Oliver Hechler

High-Performance Materials in Composite Construction

Scope of the investigations was the fatigue behavior of different shear connectors like headed studs and the puzzle-strip, which is a continuous shear connector in high-strength concrete (HSC). For both types of shear connectors, cyclic push-out tests as well as large-scale beam tests under cyclic loading were carried out. The headed studs failed after a mean lifetime of 2,3 × 106 applying 40–50% of the static resistance as a maximum amplitude and R = 0,45. The residual strength after 1,0 × 106 load cycles was reduced by about 25% in comparison with the static push-out strength. The continuous shear connectors were tested with two different stress amplitudes (R = 0,54 and R = 0,42). None of the test specimens failed in the fatigue tests with up to 2,0 × 106 load cycles. Moreover, there was no reduction in residual strength in the tests with the smaller stress range (∆P/Pu,0 = 0,2). One test with a stress range ∆P/Pu,0 = 0,25 showed a recuction in residual strength of 24%. The cyclic beam tests with headed studs show that the prediction of the fatigue failure according to the current standards is not satisfactorily. A good prediction of the crack propagation (thus fatigue) can rather be accomplished by using an approach based on the crack–slip relationship. For the continuous puzzle strip, the fatigue behavior depends on the manufactoring process, the state of the cutting-induced heat treatment of the surface material and the surface roughness. For the tested connector geometry, a threshold value for the crack propagation was determined.

Human-induced vibration of steel structures (Hivoss)

The guideline and background documents have been translated into different languages and published on a project web page (www.stb.rwth-aachen.de/projekte/2007/HIVOSS/ download.php) that may be easily found by an Internet search for ‘Hivoss’. At this site the guideline and background documents can be downloaded as a free PDF. This download page has received a lot of interest, resulting in 1 900 downloads of the footbridge guideline and 1 000 downloads of the floor guideline up to 30 March 2009.

The right choice of steel – according to the Eurocode

In general, the choice of the steel grade is ruled in Eurocode EN 1993-1-1. Several requirements are specified: choice according to the material properties, ductility requirements, toughness properties and through-thickness properties. With reference to these requirements on the mechanical characteristics, modern hot-rolled structural sections are produced by precise control of the temperature during the rolling process. Fine grain steels, produced using thermomechanical rolling (delivery condition M according to EN 10025-4), feature improved toughness values which give a lower carbon equivalent and a fine microstructure when compared with conventional or normalised steels. This paper gives guidance on and background to the right choice of the steel grade according to the Eurocode. Furthermore, the influence of the production process on this choice is highlighted and the advantages of thermomechanical steels for each criterion are discussed.

Fatigue Behavior of Shear Connectors in High Performance Concrete

The paper deals with the fatigue behavior of headed studs and continuous shear connectors in high strength concrete. For both types of shear connectors cyclic push-out tests as well as large-scale beam tests under cyclic loading were carried out. The headed studs failed after a mean lifetime of 2.3-106 applying 40% to 50% of the static resistance as a maximum amplitude and R = 0.45 and 0.65, respectively. The residual strength after 1.0-106 load cycles was reduced by about 25% in comparison to the static push-out strength. The continuous shear connector, which is called “puzzle strip”, did not fail in the fatigue tests with up to 2.0-106 load cycles, and there was no reduction in residual strength at all. The cyclic beam tests with headed studs show that the prediction of the fatigue failure according to the current standards is not satisfactory. A good prediction of the crack propagation (thus fatigue) can rather be accomplished by using an approach based on the crack-slip relationship. For the continuous puzzle strip the fatigue behavior depends on the state of the cutting-induced heat treatment of the surface material and on the surface roughness. For these connectors a threshold value for the crack propagation could be determined.

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.

Economic Design of Composite Bridges with integral Abutments

In this paper, a method for the pre-design of integral abutment bridges is presented. It is based on the use of common design tools developed for conventional bridges with bearings and joints. The soil-pile-abutment system is hereby replaced by a single rotational spring. Therefore the determination of the spring properties is described in detail. Furthermore the calculation procedure for the moment induced by uniform temperature and for the normal force in the superstructure induced by the restraint moment is presented. As these calculations are not integrated in conventional design tools, simple hand calculation formulas have been developed. Their application is shown via a design example in this paper.

Investigations on Beams with Multiple Regular Web Openings

In recent years the application of cellular beams is more and more requested by architects and designers. Not only their aesthetical appearance as visible steel structures and economic design are popular, also the possibility to pass service integrations through the openings is given. In the scope of the ECSC project 7210-PR-315 Large web openings for service integration in composite floors the performance of beams with web openings was studied experimentally and theoretically. The aim of this paper is to present the investigation on beams with multiple regular web openings with special focus on different failure mechanisms. The test program comprehended large scale tests with the following objectives: (1) Composite action close to support, (2) Behavior of elongated openings, (3) Load introduction via secondary beams, (4) Asymmetric design, and (5) Stiffening of web openings. On the basis of the test results and theoretical investigations including numerical simulations, design recommendations were established.