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Building fire is one of the most frequent disasters. The mechanical properties of concrete and steel will deteriorate to different degrees under fire exposure, thus weakening the bearing capacity of reinforced concrete (RC) members. Therefore, it is of great theoretical and practical significance to carry out research on the bearing capacity of RC members subjected to fire. To study the residual shear capacity of post-fire RC beams under indirect loading, static load tests were carried out on six full-scale RC beams to investigate the development of diagonal cracks and failure modes under an indirect load. Numerical models were established with ABAQUS to study the effect of the shear span-to-depth ratio and stirrup ratio on the residual shear capacity of the tested beams after fire exposure, and the shear capacity calculation method of indirectly loaded beams after high temperature is proposed. The results indicate that although the fire had no obvious affect on the failure mode of the beam under indirect loading, the fire aggravated the failure degree of the beams without additional transverse reinforcement. Moreover, the ultimate bending capacity of beams with additional transverse reinforcement decreased obviously after fire. The residual shear capacity of indirectly-loaded beams subjected to fire decreased compared with the directly-loaded beams due to the variation in the shear span-to-depth ratio and stirrup ratio. The shear capacity theoretical calculation results of the indirectly-loaded beam after high temperature were in good agreement with the tested results, and the average absolute error was 3.88%. Therefore, this calculation method for an indirectly loaded beam with a shear span-to-depth ratio less than 3.0 after fire as proposed in this paper was effective. The findings of this study are expected to provide a reference for the improved fire-resistant design of RC structures under indirect loading. [ABSTRACT FROM AUTHOR]

To investigate the shear capacity and failure mechanism of RC beams after fire exposure, fourteen full-scale beams without stirrups were tested at ambient temperature and after fire exposure. Three parameters, including the loading ratio, shear span-to-depth ratio and longitudinal reinforcement ratio, were considered in static load tests. The deterioration mechanism of the shear bearing capacity at the diagonal section of RC beams without stirrups after fire exposure was experimentally, numerically and theoretically revealed, and a calculation formula for the shear capacity of post-fire beams without stirrups was proposed. The results show that the shear capacity and stiffness of the specimens decreased after fire exposure, and the shear strength loss of the beams increased with fire exposure time. The shear capacity and stiffness of fire-damaged specimens decreased as the shear span ratio λ increased, and the shear strength loss of the beams decreased with λ. Compared with the theoretical calculation and experimental results of beams without stirrups, the average of the absolute errors was 10.48%. Therefore, this formula can better calculate the residual shear capacity of beam without stirrups after fire exposure. [ABSTRACT FROM AUTHOR]

This paper presents mechanical properties of fast-growing poplar specimens reinforced with carbon fibers. A total of 90 specimens including 10 contrast specimens were tested to investigate the influence from the following parameters: (a) different carbon fiber ratios (0.167%, 0.251%, 0.334%, 0.401%, and 0.501%) and (b) different fiber locations. The failure mode, compressive strength, elastic modulus, and axial deformation of specimens were analyzed. The test results indicate the following: (1) The compressive strength, elastic modulus, and axial deformation of specimens reinforced with carbon fiber were significantly improved compared with that of fast-growing poplar specimens. The compressive strength, elastic modulus, and axial deformation increased by 54.1–76.03%, 11.58–22.89%, and 24.86–60.06%, respectively. (2) There was little effect on the compressive strength of the specimen with the increase of carbon fiber ratio. With the increase of carbon fiber ratio, the elastic modulus of specimens slightly decreased and the axial deformation increased. The elastic modulus decreased by 1.39–18.69%, and the axial deformation increased by 10%–48%. (3) The different locations of the carbon fiber distribution resulted in a large difference in the compressive strength of the specimens, while the effects on the modulus of elasticity and axial deformation were not significant. Finally, the compressive strength calculation formula was proposed. [ABSTRACT FROM AUTHOR]

