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CONTENTS
Volume 21, Number 5, November 2021
 


Abstract
This study experimentally explored the behaviour of 12 concrete filled steel tube (CFST) and steel tube columns subjected to lateral cyclic loading. The L/D ratio was 12.3 while D/t ratios were 45.4, 37.8 and 32.4, classifying these 12 specimens into 3 groups. Each group included 3 CFST and 1 steel tube columns and were tested to failure. The experimental results indicated that CFST specimens reached the state of 'collapse prevention' (drift 4%) prior to the occurrence of local buckling. Strength degradation of CFST specimens did not occur up to the failure by buckling. This showed the favourable characteristic of CFST columns in preventing collapse of structures subjected to earthquakes. The high energy absorption capability in the post collapse limit state was appropriate for dissipating energy in structures. Compared to steel tube columns, CFST columns delayed local buckling and prevented inward buckling. Consequently, CFST columns exhibited their outstanding seismic performance in terms of the increased ultimate resistance, capacity to sustain 2-3 additional load cycles and significantly higher drift. A simple and reasonably accurate model was proposed to predict the ultimate strength of CFST columns under lateral cyclic loading.

Key Words
Concrete filled steel tube (CFST); cyclic loading; force-displacement relationship; hysteretic behaviour

Address
Vui Van Cao:Faculty of Civil Engineering, Ho Chi Minh City University of Technology (HCMUT), 268 Ly Thuong Kiet Street, District 10,Ho Chi Minh City, Vietnam/ Vietnam National University at Ho Chi Minh City (VNU-HCM), Linh Trung Ward, Thu Duc City, Ho Chi Minh City, Vietnam

Cuong Trung Vo:Faculty of Civil Engineering, Ho Chi Minh City University of Technology (HCMUT), 268 Ly Thuong Kiet Street, District 10,Ho Chi Minh City, Vietnam/ Vietnam National University at Ho Chi Minh City (VNU-HCM), Linh Trung Ward, Thu Duc City, Ho Chi Minh City, Vietnam

Phuoc Trong Nguyen:Faculty of Civil Engineering, Ho Chi Minh City Open University, Vietnam

Mahmud Ashraf:School of Engineering, Deakin University Geelong, Australia/ College of Engineering, Nanjing Forestry University, Nanjing, China



Abstract
Strategic structures are a potential target of the growing terrorist attacks, so their performance under explosion hazard has been paid attention by researchers in the last years. In this regard, the aim of this study is to evaluate the blast-resistance performance of lead-rubber bearing (LRB) base isolation system based on a probabilistic framework while uncertainties related to the charge weight and standoff distance have been taken into account. A sensitivity analysis is first performed to show the effect of explosion uncertainty on the response of base-isolated buildings. The blast fragility curve is then developed for three base-isolated steel moment-resisting buildings with different heights of 4, 8 and 12 stories. The results of sensitivity analysis show that although LRB has the capability of reducing the peak response of buildings under explosion hazard, this control system may lead to increase in the peak response of buildings under some explosion scenarios. This shows the high importance of probabilistic-based assessment of isolated structures under explosion hazard. The blast fragility analysis shows effective performance of LRB in mitigating the probability of failure of buildings. Therefore, LRB can be introduced as effective control system for the protection of buildings from explosion hazard regarding uncertainty effect.

Key Words
blast fragility; explosion hazard; lead-rubber bearing; probabilistic analysis; steel moment-resisting building

Address
Hamed Dadkhaha:Department of Civil Engineering, Faculty of Engineering, University of Mohaghegh Ardabili, Ardabil, Iran

Mohtasham Mohebbi:Department of Civil Engineering, Faculty of Engineering, University of Mohaghegh Ardabili, Ardabil, Iran

Abstract
This study focuses on the influence of strong ground motion duration on the response and collapse probability of reinforced concrete walls with a predominant response in flexure. Walls with different height and mass were used to account for a broad spectrum of configurations and fundamental periods. The walls were designed following the specifications of the Chilean design code. Non-linear models of the reinforced concrete walls using a distributed plasticity approach were performed in OpenSees and calibrated with experimental data. Special attention was put on modeling strength and stiffness degradation. The effect of duration was isolated using spectrally equivalent ground motions of long and short duration. In order to assess the behavior of the RC shear walls, incremental dynamic analyses (IDA) were performed, and fragility curves were obtained using cumulative and non-cumulative engineering demand parameters. The spectral acceleration at the fundamental period of the wall was used as the intensity measure (IM) for the IDAs. The results show that the long duration ground motion set decreases the average collapse capacity in walls of medium and long periods compared to the results using the short duration set. Also, it was found that a lower median intensity is required to achieve moderate damage states in the same medium and long period wall models. Finally, strength and stiffness degradation are important modelling parameters and if they are not included, the damage in reinforced concrete walls may be greatly underestimated.

