Steel fibers enhance the flexural strength, the compressive strength and the ductility of untra-high performance concrete, predicting the flexural strength and the compressive strength of ultra-high performance steel fiber reinforced concrete (UHPFRC) accurately has significant influence on controlling steel fiber volume fraction and optimizing UHPFRC mix proportion. In this study, to evaluate the effects of steel fibers on the mechanical properties of UHPFRC, two artificial neural networks were developed in order to predict the flexural strength and the compressive strength of UHPFRC, respectively. 102 test data sets and 162 test data sets from literature were trained and tested to establish the flexural strength model and the compressive strength model, respectively. In these two models, the influential parameters, including the water to binder ratio, the diameter, the length, the aspect ratio, and the volume fraction of steel fibers, as well as the compressive strength and the flexural strength of concrete without fibers were investigated as the inputs, while the compressive strength and the flexural strength of UHPFRC were the outputs. The results show that the artificial neural network models predicted the compressive strength and flexural strength of UHPFRC accurately. Then, by comparing with existing analytical models, it was determined that the proposed models had high applicability and reliability with respect to predicting the compressive strength and the flexural strength of UHPFRC.

To explore the compression behavior of confined high-performance concrete (HPC) and high-performance fiber-reinforced concrete (HPFRC), 24 HPC and HRFRC (steel fiber in 2% volume ratio) circular columns confined with spiral stirrups with compressive strengths up to 116.21 and 138.24 MPa were tested under axial compression. The investigated parameters included concrete strength in the range of 100–120 MPa, stirrups volumetric ratios in the range of 0%–2%, and steel fiber contents in the range of 0%–2%. The results indicated that all specimens fell into two damaged patterns, expansion failure and shear failure, and the stress-strain curves of the specimens had three stages: the linear, nonlinear, and descending branch. Besides, concrete strength and the volumetric ratio of stirrups mainly influenced both the load capacity and the ductility, while steel fibers mainly affected the ductility. Moreover, the Baduage model can be applied to predict the peak stress and the peak strain of confined HPC and HPFRC.