In the province of Groningen (NL), where human-induced earthquakes take place due to gas extraction, a large part of the building stock is composed of brick masonry walls and timber diaphragms. In this framework, timber-masonry connections play a crucial role in the global seismic response of the buildings, but their properties and structural behaviour have not been investigated yet for the Dutch context. This work describes the experimental campaign conducted at Delft University of Technology to characterize as-built and strengthened timber-masonry connections. The joints were tested under either quasi-static monotonic, cyclic or dynamic loading, to analyse the effect of an induced earthquake signal on the connections’ response in terms of strength, stiffness and damage evolution. The obtained test results provided more insight into the capacity and properties of existing connections, and useful knowledge on the effectiveness of the tested retrofitting methods.

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Timber diaphragms in existing buildings are often too flexible in their plane, and can thus potentially cause out-of-plane collapses of walls during earthquakes. A very efficient retrofitting method to increase their in-plane stiffness and energy dissipation is the overlay of plywood panels. However, the usual characterization of the floors by means of a general equivalent shear stiffness cannot account for their nonlinearity and dissipative properties. Therefore, in this work, an analytical model is formulated to describe the in-plane response of timber diaphragms strengthened with plywood panels screwed along their perimeter to the existing sheathing. The proposed formulation starts from the definition of the load-slip equation for a single screw connecting a plank and a plywood panel. The whole floor’s response is then derived, with the prediction of both backbone curve and pinching cycles. From the comparison between the response of tested full-scale diaphragms and the analytically calculated one, it can be concluded that the proposed model accurately predicts the in-plane behaviour and dissipative properties of timber floors retrofitted with plywood panels.@en

SIROCO investigated the slip-resistant behaviour of carbon and stainless steel preloaded connections as well as the preloading behaviour of stainless steel bolting assemblies in principle. The slip factor test procedure according to Annex G of EN 1090-2 was investigated regarding the influence of the test speed, preload level, tightening method, criteria for the slip load and load level for extended creep tests, different bolting assemblies and surface conditions (grit blasted, hot-dip galvanized, alkali/ethyl zinc silicate coating, thermally sprayed with aluminium/zinc and combinations). Improvements regarding the slip factor test procedure have been formulated which have already partly been implemented in the revision of EN 1090-2. Enhanced slip factors allow more economic slip-resistant connections. The use of stainless steel bolting assemblies in preloaded bolted slip-resistant connections joining stainless steel plates was studied through investigations into the creep/relaxation behaviour with regard to potential preload losses, the tightening and slip resistance behaviour for austenitic, duplex, lean duplex and super duplex stainless steels. Preload losses due to the viscoplastic deformation behaviour in preloaded stainless steel bolting assemblies lie in the same range as those for carbon steel. Stainless steel bolting assemblies are in principle preloadable and galling can be avoided using suitable lubricants and tightening methods. Slip factors for stainless steel slip-resistant connections show high values for grit blasted surfaces whereas even 1D and shot blasted surfaces demonstrated slip factors for practical use. Recommendations for design and execution of slip-resistant connections and amendments to EN 1993 1-4, EN 1993-1-8 and EN 1090-2 are formulated.@en

Stainless steels are becoming more and more popular as a construction material in both building and civil engineering structures, because of their high material strength, ductility and corrosion resistance. In this frame, the execution of slip-resistant connections made of stainless steel is necessary, e. g. in footbridges, facades etc. As no design regulations exist in any code, special experimental testing has to be performed in each case. Stainless steel alloys are thought to suffer more than carbon steels from time dependent viscoplastic deformation at room temperature. It could lead to higher preload losses and consequently to lower slip factors than achieved for carbon steels with comparable surface treatment. However, no evidence of this behaviour can be found in literature for preloaded bolted connections. For this reason, slip factors for the various stainless steel grades have to be determined experimentally if they want to be used in the steel structures. In the frame of the European RFCS-research project SIROCO, the preloading behaviour of stainless steel bolted connections as well as the slip-resistant behaviour of slip-resistant connections made of austenitic, various duplex and ferritic stainless steels have been investigated. In this paper, the results of slip factor tests on four stainless steel grades are presented and the influence of different surface treatments and the preload level on the slip factor of stainless steel slip-resistant connections is discussed. Finally, slip factors for various stainless steel grades with different surface treatments are proposed for a future implementation in the next revision of EN 1090-2.@en

This paper deals with the evaluation of fatigue cracks under a concentrated compression (wheel) load in an I-section with full penetration welds between the web and flange. The objective is to investigate whether cracks stop or nearly stop when they have grown through the residual tensile stress field. These experimental investigations are part of a review of a crane runway girder where after 20 years of service fatigue cracks were observed in the flange at the toe of the full penetration weld. The fatigue analysis of the actual crane runway girder is described in (Wardenier et al., 2017). The fatigue tests under a concentrated wheel compression loading show that, for the specimens considered on a scale of about 1:2 with stiffeners at one side, the cracks only initiate and grow at the non-stiffened side to about 50 to 60% of the web thickness and then stop. Based only on the nominal stress range under the wheel, determined according to EN 1993-6 and neglecting the shear stress effect, an equivalent fatigue class of about 160 N/mm² was found for crack initiation in the web, whereas the minimum ratio in life between visually observed crack initiation and maximum crack length was about a factor 3. Comparison of the codes for a wheel loading in compression shows large discrepancies in effective width and fatigue classes to be used.

