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CONTENTS
Volume 16, Number 5, May 2019
 

Abstract
A long-span transmission tower-line system is indispensable for long-distance electricity transmission across a large river or valley; hence, the failure of this system, especially the collapse of the supporting towers, has serious impacts on power grids. To ensure the safety and reliability of transmission systems, this study experimentally and numerically investigates the collapse failure of a 220 kV long-span transmission tower-line system subjected to severe earthquakes. A 1:20 scale model of a transmission tower-line system is constructed in this research, and shaking table tests are carried out. Furthermore, numerical studies are conducted in ABAQUS by using the Tian-Ma-Qu material model, the results of which are compared with the experimental findings. Good agreement is found between the experimental and numerical results, showing that the numerical simulation based on the Tian-Ma-Qu material model is able to predict the weak points and collapse process of the long-span transmission tower-line system. The failure of diagonal members at weak points constitutes the collapse-inducing factor, and the ultimate capacity and weakest segment vary with different seismic wave excitations. This research can further enrich the database for the seismic performance of long-span transmission tower-line systems.

Key Words
long-span transmission tower-line system; failure; severe earthquakes; scale model; shaking table tests, numerical studies

Address
Li Tian, Zhaoyang Fu, Haiyang Pan, Ruisheng Ma and Yuping Liu: School of Civil Engineering, Shandong University, Jinan, Shandong Province 250061, China

Abstract
Different types of gas reservoir such as Liquid Natural Gas (LNG) are among the strategic infrastructures, and have great importance for any government or their private owners. To keep the tank and its contents safe during earthquakes especially if the contents are of hazardous or flammable materials; using seismic protection systems such as base isolator can be considered as an effective solution. However, the major deficiency of this system can be the large deformation in the isolation level which may lead to the failure of bearing system. In this paper, as a solution, the efficacy of an optimally designed combined vibration control system, the combined laminated rubber isolator and rotational friction damper, is investigated to evaluate the enhancement of an existing metal tank response under both far- and near-field earthquakes. Responses like impulsive and convective accelerations, base shear, and sloshing height are studied herein. The probabilistic framework is used to consider the uncertainties in the structural modeling, as well as record-to-record variability. Due to the high calculation cost of probabilistic methods, a simplified structural model is used. By using theMont-Carlo simulation approach, it is revealed that this combined isolation system is a highly reliable system which provides considerable enhancement in the performance of reservoir, not only leads to the reduction of probability of catastrophic failure of the tank but also decrease the reservoir damage during the earthquake.Moreover, the relative displacement of the isolation level is controlled very well by this combined system.

Key Words
combined isolation system; rotational friction damper; rubber; optimization; probabilistic framework; LNG tank

Address
Ali Khansefid, Ali Maghsoudi-Barmi and Alireza Khaloo: Civil Engineering Department, Sharif University of Technology, Azadi Ave., Tehran, Iran

Abstract
This study presents an experimental investigation on six beam-column joint specimens under the lateral cyclic loading. The aim was to explore the effectiveness of steel fiber-reinforced concrete (SFRC) in reducing the transverse shear stirrups in beam-column joints of the reinforced concrete (RC) frames with strong-columns and weak-beams. Two RC and four SFRC specimens with different types of reinforcement detailing and steel fibers of volume fraction in the range of 0.75-1.5% were tested under gradually increasing cyclic displacements. The main parameters investigated were lateral load-resisting capacity, hysteresis response, energy dissipation capacity, stiffness degradation, viscous damping variation, and mode of failure. Test results showed that the diagonally bent configuration of beam longitudinal bars in the beam-column joints resulted in the shear failure at the joint region against the flexural failure of beams having straight bar configurations. However, all SFRC specimens exhibited similar lateral strength, energy dissipation potential and mode of failure even in the absence of transverse steel in the beam-column joints. Finally, a methodology has been proposed to compute the shear strength of SFRC beam-column joints under the lateral loading condition.

