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CONTENTS
Volume 65, Number 3, February10 2018
 

Abstract
The purpose of this paper is to study free vibration analysis of thick plates resting on Winkler foundation using Mindlin\'s theory with shear locking free fourth order finite element, to determine the effects of the thickness/span ratio, the aspect ratio, subgrade reaction modulus and the boundary conditions on the frequency paramerets of thick plates subjected to free vibration. In the analysis, finite element method is used for spatial integration. Finite element formulation of the equations of the thick plate theory is derived by using higher order displacement shape functions. A computer program using finite element method is coded in C++ to analyze the plates free, clamped or simply supported along all four edges. In the analysis, 17-noded finite element is used. Graphs are presented that should help engineers in the design of thick plates subjected to earthquake excitations. It is concluded that 17-noded finite element can be effectively used in the free vibration analysis of thick plates. It is also concluded that, in general, the changes in the thickness/span ratio are more effective on the maximum responses considered in this study than the changes in the aspect ratio.

Key Words
free vibration parametric analysis; thick plate; Mindlin

Address
Y. I. Ozdemir: Department of Civil Engineering, Karadeniz Technical University, 61080 Trabzon, Turkey

Abstract
A numerical investigation of the impact of steel ductility on the strength and ductility of two-way corner and edge-supported concrete slabs containing low ductility welded wire fabric is presented. A finite element model was developed for the investigation and the results of a series of concurrent laboratory experiments were used to validate the numerical solution. A parametric investigation was conducted using the numerical model to investigate the various factors that influence the structural behavior at the strength limit state. Different values of steel uniform elongation and ultimate to yield strength ratios were considered. The results are presented and evaluated, with emphasis on the strength, ductility, and failure mode of the slabs. It was found that the ductility of the flexural reinforcement has a significant impact on the ultimate load behavior of two-way corner-supported slabs, particularly when the reinforcement was in the form of cold drawn welded wire fabric. However, the impact of the low ductility WWF has showed to be less prominent in structural slabs with higher levels of structural indeterminacy. The load-deflection curves of corner-supported slabs containing low ductility WWF are brittle, and the slabs have little ability to undergo plastic deformation at peak load.

Key Words
ductility; reinforced concrete slabs; low ductility reinforcement; strength; strain localization

Address
Zafer Sakka: Energy and Building Research Center, KISR, P.O. Box 24885 Safat 13109, Kuwait
R. Ian Gilbert: School of Civil and Environmental Engineering, UNSW, Sydney, Australia

Abstract
In this paper, the Colliding Bodies Optimization (CBO), Enhanced Colliding Bodies Optimization (ECBO) and Vibrating Particles System (VPS) algorithms and the force method are used for the simultaneous analysis and design of truss structures. The presented technique is applied to the design and analysis of some planer and spatial trusses. An efficient method is introduced using the CBO, ECBO and VPS to design trusses having members of prescribed stress ratios. Finally, the minimum weight design of truss structures is formulated using the CBO, ECBO and VPS algorithms and applied to some benchmark problems from literature. These problems have been designed by using displacement method as analyzer, and here these are solved for the first time using the force method. The accuracy and efficiency of the presented method is examined by comparing the resulting design parameters and structural weight with those of other existing methods.

Key Words
force method; metaheuristic algorithms; analysis; design; optimization; truss; stress ratio; energy

Address
A. Kaveh and Sh. Bijari: Centre of Excellence for Fundamental Studies in Structural Engineering, School of Civil Engineering, Iran University of Science and Technology, Narmak, Tehran-16, Iran


Abstract
The use of blast hardened bulkheads (BHBs) is an effective vulnerability hardening technique for improving the survivability of naval warships when internal explosions occur due to being shot by an anti-surface missile. In this paper, a new concept of BHBs reinforced by aluminum (Al) foam is proposed. The new concept can significantly reduce the blast pressures transferred to bulkheads and, unlike conventional BHBs, can be easily installed to operating naval warships. Chamber model blast tests were performed to demonstrate the effectiveness of the Al-foam BHBs and the results are further supported by numerical simulations. Finally, a practical preliminary is proposed for the Al-foam BHBs.

