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CONTENTS
Volume 17, Number 6, December 2014
 

Abstract
The purpose of this study is to investigate the seismic performance of reinforced concrete (RC) frames strengthened by profiled steel sheet bracing which takes the influence of infill walls into consideration. One-bay, two-story, 1/3 scale two specimens shared same feature of dimensions, one specimen consists only beams and columns; the other one is reinforced by profiled steel sheet bracing with infill walls. Hysteretic curves, envelope curves, stiffness degradation curves and energy dissipation capacities are presented based on test data. Test results indicate that the ultimate load of strengthened specimen has been improved by 225%. The stiffness of reinforced by profiled steel sheet bracing has been increased by 108%. This demonstrates that infill walls and profiled steel sheet bracing enhanced the strength and stiffness distinctly. Energy dissipation has an obvious increase after 12 cycles. This shows that the reinforced specimen is able to bear the lateral load effectively and absorb lots of seismic energy.

Key Words
reinforced concrete frames; infill walls; profiled steel sheet bracing; seismic performance; cyclic load

Address
College of Civil and Transportation Engineering, Hohai University, Nanjing, Jiangsu, P.R. China.

Abstract
The effects of anchor on fractured specimens in splitting test are simulated by DDARF method, the results of which are compared with laboratory test results. They agree well with each other. The paper contents also use the laboratory model test. The main research objects are three kinds of specimens, namely intact specimens, jointed specimens and anchored-jointed specimens. The results showed that with the joint angle increased, the weakening effects of jointed rock mass are more obvious. At these points, the rock bolts' strengthening effects on the specimens have become more significant. There is a significant impact on the failure modes of rock mass by the joint and the anchorage.

Key Words
crack propagation; discontinuous deformation analysis for rock failure; jointed rock mass; random joints; anchored-fractured specimen; anchored rock mass; laboratory experiment

Address
(1) Jing Wang, Shu-Cai Li, Li-Ping Li, Weishen Zhu, Qian-Qing Zhang, Shu-Guang Song:
Geotechnical and Structural Engineering Research Center, Shandong University, No.17923, Jingshi Road, Jinan, 250061, P.R. China;
(2) Jing Wang, Li-Ping Li:
Key Laboratory of Coal Resources Exploration and Comprehensive Utilization, Ministry of Land and Resources, P.R. China.

Abstract
The dynamic characterization is important in making accurate predictions of the seismic response of the hybrid structures dominated by different damping mechanisms. Different damping characteristics arise from the construction of the tower with different materials: steel for the upper part; reinforced concrete for the lower main part and interaction with supporting soil. The process of modeling damping matrices and experimental verification is challenging because damping cannot be determined via static tests as can mass and stiffness. The assumption of classical damping is not appropriate if the system to be analyzed consists of two or more parts with significantly different levels of damping, such as steel/ concrete mixed structure - supporting soil coupled system. The dynamic response of structures is critically determined by the damping mechanisms, and its value is very important for the design and analysis of vibrating structures. An analytical approach capable of evaluating the equivalent modal damping ratio from structural components is desirable for improving seismic design. Two approaches are considered to define and investigate dynamic characteristics of hybrid tower of cable-stayed bridges: The first approach makes use of a simplified approximation of two lumped masses to investigate the structure irregularity effects including damping of different material, mass ratio, frequency ratio on dynamic characteristics and modal damping; the second approach employs a detailed numerical step-by step integration procedure in which the damping matrices of the upper and the lower substructures are modeled with the Rayleigh damping formulation.

Key Words
damping matrix; dynamic characteristics; hybrid tower; modal damping; non-classical damping; seismic response; structural vibration

Address
(1) Faculty of Engineering, Taibah University, Madinah, Saudia Arabia;
(2) Department of Civil Engineering, Faculty of Engineering, Assiut University, Assiut, Egypt.

Abstract
This manuscript presents an experimental investigation on the effect of multi-walled carbon nanotubes (MWCNTs) addition on the tensile, flexural and impact properties of woven Kevlar fabric reinforced epoxy composites. MWCNTs were dispersed in the epoxy resin by sonication technique and the samples were fabricated by hand layup laminating procedure. Scanning electron microscopy (SEM) was used to characterize the microstructure of produced samples. The effects of adding small amounts (

Key Words
Kevlar fiber; multi-walled carbon nanotube; thermosetting resin; laminated composite; mechanical testing

Address
(1) Iman Taraghi, Abdolhossein Fereidoon:
Department of Mechanical Engineering, Semnan University, Semnan, 35131-19111, Iran;
(2) Ali Mohyeddin:
Department of Mechanical Engineering, Parand Branch, Islamic Azad University, Parand, Iran.

Abstract
The fire resistance of composite steel and concrete structures may be determined by using the simplified methods provided in EN 1994-1-2. For the particular situations not covered by the standard, an advanced calculation model might be applied, using special purpose programs for the analysis of structures in fire. The validation of these programs has always been an important issue for software developers, but also for designers and authorities. Clause 4.4.4 from EN 1994-1-2 refers to the validation of the advanced calculation models and states that these models must be validated through relevant test results. The paper presents the calculation of fire resistance of the composite columns in a high-rise building built in Romania, and focusses on the validation of the calculation model (computer program SAFIR), for this particular case. This validation, asked by the Romanian authorities, considers the available experimental results of a fire test, performed on a similar composite steel-concrete column.

