita et al. 2012) and indirect losses buildings which is faster and capable of improving CONTACT Jianze Wang jzwang@scu.edu.cn Department of Civil Engineering and MOE Key Laboratory of Deep Earth Science and Engineering, Sichuan University, No.24, Section South Yihuan Road, Chengdu 610065, China © 2023 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group on behalf of the Architectural Institute of Japan, Architectural Institute of Korea and Architectural Society of China. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The terms on which this article has been published allow the posting of the Accepted Manuscript in a repository by the author(s) or with their consent. 2 K. DAI ET AL. United State European Union China India Japan Southeast Asia Middle East Other Less than 10-20 20-30 30-40 40-50 more than 10 years years years years years 50 years Figure 1. Age structure of existing coal power capacity by region (IEA 2020). overall estimation accuracy. Another regional seismic behaviors and resulting in unrepairable post-earth- risk assessment framework was developed by Gentile quake damages (Kiggins and Uang 2006; Sabelli, et al. (2019) based on 85 RC school buildings in Mahin, and Chang 2003). Therefore, buckling- Indonesia. The results demonstrate the effectiveness restrained brace (BRB) has been developed to provide of the proposed framework in providing a rational sufficient and consistent cyclic response both in ten- method to derive seismic risk prioritization schemes sion and compression (Xu et al. 2018). However, due to for more detailed evaluations. Similar advances are the low post-yielding stiffness, BRBs have the draw- occurring in the area of artificial intelligence making back of causing large post-earthquake residual defor- vulnerability databases readily accessible. For this rea- mation which increases difficulties related to the repair son, Stefanini et al. (2022) used a large dataset repre- work (Asgarkhani, Yakhchalian, and Mohebi 2020). For senting RC-building stock to develop a vulnerability this reason, self-centering braced frames have been assessment framework based on artificial neural net- proposed to eliminate residual drift due to provision work (ANN) capable of reliably predicting the seismic of both self-centering and energy dissipation capabil- behaviour of existing RC structures. Despite recent ities (Christopoulos et al. 2008). developments in earthquake evaluation and mitiga- Applications of innovative-damping techniques in tion technology, annual losses due to global hazards thermal power plants have been investigated in the of power plants are approximately $15 billion, which is past few years. A heavy coal-scuttle housed in coal- equivalent to 0.2% of the constructing cost of power fired thermal power plants was found to deteriorate generation infrastructure (Nicolas et al. 2019). structural seismic performance due to its significant By using supplemental energy dissipation devices, concentrated weight. As an alternative to conventional base isolation, and innovative systems, several solu- tuned mass dampers (TMDs), Dai et al. (2018) utilized tions have been proposed to improve the seismic per- coal scuttles as a non-conventional tuned mass dam- formance of sensible and strategic structures. They per (TMD) to minimize their adverse effects on the include the resilience improvement through self-cen- seismic performance of supporting structure. They tering systems (Pham 2013; Miller, Fahnestock, and demonstrated that the isolation system reduces the Eatherton 2012), the enhancement of lateral force- inertial forces imposed on heavy coal scuttles. resisting systems (Stefanini et al. 2022; Gentile et al. Furthermore, a reliability-based optimization design 2019; Giordano, De Luca, and Sextos 2021), and mini- framework was proposed for multiple coal-scuttles mizing damage using mixed concrete-steel frames housed in a thermal power plant working as multiple (Pnevmatikos, Papagiannopoulos, and Papavasileiou TMD (MTMD) (Li et al. 2019). The coal scuttles were 2019). Power plant structures are preferred to be con- utilized as MTMD by Li et al. (2019), Shu et al. (2017) structed by steel materials compared to other materi- and Peng et al. (2018), and the results proved that the als due to their versatility, lightweight properties, and MTMD mitigates seismic responses of thermal power speed of construction and recovery. Concentrically plant buildings. Kang et al. (2020) investigated the braced frame is the most commonly used primary effectiveness of MTMD system used for coal scuttles lateral force-resisting system in industrial structures by utilizing a combination of bearings and viscous (e.g. Imanpour and Tremblay 2017; Vela, Brunesi, and dampers. The analysis results showed an improvement Nascimbene 2019). Although it exhibits a sound seis- in seismic performance. Besides numerical studies, mic performance when designed strictly following Wang et al. (2021) conducted shake table tests on a modern design codes, experimental studies and pre- scaled thermal power plant building equipped with vious earthquakes demonstrated that braces have a metallic dampers (Figure 2a) and isolation systems poor energy dissipation capacity due to their buckling used for heavy coal scuttles (Figure 2b). Meanwhile, Capacity (GW) JOURNAL OF ASIAN ARCHITECTURE AND BUILDING ENGINEERING 3 (a) Scaled thermal power plant model with metallic (b) Coal scuttle isolation systems in dampers the scaled thermal power plant model Figure 2. Illustrations of a thermal power plant building with damping and isolation devices (Wang et al. 2021). groundbreaking seismic mitigation technologies con- investigated the benefit–cost analysis (BCA) and eco- tinue to be developed rapidly to enhance the seismic nomic-related consequences of the seismic design of performance of power plants in an ever-challenging building structures (Carofilis et al. 2020; Smyth et al. seismic environment. However, in previous studies, the 2004; Zerbe and Falit-Baiamonte 2002) to minimize effectiveness of damping and isolation techniques was economic loss and post-earthquake operational down- evaluated in terms of decreasing the seismic responses time. However, there is still a lack of a comprehensive of structures. The cost–benefit induced by the retrofit evaluation framework of BCA performance for indus- strategy has not been reported so far. Thus, the pre- trial power plant systems. Efforts are required to make sent study considers four common mitigation techni- a cost-effective comparison among available seismic ques to represent the general classification of seismic mitigation options. control techniques that have been applied to industrial In this paper, a BCA framework applicable to power buildings. Detailed descriptions of this classification plant industrial buildings is studied. The main motiva- are available in Alfanda, Dai, and Wang (2022). tion of this study is to optimize the selection of inno- Additionally, other, not yet used, techniques can be vative damping techniques and control the repair applied to the proposed framework provided they fall costs that are not disproportionately high compared into the class of supplementary damping, equipment to the costs of seismic control techniques. An overview isolation, hybrid system, or innovative combination of of the proposed BCA framework is shown in Figure 3. It both. has the following key stages: (1) performance-based From a structural safety and economic perspective, earthquake engineering, (2) structural analysis and per- stakeholders and professional engineers always prefer formance assessment, and (3) decision variables (DVs) a sound benefit–cost ratio (BCR). Numerous studies in the form of expected losses and downtime for Figure 3. Adopted resilience-based BCA assessment framework. 