Key Words
survivability; internal blast; blast hardened bulkhead; aluminum foam; chamber model blast test

Address
Sung-Ho Kim: Naval Ship Engineering Center, Republic of Korea Navy, Headquarthers, 543 Gamasan-ro, Yeongdeungpo-gu, Seoul 07360, Republic of Korea
Heekyu Woo: Division of Aircraft Research and Development, Korea Aerospace Industries, 78 Gondan 1-ro, Sacheon-si, Gyeongsangnam-do 52529, Republic of Korea
Gul-Gi Choi: Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology, 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea
Kyungho Yoon: Department of Radiology, Brigham and Women

Abstract
Self-centering concentrically braced frames (SCCBFs) are emerging as high performance seismically resistant braced framing system, due to the capacity of withstanding strong earthquake attacks and promptly recovering after events. To get a further insight into the seismic performance of SCCBFs, systematical evaluations are currently conducted from the perspective of modal contributions. In this paper, the modal pushover analysis (MPA) approach is utilized to obtain the realistic seismic demands by summarizing the contribution of each single vibration mode. The MPA-based results are compared with the exact results from nonlinear response history analysis. The adopted SCCBFs originate from existing buckling-restrained braced frames (BRBF), which are also analyzed for purpose of comparison. In the analysis of these comparable framing systems, interested performance indices that closely relate to the structural damage degree include the interstory drift ratio, floor acceleration, and absorbed hysteretic energy. The study shows that the MPA approach produces acceptable predictions in comparison to the exact results for SCCBFs. In addition, the high-modes effect on the seismic behavior increases with the building height, and is more evident in the SCCBFs than the BRBFs.

Key Words
modal contribution; model pushover analysis; seismic performance; self-centering; braced frame

Address
Li Tian and Canxing Qiu: School of Civil Engineering, Shandong University, Jinan 250061, Shandong, China

Abstract
In this study, we propose a frequency domain spectral element method (SEM) for the vibration analysis of a multi-span beam subjected to a moving point force. This study is an extension of the authors\' previous study for a single-span beam subjected to a moving point force, where the two-element model-based SEM was applied. In this study, each span of a multi-span beam is represented by the Timoshenko beam model and the moving point force is transformed into the frequency domain as a series of each stationary point force distributed on the multi-span beam. The span at which a stationary point force is located is represented by two-element model, but all other spans are represented by one-element models. The vibration responses to a moving point force are obtained by superposing all individual vibration responses generated by each stationary point force. The high accuracy and computational efficiency of the proposed SEM are verified by comparing the solutions by SEM with exact analytical solutions by the integral transform method (ITM) as well as the solutions by the finite element method (FEM).

Key Words
multi-span beam; moving point force; vibration response; spectral element method; two-element model; Timoshenko beam model

Address
Boseop Jeong, Taehyun Kim and Usik Lee: Department of Mechanical Engineering, Inha University, Inha-ro 100, Nam-gu, Incheon 22212, Republic of Korea

Abstract
The hygrothermal stresses in sandwich plate with composite faces due to through the thickness gradient temperature and (or) moisture content are investigated. The layer-wise theory is employed for formulation of the problem. The formulation is derived for sandwich plate with general layer stacking, subjected to uniform and non-uniform temperature and moisture content through the thickness of the plate. The governing equations are solved for free edge conditions and 3D stresses are investigated. The out of plane stresses are obtained by equilibrium equations of elasticity and by the constitutive law and the results for especial case are compared with the predictions of a 3D finite element solution in order to study the accuracy of results. The three-dimensional stresses especially the free edge effect on the distribution of the stresses is studied in various sandwich plates and the effect of uniform and non-uniform thermal and hygroscopic loading is investigated.

Key Words
thermal loading; hygroscopic loading; sandwich plate; out of plane stresses; layer-wise theory

Address
Isa Ahmadi: Advanced Materials and Computational Mechanics Lab, Department of Mechanical Engineering, University of Zanjan, 45371-38791, Zanjan, Iran


Abstract
Rigid body spring method (RBSM) is an effective tool to simulate the cracking process of structures, and has been successfully applied to investigate the behavior of reinforced concrete (RC) members. However, the theoretical researches and engineering applications of this method mainly focus on two-dimensional problems as yet, which greatly limits its applications in actual engineering projects. In this study, a three-dimensional (3-D) RBSM for RC structures is proposed. In the proposed model, concrete, reinforcing steels, and their interfaces are represented as discrete entities. Concrete is partitioned into a collection of rigid blocks and a uniform distribution of normal and tangential springs is defined along their boundaries to reflect its material properties. Reinforcement is modeled as a series of bar elements which can be freely positioned in the structural domain and irrespective of the mesh geometry of concrete. The bond-slip characteristics between reinforcing steel and concrete are also considered by introducing special linkage elements. The applicability and effectiveness of the proposed method is firstly confirmed by an elastic T-shape beam, and then it is applied to analyze the failure processes of a Z-type component under direct shear loading and a RC beam under two-point loading.

