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CONTENTS
Volume 18, Number 6, June 2015
 

Abstract
Cold-formed built-up members are compression members that are common in multiple areas of steel construction, which include cold-formed steel joints and stud walls. These members are vulnerable to unique buckling behaviors; however, limited experimental research has been done in this area. Give this gap, experimental testing of 71 built-up members was conducted in this study. The variations of the test specimens include multiple lengths, intermediate welds, orientations, and thicknesses. The experimental testing was devised to observe the different buckling modes of the built-up C-channels and the effects of the geometrical properties; to check for applicability of multiple intermediate welding patterns; and to evaluate both the 2001 and 2007 editions of the American Iron and Steel Institute (AISI) Specification for built-up members in pure compression. The AISI-2001 and AISI-2007 were found to give inconsistent results that at times were un-conservative or overly conservative in terms of axial strength. It was also found that orientation of the member has an important impact on the maximum failure load on the member.

Key Words
cold-formed steel, axial compression, column, buckling, built-up steel sections

Address
(1) Kenneth A. Biggs, Chris Ramseyer:
School of Civil Engineering and Environmental Science, The University of Oklahoma, Norman, OK 73019, USA;
(2) Suhyun Ree, Thomas H.-K. Kang:
Department of Architecture and Architectural Engineering, Seoul National University, Seoul 151-744, Korea.

Abstract
A finite element model is presented for the analysis of composite steel-concrete beams based on a refined high-order theory. The employed theory satisfies all the kinematic and stress continuity conditions at the layer interfaces and considers effects of the transverse normal stress and transverse flexibility. The global displacement components, described by polynomial or combinations of polynomial and exponential expressions, are superposed on local ones chosen based on the layerwise or discrete-layer concepts. The present finite model does not need the incorporating any shear correction factor. Moreover, in the present C1-continuous finite element model, the number of unknowns is independent of the number of layers. The proposed finite element model is validated by comparing the present results with those obtained from the three-dimensional (3D) finite element analysis. In addition to correctly predicting the distribution of all stress components of the composite steel-concrete beams, the proposed finite element model is computationally economic.

Key Words
finite element; composite steel-concrete beams; refined high-order theory; transverse shear; normal stresses

Address
Department of Civil Engineering, Hakim Sabzevari University, Sabzevar, Iran.

Abstract
In order to investigate the behaviour of lying multi-stud connectors in cable-pylon anchorage zone, twenty-four push-out tests are carried out with different stud numbers and diameters. The effect of concrete block width and tensile force on shear strength is investigated using the developed and verified finite element model. The results show that the shear strength of the lying multi-stud connectors is reduced in comparison with the lying single-stud connector. The reduction increases with the increasing of the number of studs in the vertical direction. The influence of the stud number on the strength reduction of the lying multi-stud connectors is decreased under combined shear and tension loads compared with under pure shear. Yet, due to multi-stud effect, they still can't be ignored. The concrete block width has a non-negligible effect on the shear strength of the lying multi-stud connectors and therefore should be chosen properly when designing push-out specimens. No obvious difference is observed between the strength reductions of the studs with 22 mm and 25 mm diameters. The shear strengths obtained from the tests are compared with those predicted by AASHTO LRFD and Eurocode 4. Eurocode 4 generally gives conservative predictions of the shear strength, while AASHTO LRFD overestimates the shear strength. In addition, the lying multi-stud connectors with the diameters of 22 m and 25 mm both exhibit adequate ductility according to Eurocode 4. An expression of load-slip curve is proposed for the lying multi-stud connectors and shows good agreement with the test results.

Key Words
cable-pylon anchorage zone; lying multi-stud connectors; push-out tests; strength reduction; load-slip relationship; FEM analysis

Address
(1) Zhaofei Lin, Yuqing Liu:
Department of Bridge Engineering, Tongji University, Shanghai, China;
(2) Jun He:
School of Civil Engineering and Architecture, Changsha University of Science and Technology, Hunan, China.

Abstract
A radially retractable roof structure based on the concept of the hybrid grid shell is proposed in this paper. The single-layer steel trusses of the radially foldable bar structure are diagonally stiffened by cables, which leads to a single-layer lattice shell with triangular mesh. Then comparison between the static behavior between the retractable hybrid grid shell and the corresponding foldable bar shell with quadrangular mesh is discussed. Moreover, the effects of different structural parameters, such as the rise-to-span ratio, the bar cross section area and the pre-stress of the cables, on the structural behaviors are investigated. The results show that prestressed cables can strengthen the foldable bar shell with quadrangular mesh. Higher structural stiffness is anticipated by introducing cables into the hybrid system. When the rise-span ratio is equal to 0.2, where the joint displacement reaches the minimal value, the structure shape of the hyrbid grid shell approaches the reasonable arch axis. The increase of the section of steel bars contributes a lot to the integrity stiffness of the structure. Increasing cable sections would enhance the structure stiffness, but it contributes little to axial forces in structural members. And the level of cable prestress has slight influence on the joint displacements and member forces.

