Effect of temperature on RC elements strengthened with CFRP

The strengthening of RC elements with CFRP is a technique that has been acquiring more and more potential. The bond between the CFRP reinforcement and the concrete support is usually made with epoxy adhesives. However, it is here that the integrity of the system can be affected, namely by exposure to high temperatures. In order to study the effect of an increase of air temperature on the behaviour of the epoxy adhesive, CFRP strengthened RC and reference RC specimens were tested. After cyclical thermal exposures, with temperatures rising between 20ºC and 80ºC, specimens were subjected either to compressive shear tests or bending tests. The results demonstrated that epoxy adhesive exhibits poor behaviour when subjected to increased temperatures, causing important bond deterioration. The improvement achieved with the CFRP reinforcement tends to disappear with an increase of the environment temperature. So, the thermal resistance of this strengthened system can not be considered very high. However, the inclusion of insulating materials can be a good solution to protect the strengthened RC elements. Among tested materials, the foamed polyurethane showed the best behaviour

Tests of concrete flanged beams reinforced with CFRP bars.

yesTests results of three flanged and two rectangular cross-section concrete beams reinforced with carbon fibre reinforced polymer (CFRP) bars are reported. In addition, a companion concrete flanged beam reinforced with steel bars is tested for comparison purposes. The amount of CFRP reinforcement used and flange thickness were the main parameters investigated in the test specimens. One CFRP reinforced concrete rectangular beam exhibited concrete crushing failure mode, whereas the other four CFRP reinforced concrete beams failed due to tensile rupture of CFRP bars. The ACI 440 design guide for FRP reinforced concrete members underestimated the moment capacity of beams failed due to CFRP tensile rupture and reasonably predicted deflections of the beams tested. A simplified theoretical analysis for estimating the moment capacity of concrete flanged beams reinforced with FRP bars was developed. The experimental moment capacity of the CFRP reinforced concrete beams tested compared favourably with that predicted by the theoretical analysis developed

Continuous Concrete Beams Reinforced With CFRP Bars.

yesThis paper reports the testing of three continuously and two simply supported concrete beams reinforced with carbon fibre reinforced polymer (CFRP) bars. The amount of CFRP reinforcement in beams tested was the main parameter investigated. A continuous concrete beam reinforced with steel bars was also tested for comparison purposes. The ACI 440.1R-06 equations are validated against the beam test results. Test results show that increasing the CFRP reinforcement ratio of the bottom layer of simply and continuously supported concrete beams is a key factor in enhancing the load capacity and controlling deflection. Continuous concrete beams reinforced with CFRP bars exhibited a remarkable wide crack over the middle support that significantly influenced their behaviour. The load capacity and deflection of CFRP simply supported concrete beams are reasonably predicted using the ACI 440.1R-06 equations. However, the potential capabilities of these equations for predicting the load capacity and deflection of continuous CFRP reinforced concrete beams have been adversely affected by the de-bonding of top CFRP bars from concrete

Experimental Study on Demountable Shear Connectors in Composite Slabs with Profiled Decking

yesThis paper presents an experimental study on shear strength, stiffness and ductility of demountable shear connectors in metal decking composite slabs through push-off tests. Twelve full-scale push-off tests were carried out using different concrete strength, number of connectors and different connector diameter. The experimental results showed that the demountable shear connectors in metal decking composite slabs have similar shear capacity and behaviour as welded shear studs and fulfilled the minimum ductility requirement of 6mm required by Eurocode 4. The shear capacity was compared against the prediction methods used for the welded shear connections given in Eurocode 4, AISC 360-10, ACI 318-08 and method used for bolted connection in Eurocode 3. It was found that the AISC 360-10 method overestimated the shear capacity while the ACI 318-08 method underestimated the shear capacity of specimens with single shear connector per trough. The Eurocodes method was found to provide a safe prediction for specimens with single and pair demountable connectors per trough. In addition, prediction methods given in both AISC 360-10 and ACI 318-08 for welded shear studs overestimated the shear capacity of specimens with 22 mm diameter demountable connectors that failed in concrete crushing.PhD work from EPSRC studentshi

