Viktor Borzovič

Parametrical Study of the Shear Resistance of the Approach Slabs

The transition zone of the road bridges is located right behind the abutment. Function of this structure is to ease the vehicle transition from the bridge on the rigid support to the embankment with much smaller stiffness. The main function of the approach slab is, as a part of the transition zone, helping the backfill to overcome different stiffness of the bridge foundations and embankment. The paper deals with shear resistance of the slabs for different lengths and widths. Parametrical study was performed according to Eurocode loading model 1 (Uniformed distributed load and Tandem system). Each of the analysed slabs was loaded with sets of different TS positions and location of the loading lanes. Envelopes of the shear forces of the approach slabs were analysed for each type of the slab. After that shear resistance of the slab with or without the shear reinforcement was calculated. The slab was divided into areas with same shear reinforcement distribution. The analysis is the part of the engineering tool for the bridge designers. According to length and width of the slab, the engineer can easily choose the shear reinforcement diameter and its distribution. The tool also provides the construction details of the shear reinforcement. There will be also the option for the reinforcement design of the slab, with hints for the structural scheme and calculation method.

Application of GFRP Reinforcement in the Design of Concrete Structures and its Experimental Evaluation

Abstract In the past, research on the use of FRP in civil engineering has been focused on strengthening existing structures where FRP reinforcements were applied to the surface of concrete elements. Recently, the application of FRP reinforcements has been studied to replace steel reinforcements for use in areas of increased environmental loads, with a need to exclude the corrosion of the reinforcement or to ensure the electromagnetic neutrality of the individual elements of the load-bearing structure. The GFRP reinforcement ratio was verified considering failure modes in flexure and the bond of the GFRP reinforcement with concrete. Besides classical reinforcements, GFRP has also been used in prestressed variants, and the possibility of its use as permanent formwork has been verified. In terms of extending the use of non-metallic reinforcements, it is important to note the long-term exposure and possible degradation of the mechanical properties.

Non-Linear FEM Analysis of Integral Bridges Transition Area

The transition area of bridges is non-homogeneous solid, which consists of soil embankment, transition slab and roadway layers. These transition area elements consist of various materials with different properties. Besides the imposed loads, behavior of these areas is significantly affected by uneven settlement between the bridge abutment and soil embankment. In case of integral bridges horizontal movements of a bridge caused mostly by temperature and ongoing rheological phenomena in concrete have to be taken into account. This leads to abutment deformation in combination with time dependent soil consolidation it results in varying earth pressure over the bridges lifetime together with cyclic horizontal movements of the pavement resulting in its cracks and excessive deformations. In this paper, comparison of different approaches to finite element analysis of transition areas is presented. First analysis was performed using area elements to represent the bridge structure, and volume elements to represent embankment, while second analysis was performed in more conservative way using spring based method proposed by Křížek[3], as representation of the surrounding soil. Results obtained via both methods are compared with each other as well as with data obtained from experimental measurment of a transition area conducted in Switzerland [1].

The Approach Slab Experiment - Design and Set up of the Experiment

The paper deals with experimental program concerning transition zone of road bridges with the use of approach slab. The experimental setup was constructed in the laboratory of the Slovak university of technology in the scale 1:2.The main function of the approach slab is to ease the transition from stiff foundation of the abutment to an embankment with much less stiffness. As a part of the transition zone, the slab helps to overcome different stiffness of the foundations. Good design of the approach slab and also the transition zone improves the transit of vehicle and enhances the comfort of the vehicle driver.Main goal of the experimental program is to observe the change of the structural scheme of the approach slab throughout the time via bedding stresses under the slab supported by the gravel soil, and also via the supporting forces in the connection to the abutment. The deflection of the slab is observed to confirm the slab behaviour. The possibility to observe all necessary variables with the option to adjust the height of the slab connection is provided by special construction modifications of slab to abutment joint.Due to the fact, that leading variable loading of the approach slab is traffic, loading of the specimen will be cyclic. This loading type causes dynamic response not only of the approach slab, but also of the experimental setup. Part of the experimental setup design is preliminary numerical, time depended analysis of the experiment. On the basis of results of the preliminary analysis the strain of members of experimental setup was checked to maintain the safety of the experiment during whole time. The analysis also shows predicted behaviour and strain of the approach slab, etc.

Design of Approach Slab of Road Bridges

This paper deals with the design and assessment of approach slabs of the transition zones of road bridges. The main goal of this article is to evaluate design criteria of this reinforced concrete member with attention to the requirements according to European standards. Up to these days, used procedure for the design of the approach slabs of the bridge construction in Slovakia is based on previous Czechoslovak CSN 73 6244 standard introduced 1981. The reason for using this standard nowadays is mainly because of its simple form as an engineering tool for the design of the geometrical dimension and also the reinforcement of the approach slab. Design procedures used for the analysis are taking into account the simplest and also the most conservative structural schemes, it is the slab with a hinge support in the place of the abutment and the second simple support on the other side substituting the gravel subsoil. This scheme should represent possible consolidation of the embankment under the slab. For more precise description of the behaviour, models with elastic support are used. Using these models, the approach slabs will be analysed for the ultimate limit state. The analysis of the results for various geometrical dimensions could serve as a template for similar design tool, to which bridge designers are used to.

The Crack Development Mechanism of Prestressed Girder Influenced by Different Bond between Prestressed Tendons and Concrete

The paper deals with formation and development of cracks up to the failure of two span post-tensioned concrete girder. It is focused on influence of different bond between prestressing units and surrounding grout. Monitored and analysed phenomena affected by different bond are as follows: crack initiation, crack spacing and crack width of the prestressed girder. Sources of analysis are results from experimental program focused on influence of oil based corrosion protection agents on bond of prestressing units. Two span post-tensioned girders were subjected to the loading in laboratory till the bending failure has occurred. Girders were in two cases prestressed with bonded tendons. Other two girders were post-tensioned with unbonded tendons and two girders with tendons with decreased bond, due to corrosion protection coatings. Girders have demonstrated different behaviour by loading regarding to the bond level of prestressing units. Experimental results are faced with the results of the theoretical calculation of crack width according to European standards.

Nonlinear Response of Approach Slab on Cyclic Loading

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.

Secondary Effects of Prestressing at ULS on Hyperstatic Structures

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.

Reliability of Approach Slabs and Modelling of Transition Zones of Bridges

The approach slab is the structural member of transition zones, which compensates a different settlement of bridge abutment and a road embankment. The main reason of different settlement is the consolidation of soil under the slab and the abutment. The geometry of approach slab, its length and the thickness is defined on the basis of differential settlement of embankment and the abutment. The static behaviour of slab is defined as a slab on elastic soil. The reinforced concrete slab is supported with the line rigid support on the one edge, and the rest of slab area interacts with the soil. The civil engineers design the reinforcement in those slabs based on the simplified structural scheme, without considering the elastic area support. This scheme is the simple supported slab on the both ends. The paper is dealing with the comparing of different structural models of the reinforced concrete approach slabs. The complex models of transition zones with the brick elements of the soil and the interaction with the reinforced concrete slab with the soil embankment are compared with the simplified models used by civil engineers. The analysis was performed on the transition zone of highway bridge from Slovakia based on its geometry and the subsoil consistence. In the parametric study was compared 8 soil stiffness’s on 10 structural models.

Punching of Concrete Flat and Foundation Slabs

Abstract This paper deals with punching of flat and foundation slabs. Te paper presents limiting values of maximum punching resistance of these slab structures with sudden and brittle mode of failure. In the paper are introduced graphs for design of flat and foundation slab thickness depending on load intensity, span length and reinforcement ratio.