4 K. DAI ET AL. benefit cost analysis. The subsequent sections illu- the transverse direction (Figure 4b) is focused because strated the procedures step by step. It is worth noting of the presence of the vertical and mass irregularities that the purpose of this paper is not to develop novel (Wang et al. 2018; Shu et al. 2017). Consequently, three mitigation strategies. The goal is to investigate the retrofit techniques using buckling-restrained braces, effectiveness of mitigation strategies not considered shape-memory alloy braces, and lead rubber bearing in previous studies by implementing the BCA isolators are considered to improve the seismic perfor- framework mance of the industrial building. To compare effectiveness of three retrofit techni- ques, four design schemes using different structural systems are considered: (1) Case 1: special concentri- 2. Numerical models and ground motions cally braced frame (SCBF) system; (2) Case 2: buckling- scaling restrained braced frame (BRBF) system; (3) Case 3: 2.1. Prototype building description hybrid SMA-BRB frame system; (4) Case 4: coal scuttle isolation system. The four design schemes are evalu- In this study, a 2 × 650 MW thermal power plant build- ated with the help of SAP2000 V20 (SAP 2019), and ing described by Wang et al. (2018, 2021) is considered their finite element models are built with OpenSees as a benchmark industrial structure. The elevation and (McKenna et al. 2010) for nonlinear response history plan view of case example power plant are shown in analysis. Note that the nonstructural components Fig. 4(a,b), respectively. The column has a 66.1 m × 92 (NSCs) housed in the power generation operation m layout (Figure 4b). The functional units of the power should be designed using equivalent lateral force pro- plant consisting of a turbine hall and a deaerator bay cedure as stipulated in ASCE/SEI 7–16. Seismic are designed as a moment resisting frame due to high- demands on NSCs are calculated using the parameters story clearance requirements, while the bunker bay is design-based spectral acceleration, component designed as a concentrically braced frame. The primary weight, and importance factor. Using retrofit techni- lateral-force resisting systems in both directions are ques does not affect the design of general NSCs. designed as of special concentrically braced frame Therefore, the design of NSCs is not described in detail, (SCBF) and moment-resisting frame (MRF) according but structural design information and finite element to AISC 360–16 (AISC 2016), AISC 341–16 (AISC 2016), model for the four systems are presented in the follow- and ASCE/SEI 7–16 (ASCE 2016) provisions. As thermal ing subsections. power plant building is a lifeline system, a risk category III and an importance factor of 1.25 are considered for the seismic design of structural components as recom- 2.2. Structural system design and numerical mended by ASCE/SEI 7–16 (ASCE, 2016). According to modeling ASCE/SEI 7–16 (ASCE, 2016), design load combinations include dead load due to the self-weight of structural Prior to developing finite element models in members, as well as live loads to account for equip- OpenSees, structural components are designed and ment, pipelines, cranes, wind, and seismic loads. The checked by using SAP2000. The design information structural components include columns and beams for the four design cases are separately presented in with wide-flange W-shape sections and braces with the following subsections. In the OpenSees numerical rectangular hollow structural sections. The sectional models of the four cases, all beams and columns are strengths (e.g. compression, flexure, and buckling) of modeled as nonlinear beam-column elements with each structural member were examined based on the fiber sections. Fully restrained beam-column connec- AISC 360–16 (AISC 2016) provision. A planer frame in tions are modelled in accordance with the prototype Figure 4. Schematic views of the case study thermal power plant building. JOURNAL OF ASIAN ARCHITECTURE AND BUILDING ENGINEERING 5 building. To consider nonlinear geometry under large lateral buckling of braces are explicitly considered with displacements of columns, a co-rotational geometric an initial mid-span imperfection of 1/1000 of the com- transformation is included to account for local and ponent length based on the maximum allowable out global geometric nonlinearities. The Steel02 material of straightness suggested by AISC 360-16 (2016). A model is used to simulate the Bauschinger effect, in zero-length hinge element is used to model gusset which the kinematic and isotropic strain hardening is plates at the ends of brace elements, and its mechan- considered with the yield stress F = 345 MPa, Young’s ical properties are determined following suggestions modulus E = 200 GPa, and strain hardening rate b = of Hsiao, Lehman, and Roeder (2012). In addition, low- 0.1% (accounting for the kinematic hardening of the cycle fatigue fracture in braces is simulated with fati- steel material). The required parameters, namely, R = gue material available in OpenSees and the associated 20, cR = 0.925, and cR = 0.25, and parameters related material parameters required for the fatigue model (ɛ ) 1 2 0 to isotropic hardening (a = 0.4, a = 10, a = 0.4, and are determined according to suggestions of Hsiao, 1 2 3 a = 10) were assigned to account for the transition Lehman, and Roeder (2012). from elastic phase to inelastic phase as well as the isotropic hardening of the steel, respectively. For 2.2.2. Case 2: buckling-restrained braced frame each modeling case, leaning columns are simulated (BRBF) system to consider the second-order P-Δ effects. Detailed Case 2 is retrofitted by BRB instead of conventional modeling techniques for each design case are sepa- steel braces, and the structural design is performed rately illustrated in the following subsections. according to the BRBF requirements stipulated in According to AISC 360–16 (AISC 2016), the lateral stiff - AISC 341-16 (AISC 2016) and the AISC 360-16 (AISC th ness and strength for i story are calculated using Eq. 2016) seismic provisions. The cross-section area (A ) sc (1) and (2), respectively. of the core of BRB component is determined based on cosα the axial force demands. Specifically, the axial strength K ¼ EA (1) BFi ðK =L Þ b b is calculated as ϕA F , in which ϕ = 0.9 and the nom- sc y inal yield stress,F = 290MPa. The yield strength, P , is y y V ¼ n ðϕPÞcosα (2) determined by using Eq. (3), as specified in AISC 360-16 BFi b (AISC 2016). The cross-sectional area is calculated where V and K are the lateral strength and lateral BFi BFi