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CONTENTS
Volume 20, Number 2, February 2021
 


Abstract
The paper presents a simplified force-based seismic design procedure for the preliminary design of steel haunch retrofitting for the seismic upgrade of deficient RC frames. The procedure involved constructing a site-specific seismic design spectrum for the site, which is transformed into seismic base shear coefficient demand, using an applicable response modification factor, that defines base shear force for seismic analysis of the structure. Recent experimental campaign; involving shake table testing of ten (10), and quasi-static cyclic testing of two (02), 1:3 reduced scale RC frame models, carried out for the seismic performance assessment of both deficient and retrofitted structures has provided the basis to calculate retrofit-specific response modification factor Rretrofitted. The haunch retrofitting technique enhanced the structural stiffness, strength, and ductility, hence, increased the structural response modification factor, which is mainly dependent on the applied retrofit scheme. An additional retrofit effectiveness factor (ΩR) is proposed for the deficient structure's response modification factor Rdeficient, representing the retrofit effectiveness (ΩR=Rretrofitted /Rdeficient), to calculate components' moment and shear demands for the retrofitted structure. The experimental campaign revealed that regardless of the deficient structures' characteristics, the ΩR factor remains fairly the unchanged, which is encouraging to generalize the design procedure. Haunch configuration is finalized that avoid brittle hinging of beam-column joints and ensure ductile beam yielding. Example case study for the seismic retrofit designs of RC frames are presented, which were validated through equivalent lateral load analysis using elastic model and response history analysis of finite-element based inelastic model, showing reasonable performance of the proposed design procedure. The proposed design has the advantage to provide a seismic zone-specific design solution, and also, to suggest if any additional measure is required to enhance the strength/deformability of beams and columns.

Key Words
beam-column joint; seismic strengthening; retrofitting; steel haunches; retrofit effectiveness factor

Address
Naveed Ahmad:Department of Civil Engineering, UET Peshawar 2nd Floor, Earthquake Engineering Center, CED UET Peshawar, 25120 KP, Pakistan

Abstract
Buildings made using the locally available clay materials are amongst the least expensive forms of construction in many developing countries, and therefore, widely popular in remote areas. It is despite the fact that these low-strength masonry structures are vulnerable to seismic forces. Since transporting imported materials like cement and steel in areas inaccessible by motorable roads is challenging and financially unviable. This paper presents, and experimentally investigates, adobe masonry structures that utilize the abundantly available local clay materials with moderate use of imported materials like cement, aggregates, and steel. Shake-table tests were performed on two 1:3 reduce-scaled adobe masonry models for experimental seismic testing and verification. The model AM1 was confined with vertical lightly reinforced concrete columns provided at all corners and reinforced concrete horizontal bands (i.e., tie beams) provided at sill, lintel, and eave levels. The model AM2 was confined only with the horizontal bands provided at sill, lintel, and eave levels. The models were subjected to sinusoidal base motions for studying the damage evolution and response of the model under dynamic lateral loading. The lateral force-deformation capacity curves for both models were developed and bi-linearized to compute the seismic response parameters: stiffness, strength, ductility, and response modification factor R. Seismic performance levels, story-drift, base shear coefficient, and the expected structural damages, were defined for both the models. Seismic performance assessment of the selected models was carried out using the lateral seismic force procedure to evaluate their safety in different seismic zones. The use of vertical columns in AM1 has shown a considerable increase in the lateral strength of the model in comparison to AM2. Although an R factor equal to 2.0 is recommended for both the models, AM1 has exhibited better seismic performance in all seismic zones due to its relatively high lateral strength in comparison to AM2.

Key Words
adobe; response modification factor; story-drift; base shear coefficient; confined masonry

Address
Faisal Zaman Khan:Department of Civil Engineering. UET Peshawar 25120 Peshawar. Khyber Pakhtunkhwa, Pakistan

Muhammad Ejaz Ahmad:Department of Civil Engineering. UET Peshawar 25120 Peshawar. Khyber Pakhtunkhwa, Pakistan

Naveed Ahmad:Department of Civil Engineering. UET Peshawar 25120 Peshawar. Khyber Pakhtunkhwa, Pakistan

Abstract
The structural behavior of a tensile fabric structure, known as hypar, is investigated. Seismic-induced stresses in the fabric and axial forces in masts and cables are obtained using accelerograms recorded at different regions of the world. Time-history analysis using each recording are performed for the hypar by using finite element simulation. It is found that while the seismic stresses in the fabric are not critical for design, the seismic tensile forces in cables and the seismic compressive forces in masts should not be disregarded by designers. This is important, because the seismic design is usually not considered so relevant, as compared for instance with wind design, for these types of structures. The most relevant findings of this study are: 1) dynamic axial forces can have an increase of up to twice the static loading when the TFS is subjected to seismic demands, 2) large peak ground accelerations seem to be the key parameter for significant seismic-induced axial forces, but not clear trend is found to relate such forces with earthquakes and site characteristics and, 3) the inclusion or exclusion of the form-finding in the analysis procedure importantly affects results of seismic stresses in the fabric, but not in the frame.