Key Words
reinforced concrete structures; failure process; rigid body spring model; cracks; simplex integration

Address
Xingu Zhong:
1) School of Civil Engineering, Hunan University of Science and Technology, Taoyuan Road, Yuhu District, Xiangtan, China
2) School of Mechanics and Civil Engineering, China University of Mining and Technology (Beijing), Ding No.11 Xueyuan Road, Haidian District, Beijing, China
Chao Zhao: School of Mechanics and Civil Engineering, China University of Mining and Technology (Beijing), Ding No.11 Xueyuan Road, Haidian District, Beijing, China
Bo Liu:
1) School of Mechanics and Civil Engineering, China University of Mining and Technology (Beijing), Ding No.11 Xueyuan Road, Haidian District, Beijing, China
2) State Key Laboratory of Deep Geomechanics and Underground Engineering, No.16 Qinghua East Road, Haidian District, Beijing, China
Xiaojuan Shu and Mingyan Shen: School of Civil Engineering, Hunan University of Science and Technology,
Taoyuan Road, Yuhu District, Xiangtan, China

Abstract
Shear walls are a typical member under a complex stress state and have complicated mechanical properties and failure modes. The separated-elements model Genetic Evolutionary Structural Optimization (GESO), which is a combination of an elastic-plastic stress method and an optimization method, has been introduced in the literature for designing such members. Although the separated-elements model GESO method is well recognized due to its stability, feasibility, and economy, its adequacy has not been experimentally verified. This paper seeks to validate the adequacy of the separated-elements model GESO method against experimental data and demonstrate its feasibility and advantages over the traditional elastic stress method. Two types of reinforced concrete shear wall specimens, which had the location of an opening in the middle bottom and the center region, respectively, were utilized for this study. For each type, two specimens were designed using the separated-elements model GESO method and elastic stress method, respectively. All specimens were subjected to a constant vertical load and an incremental lateral load until failure. Test results indicated that the ultimate bearing capacity, failure modes, and main crack types of the shear walls designed using the two methods were similar, but the ductility indexes including the stiffness degradation, deformability, reinforcement yielding, and crack development of the specimens designed using the separated-elements model GESO method were superior to those using the elastic stress method. Additionally, the shear walls designed using the separated-elements model GESO method, had a reinforcement layout which could closely resist the actual critical stress, and thus a reduced amount of steel bars were required for such shear walls.

Key Words
shear wall; openings; genetic evolutionary algorithm; separated-elements model GESO; elastic stress method; structural optimization design

Address
Hu Z. Zhang:
1) Hunan Provincial Key Laboratory of Structures for Wind Resistance and Vibration Control, Hunan University of Science and Technology, Xiangtan, China
2) Hunan Provincial Key Lab on Damage Diagnosis for Engineering Structures, Hunan University, Changsha, China
Xia Liu, Wei J. Yi and Yao H. Deng: Hunan Provincial Key Lab on Damage Diagnosis for Engineering Structures, Hunan University, Changsha, China

Abstract
This paper predicts the flexural behaviour of reinforced concrete (RC) beams strengthened with a precast strip of ultra-high performance fiber-reinforced concrete (UHPFRC). In the first phase, ultimate load capacity of preloaded and strengthened RC beams by UHPFRC was predicted by using various analytical models available in the literature. RC beams were preloaded under static loading approximately to 70%, 80% and 90% of ultimate load of control beams. The models such as modified Kaar and sectional analysis predicted the ultimate load in close agreement to the corresponding experimental observations. In the second phase, the famous fatigue life models such as Papakonstantinou model and Ferrier model were employed to predict the number of cycles to failure and the corresponding deflection. The models were used to predict the life of the (i) strengthened RC beams after subjecting them to different pre-loadings (70%, 80% and 90% of ultimate load) under static loading and (ii) strengthened RC beams after subjecting them to different preloading cycles under fatigue loading. In both the cases precast UHPFRC strip of 10 mm thickness is attached on the tension face. It is found that both the models predicted the number of cycles to failure and the corresponding deflection very close to the experimental values. It can be concluded that the models are found to be robust and reliable for cement based strengthening systems also. Further, the Wang model which is based on Palmgren-Miner

Key Words
RC beam; static loading; pre-damage; ultra high performance fiber reinforced concrete; retrofitting; fatigue loading; analytical models

Address
Ramachandra Murthy A: CSIR-Structural Engineering Research Centre, Chennai, India, 600113
M. Aravindan and P. Ganesh: AcSIR, CSIR-Structural Engineering Research Centre, Chennai, India, 600113

Abstract
In the steel structures design, beam-to-column connections are usually considered either rigid or pinned, while their actual behavior lies between these two ideal cases. This consideration has a major influence on the results of the local and the global behavior of steel structures. This influence is noticed in the case of a static analysis, and has an important effect in the case of a dynamic analysis. In fact, pinned and rigid nodes can be considered as two specific cases of a semi-rigid behavior. To study the efficiency of the classification adopted in Eurocode 3, a numerical simulation of semi-rigid nodes has been carried out using the software ANSYS. In the aim to validate this simulation, the numerical results are compared to those of an analytical approach. After that, the validated numerical simulation has been used, to evaluate the efficiency of the classification adopted by the Eurocode 3, regarding semi-rigid connections. Finally, a new method is proposed to define a more accurate evaluation about semi-rigid connections.

