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CONTENTS
Volume 64, Number 5, December10 2017
 

Abstract
In this work, a new hyperbolic shear deformation beam theory is proposed based on a modified couple stress theory (MCST) to investigate the bending and free vibration responses of functionally graded (FG) micro beam made of porous material. This non-classical micro-beam model introduces the material length scale coefficient which can capture the size influence. The non-classical beam model reduces to the classical beam model when the material length scale coefficient is set to zero. The mechanical material properties of the FG micro-beam are assumed to vary in the thickness direction and are estimated through the classical rule of mixture which is modified to approximate the porous material properties with even and uneven distributions of porosities phases. Effects of several important parameters such as power-law exponents, porosity distributions, porosity volume fractions, the material length scale parameter and slenderness ratios on bending and dynamic responses of FG micro-beams are investigated and discussed in detail. It is concluded that these effects play significant role in the mechanical behavior of porous FG micro-beams.

Key Words
shear deformation theory; bending; vibration; micro beam; porosity; functionally graded material

Address
Lemya Hanifi Hachemi Amar : Faculté de Technologie, Département de Génie Civil et Hydraulique, Université Dr Tahar Moulay, BP 138 Cité En-Nasr 20000 Saida, Algérie; Laboratoire des Ressources Hydriques et Environnement, Université Dr Tahar Moulay, BP 138 Cité En-Nasr 20000 Saida, Algérie

Abdelhakim Kaci : Faculté de Technologie, Département de Génie Civil et Hydraulique, Université Dr Tahar Moulay, BP 138 Cité En-Nasr 20000 Saida, Algérie; Material and Hydrology Laboratory, Faculty of Technology, Civil Engineering Department, University of Sidi Bel Abbes, Algeria

Abdelouahed Tounsi : Material and Hydrology Laboratory, Faculty of Technology, Civil Engineering Department, University of Sidi Bel Abbes, Algeria; Department of Civil and Environmental Engineering, King Fahd University of Petroleum & Minerals,
31261 Dhahran, Eastern Province, Saudi Arabia; Laboratoire de Modélisation et Simulation Multi-échelle, Département de Physique, Faculté des Sciences Exactes,
Département de Physique, Université de Sidi Bel Abbés, Algeria



Abstract
The non-linear behaviour of integral infilled frames (in which the infill and the frame are bonded together with help of various interface materials) is studied both experimentally and numerically. The experiments were carried out on one-sixth scale two-bay and three-storey reinforced concrete frames with and without infill against static cyclic loading. Three interface materials - cement mortar, cork and foam have been used in between the infill and the frame. The infill, interface and the frame are bonded together is called integral frame. The linear and non-linear behaviors of two dimensional bare frame and integral infilled frame have been studied numerically using the commercial finite element software SAP 2000. Linear finite element analysis has been carried out to quantify the effect of various interface materials on the infilled frames with various combinations of 21 cases and the results compared. The modified configuration that used all three interface materials offered better resistance above others. Therefore, the experiments were limited to this modified infilled frame case configuration, in addition to conventional (A1-integral infilled frame with cement mortar as interface) and bare frame (A0-No infill). The results have been compared with the numerical results done initially. It is found that stiffness of bare frame increased by infilling and the strength of modified frame increased by 20% compare to bare frame. The ductility ratio of modified infilled frame was 42% more than that of the conventional infilled frame. In general, the numerical result was found to be in good agreement with experimental results for initial crack load, ultimate load and deformed pattern of infill.

