RESUMEN
The study aims to investigate the fire performance of reinforced concrete (RC) slab fabricated from high volume fly ash inclusion with nano-silica (HVFANS) under ISO 834 load curve. The HVFANS concrete slab with dimensions of 1850 mm × 1700 mm × 200 mm was tested via an electrical furnace under an exposing temperature of 1100 °C for 120 min. The slab behaviour was evaluated in terms of residual compressive strength, temperature distribution along its thickness, spalling, and cracks. The results revealed that the slab was capable of maintaining 62.19% of its original compressive strength at room temperature after exposure to the above temperature. Moreover, the distribution of temperature revealed that the temperature of concrete cover and bottom reinforcement was less than 300 °C with a maximum spalling depth of 11 mm within the temperature range of 680 to 840 °C. Furthermore, the thermal conductivity index (K) of the HVFANS concrete was determined, and results indicated that thermal conductivity equalled 0.35 W/mK which is considered low, as compared with other concretes tested in current and previous studies.
RESUMEN
Concrete-filled steel tube (CFST) structural members have been widely used in engineering projects for their superior strength and ductility. However, the different lateral dilation characteristics between concrete infill and steel tube have caused imperfect composite interaction during the early loading stage. To overcome this issue, external steel confinements in the form of rings and spiral were previously suggested to minimise the lateral expansion of the steel tube and enhance the concrete confinement effects. This study presented the analytical behaviour of circular CFST short columns with an external ring or spiral confinements which are subjected to axial loading. An explicit finite element (FE) model was developed and verified based on previous experimental findings. Besides that, this study analysed the failure modes, axial load-strain relationship, stress distributions, and bond strength of the composite column components. Parametric analysis was also undertaken to evaluate the impact of material strengths, total steel ratio, and diameter-to-thickness ratio. The results suggest that the use of external steel confinement can enhance the compressive behaviour of CFSTs better than increasing the thickness of the steel tube when using the same steel ratio. Finally, simplified design formulations were developed to accurately calculate the ultimate capacity of CFST columns with and without external steel confinement.
RESUMEN
The mix design of ultra-high performance concrete (UHPC) is complicated by the presence of many "ingredients." The fundamental packing density allows a simpler mix design with fewer ingredients to achieve optimum packing density and dense microstructure. The optimum particle grading increases the flowability of UHPC and eliminates entrapped air. This study presents a simplified particle grading design approach that positively influences the strength, autogenous shrinkage, and microstructure characteristics of UHPC. Carbon nanofibers (CNFs) of superior mechanical properties were added to enhance the strength of UHPC and to reduce its autogenous shrinkage. In addition, ground granulated blast-furnace slag (GGBS) was used as a cement replacement material to reduce the amount of cement in UHPC mixes. Test results showed that the presence of homogeneously dispersed CNF increased the compressive strength and compensated the autogenous shrinkage of UHPC. The findings indicated that an ideal particle distribution, which is close to the modified Andreasen and Andersen grading model, contributed to achieving high compressive strength and CNFs were capable of providing nano-bridges to compensate the shrinkage caused by GGBS.