• Steel and Composite Structures
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• 제4권5호
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• pp.333-353
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• 2004

Strength of reinforced concrete beams can easily be increased by the use of externally bonded CFRP composites. However, the mode of failure of CFRP strengthened beam is usually brittle due to tension-shear failure in the concrete substrate or bond failure near the CFRP-Concrete interface. In order to improve the ductility of CFRP strengthened concrete beams, critical variables need to be investigated. This experimental and analytical research focused on a series of reinforced concrete beams strengthened with CFRP composites to enhance the flexural capacity and ductility. The main variables were the amount of CFRP composites, the amount of longitudinal and shear reinforcement, and the effect of CFRP end diagonal anchorage system. Sixteen full-scale beams were investigated. A new design guideline was proposed according to the effects of the above-mentioned variables. The experimental and analytical results were found to be in good agreement.

• Structural Engineering and Mechanics
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• 제63권2호
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• pp.217-223
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• 2017

Glass fiber reinforced gypsum panels (GFRG) are hollow panels made from modified gypsum plaster and reinforced with chopped glass fibers. The hollow cores of panels can be filled with in-situ concrete/reinforced concrete or insulation material to increase the structural strength or the thermal insulation, respectively. GFRG panels are unfilled when used as partition walls. As load bearing walls, the panels are filled with M 20 grade concrete (reinforced concrete filling) in order to resist the gravity and lateral loads. The study was conducted in two stages: First stage involves formulation of the alternate light weight mix by conducting experimental investigations to obtain the optimum combination of phosphogypsum and shredded thermocol. In the second stage the alternate mixes are filled in GFRG panels and experimental investigations are conducted to compare the performance against panels filled with conventional M 20 mix.

• Structural Engineering and Mechanics
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• 제73권2호
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• pp.143-152
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• 2020

Deep coupling beams are more prone to suffer brittle shear failure. The addition of steel fibers to seismic members such as coupling beams can improve their shear performance and ductility. Based on the test results of steel fiber reinforced concrete(SFRC) coupling beams with span-to-depth ratio between 1.5 and 2.5 under lateral reverse cyclic load, the shear mechanism were analyzed by using strut-and-tie model theory, and the effects of the span-to-depth ratio, compressive strength and volume fraction of steel fiber on shear strengths were also discussed. A simplified calculation method to predict the shear capacity of SFRC deep coupling beams was proposed. The results show that the shear force is mainly transmitted by a strut-and-tie mechanism composed of three types of inclined concrete struts, vertical reinforcement ties and nodes. The influence of span-to-depth ratio on shear capacity is mainly due to the change of inclination angle of main inclined struts. The increasing of concrete compressive strength or volume fraction of steel fiber can improve the shear capacity of SFRC deep coupling beams mainly by enhancing the bearing capacity of compressive struts or tensile strength of the vertical tie. The proposed calculation method is verified using experimental data, and comparative results show that the prediction values agree well with the test ones.

• Computers and Concrete
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• 제13권2호
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• pp.255-270
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• 2014

Impact performance of high-performance concrete (HPC) and SFRC at 28-day and 56-day under the action of repeated dynamic loading was studied. Silica fume replacement at 10% and 15% by mass and crimped steel fiber ($V_f$ = 0.5%- 1.5%) with aspect ratios of 80 and 53 were used in the concrete mixes. Results indicated that addition of fibers in HPC can effectively restrain the initiation and propagation of cracks under stress, and enhance the impact strengths and toughness of HPC. Variation of fiber aspect ratio has minor effect on improvement in impact strength. Based on the experimental data, failure resistance prediction models were developed with correlation coefficient (R) = 0.96 and the estimated absolute variation is 1.82% and on validation, the integral absolute error (IAE) determined is 10.49%. On analyzing the data collected, linear relationship for the prediction of failure resistance with R= 0.99 was obtained. IAE value of 10.26% for the model indicates better the reliability of model. Multiple linear regression model was developed to predict the ultimate failure resistance with multiple R= 0.96 and absolute variation obtained is 4.9%.

• Computers and Concrete
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• 제13권1호
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• pp.31-47
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• 2014

This research is focused on obtaining the fracture property of steel fiber reinforced concrete(SFRC) specimens at early ages of 1, 2, 3 and 7-day, respectively. For this purpose, three point bending tests of nine groups of SFRC beams with notch of 40mm depth and different steel fiber ratios were conducted. The experimental results of early age specimens were compared with the 28-day hardened SFRC specimens. The test results indicated that the steel fiber ratios and curing age significantly influenced the fracture properties of SFRC. A reasonable addition of steel fiber improved the fracture toughness of SFRC, while the fracture energy of SFRC developed with curing age. Moreover, a quadratic relationship between splitting strength and fracture toughness was established based on the experiment results. Additionally, afinite element (FE) method was used to investigate the fracture properties of SFRC.A comparison between the FE analysis and experiment results was also made. The numerical analysis fitted well with the test results, and further details on the failure behaviors of SFRC could be revealed by the suggested numerical simulation method.

