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CONTENTS
Volume 20, Number 6, April30 2016
 

Abstract
The objective of this work was to evaluate the ductile cracked structures with bonded composite patch used in probabilistic elastic plastic fracture mechanics subjected to tensile load. The finite element method is used to analyze the stress intensity factors for elastic case, the effect of cracks and the thickness of the patch (er) are presented for calculating the stress intensity factors. For elastic-plastic the Monte Carlo method is used to predict the distribution function of the mechanical response. According to the obtained results, we note that the stress variations are important factors influencing on the distribution function of (J/Je).

Key Words
composite; finite element method; fracture mechanics; elastic-plastic; probabilistic analysis

Address
(1) BelaÏd Mechab, Mourad Chama, Khacem Kaddouri:
LMPM, Department of Mechanical Engineering, University of Sidi Bel Abbes, BP 89 Cité Ben M'hidi 22000, Sidi Bel Abbes, Algeria;
(2) Djelloul Slimani:
Department of Mechanical Engineering, University of Sidi Bel Abbes, BP 89 Cité Ben M'hidi 22000, Sidi Bel Abbes, Algeria.

Abstract
The internal crack propagation, the failure mode and ultimate load bearing capacity of the steelconcrete-steel composite beam under the four-point-bend loading is investigated by the numerical simulation. The results of load - displacement curve and failure mode are in good agreement with experiment. In order to study the failure mechanism, the composite beam has been modeled, which part interface interaction between steel and concrete is considered. The results indicate that there are two failure modes: (a) When the strength of the interface is lower than that of the concrete, failure happens at the interface of steel and concrete; (b) When the strength of the interface is higher than that of the concrete, the failure modes is cohesion failure, i.e., and concrete are stripped because of the shear cracks at concrete edge.

Key Words
steel-concrete-steel composite beam; interface; crack propagation; failure mode; ultimate bearing capacity

Address
College of Aerospace and Civil Engineering, Harbin Engineering University, Harbin, 150001, China.


Abstract
This paper focuses on the analytical behavior of modular circular concrete-filled tubular (CFT) column with enhanced bracing details. To design a full-scale bridge pier of multiple circular concrete-filled tubes, numerical analysis was used to evaluate structural performance according to load directivity. In previous research (Ma et al. 2012, Shim et al. 2014), low cycle fatigue failure at bracing joints was observed, so enhanced bracing details to prevent premature failure are proposed in this analysis. The main purpose of this research is to investigate seismic performance for the diagonal direction load without premature failure at the joints when the structure reaches the ultimate load. The ABAQUS finite-element software is used to evaluate experimental performance. A quasi-static loading condition on a modular bridge pier is introduced to investigate structural performance. The results obtained from the analysis are evaluated by comparing with load.displacement responses from experiments. The concretefilled tubes with enhanced bracing details showed higher energy dissipation capacity and proper performance without connection failure for a diagonal load.

Key Words
modular bridge pier; CFT; non-linear analysis; quasi static; bracing

Address
Department of Civil Engineering, Chung Ang University, Seoul, Republic of Korea.


Abstract
This paper presents a new type of pre-pressed spring self-centering energy dissipation (PS-SCED) bracing system that combines friction mechanisms between the inner and outer tube members to provide the energy dissipation with the pre-pressed combination disc springs installed on both ends of the brace to provide the selfcentering capability. The mechanics and the equations governing the design and hysteretic responses of the bracing system are outlined, and a series of validation tests of components comprising the self-centering mechanism of combination disc springs, the friction energy dissipation mechanism, and a large scale PS-SCED bracing specimen were conducted due to the low cyclic reversed loadings. Experimental results demonstrate that the proposed bracing system performs as predicted by the equations governing its mechanical behaviors, which exhibits a stable and repeatable flag-shaped hysteretic response with excellent self-centering capability and appreciable energy dissipation, and large ultimate bearing and deformation capacities. Results also show that almost no residual deformation occurs when the friction force is less than the initial pre-pressed force of disc springs.

