José Samuel Giongo

Deformations in the strut of two pile caps

Resumo There are several models for the design of pile caps, one of them, is the strut and tie model. Struts are graphical representations of the flows of the compression principal stress, while, the tie represents the flows of the tensile principal stress. The NBR 6118:2003 [1] recommends the use of strut and tie model for the design and verification of pile caps. The use of simple strut and tie models is much used by engineers. Basically, the model consists in determining steel areas based on the traction tie and verifying the crushing of the concrete in the inferior and superior nodal zones (the interface between the inferior face of the pile cap and the pile is the inferior nodal zone and, the interface between the superior face of the pile cap and the column, is the superior nodal zone). The strut integrity is guaranteed when the stress intensities in the superior and inferior nodal zones are lower than the limit value. This limit value is determined in function of the mechanical properties of the concrete pile cap and the stresses in the strut are determined in function of the internal forces and the area of the inferior and superior nodal zones. The correct form of the diagonal compression inside the pile cap is unknown. In function of the experimental analysis of the principal compression strain, the geometric form of the strut to two pile caps submitted the centered and eccentric load is shown along with the intensity of the stress in the inferior nodal zone.

Influência das dimensões da seção transversal do pilar e da excentricidade da força de compressão no comportamento estrutural de blocos sobre duas estacas

Resumo To design of the pile caps are utilized the strut and tie model and bending theory. The Model Blevot and Fremy [1] is one of the models used to design of pile-caps. Another method for the design of caps is Model Beam that used bending theory. In the model of French researchers to cross section of the column is proportional to the cross section of strut near the column. To check the influence of the column cross section in the structural behaviour of the pile caps, experimental tests of the two pile caps were realized, varying the dimensions of the column and the high of the pile caps. Comparative analysis of experimental results with the results found by the Model Blevot and Fremy [1] was realized. It was observed that the increase of the column cross section conferred the pile caps greater strength capacity.

Blocos de concreto armado sobre seis estacas: simulação numérica e dimensionamento pelo método de bielas e tirantes

© 2014 IBRACON This paper presents the structural behavior of six reinforced concrete pile caps in rectangular arrangement, considering the ground deformability of pile support, different concrete strengths with square or rectangular cross section of column under central load. For this purpose, the analysis emphasizes a strut and tie method design and a three-dimensional numerical using the finite element method. So, the stress flow configuration and the formation of struts were seen in perspective. How much deformable is the ground, more uniform are the reactions distribution observed between the piles. The column cross section influenced the configuration of the connecting struts. The concrete strength variation had more influence in the pile caps strength than the stiffness. The analytical method has shown compatibility which obtained from the numerical simulation results.

Numerical analysis of two pile caps with sockets embedded, subject the eccentric compression load

The structural behavior of pile caps with sockets embedded is influenced by interface of column-socket, which can be smooth or rough. With intent to analyze the behavior of two pile caps with embedded socket, considering the friction between the column and the socket, with eccentric normal load, the numerical simulations were carried out, using a program based on the Finite Element Methods (FEM). In the numerical analysis the non-linear behavior of materials was considered, also the friction between the column and the socket. It was considered perfect bond between the reinforcement and the concrete around. It was observed that the embedded length is preponderant factor in the structural behavior of the analyzed element.

Estudo experimental de blocos de fundação com cálice externo, embutido e parcialmente embutido considerando interface lisa

Nas estruturas de concreto pre-moldado, a ligacao pilar-fundacao pode ocorrer por meio do calice de fundacao, que por sua vez pode estar embutido, parcialmente embutido com parte do colarinho saliente, ou externo com o colarinho saliente em relacao ao bloco de fundacao. Apresenta-se neste trabalho um estudo experimental de blocos de fundacao sobre duas estacas com calice externo, parcialmente embutido e embutido, submetidos a acao centrada utilizando modelos em escala reduzida 1:2. Nos modelos analisados, considerou-se a conformacao lisa nas paredes do calice e do pilar. Os resultados sao comparados a um modelo de referencia, com ligacao monolitica entre o pilar e o bloco. Observa-se que o bloco com calice externo apresenta forca ultima com a mesma ordem de grandeza do bloco de referencia, porem os blocos com calice parcialmente embutido e embutido apresentam forca ultima inferior a dos demais modelos.

Análise dos efeitos da variação da seção de pilares quadrados e retangulares com diferentes taxas de armadura longitudinal na armadura principal de tração de blocos sobre duas estacas

Resumo The pile-cap structural elements are used as a transition between the columns of buildings and foundations. The most appropriate method for the pile caps design is the Strut and Tie model. In most cases in the structural project is not considered the influence of certain parameters: the columns cross section and the amount of longitudinal reinforcement columns. This paper studies the effect of the variability of the geometric section of square and rectangular columns, with different longitudinal reinforcement rates, in the main reinforcement traction two pile caps. The basis for study was development experimental program in the Structures Laboratory of EESC-USP. The traction reinforcement bars strains are reduced the pile-caps central section to pile-caps sections that approximate cutting axis shows the experimental results. In models with columns of elongated rectangular section and with great reinforcement rates this reduction is smaller.

ANÁLISE NUMÉRICA DE BLOCOS SOBRE DUAS ESTACAS COM CÁLICE EMBUTIDO SUBMETIDO À AÇÃO DE FORÇA HORIZONTAL

The structural behavior of pile caps with sockets embedded is influenced by interface of column-socket, which can be smooth or rough. With intent to analyzer the behavior of two pile caps with embedded socket, considering the friction between the column and the socket, subjected to horizontal force, the numerical simulations were carried out, using a program based on the Finite Element Methods (FEM). In the numerical analysis the non-linear behavior of materials was considered, also the friction between the column and the socket. It was considered perfect bond between the reinforcement and the concrete around. It was observed that the embedded length is preponderant factor in the structural behavior of the analyzed element. Keywords: foundations, pile caps, numerical analysis.

Shear force and torsion in reinforced concrete beam elements: theoretical analysis based on Brazilian Standard Code ABNT NBR 6118:2007

Reinforced concrete beam elements are submitted to applicable loads along their life cycle that cause shear and torsion. These elements may be subject to only shear, pure torsion or both, torsion and shear combined. The Brazilian Standard Code ABNT NBR 6118:2007 [1] fixes conditions to calculate the transverse reinforcement area in beam reinforced concrete elements, using two design models, based on the strut and tie analogy model, first studied by Morsch [2]. The strut angle θ (theta) can be considered constant and equal to 45o (Model I), or varying between 30o and 45o (Model II). In the case of transversal ties (stirrups), the variation of angle α (alpha) is between 45o and 90o. When the equilibrium torsion is required, a resistant model based on space truss with hollow section is considered. The space truss admits an inclination angle θ between 30o and 45o, in accordance with beam elements subjected to shear. This paper presents a theoretical study of models I and II for combined shear and torsion, in which ranges the geometry and intensity of action in reinforced concrete beams, aimed to verify the consumption of transverse reinforcement in accordance with the calculation model adopted As the strut angle on model II ranges from 30o to 45o, transverse reinforcement area (Asw) decreases, and total reinforcement area, which includes longitudinal torsion reinforcement (Asl), increases. It appears that, when considering model II with strut angle above 40o, under shear only, transverse reinforcement area increases 22% compared to values obtained using model I.