Key Words
infilled frame; cement mortar; cork; foam; cyclic loading; earthquake engineering; finite element analysis

Address
S. Muthukumar : Department of Civil Engineering, SRM University, Kattankulathur, 603203, Tamil Nadu, India

K.S. Satyanarayanan : Department of Civil Engineering, SRM University, Kattankulathur, 603203, Tamil Nadu, India

K. Senthil : Department of Civil Engineering, NIT Jalandhar, Jalandhar, 144011, Punjab, India

Abstract
Fiber reinforced polymer (FRP) sheets are the most efficient structural materials in terms of strength to weight ratio and its application in strengthening and retrofitting of a structure or structural elements are inevitable. The performance enhancement of structural elements without increasing the cross sectional area and flexible nature are the major advantages of FRP in retrofitting/strengthening work. This research article presents a detailed study on the inelastic response of conventional and retrofitted Reinforced Concrete (RC) frames using Carbon Fibre Reinforced Polymers (CFRP) and Glass Fiber Reinforced Polymers (GFRP) subjected to quasi-static loading. The hysteretic behaviour, stiffness degradation, energy dissipation and damage index are the parameters employed to analyse the efficacy of FRP strengthening of brick in-filled RC frames. Repair and retrofitting of brick infilled RC frame shows an improved load carrying and damage tolerance capacity than control frame.

Key Words
retrofitting; vibration; brick infills; RC frame; frequency response function; damage index; GFRP; CFRP; vibration monitoring

Address
Balvir Singh : Department of Civil Engineering, Thapar University, Patiala, Punjab, India

R. Siva Chidambaram : CSIR-Central Building Research Institute, Uttarakhand, Roorkee-247667, India

Shruti Sharma : Department of Civil Engineering, Thapar University, Patiala, Punjab, India

Naveen Kwatra : Department of Civil Engineering, Thapar University, Patiala, Punjab, India

Abstract
The traditional design procedure of a prestressed concrete (PC) cable-stayed bridge is complex and time-consuming. The designers have to repeatedly modify the configuration of the large number of design parameters to obtain a feasible design scheme which maybe not an economical design. In order to efficiently achieve an optimum design for PC cable-stayed bridges, a multi-parameter optimization technique is proposed. In this optimization technique, the number of prestressing tendons in girder is firstly set as one of design variables, as well as cable forces, cable areas and cross-section sizes of the girders and the towers. The stress and displacement constraints are simultaneously utilized to ensure the safety and serviceability of the structure. The target is to obtain the minimum cost design for a PC cable-stayed bridge. Finally, this optimization technique is carried out by a developed PC cable-stayed bridge optimization program involving the interaction of the parameterized automatically modeling program, the finite element structural analysis program and the optimization algorithm. A low-pylon PC cable-stayed bridge is selected as the example to test the proposed optimization technique. The optimum result verifies the capability and efficiency of the optimization technique, and the significance to optimize the number of prestressing tendons in the girder. The optimum design scheme obtained by the application can achieve a 24.03% reduction in cost, compared with the initial design.

Key Words
cable-stayed bridge; prestressed concrete; multi-parameter; optimization technique; prestressing tension

Address
Qiong Gao : School of Civil Engineering, Central South University, Changsha 410075, P.R. China

Meng-Gang Yang : School of Civil Engineering, Central South University, Changsha 410075, P.R. China

Jian-Dong Qiao : School of Civil Engineering, Central South University, Changsha 410075, P.R. China

Abstract
This paper deals with the optimum cost design of partially prestressed concrete I crosssectioned beams by using Genetic Algorithms. For this purpose, the optimum cost design of two selected example problems that have different characteristics in behavior are performed via Genetic Algorithms by determining their objective functions, design variables and constraints. The results obtained from the technical literature are compared with the ones obtained from this study. The interpretation of the results show that the design of partially prestressed concrete I crossectioned beams from cost point of view by using Genetic Algorithms is 35~50 % more economical than the traditional ones (technical literature) without conceding safety.

