Steel-concrete composite beams have been extensively used in buildings and bridges in recent years to combine these two construction materials. The behavioral characteristics of steel-concrete composite beams are related to the degree of shear connection. In this article, eight steel-concrete composite beams were investigated to examine the effects of different degrees of shear connection on the static and fatigue performances of the beams. First, the ultimate capacity, ductility coefficient, failure modes, strain distribution at the midspan section, and relative slip distribution of the steel-concrete composite beams under monotonic loads were investigated with different shear connection degrees. The effect of the shear connection degree on the fatigue life, failure mode, and other mechanical properties under fatigue loading was studied. The results show that all mechanical properties of the steel-concrete composite beams under monotonic and fatigue loads decrease with a decrease in shear connection degree, and their failure modes change with the decreasing shear connection degree. Second, based on the experimental results, the fatigue life of composite beams was analyzed and predicted under different assumptions of failure modes according to EC4, AASHTO, and the Chinese code. The result shows that different failure modes should be considered according to different shear connection degrees in the fatigue design of composite beams. Finally, the issues on the difference between static and fatigue capacities with different shear connection degrees and the critical point of the failure mode were discussed.

This paper presents an experimental evaluation for comparison of the behaviors of stud and Perfobond shear connectors under static and fatigue loading based on 20 push-out tests. The push-out tests for each type of shear connectors including three series: static tests, fatigue endurance tests and residual mechanical properties test, respectively. In static tests, the failure modes of two types of connectors are different. The elastic stiffness and ultimate slip in the load-slip curves of the Perfobond are larger than that of stud. In fatigue endurance tests, the fatigue life of the studs is 2.68 million, while the Perfobond specimens do not fail after 3.0 million numbers of cycles under the same test conditions as studs'. Compared with the stud, the relative-slip of Perfobond increased sharply in the early period. In residual mechanical properties tests, the residual bearing capacity, shear stiffness and ductility are presented and discussed. The variation rules of these three indexes for two types of connectors are the same, while the indexes of Perfobond are much larger than stud’s throughout the process. The results indicate that Perfobond connector has good ductility, better fatigue resistance and higher safety reliability. However, the economy of Perfobond connectors is not as good as studs’.

In this study, the safe critical temperature that can be tolerated by CFRP tendons under normal working conditions was derived through tensile tests at room and high temperatures. Next, the times required to reach a safe critical temperature for CFRP cables protected with different types of fire-retardant materials of various thicknesses were determined through fire resistance tests, Finally, fitting the surface of the finite element simulation results allowed the establishment of the temperature rise calculation model of CFRP tendons under the protection of fire-retardant materials. The results showed that 300 °C can be regarded as the safe critical temperature. Both high-silica needled felt and ceramic fiber felt exhibited high fireproof performance. With an increase in the thickness of the fire-retardant material, the time for the CFRP tendon to reach the inflection point of the heating rate increased, and the safe fire resistance time increased exponentially. According to the HC temperature rise curve, the fire resistance time of CFRP tendons protected by 24 mm thick high-silica needled felt was 45 min, and that for CFRP tendons protected by 24 mm thick ceramic fiber felt was 39.5 min. Under the action of fire corresponding to the hydrocarbon temperature rise model, the safe fire resistance time of CFRP tendons protected by 45 mm high-silica needled felt or 50 mm ceramic fiber felt was more than 2 h, sufficient to meet the specification. The proposed model of fire resistance performance enables the determination of the thickness of the fire resistance material required to obtain different degrees of fire resistance for CFRP cables for structural use.