Key Words
hybrid structure; grid shell; retractable roof; foldable bar structure; static behavior

Address
(1) Jianguo Cai, Chao Jiang, Jian Feng:
Key Laboratory of C & PC Structures of Ministry of Education, National Prestress Engineering Research Center, Southeast University, Nanjing 210096, China;
(2) Xiaowei Deng:
Department of Structural Engineering, University of California, San Diego, USA;
(3) Yixiang Xu:
Department of Civil Engineering, Strathclyde University, Glasgow G12 8QQ, United Kingdom.

Abstract
Semi-rigid connections are the actual behavior of beam-to-column connections in steel frames. However, the behavior of semi-rigid connections is not taken into account for the simplicity in the conventional analysis and design of steel frames. A computer-based analysis and design has been studied for the three-dimensional steel frames with semi-rigid connections. The nonlinear analysis which includes the effects of the flexibility of connections is used for this study. It is designed according to the buckling and combined stress constraints under the present loading after the joint deformations and the member end forces of the space frame are determined by the stiffness matrix method. The semi-rigid connection type is limited to the top and bottom angles with a double web angle connection. The Frye-Morris polynomial model is used to describe the non-linear behavior of semi-rigid connections. Various design examples are presented to demonstrate the efficiency of the method. The results of design and analysis of unbraced semi-rigid frames are compared to the results of unbraced rigid frames under the same design requirements.

Key Words
semi-rigid connection; stiffness method; space frames; nonlinear analysis; structural analysis; structural design

Address
(1) Merve Sagiroglu:
Department of Civil Engineering, Erzurum Technical University, Erzurum, 25070, Turkey;
(2) Abdulkadir Cuneyt Aydin:
Department of Civil Engineering, Ataturk University, Erzurum, 25240, Turkey.

Abstract
The paper presents the details and results of an experimental study on bolted end-plate joints of industrial type steel building frames. The investigated joints are commonly used in Lindab-Astron industrial buildings and are optimized for manufacturing, erection and durability. The aim of the research was to provide an experimental background for the design model development by studying load-bearing capacity of joints, bolt force distribution, and end-plate deformations. Because of the special joint details, (i.e., joints with four bolts in one bolt-row and HammerHead arrangements), the Eurocode 3 standardized component model had to be improved and extended. The experimental programme included six different end-plate and bolt arrangements and covered sixteen specimens. The steel grade of test specimens was S355, the bolt diameter M20, whereas the bolt grade was 8.8 and 10.9 for the two series. The end-plate thickness varied between 12 mm and 24 mm. The specimens were investigated under pure bending conditions using a four-point-bending test arrangement. In all tests the typical displacements and the bolt force distribution were measured. The end-plate plastic deformations were measured after the tests by an automatic measuring device. The measured data were presented and evaluated by the moment-bolt-row force and momentdistance from centre of compression diagrams and by the deformed end-plate surfaces. From the results the typical failure modes and the joint behaviour were specified and presented. Furthermore the influence of the end-plate thickness and the pretension of the bolts on the behaviour of bolted joints were analysed.

Key Words
bolted end-plate connection; beam-to-beam joint; experiment; four bolts in one bolt-row; HammerHead joint arrangement

Address
Department of Structural Engineering, Budapest University of Technology and Economics, Mügyetem rkp. 3, H-1111 Budapest, Hungary.

Abstract
Recently, in recognition of their outstanding structural performance, the use of Concrete Filled Steel Tube (CFT) columns has been increased. New shape welded built-up square tube was developed by the authors for broader usability using thin steel plates which were bent to be L-shaped (Channel) and each unit members were welded to form square steel tube as an cost-efficient use of expensive steel. In addition, since the rib placed at the center of the tube width acts as an anchor; higher load capacity of buckling is achievable. In order to apply the new shape built-up square columns, the structural behavior and stress distribution with parameter width of thickness (b/t), with and without rib were predicted. The New shape welded built-up square tube effectively delayed the local buckling of the steel tube, which led to a greater strength and ductility than regular HSS.

Key Words
built-up square column; composite effect; width of thickness; concentric axial load

Address
(1) Sun-Hee Kim, Sung-Mo Choi:
Department of Architectural Engineering, University of Seoul, Cheonnong-dong 90, Dongdaemun-Gu, Seoul, 130-743, Republic of Korea;
(2) Kyong-Soo Yom:
Harmony Engineering, Guro-Gu Seoul 152-051, Republic of Korea.

