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CONTENTS
Volume 59, Number 4, August25 2016
 

Abstract
In this study, developments of an efficient visco-hyperelastic constitutive equation for describing the time dependent material behavior accurately in dynamic and impact loading and finding related materials constants are considered. Based on proposed constitutive model, behaviour of a hollow cylinder elastomer bushing under different dynamic and impact loading conditions is studied. By implementing the developed visco-hyperelastic constitutive equation to LS-DYNA explicit dynamic finite element software a three dimensional model of the bushing is developed and dynamic behaviour of that in axial and torsional dynamic deformation modes are studied. Dynamic response and induced stress under different impact loadings which is rarely studied in previous researches have been also investigated. Effects of hyperelastic and visco-hyperelastic parameters on deformation and induced stresses as well as strain rate are considered.

Key Words
visco-hyperelastic constitutive equation; elastomer bushing; impact loading; explicit FEM

Address
Masoud Asgari and Sanaz S. Hashemi: Faculty of Mechanical Engineering, K. N. Toosi University of Technology, Tehran, Iran

Abstract
A new cable-supported bridge model consisting of suspension parts, self-anchored cable-stayed parts and earth-anchored cable-stayed parts is presented. The new bridge model can be used for suspension bridges, cable-stayed bridges, cable-stayed suspension bridges, and partially earth-anchored cable-stayed bridges by varying parameters. Based on the assumption that each structural member is in either an axial compressive or tensile state, and the stress in each member is equal to the allowable stress of the material, the material quantity for each component is calculated. By introducing the unit cost of each type of material, the estimation formula for the cost of the new bridge model is developed. Numerical examples show that the results from the estimation formula agree well with that from the real projects. The span limit of cable supported bridge depends on the span-to-height ratio and the density-to-strength ratio of cables. Finally, a parametric study is illustrated aiming at the relations between three key geometrical parameters and the cost of the bridge model. The optimization of the new bridge model indicates that the self-anchored cable-stayed part is always the dominant part with the consideration of either the lowest total cost or the lowest unit cost. It is advisable to combine all three mentioned structural parts in super long span cable supported bridges to achieve the most excellent economic performance.

Key Words
cable supported bridge; new bridge model; cost estimation formula; material quantity; unit cost; span limit; parametric study; geometrical parameters; geological conditions

Address
Bin Sun, Liwen Zhang, Yidong Qin and Rucheng Xiao: Department of Bridge Engineering, Tongji University, 1239 Siping Rd., Shanghai 200092, China

Abstract
Recent earthquakes worldwide show that a significant portion of the earthquake shaking happens in the vertical direction. This phenomenon has raised significant interests to consider the vertical ground motion during the seismic design and assessment of the structures. Strong vertical ground motions can alter the axial forces in the columns, which might affect the shear capacity of reinforced concrete (RC) members. This is particularly important for non-ductile RC frames, which are very vulnerable to earthquake-induced collapse. This paper presents the detailed nonlinear dynamic analysis to quantify the collapse risk of nonductile RC frame structures with varying heights. An array of non-ductile RC frame architype buildings located in Los Angeles, California were designed according to the 1967 uniform building code. The seismic responses of the architype buildings subjected to concurrent horizontal and vertical ground motions were analyzed. A comprehensive array of ground motions was selected from the PEER NGA-WEST2 and Iran Strong Motions Network database. Detailed nonlinear dynamic analyses were performed to quantify the collapse fragility curves and collapse margin ratios (CMRs) of the architype buildings. The results show that the vertical ground motions have significant impact on both the local and global responses of non-ductile RC moment frames. Hence, it is crucial to include the combined vertical and horizontal shaking during the seismic design and assessment of non-ductile RC moment frames.

Key Words
non-ductile RC frame; collapse margin; fragility curves; vertical excitation; OpenSees

Address
E. Noroozinejad Farsangi: SERC, International Institute of Earthquake Engineering and Seismology, Tehran, Iran
T.Y. Yang: International Joint Research Laboratory of Earthquake Engineering, Shanghai, China; Department of Civil Engineering, University of British Columbia, Vancouver, Canada
A.A. Tasnimi: Department of Civil and Environmental Engineering, Tarbiat Modares University, Tehran, Iran

Abstract
In this paper, a new analytical approach has been presented for solving nonlinear conservative oscillators. Variational approach leads us to high accurate solution with only one iteration. Two different high nonlinear examples are also presented to show the application and accuracy of the presented approach. The results are compared with numerical solution using runge-kutta algorithm in different figures and tables. It has been shown that the variatioanl approach doesn\'t need any small perturbation and is accurate for nonlinear conservative equations.

