Showing papers by "Zdenek P. Bazant published in 2009"

Random Lattice-Particle Simulation of Statistical Size Effect in Quasi-Brittle Structures Failing at Crack Initiation

Abstract: The modeling of statistical size effect of concrete structures that fail at crack initiation is studied, with special attention to the interaction between the autocorrelation length and the size of the failure zone. The mechanical failure of concrete is modeled by a network of axial springs with degrading stiffness. The heterogeneity of concrete is idealized by spatial variation of the tensile strength and fracture energy. As an example, the direct tensile test in plane stress, with the size range of 1:20, is simulated. Furthermore, simulations of a four-point bending test with varying bending span are compared to the experimental results reported in the literature. The interaction of the autocorrelation length and the size of the failure zone is identified as a key parameter for the modeling of statistical size effect.

Minimizing Shrinkage, Creep, and Cracking Damage to Concrete Bridges: Part 1: Creep and Shrinkage Prediction Model for Analysis and Design of Concrete Structures: Model B3; Part 2: Creep, Shrinkage, and Durability Mechanics of Concrete and Other Quasi-Brittle Materials

Abstract: This final report consists of two parts: a paper published previously in conference proceedings and the Table of Contents from another conference proceedings. The first (designated Part 1) is part of the Adam Neville Symposium: Creep and Shrinkage--Structural Design Effects, ACI SP-194, 2000, pp 1-83. It presents a model for the characterization of concrete creep and shrinkage in design of concrete structures (Model B3), which is simpler, agrees better with the experimental data and is better theoretically justified than the previous models. The second (designated Part 2) is the table of contents of the Proceedings of the Sixth International Conference on Creep, Shrinkage and Durability Mechanics of Concrete and Other Quasi-Brittle Materials (CONCREEP-6), 20-22 August 2001, Cambridge, MA.

Does Strength Test Satisfying Code Requirement for Nominal Strength Justify Ignoring Size Effect in Shear

Abstract: The ACI 318 Code has not adopted size effect provisions for beams of depths up to 1 m, invoking a recent test in which the strength of such a beam was almost equal to the nominal strength required by the Code and was much larger than the strength obtained after applying the strength reduction factor. This paper criticizes the use of this test to justify ignoring size effect in shear. If numerous tests of 1 m (40 in.) deep beams with different shear spans and steel ratios, made of different concretes and under different hygro-thermal conditions, could be carried out, the beam strength would exhibit a similar statistical scatter, with approximately the same coefficient of variation, as the strength of beams up to 0.2 m (8 in.) deep, for which there are numerous test results in the database. Based on this expected scatter, it is shown that neglecting the size effect for beams up to 1 m (40 in.) deep is likely to increase the expected frequency of failures from approximately 1 in a million to approximately 1 in a thousand when the beam depth increases from 0.2 to 1 m (8 to 40 in.). These findings indicate the need to introduce the size effect into the ACI 318 Code for all beam sizes.