Key Words
beam-column joints; cyclic loading; failure; reinforcement detailing; steel fiber-reinforced concrete

Address
Romanbabu M. Oinam: Department of Civil and Environmental Engineering, Indian Institute of Technology Tirupati, Tirupati-517506, India
P.C. Ashwin Kumar: Department of Earthquake Engineering, Indian Institute of Technology Roorkee, Roorkee 247667, India
Dipti R. Sahoo: Department of Civil Engineering, Indian Institute of Technology Delhi, New Delhi-110016, India

Abstract
In this work, a new analytical approach using a theory of a high order hyperbolic shear deformation theory (HSDT) has been developed to study the free vibration of plates of functionally graduated material (FGM). This theory takes into account the effect of stretching the thickness. In contrast to other conventional shear deformation theories, the present work includes a new displacement field that introduces indeterminate integral variables. During the manufacturing process of these plates defects can appear as porosity. The latter can question and modify the global behavior of such plates. The materials constituting the plate are assumed to be gradually variable in the direction of height according to a simple power law distribution in terms of the volume fractions of the constituents. The motion equations are derived by the Hamilton principle. Analytical solutions for free vibration analysis are obtained for simply supported plates. The effects of stretching, the porosity parameter, the power law index and the length / thickness ratio on the fundamental frequencies of the FGMplates are studied in detail.

Key Words
functionally graded plate; shear deformation theory; free vibration; porosity; stretching effect

Address
Riadh Bennai: Department of Civil Engineering, Faculty of Civil Engineering and Architecture, University of Hassiba Benbouali of Chlef, Algeria
Hassen Ait Atmane: Department of Civil Engineering, Faculty of Civil Engineering and Architecture, University of Hassiba Benbouali of Chlef, Algeria; Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Civil Engineering Department, Algeria
Belqassim Ayache: Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Civil Engineering Department, Algeria
Abdelouahed Tounsi: Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Civil Engineering Department, Algeria; Department of Civil and Environmental Engineering, King Fahd University of Petroleum & Minerals, 31261 Dhahran, Eastern Province, Saudi Arabia
E.A. Adda Bedia: Centre of Excellence for Advanced Materials Research, King Abdulaziz University, Jeddah, 21589, Saudi Arabia
Mohammed A. Al-Osta: Department of Civil and Environmental Engineering, King Fahd University of Petroleum & Minerals, 31261 Dhahran, Eastern Province, Saudi Arabia

Abstract
When generating spectrum-compatible artificial ground motion in engineering practices, the effect of the variation in fitting parameters on the distribution of the peak ground displacement (PGD) has not yet drawn enough attention. In this study, a method for simulating ground motion matching for multiple targets is developed. In this method, a frequency-dependent amplitude envelope function with statistical parameters is introduced to simulate the nonstationarity of the frequency in earthquake ground motion. Then, several groups of time-history acceleration with different temporal and spectral nonstationarities were generated to analyze the effect of nonstationary parameter variations on the distribution of PGD. The following conclusions are drawn from the results: (1) In the simulation of spectrum-compatible artificial ground motion, if the acceleration time-history is generated with random initial phases, the corresponding PGD distribution is quite discrete and an uncertain number of PGD values lower than the limit value are observed. Nevertheless, the mean values of PGD always meet the requirement in every group. (2) If the nonstationary frequencies of the ground motion are taken into account when fitting the target spectrum, the corresponding PGD values will increase. A correlation analysis shows that the change in the mean and the dispersion values, from before the frequencies are controlled to after, correlates with the modal parameters of the predominant frequencies. (3) Extending the maximum period of the target spectrum will increase the corresponding PGD value and, simultaneously, decrease the PGD dispersion. Finally, in order to control the PGD effectively, the ground motion simulation method suggested in this study was revised to target a specified PGD. This novel method can generate ground motion that satisfies not only the required precision of the target spectrum, peak ground acceleration (PGA), and nonstationarity characteristics of the ground motion but also meets the required limit of the PGD, improving engineering practices.

