Composite slabs, consisting of steel composite profiled sheets and concrete, have been used successfully in composite construction for many years. In many cases, their cost-effectiveness depends on the span widths that can be achieved with the profiled sheets in the construction state. In order to increase the span widths, profiled sheets with high ribs are becoming used more frequently, which can minimize the number of secondary beams required and significantly increase the cost-effectiveness of the construction method.

The use of ever higher profiled sheet heights changes the load-bearing behavior of the shear connectors required to create the connection between the composite deck and the beam to greater flexibility and ductility, but also to a lower load-bearing capacity. In contrast to the application of profiled slabs in cold conditions, hardly any research results are available for fire conditions. Therefore, it is currently not possible to make any well-founded statement on the applicability of the design formula for the load-bearing capacity of head bolt anchors in case of fire according to DIN EN 1994-1-2 for high-rising profiled anchors.

Building on the already completed research project "Minimum anchoring of composite girders in the event of fire", the applicability of partial composite anchoring in the event of fire is also to be examined in greater detail. It is to be examined whether the approaches developed for composite girders with solid concrete slabs can also be transferred to composite girders with high-rising profiled sheets.The implementation of the research objectives is to be achieved by an extensive experimental test program. While the local load-bearing behavior of the shear studs in the profiled sheet beads is to be investigated by means of push-out tests in accordance with DIN EN 1994-1-1 under fire load, the overall load-bearing behavior is to be analyzed by means of large-scale fire tests on composite girders. In addition to the test program, parameter studies on composite girders and push-out test specimens are planned using the Abaqus FE software.

Responsibility

Kurt Tutzer

This research project deals with the development of a neoteric composite column, with cross-section of steel plate fins (Fig. 1). It consists of steel lamellae that are inserted in a steel tube and grouted with high-strength mortar. By using ultra-high-strength steel for the slender lamellae (with yield strength up to 1100 N/mm² and maximum thickness 40mm) as well as for the tube profile (yield strength up to 890 N/mm²) simultaneously, extreme load bearing columns can be developed.

The use of plate lamellae vis-à-vis full solid section provides added benefits because of these two reasons:

1. By using a single plate thickness of maximum 40 mm, the reduction in thickness-dependent yield strength (mainly arising due to internal residual stresses) are avoided. As with increase in plate thickness the level of residual stresses increases, because of the manufacturing process involved, which leads to early arrival of yield strength.

2. In the event of fire, by breaking the heat conduction between the steel lamellae more advantageous heating behavior can be obtained. (Fig. 4)

The individual plates are selectively joined, at specific points to set the necessary bending stiffness as required. For this purpose, various connection mechanisms are being examined such as prestressed bolted joints, stitch (partial) welding and full-length welding. The choice of various shear connections enables the possibility of achieving best targeted configuration, ideally without causing any additional residual stresses or disturbances in the high-strength steel.

To summarize, the use of high strength materials and innovative section design allows the development of extreme high load-bearing composite columns. The local use of shear connection offers an efficient way of manufacturing.

Responsibility

Michael Schäfers

The aim of the research project is to develop fire-resistant, high load-bearing and simultaneously slender composite columns.

Bar bundle columns are a new type of composite column. For this purpose, a bundle of high-strength reinforcing bars with a yield strength of 670 N/mm² is set in a steel tube and then grouted with mortar. The bundle can consist of 1,3,7 or 19 bars.

These steels are available on the market up to a diameter of 75 mm. A thickness-dependent yield strength reduction is not required here, so that the high yield strengths can be fully utilized. By bundling bars, high filling ratios of the cross sections are also possible, so that load-bearing capacities can be achieved that are otherwise only possible with much larger cross-section dimensions.

Compared to composite columns with solid cross-sections, bundled columns also exhibit more favorable heating behavior because the individual bars are only in direct contact with each other at specific points, thus limiting heat conduction between the bars.

