|Memorial tribute to the victims of the walls collapse|
|Remaining concrete foundations of the masonry wall section|
The foundations left behind appear to be intact and show no signs of rotation or sinking. This could not have been a point of failure.
|Structural steal support on northern end of wall |
where the wall remained in tact
The Nothern end of the wall that was left standing following the accident was supported by large steel piles that edged the walls driveway opening. The integrity of this part of the wall was not compromised. It is the southern end that was the fault line and was relatively unsupported point that is of the greatest concern. The walls collapse and point of failure appears to have been located here.
|Photo showing the wooden hording following the collapse|
|2009 Google Street view of the wall prior to the installation of the recent hoarding in 2012 |
Click on the above photo to access Google Street view
|Typical connection detail of a |
hoarding board to a tubular steal pole
(Photo not from the Swanston Street site)
It is also conceivable that had the hoarding been constructed in such a way that it would not have added applied load to the wall, if it was not one piece, it may not have brought the wall down.
|Debris from the hoarding left on site|
|Masonry wall foundation elevation|
The absence of additional piers or lateral support to the southern end of the wall provided the weakest point of failure. If there was a return or solid bracing, as exists on the bluestone wall on Bouverie Street end of the site, then the wall could have withstood the live load forces that were applied.
According to the City of Melbourne Construction Management Plan Guidelines:
Item 4.1 Hoardings - General Requirements
Hoarding screens must be constructed of closely boarded timber or plywood between 1.8m to 2.4m in height to secure a building site and form a barrier against noise, dust and debris. Chain wire and corrugated iron fences are considered unsuitable for this purpose.
Hoardings are to be designed to withstand wind loads to AS 1170.2 with counterweights as necessary to prevent overturning. In addition hoardings adjoining excavations are to be designed to withstand a lateral line load of 0.75 kN/m applied at a height of 1 metre from the base and suitably guarded by barriers to prevent vehicular impact.
Hoardings and barricades must be in good condition, free from graffiti and maintained to the satisfaction of the Council. They should be painted in a uniform colour preferably white
Online commentator Butterpaper also suggests that the existence and location of three story container stack used for advertising the site project may have deflected the 76Km winds recorded on the day concentrating the winds force at the weakest point on the wall and hoarding structure, the southern edge of the masonry wall
Link: For more analysis on the wall's history and its collapse by Butterpaper