The paper presents results from three large scale experiments on seven reinforced concrete panels obtained during an extensive experiemental program. This was aimed at possible application of cement reduced (fly ash replaced)) concretee in the production of precast segmental linings for tunnels created by a tunnel boring machine (TBM). In particular, this paper is focused on the comparison of fire resistance of enhanced mixtures loaded by the Rijkswaterstaat (RWS) fire curve, which assumes 50 m3 fuel tanker fire lasting for 120 minutes. The presented results include spalling, overall damage of the surface and temperature distribution of the tested panels The paper also presents description of the proposed method for the evaluation of the extent of spalling during the experiments since, due to the extreme temperatures, the direct observation of the exposed surface is not possible. and Obsahuje seznam literatury
In this contribution, a generalized Cam clay model for cohesive soil materials is introduced. A new formulation not only suppresses evolution of excessive failure stresses and dilatancy rate, but also allows for the reduction of поп-realistic softening behavior of overconsolidated soils predicted when adopting the formulation of classical Cam clay model. More realistic response of the soil is achieved by introducing a new yield function in the dilatation (supercritical or dry) domain, i.e. for OCR > 2. Further, the dependency of the yield function on the Lode angle is adopted and non-associated flow rule is assumed. Finally, the reduction of hardening modulus is shown in comparison to the classical Cam clay model formulation. and Obsahuje seznam literatury
The paper reports on the determination of basic mechanical material parameters of several concrete and alkali activated concrete and fly ash mixtures intended for the construction of segmental lining used in TBM tunneling. The results of an extensive experimental program are discussed first. The principal attention is accorded to the experimental determination of specific fracture energy from a load-deflection curve, which, when compared to numerical simulations, shows certain inconsistency with the measurements of other material data. This is supported by teh derivation of the data from inverse analysis employing the elements of soft-computing. Dynamic simulation of crack propagation experiments is suggested to reconcile the essential differences and to identify the most important impacts affecting the results of experimental measurements. and Obsahuje seznam literatury
In this contribution, we present the final outcome of the program initiated in [23], aimed at the determination of a periodic unit cell for plain weave composites with reinforcement imperfections. The emphasis is put on a realistic geometrical description of these material systems utilizing the information provided by in-situ two-dimensional micrographs. Complex geometry of an analyzed composite is approximated using a two-layer periodic unit cell allowing for a mutual shift as well as nesting of individual layers. The parameters of the idealized unit cell are derived via matching appropriate statistical descriptors related to the real material and the idealized geometrical model. Once the optimal geometry of the unit cell is determined, it can be converted to a CAD model and used ot generate the periodic finite element mesh applicable in the subsequent numerical treatment. The individual steps of this procedure are demonstrated in detail for a real world carbon-carbon composite system. and Obsahuje seznam literatury