according to Eq. (4), and parameters ω and β are stiffness of braced frame, respectively. A is the total determined by Eq (5). sectional area of braces per story, α is the angle between the diagonal brace and horizontal direction, P ¼ F A (3) y y sc and ϕP is the brace flexural strength. K and L are b b effective length factor and of brace per story, respec- A ¼ (4) sc tively. n denotes the number of brace per story. ;f ð1þ βωÞ 2.2.1. Case 1: conventional SCBF system max ω ¼ (5a) Table 1 shows the cross-sectional area of structural F A y sc components for Case 1 evaluated by SAP2000. The brace components used for the numerical simulation max β ¼ (5b) are made up of ASTM A500 grade C (F = 335MPa). For max each element, the number of integration points is determined based on a previous parametric study where E is the axial force demand primarily deter- (Uriz and Mahin 2005) with a co-rotational geometric mined by load combinations, C and T denote max max transformation to account for local and global geo- maximum compression and tension forces, respec- metric nonlinearities. Each brace is sub-divided into tively. Two factors ω and β are to account for over- 10 force-based beam-column elements. The fiber- strength of the brace. β =1:05 and ω = 1.3 are taken based section is used for elements to model the non- from the experimental results of Christopulos (2005). linear behaviors of brace components. The effects of The cross-sections of BRBs and the stiffness and Table 1. Cross-sectional area and relevant design information evaluated by SAP2000 for Case 1. Floor Height Demand/Capacity K V BFi BFi Level (m) Beam Column Brace K V Ratio of braces BFiþ1 BFiþ1 6 7.37 H600×240×8×13 H600×500×16×35 HSS210×210×14 0.64 0.48 0.39 5 7.56 H600×240×8×13 H700×583×16×40 HSS210×210×14 0.97 0.95 0.38 4 6.20 H600×240×8×13 H700×583×16×40 HSS210×210×14 0.97 0.95 0.49 3 5.57 H1000×400×12×22 H800×666×24×4 HSS240×240×18 0.78 0.68 0.35 2 9.85 H600×240×8×13 H800×666×24×48 HSS240×240×18 0.75 0.68 0.34 1 16.78 H600×240×8×13 H900×750×20×52 HSS380×380×25 0.28 0.93 0.36 6 K. DAI ET AL. Table 2. Cross-sectional area and relevant design information evaluated by SAP2000, for Case 2. T C A max max sc V K BFi BFi Story number (kN) (kN) (mm ) V K Demand/Capacity Ratio of BRB BFiþ1 BFiþ1 6 909 933 3500 0.49 0.50 0.52 5 1866 1917 7100 1.29 1.00 0.51 4 1450 1490 5500 0.24 0.28 0.66 3 6070 6235 22800 0.73 0.89 0.47 2 8283 8509 32000 0.97 1.00 0.46 1 8022 8241 32000 1.00 1.00 0.47 Table 3. Parameters used for the Steel04 material model in OpenSees. Kinematic Hardening Parameters Isotropic Hardening Parameters b Tension Compression Tension Compression b 0.3% 2.5% b 2.0% k i R 25.0 b 0.06% 0 l r 0.91 ρ 1.15 0.8 1 i r 0.15 R 3.0 2 i l 1.0 yp strength ratios between adjacent stories are summar- ized in Table 2. In the numerical model developed for Case 2 (i.e. BRBF system), the BRB component is modeled by non- linear force-based elements (Zsarnoczay 2013). The cyclic behavior of BRB is simulated by using the Steel04 material available in OpenSees. The Steel04 material considers the Bauschinger effect, and it is capable of simulating different hardening characteris- -1000 tics under both tension and compression responses by Simulation a set of independent parameters. Miner’s rule-based Test fatigue material proposed by Zsarnoczay (2013) is used -2000 -3 -2 -1 0 1 2 3 to adjust the inelastic strains in the yielding zone. To Drift (%) ensure the accuracy of the numerical model, the para- meters summarized in Table 3 are verified by the Figure 5. A comparison between the numerical simulation and the experimental test for a BRB braced frame. experimental results of a single-bay braced frame tested by Christopulos (2005). Figure 5 shows a reason- able agreement between the experimental and simu- component, respectively. With these parameters, the lation results. nominal strength P of the SMA-BRB component is determined by Eq. (8). 2.2.3. Case 3: SMA-BRBF system P ¼ F A þ F A (8) n ysc sc SMA SMA The SMA-BRB normally consists of a BRB core and a SMA rod that provide energy dissipation capacity and Note that A and A obtained from Eqs. (6)-and (7) sc SMA self-centering ability, respectively. Similarly, the analy- are used to compute the self-centering ratio defined in sis and design procedures of SMA-BRBF are compar- Eq. (9). The resulting α for SMA-BRB components of sc able to those of standard BRBF and SCBF (Miller, each story is greater than 1, as presented in Table 4. Fahnestock, and Eatherton 2012). The cross-sectional Miller, Fahnestock, and Eatherton (2012) and Pham area of BRB core and SMA rods (Table 4) is determined (2013) proved that self-centering ability is achieved by using Eqs. (6) and (7), respectively. when α ≥1.0. Hence, the prescribed condition is sc satisfied. E F u SMA A ¼ (6) SC 0:9� F ðF þ σ βωα Þ ysc SMA SMA sc F A SMA SMA α ¼ (9) sc βωF A ysc SC βωF A α βωF A ysc SC sc ysc SC A ¼ ¼ (7) SMA To compare four cases, the SMA-BRB frame is ðF Þ ðF Þ SMA SMA designed to resist the same load combinations as the where F and A are the yielding strength and the other cases. The SMA and BRB components are mod- ysc sc cross-sectional area of the BRB core, respectively. A , elled using self-centering and Steel04 materials in SMA F , and σ are the cross-sectional area, the initial OpenSees, respectively. The parameters of Steel04 SMA SMA strength, and the forward transformation stress of SMA material model, as well as the strength and stiffness Force (kN) JOURNAL OF ASIAN ARCHITECTURE AND BUILDING ENGINEERING 7 Table 4. Summary of the design of SMA-BRBF model. Self-centering Story A A ratio SMA SC V K BFi BFi 2 2 number (mm ) (mm ) Demand/Capacity Ratio (α ) V K BFiþ1 BFiþ1 sc 6 2800 1400 0.44 1.20 0.50 0.51 5 5700 2700 0.44 1.17 1.00 1.29 4 4500 2100 0.44 1.51 0.28 0.25 3 18500 9000 0.36 1.08 0.28 0.73 2 25000 12000 0.44 1.06 1.00 1.00 1 25000 12000 0.44 1.09 1.00 1.00 Table 5. Material properties of SMA model (DesRoches, McCormick, and Delemont 2004). Material Properties Value Initial stiffness k 2759N/mm Post yielding stiffness k 3882N/mm F 414MPa β 0.39 α 0.58 Maximum transformation strain (ε ) 5.5% Figure 6. Typical hysteresis curves of SMA-BRB model used in Case 3: (a) SMA model, (b) BRB model, (c) SMA-BRB hybrid model, and (d) Illustration of the hybrid model. ratios are given in Table 4. The super-elastic behavior system is used to replace the rigid support connections of SMA is simulated by the uniaxial self-centering of coal scuttles to improve the seismic performance of model reported by DesRoches, McCormick, and the main structure (Wang et al. 2021). Under normal Delemont (2004). Table 5 provides the parameters of service conditions, the mass of the scuttle includes the the SMA material model. The SMA-BRB hybrid model is self-weight of an empty scuttle and the full weight of a paralleling combination of these two material mod- fossil materials. Based on this assumption, the entire els. The hysteresis behavior of each component and seismic mass of the coal bunker is approximately 520 hybrid model under cyclic loading is shown in Figure 6. tons. In the numerical model, the coal-scuttle is simpli- fied as a concentrated mass at the top of the support nodes. Depending on the stiffness of