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This paper describes a numerical study on the flexural behavior of concrete beams prestressed with external tendons, focusing on the effect of the span-depth ratio (L/dp) on the response characteristics and the ultimate stress in tendons and ductility behavior. A nonlinear model, calibrated by the available experimental results of externally prestressed specimens, is used for the parametric evaluation. The results show that the second-order effects of externally prestressed beams with two deviators at third points become increasingly important with the increase of the L/dp and that, due to these effects, a higher L/dp registers a lower ultimate moment capacity. The effect of the L/dp on the ultimate tendon stress is dependent on the type of loading for internal unbonded tendons and on the configuration of deviators for external tendons. The analysis also indicates that, irrespective of second-order effects, the L/dp has an insignificant effect on the ductility of beams, and center-point loading mobilizes higher deflection ductility than third-point or uniform loading. [ABSTRACT FROM AUTHOR]

The service loads are often decisive in the design of concrete structures. The evaluation of the cracking moment, Mcr, is an important issue to predict the performance of the structure, such as, the deflections of the reinforced concrete beams and slabs. To neglect the steel bars of the section is a simplification that is normally used in the computation of the cracking moment. Such simplification leads to small errors in the value of this moment (typically less than 20%). However, these small errors can conduce to significant errors when the values of deflections need to be computed from Mcr. The article shows that an error of 10% on the evaluation of M~. can lead to errors over 100% in the deformation values. When the deformation of the structure is the decisive design parameter, the exact computing of the cracking moment is obviously very important. Such rigorous computing might lead to important savings in the cost of the structure. With this article the authors wish to draw the attention of the technical community to this fact. A simple equation to evaluate the cracking moment, M~ is proposed for a rectangular cross- section. This equation leads to cracking moments higher than those obtained by neglecting the reinforcement bars and is a simple rule that can be included in Eurocode 2. To verif~y the accuracy of the developed model, the results of the proposed equation was compared with a rigorous computational procedure. The proposed equation corresponds to a good agreement when compared with the previous approach and, therefore, this model can be used as a practical aid for calculating an accurate value of the cracking moment. [ABSTRACT FROM AUTHOR]

The mechanical behaviour of timber-concrete structures is significantly influenced by the stiffness of the joints, both with regard to deformations and to strength. This paper analyses the experimental and numerical assessment of the stiffness of timber-concrete joints, made with dowel-type fasteners. The objective of this analysis is to provide information to be used in the design of timber-concrete composite structures. In order to achieve this, two approaches were used: experimental tests with timber-concrete joints and numerical predictions using models available in the literature. As part of the experimental assessment, shear tests were performed with various joint configurations aiming to be representative of a wide range of practical conditions. The results obtained are presented and discussed. In terms of numerical assessment, two types of models were considered: analytical models, based on the beam on elastic foundation and empirical models. The results obtained in the experimental tests are compared with those obtained from the design models. Based on that analysis the accuracy of the numerical predictions is discussed. [ABSTRACT FROM AUTHOR]