Flexure of continuous HSC beams with external CFRP tendons: effects of fibre elastic modulus and steel ratio

The results of a theoretical study on the flexural behaviour of continuous high-strength concrete (HSC) beams prestressed with external fibre reinforced polymer (FRP) tendons are presented. A previously developed numerical model is extended to the analysis of continuous HSC beams with external FRP tendons. A numerical test is conducted on two-span externally prestressed beams made of HSC with compressive strength of 90 MPa. The external tendons are assumed to be carbon FRP (CFRP) composites covering a wide range of modulus of elasticity. Various levels of nonprestressed steel ratio are used. Comprehensive aspects of behaviour of such type of beams are examined. The results show that CFRP with high elastic modulus of 500 GPa mobilizes quite different structural responses compared to those with normal elastic modulus, and that the amount of nonprestressed steel affects remarkably the behaviour of such beams. The study also indicates that some moment redistribution knowledge valid for conventional continuous concrete beams may not be applicable to continuous HSC beams with external FRP tendons

Factors affecting moment redistribution at ultimate in continuous beams prestressed with external CFRP tendons

A numerical investigation of redistribution of moments in continuous concrete beams prestressed with external carbon fiber reinforced polymer (CFRP) tendons at failure loads is described. A finite element analysis (FEA) model is introduced, and an extensive parametric study is carried out on two-span continuous beams. The factors examined in this study include the content of non-prestressed steel, tendon eccentricities, tendon area, effective prestress, span-to-height ratio, concrete strength, CFRP modulus of elasticity and load type. The results obtained from FEA are compared with those obtained from various codes. The study shows that the importance of some factors is not reflected in the codes. When used to calculate the degree of moment redistribution in these beams, the parameter εt (net strain in extreme tension steel) seems to be more reasonable than the parameter c/d (ratio of neutral axis depth to section effective depth). A simplified equation for calculating the degree of moment redistribution at ultimate is proposed

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Inexistent

Revisiting Cracking in Reinforced Concrete Beams: An Updated Analysis

As materials and structural optimization continue to be important in design, structural safety checks for service limit states have become increasingly important. One key aspect of these checks is the controlling of cracks to prevent them from affecting the structure’s function or appearance. However, the authors have found that current regulations do not accurately reflect the reality of crack behavior. This is the case of the crack spacing. To address this issue, the authors conducted experiments on 27 reinforced concrete beams to investigate crack location, cracking moment, corresponding deflection, and crack width values as sag increases. Their main finding was that cracks tend to appear at the stirrup locations, and that crack width increases linearly with the sag-to-free-span ratio up to the yielding point. They also concluded that increasing the amount of tensile reinforcement is an effective way to reduce crack width for the same sag

Influence of the Composition of the Activator on Mechanical Characteristics of a Geopolymer

Geopolymer materials are characterized by their high durability and low carbon dioxide emissions, when compared with more traditional materials, like concrete made from ordinary Portland cement. These are interesting advantages and might lead to a more sustainable construction industry. The aim of this study is the characterization of the mechanical behavior of the materials obtained by the activation of metakaolin. The activator is a mixture of sodium hydroxide with sodium silicate in di erent proportions. The influence of the composition of activator is studied. For the analysis of the mechanical properties of the di erent mixtures two di erent types of tests were performed, bending tensile strength tests and compressive strength tests. The results show that an activator with not less than 300 g of sodium hydroxide and not exceeding 600 g of sodium silicate per 750 g of metakaolin gives the best results, for both tensile strength and compressive strength

Influence of the Composition of the Activator on Mechanical Characteristics of a Geopolymer

Geopolymer materials are characterized by their high durability and low carbon dioxide emissions, when compared with more traditional materials, like concrete made from ordinary Portland cement. These are interesting advantages and might lead to a more sustainable construction industry. The aim of this study is the characterization of the mechanical behavior of the materials obtained by the activation of metakaolin. The activator is a mixture of sodium hydroxide with sodium silicate in different proportions. The influence of the composition of activator is studied. For the analysis of the mechanical properties of the different mixtures two different types of tests were performed, bending tensile strength tests and compressive strength tests. The results show that an activator with not less than 300 g of sodium hydroxide and not exceeding 600 g of sodium silicate per 750 g of metakaolin gives the best results, for both tensile strength and compressive strength

Estudo comparativo de efeitos geometricamente não-lineares em pontes atirantadas

Este texto tem como objectivo a avaliação da importância relativa das fontes de não- linearidade geométrica na resposta estrutural de pontes atirantadas metálicas sujeitas a carregamentos estáticos. As análises linear, pseudo-linear e não-linear foram realizadas com o propósito de salientar restrições e os efeitos do comportamento não-linear. As formulações matemáticas dos elementos finitos utilizados são apresentadas e o comportamento numérico destes testado de forma a garantir uma avaliação precisa da contribuição de cada efeito não- linear – o efeito de catenária, o efeito P-∆ e o efeito P-δ – na resposta estrutural. Confirma-se que o efeito de catenária e o efeito P-∆ são as não-linearidades que mais contribuem para o comportamento altamente não-linear apresentado, especialmente quando são aplicadas sobrecargas de utilização e, mais particularmente, aquando da própria construção faseada da superstrutura. Ainda que requerendo um custo numérico mínimo e uma fácil adaptação a programas de análise linear por Elementos Finitos, conclui-se que a análise pseudo-linear se mostra extremamente limitada na obtenção de resultados satisfatórios na análise das pontes de tirantes actuais

Experimental Study on the Flexural Behavior of Alkali Activated Fly Ash Mortar Beams

This work aims to study the possibility of using alkaline activated fly ash in structural members. The work, of an experimental nature, focuses on the evaluation of the behavior of simply supported beams under two symmetrical loads (four-point tests). For such study, 10 beams were built, of which, five using fly ash and the remaining five using traditional Portland cement. The test results are compared. Conclusions on the practical application of fly ash in structures were explained and, as mention later in this document, there is room for improvement. This is one of very few works on fly ash alkali activated structures and further studies are necessary in the future. Some aspects, such as shrinkage and deformability are presented as some of the negative points concerning the potential use of fly ash. These are two aspects that need more attention in future investigations

Flexural Response of Continuous Concrete Beams Prestressed with External Tendons

This article presents the results of a numerical investigation of the flexural behavior of continuous externally prestressed concrete beams. Aspects of behavior studied include the increase in stress in external tendons, moment redistribution in the post-elastic range and secondary moments due to prestressing. A finite element model for the full-range analysis of continuous externally prestressed concrete beams is introduced. The model predictions agree well with the experimental results. The analysis shows that the ultimate stress increase in external tendons of continuous beams is dependent on both the number and rotation of plastic hinges that can be developed at failure load. The degree of moment redistribution is significantly influenced by the nonprestressed tension steel and the pattern of loading. An approach based on linear transformation concept is designed to examine the secondary moments over entire loading up to the ultimate. The results indicate that the secondary moments increase linearly with the prestressing force and can be conveniently calculated by an elastic analysis

Nonlinear and time-dependent analysis of continuous unbonded prestressed concrete beams

This paper describes a numerical model developed to predict the full-range nonlinear response, as well as time-dependent service-load behaviour, of continuous beams prestressed with internal unbonded tendons. Both geometric and material nonlinearities are considered. The strain increment in unbonded tendon, at any deformed state, is computed from the elongation of the entire tendon between end anchorages. The unbonded prestressing contributes to the concrete beam by equivalent loads, which would be updated continuously during the solution process. The analysis reproduces the experimental results of continuous beam specimens with favourable agreement. Some important aspects of behaviour of the continuous beams are examined