Key Words
optimum; partially prestressed concrete; beam; Genetic Algorithm; cost

Address
Erdem Türkeli : Construction Department, Vocational School of Technical Sciences, Ordu University, Ordu, Turkey

Hasan Tahsin Öztürk : Department of Civil Engineering, Faculty of Technology, Karadeniz Technical University, Trabzon, Turkey

Abstract
This paper is concerned with the static analysis of variable thickness of two directional functionally graded porous materials (FGPM) circular plate resting on a gradient hybrid foundation (Horvath-Colasanti type) with friction force and subjected to compound mechanical loads (e.g., transverse, in-plane shear traction and concentrated force at the center of the plate).The governing state equations are derived in terms of displacements based on the 3D theory of elasticity, assuming the elastic coefficients of the plate material except the Poisson‟s ratio varying continuously throughout the thickness and radial directions according to an exponential function. These equations are solved semi-analytically by employing the state space method (SSM) and one-dimensional differential quadrature (DQ) rule to obtain the displacements and stress components of the FGPM plate. The effect of concentrated force at the center of the plate is approximated with the shear force, uniformly distributed over the inner boundary of a FGPM annular plate. In addition to verification study and convergence analysis, numerical results are displayed to show the effect of material heterogeneity indices, foundation stiffness coefficients, foundation gradient indices, loads ratio, thickness to radius ratio, compressibility, porosity and friction coefficient of the foundation on the static behavior of the plate. Finally, the responses of FG and FG porous material circular plates to compound mechanical loads are compared.

Key Words
functionally graded Porous material; heterogeneous hybrid foundation; circular plate; elasticity; compressibility; porosity; semi-analytical method; friction

Address
A. Behravan Rad : Engineering Department, Zamyad Company, 15 Km Karaj Old Road, P.O 1386183741, Tehran, Iran

M.R. Farzan-Rad : Ministry of Education, Shahryar Branch, 3351739155, Shahryar, Iran

K. Mohammadi Majd : Engineering Department, Zamyad Company, 15 Km Karaj Old Road, P.O 1386183741, Tehran, Iran


Abstract
A new theory of weightless sagging planer elasto-flexible cables under point loads is developed earlier by the authors and used for predicting the nonlinear dynamic response of cable-suspended linear elastic beams. However, this theory is not valid for nonlinear elastic cracked concrete beams possessing different positive and negative flexural rigidity. In the present paper, the flexural response of simply supported cracked concrete beams suspended from cables by two hangers is presented. Following a procedure established earlier, rate-type constitutive equations and third order nonlinear differential equations of motion for the structures undergoing small elastic displacements are derived. Upon general quasi-static loading, negative nodal forces, moments and support reactions may be introduced in the cable-suspended concrete beams and linear modal frequencies may abruptly change. Subharmonic resonances are predicted under harmonic loading. Uncoupling of the nodal response is proposed as a more general criterion of crossover phenomenon. Significance of the bilinearity ratio of the concrete beam and elasto-configurational displacements of the cable for the structural response is brought out. The relevance of the proposed theory for the analysis and the design of the cable-suspended bridges is critically evaluated.

Key Words
cable-suspended concrete beams; configurational nonlinearity; rate-type constitutive equations; third-order equations of motion; crossover phenomenon

Address
Pankaj Kumar : Department of Civil Engineering, Indian Institute of Technology Delhi, Hauz Khas, New Delhi, India

Abhijit Ganguli : Department of Civil Engineering, Indian Institute of Technology Tirupati, Tirupati, India

Gurmail Benipal : Department of Civil Engineering, Indian Institute of Technology Delhi, Hauz Khas, New Delhi, India

Abstract
This paper reports the numerical investigation conducted to study the influence of Local-Distortional (L-D) interaction mode buckling on post buckling strength erosion in fixed ended lipped channel cold formed steel columns. This investigation comprises of 81 column sections with various geometries and yield stresses that are carefully chosen to cover wide range of strength related parametric ratios like (i) distortional to local critical buckling stress ratio (0.910.91<=FCRD/FCRL<=4.05) (ii) non dimensional local slenderness ratio (0.88<=tL<=3.54) (iii) non-dimensional distortional slenderness ratio (0.68<=tD<=3.23) and (iv) yield to non-critical buckling stress ratio (0.45 to 10.4). The numerical investigation is carried out by conducting linear and nonlinear shell finite element analysis (SFEA) using ABAQUS software. The non-linear SFEA includes both geometry and material non-linearity. The numerical results obtained are deeply analysed to understand the post buckling mechanics, failure modes and ultimate strength that are influenced by L-D interaction with respect to strength related parametric ratios. The ultimate strength data obtained from numerical analysis are compared with (i) the experimental tests data concerning L-D interaction mode buckling reported by other researchers (ii) column strength predicted by Direct Strength Method (DSM) column strength curves for local and distortional buckling specified in AISI S-100 (iii) strength predicted by available DSM based approaches that includes L-D interaction mode failure. The role of flange width to web depth ratio on post buckling strength erosion is reported. Then the paper concludes with merits and limitations of codified DSM and available DSM based approaches on accurate failure strength prediction.