Key Words
self-centering energy dissipation brace; combination disc spring; hysteretic behavior; residual deformation; low cyclic reversed loading test

Address
(1) Longhe Xu, Xiaowei Fan, Dengcheng Lu:
School of Civil Engineering, Beijing Jiaotong University, Beijing 100044, China;
(2) Zhongxian Li:
Key Laboratory of Coast Civil Structure Safety of China Ministry of Education, Tianjin University, Tianjin 300072, China.

Abstract
Modular structures consist of standardized modules and their connections. A modular bridge pier is proposed to accelerate bridge construction. Multiple concrete-filled steel tubes (CFTs) using commercial steel tubes were chosen as the main members. Buckling restrained bracings and enhanced connection details were designed to prevent premature low-cycle fatigue failure upon cyclic loading. The pier had a height of 7.95 m, widths of 2.5 m and 2.0 m along the strong and weak axis, respectively. Cyclic tests were performed on the modular pier to investigate structural performance. Test results showed that four CFT columns reached yielding without a premature failure of the bracing connections. The ultimate capacity of the modular pier was reasonably estimated based on the plastichinge- analysis concept. The modular CFT pier with enhanced bracing showed improved displacement ductility without premature failure at the welding joints.

Key Words
modular bridge pier; CFT; buckling restrained bracing; cyclic test; ductility

Address
Department of Civil Engineering, Chung Ang University, Seoul, Republic of Korea.


Abstract
The paper concerns analysis of effects of shrinkage of slab concrete in a steel-concrete composite deck of a through truss bridge span. Attention is paid to the shrinkage alongside the span, i.e., transverse to steel-concrete composite cross-beams. So far this aspect has not been given much attention in spite of the fact that it affects not only steel-concrete decks of bridges but also steel-concrete floors of steel frame building structures. For the problem analysis a two-dimensional model is created. An analytical method is presented in detail. A set of linear equations is built to compute axial forces in members of truss girder flange and transverse shear forces in steel-concrete composite beams. Finally a case study is shown: test loading of twin railway truss bridge spans is described, verified FEM model of the spans is presented and computational results of FEM and the analytical method are compared. Conclusions concerning applicability of the presented analytical method to practical design are drawn. The presented analytical method provides satisfactory accuracy of results in comparison with the verified FEM model.

Key Words
concrete shrinkage; transverse shear forces; through truss bridge; steel-concrete composite deck

Address
Institute of Civil Engineering, PoznańUniversity of Technology, ul. Piotrowo 5, 61-138 Poznań Poland.


Abstract
A precast composite column system has been developed in this study by utilizing multi interlocking spiral steel into a centrifugally-formed hollow-core precast (CHPC) column. The proposed hybrid column system can have enhanced performances in the composite interaction behavior between the hollowed precast column and cast-in-place (CIP) core-filled concrete, the lap splice performance of bundled bars, and the confining effect of concrete. In the experimental program, reversed cyclic loading tests were conducted on a conventional reinforced concrete (RC) column fabricated monolithically, two CHPC columns filled with CIP concrete, and two steelreinforced concrete (SRC) columns. It was confirmed that the interlocking spirals was very effective to enhance the structural performance of the CHPC column, and all the hollow-core precast column specimens tested in this study showed good seismic performances comparable to the monolithic control specimen.

Key Words
hollow column; precast concrete; interlocking spiral; seismic behavior; composite

Address
(1) Jin-Ha Hwang, Jae Yuel Oh, Seung-Ho Choi, Kang Su Kim:
Department of Architectural Engineering, University of Seoul, 163 Seoulsiripdae-ro, Dongdaemun-gu, Seoul 02504, Republic of Korea;
(2) Deuck Hang Lee:
Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, 205 N. Mathews Ave. Urbana, IL 61801, USA;
(3) Soo-Yeon Seo:
Department of Architectural Engineering, Korea University of Transportation, 50 Daehak-ro, Chungju-si, Chungbuk 27469, Republic of Korea.