Key Words
reinforced concrete walls; incremental dynamic analysis; ground motion duration; fragility curves

Address
Camilo Flores:Departamento de Obras Civiles, Universidad Técnica Federico Santa María, Avenida España 1680, Valparaíso, Chile

Ramiro Bazaez:Departamento de Obras Civiles, Universidad Técnica Federico Santa María, Avenida España 1680, Valparaíso, Chile

Alvaro Lopez:Escuela de Ingeniería Civil, Pontificia Universidad Católica de Valparaíso, Valparaíso, Chile

Abstract
This research aims to investigate the seismic response of RC shear wall buildings of 5-, 6-, 7-, 8-, 9-, and 10-story designed as conventional and ductile and located in moderate seismic zone in Saudi Arabia in accordance with the seismic provisions of the American code ASCE-7-16. Dynamic analysis is conducted using the developed models in ETABS and the design spectra of the selected zone. The seismic responses of a number of design variations are evaluated in terms of story displacements, drift, shear and moments of both conventional and ductile building models as performance measures and presented comparatively. In addition, pushover analysis is also performed for the lowest and highest building models. Cost estimate of ductile and conventional walls is evaluated and compared to each other in terms of weight of reinforcement bars. In addition, due to the complexity of design and installation of ductile shear walls, sensitivity analysis is performed as well. It is observed that conventional design considerably increases induced seismic responses as well as cost compared to ductile one.

Key Words
conventional; cost; ductile; performance; RC buildings; sensitivity analysis shear walls

Address
Sayed Mahmoud:Department of Civil and Construction Engineering, College of Engineering, Imam Abdulrahman Bin Faisal University, Saudi Arabia

Alaa Salman:Department of Civil and Construction Engineering, College of Engineering, Imam Abdulrahman Bin Faisal University, Saudi Arabia

Abstract
A formulation based on structural reliability and cost effectiveness is proposed to provide recommendations to select the best retrofit strategy for schools with reinforced concrete frames and masonry walls, among three proposed alternatives. The cost calculation includes the retrofit cost and the expected costs of failure consequences. Also, the uncertainty of the seismic hazard is considered for each school site. The formulation identifies the potential failure modes, among shear and bending forces for beams, and flexure-compression forces for columns, for each school, and the seismic damages suffered by the schools after the earthquake of September 17, 2017 are taken into account to calibrate the damaged conditions per school. The school safety level is measured through its global failure probability, instead of only the local failure probability. The proposed retrofit alternatives are appraised in terms of the cost/benefit balance under future earthquakes, for the respective site seismic hazard, as opposed to the current practice of just restoring the structure original resistance. The best retrofit is the one that corresponds to the minimum value of the expected life cycle cost. The study, with further developments, may be used to develop general recommendations to retrofit schools located at seismic zones.

Key Words
expected life-cycle cost; failure consequences; schools retrofitting; seismic hazard; structural reliability

Address
David De León-Escobedo:Facultad de Ingeniería, Universidad Autónoma del Estado de México, Ciudad Universitaria, Estado de México, Toluca, México

Jose Luis Garcia-Manjarrez:Facultad de Ingeniería, Universidad Autónoma del Estado de México, Ciudad Universitaria, Estado de México, Toluca, México

Abstract
In a tall reinforced concrete (RC) core wall system subjected to strong ground motions, inelastic behavior near the base as well as mid-height of the wall is possible. Generally, the formation of plastic hinge in a core wall system may lead to extensive damage and significant repairing cost. A new configuration of core structures consisting of buckling restrained braced frames (BRBFs) and RC walls is an interesting idea in tall building seismic design. This concept can be used in the plan configuration of tall core wall systems. In this study, tall buildings with different configurations of combined core systems were designed and analyzed. Nonlinear time history analysis at severe earthquake level was performed and the results were compared for different configurations. The results demonstrate that using enough BRBFs can reduce the large curvature ductility demand at the base and mid-height of RC core wall systems and also can reduce the maximum inter-story drift ratio. For a better investigation of the structural behavior, the probabilistic approach can lead to in-depth insight. Therefore, incremental dynamic analysis (IDA) curves were calculated to assess the performance. Fragility curves at different limit states were then extracted and compared. Mean IDA curves demonstrate better behavior for a combined system, compared with conventional RC core wall systems. Collapse margin ratio for a RC core wall only system and RC core with enough BRBFs were almost 1.05 and 1.92 respectively. Therefore, it appears that using one RC core wall combined with enough BRBF core is an effective idea to achieve more confidence against tall building collapse and the results demonstrated the potential of the proposed system.

