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CONTENTS
Volume 67, Number 1, July10 2018
 

Abstract
Shake table tests performed on five 1:3 reduced scale two story RC moment resisting frames having construction defects, have shown severe joint damageability in deficient RC frames, resulting in joint panels\' cover spalling and core concrete crushing. Haunch retrofitting technique was adopted herein to upgrade the seismic resistance of the deficient RC frames. Additional four deficient RC frames were built and retrofitted with steel haunch; both axially stiffer and deformable with energy dissipation, fixed to the beam-column connections to reduce shear demand on joint panels. The as-built and retrofitted frames\' seismic response parameters are calculated and compared to evaluate the viability of haunch retrofitting technique. The haunch retrofitting technique increased the lateral stiffness and strength of the structure, resulting in the increase of structure\'s overstrength. The retrofitting increased response modification factor R by 60% to 100%. Further, the input excitation PGA was correlated with the lateral roof displacement to derive structure response curve that have shown significant resistance of retrofitted models against input excitations. The technique can significantly enhance the seismic performance of deficient RC frames, particularly against the frequent and rare earthquake events, hence, promising for seismic risk mitigation.

Key Words
seismic resistance; haunch retrofitting; shake-table; joint damage; response modification factor

Address
Junaid Akbar, Naveed Ahmad, Bashir Alam and Muhammad Ashraf: Department of Civil Engineering, Earthquake Engineering Center, UET Peshawar 25120 Khyber Pakhtunkhwa, Pakistan

Abstract
In this paper, a framework is proposed for dynamic analysis of train-bridge systems with a damaged pier after barge collision. In simulating the barge-pier collision, the concrete pier is considered to be nonlinear-inelastic, and the barge-bow is modeled as elastic-plastic. The changes of dynamic properties and deformation of the damaged pier, and the additional unevenness of the track induced by the change of deck profile, are analyzed. The dynamic analysis model for train-bridge coupling system with a damaged pier is established. Based on the framework, an illustrative case study is carried out with a 5x32 m simply-supported PC box-girder bridge and the ICE3 high-speed train, to investigate the dynamic response of the bridge with a damaged pier after barge collision and its influence on the running safety of high-speed train. The results show that after collision by the barge, the vibration properties of the pier and the deck profile of bridge are changed, forming an additional unevenness of the track, by which the dynamic responses of the bridge and the car-body accelerations of the train are increased, and the running safety of high-speed train is affected.

Key Words
high-speed railway; concrete pier; barge collision; train-bridge system; dynamic response; running safety

Address
Chaoyi Xia, Fudong Song, Xuan Wu and He Xia: School of Civil Engineering, Beijing Jiaotong University, Beijing 100044, China
Qin Ma: CCCC Highway Consultants Co., Ltd, Beijing 100088, China

Abstract
In this work, the dynamic stability of carbon nanotubes (CNTs) reinforced composite pipes conveying pulsating fluid flow is investigated. The pipe is surrounded by viscoelastic medium containing spring, shear and damper coefficients. Due to the existence of CNTs, the pipe is subjected to a 2D magnetic field. The radial induced force by pulsating fluid is obtained by the Navier-Stokes equation. The equivalent characteristics of the nanocomposite structure are calculated using Mori-Tanaka model. Based on first order shear deformation theory (FSDT) or Mindlin theory, energy method and Hamilton\'s principle, the motion equations are derived. Using harmonic differential quadrature method (HDQM) in conjunction with the Bolotin\'s method, the dynamic instability region (DIR) of the system is calculated. The effects of different parameters such as volume fraction of CNTs, magnetic field, boundary conditions, fluid velocity and geometrical parameters of pipe are shown on the DIR of the structure. Results show that with increasing volume fraction of CNTs, the DIR shifts to the higher frequency. In addition, the DIR of the structure will be happened at lower excitation frequencies with increasing the fluid velocity.