Key Words
analytical methods; nonlinear vibrations; numerical solution

Address
Mahmoud Bayat: Young Researchers and Elite Club, Roudehen Branch, Islamic Azad University, Roudehen, Iran
Iman Pakar and Mahdi Bayat: Young Researchers and Elite Club, Mashhad Branch, Islamic Azad University, Mashhad, Iran

Abstract
Safety is the prime concern for a high-speed railway bridge, especially when it is subjected to a collision. In this paper, an analysis framework for the dynamic responses of train-bridge systems under collision load is established. A multi-body dynamics model is employed to represent the moving vehicle, the modal decomposition method is adopted to describe the bridge structure, and the time history of a collision load is used as the external load on the train-bridge system. A (180+216+180) m continuous steel trussedarch bridge is considered as an illustrative case study. With the vessel collision acting on the pier, the displacements and accelerations at the pier-top and the mid-span of the bridge are calculated when a CRH2 high-speed train running through the bridge, and the influence of bridge vibration on the running safety indices of the train, including derailment factors, offload factors and lateral wheel/rail forces, are analyzed. The results demonstrate that under the vessel collision load, the dynamic responses of the bridge are greatly enlarged, threatening the running safety of high-speed train on the bridge, which is affected by both the collision intensity and the train speed.

Key Words
trussed-arch bridge; vessel collision load; high-speed train; dynamic response; running safety evaluation

Address
Chaoyi Xia, Nan Zhang and He Xia: School of Civil Engineering, Beijing Jiaotong University, Beijing 100044, China; Beijing Key Laboratory of Track Engineering, Beijing 100044, China
Qin Ma: CCCC Highway Consultants Co., Ltd., Beijing 100088, China
Xuan Wu: School of Civil Engineering, Beijing Jiaotong University, Beijing 100044, China

Abstract
Masonry arch bridges present a large segment of Iranian railway bridge stock. The ever increasing trend in traffic requires constant health monitoring of such structures to determine their load carrying capacity and life expectancy. In this respect, the performance of one of the oldest masonry arch bridges of Iranian railway network is assessed through field tests. Having a total of 11 sensors mounted on the bridge, dynamic tests are carried out on the bridge to study the response of bridge to test train, which is consist of two 6-axle locomotives and two 4-axle freight wagons. Finite element model of the bridge is developed and calibrated by comparing experimental and analytical mid-span deflection, and verified by comparing experimental and analytical natural frequencies. Analytical model is then used to assess the possibility of increasing the allowable axle load of the bridge to 25 tons. Fatigue life expectancy of the bridge is also assessed in permissible limit state. Results of F.E. model suggest an adequacy factor of 3.57 for an axle load of 25 tons. Remaining fatigue life of Veresk is also calculated and shown that a 0.2% decrease will be experienced, if the axle load is increased from 20 tons to 25 tons.

Key Words
Masonry Arch Bridge; train load testing; finite element model calibration; load carrying capacity; fatigue life estimation

Address
Shervan Ataei, Mosab Tajalli and Amin Miri: School of Railway Engineering, Iran University of Science and Technology, Narmak, Tehran, Iran

Abstract
The present study investigated the earthquake behavior of R/C structures considering the vertical earthquake motion with the help of a comparative study. For this aim, the linear time-history analyses of a high-rise R/C structure designed according to TSC-2007 requirements were conducted including and excluding the vertical earthquake motion. Earthquake records used in the analyses were selected based on the ratio of vertical peak acceleration to horizontal peak acceleration (V/H). The frequency-domain analyses of the earthquake records were also performed to compare the dominant frequency of the records with that of the structure. Based on the results obtained from the time-history analyses under the earthquake loading with (H+V) and without the vertical earthquake motion (H), the value of the overturning moment and the top-story vertical displacement were found to relatively increase when considering the vertical earthquake motion. The base shear force was also affected by this motion; however, its increase was lower compared to the overturning moment and the top-story vertical displacement. The other two parameters, the top-story lateral displacement and the top-story rotation angle, barely changed under H and H+V loading cases. Modal damping ratios and their variations in horizontal and vertical directions were also estimated using response acceleration records. No significant change in the horizontal damping ratio was observed whereas the vertical modal damping ratio noticeably increased under H+V loading. The results obtained from this study indicate that the desired structural earthquake performance cannot be provided under H+V loading due to the excessive increase in the overturning moment, and that the vertical damping ratio should be estimated considering the vertical earthquake motion.