Key Words
lipped channel columns; Local-Distortional interaction; secondary bifurcation; cold formed steel; Direct Strength Method (DSM); numerical simulation; Finite Element Analysis (FEA); Generalized Beam Theory (GBT)

Address
Hareesh Muthuraj : School of Civil and Chemical Engineering, VIT University, Vellore, TamilNadu-632014, India

S.K. Sekar : School of Civil and Chemical Engineering, VIT University, Vellore, TamilNadu-632014, India

Mahen Mahendran : School of Civil and Built Environment, QUT, Brisbane, Australia

O.P. Deepak : School of Civil and Chemical Engineering, VIT University, Vellore, TamilNadu-632014, India


Abstract
In general, conventional analysis and design of reinforced concrete (RC) frame structures overlook the role of beamcolumn (RCBC) joints. Nowadays, the rigid joint model is one of the most common for RCBC joints: the joint is assumed to be rigid (unable to deform) and stronger than the adjacent beams and columns (does not fail before them). This model is popular because (i) the application of the capacity design principles excludes the possibility of the joint failing before the adjacent beams and (ii) many believe that the actual behaviour of RCBC joints designed according to the seismic codes produced mainly after the 1980s can be assumed to be nominally rigid. This study investigates the relevance of the deformation of RCBC joints in a standard pushover analysis at several levels: frame, storey, element and cross-section. Accordingly, a RC frame designed according to preliminary versions of EN 1992-1-1 and EN 1998-1 was analysed, considering the nonlinear behaviour of beams and columns by means of a standard sectional fibre model. Two alternative models were used for the RCBC joints: the rigid model and an explicit component based nonlinear model. The effect of RCBC joints modelling was found to be twofold: (i) the flexibility of the joints substantially increases the frame lateral deformation for a given load (30 to 50%), and (ii) in terms of seismic performance, it was found that joint flexibility (ii-1) appears to have a minor effect on the force and displacement corresponding to the performance point (seismic demand assessed at frame level), but (ii-2) has a major influence on the seismic demand when assessed at storey, element and cross-section levels.

Key Words
beam-column joint; reinforced concrete cast-in-situ frames structures; pushover analysis; nonlinear behaviour

Address
Ricardo Costa : Department of Civil Engineering, ISISE, University of Coimbra, Coimbra, Portugal

Paulo Providência : Department of Civil Engineering, INESC Coimbra, University of Coimbra, Coimbra, Portugal

Miguel Ferreira : CERIS, University of Lisbon, Lisbon, Portugal

Abstract
The aim of this study is to accurately estimate seismic damage and the collapse mechanism of the historical stone masonry minaret \"Hafsa Sultan\", which was built in 1522. Surveying measurements and material tests were conducted to obtain a 3D solid model and the mechanical properties of the components of the minaret. The initial Finite Element (FE) model is analyzed and numerical dynamic characteristics of the minaret are obtained. The Operational Modal Analysis (OMA) method is conducted to obtain the experimental dynamic characteristics of the minaret and the initial FE model is calibrated by using the experimental results. Then, linear time history (LTH) and nonlinear time history (NLTH) analyses are carried out on the calibrated FE model by using two different ground motions. Iron clamps which used as connection element between the stones of the minaret considerably increase the tensile strength of the masonry system. The Concrete Damage Plasticity (CDP) model is selected in the nonlinear analyses in ABAQUS. The analyses conducted indicate that the results of the linear analyses are not as realistic as the nonlinear analysis results when compared with existing damage.