Key Words
dynamic stability; nanocomposite pipe; pulsating fluid; magnetic field; Bolotin method

Address
Hemat Ali Esmaeili, Mehran Khaki and Morteza Abbasi: Department of Mechanical Engineering, Sari Branch, Islamic Azad University, Sari, Iran

Abstract
The dynamic output-feedback robust control method based on linear matrix inequality (LMI) method is presented for suppressing vibration response of a functionally graded material (FGM) beam with piezoelectric actuator/sensor layers in this paper. Based on the reduced model obtained by using direct mode truncation, the linear fractional state space representation of a piezoelectric FGM beam with material properties varying through the thickness is developed by considering both the inherent uncertainties in constitution material properties as well as material distribution and the model error due to mode truncation. The dynamic output-feedback robust H-infinity control law is implemented to suppress the vibration response of the piezoelectric FGM beam and the LMI method is utilized to convert control problem into convex optimization problem for efficient computation. In numerical studies, the flexural vibration control of a cantilever piezoelectric FGM beam is considered to investigate the accuracy and efficiency of the proposed control method. Compared with the efficient linear quadratic regulator (LQR) widely employed in literatures, the proposed robust control method requires less control voltage applied to the piezoelectric actuator in the case of same control performance for the controlled closed-loop system.

Key Words
FGM; piezoelectric layers; dynamic output-feedback robust control; linear matrix inequality; uncertainty

Address
Yalan Xu, Zhousu Li and Kongming Guo: School of Electronic & Mechanical Engineering, Xidian University, Xi

Abstract
Several techniques have been developed for shear strengthening of reinforced concrete (RC) members by using fiber reinforced polymer (FRP) composites. However, debonding of FRP retrofits from concrete substrate still deemed as a challenging concern in their application which needs to be scrutinized in details. As a result, this paper reports on the results of an experimental investigation on shear strengthening of RC beams using near surface mounted (NSM) FRP reinforcing bars. The main objective of the experimentation was increasing the efficiency of shear retrofits by precluding/postponing the premature debonding failure. The experimental program was comprised of six shear deficient RC beams. The test parameters include the FRP rebar spacing, inclination angle, and groove shape. Also, an innovative modification was introduced to the conventional NSM technique and its efficiency was evaluated by experimental observation and measurement. The results testified the efficiency of glass FRP (GFRP) rebars in increasing the shear strength of the test specimens retrofitted using conventional NSM technique. However, debonding of FRP bars impeded exploiting all retrofitting advantages and induced a premature shear failure. On the contrary, application of the proposed modified NSM (MNSM) technique was not only capable of preventing the premature debonding of FRP bars, but also could replace the failure mode of specimen from the brittle shear to a ductile flexural failure which is more desirable.

Key Words
RC beam; shear strengthening; GFRP rebars; debonding; NSM; modified NSM

Address
M. Ramezanpour, R. Morshed and A. Eslami: Department of Civil Engineering, Yazd University, Yazd, Iran

Abstract
The changes of parameters of pressure and velocity of propagation of elastic pressure and shear waves in uniformly deformed solid compressible media are studied within the nonclassically linearized approach (NLA) of nonlinear elastodynamics to create a new theoretical basis of the geomechanical interpretation of various groups of geophysical observational and experimental data. The cases of small and large deformations are considered while their describing by various elastic potentials, i.e., problems considering the physical and geometric nonlinearity. Convenient analytical formulae are obtained to calculate the indicated parameters in the deformed isotropic media within the nonclassical linear and nonlinear solution in the NLA. Specific numerical experiments are conducted in case of overall compression of various materials. It is shown that the method (generally accepted in the studies of mechanics of standard constructional materials) of additional linearization (relative to the pressure parameter) in the basic correlations of the NLA introduces substantial quantitative and qualitative errors into the results at significant preliminary deformations. The influences of the physical and geometric nonlinearity on the studied characteristics of the medium are large in various materials and differ qualitatively. The contribution of nonlinear components to the values of the considered parameters prevails over linear components at large deformations. When certain critical values of compression deformations in the medium are achieved, elastic waves with actual velocity cannot propagate in it. The values of the critical deformations for pressure and shear waves differ within different elastic potentials and variants of the theory of initial deformations.

Key Words
earth\'s core; high pressure; instability; elastic waves with actual velocity

Address
Hatam H. Guliyev: Department of Tectonophysics and Geomechanics, Institute of Geology and Geophysics of Azerbaijan National Academy of Sciences, H. Javid Ave. 119, Baku AZ 1143, Azerbaijan


Abstract
The study presented herein focused on the change in hysteretic force-deformation behavior of lead rubber bearings (LRBs). The material model used to idealize response of LRBs under cyclic motion is capable of representing the gradual attrition in strength of isolator unit on account of lead core heating. To identify the effect of loading history on the hysteretic response of LRBs, a typical isolator unit is subjected to cyclic motions with different velocity, amplitude and number of cycles. Furthermore, performance of an LRB isolated single degree of freedom system is studied under different seismic input levels. Finally, the significance of lead core heating effect on LRBs is discussed by considering the current design approach for base isolated structures. Results of this study show that the response of an LRB is governed strongly by the amplitude and number of cycles of the motion and the considered seismicity level.