Abstract
The effect of cutting off fibers on transient load in a polymeric matrix composite lamina was studied in this paper. The behavior of fibers was considered to be linear elastic and the matrix behavior was considered to be linear viscoelastic. To model the viscoelastic behavior of matrix, a three parameter solid model was employed. To conduct this research, finite difference method was used. The governing equations were obtained using Shear-lag theory and were solved using boundary and initial conditions before and after the development of break. Using finite difference method, the governing integro-differential equations were developed and normal stress in the fibers is obtained. Particular attention is paid the dynamic overshoot resulting when the fibers are suddenly broken. Results show that considering viscoelastic properties of matrix causes a decrease in dynamic load concentration factor and an increase in static load concentration factor. Also with increases the number of broken fibers, trend of increasing load concentration factor decreases gradually. Furthermore, the overshoot of load in fibers adjacent to the break in a polymeric matrix with high transient time is lower than a matrix with lower transient time, but the load concentration factor in the matrix with high transient time is lower.

Key Words
viscoelasticity; load concentration factor; transient stress; unidirectional lamina; finite difference method; break

Address
(1) Arash Reza:
Department of Mechanical Engineering, Ahvaz Branch, Islamic Azad University, Ahvaz, Iran;
(2) Hamid M. Sedighi:
Mechanical Engineering Department, Faculty of Engineering, Shahid Chamran University of Ahvaz, Ahvaz, Iran;
(3) Mahdi Soleimani:
Department of Mechanical Engineering, Shoushtar Branch, Islamic Azad University, Shoushtar, Iran.

Abstract
This study evaluated the localized stress condition of the real corroded deck surface of an orthotropic steel bridge because severe corrosion damage on the deck surface and fatigue cracking were reported. Thus, a three-dimensional finite element (FE) analysis model was created based on measurements of the corroded orthotropic steel deck surface to examine the stress level dependence on the corrosion condition. Based on the FE analysis results, it could be confirmed that a high stress concentration and irregular stress distribution can develop on the deck surface. The stress level was also increased by approximately 1.3-1.5times as a result of the irregular corroded surface. It was concluded that this stress concentration could increase the possibility of fatigue cracking in the deck surface because of the surface roughness of the orthotropic steel bridge deck.

Key Words
real corroded surface; orthotropic steel deck; stress level; principal stress; FE analysis

Address
(1) Shigenobu Kainuma, Young-Soo Jeong:
Department of Civil Engineering, Kyushu University, 819-0395, Fukuoka, Japan;
(2) Jin-Hee Ahn:
Department of Civil Engineering, Gyeongnam National University of Science and Technology, 660-758, Jinju, Gyeongnam, Korea.

Abstract
A new refined hyperbolic shear deformation theory (RHSDT), which involves only four unknown functions as against five in case of other shear deformation theories, is presented for the thermoelastic bending analysis of functionally graded sandwich plates. Unlike any other theory, the number of unknown functions involved is only four, as against five in case of other shear deformation theories. The theory presented is variationally consistent, does not require shear correction factor, and gives rise to transverse shear stress variation such that the transverse shear stresses vary parabolically across the thickness satisfying shear stress free surface conditions. The sandwich plate faces are assumed to have isotropic, two-constituent material distribution through the thickness, and the modulus of elasticity, Poisson's ratio of the faces, and thermal expansion coefficients are assumed to vary according to a power law distribution in terms of the volume fractions of the constituents. The core layer is still homogeneous and made of an isotropic ceramic material. Several kinds of sandwich plates are used taking into account the symmetry of the plate and the thickness of each layer. The influences played by the transverse shear deformation, thermal load, plate aspect ratio and volume fraction distribution are studied. Numerical results for deflections and stresses of functionally graded metal-ceramic plates are investigated. It can be concluded that the proposed theory is accurate and simple in solving the thermoelastic bending behavior of functionally graded plates.

Key Words
hyperbolic plate theory; thermoelastic bending response; functionally graded material; sandwich plate

Address
(1) Ali Bouchafa, Abdelouahed Tounsi:
Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Civil Engineering Department, Algeria;
(2) Mohamed Bachir Bouiadjra, Mohammed Sid Ahmed Houari, Abdelouahed Tounsi:
Laboratoire des Structures et Matériaux Avances dans le Génie Civil et Travaux Publics, Université de Sidi Bel Abbes, Faculté de Technologie, Département de génie civil, Algeria;
(3) Mohammed Sid Ahmed Houari:
Département de génie civil, Université de Mascara, Algeria.