This paper presents results from an experimental study on the effect of temperature on bond strength of I-shaped steel and concrete. Eleven concrete encased steel (CES) specimens were tested by home-made fire test furnace to evaluate bond strength at various constant high temperatures (20°C600°C). The test results showed that: (1) the trend of the bond-slip curves at high temperatures were much similar to that at room temperature. Compared with room temperature specimen, the ultimate bond load and the residual bond load of specimens at high temperatures were significantly decreased. The specimens with the higher temperature had the less ultimate bond load and residual bond load. (2) In the descending stage, the P-S curve of the specimens with higher temperatures had more flat slope. The P-S curve of the specimens at the temperatures higher than 250°C had invisible descending stage. The ultimate bond load of the specimen at 600°C left with only about 5% of that at room temperature. (3) The ultimate slippages (i.e. the slippage at the ultimate bond load) of specimens at high temperatures were larger than that at room temperature, and varied from 2 to 5 mm. (4) The calculation formulas of ultimate bond load, ultimate slippage, and residual bond load at different temperatures were presented, the constitutive equations of bond-slip at different temperatures were obtained, which will provide a reference for the fire-resistant design of concrete encased steel columns. [ABSTRACT FROM AUTHOR]

To investigate the shear capacity of indirectly loaded reinforced concrete beams under and after fire exposure, load tests were conducted on eight full-scale specimens exposed to fire testing in a furnace chamber, and the effects of additional transverse reinforcement in the junction region between the primary and secondary beams on the shear capacity, fire resistance, failure modes and deflection were analysed. The results indicate that the slopes of the diagonal cracks in post-fire tested reinforced concrete beams without additional transverse reinforcement were shallower than those of a similar reference beam not exposed to fire, and that the ultimate capacities of reinforced concrete beams with additional transverse reinforcement decreased obviously after fire exposure. However, beams with additional transverse reinforcement exhibited increased fire resistance times and reduced strains in their reinforcement, indicating the benefit of conservatively providing such reinforcement. The findings of this study are expected to provide a reference for the improved fire-resistant design of indirectly loaded beams. [ABSTRACT FROM AUTHOR]

To investigate fire-resistance behaviors of simple supported reinforced concrete (RC) beams with three faces exposed to fire, six full-scale specimens were designed in accordance with the principle of "strong bending and weak shearing." One beam was treated as the control case of room temperature while the other five beams were exposed to high temperature. Parameters related to shear capacity were discussed, such as longitudinal reinforcement ratio and stirrup ratio. The experimental results show that brittle shear failure under room temperature may transfer to shear-bend failure at high temperature due to thermal expansion and strength degradation of concrete and steel. The greater the longitudinal reinforcement ratio, the longer the failure time of specimens. It indicates that the pinning action of longitudinal reinforcement can significantly improve the shear capacity of beams under high temperature. In addition, the configuration of stirrup reinforcement can effectively reduce the brittle change of vertical deflection when the beam enters the failure stage. [ABSTRACT FROM AUTHOR]

With high strength and good seismic performance, T-shaped steel reinforced concrete column is widely used in high-rise building structure. Three T-shaped steel reinforced concrete columns were tested under high temperature and vertical load, to simulate fire effect. The test results indicate that failure characteristics, distribution of temperature field, vertical deformation characteristics and fire resistance were comparatively analyzed under different axial compression ratios and different eccentricity. The test also indicated that the cracks increased with the increase of axial compression ratio and eccentricity. The damages of web were severer than the flange. The cracks were mainly distributed on the eccentric side and mostly inclined cracks in specimen. The vertical expansion became more obvious as the eccentricity decreased. The fire resistance decreased as the axial compression ratio increased. Compared with, the fire resistance of large axial compression specimens (the axial compression ratio is 0.6) were decreased by 57% than small axial compression specimens (the axial compression ratio is 0.2). The fire resistance decreased by about 30min as eccentricity increased by 20mm. [ABSTRACT FROM AUTHOR]