Key Words
tensile fabric structure; time-history analysis; finite element simulation; form-finding; seismic-induced forces

Address
Jesús G. Valdés-Vázquez:Department of Civil and Environmental Engineering, Universidad de Guanajuato,
Av. Juárez 77, Colonia Centro, C.P. 36000, Guanajuato, GTO., México

Adrián D. García-Soto:Department of Civil and Environmental Engineering, Universidad de Guanajuato,Av. Juárez 77, Colonia Centro, C.P. 36000, Guanajuato, GTO., México

Michele Chiumenti:International Center for Numerical Methods in Engineering (CIMNE), Univeridad Politécnica de Cataluña,Campus Norte UPC, 08034, Barcelona, Spain

Alejandro Hernández-Martínez:Department of Civil and Environmental Engineering, Universidad de Guanajuato,
Av. Juárez 77, Colonia Centro, C.P. 36000, Guanajuato, GTO., México




Abstract
This study strives to highlight the importance of considering the vertical ground motions (VGM) in the seismic evaluation of RC buildings. To this aim, IDA (Incremental Dynamic Analysis) is conducted on three code-based designed high-rise RC frame-core wall buildings using a suite of earthquake records comprising of significant VGMs. To unravel the significance of the VGM inclusion on the performance of the buildings, IDAs are conducted in two states (with and without the vertical component), and subsequently based on each analysis, fragility curves are developed. Non-simulated collapse criteria are used to determine the collapse state drift ratio and the area under the velocity spectrum (SIm) is taken into account as the intensity measure. The outcome of this study delineates that the inclusion of VGM leads to the increase in the collapse vulnerability of the structures as well as to the change in the pattern of inter-story drifts and failure mode of the buildings. The results suggested that it would be more conservative if the VGM is included in the seismic assessment and the fragility analysis of RC buildings.

Key Words
Vertical ground motion; near-field earthquake; RC frame-core wall building; incremental dynamic analysis; fragility assessment

Address
Arsam Taslimi:Department of Civil and Environment Engineering, University of Nevada, Reno, U.S.A.

Mohsen Tehranizadeh:Department of Civil and Environment Engineering, Amirkabir University of Technology, Iran

Mohammadreza Shamlu:Department of Civil and Environment Engineering, Amirkabir University of Technology, Iran

Abstract
The main factor for the amplification of ground motions near the crest or the toe of a slope is the reflection of the incident waves. The effects of the slope topography on the surrounding lands over the crest or at the toe can amplify the seismic responses of buildings. This study investigates the seismic performance of the slope topography and three mid-rise buildings (five, ten, and fifteen-storey) located near the crest and toe of the slope by 3D numerical analysis. The nonlinear model was used to represent the real behavior of building and ground elements. The average results of seven records were used in the investigations. Based on the analysis, the amplification factor of acceleration near the crest and toe of the slope was the most effective at distances of 2.5 and 1.3 times the slope height, respectively. Accordingly, the seismic performance of buildings was studied at a distance equal to the height of the slope from the crest and toe. The seismic response results of buildings showed that the slope topography to have little impact on up to five-storey buildings located near the crest. Taking into account a topography-soil-structure interaction system increases the storey displacement and base shear in the building. Accordingly, in topography-soil-structure interaction analyses, the maximum lateral displacement was increased by 71% and 29% in ten and fifteen-storey buildings, respectively, compare to the soil-structure interaction system. Further, the base shear force was increased by 109% and 78% in these buildings relative to soil-structure interaction analyses.

