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CONTENTS
Volume 23, Number 1, January20 2017
 

Abstract
This paper is presented to solve the buckling problem of functionally graded truncated conical shells subjected to displacement-dependent pressure which remains normal to the shell middle surface throughout the deformation process by the semi-analytical finite strip method. Material properties are assumed to be temperature dependent, and varied continuously in the thickness direction according to a simple power law distribution in terms of the volume fraction of a ceramic and metal. The governing equations are derived based on first-order shear deformation theory which accounts for through thickness shear flexibility with Sanders-type of kinematic nonlinearity. The element linear and geometric stiffness matrices are obtained using virtual work expression for functionally graded materials. The load stiffness also called pressure stiffness matrix which accounts for variation of load direction is derived for each strip and after assembling, global load stiffness matrix of the shell which may be un-symmetric is formed. The un-symmetric parts which are due to load non-uniformity and unconstrained boundaries have been separated. A detailed parametric study is carried out to quantify the effects of power-law index of functional graded material and shell geometry variations on the difference between follower and non-follower lateral buckling pressures. The results indicate that considering pressure stiffness which arises from follower action of pressure causes considerable reduction in estimating buckling pressure.

Key Words
buckling; displacement dependent pressure; semi-analytical finite strip; FGM shells

Address
(1) Majid Khayat, Davood Poorveis:
Department of Civil Engineering, Shahid Chamran University, Ahvaz, Iran;
(2) Shapour Moradi:
Department of Mechanical Engineering, Shahid Chamran University, Ahvaz, Iran.

Abstract
The seismic performance of steel beam to concrete-encased composite column with unsymmetrical steel section joints is investigated and reported within this paper. Experimental and analytical evaluation were conducted on a total of 8 specimens with T-shaped and L-shaped steel section under lateral cyclic loading and axial compression. The test parameters included concrete strength, stirrup ratio and axial compression ratio. The response of the specimens was presented in terms of their hysterisis loop behavior, stress distribution, joint shear strength, and performance degradation. The experiment indicated good structural behavior and good seismic performance. In addition, a three-dimensional nonlinear finite-element analysis simulating was conducted to simulate their seismic behaviors. The finite-element analysis incorporated both bond-slip relationship and crack interface interaction between steel and concrete. The results were also compared with the test data, and the analytical prediction of joint shear strength was satisfactory for both joints with T-shaped and L-shaped steel section columns. The steel beam to concrete-encased composite column with unsymmetrical steel section joints can develop stable hysteretic response and large energy absorption capacity by providing enough stirrups and decreased spacing of transverse ties in column.

Key Words
concrete-encased structure; unsymmetrical; seismic behavior; numerical analysis

Address
School of Urban Construction, Yangtze University, Jingzhou, 434023, China.


Abstract
This article aims at presenting multi objective optimization of parameters that affect crashworthiness characteristics of bi-tubular structures using Taguchi method with grey relational analysis. To design the experiments, the L9 orthogonal array has been used and based on that, the inner tubes have been fabricated by varying the three influence factors such as reference diameter, length difference and numbers of sides of the polygon with three levels, but all the outer cylinders have the same diameter and length 90 mm and 135 mm respectively. Then, the tailor made bi-tubular steel structures were subjected into quasi static axial compression. From the test results it is found that the crushing behaviors of bi-tubular structures with different combinations were fairly significant. The important responses (crashworthiness indicators) specific energy absorption and crush force efficiency have been evaluated from load - displacement curve. Finally optimal levels of parameters were identified using grey relational analysis, and significance of parameters was determined by analysis of variance. The optimum crashworthiness parameters are reference diameter 80 mm, length difference 0 mm and number of sides of polygon is 3, i.e., triangle within the selected nine bi-tube combinations.

Key Words
bi-tubular structures; grey relational analysis; crashworthiness; specific energy absorption; crush force efficiency

Address
Department of Mechanical Engineering, Sethu Institute of Technology, Kariapatti-626115, Tamil Nadu, India.


Abstract
A C0 FE model developed based on an efficient higher order zigzag theory is used for hygrothermal analysis of laminated composite plates. The C0 FE model satisfies the inter-laminar shear stress continuity at the interfaces and zero transverse shear stress conditions at plate top and bottom. In this model the first derivatives of transverse displacement have been treated as independent variables to circumvent the problem of C1 continuity associated with the above plate theory. In the present theory the above mentioned C0 continuity of the present element is compensated in the stiffness matrix formulation by using penalty parameter approach. In order to avoid stress oscillations observed in the displacement based finite element, the stress field derived from temperature/moisture fields (initial strains) must be consistent with total strain field. Special steps are introduced by field consistent approach (e.g., sampling at gauss points) to compensate this problem. A nine noded C0 continuous isoparametric element is used in the proposed FE model. Comparison of present numerical results with other existing solutions shows that the proposed FE model is efficient, accurate and free of locking.

