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CONTENTS
Volume 19, Number 6, December 2020
 

Abstract
Unreinforced masonry (URM) walls present low shear strength and are prone to brittle failure when subjected to in-plane seismic overloads. This paper discusses the shear strengthening of URM walls with Textile Reinforced Mortar (TRM) jackets. The available literature is thoroughly reviewed and an extended database is developed including available brick, concrete and stone URM walls retrofitted and subjected to shear tests to assess their strength. Further, the experimental results of the database are compared against the available shear strength design models from ACI 549.4R-13, CNR DT 215 2018, CNR DT 200 R1/2013, Eurocode 6 and Eurocode 8 guidelines as well as Triantafillou and Antonopoulos 2000, Triantafillou 1998, Triantafillou 2016. The performance of the available models is investigated and the prediction average absolute error (AAE) is as high as 40%. A new model is proposed that takes into account the additional contribution of the reinforcing mortar layer of the TRM jacket that is usually neglected. Further, the approach identifies the plethora of different block materials, joint mortars and TRM mortars and grids and introduces rational calibration of their variable contributions on the shear strength. The proposed model provides more accurate shear strength predictions than the existing models for all different types of the URM substrates, with a low AAE equal to 22.95%.

Key Words
URM; TRM; in plane performance; strengthening; design models; diagonal compression; codes; proposed design model

Address
Athanasia K. Thomoglou, Theodoros C. Rousakis and Athanasios I. Karabinis: Civil Engineering Department, Democritus University of Thrace (DUTh), Kimmeria, 67100 Xanthi, Greece
Dimitra V. Achillopoulou: Civil Engineering Department, Democritus University of Thrace (DUTh), Kimmeria, 67100 Xanthi, Greece/ Civil and Environmental Engineering Department, University of Surrey, Guildford, GU2 7XH, United Kingdom

Abstract
The performance of an isolated horizontally curved continuous bridge with High Damping Rubber (HDR) Bearings has been investigated under seismic loading conditions. The effectiveness of response controls of the bridge by HDR bearings for various aspects viz. variation in ground motion characteristics, multi-directional effect, level of earthquake shaking, varying incidence angle, have been determined. Three recorded ground motions, representative of historical earthquakes along with near-field, far-field and forward directivity effects, have been considered in the study. The efficacy of the bearings with bi-directional effect considering interaction behavior of bearing and pier has also been investigated. Modeling and analysis of the bridge have been done by finite element approach. Sensitivity studies of the bridge response with respect to design parameters of the bearings for the considered ground motions have been performed. The importance of the nonlinearity of HDR bearings along with crucial design parameters has been identified. It has been observed that the HDR bearings performed well in different variations of ground motions, especially for controlling torsional moment. However, the deck displacement has been found to be increased significantly in case of Turkey ground motions, considering forward directivity effect, which needs to be paid more attention from designer point of view.

Key Words
curved bridge; isolation; high damping rubber bearing; earthquake; bi-directional effect

Address
Praveen K. Gupta:Department of Civil Engineering, Kamla Nehru Institute of Technology Sultanpur, -228001, U.P., India
Goutam Ghosh: Department of Civil Engineering, Motilal Nehru National Institute of Technology Allahabad, Prayagraj-211004, U.P., India

Abstract
An ultra-high voltage (UHV) transmission system has the advantages of low circuitry loss, high bulk capacity and long-distance transmission capabilities over conventional transmission systems, but it is easier for this system to cross fault rupture zones and become damaged during earthquakes. This paper experimentally and numerically investigates the seismic responses and collapse failure of a UHV transmission tower-line system crossing a fault. A 1:25 reduced-scale model is constructed and tested by using shaking tables to evaluate the influence of the forward-directivity and fling-step effects on the responses of suspension-type towers. Furthermore, the collapse failure tests of the system under specific cross-fault scenarios are carried out. The corresponding finite element (FE) model is established in ABAQUS software and verified based on the Tian-Ma-Qu material model. The results reveal that the seismic responses of the transmission system under the cross-fault scenario are larger than those under the near-fault scenario, and the permanent ground displacements in the fling-step ground motions tend to magnify the seismic responses of the fault-crossing transmission system. The critical collapse peak ground acceleration (PGA), failure mode and weak position determined by the model experiment and numerical simulation are in relatively good agreement. The sequential failure of the members in Segments 4 and 5 leads to the collapse of the entire model, whereas other segments basically remain in the intact state.

Key Words
UHV transmission system; cross-fault ground motions; shaking table tests; numerical studies; collapse failure

Address
Li Tian, Wenzhe Bi, Juncai Liu, Xu Dong and Aiqiang Xin:School of Civil Engineering, Shandong University, Jinan, Shandong Province 250061, China

Abstract
An external prestressed steel-bar truss unit was developed as a new strengthening technology to enhance the seismic performance of an in-plane masonry wall structure while taking advantage of the benefits of a prestressed system. The presented method consists of six steel bars: two prestressed vertical bars to introduce a prestressing force on the masonry wall, two diagonal bars to resist shear deformation, and two horizontal bars to maintain the configuration. To evaluate the effects of this new technique, four full-scale specimens, including a control specimen, were tested under combined loadings that included constant-gravity axial loads and cyclic lateral loads. The experimental results were analyzed in terms of the shear strength, initial stiffness, dissipated energy, and strain history. The efficiency of the external prestressed steel-bar truss unit was validated. In particular, a retrofitted specimen with an axial load level of 0.024 exhibited a more stable post behavior and higher energy dissipation than a control specimen with an observed complete sliding failure. The four vertical bars of the adjacent retrofitting units created a virtual column, and their strain values did not change until they reached the peak shear strength. The shear capacity of the masonry wall structure with external prestressed steel-bar truss units could be predicted using the model suggested by Yang et al.