Key Words
simulation of ground motion; peak ground displacement; nonstationary; spectrum compatible; multiple targets

Address
Shaoqing Wang, Ruifang Yu, Xiaojun Li and Hongshan Lv: Institute of Geophysics, China Earthquake Administration, No. 5, Minzu Daxue South Road, Haidian District, Beijing, 100081, China

Abstract
Seismic design method based on bearing capacity has been widely adopted in building codes around the world, however, damage and collapse state of structure under strong earthquake can not be reflected accurately. This paper aims to present a deformation-based seismic design method based on the research of RC component deformation index limit, which combines with the feature of Chinese building codes. In the proposed method, building performance is divided into five levels and components are classified into three types according to their importance. Five specific design approaches, namely, \"Elastic Design\", \"Unyielding Design\", \"Limit Design\", \"Minimum Section Design\" and \"Deformation Assessment\", are defined and used in different scenarios to prove whether the seismic performance objectives are attained. For the components which exhibit ductile failure, deformation of components under strong earthquake are obtained quantitatively in order to identify the damage state of the components. For the components which present brittle shear failure, their performance is guaranteed by bearing capacity. As a case study, seismic design of an extremely irregular twin-tower high rise building was carried out according to the proposed method. The results evidenced that the damage and anti-collapse ability of structure were estimated and controlled by both deformation and bearing capacity.

Key Words
component deformation-based; component deformation limit; design method; performance assessment; high-rise reinforced concrete structure; irregular building

Address
Xiaolei Han, Difang Huang, Jing Ji and Jinyue Lin: School of Civil and Transportation Engineering, South China University of Technology, Tianhe, Guangzhou, 510641, China

Abstract
Conventional buckling restrained braces used in concentrically braced frames are expected to yield in both tension and compression without major degradation of capacity under severe seismic ground motions. One of the weakness points of a standard buckling restrained braced frame is the low post-yield stiffness and thus large residual deformation under moderate to severe ground motions. This phenomenon can be attributed to low post-yield stiffness of core member in a BRB. This paper introduces a multi-core buckling restrained brace. The multi-core term arises from the use of more than one core component with different steel materials, including high-performance steel (HPS-70W) and stainless steel (304L) with high strain hardening properties. Nonlinear dynamic time history analyses were conducted on variety of diagonally braced frames with different heights, in order to compare the seismic performance of regular and multi-core buckling restrained braced frames. The results exhibited that the proposed multi-core buckling restrained braces reduce inter-story and especially residual drift demands in BRBFs. In addition, the results of seismic fragility analysis designated that the probability of exceedance of residual drifts in multi-core buckling restrained braced frames is significantly lower in comparison to standard BRBFs.

Key Words
buckling restrained brace; multi-core BRB; nonlinear time history analysis; fragility analysis

Address
Nader Hoveidae: Faculty of Engineering, Department of Civil Engineering, Azarbaijan Shahid Madani University, Tabriz, Iran

Abstract
The effect of the porosity and its distribution shape on the normal and shear interfacial stresses of the FGM beam strengthened with FRP plate subjected to a uniformly distributed load are investigated analytically in the present paper. Basically, the governing equations of FGM beams with porosity strengthened with composite plates are identical to the ones without porosity. Nonetheless, when the effect of the porosity and its distribution shape are taken into account, the rule of mixture was reformulated to assess the material characteristics with the porosity phases and its distribution shape. This work discusses the influence of the gradient index, the porosity and its distribution shape on the interfacial stresses.

