Civil Engineering Reference
In-Depth Information
To prepare the concrete, the corners of the columns were ground to a
15-20 mm radius, and then they were water jetted to remove any laitance.
All of this work was carried out at night when the car park was empty.
Cutting of the fibres was carried out using mechanical shears to quicken the
application. All of the fabrics, where possible, were cut off site, at the offices
of the specialist contractor. As the columns were of similar size, this method
was found to be quicker.
Mixing of the resin at the preparation area made the job simpler. A resin
application area was made at the job site; two lengths of Kevlar® could then
be saturated, rolled up and moved to the prepared columns.
The columns were then covered with the Kevlar in the hoop direction. A
minimum of two layers was specified with a minimum overlap of 200 mm.
The coating system was then applied the following day and the car park
spaces were passed back to the client.
Eight years after the car park was strengthened and the extra floors were
added to the structure, there are no signs of distress to the structure; in fact
more clients are looking at this method as a solution to the shortage of car
parking in our inner cities.
16.5 West Burton Power Station
The cooling towers at West Burton Power Station were built in the 1960s. It
has eight reinforced concrete cooling towers, each 118 metres high with a
46.3 metre internal throat diameter and a distinctive hyperbolic profile. The
original tower shells are only 125 mm thick, making them thinner than an
eggshell by scale.
Since the 1970s, when a number of high-profile cooling tower collapses
such as Ferrybridge occurred, the issue of strengthening existing cooling
towers has had to be addressed. Older cooling towers built to a CEGB standard
design were under-designed and failed to take properly into account the
effects of wind loading. Subsequent collapses led to a nationwide programme
of inspection to prioritise those towers which required strengthening, and
strengthening works throughout the country ensued.
Typically, the technique used to strengthen cooling towers, according to
the CEGB design, involved building a 125 mm thick mantle - an outer skin
of reinforced concrete - on top of the existing shell. While 125 mm was the
standard thickness according to the design, mantles, however, were usually
75 to 100 mm thick. In the 1970s a 'gunite or shotcrete' (sprayed concrete)
shroud was applied to the surface to help strengthen the shell, especially
against wind loading.
After a survey by Jacobs Babtie, it was noted that the cooling tower was
still continuing to crack and deform. The engineers came up with a solution
to this problem by tying into the cooling tower a series of concrete ring
beams to provide the required circumferential stiffness. Was this enough
though to ensure that the tower would regain the anticipated strength and
