Stainless steel material is a suitable choice for modern steel constructions as it has a high resistance to corrosion combined with high material strength and ductility. Furthermore, its use leads to significant reductions in maintenance. In this frame, bolted connections made of stainless steel components become more and more important to enhance the application of stainless steel not only to small parts of steel structures but also to complex structures. Whereas non preloaded stainless steel bolted connections are already widely used, according to EN 1090-2, the application of preloaded stainless steel bolting assemblies is not allowed unless otherwise specified. If they shall be used, they shall be treated as special fasteners and a procedure test is mandatory. Also EN 1993-1-4 requires that their acceptability in a particular application has to be demonstrated from test results. These restrictions are mainly caused by two facts: firstly, the viscoplastic deformation behaviour of stainless steel which might result in not negligible preload losses in the bolting assemblies themselves and secondly, the gap of knowledge regarding suitable tightening parameters and procedures for stainless steel bolting assemblies to secure a required preload in the bolting assemblies and to avoid galling. To solve these questions, research activities have been carried out in the frame of the European RFCS-research project “Execution and reliability of slip resistant connections for steel structures using CS and SS” SIROCO. The present contribution gives an initial insight into the viscoplastic deformation behaviour of stainless steel bolting assemblies which were achieved in SIROCO which shows that preloaded bolted stainless steel connections can be treated similar to those made of carbon steel.

Preloaded bolting assemblies made of stainless steel are currently not permitted in steel structures due to the unknown viscoplastic deformation behaviour as well as the unknown tightening behaviour and tightening procedures for these kinds of bolting assemblies. Nonetheless, the construction industry wishes to carry out these types of connections in special cases, e.g. when special requirements exist with regard to corrosion resistance or for architectural reasons. Generally, the tightening behaviour of carbon steel HR and HV bolting assemblies according to EN 14399-3 and -4 cannot simply be transferred uncritically to stainless steel bolting assemblies due to several reasons. Within the scope of the European RFCS research project SIROCO, extensive investigations are currently being conducted on the tightening and preloading behaviour of EN ISO 4014 and EN ISO 4017 bolting assemblies made of austenitic and duplex stainless steels. First results from this project show that a targeted tightening of such assemblies is in principle possible. Specified preloading levels, e. g. Fp, C* and Fp, C, can be achieved with sufficient reliability using suitable lubricants. Herewith, it is possible to define feasible tightening procedures. Furthermore, it could be shown that these bolting assemblies show sufficient ductility and galling of the assemblies can be for sure avoided. The present paper provides an initial insight into the results of the project.

The use of stainless steel components can lead to a significant reduction of maintenance costs compared to a structure executed in carbon steel. Because of its high material strength, ductility and corrosion resistance stainless steels are becoming more and more popular as a construction material in both building and civil engineering structures. Consequently slip-resistant bolted connections made of stainless steel are becoming more important. Slip-resistant bolted connections are used in joints where slip is not acceptable (because they are subject to reversal of shear load or any other reason) or in joints that are subject to cyclic shear load (to improve the fatigue class of the connecting plates). Existing design codes/standards do not specify slip factors for surface treatments of stainless steel grades, the minimum values of slip factors for common surface treatments/coatings that are specified in EN 1090-2 are exclusively valid for carbon steels. One of the reasons for this is that stainless steel alloys are thought to suffer more than carbon steels from time dependent behaviour (creep and relaxation) at room temperature. This could lead to higher preload losses and consequently to lower slip factors than used for carbon steels with comparable surface treatment. However, no evidence of this can be found in literature. Creep and relaxation are stress dependant phenomena and the stresses in the components of preloaded bolted connections are locally highly non-uniform. Therefore, slip factors of different stainless steel grades have to be determined by experiments to investigate the effects of time dependant material behaviour. In this paper the results of slip factor tests on four stainless steel grades are presented and the influence of surface treatments and the preload level on the slip factor of stainless steel slip-resistant connections is discussed.

The use of stainless steel in construction has become more popular in recent years. It is used for a wide range of structural applications in aggressive environments where reliable performance over long periods with little maintenance is required. Although structural design standards are available for stainless steel, currently there are no rules covering the design of preloaded slip-resistant bolted connections because of the lack of knowledge about their long-term viscoplastic behaviour. Viscoplastic creep and stress relaxation in the preloaded bolt assemblies will lead to a certain loss of clamping force and may cause the failure of the connection if not accounted for. This paper presents the development of material models and finite element models for bolt assemblies based on an extensive experimental study of creep, relaxation and tension effects on austenitic, ferritic, duplex and lean duplex steel plates and bars for different loading rates. These models were verified against slip tests with stainless steel bolt assemblies according to EN 1090-2 and then used in a parametric study to extend the scope of the connections investigated. Both experimental programmes were carried out in the European RFCS research project SIROCO (Execution and reliability of slip-resistant connections for steel structures using Carbon Steel and Stainless Steel) as well as finite element calculations.