the selected iso- 2.2.4. Case 4: coal scuttle isolation system lator and the seismic weight of a coal bunker, a single Coal scuttles are essential equipment positioned at a coal bunker has a fundamental period of 0.05 s when height of 32.2 m in the bunker bay of the benchmark its base is fixed, and 2.01 s when using isolation tech- power plant building (Figure 7). Such equipment has nique. The lead-rubber bearing (LRB) devices used for significant weight which may increase demand on the the isolation of coal-scuttle are modelled using supporting structure under seismic loadings (Kang Elastomeric Bearing (Bouc-Wen) element available in et al. 2020). Therefore, in Case 4, a coal-scuttle isolation 8 K. DAI ET AL. Figure 7. A schematic view of partial coal scuttle isolation system used in Case 4. Figure 8. Target hazard spectrum with response spectrum of selected ground motions. OpenSees. The LRB component connects every mass target hazard spectrum and the average spectrum of node and the support node on the girder. Body con- selected ground motions is less than 10%. Detailed straints are also assigned to the support nodes to information on the selected ground motions and the ensure that they act as coal-scuttle equipment. The hazard consistency to the target hazard spectrum can primary mechanical properties of the isolator are con- be found in Wang et al. (2018). sidered as K = 7.1kN/mm, K = 0.71kN/mm, Q = 63kN, 1 2 d α = 0.1, and K = 1800kN/mm, corresponding to initial 3. Seismic demand and development of stiffness, yield stiffness, yield strength, post-yield stiff - fragility curves ness ratio, and vertical stiffness, respectively. These parameters are determined based on the design pro- The concept of risk assessment has been developed in cedure proposed by Dai et al. (2018). A schematic view the first-generation PBEE design codes (ASCE-41 2013) of the simplified model can be seen in Figure 7. focusing mainly on conventional buildings and bridges. Its application to industrial plants and critical components (e.g. boiler, pressure vessels, silo, and 2.3. Ground motions selection piping systems) is still limited. Basically, seismic risk The example thermal power plant building is situated analysis could be classified into two approaches. The in a seismically active region of China. The building site first alternative is to use building-based approach by is classified as a soft soil with a reference shear wave integrating hazard curves with fragility models to velocity (179 m/s < V <280 m/s). To perform response assess the seismic risk. A typical example of such s30 history analyses, three suites of 15 ground motions are approach is HAZUS (FEMA 2003) which covers fragility selected and scaled to match the uniform hazard spec- models of industrial facilities, like oil system, commu- trum at three levels: service level earthquake (SLE), nication system, and water system. An alternative design-based earthquake (DBE), and maximum consid- approach is to use the next-generation PBEE frame- ered earthquake (MCE). The DBE hazard level work, which has been in FEMA P58 (FEMA 2012) with (Figure 8b) refers to an earthquake with 10% probabil- more details. However, the companion software, PACT, ity of occurrence in 50 years (i.e. 475-year return per- has few special industrial equipment and nonstructural iod). The earthquake ground motions are scaled in components. As PBEE advances from risk-based to such a way that the mean squared error between the resilience-based approaches, several projects such as JOURNAL OF ASIAN ARCHITECTURE AND BUILDING ENGINEERING 9 Figure 9. Peak story drift ratio under different seismic hazard levels: (a) SLE, (b) DBE, and (c) MCE. XP-RESILIENCE (Caputo et al. 2019), SYNER-G (Pitilakis, difference between the drift ratios of Case 1 and other Crowley, and Kaynia 2014), PROINDUSTRY (Kanyilmaz cases becomes more evident below MCE level. In par- and Castiglioni 2017), and INDUSE (Bursi, Paolacci, and ticular, the SMA-BRB and BRB components provide an Taniguchi 2019) have been proposed and applied to additional damping ratio for the structure, and conse- assess seismic performance and post-earthquake quently reduce the drift response of Case 2 and Case 3 restoration of complex urban infrastructures (Caputo below MCE level. et al. 2019). In addition to the recent resilience frame- Compared with the response of Case 2 equipped work developed by Caputo et al. (2019) for the assess- with BRB, the residual drift of Case 3 is smaller due to ment of process plants under Na-Tech events, Wang the self-centering capability provided by the SMA com- et al. (2020) performed building-based fragility models ponent (Figure 10). Further, the results showed that for a typical thermal power plant to quantify the detri- under all hazard levels, Case 3 has the lowest residual mental and beneficial effects induced by retrofit stra- drift, followed by Case 2 and Case 4, and the corre- tegies. This study does not go beyond vulnerability sponding average residual drifts are 0.09%, 0.19%, and analysis with little consideration of seismic-induced 0.24%, respectively. FEMA P-58 (2012) suggested that a losses and downtime. The following sections put a residual drift higher than 0.5% indicates significant step forward to estimate the seismic loss risk in a way difficulty in post-earthquake repair. The residual drifts that incorporates economic loss and downtime. of the retrofitted frame structures for all cases meet the residual drift requirements under SLE and DBE levels. Under MCE level, only Case 3 has a residual drift smal- 3.1. Drift demands ler than 0.5%, while the residual drifts of the first story of the other cases are beyond this limit. With the selected ground motions and developed numerical models, nonlinear time history analyses are performed. The resulting peak story drift ratio and 3.2. Fragility and risk analyses residual drift ratio along the transversal axis marked in Figure 4b are plotted in Figs. 9 and 10, respectively. Establishing the probabilistic seismic demand model It is clear that the effectiveness of the retrofit technique (PSDM) is the first step of development of fragility increases with increasing the intensity of ground functions. Due to the lack of peer-reviewed compo- motions. Specifically, the drift ratios of Case 1 are nent fragility applicable to thermal power plant, the comparable to those of Cases 2, 3, and 4 under SLE global seismic fragility of the considered four cases is and DBE levels. This is because all braces remain elastic developed using the cloud analysis approach (Jalayer under low-intensity ground motions. In contrast, the 2003). Specifically, a non-linear regression is used to 10 K. DAI ET AL. Case1 Case2 Case3 Case4 6 6 (b) (a) (c) 5 5 5 4 4 4 3 3 2 2 2 1 1 1 0 0.5 0 0.5 0 0.5 1 Residual Drift (%) Residual Drift (%) Residual Drift (%) Figure 10. Peak residual drift ratio under different seismic hazard levels: (a) SLE, (b) DBE, and (c) MCE. Figure 11. Demand model based on the cloud analysis approach: (a) Case 1, (b) Case 2, (c) Case 3, and (d) Case 4. derive the relationship between the seismic intensity acceleration at the fundamental period (Sa(T )) are measure (IM) and the engineering demand parameter the most popular intensity measures regarding their (EDP). The peak story drift θ is considered as an EDP, efficiency and effectiveness, the results of Wang et al. max mainly because of its correlation with the global (2018) showed that Sa(T ) is suitable for planer and damage states of thermal power plants. This has irregular braced frames. Therefore, a regression analy- been proven based on the results of recent studies sis between θ and Sa(T ) is carried out based on Eq. max 1 (Shu et al. 2017; Kang et al. 2020) and past earthquake (10). Figure 11 shows the results of regression for the surveys (Rahnama and Morrow 2000; Uckan et al. four cases. 