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CONTENTS
Volume 44, Number 6, December25 2012
 

Abstract
In this work, an experimental examination was carried out to study interfacial stresses developed at the junction zones between carbon fiber reinforced plastic (CFRP) fabrics (~1 mm thickness) and tensile concrete portion in CFRP retrofitted RC beams. In this respect, initially six similar RC beams of 150 x 150 x 1000 mm dimensions were prepared. Three of which were strengthened with CFRP fabrics at the tensile side of the beams. Furthermore, a notch was cut at the center of the bottom surface for all of the studied beams. The notch was 15 mm deep and ran across the full width of tension side of the beams. The mentioned interfacial stresses could be calculated from strains measured using strain gauges mounted on the interface zone of the tensile concrete and the CFRP sheet. Based on the results obtained, it is shown that interfacial stresses developed between CFRP fabrics and RC beam had a noticeable effect on debonding failure mode of the latter. The load carrying capacity of CFRP strengthened RC specimens increased ~75% compared to that of the control RC beams. This was attributed to the enhancement of flexural mode of the former. Finally, finite element analysis was also utilized to verify the measured experimental results.

Key Words
experimental examination; CFRP strengthened RC beam; interfacial stress; critical zones; debonding failure mode; finite element analysis

Address
Ata Hojatkashani: University of Applied Science and Technology, Tehran, Iran
Mohammad Zaman Kabir: Civil Engineering Department, Amirkabir University of Technology (Tehran Polytechnic), Tehran, Iran

Abstract
Although being one of the most popular strengthening techniques in reinforced concrete beams, the use of steel plates bonded to the soffit raises problems of ductility. This study aims at investigating the influence of the use of perforated steel plates instead of solid steel plates on the ductility of reinforced concrete beams. A total of nine reinforced concrete beams were tested. In addition to an unplated beam, eight beams with perforated steel plates of two different thicknesses (3 mm and 6 mm) were subjected to monotonic loading. Effect of bonding the plates to the beams with anchor bolts and with additional side plates bonded to the sides of the beam with and without anchors is also investigated. The use of bolts in addition to epoxy was found to greatly contribute to the ductility and energy absorption capacity of the beams, particularly in specimens with thick plates (6 mm) and the use side plates in addition to the bottom plate was found to be ineffective in increasing the ductility of a concrete beam unless the side plates are attached to the beam with anchors bolts. The thickness of the plate was found to have little effect on the bending rigidity of the beam.

Key Words
perforated steel plate; beam strengthening; beam repair; plated beam; reinforced concrete beam; bending stiffness; ductility; modulus of toughness; flexural behavior

Address
Sabahattin Aykac: Civil Engineering Department, Engineering Faculty, Gazi University, 06570 Ankara, Turkey
Ilker Kalkan: Department of Civil Engineering, Faculty of Engineering, Kirikkale University, 71450 Kirikkale, Turkey
Ali Uysal: Turkish Army Corps of Engineers, Civil Engineering Group, 06170 Ankara, Turkey

Abstract
The ratcheting characteristics of cylindrical shell under cyclic axial loading are investigated. The specimens are subjected to stress-controlled cycling with non-zero mean stress, which causes the accumulation of plastic strain or ratcheting behavior in continuous cycles. Also, cylindrical shell shows softening behavior under symmetric axial strain-controlled loading and due to the localized buckling, which occurs in the compressive stress-strain curve of the shell; it has more residual plastic strain in comparison to the tensile stress-strain hysteresis curve. The numerical analysis was carried out by ABAQUS software using hardening models. The nonlinear isotropic/kinematic hardening model accurately simulates the ratcheting behavior of shell. Although hardening models are incapable of simulating the softening behavior of the shell, this model analyzes the softening behavior well. Moreover, the model calculates the residual plastic strain close to the experimental data. Experimental tests were performed using an INSTRON 8802 servo-hydraulic machine. Simulations show good agreement between numerical and experimental results. The results reveal that the rate of plastic strain accumulation increases for the first few cycles and then reduces in the subsequent cycles. This reduction is more rapid for numerical results in comparison to experiments.

Key Words
cylindrical shell; cyclic axial loading; ratcheting; hardening model; finite element model

Address
M. Shariati, H. Hatami and H.R. Epakchi: Department of Mechanical Engineering, Shahrood University of Technology, Daneshgah Blvd, Shahrood, Semnan, Iran
H. Torabi: Young Researchers Club, Mashhad Branch, Islamic Azad University, Mashhad,

Abstract
Reinforced concrete frame structures with masonry infill walls constitute the significant portion of the building stock in Turkey. Therefore it is very important to understand the behavior of masonry infill frame structures under earthquake loads. This study presents an experimental work performed on reinforced concrete (RC) frames with different types of masonry infills, namely standard and locked bricks. Earthquake effects are induced on the RC frames by quasi-static tests. Results obtained from different frames are compared with each other through various stiffness, strength, and energy related parameters. It is shown that locked bricks may prove useful in decreasing the problems related to horizontal and vertical irregularities defined in building codes. Moreover tests show that locked brick infills maintain their integrity up to very high drift levels, showing that they may have a potential in reducing injuries and fatalities related to falling hazards during severe ground shakings.