In Eurocode 3 the strength functions are derived from simple engineering models, which always require a certain degree of material ductility. With regard to high-strength steels and the accuracy of the design models themselves, several problems are involved due to a lack of sound consideration of the plastification and damage process. Additionally, the current ductility requirements of EC3 obstruct the use of high-strength steels with fy > 500 MPa. Within the current revision of EC3, comprehensive investigations have been conducted to overcome these obstacles. To complement extensive experimental tests, improved numerical methods considering damage mechanics have been used to predict the real plastification and damage process for relevant details. The numerical models were validated by comparing them with experimental results. Subsequently, a parametric study was conducted to investigate the influence of strength and toughness properties separately. It could be shown that the reduction factor of 0.9 to account for the net section resistance can be omitted if cracks can be excluded. Furthermore, it became clear that a strain requirement based on the uniform elongation &egr;u is not appropriate. Moreover, it was revealed that the yield ratio fu/fy has a significant impact on the toughness requirements necessary to reach the full net section resistance. Owing to a lack of minimum upper-shelf toughness requirements in delivery standards, which would secure an appropriate inner damage resistance of the material, a substitution criterion is proposed.

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In memoriam: Bent Johansson
Jan Brekelmans

No short description available.

No short description available.

Experience with the operation and maintenance of cable-borne bridges of various ages over the last 20 years shows that water ingress into steel cable systems often occurs and causes a high risk of serious corrosion that may lead to traffic restrictions, extraordinary inspection and maintenance costs and, in the worst case, bridge closures. Examples of such experience cover suspension bridges as well as cable-stayed bridges in the USA, UK, Germany, France, Argentina, Sweden, Norway, Denmark and many other countries. The problem of water ingress is particularly critical as inspections for corrosion in cable systems are difficult to carry out and early warnings difficult to obtain.
Water ingress into a cable system means that there is a significant risk of steel corrosion even with precautions such as the use of galvanization and HDPE coating of cable wires. Although cable system designs generally comprise multiple barriers against corrosion, there is often a weak link in the design. This, combined with an unintended outcome in the construction phase or inadequate maintenance, may allow water to start accumulating and lead to corrosion.
This paper will explain and discuss cases from main cable and cable-stay systems and point out the water ingress modes and their causes for main cable systems and different cable-stay systems. Based on that, the paper discusses the weaknesses of the different steel cable concepts and different mitigations. The discussion also includes the mitigation of the water ingress problem through the use of dehumidification. This concept has been successfully used for the main cables of suspension bridges for more than 15 years. Considering the number of known problems with water in cable stays, the paper also contemplates the possibility of using dehumidification for cable-stayed bridges as a way of handling the large number of existing cable-stayed bridges.

A great number of fatigue cracks have been found in the welded joints at the top end of web gap plates in the transverse beam connection, at the top end of vertical stiffeners in the sway bracing connection, and at the web penetrations with the transverse beam bottom flange.
The present paper is a report on the verification of the effectiveness of 3 new types of retrofit methods proposed against those fatigue crackings. Stress measurements were carried out before and after retrofit works in a 45 years old bridge located in one of the heaviest traffic routes in Japan. As a result, fatigue life was considerably improved after the retrofit works, except for the case of vertical stiffener upper end retrofitted by the jack-up method. Fatigue life was improved to more than a several times by the TRS method for the vertical stiffener upper end and web gap, and to more than tens of times at the girder web slot area after retrofitting.

The length-dependent behaviour domains of thin elastic cylindrical shells under uniform bending have recently received significant research attention. Ovalization is known to affect very long cylinders that undergo significant cross-sectional flattening before failing by local buckling. This effect is restrained by the end boundary conditions in shorter cylinders, which instead fail by local buckling at moments close to the classical analytical prediction. In very short cylinders, however, even this local buckling is restrained by the end boundary, and failure occurs instead through the development of a destabilizing meridional fold on the compressed side. Although this is a limit point instability under bending, ovalization does not play any role at all. This 'very short' length domain has only recently been explored for the first time with the aid of finite element modelling.
A brief overview of the non-linear buckling behaviour of very short elastic cylinders under uniform bending is presented in this paper. Two types of edge rotational restraint are used to illustrate the influence of a varying support condition on the stability in this short length range. It is shown that short cylinders under bending do not suffer at all from local short-wave buckling. Additionally, when the meridional dimension of such cylinders becomes particularly short, the resulting numerical models may predict indefinite stiffening without a limit point, even when the shell is modelled using more complete 3D solid continuum finite elements. Idealized weld depressions, which are realistic representations of a systemic manufacturing defect, are used to demonstrate only a very mild sensitivity to geometric imperfections at such short lengths owing to a pre-buckling stress state dominated by local compatibility bending. The topic should be of interest to researchers studying shell problems dominated by local bending with computational tools and designers of multi-segment shells with very close segment spacing.

