Key Engineering Materials Vol. 691

Abstract: Containment is the last barrier protecting the environment from contamination in case of serious accident in nuclear power plant. Steel liner is often used to guarantee leaktightness of concrete containment and therefore the design of the liner must be done with utmost care. Several methods are used in practice to anchor the liner plate to concrete containment wall, differing in layout and type of anchorage elements used. The anchorage system must ensure full connection of the liner to the wall, liner buckling and tearing have to be prevented. The objective of the research was to determine the behavior of typical details of steel liner of concrete containment subjected to axial and shear loads. Two types of experiments were proposed. The first one was aimed at defining the response of two different types of liner anchorage system – L-profiles and headed studs – to the axial loads imposed on the liner plate. Behavior of specimens with and without initial imperfection of the steel plate was also compared. The goal of the second experiment was to determine the shear load-bearing capacity of the anchorage and to verify that liner tearing will not occur before the failure of the anchorage – this one of the main conditions of the safe design. The experimental program was successfully executed and the results are presented in the paper.

Abstract: Early-age volume changes in concrete induced by temperature change, hydration, autogenous and drying shrinkage can lead to concrete cracking and this can have lasting effects on serviceability, durability or aesthetics of the structure. The restraint to thermal movement is the product of the coefficient of the temperature fall from a peak level during cement hydration and a restraint factor. In most cases it is not necessary and also not economical to avoid cracks. In these cases, crack widths are limited due to water tightness, durability or aesthetic reasons. If early-age thermal cracking cannot be prevented, crack width can be controlled with reinforcement. The reinforcement distributes cracks and consequently reduces their widths and spacing. As a result, there forms a large number of smaller cracks instead of a few through-cracks. This means, that due to the formation of fine cracks, the strain capacity of a reinforced concrete element before the occurrence of through cracks can be increased with the help of skin reinforcement. This paper discusses the parameters of reinforcement affecting the width and spacing of early-age cracks in concrete. The effect of reinforcement on early-age cracking in concrete was investigated on numerical simulation and in full-scale experiments. The test variables were the reinforcement ratio and the cover thickness of the longitudinal reinforcing bars.

Abstract: Based on the results of previous research it could be stated that the deterioration of concrete elements by leaching process could be described by the simplified diffusion function. However the results of Schneider and Chen showed that the deterioration of concrete elements by leaching could differ significantly if they are subjected to permanent bending performance. Their experimental data pointed out that after a certain time the deterioration course of loaded concrete elements significantly changes and these elements lose their strength faster than the unloaded control specimens.Article outlines the possible theoretical solution of this phenomenon. The developed theoretical models where applied to the experimental results of Schneider and Chen [3], [2]. The main task was to find a simplified engineering solution to the problem of the stress corrosion of the concrete in ammonium nitrate solution.

Abstract: Composite steel and concrete columns have been used in the tall buildings due theirs high-resistance and the possibility to reduce cross sections when we compered composite columns with reinforced concrete columns. There are a lot of types of composite columns. We are concerned with columns, which are completely or partially concrete-encased steel members. In practice, a lot of composite columns are relatively slender and in design the second - order effects will usually need to be included. A partially concrete encased steel cross-section was selected for laboratory tests of composite columns. According to the results of the experiments (total of 18 columns were tested in two series), we analyzed the effects of the second - order theory. The experimental results were compared with theoretical results obtained from the model developed in the non-linear software. The evaluation of the results is also shown in comparison with the general design method according to Eurocode 4, Design of composite steel and concrete structures - Part 1.1 General rules and rules for buildings.

Abstract: The issue of strengthening the damaged linear reinforced concrete elements have been engaged since 2008. We focused on the analysis of resistance and the characteristics of limit states of serviceability in the damaged and subsequently strengthened elements at a short-term loading. In the introduction phase, the strengthening of the elements was carried out with the following procedures – installation of an overlayer on the coupling board or a combination of the board and use of glass – fiber fabric (GFRP). The strengthening was also affected by the type of contact (reinforced/non-reinforced) – the deformed element/coupling board and its effect on resistance, type of deformation and serviceability. In the non-reinforced contact, we applied some of the types of adjustments to the surface of the strengthened element. At the moment, we are dealing with the effects of time and repeated load on the strengthened elements. The results correspond to the reinforced contact. The values are compared with the short-term results of the strengthened beams and with the long-term results of the beams prepared for strengthening.

