The goal of this study is to investigate the prestressing effect of shape memory alloy bars in reinforced concrete beams; bars are prestressed by external force or recovery stress due to shape memory effect. The shape memory alloy bars are heated by hydration heat of concrete during curing to induce the shape memory effect. To achieve this goal, this study conducts bending tests of concrete beams reinforced by shape memory alloy bars as well as those reinforced by steel bars. The beams with shape memory alloy bars with recovery stress show the same or slightly larger flexural strength than those with shape memory alloy bars prestressed with external force. Thus, this study indicates that the recovery stress of shape memory alloy bars plays the same role as the prestressing force, and that the shape memory effect can be induced by hydration heat of concrete instead of heating by electronic resistance.

Concrete edge failure of a single anchor in concrete is strongly dependent on the tensile performance of the concrete, which can be greatly improved by the addition of steel fibers. This study investigated the effect of steel fibers on the shear failure mode and edge breakout resistance of anchors installed in steel fiber-reinforced concrete (SFRC) with fiber volume percentages of 0.33, 0.67, and 1.00%. The anchor used in the study was 30 mm in diameter, with an edge distance of 75 mm and embedment depth of 240 mm. In addition to the anchor specimens, beam specimens were prepared to assess the relationship between the tensile performance of SFRC beams and the shear resistance of SFRC anchors. The ultimate flexural strength of the beam and the breakout shear resistance of the anchor increased almost linearly with increasing volume fractions of fiber. Therefore, based on the ACI 318 design equation, a term was proposed using the ultimate flexural strength of concrete instead of the compressive strength to determine the concrete breakout shear resistance of an anchor in the SFRC. The calculated shear resistance of anchors in both the plain concrete and SFRC were in good agreement with the measurements. In addition to the load capacity of the SFRC anchors, the energy absorption capacity showed a linear increase with that of the SFRC beam.

This study suggests the utilization of heat of hydration of concrete to activate the shape memory effect (SME) of shape memory alloy (SMA) wires embedded in concrete and produce recovery and residual stress on the wires. This method is more convenient than the previous electronic resistance heating. For the purpose, this study prepares NiTiNb SMA wires that show appropriate temperature window for the use of heat of hydration. Axial compressive tests of concrete cylinders confined by the NiTiNb SMA wire jackets are used to prove that the utilization of heat of hydration is valid to generate recovery and residual stress in the SMA wires. The confined cylinders show increased peak strengths and much larger failure strains than those of the plain concrete. The general behavior of the SMA wire-confined specimens in this study is similar to that of specimens heated by electronic heating jacket. Also, this study explains two examples for the utilization of heat of hydration for the SME in reinforced concrete beams and columns.

This study suggests a dense lateral reinforcement for a Reinforced Concrete (RC) column whose spacing is smaller than the maximum gravel size. This study conducts axial compressive tests of concrete cylinders confined by dense reinforcement to verify the effectiveness of the dense lateral reinforcement. Stainless steel rings are used for the reinforcement since they are corrosion resistant. The dense reinforcing method with stainless steel rings successfully increases the peak strength of the concrete. The strains at the peak strength are much larger than those for the concrete confined by a conventional method with steel reinforcing bars. The failure mode of concrete densely confined by steel rings is due to the gradual fracture of each ring; the fracture of each ring reduces the stress on the concrete. The cyclic behavior of the densely confined concrete is similar to that of concrete confined by conventional steel reinforcement.