Steel poles made from polygonal sections are an economic alternative to circular hollow sections for use as lighting towers or transmission line pylons. For transmission lines especially, the intention behind the design of the poles is to make them more compact in order to avoid land usage and achieve an inconspicuous appearance. If the pole diameter is reduced, the slenderness of the sections needs to be reduced as well in order to achieve the desired resistance, but increasing the wall thickness disproportionately reduces the cost-effectiveness of the structure. The European design rules for overhead electrical lines [1] do not allow plastic behaviour of stocky sections to be used, which reduces the advantages of compact sections.
In modern standards for steel structures, such as Eurocode 3 (EC3) [2], activating plastic reserves is generally acknowledged as state of the art. According to EC3-1-1, the slenderness of the section determines whether the cross-section is allocated to class 1 or 2, where plastic design is allowed, class 3, where only elastic behaviour is used, or class 4, where local buckling is assumed. When changing from class 2 to class 3 sections, EC3-1-1 prescribes a sudden drop in resistance, which has long been recognized as unjustified. Research has been done to overcome this mismatch for circular hollow sections [3].
In this paper the transition between the plastic bending moment capacity and the limit state of buckling is investigated in order to identify the ultimate load of polygonal sections. The 16-sided polygon investigated can be treated as a collection of plate strips using the plate buckling design rules of EC3-1-5 for class 4 cross-sections. Detailed examinations illustrate the inconsistency of EC3 when it comes to the bending capacity of compact sections even before the start of stability problems.
Numerical investigations have been performed on the basis of experimental data gained from full-scale bending tests, along with imperfection measurements via laser scanning. These results suggest that the bending moment capacity can be increased beyond the calculated elastic capacity for more compact sections, but might be overestimated when calculating the full plastic capacity according to EC3-1-1.

Post-buckling Strength of Plate Girders subjected to Shear

A consistent and simplified direct strength method (DSM) is proposed for the design of cold-formed (or thin-walled) sections under localized loading, which is called web crippling. The development of this method proposes generalized equations for the design of thin-walled sections under the four different localized load cases: interior one-flange (IOF), end one-flange (EOF), interior two-flange (ITF) and end two-flange (ETF). The same parameters are used in the DSM equations for both the IOF and the EOF load cases. However, the ITF and ETF load cases require different parameters in the DSM equations to predict the capacities of structural members. The equations contain both an inelastic reserve component and a yield load component which are different from those proposed previously in this regard.
This paper briefly introduces the calculation of the buckling load and the yield load. From these two main input variables, DSM equations are used to determine the capacities of structural members under localized loading. Calibration was performed against all available experimental data to validate the accuracy of the DSM predictions.

Slender steel structures such as masts and towers consisting of or supporting cylindrical elements or chimneys can be susceptible to vortex shedding. Vortex-induced vibrations (VIV) can occur in slender structures because a fluctuating cross-wind force is generated from vortices shed alternately from opposite sides of the structure. Significant VIV occur when the frequency of the vortex shedding is the same as the natural frequency of the structure. If the critical wind speed for VIV often occurs for a structure and the vibration amplitudes caused by the VIV are critical with respect to fatigue, the result can be failure of the structure. An effective method of damping the vibrations can be to install a tuned liquid sloshing damper (TLSD). This paper focuses on the design of a TLSD and compares this with the tuned mass damper (TMD) solution.
Compared with the fabrication and installation of a TMD, it is much simpler to make a container and fill it with liquid. The container is often made as a square box or a cylinder that is easily mounted at the top of a mast, tower or chimney, thus providing the most efficient damping of the critical vibration mode. A TLSD is also preferred when it comes to maintenance as only the liquid level has to be checked, whereas a TMD needs maintenance and possibly repair or even replacement of damper parts.
A TLSD is designed by calculating the dimensions that will result in a mode shape of the sloshing liquid with a frequency close to the natural frequency of the structure that is to be damped. As the liquid moves in the container, so the sloshing energy of the water reduces the dynamic response of the structure subjected to VIV. Experiments have shown that the TLSD has a rather broadband efficiency and also that it is effective with sloshing liquid mass values down to < 1 % of the effective mass of the mode it is designed to damp.
Ramboll has experience with the design of both types of dampers, TMD and TLSD, for broadcast masts and towers and for chimneys. In particular, at a broadcast tower in Norway where a TMD has been replaced by a TLSD, Ramboll has tested the efficiency of the TLSD for comparison with the TMD replaced. This paper will present these results and give an introduction to TSLD design.