Abstract
Steel plates and carbon-fiber-reinforced polymer (CFRP) laminates or plates bonded to concrete substrates have been widely used for concrete strengthening. However, this technique cause plate debonding, which makes the strengthening system inefficient. The main objective of this study is to enhance the bond strength of externally bonded steel plates and CFRP laminates to the concrete surface by proposing new embedded adhesive and steel connectors. The effects of these new embedded connectors were investigated through the tests on 36 prism specimens. Parameters such as interfacial shear stress, fracture energy and the maximum strains in plates were also determined in this study and compared with the maximum value of debonding stresses using a relevant failure criterion by means of pullout test. The study indicates that the interfacial bond strength between the externally bonded plates and concrete can be increased remarkably by using these connectors. The investigation verifies that steel connectors increase the shear bond strength by 48% compared to 38% for the adhesive connectors. Thus, steel connectors are more effective than adhesive connectors in increasing shear bond strength. Results also show that the use of double connectors significantly increases interfacial shear stress and decrease debonding failure. Finally, a new proposed formula is modified to predict the maximum bond strength of steel plates and CFRP laminates adhesively glued to concrete in the presence of the embedded connectors.

Key Words
steel plate; CFRP; bond strength; connectors; debonding; concrete

Address
Department of Civil Engineering, Universiti Tenaga Nasional, kajang st. 43000, Malaysia.


Abstract
This paper presents the results of experimental and numerical model analyses on partially encased composite columns under concentric loads. The main objective of this study is to evaluate the influence of replacing the conventional longitudinal and transverse steel bars by welded wire mesh on the structural behavior of these members under concentric loads. To achieve these goals experimental tests on four specimens of partially encased composite columns submitted to axial loading were performed and the results were promising in terms of replacing the traditional reinforcement by steel meshes. In addition, a numerical FE model was developed using the software DIANA® with FX+. The experimental results were used to validate the numerical model. Satisfactory agreement between experimental and numerical results was observed in both capacity and deformability of the composite columns. Despite of the simplifying assumptions of perfect bond between steel and concrete, the numerical model adequately represented the columns behavior. A finite element parametric study was performed and parameters including thickness of the steel profile and the concrete and steel strengths were evaluated. The parametrical study results found no significant changes in the partially encased columns behavior due to variations of the steel profile thickness or yield strength. However, significant changes in the post peak behavior were observed when using high strength concrete and these results suggest a change in the failure mode.

Key Words
partially encased composite column; axial loads; experimental analysis; numerical model; concentric load

Address
(1) Margot F. Pereira, Ana L.H.C. El Debs:
Department of Structural Engineering, University of Sao Paulo, Sao Carlos, Brazil / Avenida Trabalhador Saocarlense 400, Centro, Sao Carlos-SP - CEP: 13.566-590, Brazil;
(2) Silvana De Nardin:
Department of Civil Engineering, Federal University of Sao Carlos, Sao Carlos, Brazil / Rodovia Washington Luis, km 235 - SP-310 Sao Carlos-SP - CEP 13565-905, Brazil.

Abstract
This paper presents the results of an extensive numerical analysis program devoted to the investigation of the mechanical behaviour of bolted ball-cylinder joints. The analysis program is developed by means of finite element (FE) models implemented in the non-linear code ABAQUS. The FE models have been accurately calibrated on the basis of available experimental results. It is indicated that the FE models could be used effectively to describe the mechanical performance of bolted ball-cylinder joints, including failure modes, stress distributions and loaddisplacement curves. Therefore, the proposed FE models could be regarded as an efficient and accurate tool to investigate the mechanical behavior of bolted ball-cylinder joints. In addition, to develop a further investigation, parametric studies were performed, varying the dimensions of hollow cylinders, rectangular tubes, convex washers and ribbed stiffener. It is found that the dimensions of hollow cylinders, rectangular tubes and ribbed stiffener influenced the mechanical behaviour of bolted ball-cylinder joints significantly. On the contrary, the effects of the dimensions of convex washers were negligible.

