Racking structures are an important application of cold-formed steel components in a load bearing structure, with the aim to store goods as part of a logistic chain. The most important rack type is “pallet racking”. The Unit Loads (e.g. wooden pallet with goods) supporting beams in a pallet rack structure are important components. Structurally but also in terms of costs. Pallet racking is in general manufactured by mass production of standardised cold-formed components with subsequently a relative high cost effectiveness priority. This report deals with the lateral torsional stability of the beams taking into account the restraint that the stored goods provide to the beams.

Editorial

Based on the stationary value principle of energy and considering the influence of the distribution of prying forces on the initial stiffness of thin-walled steel T-stubs, the prediction formula for the position of prying force is derived. According to this formula, the theoretical calculation procedure of initial stiffness of thin-walled steel T-stubs is proposed. To validate the accuracy of this theoretical method, the proposed procedure is adopted to calculate the initial stiffness of a series of cases, afterwards the results of theoretical calculation and FE simulation are compared, in which the maximum deviation is within 10%.

Application of longitudinally profiled (LP) steel plate in the flange of flexural members may provide a good solution to optimize their mechanical performance and to improve the efficiency of steel use, whilst existing design codes provide no design guidance or prediction methodology for such advanced beams in terms of flexural behaviour. To clarify their flexural strength and rotation capacity, tests on two full-scale welded I-section steel beams with longitudinally profiled flanges (LPB members) are carried out herein, as well as two traditional beams with uniform cross-section for comparison. All the specimens exhibit sufficient flexural strength and rotation capacity for seismic plastic design, and specifically, the LPB members possess even better performance in case of identical steel usage. Parametric analyses of 250 beams incorporating a wide range of flange slenderness and steel grades, are conducted by employing the validated nonlinear FE model to investigate the effects of rate of thickness change for the LP flanges. The results show that the effect is limited on the flexural strength but significant on rotation capacity. The existing design provisions for beams with uniform cross-section give generally conservative design results for the flexural strength of the LPB members, but limiting values of flange slenderness needs to be reduced. The research outcomes may provide an important basis for promoting the application of LP plates in flexural members.

Pultruded FRP composite material was increasingly used in the applications of civil infrastructures, especially for bridge decks. Thus, the long-term life of these materials in hostile environments is critical. In this paper, experimental studies have been undertaken to characterise the moisture diffusion of pultruded FRP composite materials and adhesives. Gravimetric experiments were carried out for the rectangular FRP composite specimens, which were exposed to the vapour environmental condition and also immersed in water. Moisture uptake curves as a function of time were obtained. Correspondingly, based on the moisture diffusion theory, the diffusion coefficients of FRP composite material parallel to the pultrusion direction were identified. All the FRP specimens reached the moisture saturation level within two days. Comparing with the moisture diffusion process in different aging conditions, the conclusion can be drawn that the rates of moisture uptake are more sensitive to temperature and the moisture saturation levels of FRP material are only dominated by relative humidity and immersed water. For the gravimetric experiments of adhesive specimens，after 37 day environmental ageing, only polyurethane adhesive material reached the moisture equilibrium as 2.667% of the initial self-weight within 6 days. This value is much higher than that of FRP material in the same ageing condition of 40℃, 96% RH. But the moisture diffusion process into adhesives is quite slower.

Torsional effects in joints need to be investigated in order to get a complete model of the joint and also to assess the real boundary conditions for the lateral torsional effects in the beams of structural frames. Phenomena such as: torsion, warping, lateral buckling, etc. are usually analysed assuming simplified boundary conditions, namely pinned or rigid, in frame analysis which can lead to erroneous and non-conservative results. With the aim of knowing the correct boundary conditions and real behaviour of the joints under torsion, an experimental program is carried out consisting of two tests of mayor axis doubled extended bolted end plate joints subjected to torsion about the axis along the length of the beam. These experimental results have allowed the validation of the finite element models carried out using the program Abaqus. Once the models are validated models, a parametric study is performed to assess the stiffness and resistance. This study also verifies that these joints behave in a semi-rigid way when compared with the torsional characteristics of the attached beam. Besides, the beam fails prior to the connection in most cases, and therefore, the joints can be assumed to behave as full-strength. Analytical expressions are proposed and checked with the FEM results proving that the proposed analytical formulae and the proposed mechanical model can predict the stiffness quite accurately, with an average error of 8.5%. Despite these joints can be classified as full-strength under torsion, an assessment of their resistance is done as well.