Key Words
hygrothermal; finite element; zigzag theory; laminated composites; C0
Address
(1) S.K. Singh:
School of Civil Engineering, Galgotias University, Greater Noida, 201306, U.P., India;
(2) A. Chakrabarti:
Department of Civil Engineering, Indian Institute of Technology, Roorkee-247 667, India.

Abstract
Structures submitted to Fire-After-Earthquake loading situations, are first experiencing inelastic deformations due to the seismic action and are then submitted to the thermal loading. This means that in the case of steel framed structures, at the starting point of the fire, plastic hinges have already been formed at the ends of the beams. The basic objective of this paper is the evaluation of the rotational capacity of steel I-section beams damaged due to prior earthquake loading, at increased temperatures. The study is conducted numerically and three-dimensional models are used in order to capture accurately the nonlinear behaviour of the steel beams. Different levels of earthquake-induced damage are examined in order to study the effect of the initial state of damage to the temperature-evolution of the rotational capacity. The study starts with the reference case where the beam is undamaged and in the sequel cyclic loading patterns are taken into account, which represent earthquakes loads of increasing magnitude. Additionally, the study extends to the evaluation of the ultimate plastic rotation of the steel beams which corresponds to the point where the rotational capacity of the beam is exhausted. The aforementioned value of rotation can be used as a criterion for the determination of the fire-resistance time of the structure in case of Fire-After-Earthquake situations.

Key Words
rotational capacity; steel beams; fire-after-earthquake; numerical analysis

Address
Laboratory of Structural Analysis and Design, Department of Civil Engineering, University of Thessaly, Pedion Areos, Volos, Greece.


Abstract
This study investigates numerically the behavior of tilted angle shear connectors embedded in solid concrete slabs. Two different tilted angle connectors were used, titled angle with 112.5 and 135 degrees between the angle leg and steel beam flange. A nonlinear finite element model was developed to simulate and validate the experimental push-out tests. Parametric studies were performed to investigate the variations in concrete strength and connector's dimensions. The results indicate that the ultimate strength of a tilted angle shear connector is directly related to the square root of the concrete compressive strength. The effects of variations in the geometry of tilted angle connectors on the shear capacity are discussed in details. Based on the numerical analyses, two equations are proposed to estimate the ultimate capacity of tilted angle shear connectors of 112.5 and 135 degrees in the defined range of parameters.

Key Words
shear connector; composite; tilted angle; push-out test; finite element method

Address
(1) Koosha Khorramian, Shervin Maleki:
Department of Civil Engineering, Sharif University of Technology, Tehran, Iran;
(2) Mahdi Shariati, Abdolrahim Jalali:
Faculty of Civil Engineering, University of Tabriz, Tabriz, Iran;
(3) M.M. Tahir:
UTM Construction Research Centre, Faculty of Civil Engineering, Institute for Smart Infrastructure and Innovative Construction, UTM, 81310, Johor Bahru, Johor, Malaysia.

Abstract
Steel structures often require strengthening due to the increasing life loads, or repair caused by corrosion or fatigue cracking. Carbon Fiber Reinforced Polymers (CFRP) is one of the materials used to strengthen steel structures. Most studies on strengthening steel structures have been carried out on steel beams and steel columns under centric compression load. No independent article, to the author's knowledge, has studied the effect of CFRP strengthening on steel columns under eccentric compression load, and it seems that there is a lack of understanding on behavior of CFRP strengthening on steel columns under eccentric compression load. However, this study explored the use of adhesively bonded CFRP flexible sheets on retrofitting square hollow section (SHS) steel columns under the eccentric compression load, using numerical investigations. Finite Element Method (FEM) was employed for modeling. To determine ultimate load of SHS steel columns, eight specimens with two types of section (Type A and B), strengthened using CFRP sheets, were analyzed under different coverage lengths, the number of layers, and the location of CFRP composites. Two specimens were analyzed without strengthening (control) to determine the increasing rate of the ultimate load in strengthened steel columns. ANSYS was used to analyze the SHS steel columns. The results showed that the CFRP composite had no similar effect on the slender and stocky SHS steel columns. The results also showed that the coverage length, the number of layers, and the location of CFRP composites were effective in increasing the ultimate load of the SHS steel columns.

Key Words
steel columns; CFRP; strengthening; eccentric compression load; FEM

Address
Department of Civil Engineering, Zahedan Branch, Islamic Azad University, Zahedan, Iran.

