[pt] A utilização do concreto de alta resistência já é uma realidade e muitos países estão adaptando suas normas para levar em conta as propriedades deste material. No dimensionamento de pilares esbeltos e seções com concreto de alta resistência é importante observar a relação tensão- deformação adotada no cálculo, pois enquanto para o concreto convencional a deformação máxima, ecu, é 0,0035, para o de alta resistência esta deformação depende do valor da resistência do concreto, diminuindo com o aumento do fck. Para um concreto com fck = 80 MPa, por exemplo, ecu é em torno de 0,0022 de acordo com as relações tensão - deformação propostas pelo MC90-CEB. A relação tensão- deformação com ecu dependente de fck irá alterar os diagramas de interação adimensionais para o dimensionamento de pilares esbeltos e concreto de alta resistência. São construídos neste trabalho diagramas de interação força normal - momento fletor - curvatura (n,m,f) e força normal - momento fletor - índice de esbeltez (n,m,l) para o dimensionamento de pilares esbeltos e diagramas de interação (nd,md) e (nd,mdx,mdy) para o dimensionamento de seções submetidas a flexão composta reta e oblíqua. Adotou- se a relação tensão-deformação proposta pelo MC90-CEB e valores de fck de 50 a 80 MPa. Os diagramas para pilares esbeltos foram construídos com auxílio do programa PCFRAME (KRÜGER, 1989) e os diagramas para o dimensionamento de seções foram construídos com um programa desenvolvido neste trabalho. Através dos resultados, observa-se que, como ecu depende de fck, todos os diagramas de interação sofreram diferenças, podendo ser dito ainda que o uso dos diagramas já existentes, construídos com ecu constante e igual a 0,0035, pode conduzir a erros contra a segurança estrutural. / [en] The use of high strength concrete is already a reality and many countries are adapting their design codes to take into account the properties of this material. For the design of slender columns and sections subjected to combined axial force and bending, the most important property is the stress-strain relationship. While for normal concrete the strain at ultimate, ecu, can be considered constant and equal to 0,0035, for high strength concrete ecu depends on the concrete strength, decreasing as the strength increases. For a concrete with fck of 80 MPa, for instance, ecu is around 0,0022 according to the CEB Model Code (1990). Stress-strain relationship with ecu dependent of fck will affect the nondimensional interaction diagrams for the design of slender columns and sections of high strength concretes. Nondimensional interaction diagrams moment-axial load-curvature (m,n,f) and diagrams moment-axial load- slenderness ratio (m,n,l), for the design of slender columns, and nondimensional interaction diagrams (md,nd) and (nd,mdx,mdy) , for compression plus axial and biaxial bending of sections, are constructed in this work. The diagrams were constructed for concretes with strength between 50 MPa and 80 MPa, adopting suitable stress-strain relationships recommended by the CEB Model Code 1990. The diagrams for slender columns were constructed with the aid of an existing computational program developed in an earlier thesis, while the diagrams for the design of sections were constructed with a new program, specially developed in this work. The results have shown that all these diagrams are affected, even when presented in a nondimensional form, when stress-strain diagrams with ecu dependent of fck are adopted. The use of traditional nondimensional interaction diagrams, constructed with ecu constant and equal to 0,0035, may lead to errors against structural safety. / [es] La utilización del concreto de alta resistencia es una realidad actual y muchos países estan adaptando sus normas para tener en cuenta las propiedades de este material. En el dimensionamiento de pilares esbeltos y secciones con concreto de alta resistencia es importante observar la relación tensión-deformación que se adopta en el cálculo, porque mientras para el concreto convencional la deformación máxima, ecu, es 0,0035, para el de alta resistencia esta deformación depende del valor de la resistencia del concreto, diminuyendo con el aumento del fck. Para un concreto con fck = 80 MPa, por ejemplo, ecu es en torno de 0,0022 de acordo con las relaciones tensión - deformación propostas por el MC90-CEB. La relación tensión- deformación con ecu dependente de fck alterará los diagramas de interacción adimensionales para el dimensionamiento de pilares esbeltos y concreto de alta resistencia. En este trabajo se construyen diagramas de interacción fuerza normal - momento flector - curvatura (n,m,f) y fuerza normal - momento flector - índice de esbeltez (n,m,l) para el dimensionamiento de pilares esbeltos y diagramas de interacción (nd,md) y (nd,mdx,mdy) para el dimensionamiento de secciones sometidas a flexión compuesta recta y obliqua. se adoptó la relación tensión-deformación propuesta por el MC90-CEB y valores de fck de 50 la 80 MPa. Los diagramas para pilares esbeltos fueron construidos con auxilio del programa PCFRAME (KRÜGER, 1989) e implementamos un programa para obtener los diagramas para el dimensionamiento de las secciones. A través de los resultados se observa que, como ecu depende de fck, todos los diagramas de interacción sufren diferencias, y puede decirse que el uso de los diagramas construidos con ecu constante e igual la 0,0035, pueden conducir a errores que afectan la seguridad extructural.

