1,721,122 research outputs found
On the Effects of Structural Stability on the M-N Envelopes of Thermally-Damaged R/C Sections
No full text
Size effect in the bonding of smooth and deformed bars: a comparison between Normal-Strength and High-Performance Concrete
No full textSize effect is unanimously recognized as a peculiar – and critical – aspect of the mechanical behavior of many structures, provided that either their material or the interfaces among their parts have a quasi-brittle behavior. In this paper, the results obtained during two experimental campaigns carried out at Politecnico di Milano on long smooth bars and on short deformed bars are recalled. In both cases size effect is shown to be very strong and in good agreement with the well-known size-effect power law proposed by Bažant and coworkers. Size effect is also modeled by numerically solving the 2nd-order bond equation in one dimension. In the case of smooth bars, a simple but effective approach is adopted, by assuming for the interface an elastic-frictional behavior. In the case of deformed bars, the test results make it possible to formulate a size-dependent local bond-stress/slip law, that fits fairly well also the results obtained by other authors
Fire Scenario and Structural Behaviour in Underground Parking Garages
No full textThe objective of this paper is to investigate the main factors governing the fire behaviour of a typical underground garage roof consisting of a flat concrete slab supported by a number of relatively slender columns. On the basis of the available literature, and of reasonable assumptions, the fire scenario is worked out first, by properly modelling the temperature evolution in the ambient surrounding the structural members. This preliminary step is instrumental in solving the heat transfer problem from the ambient to the structural members. The calculated thermal field makes it possible to evaluate the decay of the mechanical properties as a function of the temperature. The stiffness decay,
together with the thermal deformations, often brings in significant redistributions of the internal forces. The main factors are studied, and some general considerations are drawn on the overall safety of the structure under examination
High-Temperature Behaviour of Concrete in Tension
No full textThe mechanical properties of concrete at high temperature and in fire conditions have been the subject of a number of investigations over the past 50 years. Nonetheless, the wide range of materials at hand, especially after the advent of high-performance and high-strength concretes, makes these results difficult to be generalized. This is particularly true of tensile response, due to the challenging experimental conditions and to the still not standardized test methods: “hot” vs. residual test conditions, direct vs. indirect tensile loading, restrained vs. free strain localization, notched vs. unnotched specimens are only some of the possible options that make the comparison between tests from different sources a really difficult task.
In this paper, the results collected by the authors on several different concrete mixes are illustrated, with the twofold objective of clarifying the relations among the most common direct and indirect testing techniques and to sketch any possible general trend in the tensile properties of ordinary and special concretes
exposed to high temperature.
Among the conclusions are the variable influence of the restraint exerted on the specimen ends in direct tension, the relatively good reliability of the splitting tests, the strong influence of specimen size and increasing material deformability in the bending tests, and the good agreement between the thermally induced decays of tensile strength and modulus of elasticity
General trends in the tensile behaviour of thermally-damaged concrete
No full textThe mechanical properties of concrete exposed to fire have been the subject of a number of investigations in the last fifty years. Nonetheless, the wide range of materials at issue, after the advent of high-performance concrete, makes the results of the previous studies difficult to be generalized. This is particularly true for the tensile response, due to the challenging experimental conditions and to the still not standardized test methods. Hot vs. residual test conditions, direct vs. indirect tensile loading, restrained vs. free strain localization, notched vs. unnotched specimens are some of the possible options that make the tests from different sources hard to compare.
In this paper the results collected by the authors on several different concrete mixes are drawn together with the twofold objective to clarify the relations among the most common direct- and indirect-testing techniques and to sketch any possible general trend in the tensile properties of ordinary and special concretes exposed to high temperature
On the tensile behaviour of thermally-damaged concrete
No full textThe mechanical properties of thermally-damaged concrete have been the subject of many investigations in the last fifty years. Nonetheless, a noteworthy impulse in this field has been promoted in recent times by the advent of high-performance concrete, because the wide range of materials at issue makes the well-established references difficult to be generalized. This is particularly true for the tensile response, due to the challenging experimental conditions and to the still not standardized test methods. In this paper the results collected by the authors on a number of different concrete mixes are drawn together with the twofold objective to clarify the relations among the most common direct- and indirect-testing techniques and to sketch any possible general trend in the tensile properties of ordinary and special concretes exposed to high temperature
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