Wojciech Lorenc

Testing procedures in evaluation of resistance of innovative shear connection with composite dowels

The article constitutes an introduction to the issue associated with modern steel-concrete composite girders having open continuous connectors of the composite dowels type. The way of fabrication of the steel portion of the composite girders has been presented as well as the details connected with experimental investigations on the new type of composition which demands broader approach of researches than attempts of determining the load-bearing capacity used so far, known as POST. The steel connector constitutes an integral part of the steel part of composite beam, in which it is subjected apart from the local longitudinal shear acting between steel and concrete, to the global effects of bending and axial loading as well. Thus, the stress criteria describing the composite dowels behaviour have to be established and it is much more than pure load-bearing capacity criteria used in present. The test procedures combining the concept of the load-bearing capacity for the concrete part of the connector and the elasticity of its steel part lead to an efficient designing of the composite structures.

Study on fatigue cracks in steel-concrete shear connection with composite dowels

In recent years many research on composite beams with innovative shear transmission with composite dowels have been conducted (mainly within PreCo-Beam project [15] ) and innovative composite constructions have been designed and built. As this shear connection is to be applied mainly for bridges, problems concerning fatigue behaviour appear [1] , [16] . Composite dowels behaviour in aspect of fatigue resistance and fatigue cracks investigations is extremely complex. It is caused not only by complicated stress distribution from external loads but also by eigenstresses which are released during beam cutting and cutting technology itself as well. It will be proved in detail macroscopic studies how production and cutting process may influence the fatigue crack initiation and propagation process. This paper presents investigations undertaken after finished PreCo-Beam project [15] which is part of the research to be conducted years 2009–2011 at Wroclaw University of Technology. Results of detailed metallographic inspections of fatigue cracks obtained during full-scale tests, and schedule of next full-scale tests to be performed at Wroclaw University of Technology are presented. Described researches are carried out in order to determine fatigue lifespan of composite beams with shear transmission realized with composite dowels of MCL shape [5] , [10] . MCL shape is currently the most often used shape of steel dowel because of its fatigue behaviour as well as technological aspects of its production process and therefore all foreseen research will focus mainly on this shape. The MCL shape is shown in Fig. 33 , Fig. 34 , Fig. 35 , Fig. 36 , Fig. 37 , Fig. 38 .

Study on Fatigue Cracks in Steel – Concrete Shear Connectors Composite Dowels MCL

In recent years many experimental researches were carried out on steel-concrete composite beams with shear connectors of composite-dowels type. Shear connection is mainly used in bridge construction, where strength and fatigue durability of structure are important issues. Research on fatigue in the Preco-Beam project [1] have confirmed the hypothesis that the initiating and propagating crack in steel connecting beam may lead to the loss of its continuity, resulting in failure or even destruction of superstructure [2,. However, it should be noted that these studies were carried out for a specific type of mechanical connector, called PZ-type (Fig. 1). Within next years different shape was developed (MCL shape), which combines many advantages and eliminates disadvantages of the previous types of shapes [4]. In the study [5] complex fatigue tests of beams (in scale similar to natural) were conducted at the Wrocław University of Technology. The objective of that study was to describe the behavior of MCL-type steel connectors. Two failure mechanisms of steel connectors were presented: so-called tearing of steel flange and pulling out of steel dowel. This paper presents the course and the results of macroscopic and microscopic tests of observed fatigue cracks. For the selected crack a profilogram was prepared, which allowed explaining causes of its initiation and characteristics of its development.

Boundary Approach in Shape Study of Composite Dowel Shear Connector

An approach for analysis of shape of composite dowel shear connector focused on finding a location of the point of maximal principal stress in steel dowel is presented. It is based on analogy between equations of boundary of closed area under plane stress conditions and beam in two dimensional space. Equations are derived from Airys potential and polar coordinates are used.

Development of Shear Connections in Steelconcrete Composite Structures

Abstract Different types of shear connectors and modelling techniques are presented. Basic research conducted or presented after year 2000 is taken into consideration, following the idea of concrete dowel implemented in the form of perfobond strip at the beginning of the 1980s by F. Leonhardt. The latest research in the field of continuous shear connectors applied in bridges is highlited with special focus at the composite dowel shear connection, as it seems to be the most modern solution being strongly introduced to the industry. Final shape of composite dowel shear connection is presented.

Connection Capacity of the Transition Zone in Steel-Concrete Hybrid Beam

Abstract The problem of transition zone of structural steel element connected to concrete is discussed in the following paper. This zone may be located for instance in specific bridge composite girder. In such case the composite beam passes smoothly into concrete beam. Because of several dowels usage in the transition zone, the problem of uneven force distribution were discussed through analogy to bolted and welded connections. The authors present innovative solution of transition zone and discuss the results, with emphasis put on the transition zone structural response in term of bending capacity, failure model and force distribution on the connection length. The article wider the already executed experimental test and presents its newest results.

Economic Composite Constructions for Bridges: Construction Methods Implementing Composite Dowel Strips

Composite dowel strips find a wide application in bridges. They are easy to manufacture and the transmission of shear forces of the composite action is long lasting and robust. Beside the innovative composite action new construction methods for composite bridges are established. The article summarizes already executed bridge structures implementing composite dowel strips due to construction details and economic aspects.

Continuous Shear Connectors in Bridge Construction

Continuous shear connectors offer an upcoming solution for composite beams. They are characterized by a high initial stiffness, bearing capacity and ductility. With their use new and economic construction methods have been invented, e.g. the PreCoBeams (Prefabricated Composite Beam). PreCoBeams are composite beams associating T-sections acting as tension member with a concrete top chord acting as compression member. Steel parts are generally obtained from rolled steel profiles that are longitudinally cut, with a special shape, in two T-sections. The shape of the cut allows for shear transmission between steel and reinforced concrete, which is continuous regarding the steel. In general, prefabricated composite bridge elements are produced, consisting of the steel T-section with a precast first phase concrete flange. The second phase concrete layer is then completed in-situ after placing of the bridge elements on the abutments. These PreCoBeam bridges are very economic in design and construction, though the main market drawback for PreCoBeams is the missing design approach for the shear connection. This paper introduces the static and fatigue design of continuous shear connections used for PreCoBeams derived from recent research activities; however the focus is on the steel design.

Modern composite bridges by VFT-WIB method in Poland realized at new express road S7 at Olsztynek-Nidzica sector

The design-an-build formula allowed for several new bridges, including road bridges and animal crossings, to be built using the VFT-WIB solution for the road S7 at Olsztynek – Nidzica in Poland. The designers took advantage of the versatility and adaptation capability of VFT-WIB, overrunning some of the encountered situations, which include the difficult geometry or the contractor’s demands.

Bridges by VFT method in Poland: state-of-the-art

Bridges with VFT method have been built in Poland since the year 2000. Many diverse solutions and structures were developed, each adapting to the different conditions and requirements. The experience gained in time and the well behavior of the VFT bridges, allowed for the solution to be appreciated.