Key Engineering Materials Vol. 691

Abstract: Main advantage of composite concrete columns, in comparison with traditional reinforced concrete columns, is its increased load-bearing capacity by using of solid steel reinforcing core. Ordinary type of such a steel-concrete (S-C) composite column consists of normal concrete and different type of solid steel core. In last decades high quality concrete is more and more used for load-bearing structural members exposed compression like columns. Present knowledge level in the area of ultra-high quality of concrete open a new chance for utilization of this progressive structural material in concrete building industry. This paper presents some new information and laboratory test results of concrete-concrete (C-C) composite columns by utilizing of UHPFRC.

Abstract: The quality and durability of the concrete structures are affected by many degradation processes. The reliability of existing bridge structures is significantly affected by numerous factors, from which the reinforcement and structural steel corrosion, together with effect of traffic action, are the most important. Corrosion is the destructive attack on metal by chemical or electrochemical reaction with its environment. In the case of reinforced concrete (RC) structures, the most known degradation process is corrosion of reinforcement. RC members have to fulfill the conditions given in Eurocode [1, 2]. Horizontal beams are mainly subjected to bending and shear. The paper deals with reinforcement corrosion of main longitudinal reinforcements (reinforcement against bending) and its influence on the moment resistance of the existing bridge concrete structures. The two types of active stage calculation of corrosion were considered in this paper. The length of passive stage was not known, so it was calculated backwards.

Abstract: Many factors play important role during concreting the base slabs, industrial floors and concrete pavements. Often, there is a tendency to design the structure so that the crack does not arise or arise only with the limited crack width. The parametric study of selected climatic factors which have crucial affect on the temperature or cracking development of the structure at an early stage is elaborated in the paper.The results were obtained using thermodynamic and stress numerical model TD&SM, which was developed in the last four years at the Department of Concrete Structures and Bridges. The outputs from program TD&SM were tested and compared with experimental measurements on real structures, and showed very good agreement. It is possible to calculate the temperature development at any time and place of base slab, industrial floor or concrete pavement at the early stage using this model . It enables afterwards to investigate the risk of crack creation.

Abstract: Secondary (parasitic) effects of prestressing develop in hyperstatic structures (continuous beams) due to restraining of imposed deformation by hyperstatic restraints. These effects may, in some case, significantly influence internal forces and stresses in prestressed structures. Internal forces due to the secondary effects should be included in design combinations for verification of both ultimate and serviceability limit state. Because secondary effects are influenced by structural system, there is a question how they will change after changing of the structural system e.g. due to development of plastic hinge (s) in a critical cross-section (s) or after development of kinematic mechanismThis article describes an experimental program at Slovak University of Technology in Bratislava, Department of concrete structures and bridges and its results. Program were focused on investigation of behavior of continuous post-tensioned beams with significant secondary effects of prestressing subjected to ultimate load. Together six, two span beams were tested, with maximum load changing structural system into kinematic mechanism. Secondary effects of prestressing were detected by measurement of reactions in all supports, further there were measured displacements in the quarters of both spans and strains in critical sections of the beams.

Abstract: This contribution describes the formulation of DBSO (deterministic based structural optimization) design of a tunnel lining. The principle by which a solution may be obtained for a problem concerning the dimensional and reinforcement design optimization of a concrete structure is introduced. The target function is defined as the minimum cost of used materials. The range of allowable solutions from the mathematical viewpoint is defined by constraining conditions expressed by relations derived from:equations of equilibrium (the solution of optimization calculations for a structure with a Winkler foundation using the finite element method),the reliability conditions of a reinforced concrete structure and from the continuity of deformations.The method (algorithm) for obtaining a serviceable reinforcement design (via the implementation of reinforcement types) from an optimal solution is described. The algorithm will be applied to the optimization of a tunnel lining design. FRP reinforcing bars will be used as reinforcement. The thickness of the tunnel lining and the areas of top and bottom reinforcement in cross-sections will be optimized. The obtained results will be compared with an optimized design created for the same tunnel structure but made from steel-reinforced concrete.

Abstract: This article presents the results of experimental research focused on the shear strengthening of reinforced concrete beams with one of the latest and most promising method: NSM - Near surface mounted reinforcement. In recent years, research in this area focuses on combination of epoxy and FRP (fiber reinforced polymer) materials suitable for strengthening concrete elements. A traditional material: stainless steel was also used in this study but in non-traditional T-cross section in terms of strengthening of concrete members. Structural epoxy adhesives offer excellent properties but are very sensitive to elevated temperatures. Effect of increasing temperature gradually degrade their properties and subsequently decreased bond strength, whereas during cooling may acquire significant parts of the original strength. The influences of these factors were investigated in shear resistance of NSM strengthened concrete beams under four point bending at ambient temperature, at elevated temperature and after cooling to ambient temperature.

Abstract: In the frame of global European standardization and in consequence of new knowledge related to existing bridges, the need for revision of the service handbook "Determination of load-carrying capacity of railway bridges" grown up. The paper presents general concepts and basic assumptions for determining the railway bridge load-carrying capacity. In contrast to design of a new bridge, additional data related to existing bridge condition and behavior like information from regular inspections and real state of degradation can be taken into account. Based on these data together with the remaining lifetime, a modification of reliability levels for existing bridges based on the mathematic theory of probability can be adopted in the evaluation process. Special attention is also paid to the specific features of determination of load caring capacity of steel-concrete composite bridges in exploitation. Recommendation and allowances for global analysis of existing composite steel and concrete superstructures for the purpose of the load-carrying capacity estimation are discussed as well.

Abstract: Experimental verification of global reliability of slender reinforced concrete columns from the regular concrete C45/55 and high performance concrete C70/85 was realized within the applied research of the Faculty of Civil Engineering at Slovak University of Technology in Bratislava (SUT). Production of test columns and samples was in cooperation with ZIPP Bratislava Ltd. Columns are designed in the way to collapse due to stability before the resistance of the critical cross-section is reached. The relative compression of concrete was scheduled about 1,5 ‰. For performed experimentally verified slender columns, the reliability of simplified and nonlinear design methods according to European standards was compared.

Abstract: This paper presents some results of theoretical and experimental investigations of composite steel-concrete columns with solid steel profiles - steel cores. Due to absence of simplified design method according to EN 1994-1-1 [1], design of these columns in practice is limited in general. Reasons for this are residual stresses in steel profile caused by fabrication process and limitation of strains in concrete. Recommendations have been determined for simplified design method according to EN 1994-1-1 for composite columns made of high strength concrete filled steel tube with central steel core. Results of experimental research on composite columns with the cross-section made of steel core covered by reinforced concrete are presented.

Abstract: For various underground concrete structures (basements, tunnels), which remain permanently in the groundwater, watertight concrete is of increasing importance. Watertight concrete structures have several advantages over structures with exterior waterproofing membrane. The design and execution of watertight concrete structures is regulated by guidelines. Although these principles and procedures are widely used, it can be problematic to make them failure-free. The causes of this situation are manifold, but primarily related to the lack of designer’s knowledge and contractor’s technological indiscipline. Considering the importance of leaking separation cracks in terms of serviceability and durability of watertight structures, the contribution analyses constructional, technological and execution measures to reduce the occurrence of failures. Perhaps the paper can contribute to a better understanding of the behaviour and reasons of failures of this advanced technology.