Bolt-and-nut assemblies under tension loading can either fail by bolt fracture or thread failure. The latter failure mode is arguably undesirable because it leads to failure at a comparatively low deformation level. Moreover, incipient thread failure is challenging to detect in the case of over-tightening since the bolt remains in the bolt hole after this type of failure occurs. The failure mode of bolt-and-nut assemblies is determined by several well-known factors such as the thread engagement length and the relative strength of bolt and nut. However, one factor that has received limited attention in the literature is the placement of the nut along the threaded portion of the bolt. We have performed a series of direct tension tests on various single M16 bolt-and-nut assemblies where the placement of the nut was varied. Some of the assemblies experienced that placing the nut close to the thread run-out, i.e. near the unthreaded portion of the bolt (the shank), led to thread failure, whereas placing the nut sufficiently far from the thread run-out led to bolt fracture. We carried out finite element simulations of the tests in order to investigate further the mechanisms occurring during failure. In the case where the nut was located close to the thread run-out, the simulations revealed that necking of the bolt affected the effective overlap of the internal and external threads. This effect seemed to contribute to thread failure in both tests and simulations.

The resistance of a typical shear connection with headed shear studs in a composite beam is analysed for the normal case in accordance with EN 1994-1-1. The reducing effect of a trapezoidal metal decking to the ultimate loadbearing capacity is considered with empirically derived reduction factors and equations that were developed between the late 1970s and early 1980s. The RFCS research project “DISCCO” [1] investigated the shear stud resistance with novel types of steel decking. In many cases, the shear resistance predicted by EN 1994-1-1 [2] was not reached in tests.
In the respective experiments with composite beams and deep decking, a concrete cone failure mode was identified and not a pure shear failure of the stud. This failure mode acted in combination with the loadbearing capacity of the shear stud, which formed one or two plastic hinges in the shaft depending on the actual geometry.
Based on these observations, new equations have been developed to predict the shear connection's resistance with more accuracy. The yield hinge mechanism of the shear stud, which was developed by Lungershausen [3], was extended by the aforementioned loadbearing component “concrete cone”. The formulae consider the geometry of the stud and the steel decking and the material strength of the stud and the concrete. The statistical evaluation of the equations developed demonstrates good agreement with test results.

No short description available.

This article provides an overview of the outcomes of a European-funded project called BarrierPlus. A new type of water-based barrier coating was developed for structural steel applications. The advantages of this coating include enhanced moisture resistance, low volatile organic compounds (VOCs) and one-component self-crosslinking free of isocyanates. To enable this performance, a latex polymer binder was uniquely designed without using soap-like molecules, known as surfactants, to form the dispersion. By minimizing surfactants in the coating, the barrier properties were significantly enhanced. The latex was successfully scaled up to 15 kg quantities by an SME, coating formulations were scaled to pilot quantities and a variety of characterization and coating performance tests were completed. A life cycle assessment found that the BarrierPlus coating has a better environmental profile than an industry benchmark solvent-borne coating and showed promising results relative to commercial waterborne benchmarks.

Events:
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Book review: Shear Connections in Composite Flexural Members of Steel and Concrete

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The Kienlesberg Bridge is the new link for trams, pedestrians and cyclists between the inner city and the science centre in the northwest of Ulm, Germany. The bridge crosses a railway junction near the main station and a new high-speed rail link. The geometric boundary conditions lead to unequal spans and complex alignments. Therefore, the scheme that won the design competition, which is now under construction, proposed a bridge made of steel. The superstructure was designed as a semi-integral continuous beam with main girders of varying depth. Owing to the pedestrian and cyclists'path on one side, the orthotropic plate cross-section is asymmetric and the main girders have varying depths. Special calculations and details were necessary for dynamic and noise control reasons. The bridge is being built using incremental launching See article on pages 189-195 (photo: W. Dechau).

No short description available.

No short description available.

The objective of this article is to facilitate the use of semi-continuous joints by providing ready-to-use tables and charts for design, which also permit the benefits accruing from the use of semi-continuous composite beams to be directly identified. The relevant features for the design of composite beams, such as bending moment distribution, maximum deflection and natural frequency, are derived analytically. The influence of semi-continuous steel joints on the performance of single-span composite beams is analysed. The article concludes with an example of the use of a new slim-floor beam type - the composite slim-floor beam (CoSFB). The tables and charts derived are applied in this example with the intention of demonstrating the advantages of using semi-continuous joints in combination with composite beams. The present article extends the design of semi-continuous steel beams presented in the previous article on this subject [1].