Guest Post By James L. Gordon, P. Eng. (Ret'd)
On
May 1st, I read with mounting astonishment the aDB Engineering
report dated April 20, 2017, on their investigations into the causes of the
collapse, which occurred on 29th May, 2016.
The
level of incompetence described in the report is so widespread that it brings
into question the integrity of all other structures in the development. All
staff, from carpenters to engineers are included within the ranks of the
incompetent. The sub-standard construction was clearly visible to all, but
nothing was done to rectify the errors.
The
collapse occurred in the lower portion of the draft tube as shown on the
following Figure1, copied from Figure 2 in the aDb report. In this area, the
water passage changes from a vertical expanding cone to an almost horizontal
expanding rectangle as shown in Figure 2. It is the most complex double-curved
shape in the project and very difficult to build.
For
small turbines, the shape is formed in timber, with an east coast shipwright
engaged as the carpenter foreman. A shipwright carpenter is the only person
capable of cutting and shaping the timber to the required complex shape.
For
large turbines, the shape is usually formed with collapsible steel forms, since
wood does not possess the required strength. Unfortunately, the contractor
elected to use timber.
FIGURE 1 – LOCATION OF FAILURE AND
LATTICE WOOD TOWERS
The
forms were supported with untreated southern pine softwood timber lattice
towers as shown in the Figure 2 obtained from the Independent Engineer’s report
dated July 2016.
FIGURE 2 – VIEW LOOKING
DOWN THE DRAFT TUBE AT THE LATTICE WOOD TOWERS.
The tower height is about 5.4m. The vertical lattice tower portions
are formed with built-up 2” x 10” timbers which were exposed to weathering,
with the bottom immersed in stagnant water, fungus was growing at the bottom,
parts of the wood were rotten, assembly was deficient with inadequate shims,
alignment was off with beams only partially supported by the towers, all as
shown in the following photos copied from the aDB report.
FIGURE 3 – FAILURE SCENE AND WEATHERED TOWERS (above) – NOTE STAGNANT WATER (below)
FIGURE 4 – BUCKLED TIMBER AND GAP IN TIMBER
FIGURE 5 – DRY ROT AND
INADEQUATE SHIMS. TIMBERS ARE 2” X 10”
From
the photographic evidence it is obvious to any observer that the timber lattice
towers were deficient and should never have been used to support a heavy load
of concrete.
At
the time of the collapse, there were 5 workers at the site. All fell into the
concrete mix during the collapse, and one was fully submerged but luckily
managed to extricate himself from the liquid concrete with the aid of another
worker.
FIGURE 6 – FUNGUS GROWTH (Left) AND DAMAGED
TOWER TOP (Below)
There
were 6 towers supporting the forms, and all collapsed. The failure destroyed
all evidence, hence the report was based on observations of the condition of
the lattice towers in the other units.
The list of unacceptable work is long,
with details as follows –
1.
Flooding up to
about 3 feet above the tower foundation.
2.
Fungus and decayed
wood in towers with mushroom growth.
3.
Exposure of the
untreated wood to rain and snow.
4.
Severe weathering,
with some weathering occurring during storage at site.
5.
Ice built up
between ribs, in June!
6.
Buckling of tower
timbers.
7.
Compression
failure in some towers.
8.
Gaps between
timbers and lack of shims at top.
9.
Wood saw marks
indicating no quality control at the fabrication plant.
10.
Incorrect
alignment of some towers.
11.
Inadequate nailing
of braces.
12.
Splices not
conforming to CSA standards.
13.
No protection of
the untreated lumber on site prior to installation of the towers
from
fabrication in summer of 2014, to use in the spring of 2016.
14.
Tower load
calculated at 57,700 lbs, and capacity at 40,500 lbs.
15.
No allowance for
expansion of the timber due to moisture retention, compromising structural
integrity.
From
the foregoing, it is obvious that there was no quality control at the
fabrication plant and on site, and no NALCOR staff with sufficient experience
to realize that the towers were totally inadequate. This is astonishing, since
any carpenter looking at the towers would conclude that something was wrong.
Also, an engineer looking at the towers would immediately observe the errors in
fabrication, installation and deterioration due to weathering. This indicates
that either no engineers inspected the structure, an almost impossible
conclusion, or, more likely, they were totally inexperienced to such an extent
that their competence to practice engineering in Newfoundland should be
questioned!
Jim
Gordon, PEng. (Retired)