Key Words
steel frames; semi rigid connection; fixity factor; dynamic analysis

Address
Djouaher Fatma Zohra and Ihaddoudene Touati Abd Nacer: Faculty of Civil Engineering, University of Sciences and Technology HOUARI BOUMEDIENE, BP 32 EL ALIA 16111
BAB EZZOUAR Algiers Algeria


Abstract
The transverse free vibration of chiral double-walled carbon nanotube (DWCNTs) embedded in elastic medium is modeled by the non-local elasticity theory and Euler Bernoulli beam model. The governing equations are derived and the solutions of frequency are obtained. According to this study, the vibrational mode number, the small-scale coefficient, the Winkler parameter and chirality of double-walled carbon nanotube on the frequency ratio (xN) of the (DWCNTs) are studied and discussed. The new features of the vibration behavior of (DWCNTs) embedded in an elastic medium and the present solutions can be used for the static and dynamic analyses of double-walled carbon nanotubes.

Key Words
vibration; nanotube; zigzag; armchair; chirality; non-local

Address
Ahmed Dihaj and Mustapha Meradjah: Laboratoire des Materiaux et Hydrologie, Universite de Sidi Bel Abbes, BP 89 Cite Ben M\'hidi, 22000 Sidi Bel Abbes, Algerie
Mohamed Zidour:
1) Universite Ibn Khaldoun, BP 78 Zaaroura, 14000 Tiaret, Algerie
2) Laboratoire de Geomatique et Developpement Durable, Universite Ibn Khaldoun de Tiaret, Algerie
Kaddour Rakrak:
1) Laboratoire de Modelisation et Simulation Multi-echelle, Universite de Sidi Bel Abbes, Algerie
2) UniversiteIbn Khaldoun, BP 78 Zaaroura, 14000 Tiaret, Algerie
Houari Heireche and Awda Chemi: Laboratoire de Modelisation et Simulation Multi-echelle, Universite de Sidi Bel Abbes, Algerie

Abstract
This paper reports mechanical behavior of recycled fine aggregate concretes after high temperatures. It is found that compressive strength of recycled fine aggregate concretes decline significantly as the temperature rises. The elastic modulus of recycled fine aggregate concretes decreases with the increase in temperature, and the decrease is much quicker than the decrease in compressive strength. The split tensile strength of recycled fine aggregate concrete decrease as the temperature rises. Through the regression analysis, the relationship of the mechanical behavior with temperature are proposed, including the compressive behavior, elastic modulus and split tensile strength, which are fitting the test data.

Key Words
compressive behavior; split tensile strength; elevated temperature; elastic modulus; recycled fine concrete aggregate

Address
Jiong-Feng Liang:
1) State Key Laboratory Breeding Base of Nuclear Resources and Environment, East China Institute of Technology, 418 Guanglan Road, Nanchang, P.R.China
2) Faculty of Civil & Architecture Engineering, East China Institute of Technology, 418 Guanglan Road, Nanchang, P.R.China
En Wang, Chun-Feng He and Peng Hu: Faculty of Civil & Architecture Engineering, East China Institute of Technology, 418 Guanglan Road, Nanchang, P.R.China

Abstract
An extensive research was undertaken to study the vibration serviceability of a long-span and light-weight floor subjected to human loading experimentally and numerically. Specifically, heel-drop test was first conducted to capture the floor\'s natural frequencies and damping ratios, followed by jumping and running tests to obtain the acceleration responses. In addition, numerical simulations considering walking excitation were performed to further evaluate the vibration performance of a multi-panel floor under different loading cases and walking rates. The floor is found to have a high frequency (11.67 Hz) and a low damping ratio (2.32%). The comparison of the test results with the published data from the 1997 AISC Design Guide 11 indicates that the floor exhibits satisfactory vibration perceptibility overall. The study results show that the peak acceleration is affected by the walking path, walking rate, and adjacent structure. A simpler loading case may be considered in design in place of a more complex one.

Key Words
vibration serviceability; concrete floor; human-induced loads; loading case; peak acceleration

Address
Liang Cao, Jiepeng Liu and Xuhong Zhou:
1) School of Civil Engineering, Chongqing University, Chongqing, China
2) Key Laboratory of New Technology for Construction of Cities in Mountain Area (Chongqing University), Ministry of Education, Chongqing, 400045, China
Y. Frank Chen: Department of Civil Engineering, The Pennsylvania State University, Middletown, USA


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