Within the scope of this project, the load-bearing behavior of bar-bundle columns in cold and fire conditions was investigated. In order to analyze the load-bearing behavior, the individual material parameters were determined in cold and fire conditions. Subsequently, large-scale tests were carried out; an FE model was created or calibrated from the collected results. With the help of the FE model, numerous parameter studies were carried out, on the basis of which a design concept based on DIN-EN-1994 was created so that the columns can be used in practice.

The final report will be published shortly by FOSTA (Forschungsvereinigung Stahlanwendung e.V.).

Responsibility

Rudolf Röß

Research Funding

AiF - Arbeitsgemeinschaft industrieller Forschungsvereinigungen
FOSTA - Forschungsvereinigung Stahlanwendung e.V.

Within the scope of AIF-Zutech Project P881 the construction of sustainable offices and administration buildings in steel and steel composite construction, planning tools and methods for the design and evaluation of these buildings are developed by an interdisciplinary research team. Apart from ecological and economic criteria, architectural, socio-cultural and socio-technological criteria are also taken into account. The benefit of their flexibility and their evaluation are in focus, as this has significant consequences on buildings’ design and their subsequent marketability. Based on various usages, developments and trends in the structural organization of office buildings, the socio-cultural and socio-technological requirements are formulated. Strategies for life-cycle-oriented economic evaluation are developed, including value-added accounting. The development of sustainable load-bearing structures in steel and steel composite constructions are one of the construction-related topics. The Chair of Metal Construction at TUM is leading the project and developing intuitive CAD-supported software for the ecological optimization of the steel load-bearing structure of office buildings with the help of genetic algorithms, which enables a right direction to be set during early design phase with respect to a particular ecological building design.

Responsibility

Dipl.-Ing. Heidrun Möller, Li Huang M.Sc.

Sustainable building requires innovative construction methods such as a resource-saving innovative TopFLOOR INTEGRAL ceiling system. Together with ETH Zurich and H. Wetter AG, Stetten, a Swiss steel construction company, a sustainable multifunctional ceiling system in composite construction was developed in which the installation level or raised floor is integrated into the static construction height. The system consists of half honeycomb girders that are connected to a concrete slab in a shear-resistant manner using conventional reinforcement bars, thus forming a pi-slab allowing large spans and column-free constructions. Depending on the requirements, the slabs can be used in positive or negative position. Design concepts were developed and tested for system and necessary connection details. Intensive investigations against vibration behaviour of the structure were carried out at Chair of Building Mechanics at TUM. This construction method reduces material consumption by approx. 50% as compared to conventional concrete structures. TopFLOOR INTEGRAL has meanwhile been proven outstanding for several buildings in Switzerland allowing the shortest possible construction times. For example, the shell including the facade of the eight-story Lindenplatz school building in Baden (CH) was erected in less than 10 weeks over a rail tunnel.

Responsibility

Prof. Dr.-Ing. Martin Mensinger

Flexible secondary beam connections are the most common, but at the same time least researched connection types in steel composite construction. In steel and composite construction, the connection of secondary beams to main beams is often made with long flange plates since these are easy and inexpensive to manufacture. In the past, flange plate connections were considered to be ideally flexible, although an unplanned continuity effect occurs with secondary beams over two or more spans. Because of the continuity of concrete section of secondary girders across the main girders, the continuity becomes relevant for composite girders. Within the scope of this research project, fundamental findings on actual load-bearing behaviour of such secondary girder connections were obtained with the help of large-scale tests and corresponding numerical simulations. Based on these findings, a design model was developed for practical applications. An essential component of the model is a plastic moment-shear force interaction relationship, derived individually for the respective connection, with the help of which the moment load capacity of the connection can be determined quickly and easily as a function of acting shear force. Consideration of the moment capacity of the connections allows a more economical design of the secondary beams than if the connections were considered in a hinged manner.

The research report can be obtained from the German Committee for Steel Construction (DASt).

Responsibility

Dr.-Ing. Karl Schwindl