• Steel and Composite Structures
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• 제2권4호
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• pp.259-276
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• 2002

In the present investigation the experimental and theoretical flexural and compressive behavior of short tubular steel columns filled with plain concrete and fiber-reinforced concrete (FRC) was examined. For a given length of the members, the effects of different geometry and dimensions of the transverse cross-section (square and circular) were investigated. Constituent materials were characterized through direct tensile tests on steel coupons and through compressive and split tension tests on concrete cylinders. Load-axial shortening and load-deflection curves were recorded for unfilled and composite members. Finally, simplified expressions for the calculus of the load-deflection curves based on the cross-section analysis were given and the ultimate load of short columns was predicted.

• Steel and Composite Structures
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• 제32권1호
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• pp.21-35
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• 2019

This study investigates the flexural behavior of steel-concrete composite beams strengthened with prestressed carbon fiber-reinforced polymer (CFRP) plates. An innovative mechanical anchorage system was developed. The components of the system can be easily assembled on site before applying a prestressing force, and removed from the structures after strengthening is completed. A total of seven steel-concrete composite specimens including four simply supported beams strengthened at the positive moment region and three continuous beams strengthened at the negative moment region were tested statically until failure. Experimental results showed that the use of prestressed CFRP plates enhanced the flexural capacity and reduced the mid-span deflection of the beams. Furthermore, by prestressing the CFRP laminates, the material was used more efficiently, and the crack resistance of the continuous composite specimens at the central support was significantly improved after strengthening. Overall, the anchorage system proved to be practical and feasible for the strengthening of steel-concrete composite beams. The theoretical analysis of ultimate bearing capacity is reported, and good agreement between analytical values and experimental results is achieved.

• Computers and Concrete
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• 제24권1호
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• pp.19-35
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• 2019

In this paper, the effect of the type and amount of fibers on the physicomechanical properties of concrete containing fine recycled refractory brick (RRB) and natural aggregate subjected to elevated temperatures was investigated. For this purpose, forta-ferro (FF), polypropylene (PP), and polyvinyl alcohol (PVA) fibers with the volume fractions of 0, 0.25, and 0.5%, as well as steel fibers with the volume fractions of 0, 0.75, and 1.5% were used in the concrete containing RRB fine aggregate replacing natural sand by 0 and 100%. In total, 162 concrete specimens from 18 different mix designs were prepared and tested in the temperature groups of 23, 400, and $800^{\circ}C$. After experiencing heat, the concrete properties including the compressive strength, ultrasonic pulse velocity (UPV), weight loss, and surface appearance were evaluated and compared with the corresponding results of the reference (unheated) specimens. The results show that using RRB fine aggregate replacing natural fine aggregate by 100% led to an increase in the concrete compressive strength in almost all the mixes, and only in the PVA-containing mixes a decrease in strength was observed. Furthermore, UPV values at $800^{\circ}C$ for all the concrete mixes containing RRB fine aggregate were above those of the natural aggregate concrete specimens. Finally, regarding the compressive strength and UPV results, steel fibers demonstrated a better performance relative to other fiber types.

• Structural Engineering and Mechanics
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• 제30권4호
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• pp.403-426
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• 2008

Externally bonding fiber reinforced polymer (FRP) sheets with an epoxy resin is an effective technique for strengthening and repairing reinforced concrete (RC) beams under flexural loads. Their resistance to electro-chemical corrosion, high strength-to-weight ratio, larger creep strain, fatigue resistance, and nonmagnetic and nonmetallic properties make carbon fiber reinforced polymer (CFRP) composites a viable alternative to bonding of steel plates in repair and rehabilitation of RC structures. The objective of this investigation is to study the effectiveness of CFRP sheets on ductility and flexural strength of reinforced high strength concrete (HSC) beams. This objective is achieved by conducting the following tasks: (1) flexural four-point testing of reinforced HSC beams strengthened with different amounts of cross-ply of CFRP sheets with different amount of tensile reinforcement up to failure; (2) calculating the effect of different layouts of CFRP sheets on the flexural strength; (3) Evaluating the failure modes; (4) developing an analytical procedure based on compatibility of deformations and equilibrium of forces to calculate the flexural strength of reinforced HSC beams strengthened with CFRP composites; and (5) comparing the analytical calculations with experimental results.

• Steel and Composite Structures
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• 제21권6호
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• pp.1265-1285
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• 2016

This paper presents experimental results of advanced investigation carried out on the beams reinforced with Glass Fiber Reinforced Polymer (GFRP) rebar and stirrups. Twelve beams reinforced with GFRP and one beam with steel reinforcement of size $230{\times}300{\times}2000mm$ were investigated. Longitudinal reinforcement, shear span and spacing of stirrups were the main variables to form the set. In advanced testing three types of strain gauges for steel, composite and concrete surface were applied to observe strain/stress development against the applied load. Live data were recorded from four strain gauges applied on stirrups, one at center on longitudinal reinforcement, two on the concrete surface and central deflection during the test. Although the focus of the paper was mainly on the behavior of GFRP shear reinforcement, other parallel data were observed for the completeness of the test. Design recommendations of ISIS Canada Design Manual (2007), Japan Society of Civil Engineers (1997) and American Concrete Institute (ACI-440.1R-06) were reviewed. Shear design predictions were compared with experimental results in which it was observed that all the three standards provided conservative predictions. However, ACI found most efficient compare to other two there is room to improve the efficiency of the recommendations.