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

127to wrought iron that had not. The wrought iron that experienced significant damageexhibited a much lower percent elongation and, therefore, was much less ductile.5.7 Investigation and Repair of Damaged and Bent MembersMany existing historic iron truss bridges have been damaged by vehicular trafficor severe storms. In these bridges, there are typically a number of members that havebeen bent or twisted to the point where the member either fails or its strength iscompromised. In extreme cases, the bridge may collapse due to severe damage. Forexample, Figure 5.13 shows a number of members from the Bell Ford Bridge after it hadcollapsed. As seen in the photograph, the members are severely misshaped and damaged.In the testing that was completed for this study, some of the damaged Bell FordBridge members were machined into tensile testing coupons and then tested to determinetheir strength. Of the damaged members, some had been heat straightened and one hadbeen mechanically straightened. The results from the heat straightened samples weresuperior to the results of the mechanically straightened specimen. The heat straightenedsamples were more ductile and had adequate tensile strength, while the mechanicallystraightened specimen was less ductile and failed at a lower tensile stress.The mechanically straightened tensile coupon had poor percent elongation resultsand a lower ductility because repeated straightening of the specimen without heatdepleted the amount of plastic strain that was available in the material. When using heatto straighten a wrought iron member, the plastic strain in the material is not affected.Therefore, it is recommended that when straightening any damaged wrought iron bridgemember, heat should be added.Figure 5.14 illustrates the method that was used to heat straighten the eyebarsfrom the Bell Ford Bridge. In this method, the wrought iron is first heated slowly in a