Abstract
Eccentrically braced frames (EBFs) often use conventional steel with medium yield strength. This system requires structural members with large cross-sections for well seismic behavior, which leads to increased material costs. In eccentrically braced frames with high strength steel combination (HSS-EBFs), links use Q345 steel (specified nominal yield strength 345 MPa), braces use Q345 steel or high strength steel while other structural members use high strength steel (e.g., steel Q460 with the nominal yield strength of 460 MPa or steel Q690 with the nominal yield strength of 690 MPa). For this approach can result in reduced steel consumption and increased economic efficiency. Several finite element models of both HSS-EBFs and EBFs are established in this paper. Nonlinear hysteretic analyses and nonlinear time history analyses are conducted to compare seismic performance and economy of HSS-EBFs versus EBFs. Results indicate that the seismic performance of HSS-EBFs is slightly poorer than that of EBFs under the same design conditions, and HSS-EBFs satisfy seismic design codes and reduce material costs.

Key Words
high strength steel; eccentrically braced frames; seismic performance; finite element; nonlinear analysis

Address
College of Civil Engineering, Xi'an University of Architecture and Technology, Xi'an 710055, P.R. China.

Abstract
In this paper mechanical behavior of the functional gradient materials (FGM) micro-gripper under thermal load and DC voltage is numerically investigated taking into account the effect of intermolecular forces. In contrary to the similar previous works, which have been conducted for homogenous material, here, the FGM material has been implemented. It is assumed that the FGM micro-gripper is made of metal and ceramic and that material properties are changed continuously along the beam thickness according to a given function. The nonlinear governing equations of the static and dynamic deflection of microbeams have been derived using the coupled stress theory. The equations have been solved using the Galerkin based step-by-step linearization method (SSLM). The solution procedure has been evaluated against available data of literature showing good agreement. A parametric study has been conducted, focusing on the combined effects of important parameters included DC voltage, temperature variation, geometrical dimensions and ceramic volume concentration on the dynamic response and stability of the FGM micro-gripper.

Key Words
FGM micro-gripper; electrostatic force; intermolecular force; natural frequency; stability

Address
(1) Reza Jahangiri, Hadi Jahangiri:
Department of Mechanical Engineering, Salmas Branch, Islamic Azad University, Salmas, Iran;
(2) Hamed Khezerloo:
Department of Civil Engineering, Salmas Branch, Islamic Azad University, Salmas, Iran.

Abstract
The nonlinear static analysis of structure, which is under the effect of lateral loads and provides the capacity curve of the structure, is defined as a push-over analysis. Ordinarily, by using base shear and the lateral displacement of target point, the capacity curve is obtained. The speed and ease of results interpretation in this method is more than that of the NRHA responses. In this study, the nonlinear static analysis is applied on the semi-rigid steel gabled frames. It should be noted that the members of this structure are analyzed as a prismatic beam-column element in two states of semi-rigid connections and supports. The gabled frame is modeled in the OpenSees software and analyzed based on the displacement control at the target point. The lateral displacement results, calculated in the top level of columns, are reported. Furthermore, responses of the structure are obtained for various support conditions and the rigidity of nodal connections. Ultimately, the effect of semi-rigid connections and supports on the capacity and the performance point of the structure are presented in separated graphs.

Key Words
nonlinear static analysis; gabled steel frame; beam-column element; semi-rigid connection; OpenSees software

Address
Department of Civil Engineering, Engineering Faculty, Ferdowsi University of Mashhad, Mashhad, Iran.

Abstract
This study explores the lateral deflections of diagonal braces in concentrically-braced earthquakeresisting frames. The performance of this widely-used system is often compromised by the flexural buckling of slender braces in compression. In addition to reducing the compressive resistance, buckling may also cause these members to undergo sizeable lateral deflections which could damage surrounding structural components. Different approaches have been used in the past to predict the mid-length lateral deflections of cyclically loaded steel braces based on their theoretical deformed geometry or by using experimental data. Expressions have been proposed relating the mid-length lateral deflection to the axial displacement ductility of the member. Recent experiments were conducted on hollow and concrete-filled circular hollow section (CHS) braces of different lengths under cyclic loading. Very slender, concrete-filled tubular braces exhibited a highly ductile response, undergoing large axial displacements prior to failure. The presence of concrete infill did not influence the magnitude of lateral deflection in relation to the axial displacement, but did increase the number of cycles endured and the maximum axial displacement achieved. The corresponding lateral deflections exceeded the deflections observed in the majority of the previous experiments that were considered. Consequently, predictive expressions from previous research did not accurately predict the mid-height lateral deflections of these CHS members. Mid-length lateral deflections were found to be influenced by the member non-dimensional slenderness (

Key Words
cyclic loading; concentrically-braced frames; tubular structures; concrete-filled tubes; earthquake-resisting buildings

Address
(1) Therese Sheehan, Dennis Lam:
School of Engineering and Informatics, University of Bradford, Richmond Road, Bradford BD7 1DP, United Kingdom;
(2) Tak-Ming Chan, Dennis Lam:
Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong.


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