Key Words
seismic response; slope topography; nonlinear analysis; topography-soil-structure interaction; MIDAS GTS/NX software

Address
Mohammad J. Shabani:Department of Civil Engineering, Kharazmi University, No. 49 Mofatteh Avenue, Tehran 15719-14911, Iran

Mohammad Shamsi:Department of Civil Engineering, Kharazmi University, No. 49 Mofatteh Avenue, Tehran 15719-14911, Iran

Ali Ghanbari:Department of Civil Engineering, Kharazmi University, No. 49 Mofatteh Avenue, Tehran 15719-14911, Iran

Abstract
Contrast to the conventional jointed bridge design, integral abutment bridges (IABs) offer some marked advantages like reduced maintenance and enhanced service life of the structure due to elimination of joints in the deck and monolithic construction practices. However, the force transfer mechanism during seismic and thermal movements is a topic of interest owing to rigid connection between superstructure and substructure (piers and abutments). This study attempts to model an existing IAB by including the abutment backfill interaction and soil-foundation interaction effects using Winkler foundation assumption to determine its seismic response. Keeping in view the significance of abutment behavior in an IAB, the probability of damage to the abutment is evaluated using fragility function. Incremental Dynamic Analysis (IDA) approach is used in this regard, wherein, nonlinear time history analyses are conducted on the numerical model using a selected suite of ground motions with increasing intensities until damage to abutment. It is concluded from the fragility analysis results that for a MCE level earthquake in the location of integral bridge, the probability of complete damage to the abutment is minimal.

Key Words
integral abutment bridge; winkler foundation; incremental dynamic analysis; abutment backfill interaction; soil-foundation interaction; fragility analysis

Address
Sunil J.C.:CSIR-Structural Engineering Research Centre, Chennai, Tamil Nadu, India

Atop Lego:Department of Civil Engineering, Indian Institute of Technology, Guwahati, Assam, India


Anjan Dutta:Department of Civil Engineering, Indian Institute of Technology, Guwahati, Assam, India

Abstract
The carbon dioxide present in the atmosphere is one of the main reasons for the corrosion of bridges, buildings, tunnels, and other reinforced concrete (RC) structures in most industrialized countries. With the growing use of fossil fuels in the world since the Industrial Revolution, the amount of carbon dioxide in urban and industrial areas of the world has grown significantly, which increases the chance of corrosion caused by carbonation. The process of corrosion leads to a change in mechanical properties of rebars and concrete, and consequently, detrimentally impacting load-bearing capacity and seismic behavior of RC structures. Neglecting this phenomenon can trigger misleading results in the form of underestimating the seismic performance metrics. Therefore, studying the carbonation corrosion influence on the seismic behavior of RC structures in urban and industrial areas is of great significance. In this study, a 2D modern RC moment frame is developed to study and assess the effect of carbonation corrosion, in 5-year intervals, for a 50 years lifetime under two different environmental conditions. This is achieved using the nonlinear static and incremental dynamic analysis (IDA) to evaluate the reinforcement corrosion effects. The reduction in the seismic capacity and performance of the reinforced concrete frame, as well as the collapse probability over the lifetime for different corrosion scenarios, is examined through the capacity curves obtained from nonlinear static analysis and the fragility curves obtained from IDA.

Key Words
corrosion effects; carbonation corrosion; nonlinear static analysis; incremental dynamic analysis (IDA)

Address
Hossein Vaezi:The Centre of Excellence for Fundamental Studies in Structural Engineering, Iran University of Science and Technology,P.O. Box: 16765-163; Narmak, Tehran, Iran
Amir Karimi:Rehabilitation and Retrofitting Research Centre, Iran University of Science and Technology, Tehran, Iran

Mohsenali Shayanfar:The Centre of Excellence for Fundamental Studies in Structural Engineering, Iran University of Science and Technology,P.O. Box: 16765-163; Narmak, Tehran, Iran

Amir Safiey:Department of Civil, Environmental and Architectural Engineering, University of Colorado Boulder, CO, U.S.A.

Abstract
Supplemental passive dampers are widely employed to improve the structural performance of buildings under seismic excitations. Nevertheless, the added damping could be counter-productive if the axial forces induced by the damper reaction forces are not routed properly in the columns. A few researchers engaged to optimize the width-wise damper arrangement to improve the delivered path of the axial column forces. However, most of these studies are limited under the design-based seismic level and few of them has evaluated the collapse performance of buildings under strong earthquakes. In this paper, the strategic width-wise placement method of viscous dampers is explored regarding the building performance under collapse state. Two realistic steel buildings with different storeys are modelled and compared to explore higher mode effects. Each building is designed with four different damper arrangement scenarios based on a classic damper distribution method. Both a far-fault and a near-fault seismic environment are considered for the buildings. Incremental Dynamic Analysis (IDA) is performed to evaluate the probability of collapse and the plastic mechanism of the retrofitted steel buildings.

Key Words
viscous damper; damper optimization; Incremental Dynamic Analysis; probability of collapse; plastic hinges

Address
Xiameng Huang:School of Navigation Engineering, Guangzhou Maritime University,101 Hongshansan Road, Huangpu District, Guangzhou, Guangdong, China


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