Key Engineering Materials Vol. 738

Abstract: Calculation of the cross-sectional properties of the concrete box-girder with two-cells using Vlasov`s theory and Generalized Beam Theory. Calculation of the internal forces of the St. Venant torsion, the warping torsion, the antisymmetrical and the symmetrical distortion on the basis analogy with beam on the elastic foundation loaded by transverse actions and tension force at the end of the beam. Creating of influence lines of torsion, antisymmetrical distortion and symmetrical distortion internal forces of large concrete cable-stayed bridge with continuous box-girders with two spans. The application for real reinforced concrete Harp bridge over pond Jordán near Tábor in Czech Republic is investigated. Evaluation of internal lines for action according to Eurocode EN 1991-2.

Abstract: Voided slabs using voids formed by permanent fillers or removable forms have been used in reinforced concrete floor systems for more than 100 years. In this article we will focus on the natural frequency of voided biaxial slabs system Cobiax. Cobiax void former modules are synthetic hollow spheres or rotational ellipsoids mounted in the relevant spaces between the upper and lower reinforcement. We have analyzed the slabs of different thicknesses with adequate void former modules and spans following the manufacturer's recommendations. All models were considered as simply supported slabs. Natural frequencies calculated using simplified analytical methods have been compared with those obtained by numerical methods. Numerical calculation was done using the 2D elements with reduced properties and using the accurate 3D model of a structure.

Abstract: The use of flat slabs in constructions due to its many functional and economic advantages is wide-spread. Behavior of flat slabs in shear and flexure is a fairly complex problem. Therefore, the punching shear failure belongs to one of the most critical aspects in the design of concrete buildings.The purpose of this paper is to describe a framework of the proposed method for predicting the punching shear of flat slabs with shear reinforcement. Most of the current codes in force are mainly based on empirical formulation. The proposed method is based on a strut-and-tie model and therefore could be considered as an analytical approach. For the purpose of demonstrating the effectiveness of the proposed method, the method is compared with some of the main methods currently in use, such as Eurocode EC2, ACI 318 and Model Code 2010. The comparison consists of results of more than 90 experiments on flat slabs with shear reinforcement, gathered from publications from all around the world.

Abstract: In this paper the response of a reinforced concrete slab to a time variable load is presented. The time course of loading is in the first phase defined by a linearly increasing function and in the second phase by a constant function. The response is solved by a modified method of matrix functions.

Abstract: When concrete structures with specific performance requirements call for cracking to be avoided, a reliable crack assessment of hardening concrete members is a crucial task for the design. Concrete walls cast onto already hardened foundation slabs represent an example of externally restrained members commonly subjected to strains resulting from early-age movements. As a consequence, unacceptable cracks may develop. The key parameter for a reliable design of such members is a correct assessment of the hardening phase with respect to the deformation behavior followed with parallel evolution of stiffness and strength properties.This contribution aims to present a macroscopic numerical thermodynamic model which can be used for solving the transient thermal field of a chosen structural detail subjected to thermal loads during early ages. In connection with stress development control, the model represents a mechanical based crack assessment tool for hardening concrete members. Its applicability is discussed at a model solution of a wall-to-slab connection detail in a waterproof concrete basement structure. The model outcome values are verified using data from experimental field measurements.

Abstract: Mathematical models which can sufficiently describe processes proceeding in concrete during fire play an important role when assessing a load bearing capacity of concrete structures. In this paper a coupled heat and mass transport model based on principles of conservation of mass and energy is presented. A 2D computational solver using FEM was created to find three unknowns – a temperature, an amount of free water and a magnitude of pore pressure in concrete cross section during rapid heating. These variables, mutually connected through state equation, are necessary not only for determination the load bearing capacity of concrete element but also for prediction of concrete spalling. A parametric study of numerical results influenced by material properties of concrete (e.g. permeability, thermal conductivity) and initial conditions (e.g. relative humidity, temperature) is introduced and discussed in the end.

Abstract: Wind climate influencing wind loads on buildings and other structures, as well as the dispersion of pollutants from various surfaces is essentially determined by small-scale motions and processes occurring in the atmospheric boundary layer (ABL). The physical and thermal properties of the underlying surface, in conjunction with the dynamics and thermodynamics of the lower atmosphere influence the distribution of wind velocity in thermally stratified ABL. Atmospheric turbulence is characterized by a high degree of irregularity, three-dimensionality, diffusivity, dissipation, and a wide range of motion scales. This article describes a change of selected turbulent variables in the surroundings of flow around a thermally loaded object. The problem is solved numerically in Ansys Fluent 13.0 software using LES (Large eddy simulation) models as well as the Transition SST (Shear Stress Transport) model that is able to take into account the difference between high and low turbulence at the interface between the wake behind an obstacle and the free stream. The results are mutually compared and verified with experimental measurements in the wind tunnel.

Abstract: This article deals with determination of the strain of the beam caused by the creep effect. Instant deflection and simulation of creep function have been examined by SCIA Engineer, ANSYS and Marc software. Creep is a complex phenomenon, which is in every software configured differently. Therefore we would like to compare results of calculations obtained using various finite element method software. With increasing time, the deformation of a beam becomes non-linear analysis. Analysis involved monitoring of deflection in the middle of the beam depending on the time. In SCIA Engineer construction stages were created with the creep factor based on period of load. In the ANSYS software different method was selected and creep curve of concrete had been defined.

Abstract: This paper is devoted to an analysis of the ceiling slab using conventional and advanced technologies, namely, lightweight panels using Cobiax bodies. The design was modeled in Scia Engineer 1.15. Lightened variant was based on the classical model slab on which it was necessary to optimize the hollow core and solid parts. To speed up the optimal distribution of the massive and lightweight panels, computer equipment was used. Acquired results were verified by manual calculation. After the overall design and assessment of the both types of slabs the results were mutually compared in order to find a preferable variant.