Key Words
masonry wall structures; in-plane seismic performance; prestressed steel-bar truss unit; retrofitted method

Address
Seung-Hyeon Hwang, Sanghee Kim and Keun-Hyeok Yang:Department of Architectural Engineering, Kyonggi University,
154-42 Gwanggyosan-ro, Youngtong-gu, Suwon, Kyonggi-Do, 16227, Republic of Korea

Abstract
Previous earthquakes show that, structural safety evaluations should include the evaluation of nonstructural components. Failure of nonstructural components can affect the operational capacity of critical facilities, such as hospitals and fire stations, which can cause an increase in number of deaths. Additionally, failure of nonstructural components may result in economic, architectural, and historical losses of community. Accelerations and random vibrations must be under the predefined limitations in structures with high technological equipment, data centers in this case. Failure of server equipment and anchored server racks are investigated in this study. A probabilistic study is completed for a low-rise rigid sample structure. The structure is investigated in two versions, (i) conventional fixed-based structure and (ii) with a base isolation system. Seismic hazard assessment is completed for the selected site. Monte Carlo simulations are generated with selected parameters. Uncertainties in both structural parameters and mechanical properties of isolation system are included in simulations. Anchorage failure and vibration failures are investigated. Different methods to generate fragility curves are used. The site-specific annual hazard curve is used to generate risk curves for two different structures. A risk matrix is proposed for the design of data centers. Results show that base isolation systems reduce the failure probability significantly in higher floors. It was also understood that, base isolation systems are highly sensitive to earthquake characteristics rather than variability in structural and mechanical properties, in terms of accelerations. Another outcome is that code-provided anchorage failure limitations are more vulnerable than the random vibration failure limitations of server equipment.

Key Words
nonstructural components; risk assessment; seismic demand; data center; risk matrix

Address
Kubilay Cicek and Ali Sar

Abstract
Non-ductile detailing of Reinforced Concrete (RC) frames may lead to structural failure when the structure is subjected to earthquake response. These designs are generally encountered in older RC frames constructed prior to the introduction of the ductility aspect. The failure observed in the beam–column joints (BCJs) and accompanied by excessive column damage. This work examines the seismic performance and failure mode of non-ductile designed RC columns and exterior BCJs. The design was based on the actual building in Tainan City, Taiwan, that collapsed due to the 2016 Meinong earthquake. Hence, an experimental investigation using cyclic testing was performed on two columns and two BCJ specimens scaled down to 50%. The experiment resulted in a poor response in both specimens. Excessive cracks and their propagation due to the incursion of the lateral loads could be observed close to the top and bottom of the specimens. Joint shear failure appeared in the joints. The ductility of the member was below the desired value of 4. This is the minimum number required to survive an earthquake with a similar magnitude to that of El Centro. The evidence provides an understanding of the seismic failure of poorly detailed RC frame structures.

Key Words
columns; beam-column joints; quasi-static cyclic test; non-ductile detailing; plastic hinges

Address
Banu A. Hidayat:Department of Civil Engineering, College of Engineering, National Cheng Kung University,
No. 1 University Road, Tainan, 701, Taiwan (R.O.C.)
Department of Civil Engineering, Faculty of Engineering, Diponegoro University,
Jalan Prof. Soedarto, Tembalang, Semarang, 50375, Indonesia
Hsuan-Teh Hu: Department of Civil Engineering, College of Engineering, National Cheng Kung University,
No. 1 University Road, Tainan, 701, Taiwan (R.O.C.)/Department of Civil and Disaster Prevention Engineering, College of Engineering and Science, National United University,
No. 2, Lien Da, Nan Shih Li, Miaoli, 36063, Taiwan (R.O.C.)
Fu-Pei Hsiao:Department of Civil Engineering, College of Engineering, National Cheng Kung University,
No. 1 University Road, Tainan, 701, Taiwan (R.O.C.)/National Center for Research on Earthquake Engineering,
200 Sec. 3, Xinhai Road, Taipei, 10668, Taiwan (R.O.C.)
Ay Lie Han:Department of Civil Engineering, Faculty of Engineering, Diponegoro University,
Jalan Prof. Soedarto, Tembalang, Semarang, 50375, Indonesia
Panapa Pita :Department of Civil Engineering, College of Engineering, National Cheng Kung University,
No. 1 University Road, Tainan, 701, Taiwan (R.O.C.)
Yanuar Haryanto:Department of Civil Engineering, College of Engineering, National Cheng Kung University,
No. 1 University Road, Tainan, 701, Taiwan (R.O.C.)/Department of Civil Engineering, Faculty of Engineering, Jenderal Soedirman University,
Jalan Mayjen. Sungkono KM 5, Blater, Purbalingga, 53371, Indonesia




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