Axial behavior of reinforced concrete short columns strengthened with wire rope and T-shaped steel plate units.

yesThis paper presents a relatively simple column strengthening procedure using unbonded wire rope and T-shaped steel plate units. Twelve strengthened columns and an unstrengthened control column were tested to failure under concentric axial load to explore the significance and shortcomings of the proposed strengthening technique. The main variables investigated were the volume ratio of wire ropes as well as geometrical size and configuration of T-shaped steel plates. Axial load capacity and ductility ratio of columns tested were compared with predictions obtained from the equation specified in ACI 318-05 and models developed for conventionally tied columns, respectively. The measured axial load capacities of all strengthened columns were higher than predictions obtained from ACI 318-05, indicating that the ratio of the measured and predicted values increased with the increase of volume ratio of wire ropes and flange width of T-shaped steel plates. In addition, at the same lateral reinforcement index, a much higher ductility ratio was exhibited by strengthened columns having a volume ratio of wire ropes above 0·0039 than tied columns. The ductility ratio of strengthened columns tested increased with the increase of flange width, thickness, and web height of T-shaped steel plates. A mathematical model for the prediction of stress–strain characteristics of confined concrete using the proposed strengthening technique is developed, that was in good agreement with test results

Structural Behaviour of Reinforced Concrete Continuous Deep Beams with Web Openings.

yesTen reinforced-concrete continuous deep beams with openings were tested to failure. The main variables investigated were the shear span-to-overall depth ratio, and the size and location of openings. Two failure modes influenced by the size and location of web openings regardless of the shear span-to-overall depth ratio were observed. The normalised load capacity of beams having a web opening area ratio of 0·025 within exterior shear spans was approximately similar to that of their companion solid beams. Continuous deep beams having web openings within interior shear spans exhibited a higher load capacity reduction with the increase of the opening size, similar to simply supported deep beams with web openings. Formulae based on the upper bound analysis of the plasticity theory were proposed to predict the load capacity of continuous deep beams with web openings. Comparisons between the measured and predicted load capacities showed a good agreement

Shear capacity of reinforced concrete corbels using mechanism analysis

A mechanism analysis is developed to predict the shear capacity of reinforced concrete corbels. Based on shear failure observed in experimental tests, kinematically admissible failure mechanisms are idealised as an assemblage of two rigid blocks separated by a failure plane of displacement discontinuity. Shear capacity predictions obtained from the developed mechanism analysis are in better agreement with corbel test results of a comprehensive database compiled from the available literature than other existing models for corbels. The developed mechanism model shows that the shear capacity of corbels generally decreases with the increase of shear span-to-depth ratio, increases with the increase of main longitudinal reinforcement up to a certain limit beyond which it remains constant, and decreases with the increase of horizontal applied loads. It also demonstrates that the smaller the shear span-to-overall depth ratio of corbels, the more effective the horizontal shear reinforcement

Experimental Technique for Measuring the Long-term Transfer Length in Prestressed Concrete

