Alena Kohoutková

Experimental Verification of the Behavior of Protective Steel Liner of Concrete Containment

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.

Structural Fiber Reinforced Concrete Elements

The building industry offers a wide range of materials which can be used for the production of various structural elements. Fibre reinforced concrete (FRC) is a material which is more frequently utilized for concrete structures. The reason is its physical and mechanical properties which contribute to traditional concrete elements and structures various economical benefits such as structure subtlety, part or full elimination of conventional reinforcement, resistance to mechanical loading and surrounding environment. Therefore, it is necessary to search for appropriate structures where the benefits of FRC could be used. First of all it is necessary to seek for structures which owing to their geometry and intended use seem to be appropriate for FRC application. It can be either new structural elements or existing structural elements made of a different material. During a material optimization there are many parameters to take into account which include production costs, manufacturing technology, structural behaviour, ultimate bearing capacity and durability of proposed member. The efficiency of material optimization is determined by comparing these parameters. While it is relatively easy and cost efficient to determine and evaluate the production costs, structure durability and manufacturing technology, to describe the structural behaviour of innovative elements is a complex task. However there are many sophisticated software which are capable to accurately simulate the behaviour of structural elements by using modern computational methods. At the end of feasibility study, experimental testing is conducted on full-scale pilot elements with the aim to verify their real behaviour as well as to optimize the computational model. As a result, many innovative FRC based structural elements have been developed at Czech Technical University in Prague in cooperation with construction companies.

Flexural stiffness of the composite steel and fibre-reinforced concrete circular hollow section column

The recent development in technology of production and transportation of steel fibre-reinforced concrete enables its utilization in composite steel-concrete structures. This work is a part of a project which focuses on development of mechanical behaviour of circular hollow section (CHS) composite steel and fibre-concrete (SFRC) columns at elevate temperature. Research includes two levels of accuracy/complexity, allowing simplified or advanced approach for design that follows upcoming changes in European standard for composite member design in fire EN1994-1-2 [1]. One part is dedicated to determination and description of flexural stiffness of the SFRC CHS columns. To determinate flexural stiffness were prepared series of pure bending tests at elevated and ambient temperature. Presented paper focuses on the results of the tests and determination of flexural stiffness at ambient temperature. Obtained outputs were compared to data of existing studies about concrete-filled tube members with plain concrete and values analytically calculated according to the existing European standard EN1994-1-1 [2].

FEM simulation of static loading test of the Omega beam

The paper deals with a FEM simulation of static loading test of the Omega beam. Omega beam is a precast prestressed high-performance concrete element with the shape of Greek letter omega. Omega beam was designed as a self-supporting permanent formwork member for construction of girder bridges. FEM program ATENA Science was exploited for simulation of load-bearing test of the beam. The numerical model was calibrated using the data from both static loading test and tests of material properties. Comparison of load-displacement diagrams obtained from the experiment and the model was conducted. Development of cracks and crack patterns were compared. Very good agreement of experimental data and the FEM model was reached. The calibrated model can be used for design of optimized Omega beams in the future without the need of expensive loading tests. The calibrated material model can be also exploited in other types of FEM analyses of bridges constructed with the use of Omega beams, such as limit state analysis, optimization of shear connectors, prediction of long-term deflections or prediction of crack development.

Precast concrete pavement – systems and performance review

Long-term traffic restrictions belong to the key disadvantages of conventional cast-in-plane concrete pavements which have been used for technical structures such as roads, parking place and airfield pavements. As a consequence, the pressure is put on the development of such systems which have short construction time, low production costs, long-term durability, low maintenance requirements etc.. The paper presents the first step in the development of an entirely new precast concrete pavement (PCP) system applicable to airfield and highway pavements. The main objective of the review of PCP systems is to acquire a better understanding of the current systems and design methods used for transport infrastructure. There is lack of information on using PCP systems for the construction of entirely new pavements. To most extensive experience is dated back to the 20th century when hexagonal slab panels and system PAG were used in the Soviet Union for the military airfields. Since cast-in-situ pavements became more common, the systems based on precast concrete panels have been mainly utilized for the removal of damaged sections of existing structures including roads, highways etc.. Namely, it concerns Fort Miller Super Slab system, Michigan system, Uretek Stitch system and Kwik system. The presented review indicates several issues associated with the listed PCP systems and their applications to the repair and rehabilitation of existing structures. Among others, the type of manufacturing technology, particularly the position of slots for dowel bars, affects the durability and performance of the systems. Gathered information serve for the development of a new system for airfield and highway pavement construction.

Experimental and Theoretical Analysis of I-Pillars of Noise Barriers Made of Prestressed Steel Fiber Concrete, Prestressed Concrete and Reinforced Concrete with Footings Length of 600 mm

This paper deals with the experimental testing and theoretical analysis of the flexural load-bearing capacity of I-shaped pillars in noise barriers made of reinforced concrete, prestressed concrete and prestressed steel fiber reinforced concrete. The pillars were loaded as a cantilever under a flexural load, which corresponds to their actual loading when the effect of wind on the panels of the noise barrier is taken into account. For the purpose of the present research, three specimens of I-pillars were tested. The results of the experimental loading tests, as well as the calculated results and the comparison between them, are herein presented.

Finite Element Simulation of Hydration Heat Using Fuzzy Logic Model of Hydration

This paper deals with heat of hydration in a concrete structure at the early age. The influence of temperature on development of hydration heat in the concrete structure is implemented through a fuzzy-logic model of the degree of hydration. The transient heat transfer problem was solved as a three-dimensional finite element simulation. The whole process of calculation is implemented in MATLAB Environment. The result of this work provides temperature distribution in the structure for each time step, the maximum temperature in the structure, and the time when it occurs.

Experimental Analysis of Strengthening of Dapped-End Beams

Technology of precast reinforced concrete finds its application in construction of buildings as well as transport infrastructure. Placement of a dapped-end beam on a corbel is one of the typical details for this construction technology. Designing of a dapped-end is crucial for the whole beam because any potential crack decreases the overall stiffness of the beam and can cause a collapse of the whole structure in the worst case. This paper presents results of an experimental research which was performed on a set of 6 small-scale dapped-end beams. Two different ways of prestressing were applied to experimental specimens and their ultimate-load bearing capacity were compared with plain concrete samples and with reinforced concrete samples. The results of this work suggest that horizontal prestressing technique is more efficient than vertical prestressing technique if the same prestressing force is applied.

Structural Performance and Crack Control of Fibre Concrete Beams with Conventional Reinforcement

Abstract Experimental study includes investigation of performance of concrete beams reinforced with conventional steel bars and with synthetic fibres. Several sets of beams have been tested to determine the influence of polypropylene fibre reinforcement on the mechanical behaviour of conventionally reinforced concrete beams in bending. The present study indicates that polypropylene fibre reinforcement can reduce crack width and deflections and improve ductility of beams and that the combination of polypropylene fibres, longitudinal steel bars (without stirrups) may meet strength and ductility requirements. The basic material characteristics were obtained from laboratory tests on prisms in four or three point bending and by an inverse analysis procedure the load-deflection relation were transformed into constitutive relations used in simulation. The test was simulated by means of a non-linear program system using various constitutive relations, which enable fibre concrete modelling.