Key Words
buckling restrained braces; core structures; incremental dynamic analysis; reinforced concrete wall

Address
Ali Alinaghi:Department of Civil Engineering, Mahdishahr Branch, Islamic Azad University, Mahdishahr, Iran

Hamid Beiraghi:Department of Civil Engineering, Mahdishahr Branch, Islamic Azad University, Mahdishahr, Iran

Abstract
Analytical models were developed and seismic behaviors were analyzed for a three-story stone pagoda at the Cheollyongsa temple site, which was damaged by the Gyeongju earthquake of 2016. Both finite and discrete element modeling were used and the analysis results were compared to the actual earthquake damage. Vulnerable parts of stone pagoda structure were identified and their seismic behaviors via sliding, rocking, and risk analyses were verified. In finite and discrete element analyses, the 3F main body stone was displaced uniaxially by 60 and 80 mm, respectively, similar to the actual displacement of 90 mm resulting from the earthquake. Considering various input conditions such as uniaxial excitation and soil-structure interaction, as well as seismic components and the distance from the epicenter, both models yielded reasonable and applicable results. The Gyeongju earthquake exhibited extreme short-period characteristics; thus, short-period structures such as stone pagodas were seriously damaged. In addition, we found that sliding occurred in the upper parts because the vertical load was low, but rocking predominated in the lower parts because most structural members were slender. The third-floor main body and roof stones were particularly vulnerable because some damage occurred when the sliding and rocking limits were exceeded. Risk analysis revealed that the probability of collapse was minimal at 0.1 g, but exceeded 80% at above 0.3 g. The collapse risks at an earthquake peak ground acceleration of 0.154 g at the immediate occupancy, life safety, and collapse prevention levels were 90%, 52%, and 6% respectively. When the actual damage was compared with the risk analysis, the stone pagoda retained earthquake-resistant performance at the life safety level.

Key Words
analytical model; discrete element analysis; finite element analysis; Gyeongju earthquake; seismic performance; stone pagoda

Address
Ho-Soo Kim:Department of Architectural Engineering, Cheongju University, 298, Daeseong-ro, Cheongwon-gu, Cheongju-si, Chungcheongbuk-do,Republic of Korea

Dong-Kwan Kim:Department of Architectural Engineering, Cheongju University, 298, Daeseong-ro, Cheongwon-gu, Cheongju-si, Chungcheongbuk-do,Republic of Korea

Geon-Woo Jeon:Department of Architectural Engineering, Cheongju University, 298, Daeseong-ro, Cheongwon-gu, Cheongju-si, Chungcheongbuk-do,Republic of Korea

Abstract
In this study, the generalized intensity measure (IM) named INpg is analyzed. The recently proposed proxy of the spectral shape named Npg is the base of this intensity measure, which is similar to the traditional Np based on the spectral shape in terms of pseudo-acceleration; however, in this case the new generalized intensity measure can be defined through other types of spectral shapes such as those obtained with velocity, displacement, input energy, inelastic parameters and so on. It is shown that this IM is able to increase the efficiency in the prediction of nonlinear behavior of structures subjected to earthquake ground motions. For this work, the efficiency of two particular cases (based on acceleration and velocity) of the generalized INpg to predict the peak floor acceleration demands on steel frames under 30 earthquake ground motions with respect to the traditional spectral acceleration at first mode of vibration Sa(T1) is compared. Additionally, a 3D reinforced concrete building and an irregular steel frame is used as a basis for comparison. It is concluded that the use of velocity and acceleration spectral shape increase the efficiency to predict peak floor accelerations in comparison with the traditional and most used around the world spectral acceleration at first mode of vibration.

Key Words
efficiency; intensity measure; peak floor acceleration; seismic response; spectral shape

Address
José I. Torres: Facultad de Ingeniería, Universidad Autónoma de Sinaloa, Calzada de las Américas y B. Universitarios s/n,C.P. 80040, Culiacán, Sinaloa, México

Edén Bojórquez: Facultad de Ingeniería, Universidad Autónoma de Sinaloa, Calzada de las Américas y B. Universitarios s/n,C.P. 80040, Culiacán, Sinaloa, México

Robespierre Chavez: Facultad de Ingeniería, Universidad Autónoma de Sinaloa, Calzada de las Américas y B. Universitarios s/n,C.P. 80040, Culiacán, Sinaloa, México

Juan Bojórquez: Facultad de Ingeniería, Universidad Autónoma de Sinaloa, Calzada de las Américas y B. Universitarios s/n,C.P. 80040, Culiacán, Sinaloa, México

Alfredo Reyes-Salazar: Facultad de Ingeniería, Universidad Autónoma de Sinaloa, Calzada de las Américas y B. Universitarios s/n,C.P. 80040, Culiacán, Sinaloa, México

Víctor Baca: Facultad de Ingeniería, Universidad Autónoma de Sinaloa, Calzada de las Américas y B. Universitarios s/n,C.P. 80040, Culiacán, Sinaloa, México

Federico Valenzuela: Facultad de Ingeniería, Universidad Autónoma de Sinaloa, Calzada de las Américas y B. Universitarios s/n,C.P. 80040, Culiacán, Sinaloa, México

Joel Carvajal: Facultad de Ingeniería, Universidad Autónoma de Sinaloa, Calzada de las Américas y B. Universitarios s/n,C.P. 80040, Culiacán, Sinaloa, México

Omar Payán: Department of Mechanical and Mechatronic Engineering, Tecnológico Nacional de México Campus Culiacán, Culiacán, Sinaloa, México

Martín Leal: Facultad de Ingeniería, Universidad Autónoma de Sinaloa, Calzada de las Américas y B. Universitarios s/n,C.P. 80040, Culiacán, Sinaloa, México


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