Residual Performance of Structural Steel After Cyclic Plastic Deformation and Strain Aging

The sustainability of steel construction can be improved dramatically by establishing reuse, in a new structure, steel components procured from an older structure. To achieve this goal, the residual performance of used steel must be evaluated. For seismic areas, the residual performance after experiencing an earthquake, large or small, must be quantified. Therefore, the residual performance of hot rolled I-shapes, of grades SS400, SN400B and SN490B, after plastic deformation and strain aging was examined through three test series: (I) tension coupon tests; (II) cyclic tension-and-compression coupon tests; and (III) cyclically loaded beam tests. The tests were conducted in two phases: pre loading to predetermined plastic deformation, and subsequently, after curing for 1 or 3 months at ambient temperature, loading to larger plastic deformation. The SS400 with free nitrogen content of 0.006 wt% saw substantial strain aging effects, while SN400B and SN490B with free nitrogen content of 0.003 and 0.002 wt% saw smaller effects. In the beam tests, pre-loading to ±0.02 rad resulted in up to 25% increase in yield strength but little change in maximum strength and plastic deformation capacity. Residual deformation of the beam was within geometric tolerances after cyclic loading to ±0.01 rad, but exceeded some tolerance items after cyclic loading to ±0.02 rad.