Key Words
composite columns; fire design; advanced calculation model; validation; fire test

Address
Politehnica University of Timisoara, Timisoara, Romania.

Abstract
Full penetration welded steel moment-resisting frame (SMRF) structures with welded box sections are widely employed in steel bridges, where a large number of steel bridges have been in operation for over fifty years in Japan. Welding defects such as incomplete penetration at the beam-column connections of these existing SMRF steel bridge piers were observed during inspection. Previous experiments conducted by the authors' team indicate that gusset stiffeners (termed fillets in this study) at the beam-web-to-column-web joint of the beam-column connections may play an important role on the seismic performance of the connections. This paper aims to experimentally study the effect of the fillet radius on seismic performance of the connections with large welding defects. Four specimens with different sizes of fillet radii were loaded under quasi-static incremental cyclic loading, where different load-displacement relations and cracking behaviors were observed. The experimental results show that, as the size of the fillet radius increases, the seismic performance of the connections can be greatly improved.

Key Words
connection detail; welding defect; cyclic loading; beam-column connection; thick-walled steel member

Address
(1) Hanbin Ge:
Deptartment of Civil Engineering, Meijo University, 1-501 Shiogamaguchi, Tempaku-ku, Nagoya, 468-8502, Japan;
(2) Liang-Jiu Jia:
Advanced Research Center for Natural Disaster Risk Reduction, Meijo University, 1-501 Shiogamaguchi, Tempaku-ku, Nagoya, 468-8502, Japan;
(3) Lan Kang:
School of Civil Eng. and Transportation, South China University of Technology, Wushan RD., Tianhe District, Guangzhou, 510006, China (Former Japan Society for the Promotion of Science Research Fellow, Meijo Univ., Japan);
(4) Toshimitsu Suzuki:
Hiroshima Machinery Works, Mitubishi Heavy Industries, Ltd., 5-1 Ebaokimachi, Naka-ku, Hiroshima, 730-8642, Japan.

Abstract
This paper deals with the geometric nonlinear bending analysis of laminated composite stiffened plates subjected to uniform transverse loading. The eight-noded degenerated shell element and three-noded degenerated curved beam element with five degrees of freedom per node are adopted in the present analysis to model the plate and stiffeners respectively. The Green-Lagrange strain displacement relationship is adopted and the total Lagrangian approach is taken in the formulation. The convergence study of the present formulation is carried out first and the results are compared with the results published in the literature. The stiffener element is reformulated taking the torsional rigidity in an efficient manner. The effects of lamination angle, depth of stiffener and number of layers, on the bending response of the composite stiffened plates are considered and the results are discussed.

Key Words
degenerated shell element; degenerated curved beam element; nonlinear analysis; green-lagrange nonlinearity; stiffened plate and laminated composite

Address
Department of Civil Engineering, BITS Pilani, Pilani Campus, Pilani - 333031, Rajasthan, India.

Abstract
This study aims to present a three dimensional finite element model to investigate the wave propagation in a concrete filled steel tubular column (CFSC) due to transient impact load. Both the concrete and steel are regarded as linear elastic material. The impact load is simulated by a semi sinusoidal impulse. Besides the CFSC models, a concrete column (CC) model is established for comparing under the same loading condition. The propagation characteristics of the transient waves in CFSC are analyzed in detail. The results show that at the intial stage of the wave propagation, the velocity waves in CFSC are almost the same as those in CC before they arrive at the steel tube. When the waves reach the column side, the velocity responses of CFSC are different from those of CC and the difference is more and more obvious as the waves travel down along the column shaft. The travel distance of the wave front in CFSC is farther than that in CC at the same time. For different wave speeds in steel and concrete material, the wave front in CFSC presents an arch shape, the apex of which locates at the center of the column. Differently, the wave front in CC presents a plane surface. Three dimensional effects on top of CFSC are obvious, therefore, the peak value and arrival time of incident wave crests have great difference at different locations in the radial direction. High-frequency waves on the waveforms are observed. The time difference between incident and reflected wave peaks decreases significantly with r/R when r/R < 0.6, however, it almost keeps constant when r/R

Key Words
wave propagation; concrete filled steel tubular column; transient impact load; finite element method; three dimensional effects

Address
(1) Xuanming Ding:
Key Laboratory of New Technology for Construction of Cities in Mountain Area, Chongqing University, Chongqing 400045, China.
(2) Yuming Fan, Gangqiang Kong, Changjie Zheng:
Key Laboratory of Ministry of Education for Geomechanics and Embankment Engineering, Geotechnical Research Institute, Hohai University, 1 Xikang Road, Nanjing 210098, China.