Yes / Although several research studies have been conducted on investigating the bond stress – slip behaviour of Glass-Fibre Reinforced Polymer (GFRP) bars embedded in high strength concrete (HSC) using a pull-out method, there is no published work on the bond behaviour of GFRP bars embedded in high strength concrete using a hinged beam. This paper presents the experimental work consisted of testing 28 hinged beams prepared according to RILEM specifications. The investigation of bond performance of GFRP bars in HSC was carried out by analysing the effect of the following parameters: bar diameter (9.5, 12.7 and 15.9 mm), embedment length (5 and 10 times bar diameter), surface configuration (helical wrapping with slight sand coating (HW-SC) and sand coating (SC)) and bar location (top and bottom). Four hinged beams reinforced with 16 mm steel bar were also tested for comparison purposes. The majority of beam specimens failed by pull-out. Visual inspection of the test specimens showed that the bond failure of GFRP (HW-SC) bars usually occurred owing to the bar surface damage, while the bond failure of GFRP (SC) bars was caused due to the detachment of sand coating. The GFRP bars with helical wrapping and sand coated surface configurations showed different bond behaviour and it was found that the bond performance of the sand coated surface was better than that of the helically wrapped surface. Bond strength reduced as the embedment length and bar diameter increased. It was also observed that the bond strength for the bottom bars was higher than that of the top bars. The bond strength was compared against the prediction methods given in ACI-440.1R, CSA-S806 and CSA-S6 codes. All design guidelines underestimated the bond strength of both GFRP re-bars embedded in high strength concrete. / Ministry of Higher Education in Libya for funding.

This research was conducted to characterize the flexural and tensile characteristics of thin, very high-strength, discontinuously reinforced concrete panels developed by the U.S. Army Engineer Research and Development Center. Panels were produced from a unique blend of cementitous material and fiberglass reinforcing fibers, achieving compressive strength and fracture toughness levels that far exceeded that of typical concrete.The research program included third-point flexural experiments, novel direct tension experiments, implementation of micromechanically based analytical models, and development of finite element numerical models. The experimental, analytical, and numerical efforts were used conjunctively to determine parameters such as elastic modulus, first-crack strength, post-crack modulus and fiber/matrix interfacial bond strength. Furthermore, analytical and numerical models implemented in the work showed potential for use as design tools in future engineered material improvements.

No description available.

No description available.

Effective determination of long-term prestress losses is important in the design of prestressed concrete bridges. Over-predicting prestress losses results in an overly conservative design for service load stresses, and under-predicting prestress losses, can result in cracking at service loads. Creep and shrinkage produce the most significant time-dependent effect on prestress losses, and research has shown that high performance and high strength concretes (HPC and HSC) exhibit less creep and shrinkage than conventional concrete. For this reason, the majority of traditional creep and shrinkage models and methods for estimating prestress losses, over-predict the prestress losses of HPC and HSC girders. Nine HPC girders, with design compressive strengths ranging from 8,000 psi to 10,000 psi, and three 8,000 psi lightweight HPC (HPLWC) girders were instrumented to determine the changes in strain and prestress losses. Several creep and shrinkage models were used to model the instrumented girders. For the HPLWC, each model over-predicted the long-term strains, and the Shams and Kahn model was the best predictor of the measured strains. For the normal weight HPC, the models under-estimated the measured strains at early ages and over-estimated the measured strains at later ages, and the B3 model was the best-predictor of the measured strains. The PCI-BDM model was the most consistent model across all of the instrumented girders. Several methods for estimating prestress losses were also investigated. The methods correlated to high strength concrete, the PCI-BDM and NCHRP 496 methods, predicted the total losses more accurately than the methods provided in the AASHTO Specifications. The newer methods over-predicted the total losses of the HPLWC girders by no more than 8 ksi, and although they under-predicted the total losses of the normal weight HPC girders, they did so by less than 5 ksi. / Ph. D.