Key Words
historical structure; masonry; operational modal analysis; concrete damage plasticity; seismic damage estimation; tall structure

Address
H. Nohutcu : Department of Civil Engineering, Manisa Celal Bayar University, 45140, Manisa, Turkey

E. Hokelekli : Department of Civil Engineering, Bart

Abstract
The dynamic model test of dam-reservoir coupling system for a 203m high gravity dam is performed to investigate effects of reservoir water on dynamic responses of dam during earthquake. The hydrodynamic pressure under condition of full reservoir, natural frequencies and acceleration amplification factors along the dam height under conditions of full and empty reservoir are obtained from the test. The results indicate that the reservoir water have a stronger influence on the dynamic responses of dam. The measured natural frequency of the dam model under full reservoir is 21.7% lower than that of empty reservoir, and the acceleration amplification factor at dam crest under full reservoir is 18% larger than that under empty reservoir. Seismic dynamic analysis of the gravity dams with five different heights is performed with the Fluid-Structure Coupling Model (FSCM). The hydrodynamic pressures from Westergaard formula are overestimated in the lower part of the dam body and underestimated in its upper part to compare with those from the FSCM. The underestimation and overestimation are more significance with the increase of the dam height. The position of the maximum hydrodynamic pressure from the FSCM is raised with the increase of dam height. In view of the above, the Westergaard formula is modified with consideration in the influence of the height of dam, the elasticity of dam on the hydrodynamic pressure. The solutions of modified Westergaard formula are quite coincident with the hydrodynamic pressures in the model test and the previous report.

Key Words
dynamic model test; Fluid-Structure Coupling Model; hydrodynamic pressure; modified Westergaard formula; shaking table

Address
Mingming Wang : Faculty of Electric Power Engineering, Kunming University of Science and Technology, Kunming 650500, China

Yi Yang : Faculty of Electric Power Engineering, Kunming University of Science and Technology, Kunming 650500, China

Weirong Xiao : Faculty of Electric Power Engineering, Kunming University of Science and Technology, Kunming 650500, China

Abstract
This study investigates the structural performance of 3D steel pipe rack suspended scaffolding systems. For the purpose, a standard full scale 3D steel pipe rack suspended scaffolding system considering two frames, two plane trusses, purlins and wooden floor is constructed in the laboratory. A developed load transmission system was placed in these experimental systems to distribute single loads to the center of a specific area in a step-by-step manner using a load jack. After each load increment, the displacements are measured by means of linear variable differential transducers placed in several critical points of the system. The tests are repeated for five different system conditions to determine the structural performance. The means of system conditions is the numbers of the tie bars which are used to connect plane trusses under level. Finite elements models of the 3D steel pipe rack suspended scaffolding systems considering different systems conditions are constituted using SAP2000 software to support the experimental tests and to use the models in future studies. Each of models including load transmission platform is analyzed under a single loading and the displacements are obtained. In addition, to calibrate the numerical models some uncertain parameters such as elasticity modulus of wooden floor and connection rigidity of purlins to plane trusses are assessed experimentally. The results of this work demonstrate that when increasing numbers of tie bars the displacement values are decreased. Also the results obtained from developed numerical models have harmony with those of experimental. In addition, the scaffolding system with two tie bars at the beginning and at the end of the plane truss has the optimum structural performance compared the results obtained for other scaffolding system conditions.

Key Words
3D steel pipe rack suspended scaffolding system; developed load transmission platform; experimental test; finite element model; laboratory model; structural performance; tie bar

Address
Guray Arslan, Barns Sevim and Serkan Bekiroglu: Department of Civil Engineering, Yildiz Technical University, 34220, İstanbul, Turkey


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