The Story
A mere 114-millimeter discrepancy in camber between two half girders seemed like a minor issue at the time – one that could be rectified by adding weight. But it was a miscalculation of deadly proportions.
As construction proceeded on the West Gate Bridge, engineers discovered that when the two half girders on the west side, spanning piers 10-11, were brought into close proximity, there was a significant camber difference of about 114mm. JHC, the contractor, proposed an expedited solution: using kentledge to push down the northern half-span to bring it level with its southern counterpart.
It just so happened that ten large, cube-shaped concrete blocks, each weighing approximately eight tons, were already on-site from a previous operation. These blocks seemed to provide the necessary load to correct the camber difference if positioned as a concentrated weight near the mid-span. The assumption was that this would resolve the misalignment quickly and efficiently. But the consequences of this decision were not fully understood at the time.
Jack Hindshaw, M.I.C.E, the Resident Engineer from Freeman Fox and Partners, documented the events in his diary. His entry for Wednesday, 9 September 1970, recorded an alarming observation: “Obvious overstress due to concrete kentledge.”
What Hindshaw did not explicitly state – either in his diary or elsewhere – was whether JHC had used more kentledge than what had initially been approved. Regardless, the act of adding the ballast had an immediate and dangerous effect: it caused a buckle to form in the structure. The buckle appeared on the inner upper panel near joint 4-5 north, a clear indication that the bridge was under undue stress and partial failure had already begun.
Lessons Not Learned
Just a few months earlier, on 2 June 1970, another bridge – the Milford Haven Bridge in Wales – had collapsed during construction. The Milford Haven Bridge had many design similarities to the West Gate Bridge, including the use of a trapezoidal box girder. Following that disaster, additional steps were implemented to strengthen the steel spans of the West Gate Bridge. However, these reinforcements were not enough to prevent catastrophe.
By the time JHC took over Contract E, work had progressed in various stages. On the east side of the Yarra River, between piers 14 and 15, WSC had already assembled two half spans and successfully lifted them into place atop a pier. However, they had not yet completed the crucial process of bolting the two sections together. JHC inherited the responsibility of completing this jointing process.
On the west side, work was less advanced. The northern half-span between piers 10 and 11 was partially assembled but still on the ground when JHC took over. The jacking process for this north half-span began on 15 May 1970. However, delays due to strikes and adverse weather conditions meant that it wasn’t until 9 June that the rolling beam level was reached. On 19 June, the process of rolling the north half-span across the rolling beam commenced, and by 22 June, it was in place.
Similarly, work on the southern half-span began on 17 August. Within eleven days, it had also reached the rolling beam level, and by 1 September, it had been rolled into position. By 15 October, significant progress had been made, particularly on the east side, where the half spans between piers 14-15 had been joined. Cantilevering for the next span reached box 12, which was temporarily supported by a trestle mid-way between piers 11 and 12.
On the west side, however, the situation was less stable. The two half spans for piers 10-11 had been elevated and positioned, but the longitudinal jointing between the halves was still incomplete, with less than a third of the necessary bolting finished. The structural integrity of the section was precarious at best.
A Flawed Fix
On Wednesday, 14 October, D. Ward, M.I.C.E., Section Engineer of Freeman Fox and Partners on the West Side, issued formal written instructions for immediate corrective action. His directive was clear: the buckle on span 10-11 needed to be straightened “without further delay.”
The first step involved completing the bolting of the No. 4 diaphragm. Then, engineers were to unbolt the 4-5 splice to facilitate the completion of the diaphragm connection. The work commenced at approximately 8:30 AM on 15 October.
As engineers began loosening the bolts – around 16 in total – unexpected movement occurred. The two plates began to slip, jamming the bolts in their holes. Senior Inspector Enness of Steel Work for Freeman Fox and Partners suggested using an air gun to tighten the bolts until they broke. The broken bolts would then be dislodged, clearing the holes. This crude method was employed, and soon, around 30 bolts on the box 5 side of the splice had been removed. Another seven bolts were removed from the box 4 side, primarily near the longitudinal centerline.
As bolts were removed, the bulge in the metal began to flatten – from its initial 3.5-inch deformation down to 1 1/8 inches. However, near the longitudinal centerline, the shift was so pronounced that some bolt holes became entirely misaligned.
Then, a catastrophic change occurred.
The distress signals that Ward had been monitoring suddenly escalated. The initial buckle, which had been limited to the inner upper panel, spread outward into the adjacent two outer upper panels. Almost simultaneously, buckling appeared in the upper part of the inner web plate. Around this time, Ward and other witnesses reported feeling a subtle but unmistakable downward movement of the north half-span.
A Warning Too Late
By 11:00 AM, Ward knew things were deteriorating. He attempted to contact Hindshaw, urging him to come to the west side immediately. However, Peter Crossley, B.A., M.I.C.E, the Site Engineer for Freeman Fox and Partners, took the call instead. Crossley left immediately to find Hindshaw and relay the urgency of the situation.
Despite the concerning developments, work continued. The re-bolting process was progressing, and the buckle had been reduced enough that bolting between the transverse diaphragm in box 4 and the inner upper flange plate became possible. However, to complete the connection, the diagonal brace had to be removed, as its plastically yielded end palm plates would have otherwise prevented the top plating from being drawn down properly.
Hindshaw and Crossley arrived on the west span and quickly assessed the situation. At first glance, it did not appear to be worsening, but Hindshaw knew the potential danger was grave. He decided to seek the advice of Gerit Hardenberg, M.C.E., the Senior Representative of Werkspoor-Utrecht, Wescon, and WSC in Melbourne. Hindshaw made a call, providing a brief outline of the unfolding crisis.
Tragically, whatever response or advice Hardenberg might have given never had the chance to be implemented. Moments later, disaster struck.
At 11:50 AM on 15 October 1970, the weight of the structure proved too much. The west span of the West Gate Bridge collapsed in a catastrophic failure, taking 35 lives with it. The attempt to correct a small misalignment with heavy ballast had led to one of Australia’s worst industrial disasters.
What had seemed like a minor miscalculation became a lesson written in blood – a stark reminder of the dangers of engineering shortcuts and the devastating cost of misjudging structural integrity.