The use of high compressive strengths in prestressed bridge girders can lower costs by allowing for longer spans, increased girder spacing, and smaller cross-sections. If high strength lightweight concrete (HSLWC) is used, these advantages are further enhanced due to the corresponding reduction in self-weight. Additional benefits can then be realized in the form of more traffic lanes, increased load capacity, smaller substructures, reduced crane capacity requirements, and lower shipping costs. Despite the possible economic savings, HSLWC has been used infrequently in prestressed bridge girder applications across the nation. While recent research has been performed to extend the applicability of current bridge design specifications to normal weight concretes with strengths as high as 18 ksi, little has been done by comparison with regards to HSLWC. The purpose of the research in this report was to assess whether current bridge design specifications for transfer length, development length, prestress loss, camber, and flexural capacity are satisfactory for use with fully-bonded, pretensioned flexural members consisting of HSLWC and to make recommendations for improvements where necessary. Twelve high strength pretensioned beams of variable unit weight (eight lightweight beams and four normal weight beams) and strand size (eight beams with 0.5-in. strand and four beams with 0.6-in. strand) were cast at the Thomas M. Murray Structural Engineering Laboratory at Virginia Tech. These beams were allowed to sit for a period of several months after fabrication while measurements were taken regarding transfer length, prestress loss, and camber. After this period, the beams were load tested to collect development length data, flexural data, and further data related to prestress loss. In addition to the laboratory cast beams, prestress loss and camber data from six full-size bridge beams (five lightweight beams and one normal weight beam) cast as part of a separate project at Virginia Tech was examined. Analysis of the results for all beams shows that with a few caveats, the current AASHTO LRFD Specifications and other design methods examined regarding the topics under consideration are satisfactory for use in the design of HSLWC pretensioned bridge girders with properties similar to those of the beams studied. / Ph. D.

Prestressed concrete structural members camber upwards or downwards depending upon the location of application of prestress force. Identical members do not camber equally due to variability of the factors influencing it. Differential camber in the beams, if significant, results in excessively tall haunches or girder top flange extending into the bottom of the slab. For adjacent members like deck bulb-tees and box girders that are to be transversely post-tensioned the differential camber causes problems during the fit up process. This variation is undesirable and hinders the smooth progress of construction work if not properly accounted for at the design stage. Various factors influence camber and camber growth in prestressed members. Some of the factors are concrete strength and modulus, concrete creep and shrinkage properties, curing conditions, maturity of concrete at release of prestress force, initial strand stress, climatic conditions in storage and length of time in storage. Combinations of these variables result in variation of camber of otherwise similar beams at the time they are erected. One way to increase the precision of camber estimation is to use Monte Carlo simulation based upon the randomized parameters affecting the camber and camber growth. In this method, the parameters, in the form of a probability distribution function, are combined and passed through a deterministic model resulting in camber and camber growth prediction with narrowed probability bounds as compared to single definite value given by most contemporary methods. This outcome gives the expected range of cambers for a given girder design. After determining the expected range of camber, the ultimate goal is to provide guidelines for using unbonded monostrands for camber adjustment. / Master of Science

Yes / In this study, bond properties of glass fibre reinforced polymer (GFRP) bars embedded in high-strength concrete (HSC) were experimentally investigated using a pull-out test. The experimental program consisted of testing 84 pull-out specimens prepared according to ACI 440.3R-12 standard. The testing of the specimens was carried out considering bar diameter (9.5, 12.7 and 15.9 mm), embedment length (2.5, 5, 7.5 and 10 times bar diameter) and surface configuration (helical wrapping with slight sand coating (HW-SC) and sand coating (SC)) as the main parameters. Twelve pull-out specimens reinforced with 16 mm steel bar were also tested for comparison purposes. Most of the specimens failed by a pull-out mode. Visual inspection of the tested specimens reinforced with GFRP (HW-SC) bars showed that the pull-out failure was due to the damage of outer bar surface, whilst the detachment of the sand coating was responsible for the bond failure of GFRP (SC) reinforced specimens. The bond stress – slip behaviour of GFRP (HW-SC) bars is different from that of GFRP (SC) bars and it was also found that GFRP (SC) bars gave a better bond performance than GFRP (HW-SC) bars. It was observed that the reduction rate of bond strength of both GFRP types with increasing the bar diameter and the embedment length was reduced in the case of high-strength concrete. Bond strength predictions obtained from ACI-440.1R, CSAeS806, CSA-S6 and JSCE design codes were compared with the experimental results. Overall, all design guidelines were conservative in predicting bond strength of both GFRP bars in HSC and ACI predictions were closer to the tested results than other codes.

In this thesis the experimental results of seven full-scale glass fiber-reinforced polymer (GFRP) reinforced concrete (RC) slab-column edge connections are presented. The dimensions of the slabs were 2,800×1,550×200 mm with a square column measuring 300×300×2,200 mm. The test connections were divided into two series. Series I included three connections investigating the effect of flexural reinforcement ratio (0.90, 1.35 and 1.80%) when high strength concrete (HSC) is used, while Series II included four connections investigating the effect of GFRP shear reinforcement type and pattern on normal strength concrete (NSC) connections. Test results showed that increasing the reinforcement ratio increased the punching capacity and the post-cracking stiffness of the HSC connections. Furthermore, the use of headed studs and corrugated bars increased the punching capacity and the deformability of the NSC connections. Test results were compared to the predictions of the Canadian and American design provisions for FRP-RC structures. / February 2017