Key Words
lead rubber bearing; isolator tests; quality control tests; seismic isolation; lead core heating

Address
Gokhan Ozdemir: Dept. of Civil Eng., Anadolu University, Eskişehir 26555, Turkey
Beyhan Bayhan: Dept. of Civil Eng., Bursa Technical University, Bursa 16330, Turkey
Polat Gulkan: Dept. of Civil Eng., Middle East Technical University, Northern Cyprus Campus, 99738 Kalkanli, Guzelyurt, Mersin 10, Turkey

Abstract
Topology optimization of steel and concrete composite based on truss-like material model is studied in this paper. First, the initial design domain is filled with concrete, and the steel is distributed in it. The problem of topology optimization is to minimize the volume of steel material and solved by full stress method. Then the optimized steel and concrete composite truss-like continuum is obtained. Finally, the distribution of steel material is determined based on the optimized truss-like continuum. Several numerical results indicate the numerical instability and rough boundary are settled. And more details of manufacture and construction can be presented based on the truss-like material model. Hence, the truss-like material model of steel and concrete is efficient to establish the distribution of steel material in concrete.

Key Words
strut-and-tie; topology optimization; truss-like continuum; steel; concrete

Address
Yang Zhiyi and Zhou Kemin: College of Civil Engineering, Huaqiao University, Jimei, Xiamen, 361021, China
Qiao Shengfang: School of Civil Engineering and Transportation, South China University of Technology, Tianhe, Guangzhou, 510641, China

Abstract
Concrete is the most widely used building material all over the world, because of its many technical and economic qualities. This pressure on the concrete resource causes an intensive exploitation of the quarries of aggregates, which results in a exhaustion of these and environmental problems. That is why recycling and valorization of materials are considered as future solutions, to fill the deficit between production and consumption and to protect the environment. This study is part of the valorization process of local materials, which aims to reuse marble waste as fine aggregate (excess loads of marble waste exposed to bad weather conditions) available in the marble quarry of Fil-fila (Skikda, East of Algeria) in the manufacture of self- compacting concretes. It consists of introducing the marble waste as sand into the self-compacting concrete formulation, with variable percentages (25%, 50%, 75% and 100%) and to study the development of its properties both in fresh state (air content, density, slump flow, V-funnel, L-box and sieve stability) as well as the hardened one (compressive strength and flexural strength). The results obtained showed us that marble wastes can be used as sand in the manufacture of self compacting concretes.

Key Words
self-compacting concrete; marble waste; sand; performance

Address
Rachid Djebien, Houria Hebhoub, Mouloud Belachia and Leila Kherraf: Department of Civil Engineering, LMGHU Laboratory, University of Skikda, Algeria
Said Berdoudi: Department of Mining Engineering, Badji Mokhtar university, Annaba, Algeria

Abstract
The seismic behavior of reinforced concrete (RC) short columns with limited transverse reinforcement is investigated in this paper through an experimental program. The experimental program consists of four small-scale RC columns with an aspect ratio of 1.7, which are tested to the axial failure stage. The cracking patterns, hysteretic responses, strains in reinforcing bars, displacement decomposition and cumulative energy dissipation of the tested specimens are reported in detail in the paper. The effects of column axial load are investigated to determine how this variable might influence the performance of the short columns with limited transverse reinforcement. Brittle shear failure was observed in all tested specimens. Beneficial and detrimental effects on the shear strength and drift ratio at axial failure of the test specimens due to the column axial load are found in the experimental program, respectively.

Key Words
reinforced concrete; short column; light transverse reinforcement; column axial load; drift ratio at axial failure

Address
Cao Thanh Ngoc Tran: Department of Civil Engineering, International University, Vietnam National University, Hochiminh, Vietnam
Bing Li: School of Civil and Environment Engineering, Nanyang Technological University, 639798, Singapore


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