Ulrike Kuhlmann

Finite element simulation of slender thin-walled box columns by implementing real initial conditions

This paper deals with the numerical simulation of tests on slender thin-walled box columns, susceptible to combined instability: to global Euler buckling and to local buckling of steel plates. Eight full-scale tests were carried out with different global slenderness of welded and cold-formed columns subjected to centric and eccentric compression. Initial column geometry and residual stresses were measured and carefully implemented in numerical models. The results of FEA simulations show good agreement with the test results. On verified numerical model the influence of different initial imperfections was studied and various equivalent geometric imperfections were tested for the considered column configurations.

Numerical studies on web breathing of unstiffened and stiffened plate girders

Abstract By repeated web breathing high ranges of secondary bending stresses due to post-buckling out-of-plane deformations at the boundaries of the web lead to local fatigue failure, which might limit the life of bridge girders. Based on recent experimental research, numerical studies on web breathing of longitudinally unstiffened and stiffened plate girders are presented. A new comprehensive fatigue assessment method is used to study the breathing phenomenon in bridge girders. By a large number of parametric studies on typical highway and railway bridges, easily applicable slenderness limitations have been derived for longitudinally unstiffened web panels, by which fatigue failure due to web breathing can be excluded.

A Timber–Concrete Composite Slab System for Use in Tall Buildings

The increasing demand for fire resistance and sound insulation in multi-storey buildings has made composite slabs of board stacks (side by side timber members) and concrete a desirable structural system. While it has been implemented in several cases, the floor plan is restricted because the anisotropy of timber requires continuous support of the board stacks. Steel slim-floor profiles can be integrated into the timber–concrete composite slab, acting as a continuous support. In comparison to usual reinforced concrete slabs, the reduced dead load allows larger spans with the same thickness, which requires fewer columns and extends the range of the application for the structural system.

Welded Connections of High-Strength Steels For The Building Industry

The developments of steel structures aim at light and slender constructions. Therefore, high-strength steels with good welding characteristics and a high ductility, aside from higher strength, have been developed by the steel industry. With increasing strength of the steel, the loads which have to be transferred in the welded connections are also growing. In building constructions, fillet and partial penetration connections are commonly used. When using high-strength steels, it is very important to ensure strength, as well as sufficient ductility and toughness of these welded connections, in order to allow for the necessary redistribution of stresses and internal forces. The use of high-strength steels can bring significant savings in terms of material consumption, weight, transportation and fabrication costs. Beside the savings due to the reduced material consumption, advantages result from the smaller construction weight and a faster fabrication by reduction of the weld thickness. However, especially for high-strength steel grades S460 and S690, the benefit of saving of material cannot be used, dzue to the present restrictive design rules. Therefore, the aim of this research project, realized by four partners, was the development of appropriate and modern construction and design rules, as well as manufacturing principles, in order to achieve an economical use of high-strength fine grained steels. This paper presents the results of a research project, investigating the strength and ductility of fillet welded connections of high-strength steels S460 and S690, by means of experimental and numerical analyses. Experimental and numerical investigations of the load bearing capacity and safety against brittle fracture at lap joints with longitudinal fillet welds, cruciform joints with transverse fillet welds and butt joints with partial penetration double-V-groove welds of high-strength steels S460M/ML and S690Q/QL have been carried out. Numerical investigations in terms of welding simulation and measurements of residual stresses have been performed, in order to identify the local microstructure, hardness, residual stresses and strength in the weld profile. These results support the assessment of strength and ductility of welded connections. Based on the investigations, recommendations for the design of welded connections of high-strength steels, in terms of load bearing capacity and safety against brittle fracture, as well as manufacturing principles, were derived. The results of the research project thus contribute significantly to an optimized use of high-strength steel in welded constructions.

Rehabilitation of Welded Joints by Ultrasonic Impact Treatment (UIT)

Due to the increasing traffic and life loading fatigue becomes of high relevance in order to maintain the integrity of existing steel bridge structures. Poor construction details which used to be regarded as less important when applied e.g. to road bridges are nowadays often the starting point of fatigue cracks. Repair and strengthening of welded details are thus of great importance in order to extend the life time and safety of existing bridges. For welded details under fatigue loading one effective possibility to do this is the application of local post-weld treatment methods. This paper presents the application of a relatively new post-weld treatment method called “Ultrasonic Impact Treatment” (UIT). The paper summarizes the results obtained on a series of experimental fatigue tests where UIT has been applied in order to extend the life time of partially damaged non load carrying fillet welded joints.