Abstract
The use of superelastic shape memory alloys (SMAs) as reinforcements in concrete structures is gradually gaining interest among researchers. Because of different mechanical properties of SMAs compared to the regular steel bars, the use of SMAs as reinforcement in the concrete may change the response of structures under seismic loads. In this study, the effect of SMAs as reinforcement in concrete structures is analytically investigated for 3-, 6- and 8-story reinforced concrete (RC) buildings. For each concrete building, three different reinforcement details are considered: (1) steel reinforcement (Steel) only, (2) SMA bar used in the plastic hinge region of the beams and steel bar in other regions (Steel-SMA), and (3), beams fully reinforced with SMA bar (SMA) and steel bar in other regions. For each case, columns are reinforced with steel bar. Incremental Dynamic Analyses (IDA) are performed using ten different ground motion records to determine the seismic performance of Steel, Steel-SMA and SMA RC buildings. Then fragility curves for each type of RC building by using IDA results for IO, LS and CP performance levels are calculated. Results obtained from the analyses indicate that 3-story frames have approximately the same spectral acceleration corresponding with failure of frames, but in the cases of 6 and 8-story frames, the spectral acceleration is higher in frames equipped with steel reinforcements. Furthermore, the probability of fragility in all frames increases by the building height for all performance levels. Finally, economic evaluation of the three systems are compared.

Key Words
concrete structures; superelastic shape memory alloys; incremental dynamic analysis; fragility curves

Address
Department of Civil Engineering, K.N.Toosi University of Technology, No. 1346, ValiAsr-Street, Mirdamad Intersection, P.O. Box 15875-4416, Tehran, Iran.


Abstract
Design of stepwise foam claddings subjected to air-blast is performed based on random Voronoialgorithm. FE models are constructed using the random Voronoialgorithm, and numerical analysis is carried out to simulate deformation mode and energy absorption of the cladding by the ABAQUS/Explicit software. The FE model is validated by test result, and good agreement is achieved. The deformation patterns are presented to give an insight into the influences of distribution on deformation mechanisms. The energy absorbed by the stepwise foam cladding is examined, and the parameter effects, including layer number, gradient, and blast loading, are discussed. Results indicate that the energy absorption capacity increases with the number of layer, gradient degree, and blast pressure increasing.

Key Words
Voronoi; air-blast; foam; cladding

Address
College of Science, National University of Defense Technology, 410073 Changsha, P.R. China.


Abstract
A new type of moment-resisting bolted connection was developed for use in composite steel- concrete construction to connect composite open section steel beams to concrete filled steel square tubular columns. The connection was made possible using anchored blind bolts along with two through bolts. It was designed to act compositely with the in-situ reinforced concrete slab to achieve an enhanced stiffness and strength. The developed connection was incorporated in the design of a medium rise (five storey) commercial building which was located in low to medium seismicity regions. The lateral load resisting system for the design building consisted of moment resisting frames in two directions. A major full scale test on a sub-assembly of a perimeter moment-resisting frame of the model building was conducted to study the system behaviour incorporating the proposed connection. The behaviour of the proposed connection and its interaction with the floor slab under cyclic loading representing the earthquake events with return periods of 500 years and 2500 years was investigated. The proposed connection was categorized as semi rigid for unbraced frames based on the classification method presented in Eurocode 3. Furthermore, the proposed connection, composite with the floor slab, successfully provided adequate lateral load resistance for the model building.

Key Words
Ajax anchored blind bolts; concrete filled steel hollow sections; composite steel-concrete connections; T-stub connections; moment-rotation behaviour; reinforced concrete slab on metal decking

Address
(1) Hossein Agheshlui, Helen Goldsworthy:
Department of Infrastructure Engineering, The University of Melbourne, Vic 3010, Australia;
(2) Emad Gad:
Faculty of Engineering & Industrial Sciences, Swinburne University of Tech., Vic 3122, Australia;
(3) Olivia Mirza:
School of Computing, Engineering & Mathematics, University ofWestern Sydney, NSW, 2751, Australia.

Abstract
Determining limit load for a pressure bearing structure using elastic-plastic finite element analysis was computationally very expensive. A series of robust methods using elastic modulus adjustment techniques (EMAP) to identify the limit load directly were proposed. The numerical implementation of the robust method had the potential to be an attractive alternative to elastic-plastic finite element analysis since it was simple, and required less computational effort and computer storage space. Another attractive feature was that the method provided a go/no go criterion for the limit load, whereas the results of an elastic-plastic analysis were often difficult to interpret near the limit load since it came from human sources. To explore the performance of the method further, it was applied to a number of configurations that include two-dimensional and threedimensional effects. In this study, limit load of cylinder with nozzle was determined by the robust methods.

Key Words
pressure vessel; limit load; robust method; ANSYS

Address
(1) Xiaohui Chen, Xingang Wang:
School of Control Engineering, Northeastern University, Qinhuangdao, 066004, China;
(2) Xiaohui Chen:
College of Mechanical Engineering, Yanshan University, Qinhuangdao, 066004, China;
(3) Bingjun Gao:
School of Chemical Engineering and Technology, Hebei University of Technology, Tianjin, 300000, China.


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