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.

To investigate the mechanical degradation of the shear properties of glass fiber-reinforced polymer (GFRP) laminates in bridge decks under hygrothermal aging effects, short-beam shear tests were performed following the ASTM test standard (ASTM D790-10A). Based on the coupled hygro-mechanical finite element (FE) analysis method, an inverse parameter identification approach based on short-beam shear tests was developed and then employed to determine the environment-dependent interlaminar shear modulus of GFRP laminates. Subsequently, the shear strength and modulus of dry (0% M_t/M∞), moisture unsaturated (30% M_t/M∞ and 50% M_t/M∞), and moisture saturated (100% M_t/M∞) specimens at test temperatures of both 20 °C and 40 °C were compared. One cycle of the moisture absorption-desorption process was also investigated to address how the moisture-induced residual damage degrades the shear properties of GFRP laminates. The results revealed that the shear strength and modulus of moisture-saturated GFRP laminates decreased significantly, and the elevated testing temperature (40 °C) aggravated moisture-induced mechanical degradation. Moreover, an unrecoverable loss of shear properties for the GFRP laminates enduring one cycle of the moisture absorption-desorption process was evident.

In order to reveal more information and better understanding on the behavior and failure mechanisms of high strength steel (HSS) extended endplate connections at ambient temperature and after fire, an experimental and theoretical study has been conducted and presented in this paper. The provisions of Eurocode 3 are verified with the test results. Because strength of bolts decreases more rapidly than that of structural steels, failure modes of endplate connections may change after fire. Hence, a series of equations are proposed to predict failure modes of endplate connections after fire. Furthermore, FE simulations which can predicate the performance of HSS extended endplate connections with reasonable accuracy are adopted to study the behaviors of the connections after cooling down from various fire temperatures and to validate the accuracy of the proposed equations. Moreover, a parametric study is carried out to explore an optimization design method. It is found that the current provisions of EC3 can justifiably predict failure modes and plastic flexural resistances of HSS extended endplate connections both at ambient temperature and cooling down from 550 °C, but it is not the case for their initial rotational stiffness and rotation capacity. In order to avoid brittle failure mode of endplate connections after fire, appropriately increasing the diameter or grade of bolts in the design is suggested. What is more, the match of steel grade and thickness of column flange and endplate as well as beam should be considered in the optimization design of beam-column endplate connections.

Modern steel manufacturing techniques make it possible to produce steel with the nominal yield strength up to 1300 MPa for structural purposes. However, the application of very high strength steels is still limited in the civil engineering structures due to lack of knowledge about the effects of the manufacturing process and experimental results regarding the structural behaviour of the material. Moreover, in a fatigue loaded very high strength steel structure absolute and relative stress variations will be higher compared to stresses in structures made of lower steel grades. Accordingly, the fatigue issue will be one of the most important design criteria for very high strength steel structures. In this current study, V-shape welded specimens were manufactured from S690 and S890 rolled steels and cast steels with similar yield strengths. Fatigue cracks were created in the weld toe of the specimen under a fluctuated loading and subsequently the fatigue damaged specimens were repaired by the removal of the cracks with subsequent welding. The fatigue strength curves of repaired specimens are compared with the detail categories of EN 1993-1-9 [8] and the fatigue strength curves of the test results in the as-welded condition from literature. The fatigue strength of the fatigue damaged connections was completely recovered by the established repair procedure.