Key Words
engineered infills; locked brick masonry infill; reinforced concrete frames; cyclic testing; experimental methods; earthquake engineering

Address
I. Serkan Misir, Ozgur Ozcelik, Sadik Can Girginb and Serap Kahraman: Department of Civil Engineering, Faculty of Engineering, Dokuz Eylul University, 35160, Izmir, Turkey

Abstract
This work approaches the structural performance of masonry arches that have a small ratio between number of vossoirs and span length. The aim of this research is to compare and validate three different methods of analysis (funicular limit analysis F.L.A., kinematic limit analysis K.L.A. and plane stress Finite Element Analysis F.E.A.) with an experimental campaign. 18 failure tests with arches of different shapes and boundary conditions have been performed. The basic failure mechanism was the formation of enough hinges in the geometry. Nevertheless, in few cases, sliding between vossoirs also played a relevant influence. Moreover, few arches didn\'t reach the collapse. The FLA and KLA didn\'t find a solution close to the experimental values for some of the tests. The low number of vossoirs and joints become a drawback for an agreement between kinematic mechanism, equilibrium of forces and geometry constraints. FLA finds a lower bound whereas KLA finds an upper bound of the ultimate load of the arch. FEA is the most reliable and robust method and it can reproduce most of the mechanism and ultimate loads. However, special care is required in the definition of boundary conditions for FEA analysis. Scientific justification of the more suitability of numerical methods in front of classic methods at calculating arches with a few vossoirs is the main original contribution of the paper.

Key Words
dry-joint arches; collapsing mechanism; experimental testing; FEA simulation; funicular analysis; kinematic analysis

Address
Ernest Bernat-Maso, Lluis Gil and Jordi Marce-Nogue: Department of Strength of Materials and Engineering Structures, Universitat Politccnica de Catalunya. Barcelona-Tech., ETSEIAT Campus Terrassa, c/Colom, 11, 08222 Terrassa, Spain

Abstract
The strain rate effects on the interaction between a Mode I matrix crack and an inclined elliptic matrix-inclusion interface under dynamic tensile loadings were investigated numerically, and the results are in agreement with previous experimental data. It is found, for a given material system, that there are the first and the second critical strain rates, by which three kinds of the subsequent crack growth patterns can be classified in turn with the increasing strain rate, namely, the crack deflection, the double crack mode and the perpendicular crack penetration. Moreover, such a crack deflection/penetration behavior is found to be dependent on the relative interfacial strength, the inclined angle and the inclusion size. In addition, it is shown that the so-called strain rate effect on the dynamic strength of granule composites can be induced directly from the structural dynamic response of materials, not be entirely an intrinsic material property.

Key Words
cohesive crack; dynamic strength; strain rate effects; crack propagation; crack penetration; composites

Address
Ying Li, Wan-Chao Qiu, Zhuo-Cheng Ou, Zhuo-Ping Duan and Feng-Lei Huang: State Key Laboratory of Explosion Science and Technology, Beijing Institute of Technology, Beijing 100081, China

Abstract
A plated beam is strengthened by bonding a thin plate to the tension face; it often fails because of premature debonding of the thin plate from the original beam in a brittle manner. A sound understanding of the mechanism of such debonding failure is very important for the effective use of this strengthening technique. This paper presents an improved analytical solution for interfacial stresses that incorporates multiple loading conditions simultaneously, including prestress, mechanical and thermal loads, and the effects of adherend shear deformations and curvature mismatches between the beam and the plate. Simply supported beams bonded with a thin prestressing plate and subjected to both mechanical and thermal loading were considered in the present work. The effects of the curvature mismatch and adherend shear deformations of the beam and plate were investigated and compared. The main mechanisms affecting the distribution of interfacial stresses were analyzed. Both the normal and shear stresses were found to be significantly influenced by the coupled effects of the elastic moduli with the ratios Ea/Eb and Ea/Ep.

Key Words
interfacial stress; debonding; beam; prestress; temperature; strengthening

Address
Sheng-Wang Hao, Yan Liu and Xiao-Dan Liu: School of Civil Engineering and Mechanics, Yanshan University, Qinhuangdao 066004, People\'s Republic of China

Abstract
To enable remodeling of the exterior of buildings more convenient, such finishing materials as curtain walls, metal panels, concrete panels or dry stones need to be easily detached. In this respect, this study proposed a new design of the slab for the purposes. In the new design, the sides of the slab were properly modified, and the capabilities of anchors fixed in the modified slab were experimentally tested. In details, a number of concrete specimens with different sizes and compressive strengths were prepared, and the effect of anchors with different diameters and embedment depths applied in the concrete specimens were tested. The test results of the maximum capacities of the anchors were compared with the number of current design codes and the stress distribution was identified. This study found that the embedment depth specified in the current design code (ACI318-08) should be revised to be more than 1.5 times the edge distance. However, with the steel sheet reinforcement, the experiment acquired higher tensile strength than the design code proposed. In addition, for two types of specimens in the tensile strength experiment, the current design code (ACI 318-08) is overestimated for the anchor depth of 75 mm. This study demonstrated that the ideal breakout failure was attainable for the side slot details of a slab with more than 180 mm of a slab thickness and less than 75 mm of an anchor embedment depth. It is expected that these details of the modified slab can be specified in the upgraded construction design codes.

Key Words
anchor; pullout tests; failure cone; fastener; tensile capacity

Address
Kyu Won Yeun and Jong Kim: Institute of Construction Technology, Seon Engineering, Cheongju, Chungbuk, Korea
Ki Nam Hong: School of Civil Engineering, Chungbuk National University, Cheongju, Chungbuk, Korea


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