Jörg Lange

Constitutive Equations and Empirical Creep Law of Structural Steel S460 at High Temperatures

Although the constitutive equations at elevated temperatures given in Eurocode 3 Part 1-2 are valid for steel grades up to S460, the experimental data base concerning the mechanical behaviour of this particular high strength fine-grained structural steel is very small. Especially its short time creep behaviour at high temperatures has not yet been analysed. A current research project, predominantly consisting of transient testing of numerous commercial S460 steels, targets a more precise determination of the stresss-train relationships at high temperatures. Additionally, the time-dependent strain components are extracted from test results gained at varying heating rates, and an empirical creep law, based on the concept of temperature-compensated time, is derived. As a result, the constitutive equations can be formulated taking the heating rate into account. The differences in the high temperature load-carrying capacity of steel structures made of S460 according to the research results and under the terms ...

Examination of the Mechanical Properties of Steel S460 for Fire

To establish a basis for calculating the load-bearing capacity of steel members made of S460 in a fire, corresponding to EN 1993-1-2, the mechanical properties of the micro-alloyed grain refined steel S460 under high temperatures have been examined. Two different types of steel have been considered: a normalized rolled S460 N and a thermo-mechanically rolled S460 M, that differ in their chemical composition and the temperature control during the hot-rolling process. On the basis of transient warm-creep tests, constitutive laws have been derived for the temperature range 20-900°C. The testresults show an increased strength of S460 M at elevated temperatures in comparison to S460 N. This is a result of the strain hardening caused by the thermo-mechanical rolling and the reduction of the creep-velocity caused by niobium- and titanium-precipitations. The data derived from the tests show that the stress-strain curves given in EN 1993-1-2 for S460 overestimate both the strength and the stiffness of the examined...

Experimental study of post-fire performance of high-strength bolts under combined tension and shear

Purpose This study aims to verify whether the reduction factors for the post-fire performance of Grade 10.9 bolts stated in an earlier study at the TU Darmstadt are also valid for shear and combined tension and shear. Design/methodology/approach Tests on Grade 10.9 bolt sets under combined tension and shear were carried out. The tested bolts were heated and cooled without being stressed by an additional mechanical load before being tested. Findings The test results show that the reduction factors can also be adopted for bolts under combined tension and shear, but the tension-shear-ratio has an influence on the load bearing capacity. Originality/value The post-fire performance of high-strength bolts is of special interest when a building structure is evaluated after an event of fire. In contrast to conventional structural steel, high-strength bolts do not recover their original strength and material properties.

Harmonization of Design Rules in Europe

In the last decades the Eurocodes have been developed in order to harmonize the technical rules for the structural design in Europe. Since the beginning in 1975 the aim was the elimination of technical obstacles in trades throughout Europe. Today most of the Eurocodes are published. The ECs are no rigid technical rules; they keep room for national differences. The National Annex which is valid in conjunction with the relevant Eurocode contains information on those parameters which are left open for national choice. Due to the fact that the Eurocodes are still not mandatory in Europe and not even used by some of the European Countries, it is necessary to make the engineers sensitive to the Eurocodes and to train the use. The European Union launched in 1995 the Leonardo Da Vinci Programme with the objective of improving the provision of vocational education and training across Europe. The paper will describe the current Leonardo Project named “Eur-Ing” and show some results.

Influence of the Bauschinger Effect on the Deflection Behaviour of Cambered Steel and Steel Concrete Composite Beams

Steel concrete composite beams are an economical alternative for the construction of wide-spanned slender structures in parking lots, office and industrial buildings. They combine the tensile strength and stiffness of steel sections with the good compressive strength of concrete slabs. To ensure an unrestricted use of the building, the expected deformations, vibrations and cracks are calculated during the analysis of the serviceability limit state. In reality, major differences between the calculations and the real deflections of beams are observed. Therefore, the deflection behaviour of composite beams was analysed and recommendations were developed to improve the calculation of the deformations. The deflection history was measured continuously during construction of four parking lots built with steel concrete composite beams. One result was that the fabrication of the beams at the manufacturing plant has an important influence on the subsequent deflection of the beam.