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Steel-to-glass laminated connections, which have recently been developed, limit stress intensifications on the glass and combine strength and transparency. Transparent Structural Silicone Adhesive (TSSA) connections have been used in several projects worldwide; however, the hyperelastic and viscoelastic nature of the material has to date not been fully investigated. In this work, the first objective is to investigate the mechanical response of TSSA connections under static and cyclic loading by means of experimental tests. Firstly, the shear behaviour of TSSA circular connections is characterized by means of monotonic and cyclic loading tests. The adhesive exhibits significant stress-softening under repeated cycles that becomes@en

Slip-resistant connections are always used when slip and deformation in a bolted connection must be avoided at all costs, e.g. in radio masts and bridges. For some popular surface treatments, slip factors are given in EN 1090-2, the execution standard for steel structures. For those surface conditions not considered in EN 1090-2, the slip factor can be determined experimentally according to Annex G of EN 1090-2. By reviewing slip factor values obtained with the Annex G test procedure and reported in the literature, it becomes obvious that in most cases the slip factors achieved experimentally are not comparable for identical surface conditions. This is potentially caused by different interpretations of the Annex G slip test procedure. As the slip factor is one of the main parameters influencing the bearing capacity of slip-resistant connections, its determination should be on the safe side and not dependent on the various interpretation possibilities of the test procedure itself. For this reason, the optimization of the Annex G test procedure was thoroughly investigated in the European RFCS research project SIROCO, with the final objective being to enhance its reliability. The focus was on investigating the various test parameters such as type of preload measurement, ascertaining the possible slip planes, test speed, position of slip measurement, clamping length, preload level, evaluation of critical slip load and the performance of the extended creep test. The results achieved in these investigations have already been partly implemented in the revision of the current draft version of EN 1090-2.

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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.@en

Preloaded bolts are used to achieve slip-resistant shear connections. The actual preload force in each bolt has a direct influence on the fatigue and slip resistance of the connection. The strain gauge method is examined for practical assessment of the actual preload because its use is no longer limited by the demands on adhesive curing conditions. The main objective of the paper is to describe how measured strain in the bolt shank and statistical variation of the nominal mechanical and geometrical properties of the bolt are used to determine the actual bolt preload without calibrating every single bolt. The calibration factors established by laboratory and in situ measurements exhibit rather small scatter. The minimum bolt preload required is achieved with a 95 % probability of being exceeded in a bolted connection on a Dutch highway bridge (Middachterbrug).@en

This paper is part of an evaluation of fatigue cracks in a crane runway girder with full penetration welds between the web and flange. The fatigue analysis of this actual crane runway girder is described in [1]. The investigation described in this paper deals with additional experimental tests on equivalent welded I sections on scale of approximately 1:2 subjected to a fluctuating line load in compression. The objective of these experimental investigations is to investigate whether cracks stop or nearly stop when they have grown through the residual tensile stress field. The test results show that, in some cases the cracks in the weld, at the weld toe with the web or with the flange initiate and grow from one side to about 50 to 60% of the web thickness and then stop. However, at the weld toe with the flange the cracks grow sometimes from both sides but with the cracks at one side having a small length and/or a small depth. The minimum ratio in life between crack initiation and maximum crack was a factor 1.2 for cracks occurring at one side only and 1.5 to 3.1 for cracks at both sides.

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This paper deals with the evaluation of fatigue cracks in a box type radial crane runway girder with full penetration welds between the web and flange. After 20 years of service fatigue cracks were observed which were initiated in the flange at the toe of the full penetration weld with the web. The observed cracks in the crane runway girder vary in length from a few mm to 330 mm with a summation of the lengths of all observed cracks being 750 mm, on a total length of 56000 mm, thus being only 1.3 %. The investigation consists of the fatigue analysis described in this paper and additional experimental investigations with scale tests of approximately 1:2 on equivalent I sections with a concentrated load and with a line load to investigate whether cracks stop when they have grown through the residual tensile stress field. For this analyzed crane runway girder with multi-layered full penetration welds and with small cracks at the weld toes in the flange, based on EN 1993-6 the damage would be 1.0 for a design class 98 which is not far from the “class” 92 found by Kuhlmann et al, [1] for tests with rolling wheels, however, related to weld failures from the root of not fully penetrated fillet welds in combination with crack initiations at the weld toe. @en

The current shear strength values for high density tropical hardwoods are very low compared to the values for softwoods, according to European strength class tables. The reason for this is that standardized tests according to European standard EN 408 have not been performed yet for tropical hardwoods. In this research, tropical hardwood species massaranduba was investigated according to EN 408. The test results give a 5%-value for the shear strength of massaranduba that is twice as high as the standardized value for strength class D70. No relation was found between the density and the shear strength for massaranduba. Shear strength was proportional to the density when compared to spruce. @en