2015). Also, the peak story drift is suggested by perfor- lnðθÞ ¼ b ln½SaðT Þ�þ lnðaÞ (10) mance assessment guidelines to quantify the global damage of braced frames (FEMA 2003). Although the To define fragility function, the probability of peak ground acceleration (PGA) and the spectral exceeding a certain EDP conditioned on a given Story Number Story Number Story Number JOURNAL OF ASIAN ARCHITECTURE AND BUILDING ENGINEERING 11 Table 6. Performance levels and corresponding story drift limit states for fragility development. Peak story drift Retrofit scheme Damage severity Damage Description (%) Case 1 Slight Minor yielding or buckling of braces 0.5 (SCBF) Moderate Yielding or buckling of many braces,without complete failure. Possible failure of 1.5 connections. Extensive Extensive yielding and buckling of braces. 2.0 Failure of many braces and connections. Case 2 Slight Minor yielding of braces 0.5 (BRBF) Moderate Extensive yielding of braces 2.0 Extensive Failure of braces or connections 3.0 Case 3 Slight Major yielding of SMA braces 0.5 (SMA-BRBF) Moderate Superelastic strain length of SMA 2.5 Extensive Strain limitation to prevent second strain hardening 3.5 Case 4 Slight Scuttle tripping or light damage to scuttle 0.5 (Coal-scuttle Moderate Chattering of coal scuttle and racks 1.5 isolation) Extensive Considerable damage to coal scuttle 2.0 Figure 12. Comparison of seismic fragility curves for four cases: (a) Slight damage, (b) Moderate damage, (c) Extensive damage. hazard level, the drift response obtained from hybrid frames have higher deformation limit states Section 3.1 is taken as the EDP and along with compared to BRBF and SCBF but still remain functional. damage states predefined in Table 6, the seismic It should be mentioned that the present study only fragilities are developed following Eq. (11), and the considers three repairable damage states. If a power results are shown in Figure 12. plant suffers more severe damage like total collapse, its � � demolition and replacement are highly recommended. lnðedp=edp Þ 0:5 PðEDP � edpjSaðT ÞÞ ¼ 1 Φ (11) Figure 12 compares seismic fragility curves for slight, moderate, and extensive damage states of four where Φ½�� is the standard normal cumulative distribu- cases. It can be seen that seismic intensity increases tion function, edp is the median capacity of the with the probability of exceeding more intense 0:5 structural demand for a given seismic intensity mea- damage states, i.e. for the states of extensive damage sure (IM) and β is the logarithmic standard deviation of (see Figure 12c) and moderate damage (see the demand conditioned on the IM. Figure 12b), while increases slightly with the probabil- Three commonly adopted damage states (DS) in ity of exceeding slight damage state (see Figure 12a). steel frames and industrial buildings (Kang et al. The reference case and the one retrofitted with equip- 2020; Wang et al. 2018), namely slight (DS ), moderate ment isolation system have a considerably higher (DS ), and extensive (DS ) damage states, are consid- probability of exceeding slight damage state as com- 2 3 ered in this study. The threshold values of the damage pared to the cases retrofitted by BRB and SMA-BRB states indicated in Table 6 are used to classify the retrofit. The difference is more pronounced for prob- overall severity of damage to both structural and non- ability exceeding the extensive damage states (differ - structural components. Accordingly, the description of ences with respect to Case 1) as follows: Case 2: 24% damage states for Cases 2 and 3 is judgmental with (64%), Case 3: 8% (88%), and Case 4: 29% (57%). consideration of the findings of recent studies on per- As mentioned earlier, the considered power plant formance assessment of hybrid SMA frames, such as building is located in a seismically active region of Pham (2013), Christopoulos et al. (2008), and Fang and China. The hazard curves of the four cases were Wang (2020). These studies have shown that SMA obtained from the local geological bureau (Wang 12 K. DAI ET AL. -10 -20 Case 1 Case 2 Case 3 Case 4 -30 -2 -1 0 1 10 10 10 10 Sa(T ) (g) Figure 13. Hazard curves of alternative seismic mitigation cases: Probability of exceeding at Sa(T ) level. Table 7. Probability of exceeding different damage states for four mitigation strategies over a service life of 50 years. Probability of Exceedance (%) Building case DS DS DS 1 2 3 Case 1 82.3 12 7.6 Case 2 54.1 3.9 2.8 Case 3 39.8 2.4 0.9 Case 4 72 6.0 3.4 et al. 2018), as shown in Figure 13. The annual prob- especially between Cases 1 and 3. Besides Case 1, Case ability of exceedance of θ for the four cases is 4 has the highest probability of exceedance among max obtained by convoluting the corresponding seismic three retrofit schemes, where the probability of hazards (Figure 13) and fragility curves (Figure 12), exceeding DS (i.e. 72%) for this case is about 10% according to Eq. (12). smaller than that for Case 1. N � � � � λðxÞ ¼ ∫ P½θ > xjS ðT Þ ¼ S � dλ ðS Þ (12) � � max a 1 a sa a 3.3. Seismic loss estimation where λ (x) is the mean annual frequency that drift θ Unlike common residential (Smyth et al. 2004; Stefanini exceeds the value x, P½θ> xjS ðT Þ ¼ S � (Figure 12) a 1 a et al. 2022) and strategic and commercial buildings donates the probability that drift θ exceeds the value � � (Carofilis et al. 2020) with relatively high human occu- � � x for the given spectral acceleration, and � dλ ðS Þ�is sa a pancy, industrial buildings have large financial losses due to equipment damage and interruption of opera- the absolute value of the derivative of the hazard curve tions (Wang et al. 2018, 2020). Therefore, this study is with respect to Sa (T ). limited to quantifying expected repair cost and down- As the prototype power plant building is expected time as decision variables (DVs) obtained by consider- to provide a service life of 50 years, the probability of ing probability propagation as: exceeding DS , DS , and DS in 50 years is computed 1 2 3 using Eq. (13) and Figure 12 as follows: λðDVÞ ¼ ∫ ∫ ∫ dPðDVDMÞ dPðDMEDPÞ dPðEDPIMÞ |fflffl{zfflffl} |fflfflfflfflfflfflffl{zfflfflfflfflfflfflffl} |fflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflffl} |fflfflfflfflfflfflffl{zfflfflfflfflfflfflffl} λ� 50 Decision Variable Loss Analysis Fragility Analysis Structural Analysis P½D in50� ¼ 1 e (13) dλðIMÞ (14) |fflfflffl{zfflfflffl} The probability of exceedance over a period of 50 Hazard Analysis years for the four cases is shown in Table 7. It is clear that Case 3 has a probability of exceedance of DS and where λ is the