Full-scale experimental study and numerical analysis on behaviors and failure mechanisms of full high strength steel extended endplate connections in fire have been carried out and presented in this paper. The experimental behaviors of the connections were compared with the provisions of Eurocode 3. The test results show that the failure modes of the connections in fire are bolt failure with yielding of the flange, as same as those at ambient temperature. The failures of the bolts in fire are ductile while they are brittle at ambient temperature. The rotation capacity of the connections in fire is proved sufficient. What is more, at elevated temperature 550 °C, the plastic moment resistances of Q690 and Q960 full high strength steel endplate connections are only 40% of those at ambient temperature, while their initial rotation stiffness are 66 and 63% respectively. But the rotation capacities of Q690 and Q960 high strength steel endplate connections are 1.38 and 1.74 times of those at ambient temperature. Moreover, it is found that the component method Eurocode 3 proposed based on connections made of mild steels can be used to calculate plastic resistances and to predict failure modes of high strength steel endplate connections in fire, but it is not suitable to predict their stiffness. The suggestions about rotation capacity of connections in Eurocode 3 are found too conservative for high strength steel endplate connections in fire.

In Memoriam of Prof. Dr. Bernt Johansson. European standard EN 1993 does not permit the design of joints made from steel with a yield stress > 460 MPa using the principles of semi-continuous/partially restrained construction, and will remain forbidden in its current revision within the scope of the CEN/2014-02 programme for the evolution of the structural Eurocodes. The findings of a comprehensive research programme on the non-linear behaviour of moment-resisting joints with components made from high-strength steel grades (yield stresses of 690 and 960 MPa) carried out at Delft University of Technology are summarized in this paper and used to reappraise these restrictions.

Full-scale fatigue tests were performed on two retrofitted orthotropic bridge decks (OBDs). The retrofitting systems consist of adding a second steel plate on the top of the existing deck. The aim is to reduce the stresses at the fatigue-sensitive details and therefore extend the fatigue life of the OBD by stiffening the existing deck plate. Two retrofitting systems were studied. The bonded system consists of bonding a second steel plate to the existing deck by vacuum infusing a thin adhesive layer (2 mm) between the two steel plates. The sandwich system consists of bonding the second steel plate through a thick polyurethane core (15 mm). The aim of the study was to assess the fatigue performance of both retrofittings. No fatigue damage was detected in the retrofitting layers during fatigue tests after three million cycles of wheel load. The stresses close to the deck-plate-to-stiffener welds decreased by at least 55% when using the bonded steel plates system and 45% when using the sandwich steel plates system. Both systems proved to have sufficient fatigue life to withstand traffic wheel loads running on orthotropic bridge decks and help extend the fatigue life of the existing OBD.

Fatigue crack formation is an inevitable issue for welded steel structures subjected to cyclic loading. Accordingly, repair of the fatigue crack in welded steel structures is unavoidable to prolong fatigue life. However, there is limited knowledge available about the procedure to be adopted for the repair and the life extension to be expected after the repair. The current paper is focused on the effects of the repaired an artificial crack in the base material of S690 and S890 high strength rolled steels on the fatigue strength of the material. An artificial crack was created in the middle of the plate test specimens by spark machining and subsequently, the crack was repaired by using the FCAW (flux-cored arc welding) process. The repaired specimens were tested in a four point bending test rig with a constant amplitude loading for creating a uniform bending moment at the weld region such that the weld cap to be exposed to tensile stresses. The test results show that most of the fatigue cracks initiated at the start-stop points of the weld cap and the fatigue crack initiation life of the specimens occupy approximately 45% of the total fatigue life. The statistical analysis of the test results revealed that the characteristic fatigue strength of the repaired specimens is very close to the detail category 160 of EN 1993-1-9 [5].

Purpose – This study aims to reveal more information and understanding on performance and failure mechanisms of high strength steel endplate connections after fire. Design/methodology/approach – An experimental and numerical study on seven endplate connections after cooling down from fire temperature of 550°C has been carried out and reported herein. Moreover, the provisions of European design standard for steel structures, Eurocode 3, were validated with test results of high strength steel endplate connections. Findings – In endplate connections, a proper design using a thinner high strength steel endplate can achieve the same failure mode, similar residual load bearing capacity and comparable or even higher rotation capacity after cooling down from fire. It is found that high strength steel endplate connection can regain more than 90 per cent of its original load bearing capacity after cooling down from fire temperature of 550°C. Originality/value – The post-fire performance of high strength steel endplate connection has been reported. The accuracy of Eurocode 3 for endplate connections is validated against test results. Keywords Numerical study, Experimental study, High strength steel, After fire, Endplate connection

