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Home > Publications > International Concrete Abstracts Portal
The International Concrete Abstracts Portal is an ACI led collaboration with leading technical organizations from within the international concrete industry and offers the most comprehensive collection of published concrete abstracts.
Showing 1-5 of 26 Abstracts search results
August 1, 1978
Editor: B. Bresler
This symposium volume was conceived as a tribute to Douglas McHenry in recognition of his outstanding contributions to concrete engineering. The 10 papers dealing with plain concrete and the 14 papers dealing with concrete structures reflect the needs of advanced technological development for the concrete industry. The theme of the symposium was concrete and concrete structures in severe environments and/or complex loading conditions. Papers deal with effects of transient high temperatures, cryogenic temperatures, nuclear radiation, with prediction of overall structural behavior in fires, earthquakes, and with behavior of elements under complex loading conditions.
Ian J. Jordaan and Magdi M.A. Khalifa
The time-dependent behaviour of concrete structures subjected to thermal gradients and, in addition, to mechanical loading is considered. Redistribution of stress with time results from two kinds of nonhomogeneity; firstly, there is a stress transfer from concrete to steel and secondly, the spatial variation of creep parameters (resulting from the temperature variation) causes stress redistribution. The constitutive laws for concrete creep are discussed in the light of recent experimental findings and a simple constitutive equation is found to account for the major features with sufficient accuracy in the analysis of static temperature fields. Because of the form of the equation, viscoelastic methods can be used; based on this fact, two approximate methods are proposed. Both use effective modulus calculations which must incorporate a spatially varying elastic modulus to account for the spatially varying creep properties; this is easy to achieve through the use of the finite element method. Two examples are given; the first is a reinforced cylinder subjected to internal pressure and a temperature gradient and the second is concerned with prestressed beams subjected to external loads and a temperature gradient. A comparison of the approximate methods with step-by-step calculations is given and good agreement is demonstrated.
The random behavior of reinforced concrete elements at de-formational limit states and at the ultimate limit state is analyzed by a second moment approximation. The deterministic and stochastic parameters involved, their functional and stochastic dependences, and their experimentally based statistics are discussed. The resulting variances of ultimate carrying capacity and ductility and of crack development are shown. It should be noted that ultimate ductility has an especially strong statistical variation independent of the amount of compressive reinforcement. A two-span beam is analytically modeled to elaborate first order approximations of the means and variances of simultaneously acting live loads and temperature effects which cause different limit states. Imposed deformations do not greatly influence ultimate load-carrying capacity provided that there is sufficient ultimate ductility. However, load-carrying capacity with respect to a limit state of allowable crack width is substan-tially reduced by simultaneously acting imposed deformations.
Kurt H. Gerstle, Diethelm L. Linse, Paolo Bertacchi, M.D.
Past investigations of the multiaxial behavior and strength of concrete have used both a wide variety of different materials, and of different test methods. In order to isolate the effects of these two variables, seven institutions cooperated in a test program in which mortar and concrete specimens were subjected to a variety of biaxial and triaxial compressive loading conditions, common to all participants. Identical materials were used in all tests, so that any systematic differences in the results could be attributed entirely to the differences in test methods. The effect of test method is predominantly a function of the specimen boundary conditions, which range from a specified stress boundary condition for perfectly flexible fluid cushion loadings, to a specified displacement boundary condition for perfectly rigid, rough platens. Mixed boundary conditions of various types occur with the use of conventional triaxial test cells, brush bearing platens, and lubricated loading plates. All of these loading conditions were represented in the program. Only strength results are presented in this paper. They clearly indicate the effects of surface constraints on the specimen; with increased boundary constraint, the ratio of multiaxial to uniaxial strength, as well as the ratio of cube to cylinder strength increases. Uniaxial, biaxial, and triaxial strengths of the materiaqs are compared by expressing them within a common octahedral normal-octahedral shear stress space. It appears possible to represent all observed failure points by a common compressive multiaxial strength criterion.
J. Komendant, V. Nicolayeff, M. Polivka, and D. Pirtz
concrete ra-Creep tes ts were performed in high-strength sealed to evaluate the effects of va ious combinations of temperature, stress level, and age of loading. Test conditions included temperatures of 73, 110, and 160F (23, 43, and 71C), stress levels of 30, 45, and 60 percent of compressive strength, and ages of loading of 28, 90, and 270 days. The creep loads were maintained for over one year, with creep recovery observed on selected groups of specimens for a period of 90 days. Tests were made on two concrete mixes, each made with the same brand of cement and sand but different coarse aggregates. The nominal strength of the concrete at age 60 days was 7500 psi (527 kgf/cm2) for moist-cured specimens and 7000 psi (492 kgf/cm2) for sealed specimens. Also reported are results of tests made to determine the effect of testing temperature on compressive strength as well as the influence of thermal cycling between 73 and 16OF (23 and 71C) on strength and elastic properties.
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