Abstract: The paper focuses on strengthening of loadbearing reinforced concrete vertical members by composite materials. These modern materials are used more and more in the last years. Usage of the FRP fabrics as confinement has several advantages, however there are some uncertainties regarding the design (eg. determining the compressive strength of confined concrete and limit strain of confined concrete). An assessment of influence of the confinement on the elements (its load bearing capacity and ductility) is necessary for design. There is a large number of analytical formulas, standardized approaches and regulations, which specify the resulting influence on the confinement. The paper draws attention to the considerable dispersion between those obtained results.The paper presents an analysis of the influence of reinforced concrete columns strengthening, which are confined with FRP fabric. The obtained theoretical results were compared with a real behaviour of several specimens of confined concrete columns. The short reinforced concrete circular columns were used as the test specimens. The height-diameter ratio of the columns was set as 2:1, therefore an influence of slenderness to loadbearing capacity of the column can be neglected. Consequently, the influence of confinement can be maximized and the dispersion of results according to different methodologies can be emphasized.

Abstract: The approach slab is in the terms of structural behaviour an area element with interaction with a subsoil, where one of its edge is connected thru the hinge on the abutment of the bridge. In a simplified structural schemes it is possible to model this slab element with a hinged connection to the abutment and the subsoil interaction is represented by a spring area under the approach slab. More difficult approach of modelling the reinforced concrete slab and the subsoil interaction is by 3D soil elements with the properties of soil embankment. In both cases of those linear approaches exists few imperfections, which does not represent the real behaviour. Load from the traffic acts on the slab cyclic. Therefore special problems occur in modelling of those transition areas. By crossing vehicles and its acting in time, continuous consolidation of the soil under the approach slab is being in progress. It can possibly cause creation of the void and consequently loss of a contact between the slab and subsoil. The paper deals with modelling of the reinforced concrete approach slab and the soil interaction with a nonlinear soil element, and also response of the slab on the cyclic load. All these effects can cause changes in structural scheme, and therefore changes in a strain of the slab member. The model is trying to describe the subsoil consolidation in time. In a connection with that fact, the fatigue failures of the approach slab are examined too.

Abstract: Lateral-torsional buckling is one of the criteria in the design of steel and composite beams in ultimate limit state. This paper deals with lateral-torsional buckling of double-span continuous composite beams subjected to two different loadings. The main objective of the paper is the comparison of the elastic buckling moment values of composite continuous beams performed according to approximation formulas of M_cr,A from codes [2] and different sources [3] to more exact values M_cr,E obtained by computer programs based on finite element method [1P]. The results will be presented in the form of elastic buckling moment ratios M_cr,A / M_cr,E.

Abstract: This paper deals with the slab concreting sequence and its influence on a composite steel and concrete continuous highway girder bridge. The bridge has a symmetrical composite two-girder structure with three spans of 60 m, 80 m, 60 m (i.e. a total length between abutments of 200.0 m). The horizontal alignment is straight. The top face of the deck is flat. The bridge is straight. The transverse cross-section of the slab is symmetrical with respect to the axis of the bridge. The total slab width is 12 m. The slab thickness varies from 0.4 m on main girders to 0.25 m at its free edges and 0.3075 m at its axis of symmetry. The center-to-center spacing between main girders is 7 m and the slab cantilever on either side is 2.5 m long. Every main girder has a constant depth of 2800 mm and the thicknesses of the upper and lower flanges are variable. The lower flange is 1200 mm wide whereas the upper flange is 1000 mm wide. The two main girders have transverse bracing at abutments and at internal supports and at regular intervals in every span. The material of concrete slab is C35/45 and of steel members S355. The on-site pouring of the concrete slab segments is performed by casting them in a selected order and is done after the launching of the steel two girder bridge. The paper presents several concreting sequences and their influence on the normal stresses and deflections of the composite bridge girder.