The FRP-steel girder composite bridge system is increasingly used in new constructions of bridges as well as rehabilitation of old bridges. However, the understanding of composite action between FRP decks and steel girders is limited and needs to be systematically investigated. In this paper, depending on the experimental investigations of FRP to steel girder system, the Finite Element (FE) models on experiments were developed and analyzed. Comparison between experiments and FE results indicated that the FE models were much stiffer for in-plane shear stiffness of the FRP deck panel. To modify the FE models, rotational spring elements were added between webs and flanges of FRP decks, to simulate the semirigid connections. Numerical analyses were also conducted on four-point bending experiments of FRP-steel composite girders. Good agreement between experimental results and FE analysis was achieved by comparing the load-deflection curves at midspan and contribution of composite action from FRP decks. With the validated FE models, the parametric studies were conducted on adhesively bonded connection between FRP decks and steel girders, which indicated that the loading transfer capacity of adhesive connection was not simply dependent on the shear modulus or thickness of adhesive layer but dominated by the in-plane shear stiffness K.

Influence of moisture absorption/desorption on the flexural properties of Glass-fibre-reinforced polymer (GFRP) laminates was experimentally investigated under hot/wet aging environments. To characterize mechanical degradation, three-point bending tests were performed following the ASTM test standard (ASTM D790-10A). The flexural properties of dry (0% M_t/M_∞), moisture unsaturated (30% M_t/M_∞ and 50% M_t/M_∞) and moisture saturated (100% M_t/M_∞) specimens at both 20 and 40 °C test temperatures were compared. One cycle of moisture absorption-desorption process was considered in this study to investigate the mechanical degradation scale and the permanent damage of GFRP laminates induced by moisture diffusion. Experimental results confirm that the combination of moisture and temperature effects sincerely deteriorates the flexural properties of GFRP laminates, on both strength and stiffness. Furthermore, the reducing percentage of flexural strength is found much larger than that of E-modulus. Unrecoverable losses of E-modulus (15.0%) and flexural strength (16.4%) for the GFRP laminates experiencing one cycle of moisture absorption/desorption process are evident at the test temperature of 40 °C, but not for the case of 20 °C test temperature. Moreover, a coupled hygro-mechanical Finite Element (FE) model was developed to characterize the mechanical behaviors of GFRP laminates at different moisture absorption/desorption stages, and the modeling method was subsequently validated with flexural test results.

This paper deals with a proposal to revise the effective width terms in the brace shear criterion for overlap joints in rectangular hollow sections (RHS). The background to the design equations in ISO 14346 for the failure modes, brace effective width, chord M-N interaction and brace shear are described first. That is followed by the relation between overlap joints in circular hollow sections and those in rectangular hollow sections and those with an I- or H-section chord. Finally, it is shown that the effective width terms in the brace shear criterion can – in the case of 100 % overlap joints – be better related to the thickness of the overlapped brace. In the case of smaller overlaps, lov,limit ≤ lov ≤ 100 %, the effective width should also be related to the thickness of the overlapping brace, where lov,limit depends on whether the hidden seam at the toe of the overlapped brace has been welded.

Purpose-This paper aims to investigate and assess a perspective of combining high-strength-steel endplate with mild-steel beam and column in endplate connections. Design/methodology/approach-First, experimental tests on high strength steel endplate connections were conducted at fre temperature 550°C and at an ambient temperature for reference. Findings-The moment-rotation characteristic, rotation capacity and failure mode of highstrength-steel endplate connections in fre and at an ambient temperature were obtained through tests and compared with those of mild-steel endplate connections. Further, the provisions of Eurocode 3 were validated with test results. Moreover, the numerical study was carried out via ABAQUS and verifed against the experimental results. Originality/value-It is found that a thinner high-strength-steel endplate can enhance the connection's rotation capacity both at an ambient temperature and in fre (which guarantees the safety of an entire structure) and simultaneously achieve almost the same moment resistance with a mild steel endplate connection.