Key Words
bolted ball-cylinder joints; FE models; failure modes; parametric studies; mechanical behaviour

Address
(1) Xiaonong Guo, Zewei Huang, Zhe Xiong, Shangfei Yang:
Department of Building Engineering, Tongji University, Shanghai 200092, China;
(2) Li Peng:
Shanghai T&D Architechral Technology Co., Ltd., Shanghai 200092, China.

Abstract
This paper presents the probabilistic-based assessment of composite steel-concrete structures through an innovative framework. This framework combines model identification and reliability assessment procedures. The paper starts by describing current structural assessment algorithms and the most relevant uncertainty sources. The developed model identification algorithm is then presented. During this procedure, the model parameters are automatically adjusted, so that the numerical results best fit the experimental data. Modelling and measurement errors are respectively incorporated in this algorithm. The reliability assessment procedure aims to assess the structure performance, considering randomness in model parameters. Since monitoring and characterization tests are common measures to control and acquire information about those parameters, a Bayesian inference procedure is incorporated to update the reliability assessment. The framework is then tested with a set of composite steel-concrete beams, which behavior is complex. The experimental tests, as well as the developed numerical model and the obtained results from the proposed framework, are respectively present.

Key Words
probabilistic-based assessment; uncertainty sources; model identification; reliability assessment; Bayesian inference; composite steel-concrete structures

Address
(1) José C. Matos, Isabel B. Valente, Vicente N. Moreira:
ISISE, Department of Civil Engineering, School of Engineering, University of Minho, Guimarães, Portugal;
(2) Paulo J.S. Cruz:
Lab2PT, School of Architecture, University of Minho, Guimarães, Portugal.

Abstract
This paper investigates the flexural stiffness of simply supported steel-concrete composite I-beams under positive bending moment through combined experimental, numerical, and different standard methods. 14 composite beams are tested for experimental study and parameters including shear connection degree, transverse and longitudinal reinforcement ratios, loading way are also investigated. ABAQUS is employed to establish finite element (FE) models to simulate the flexural behavior of composite beams. The influences of a few key parameters, such as the shear connection degree, stud arrangement, stud diameter, beam length, loading way, on the flexural stiffness is also studied by parametric study. In addition, three widely used standard methods including GB, AISC, and British standards are used to estimate the flexural stiffness of the composite beams. The results are compared with the experimental and numerical results. The findings have provided comprehensive understanding of the flexural stiffness and the modelling of the composite beams. The results also indicate that GB 50017-2003 could provide better results in comparison to the other standards.

Key Words
steel-concrete composite beam; flexural stiffness; finite element; degree of shear connection

Address
(1) Fa-Xing Ding, Jing Liu, Feng-Qi Guo:
School of Civil Engineering, Central South University, Changsha, Hunan Province, 410075, P.R. China;
(2) Xue-Mei Liu:
School of Civil Engineering and Built Environment, Queensland University of Technology, Brisbane, QLD 4000, Australia;
(3) Li-Zhong Jiang:
National Engineering Laboratory for High Speed Railway Construction, Changsha, 410075, P.R. China.

Abstract
Masonry infill has a significant effect on stiffness contribution, strength and ductility of masonry-infilled frames. These effects may cause damage of weak floor, torsional damage or short-column failure in structures. This article presents experiments of 1/2.5-scale steel reinforced recycled aggregates concrete (SRRC) frames. Three specimens, with different infill rates consisted of recycled concrete hollow bricks (RCB), were subjected to static cyclic loads. Test phenomena, hysteretic curves and stiffness degradation of the composite structure were analyzed. Furthermore, effects of axial load ratio, aspect ratio, infill thickness and steel ratio on the share of horizontal force supported by the frame and the infill were obtained in the numerical example.

Key Words
steel reinforced recycled aggregates concrete; infilled frames; frame-infill interaction; shear distribution; axial load ratio; aspect ratio; infill thickness; steel ratio

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



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