Markus Feldmann

Guidance for European Structural Design of Glass Components

Keywords: structural glass Reference EPFL-REPORT-196634 Record created on 2014-02-13, modified on 2016-08-09

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.

Ermittlung der Rissanfälligkeit von Baustählen beim Stückverzinken

Kurzfassung In jüngster Vergangenheit gehäuft auftretende Risse beim Feuerverzinken von großen Stahlkonstruktionen gaben Anlass, die Ursachen und Einflussfaktoren der Rissbildung genauer zu untersuchen. Zielsetzung einer von der Industrie zusammen mit der RWTH Aachen gestarteten Forschungsinitiative ist es, die wirksamen Mechanismen zu klären, die vielfältigen und sich in komplexer Weise beeinflussenden Parameter zu untersuchen, sowie die Einflüsse auf Beanspruchung und Beanspruchbarkeit des Stahls beim Verzinken zu separieren und zu quantifizieren. Es wurde ein neuer, aussagekräftiger Versuch zur Untersuchung der wirksamen Effekte bei der Versprödung von Baustählen durch Angriff aus Zinkschmelzen entwickelt, der den vorherrschenden Spannungs-Dehnungszustand berücksichtigt.

Characterization of Adhesive Joints for Hybrid Steel-Glass Beams by Means of Simplified Small Scale Tests

In the recent past there have been calls for transparent and filigree structures in the building industry. Therefore, glass plays an increasing role not only in a classic way, as a space enclosing element, but also more and more in terms of offering load carrying functions. Glass beams for facade elements or floor girders, glass columns, or bracing facade elements are examples of this. To realize such architecturally attractive structures, bonded hybrid steel-glass elements have been developed in which each material is used in an optimized way according to its material properties. Promising examples for such bonded structures are I-beams in which steel flanges and glass webs are connected by linear adhesive bonds. The shear force is carried by the glass web, whereas the bending capacity of the hybrid beam is significantly increased by slender steel flanges compared to the pure glass pane. The shear forces between steel and glass are sustained only by the adhesive between them. In order to maximize the exploitation of both steel and glass, the adhesive on the one hand has to ensure an adequate stiffness but on the other hand has to be flexible enough to allow for a reduction or redistribution of local stress peaks, as well as other constraints such as thermal dilatation. However, the load-bearing capacity of such beams is governed, besides by the mechanical and geometrical characteristics of the adhesive joint, by aging, temperature, and creeping. In this contribution, an approach is shown for characterizing the adhesive joints for hybrid steel-glass beams by means of simplified small-scale tests. Standardized specimens (block shear and tension bulk specimens) and small-scale push-out tests are used to derive adequate mechanical values for analytical and numerical calculations, allowing one to draw conclusions regarding the general load carrying behavior of large-scale hybrid steel-glass beams. The results show that full-scale hybrid steel-glass beams, especially those with butt splice bonded and U-bonded geometries, are feasible using new structural adhesives, predominantly elasto-plastics such as polyurethanes or epoxy resins.

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.

Design of composite dowels as shear connectors according to the German technical approval

Composite dowels are known as powerful shear connectors in steel-concrete-composite girders. More and more they are used in practice especially for prefabricated composite bridges. Advantages over headed studs are in particular the increased strength, the sufficient deformation capacity even in high strength concrete and the simple application in steel sections without upper flange. However, missing provisions in standards for composite dowels with the economic clothoid and puzzle strip have led to retentions of clients and delays in the approval process. Hence, the aim of the recently finished German research project P804 [15] founded by FOSTA- Research Association for Steel Application was to solve open questions concerning these innovative shear connectors and to prepare a general technical approval available for any design office and construction company. In this paper design concepts for ultimate limit state and fatigue limit state, structural design principles and instructions for production and construction are presented and background information are given.

A New Simplified Design Method For SteelStructures Under Impulsive Loading

The dynamic response of structures under impulsive loading is a complex process where both geometric and material nonlinearities play a very important role. The use of Finite Element calculations is advisable for the design of structures that must withstand impulsive action (blast or impact), but designers very often lack the resources to perform these calculations, thus simplified design methods are often used, mainly based on the reduction of the original system to dynamically equivalent SDOF system. Most of the existing approaches suffer from shortcomings when having to deal with arbitrary support conditions, to consider catenary effects or to consider interaction effects with surrounding parts of the structure. In order to overcome these limitations, the Institute of Steel Construction has proposed a new 2-DOF dynamically equivalent system reduction, which allows for the explicit consideration of catenary action including connector failure and opens new possibilities for integration with more complex Finite Element models. Within this new approach, the connectors are treated distinctly, so that a separate assessment of its failure is possible.

Wind turbine tower design, erection and maintenance

: Higher towers for wind turbines are the main trend to achieve better effectiveness in the conversion of wind energy to electrical energy. This leads to an increasing contribution of the tower costs to the total investment costs. Optimization of the structural design by improving the design of connections in the tower is an important issue for the competitiveness of the wind energy sector. The basis of the design model of the flange connection and the possibilities of retrofitting are shown. A short overview of the main structural solutions for towers and the most common criteria for the design are provided in the text.

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.

Safety considerations of annex j of eurocode 3

Publisher Summary The new Annex J of ENV 1993 -Eurocode 3 presents rules for the design of joints both for stiffness and strength. Due to the different components and materials of which a joint may exist, the safety assessment of structural joints is complex. This chapter provides considerations of the influence of unexpected over strength on the ductility and safety of joints. For seismic loading a method is suggested, which allows an extension of plastic design to joints with alternating rotations. Furthermore, the ULS-design of a steel structure consisting of elements and joints may be performed with two options. The first option is the consideration of the whole true moment-rotation characteristic of the joints. The second option is the use of a standardized model, which describes the moment rotation behavior of a joint in a simplified way: the initial stiffness, the transition from the elastic part to the plastic part of the curve and the ultimate resistance level without an a priori limitation of the rotation.