This article presents a proposal of a test set-up and methodology for testing the transfer length evolution through time of prestressing reinforcement in pretensioned prestressed concrete members, aimed at providing a basis for standardization. The proposed test method is based on the instantaneous and time-related analysis of the prestressing reinforcement force profile at only one end of a pretensioned prestressed concrete member. The basis of the test method and the requirements of the prestressing frame and its components are presented, as well as the test procedure stages and the measurement devices. The interpretation of the test results and the criteria to determine both the initial and the long-term transfer lengths are explained. A test method application and the equipment for testing seven-wire prestressing strands have been designed. Some experimental results are provided to validate the test. A comparative analysis of test reliability with other existing experimental methods is also included. © 2012 Wiley Publishing Ltd.Funding for this experimental research work was provided by the Spanish Ministry of Education and Science and ERDF (Projects BIA2006-05521 and BIA2009-12722). Tests were conducted in the Institute of Concrete Science and Technology (ICITECH), Universitat Politecnica de Valencia (Spain).Martí Vargas, JR.; Caro Forero, LA.; Serna Ros, P. (2013). Experimental Technique for Measuring the Long-term Transfer Length in Prestressed Concrete. Strain. 49(2):125-134. doi:10.1111/str.12019S125134492Balaji Rao, K., Anoop, M. B., Sreeshylam, P., Sridhar, S., Kesavan, K., & Ravisankar, K. (2009). Assessment of Pre-Stress Losses in Instrumented Pre-Stressed Concrete Beams Using Stochastic Analysis. Strain, 47, e175-e188. doi:10.1111/j.1475-1305.2008.00551.xBase, G. D. (1957). Some tests on the effect of time on transmission length in pre-tensioned concrete. Magazine of Concrete Research, 9(26), 73-82. doi:10.1680/macr.1957.9.26.73Grace, N. F. (2000). Transfer Length of CFRP/CFCC Strands for Double-T Girders. PCI Journal, 45(5), 110-126. doi:10.15554/pcij.09012000.110.126Russell, B. W., & Burns, N. H. (1996). Measured Transfer Lengths of 0.5 and 0.6 in. Strands in Pretensioned Concrete. PCI Journal, 41(5), 44-65. doi:10.15554/pcij.09011996.44.65Marti-Vargas, J. R., Arbelaez, C. A., Serna-Ros, P., Navarro-Gregori, J., & Pallares-Rubio, L. (2007). Analytical model for transfer length prediction of 13 mm prestressing strand. Structural Engineering and Mechanics, 26(2), 211-229. doi:10.12989/sem.2007.26.2.211Floyd, R. W., Howland, M. B., & Micah Hale, W. (2011). Evaluation of strand bond equations for prestressed members cast with self-consolidating concrete. Engineering Structures, 33(10), 2879-2887. doi:10.1016/j.engstruct.2011.06.012Weerasekera , I. 1991 Transfer and flexural bond in pretensioned prestressed concrete University of Calgary, UMI Dissertation ServicesArango, S. E., Serna, P., Martí-Vargas, J. R., & García-Taengua, E. (2011). A Test Method to Characterize Flexural Creep Behaviour of Pre-cracked FRC Specimens. Experimental Mechanics, 52(8), 1067-1078. doi:10.1007/s11340-011-9556-2Wu, C.-H., Zhao, W., Beck, T., & Peterman, R. (2009). Optical Sensor Developments for Measuring the Surface Strains in Prestressed Concrete Members. Strain, 47, e376-e386. doi:10.1111/j.1475-1305.2009.00621.xDeatherage, J. H., & Burdette, E. G. (1994). Development Length and Lateral Spacing Requirements of Prestressing Strand for Prestressed Concrete Bridge Girders. PCI Journal, 39(1), 70-83. doi:10.15554/pcij.01011994.70.83Lu, Z., Boothby, T. E., Bakis, C. E., & Nanni, A. (2000). Transfer and Development Lengths of FRP Prestressing Tendons. PCI Journal, 45(2), 84-95. doi:10.15554/pcij.03012000.84.95Kahn, L. F., Dill, J. C., & Reutlinger, C. G. (2002). Transfer and Development Length of 15-mm Strand in High Performance Concrete Girders. Journal of Structural Engineering, 128(7), 913-921. doi:10.1061/(asce)0733-9445(2002)128:7(913)Martí-Vargas, J. R., Fernández-Prada, M. A., Arbeláez, C. A., Serna-Ros, P., & Miguel-Sosa, P. F. (2006). Transfer and Development Lengths of Concentrically Prestressed Concrete. PCI Journal, 51(5), 74-85. doi:10.15554/pcij.09012006.74.85Martí-Vargas, J. R., Serna, P., Navarro-Gregori, J., & Bonet, J. L. (2012). Effects of concrete composition on transmission length of prestressing strands. Construction and Building Materials, 27(1), 350-356. doi:10.1016/j.conbuildmat.2011.07.038Martí-Vargas, J. R., Serna, P., Navarro-Gregori, J., & Pallarés, L. (2012). Bond of 13mm prestressing steel strands in pretensioned concrete members. Engineering Structures, 41, 403-412. doi:10.1016/j.engstruct.2012.03.056EVANS, R. H., & ROBINSON, G. W. (1955). BOUND STRESSES IN PRESTRESSED CONCRETE FROM X-RAY PHOTOGRAPHS. Proceedings of the Institution of Civil Engineers, 4(2), 212-235. doi:10.1680/iicep.1955.11375Linger, D. A., & Bhonsle, S. R. (1963). An Investigation of Transfer Length In Pretensioned Concrete Using Photoelasticity. PCI Journal, 8(4), 13-30. doi:10.15554/pcij.08011963.13.30Chen, H.-L. (Roger), & Wissawapaisal, K. (2001). Measurement of Tensile Forces in a Seven-Wire Prestressing Strand Using Stress Waves. Journal of Engineering Mechanics, 127(6), 599-606. doi:10.1061/(asce)0733-9399(2001)127:6(599)Caro, L. A., Martí-Vargas, J. R., & Serna, P. (2012). Time-dependent evolution of strand transfer length in pretensioned prestressed concrete members. Mechanics of Time-Dependent Materials, 17(4), 501-527. doi:10.1007/s11043-012-9200-