average annual rate of seismic events DS smaller than 10% in 50 years. The probability of with IM ≥ im, im is a threshold of IM, the DM is the exceedance of DS for Case 3 is smaller than those of damage measure which is categorized into three dis- Cases 2 and 4 by 2.8% and 3.4%, respectively. For Case crete damage states DS as described in Sec. 3.2, P(DM| 1, which represents the original power plant building, EDP) is the probability of exceedance of a damage the probability of being in extensive damage (DS ) is measure given an engineering demand parameter, 7.6%. As for probability of exceeding DS , the differ - and P(EDP|IM) is the probability of exceedance of an ence between these four cases is more pronounced, EDP parameter for a given intensity measure, IM. Probability of Exceedance JOURNAL OF ASIAN ARCHITECTURE AND BUILDING ENGINEERING 13 Table 8. Unit costs of components and materials. Item Average unit cost (2020$) BRB $1,000/EA LRB $550/EA SMA bar $544/EA Cost Category Cost Estimate (2020$) Civil/Structural Material and Installation 54,150,735 Mechanical Equipment Supply and Installation 217,570,769 Electrical Supply and Installation 32,033,789 Indirect Cost (Engineering, distributable cost, construction management and start-up) 79,709,609 Sub-total (less Contingency) 383,464,903 Contingency (10% sub-total) 38,346,490 Owner Cost (engineering studies, permits, licensing fees, training etc.) 76,271,220 Total Cost of the prototype building (i.e. Case 1) 500,000,000 Replacement Cost (C ) 590,000,000 rep Table 9. Additional cost due to retrofit actions for cases. Retrofitting Option Case 2 Case 3 Case 4 Quantity (Q ) 91 BRB components 91 BRB-SMA components 84 LRB devices Q C 91,000 140,504 46,200 m m (91 × 1000) (91×1000+91×544) Skilled labour/Installation Cost 14,924 16,562 57,200 C ($) ($164 per BRB) ($182 per SMA-BRB) ($681 per LRB device) Contingency ($) 10,593 15,707 10,340 10% (Sub-total) Additional Cost ($) 187,250 187,250 182,000 (Connections & (Connections & (Supporting girders upgrading per coal scuttle, Adjacent members retrofitting, Adjacent members retrofitting, $26000 per frame × 7) $26750 per frame ×7 frames) $26750 per frame ×7 frames) Total ($) 303,767 360,023 295,740 The expected economic loss for each design case is corresponding replacement cost for Cases 2–4 are pre- appraised following the recommendations by FEMA sented in detail in Table 9. Note that the cost values for P-58 (FEMA 2012, HAZUS (FEMA 2003), EIA (EIA 2018), all considered items are based on the production capa- Schröder et al. (2013), and Kumar, Sharma, and Tewari city and economic development level of China (2015). Economic loss from potential repair activities (Alibaba 2022). The cost–benefit analysis results pre- that are not provided by these references, such as cost sented are thereby more suitable for industrial build- of material supply, skilled labor, and installation and ings located or invested by China. other additional costs, are assumed to be the same for Figure 14(a,b) shows the expected loss and ratios the four design schemes and hence this part of cost is with respect to replacement values under each of exempted in benefit-cost analysis. To further compen- the four cases considered. It is observed that the sate the limitation of global-based analysis, the expected losses increase with increasing seismic approximate replacement costs were estimated by intensity. At the intensity of DBE (i.e., Sa(T1) = 0.6 summing up the cost values associated with structural g), the loss ratios are estimated to be 0.46, 0.06, components, non-structural components, and equip- 0.02, and 0.14 for Case 1, Case 2, Case 3, and Case ment as indicated in Table 8. Note that the replace- 4, respectively. And at the intensity of MCE (i.e. Sa ment cost encompasses construction cost, demolition (T ) = 0.9 g), the loss ratios increase to 0.65, 0.11, cost, and replacement of damaged components, as 0.04, and 0.25 for Case 1, Case 2, Case 3, and Case well as costs of recovery due to impending factors 4, respectively. (Bradley et al. 2009). Therefore, additional costs are For further comparison of the four cases in terms of included to account for building demolition and site economic loss, the average annual loss (AAL) is calcu- clean-up. Specifically, 118% of the total cost in Table 8 lated using Eq. (16): was considered to arrive at the average replacement � � � � cost (C ) for the power plant. Rep AAL ¼ ∫ E½LijS ðT Þ�� dλ ðS Þ� a 1 sa a In addition, the retrofit costs attributed to material 3 � � � � usage for retrofit implementation were estimated as ¼ C ∫ P½DSijS ðT Þ�L ½DSi� dλ ðS Þ (16) � � Rep a 1 Ri sa a (Babaei and Zarfam 2019): where C is the replacement value, P[DS |Sa(T )] is the C ¼ Q C þ C (15) Rep i 1 m m l probability of a given damage state given SaðT Þ; � � where Q = the quantity of material required and C = m m � � � dλ ðS Þ�is the absolute value of the derivative of sa a unit cost of material (Alibaba Group Holding Limited. 1 2020), and C is the cost of labor and installation. The the hazard curve with respect to SaðT Þ (Figure 12) and total additional cost due to retrofit actions and the L [DS ] denotes loss ratio of 0.1, 0.4, and 0.8 (FEMA Ri i 14 K. DAI ET AL. 0.8 0.6 0.4 Case1 Case1 0.2 Case2 Case2 Case3 Case3 Case4 Case4 0 0 1 2 3 4 5 0 1 2 3 4 5 Sa(T ) Sa(T ) (a) Expected loss of four cases (b) Normalized loss of four cases 800,000 DS DS 150 2 600,000 DS 400,000 200,000 Case 1 Case 2 Case 3 Case 4 0 Case 1 Case 2 Case 3 Case 4 Mitigation Options Mitigation Options (c) Average annual loss of retrofit cases (d) Average annual recovery time Figure 14. Loss estimation results for the considered retrofit alternatives. 2020) for DS , DS , and DS , respectively. The AAL earthquake losses do not occur in annual increments, 1 2 3 values were computed to be $186,283 (Case 2), the AAL could be accumulated to the total loss over $73,579 (Case 3), and $227,863 (Case 4) with the corre- the service lifespan, 50 years (FEMA 2020). As a result, sponding reduction of 75%, 89%, and 69% relative to the benefits of the retrofit design cases (abbreviated as $731152 (Case 1), respectively. B) were estimated using Eq.(18) where the difference in Similarly, the recovery time for the four cases was AAL values between the original design and the retro- evaluated using Eq. (17) and the associated average fit designs is considered divided by the discount rate (r annual recovery time is derived following Eq. (16) and = 3%) over time t, within a useful lifespan T of 50 years. presented in Figure 14(d). Then, given B, the BCR is calculated using Eq. (18). X T � ðAAL AAL Þ t¼ 1 EðDaysjDSÞ ¼ EðDaysjDSÞP½DSijS ðT Þ�� MOD i i a 1 DSi BðtÞ ¼ (18) ð1 þ rÞ i¼1 (17) B BðtÞ where E(Days|DS ) is the DS recovery time given DS i i 1 BCR ¼ ¼ (19) C Cost of Retrofit (10 days), DS (90 days), and DS (240 days) as sug- 2 3 gested by HAZUS (FEMA 2020). MOD is the con- DSi Based on Eq. (16), the effectiveness for each seismic struction time modifiers with 0.5, 1, and 1 assigned mitigation option is compared with AAL. Again, the to DS , DS , and DS , respectively (FEMA 2020). 