Sometimes repairing a non-compliant weld can lead to more problems than the repair solves. Defects in the metal around the weld not previously distressed may develop cracks due to the localised heat input of the repair. Lamellar cracking in column flanges has sometimes occurred where thick complete penetration welds connecting steel girders to the columns have been repaired.

Sometimes repairing a weld is also economically prohibitive or technically or logistically very difficult.

So what criteria can be used to determine if a particular weld should in fact be repaired? This is where a fitness for purpose assessment is required. Put simply: will the weld in its current condition perform as required for the design life of the structure?

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A new prediction has been recently made for the remaining life of the Auckland Harbour Bridge. Assessments for the life of steel bridges like the harbour bridge that can be maintained indefinitley against corrosion damage tend to focus on the fatigue life of critical structural components. Huge capital investment and planning decisions can rest on the reliability of such predictions.

So how reliable are fatigue assessments of steel bridges?

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Author: Dr Clark Hyland
Affiliation: Hyland Fatigue and Earthquake Engineering
Author: Scott Miller
Affiliation: Silvester Clark Ltd
Date: 30th October 2009

Introduction
A M7.6 earthquake, with depth 80 km, occurred near Padang City, Sumatra, Indonesia on September 30, 2009. The overwhelming majority of the buildings damaged were reinforced concrete frames with unreinforced brick infill panels, reflecting the popularity of this form of construction in the affected area. However some important lessons can be learned from observations of the performance of the few steel structures affected. Two of these collapsed dramatically, tragically killing over 200 people. read article »