Inclined reinforcement around web opening in concrete beams

YesTwelve reinforced-concrete continuous deep beams having web openings within interior shear spans were tested to failure. The main variables investigated were the opening size and the amount of inclined reinforcement around openings. An effective inclined reinforcement factor combining the influence of the amount of inclined web reinforcement and opening size is proposed and used to analyse the structural behaviour of continuous deep beams tested. It was observed that the end support reaction, diagonal crack width and load capacity of beams tested were significantly dependent on the proposed effective inclined reinforcement factor. As this factor increased, the end support reaction and increasing rate of diagonal crack width were closer to those of companion solid deep beams. In addition, a higher load capacity was exhibited by beams having an effective inclined reinforcement factor above 0.077 than the companion solid deep beam. A numerical procedure based on the upper-bound analysis of the plasticity theory was proposed to estimate the load capacity of beams tested. Comparisons between the measured and predicted load capacities showed good agreement

Flexural Rigidity Evaluation of Seismic Performance of Hollow-Core Composite Bridge Columns

This paper investigates experimentally the seismic behavior of two hollow-core fiber-reinforced polymer-concrete-steel HC-FCS columns under cyclic loading as a cantilever. The typical precast HC-FCS member consists of a concrete wall sandwiched between an outer fiber-reinforced polymer (FRP) tube and an inner steel tube. The FRP tube provides continuous confinement for the concrete wall along the height of the column. Five large-scale HC-FCS columns were investigated during this study to estimate the effective flexural (which is an important factor to define the buckling capacity and deflection of such columns) and the effective structural stiffness of the composite columns. These columns have the same geometric properties; the only difference was in the thickness of the inner circular steel tubes and the steel tube embedded length into the footing. A three-dimensional numerical model has been developed using LS_DYNA software for modeling this large scale HC-FCS columns. The nonlinear FE models were designed and validated against experimental results gathered from HC-FCS columns tested under cyclic lateral loading and used to evaluate the effective stiffness’s results. The estimated effective stiffness results that obtained from the experimental work were compared with the FE results. This study revealed that the effective flexural and the effective structural stiffness for the HC-FCS columns need more investigation to be addressed in the standard codes. Since the embedded hollow core steel tube socket connections cannot reach the fully fixed end condition to act as a cantilever member subjected to a lateral load with a fully fixed end condition. Moreover, the effective stiffness results were found to be highly sensitive to the steel tube embedded length and slightly to the unconfined concrete strength