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.@en

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.

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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.

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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

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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.

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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.

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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.

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