Search Results (2)

The mechanical behavior of corroded steel reinforcement under dynamic loadings is crucial for the entire structural response of reinforced concrete elements located in seismic regions. Taking into account the need to assess the structural integrity of existing building stock and the fact that the majority of the existing RC structures in Greece are constructed with the use of steel grades of S400 (equivalent to BSt 420s) and Tempcore B500c, the present study examines the dynamic behavior of rebars of different grades under low cycle fatigue (LCF) at a constant strain amplitude of ±2.5% and compares their performance through a quality material index. In the margin of the current research, the study also included two different grades of hybrid rebars, Tempcore B450 and dual-phase F (DPF). The outcomes demonstrated that single-phase S400 steel underwent mild degradation in its ductility, whereas its bearing capacity was significantly decreased due to corrosion. In contrast, B500c illustrated its superiority in terms of strength, yet recorded extremely limited service life, even in uncorroded conditions, raising questions about its reliability and the structural integrity of existing building stock. However, in corroded conditions, even if B500c corroded rebars showed higher mass loss values than the other examined grades, the degradation of their mechanical behavior due to corrosion was found to be minimal. Furthermore, dual-phase DPF rebars, with their homogeneous microstructure, appeared particularly promising with respect to Tempcore B450 if one considers the span of its service life compared to the extent of corrosion damage. Full article

Two B400B-R and B500B grade rebars were industrially produced through a Tempcore process. The standard chemical composition of B500B grade was additionally alloyed with 0.067 wt.% V to enhance its mechanical properties. A set of optimized processing parameters were applied to manufacture two different diameters D20 (Ø 20 mm) and D32 (Ø 32 mm). The microstructure -mechanical properties relationships were evaluated using optical and scanning electron microscopes, hardness, and tensile testing. In addition, a thermal model was developed to define the thermal cycle evolution during cooling in the quenching & tempering box (QTB) to simulate the kinetics of V(C,N) precipitation. The microstructure observations showed a typical graded microstructure consisting of ferrite-pearlite core and outer tempered martensite ring for both grades of both diameters. The optimized processing parameters for B400B-R of D32 (compared with D20) resulted in softening of the core (from 160 to 135 HV10) and tempered martensite surface (from 220 to 200 HV10) as well as in decreasing the yield strength (from 455 to 413 MPa) and tensile strength (from 580 to 559 MPa). On the contrary, an increase in hardness of the core (from 165 to 175 HV10) and the outer tempered martensite (from 240 to 270 HV10), in addition to an increase in yield strength (from 510 to 537 MPa) at almost the same level of tensile strength of 624–626 MPa are observed for B500B grade D32 compared with D20. The modeling and simulation calculations suggest that the manufacturing D32 rebars of B500B grade involves longer quenching time in the QTB which allow deeper tempered martensite surface along with a relatively higher core temperature that renders faster kinetics and larger volume fraction of V(C,N) precipitates. The current study demonstrates that the full potential of V-alloying can be exploited when a sufficient quenching time at the equalization temperature is achieved, which is valid for D32 rebars. Full article