Application of Probabilistic Robustness Framework: Risk Assessment of Multi-Storey Buildings under Extreme Loading

Abstract Risk assessment is a requirement for robustness design of high consequence class structures, yet very little guidance is offered in practice for performing this type of assessment. This paper demonstrates the application of the probabilistic risk assessment framework arising from COST Action TU0601 to multi-storey buildings subject to extreme loading. A brief outline of the probabilistic framework is first provided, including the main requirements of describing uncertainty in the hazards and the associated local damage as well as the consequences of global failure. From a practical application perspective, it is emphasised that there is a need for (a) computationally efficient deterministic models of global failure for specific local damage scenarios, and (b) effective probabilistic simulation methods that can establish the conditional probability of global failure on local damage. In this respect, this work utilises a recently developed multi-level deterministic assessment framework for multi-storey buildings subject to sudden column loss, which is coupled with a response surface approach utilising first-order reliability methods to establish the conditional probability of failure. The application of the proposed approach is illustrated to a multi-storey steel-composite building, where it is demonstrated that probabilistic risk assessment is a practical prospect. The paper concludes with a critical appraisal of probabilistic risk assessment, highlighting areas of future improvement.

Ductility in Timber Structures: Investigations on Over-Strength Factors

This paper presents a study on the implementation of connection ductility in timber structures. Regardless for which purpose ductility in timber structures is needed, it is necessary to avoid a brittle failure of the timber element before the ductile element is in the stage of yielding. An over-strength factor is introduced to consider the required distance of the load-bearing resistance of the beam element from the introduced bending moment initiated by the load-carrying capacity of the fasteners. Hence, a Monte-Carlo simulation was conducted, focusing particularly on the scattering of the material properties to determine a reliability index of a joint loaded in bending. Since the reliability index is based on the application of the ductility, a range of over-strength factors is given for different reliability indices. The Monte-Carlo simulation is based on the mean material properties of the experimental specimens. The experiments are explained and the non-linear behaviour is displayed not only for connections loaded in tension but also for joints loaded in bending.

Design of Anchor Plates Based on the Component Method

Steel or composite joints can be designed and optimised by the component method according to Eurocodes [EN 1993-1-8:2005] and [EN 1994-1-1:2004]. The structural behaviour (strength, stiffness, ductility) of these joints is defined by assembled components. Their individual behaviour is described by a mechanical spring model. For the extension of the component method to anchor plates, which are used to transfer loads between steel and concrete structures, a mechanical model has been developed. The model is based on several test series with anchor plates carried out by the Institute of Structural Design (Universita¨t Stuttgart) and describes the load-carrying capacity of anchor plates. In some tests supplementary reinforcement has been taken into account influencing the load capacity and ductility of these steel-to-concrete joints. Additional tests have been performed to study the influence of a flexible anchor plate on the structural behaviour of the joint. Altogether, the component model shows transparency of load distribution and may easily be transferred to alternative situations.

Headed Studs Used in Trapezoidal Steel Sheeting According to Eurocode 4

This paper presents the results of a recently completed research project at the Institute of Structural Design, Universität Stuttgart funded by Deutsches Institut für Bautechnik (DIBt). The main focus of the project was to assess the quality of the given approach in Eurocode 4 to determine the bearing resistance of headed studs used in trapezoidal steel sheetings. Therefore, 17 new push-out tests with steel sheeting within the field of application of Eurocode 4 have been performed. The main focus of the investigation has been the influence of the position of the headed stud in the trough and the influence of the various geometric parameters on the failure mode. At the moment, the existing design rules in Eurocode 4 for headed studs in trapezoidal steel sheeting do not take into account the position of the stud in the trough nor the variety of failure modes. The test results showed that in a number of cases the bearing resistance reached was smaller than predicted by Eurocode 4. Moreover, the construction rules of Eurocode 4 aiming at a ductile behavior could not always assure this. On the other hand, ductile failure occurred though some of the construction rules were not respected. As a result, the need for further in-depth investigation is emphasized.

Alternate Load Path Method for Robust Design by Ductile Steel and Composite Joints

This paper reports briefly on the experimental and numerical investigations of steel and composite joints aiming at the development of semi-rigid and partial-strength joint solutions allowing large deformations and rotations for redistribution of internal forces in the structural system when local damage e.g. “column loss” occurs. Investigations of steel and composite joints with highly ductile behaviour are presented. Thereby special focus is given to the adjustment of the single joint components to ensure a high deformation capacity during pure bending as well as combined bending and membrane exposure.