Office Building Junghof - Visible Steel for a Fire Safe Structure

Structural Engineering International 1/2007 developed. To prepare buildable structural details it became necessary to develop plane glass surfaces and a roof structure with constant depth. This was done by defining a mathematical net for the outer surface. Relating to the net nodes, all additional design depths of the structure and dry ceiling were defined. The system lines of the structural model for the calculation of the design forces were also taken from this net. This structural model then served as the basis for the final design drawings.

TESTS ON 10.9 BOLTS UNDER COMBINED TENSION AND SHEAR DURING AND AFTER FIRE

Prior investigations of the load bearing capacity of bolts during fire have shown differing behaviour between bolts that were loaded by shear or by tensile loads. The interaction of the two loads has not yet been examined under fire conditions. This paper describes a preliminary test series on the post-fire performance of high-strength bolts of the property class 10.9 under combined tension and shear. The results show that how the bolt is loaded influences the load bearing capacity. It is assumed that this is also true at elevated temperatures. Further, atest set-up for experiments at elevated temperatures and a more detailed test series on the post-fire performance under combined tension and shear is presented.

TESTS ON 10.9 BOLTS UNDER COMBINED TENSION AND SHEAR

Prior investigations of the load-bearing capacity of bolts during fire have shown differing behaviour between bolts that have been loaded by shear or by tensile loads. A combination of the two loads has not yet been examined under fire conditions. This paper describes a series of tests on high-strength bolts of property class 10.9 both during and after fire under a combined shear and tensile load.

Numerical Calculation of the Deflections of Composite Girders

To get good results in the prediction of deflections of composite girders a good mechanical model is needed. For research 3-dimensional finite elements with nonlinear geometry and material laws are a very good tool. Unfortunately they generate very much effort in the modeling of the structure which reduces their applicability to special problems that have to be solved by specially trained engineers. In our paper we will show how very good results can be obtained by using a combination of simple beam and shell elements. Special emphasis is laid on the modeling of the effective width, shear lag effects in the beam and the slab, creep and shrinkage, and the non-linear behavior of the steel element due to the cambering process. First results show very well the influence of shear lag effects for short beams with thick concrete slab as they are mainly used in experimental evaluations. Comparisons with the test results of [Rieg 2006] prove the necessity of calculating deflections with a “deflection based effective width” in contrast to the current practice of using the same width for stress and deflection analyses. 1 STATE OF THE ART A significant number of scientific publications on the load and deformation behavior of composite girders exist. With the exception of [Menrath 1999] the authors used 1D Beam-Elements with or without consideration of slip between concrete slab and steel profile. For the calculation the effective width has to be set by the user. [Rieg 2006] and [Amadio et al. 2004] assess the variable effective width in case of composite girders with shallow height. Rieg developed a model which considers changes of the deformation-related effective width directly in moment-curvature-relations. In [Rieg 2006] the model was developed only for simple one span systems which are statically determined. In this presentation the effect will be analyzed using a 3dimensional Finite Element Model to verify the dimension of the practical influence. The reason is that there is an additional effect especially in case of short beams as they are used in experiments. Because of the high inner shear forces the influence of the shear deformation cannot be neglected. The fact that both effects are not independent worsens the situation.

New Results of Material Analysis regarding the Bauschinger- Effect on the Deflection of Composite Beams

Aim of the project was to measure deflections of standard steel concrete composite beams, used in office and industrial buildings assess and analyze the reasons for those deformations and develop simple design aids for a realistic calculation of the deflections. This research was necessary, since experience has shown that results do frequently not match the deflections measured on site. This can reduce the serviceability of a structure and lead to high rectification costs. The focus was on the differences between calculations and in-situ behavior by analyzing the measured deflections of beams in structures under construction. During the measurements it appeared that cambered beams deform more than straight beams. This effect was analyzed in tests and it was found that the reason for this behavior lies in the Bauschinger Effect, rather than in residual stresses. It will be shown when and how this effect should be considered.