Incorporating intelligent materials in concrete allows for self-sensing capabilities by reflecting the concrete’s strain and tensile status through the electrical properties. In order to enhance the self-diagnostic abilities of intelligent concrete, we conducted research on how intelligent materials affect the fracture mechanics of concrete. This study examines the fracture mechanical properties of the carbon nanofiber cement mortar and paste based on three-point bending and nanoindentation tests. The results showed that the carbon nanofiber content has negligible influence on the crack initiation toughness of the specimens. However, the instability toughness exhibited an initial increase followed by a decrease as the carbon nanofiber content increased. At a fiber content of 0.2%, the crack initiation toughness improved maximally by 13.1% compared to the control group. At a fiber content of 0.5%, both the ductility index and fracture energy increased with the nanofiber content, improving by 84% and 66.3%, respectively. The incorporation of carbon nanofibers did not alter the composition of cement paste hydration products; the fracture toughness of each hydration product varies from 0.14 to 0.59 MPa·m^1/2. However, the fracture toughness of individual hydration products and un-hydrated particles is higher than the macroscopic three-point bending fracture toughness values of the specimens.

This study investigates the seismic behavior of the T-shaped concrete-filled steel tubular (CFST) column to steel beam joints, aimed at expanding their applicability in areas with high-seismic fortification intensity. A construction form of T-shaped CFST column to steel beam joint with side plates is presented. The variables studied in these experiments include the side plate length, the axial compression ratio, the presence of side plates, and the presence of binding bars. The force mechanism, failure modes, load–displacement curves, strength, stiffness, ductility, and energy dissipation capacity of seven specimens were evaluated under low-cycle reciprocating load. The experimental results demonstrate that the joints of side plates show a full hysteresis curve, with the ductility coefficient ranging from 1.67 to 2.49, and the equivalent viscous damping coefficient between 0.147 and 0.234. The joint panel zone displays strong deformation and energy dissipation capacity. The inclusion of side plates and binding bars improves the seismic behavior of the joint. The setting of side plates enables the formation of a plastic hinge on the steel beam, creating a beam hinge failure mechanism and satisfying the seismic design principle of “strong column and weak beam, strong joint and weak member” as required by the building structures.

U-shaped steel−concrete composite beams (USCCBs) have been widely used in civil engineering due to their numerous advantages, including high load-bearing capacity, high rigidity, good ductility, short construction periods, and compatibility with the development of prefabricated buildings. In particular, USCCBs have been increasingly applied to super high-rise buildings and extra-large span bridges. Over the past decade or so, many new types of shear connectors and structural forms for USCCBs have been developed. Meanwhile, significant progress has been achieved in research on the flexural, shear, torsional, and fire-resistance performance of USCCBs, the seismic behavior of beam−column joints, and the strengthening of concrete beams with U-shaped steel casings. Nevertheless, challenges and limitations remain in both experimental research and practical applications. This paper presents a systematic review of recent research advances in USCCBs. Existing problems, development prospects, and future research priorities are comprehensively summarized and discussed, with the aim of further promoting the development and engineering application of USCCBs.

This study investigated the post-fire seismic characteristics of reinforced concrete frame joints with carbon fiber-reinforced polymer (CFRP) under low-cycle reciprocating loads through numerical analysis. Finite element simulations were conducted to examine the hysteretic curve, skeleton curve, energy dissipation, and stress distribution of the reinforced joints. The findings revealed that, relative to unreinforced joints post-fire, the bearing capacity of the reinforced joints remained essentially unaltered during the elastic phase. However, their ultimate bearing capacity, energy dissipation capacity, and ductility exhibited varying degrees of enhancement. Interestingly, this augmentation did not persist as the number of reinforcement layers increased. The optimal reinforcing effect was observed with the application of two reinforcement layers, resulting in a 30.3% increase in ultimate bearing capacity and a 26.5% improvement in energy dissipation capacity. Moreover, as the axial compression ratio increased, the high-stress zones within the joint expanded, and the failure mode transitioned from plastic damage at the beam end of the joint under low axial compression ratios to column crushing failure under high axial compression ratios.