An improved theoretical formulation is proposed here to predict the moment field induced in laterally loaded RC rectangular stiffened plates including the effect of strength and stiffness of the internal stiffening beams. Design charts are also presented for their quick proportioning. The study reveals the effect of strength and stiffness of the internal beams on the moment field induced in the plate-system which was not considered, currently, by various methods prescribed by different design codes. The use of stiffened-plates becomes mandatory in buildings to accomodate some architectural constraints as well as for satisfying the serviceability criterion of design codes. This type of a structural system is efficient, economical and readily constructible in most of common materials. Moreover, it can be built as a monolithic unit or as a composite system comprising a plate cast in concrete and beams constructed in prestressed concrete, fabricated sections in steel, and so forth. A working example is presented to demonstrate the validity and efficiency of the simplified approach in comparison to finite element based design and other code prescribed methods. and Obsahuje seznam literatury a Appendix A
This paper evaluates the feasibility of using an Artificial Neural Network (ANN) model for estimating the nominal shear capacity of Reinforced Concrete (RC) beams against diagonal shear failure subjected to shear and flexure. A feedforward back-propagation ANN model was developed utilizing 622 experimental data points of RC beams, which include 111 deep beams data and 20 beams tested for low longitudinal steel ratios. The ANN model was trained on 70% of the data and then it was validated using the remaining 30% data (new data were not used for training). The trained ANN model was compared with three existing approaches, including the American Concrete Institute (ACI) code. The ANN model predictions when compared to the experimental data were very favorable, regarding also the other approaches. The prediction of ANN model was also checked for size effect and deep beams separately. The ANN model was found to be very robust in all situations. The safe form of ANN model was also derived and compared with the design equations of the three methods.
Content-based composites are traditionally a commonly used material in civil engineering structures. The basic representative of this type of material is concrete, a quasi-brittle composite in which crack resistance can be achieved by the addition of fibres. The double-K fracture model can be used to calculate the fracture-mechanical parameter values of structural concrete with and without popypropylene fibres. This model combines the concept of cohesive forces acting on the crack length with a criterion based on the stress intensity factor, using a ‘softening function‘ to determine the cohesive part of fracture toughness. In this paper, authors determine the effect of the type of this softening function on the evaluation of fracture tests performed on sets of concrete specimens with and without polypropylene fibres. and Obsahuje seznam literatury
The molten reactor core-concrete interaction, which describes the effect of molten reactor spread on the concrete oor of the reactor cavity, is a very complex process to simulate and predict, but the knowledge of this process is of major importance for planning the emergency counteractions for severe accidents with respect to the Stress Tests requirements after the Fukushima-Daiichi accident. The key issue is to predict the rate and most probable focusation of the melt-through process which is affected by the concrete composition, especially by the aggregate type. A limited number of small-scale experiments have been conducted over the past years along with accompanying numerical models which focused mainly on the siliceous type of aggregate. It is common for the concrete structures that the limestone type or the mixture of these two types of aggregate are used as well. Then, the objective of this paper is to extend the knowledge gained from the experiments with the siliceous aggregate to the concrete structures which are made of limestone aggregate or their combination, such as limestone sand and siliceous gravel. The proposed one-dimensional model of the melt-through process is based on the fuzzy-logic interpretation of the thermodynamic trends which reflect the aggregate type. This approach allows estimating the asymptotic cases in terms of the melt-through depth in the concrete oor over time with respect to the aggregate type, which may help to decide the rather expensive further experimental efforts.
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
The paper presents stochastic discrete simulations of concrete fracture behavior. The spacial material randomness of local material properties is introduced into a discrete lattice-particle model via an autocorrelated random field generated by the Karhunen-Loève expansion method. The stochastic discrete model is emploeyd to simulate failure of the three-point-bent beams with and without a central notch.. The effect of spatial randomness on the peak load and energy dissipation is studied. and Obsahuje seznam literatury
For assessment of safety and durability of any large-scale concrete structure, prediction of the behaviour of the structure under various service and extreme conditions is crucial. To perform reliable analysis of the complete structure, a sufficiently realistic but still feasible numerical model must be used, in which the relevant physical phenomena are reflected. Therefore, a constitutive model for concrete including effects on moisture and heat transfer, cement hydration, creep, shrinkage and optionally microcracking of concrete should be chosen.
The present paper focuses on the simulation of the service life of a NPP containment, aiming to determine the material and model parameters to enable reliable prediction of durability and structural behaviour under various conditions. The purpose of the work is to provide a numerical model calibrated using existing measurements to predict the long-term behaviour reliably. Extensive in situ measurements are used to calibrate the model and to check the validity of model hypotheses. Moreover, the material model parameters are systematically re-calibrated based on continuous monitoring of the structure. The structural integrity test is reanalysed numerically to show the model capability of predicting behaviour of the structure under given loading and climate conditions. 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
The present paper describes a semi-analytical fracture model based on the cracked hinge approach by Ulfkjær [1]. Some extensions of the original fomrulation are introduced and also implemented (as JAVA code) to enable the use of any softening function with arbitrary shape for the cracked part of the model, which is considered as a fictitious (cohesive) crack. The application of the model to the wedge-splitting test (WST) is validated, showing the consistency of the adopted formulations with reference data. Furthermore, the capability of the model to integrate various softening curves is verified using FEM simulations. and Obsahuje seznam literatury
The paper presents cellular automata as a promising modeling approach to simulate the diffusion process as a 2D task. The proposed methodology is applied to the degradation assessment of civil engineering structures describing more realistically the spatial and temporal variability of harmful substance ingress (e.g. chloride ions in concrete). Some illustrative examples are presented together with an example of application to a particular bridge. and Obsahuje seznam literatury