Key Words
vertical earthquake motion; V/H ratio; modal damping; R/C structure; overturning moment; vertical displacement

Address
Selcuk Bas: Department of Civil Engineering, Faculty of Engineering, Bartin University, 74100 Bartin, Turkey; Graduate School of Science, Engineering and Technology, Istanbul Technical University, 34496 Istanbul, Turkey
Ilker Kalkan: Department of Civil Engineering, Faculty of Engineering, Kirikkale University, 71450 Kirikkale, Turkey

Abstract
The failure of civil engineering systems is a consequence of decision making under uncertain conditions. Generally, buried flexible pipes are designed for their transversal behavior to prevent from the important failure mode of buckling. However, the interaction effects between soil and pipe are neglected and the uncertainties in their properties are usually not considered in pipe design. In this regard, the present research paper evaluates the effects of these uncertainties on the uncertainty of the critical buckling hoop force of flexible pipes shallowly buried using the subgrade reaction theory (Winkler model) and First-Order Second-Moment (FOSM) method. The results show that the structural uncertainties of the studied pipes and those of the soil properties have a significant effect on the uncertainty of the critical buckling hoop force, and therefore taking into account these latter in the design of the shallowly flexible pipes for their buckling behavior is required.

Key Words
uncertainty; soil-structure interaction; flexible buried pipes; subgrade reaction modulus; critical uniform hoop force; FOSM

Address
Asma Khemis and Abdelmadjid Hacene Chaouche: Department of Civil Engineering, Laboratory of Materials, Geomaterials and Environment, University of BADJI Mokhtar - Annaba, P.O. Box 12, 23000, Annaba, Algeria
Allaeddine Athmani: Department of Civil Engineering, Laboratory of Civil Engineering, University of BADJI Mokhtar - Annaba, P.O. Box 12, 23000, Annaba, Algeria
Kong Fah Tee: Faculty of Engineering and Science, University of Greenwich, Central Avenue, Chatham Maritime, Kent ME4 4TB, United Kingdom

Abstract
Curved beams\' dynamic behavior on viscoelastic foundation is the subject of the current paper. By rewritten the Timoshenko beams theory formulation for the curved and twisted spatial rods, governing equations are obtained for the circular beams on viscoelastic foundation. Using the complementary functions method (CFM), in Laplace domain, an ordinary differential equation is solved and then those results are transformed to real space by Durbin\'s algorithm. Verification of the proposed method is illustrated by solving an example by variating foundation parameters.

Key Words
inverse laplace transform; complementary functions method; circular beam; viscoelastic foundation; forced vibration

Address
Faruk Firat Calim: Department of Civil Engineering, Adana Science and Technology University, Adana, Turkey

Abstract
This paper presents a numerical method for estimating the curvature, deflection and moment capacity of FRP reinforced concrete encased steel composite beams (FRP-RCS). A sectional analysis is first carried out to predict the moment-curvature relationship from which beam deflection and moment capacity are then calculated. Comparisons between theoretical and experimental results of tests conducted elsewhere show that the proposed numerical technique can accurately predict moment capacity and deflection of FRPRCS composite beam. The numerical results also indicated that beam ductility and stiffness are improved when encased steel is added to FRP reinforced concrete beams. ACI, ISIS and Bischoff models for deflection prediction compared well at low load, however, significantly underestimated the experimental results for high load levels.

Key Words
fiber reinforced polymers; deflection; ductility; concrete; encased steel beam

Address
Ilker Fatih Kara: Civil Engineering Department, Bursa Technical University, 152 Evler Mahallesi Egitim Caddesi, 1. Damla Sok. No: 2/10, 16330, Bursa, Turkey


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