Evaluation and Repair of Wrought Iron and - Purdue e-Pubs ...

483.6 Fatigue TestingTo develop a better understanding of the fatigue behavior of wrought iron foundin many historic bridges, some limited fatigue testing was completed during this study.Four un-notched, smooth tensile coupon specimens were prepared from round bars of theAdams Mill Bridge. The larger diameter round bar material was machined to a reducedhalf inch diameter coupon, the same as tensile coupons as seen in Figure 3.9.The specimens were tested under constant-amplitude alternating stress until eitherfailure or three million cycles occurred. The stress ranges utilized in testing were 20 ksi,30 ksi, and 35 ksi (two specimens). The R value, which is the ratio of minimum tomaximum stress, was maintained at 0.05; hence, compressive loading was never placedon the specimens during testing. This simulates the type of loading that an actualwrought iron bridge tension member would experience throughout its life, since themember is typically under some tension stress to support the dead load of the bridge.The fatigue specimens were tested using a 220-kip MTS four-pole servohydraulictesting machine in the Kettelhut Structural Engineering Laboratory at PurdueUniversity. Each specimen was cycled at a rate of 2.5 Hz, in a sinusoidal pattern. Amechanical counter attached to the MTS testing machine was utilized to record thenumber of cycles each specimen had undergone. The amount of time passed was alsorecorded to serve as a back-up check of the counter accuracy. For each fatigue testperformed, the alternating stress and number of cycles were recorded.3.7 Charpy Impact TestingMaterial from the Bell Ford Bridge and Adams Mill Bridge were used to createspecimens for Charpy impact testing completed during this study. The specimensmachined from the eyebars in the Bell Ford Bridge where orientated in different