Abstract
Ultra-lightweight cement composite (ULCC) with a compressive strength of 60 MPa and density of 1450 kg/m3 has been developed and used in the steel-concrete-steel (SCS) sandwich structures. ULCC was adopted as the core material in the SCS sandwich composite beams to reduce the overall structural weight. Headed shear studs working in pairs with overlapped lengths were used to achieve composite action between the core material and steel face plates. Nine quasi-static tests on this type of SCS sandwich composite beams were carried out to evaluate their ultimate strength performances. Different parameters influencing the ultimate strength of the SCS sandwich composite beams were studied and discussed. Design equations were developed to predict the ultimate resistance of the cross section due to pure bending, pure shear and combined action between shear and moment. Effective stiffness of the sandwich composite beam section is also derived to predict the elastic deflection under service load. Finally, the design equations were validated by the test results.

Key Words
cement composite; bond strength; connector; shear connector; sandwich structure; tension connector

Address
Department of Civil and Environmental Engineering, National University of Singapore, E1A-07-03, One Engineering Drive 2, Singapore 117576.

Abstract
Thirty one push-out tests were carried out in order to investigate the bond behavior between shape steel, steel tube (named steels) and recycled aggregate concrete (RAC), including 11 steel reinforced recycled aggregate concrete (SRRAC) columns, 10 recycled aggregate concrete-filled circular steel tube (RACFCST) columns and 10 recycled aggregate concrete-filled square steel tube (RACFSST) columns. Eleven recycled coarse aggregate (RCA) replacement ratios (i.e., 0%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% and 100%) were considered for SRRAC specimens, while five RCA replacement ratios (i.e., 0%, 25%, 50%, 75% and 100%), concrete type and length-diameter ratio for recycled aggregate concretefilled steel tube (RACFST) specimens were designed in this paper. Based on the test results, the influences of all variable parameters on the bond strength between steels and RAC were investigated. It was found that the load-slip curves at the loading end appeared the initial slip earlier than the curves at the free end. In addition, eight practical bond strength models were applied to make checking computations for all the specimens. The theoretical analytical model for interfacial bond shear transmission length in each type of steel-RAC composite columns was established through the mechanical derivation, which can be used to design and evaluate the performance of anchorage zones in steel-RAC composite structures.

Key Words
recycled aggregate concrete (RAC); shape steel; steel tube; bond mechanism; transmission length

Address
(1) Zongping Chen, Jinjun Xu, Ying Liang, Yisheng Su:
College of Civil Engineering and Architecture, Guangxi University, Nanning, 530004, P.R. China;
(2) Zongping Chen:
Key Laboratory of Disaster Prevention and Structural Safety of Chinese Education Ministry, Guangxi University, Nanning, 530004, P.R. China.

Abstract
Point bending is commonly used for cambering and curving steel girders to large radii. In this system, a hydraulic ram or press is used to apply concentrated loads at selected points to obtain the required vertical (cambering) or horizontal (curving) curved profile from induced permanent deformations. This paper derives closed form solutions that relate loads to permanent deformations for horizontally curving wide flange steel beams based on their post-yield response. These solutions are presented in a parametric form to identify the relationship between key variables and their impact on the accuracy of the curving operation. It is shown that point bending could yield parabolic curved profiles that are within 1% of a desired circular curve if the span length to radius of curvature ratio (L/R) is less than 1.5 and the point loads are spaced at one third the beam length. Safe limits are then established on loads, strains and curvatures to avoid damaging the steel section. This leads to optimization of the point bending operation for inducing a circular profile in wide flange steel beams of any size.

Key Words
steel; wide flange; non-linear; point bending; radius; inelastic

Address
(1) Antoine N. Gergess:
Department of Civil Engineering, University of Balamand, Al-Koura, P.O. Box 100, Lebanon;
(2) Rajan Sen:
University of South Florida, Tampa, Florida, USA.

Abstract
In regions of high shear forces in composite bridges, headed stud shear connectors need to be arranged with a small spacing in order to satisfy the design requirement of resisting the high interface shear force present at this location. Despite this, studies related to groups of headed studs are somewhat rare. This paper presents an investigation of the static behaviour of grouped stud shear connectors in high-strength concrete. Descriptions are given of five push-out test specimens with different arrangements of the studs that were fabricated and tested, and the failure modes, load-slip response, ultimate load capacities and related slip values that were obtained are reported. It is found that the load-slip equation given by some researchers based on a single stud shear connector in normal strength concrete do not apply to grouped stud shear connectors in high-strength concrete, and an algebraic load-slip expression is proposed based on the test results. Comparisons between the test results and the formulae provided by some national codes show that the equations for the ultimate capacity provided in these codes are conservative when used for connectors in high-strength concrete. A reduction coefficient is proposed to take into account the effect of the studs being in a group.

Key Words
composite beams; ductility; group; high-strength concrete; push-out tests; slip; stud shear connectors

Address
(1) Qingtian Su:
Department of Bridge Engineering, Tongji University, Shanghai 200092, China;
(2) Guotao Yang, Mark A. Bradford:
Centre for Infrastructure Engineering and Safety, School of Civil and Environmental Engineering, The University of New South Wales, UNSW Sydney, NSW 2052, Australia.


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