1 2 3 AALs reported in Table 10 were approximately When compared to Case 1, the reduction in the $186,283 (Case 2), $73,579 (Case 3), and $227,863 downtime by different retrofit schemes are 58%, (Case 4) with the corresponding reduction of 75%, 83%, and 52% for Case 2, Case 3, and Case 4, 89% and 69% relative to $731152 (Case 1), respectively. respectively. This further indicates the effectiveness of the three retrofit strategies as AAL values obtained with both retrofit alternatives are lower than the values of the 4. Benefit–cost analysis original building (Case 1). However, after taking the The resulting benefits are considered in terms of AAL cost of each retrofit strategy into account, the BCR for reduction (with respect to the AAL of the Case 1) due case 4 with isolated coal scuttle is derived as 1.70, to different retrofit actions. It is worth pointing out that while for case 2 with BRB, the value goes up to 1.79. AAL($) Loss Value (Billion $) Recovery Time (Days) Loss Ratio JOURNAL OF ASIAN ARCHITECTURE AND BUILDING ENGINEERING 15 Table 10. Comparison of decision variables for BCA of different mitigation options. Design Case Parameters Case 1 Case 2 Case 3 Case 4 Downtime 178 75 30 86 (Days) AAL($) 731152 186283 73579 227863 Benefit ($) - 544868 657572 503289 Cost of _ 303,767 360,023 295,740 Retrofit ($) Benefit- cost - 1.79 1.83 1.70 ratio (BCR) USRC rating 2-stars 3-stars 3-stars 3-stars (Within months to a year) (Within weeks to months) (Within weeks to months) (Within weeks to months) R-index (%) 62 85 92 83 Better results can be seen for case 3 with SMA-BRB priorities, such as recovery time, reduced economic which has a BCR of 1.83. Based on the BCRs, the use losses, short payback period, retrofit feasibility, and of SMA-BRB as a resilient improving solution is the the remaining life span of the facility. They are also more economically beneficial, followed by strategies important indicators for insurance companies to cover of BRB and then coal-scuttle isolation. Given that the seismic loss in the event of an earthquake and/or retrofitted power plant has 50 service years at a dis- business interruption. Although SMA-BRBF achieves a count rate of 3%, the BCRs corresponding to Case 2, sound performance and is relatively cost-effective, the Case 3, and Case 4 are in the ranges of 1.79–46.45, availability of suitable retrofitting materials, financing, 1.83–47.3, and 1.7–44.1, respectively. The highest BCR and availability of skilled workmanship are the factors was achieved for SMA-BRBF followed by BRBF and then that would define the suitability of retrofitting coal scuttles isolation. schemes. High cost of hybrid BRB-SMA installation in Downtime and repair cost are complementary and terms of machining and fabrication which required should be used in an integrated perspective. To further highly skilled workmanship (Miller, Fahnestock, and demonstrate the benefit of the retrofit cases in terms Eatherton 2012). of business downtime, a resilience index (R-index) as a Despite the above-mentioned factors, SMA-BRBF function of the recovery time, is estimated based on remains the most cost-effective retrofit strategy. It is Eq. (20): important to note that the proposed framework adopts BCAs that are based on a single criterion (repair t þT O RE ∫ QðtÞ costs) and corresponding recovery times. The analysis R index ¼ dt (20) does not consider the combined effects of multiple LC criteria, such as the payback period, the feasibility of where Q (t) is the functionality of the facility, T is the LC retrofitting, and the availability of skilled labor. This control time-horizon assuming that a retrofit is com- framework can be further improved by integrating pleted in a given year,T is the recovery time from RE multi-criteria decision-making tools such as TOPSIS disruption, event and t is the time of occurrence of an (technique for ordering preference by similarity to earthquake event. ideal solution), which can be used to identify and With the estimated downtime, the resilience index select the optimal alternative among a variety of (R-index) of the design cases is computed using Eq. options that meet a specific set of criteria to match (18). The resulting R-index values are classified accord- the profiles of different owners. ing to the USRC (US Resiliency Council) rating system (Table 10). The results show that Case 1 has the lowest seismic resilience of 62% compared to the other three 5. Discussion retrofit strategies. When the retrofitting actions of Case 4 and Case 3 are considered, the resilience index As observed from the response history analysis results in increases slightly by 33% and 37%, respectively. terms of drift demands, Case 1 is prone to large residual Despite the high retrofitting costs ($360,023) com- story drifts after severe earthquakes due to the low pared to Case 2 ($303,767) and Case 4 ($295,740), post-yield stiffness of the bracing components. This Case 3 (R-index = 92%) would be highly recommended explains why the cost of repair would be higher com- because it yields the shortest recovery time and the pared to the other three options. Moreover, Cases 2 and largest BCR. In principle, the time required for retro- 3 were found to be more effective than lead rubber fitting and the expected losses usually decide which bearing isolators of Case 4 in reducing seismic drift retrofitting option to be chosen. Although there are demands. As indicated in a shaking table test (Wang few indicators estimated to guide the retrofit scheme et al. 2021) of a scaled thermal power plant building, selection, it is important to recognize that decision- failure of isolators, and permanent displacement of coal making solely depends on the facility owner’s top bunkers were observed. Therefore, the residual 16 K. DAI ET AL. displacement of the LRB devices may become an obsta- irregularities and torsional effects typically asso- cle to recovery operations if Case 4 is adopted. The ciated with industrial buildings. isolation effect can be further enhanced by employing ● On improving efficiency and practicality of the IM, hysteretic viscous damping or hybrid self-centering instead of the spectral acceleration at the funda- bearings. mental period of the structure Sa(T ), better IMs In this study, the peak story drift is taken as the such as the recently proposed average spectral engineering demand parameter to quantify the acceleration could be used which is capable of damage state of the building system. The develop- producing more accurate results, especially for ment of PBEE provides another approach to estimate higher modal effects and periods in the inelastic seismic loss based on the damage of individual struc- response range. tural and nonstructural components. However, such ● Since saving direct investment costs is the main approach requires a database of fragility models for focus of this study, further improvement and critical NSCs in the thermal power plant building. At active participation of relevant decision-makers present, there are few studies performed to verify the can be encouraged by including detailed mone- intensity measure of special NSCs such as deaerator, tary losses for secondary components, recovery turbines, ash handlings, etc. and much less to propose time and other environmental impacts. adequate fragility models. Therefore, for the sake of ● SMA hybrid brace is relatively expensive, there estimating seismic loss based on damage of compo- might be reasonable sources of cost savings in nents, more efforts are required in the future for the the fabrication and repair phases by employing development of fragility models of NSCs that are parti- potential substitutes available in the form of SMA cularly essential in industrial process. Although Cases 2 wires, SMA-cables, spring-rings, SMA bolts, or and 3 have similar drift ratios, the most significant SMA-plates requiring less fabrication and installa- finding is that the BRBF does not reduce significantly tion efforts. the residual story drifts. Such permanent deformations ● It is noted that in the seismic design of damping provide another justification for self-centering framing devices and isolators following ASCE/SEI 7, the system as an incentive for design options to be inves- property modification factors shall be considered tigated in our future research. Furthermore, SMA-BRB to account for variation of the nominal design hybrid-frame experienced relatively lower peak story parameters of components caused by dynamic and residual drifts along the building height, com- loading features, production bearing properties, pared to the BRBF, SCBF, and coal scuttles isolation temperature, aging, environmental exposure, and implying less damage concentration due to its re-cen- contamination, etc. For retrofit strategy selection tering capabilities not possessed by other bracing sys- based on BCR analysis, such seismic examination tems as well as the reduced functionality and at every single component is not considered in maintenance requirements. this study and once the retrofit design scheme is At a lower discount rate with a longer service life determined, the detailed design efforts should be of the retrofitted structures, a higher benefit can be further developed. obtained. By comparing the benefits of different retrofit alternatives, stakeholders, facility owners, 6. Conclusions and relevant decision-makers can express retrofit feasibility more clearly. In this way, decision-makers The present study compared the cost-effectiveness of may be interested in losses in a particular payback different design options in terms of AAL reduction for period, for example, in this case, a 50-year loss at a retrofitting an industrial thermal power plant building discount rate of 3%. The owner may be willing to using techniques of BRB, SMA-BRB, and isolation of invest up to the value of this loss in the form of heavy equipment. The response history analysis results earthquake mitigation to avoid recurring losses in under ground motions at intensities of SLE, DBE, and the future during this period. This helps to show MCE show that SMA-BRB hybrid system can be a pro- the reasonable value of insurance premiums due to mising option for enhancing the seismic performance business interruption. Tackling the following limita- of the lateral seismic resistance system of the power tions is worth recommending: plant building. Compared with the other two seismic control options, SMA-BRBF has the lowest average In this study, the planner frames are considered residual drift and peak drift demands achieving 71% with the purpose of comparing benefit-cost ratios and 28% reduction rates, respectively. The seismic fra- of using various retrofit strategies. As per a deter- gilities of the original design and the three retrofit mined retrofit design scheme, 3D structural ana- designs were developed. Convolved with seismic lysis and component-based seismic loss analysis is hazard, the AALs of the four design cases were calcu- recommended since it is capable of quantifying lated and compared. The results show that Case 1 has the exact damage states and capturing the the highest AAL with the lowest R-index of 62% JOURNAL OF ASIAN ARCHITECTURE AND BUILDING ENGINEERING 17 compared to the other three retrofit strategies. When Disclosure statement the retrofitting actions of Case 2 and Case 4 are con- No potential conflict of interest was reported by the authors. sidered, the R-index increases to a value around 84%. Despite the high retrofitting costs of Case 3 ($360,023) compared to Case 2 ($303,767) and Case 4 ($295,740), Funding Case 3 (R-index = 92%) would be highly recommended The work was supported by the Natural Science Foundation because it yields the shortest recovery time as well as of Sichuan Province [2022NSFSC0988 & 2022NSFSC0432]; the highest BCR. Similarly, the average annual repair State Key Lab of Subtropical Building Science [2022ZB23]; time is reduced to 30, 75, and 86 days for Cases 3, 2, 4 International Collaboration Program of Sichuan Province with respect to Case 1, respectively. These values [2023JDGD0042]. match very well with the USRC (US Resiliency Council) rating system (Table 10). A good balance is achieved between cost and savings as a result of reduced Notes on contributors damage from the self-centering ability of the SMA- Kaoshan Dai is a professor in civil engineering. His research BRB bracing members. interests include wind turbine structures and structural vibra- Overall, this study offers some practical insights into tion control. the use of common seismic mitigation strategies in Abba Mas’ud Alfanda is a Ph.D. student in civil engineering determining the most economical option for prelimin- and his research topic is seismic risk analysis of industrial ary risk assessment and insurance premiums of indus- buildings. is a Ph.D. student in civil engineering and his trial facilities. This is required by decision-makers to research topic is seismic risk analysis of industrial buildings. have full knowledge of all the available options and Jianze Wang is an associate professor in civil engineering. His estimates that must be paid today or benefits in the research interests include seismic risk and performance future for adequate recovery plans of essential facilities. assessment of engineering structures. Clearly, the AAL could serve as a useful decision variable Solomon Tesfamariam is a professor in civil engineering. His as well as a performance measure for determining a research interests include the seismic design of wood struc- rational investment cost, accounting for the possible tures, machine-learning-based techniques in earthquake future benefit of a seismic control action when selected engineering. from a wide range of options. Tao li is an associate professor in civil engineering. His Furthermore, for different mitigation actions con- research interests include near-falut ground motions, seismic sidered and the loss evaluation at the specified perfor- performance of SCBF. mance levels is a conservative estimate based on a Reza Sharbati is a postdoc in civil engineering and his global (building-based) level approach, not a compo- research interests include seismic design and performance nent-based due to the lack of some technical data. assessment of engineering structures. 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Journal
Journal of Asian Architecture and Building Engineering – Taylor & Francis
Published: Nov 2, 2023
Keywords: Benefit-cost analysis; industrial power plant; seismic resilience; seismic retrofit; loss estimation