Key Words
interfacial stresses; FGM beam; FRP composites; porosity

Address
Benferhat Rabia, Tahar Hassaine Daouadji and Rabahi Abderezak: Departement de Genie Civil, Universite Ibn Khaldoun Tiaret; BP 78 Zaaroura, Tiaret, Algerie; Laboratoire de Geomatique et Developpement Durable, Universite de Tiaret, Algerie

Abstract
A set of mid-rise bare and uniformly infilled reinforced-concrete frame buildings are analyzed for two different seismic intensities of ground-motions (i.e., \"Design Basis Earthquake\" and \"Maximum Considered Earthquake\") to study their floor response. The crucial parameters affecting seismic design force for acceleration-sensitive non-structural components are studied and compared with the guidelines of the European and the United States standards, and also with the recently developed NIST provisions. It is observed that the provisions of both the European and the United States standards do not account for the effects of the period of vibration of the supporting structure and seismic intensity of ground-motions and thereby provides conservative estimates of the in-structure amplification. In case of bare frames, the herein derived component amplification factors for both the design basis earthquake and the maximum considered earthquake exceeds with their recommended values in the European and the United States standards for non-structural components having periods in vicinity of the higher modes of vibration, whereas, in case of infilled frames, component amplification factors exceeds with their recommended value in the European standard for non-structural components having periods in vicinity of the fundamental mode of vibration, and only for the design basis earthquake. As a consequence of these observations, as well as capping on the design force (in case of United states standard and NIST provisions), in case of the design basis earthquake, the combined amplification factor is underestimated for non-structural components having periods in vicinity of the higher modes of vibration of bare frames, and also for nonstructural components having periods in vicinity of the fundamental mode of vibration of infilled frames. At the maximum considered earthquake demand, excepting non-structural components having periods in vicinity of the higher modes of vibration of bare frames, all provisions generally provide conservative estimates of the design floor accelerations.

Key Words
RC frame buildings; seismic design; non-structural components; component amplification; in-structure amplification

Address
Mitesh Surana: Department of Civil Engineering, Indian Institute of Technology Ropar, Rupnagar-140001, Punjab, India

Abstract
The concept of the combined seismic and energy retrofitting of existing reinforced concrete (RC) buildings was examined in this paper through a number of case studies conducted on model buildings (simulating buildings of the „60s-‟80s in southern Europe) constructed according to outdated design standards. Specifically, seismic and thermal analyses have been conducted prior to and after the application of selected retrofitting schemes, in order to quantify the positive effect that retrofitting could provide to RC buildings both in terms of their structural and energy performance. Advanced materials, namely the textile reinforced mortars (TRM), were used for providing seismic retrofitting by means of jacketing of masonry infills in RC frames. Moreover, following the application of the TRM jackets, thermal insulation materials were simultaneously provided to the RC building envelope, exploiting the fresh mortar used to bind the TRM jackets. In addition to the externally applied insulation material, all the fenestration elements (windows and doors) were replaced with new high energy efficiency ones. Afterwards, an economic measure, namely the expected annual loss (EAL) was used to evaluate the efficiency of each retrofitting method, but also to assess whether the combined seismic and energy retrofitting is economically feasible. From the results of this preliminary study, it was concluded that the selected seismic retrofitting technique can indeed enhance significantly the structural behaviour of an existing RC building and lower its EAL related to earthquake risks. Finally, it was found that the combined seismic and energy upgrading is economically more efficient than a sole energy or seismic retrofitting scenario for seismic areas of south Europe.

Key Words
advanced materials; building envelope; energy retrofitting; infill strengthening; textile reinforced mortar (TRM); thermal insulation

Address
Panagiotis D. Gkournelos: Department of Civil Engineering, University of Patras, Patras GR-26504, Greece; Division of Engineering, New York University Abu Dhabi, UAE
Dionysios A. Bournas: European Commission, Joint Research Centre (JRC), Ispra, Italy
Thanasis C. Triantafillou: Department of Civil Engineering, University of Patras, Patras GR-26504, Greece; Division of Engineering, New York University Abu Dhabi, UAE


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