The aim of this work is to present a strut-and-tie model for design of reinforced concrete pile caps. The model considers both failure by crushing of the compressed struts and by yielding of the tie reinforcement. Unlike some traditional models, crushing of the compressed concrete is not checked at the section in direct contact with the column base (column/pile cap interface). In this work, crushing of concrete is verified in a section at a certain depth inside the pile cap. Thus, this verification is replaced by determining the height of the nodal zone at the top of the pile cap required not to cause crushing of the struts. An iterative algorithm is used for this purpose. Comparison with a large number of experimental results available in the literature demonstrates the effectiveness of the proposed model for the design of concrete pile caps. Numerical examples of practical use of the model are also presented.
The aim of this work is to present a new strut-and-tie model for design of rigid pile caps based on the concept of magnified area under the column. In this magnified area, compressive stresses have been reduced enough not to cause crushing of the struts. An iterative algorithm is used to determine the required depth of the magnified area. The model considers both failure by crushing of the compressed struts and by yielding of the tie reinforcement. A large number of experimental results available in the literature is used to test the model. The partial safety factors method is employed for pile caps design and structural safety is evaluated by means of the reliability index. The small failure probability, estimated through the reliability index, demonstrates the safety of the proposed method. A numerical example of practical use of the model is also presented.
The purpose of this paper is to present a non-linear model for analysis and design of slender reinforced-concrete columns subjected to uniaxial and biaxial bending. This model considers both material and geometric non-linearities, as well as creep effects. The structural analysis is performed by the finite-element method associated with an iterative process to solve the system of non-linear equations. The column may have an arbitrary polygonal cross-section, including openings. Green's theorem is used to perform the integration at the level of the cross-sections, which is greatly simplified with the use of a new parabola–rectangle diagram proposed for concrete in compression. This new diagram provides the correct value of the tangent modulus of elasticity of concrete, allowing its use for non-linear analysis of slender columns. By changing the strain value corresponding to the maximum stress, it is possible to use a single stress–strain diagram for displacement calculation and rupture verification, which facilitates the design of slender columns. The accuracy of the method is demonstrated through the analysis of several columns tested experimentally by other authors.
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