Showing papers by "Zdenek P. Bazant published in 1973"
TL;DR: In this paper, a simple method is presented by which the linear creep function of concrete can be approximated, with any desired accuracy, by Dirichlet series with variable coefficients, and smooth fits of the best known data on creep at constant temperature and water content are demonstrated.
Abstract: A simple method is presented by which the linear creep function of concrete can be approximated, with any desired accuracy, by Dirichlet series with variable coefficients. Smooth fits of the best known data on creep at constant temperature and water content are demonstrated. It is shown that the approximation is equivalent to the Kelvin chain model with age-dependent properties. Other approximations leading to the Kelvin chain are also presented. It is found, however, that no Kelvin chain approximation can avoid negativeness of some spring moduli for some periods of time, which precludes physical interpretation of hidden strains. But representations with Maxwell chain are free from this deficiency. The Dirichlet series approximation allows formulation of an efficient algorithm of step-by-step time integration of creep problems, for which arbitrary increase of the time step is possible and storage of the stress history can be dispensed with.
113 citations
TL;DR: In this paper, the potential energy expression and stiffness matrix of a straight thin-walled beam element of open asymmetric cross section, subjected to initial axial force, initial bending moments, and initial bimoment, are derived.
Abstract: The potential energy expression and the (14 by 14) stiffness matrix of a straight thin-walled beam element of open asymmetric cross section, subjected to initial axial force, initial bending moments, and initial bimoment, are derived. The transformation matrix relating the forces and displacements (including bimoment and warping parameter) at the adjacent end cross section of two elements meeting at an angle is deduced as the limiting case of a transfer matrix of a curved beam. To cope with asymmetric cross sections, some element displacements and forces are referred to the shear center and others to the cross-sectional centroid and the matrix for transformation from shear center to centroid is set up. The incremental larger-displacement analysis is formulated using the Eulerian coordinate approach with updating of the local coordinate systems at each load increment. The deformed beams are imagined to be composed of straight elements. Results of lateral post-buckling analysis of various beams are presented.
99 citations
TL;DR: In this article, the authors compared the performance of various approximate methods for prediction of structural effects of creep, such as the effective modulus (EMM), age-adjusted effective Modulus, rate of creep (RCM), rate of flow (RFM), and Levi's and Arutyunian's methods.
Abstract: The approximate methods for prediction of structural effects of creep, such as the effective modulus (EMM), age-adjusted effective modulus (AEMM), rate of creep (RCM), rate of flow (RFM), and Levi's and Arutyunian's methods are all linear and satisfy the principle of superposition. Predictions of the approximate methods are compared with the exact numerical solutions based on the principle of superposition and given (undistorted) realistic unit creep curves. It is found that AEMM is in general superior to all other methods and along with EMM is also the simplest one. RFM (with effective modulus treatment of delayed elastic strain) appears as second best and should be resorted to when the table of aging coefficient required by AEMM is unavailable.
53 citations