Cooling tower inside job
By Euan Youdale14 April 2011
Russian construction contractor OAO Metrostroy put its Terex CTT 331-16 flat top tower crane to the test during a 150 m high cooling tower build in Saint Petersburg.
Local distributor JSC GRPM supplied the 16 tonne capacity crane for use at the federal power station where the 120 m diameter cooling tower is part of a project to replace the existing 1973 facility.
"It was clear that we had to work fast to provide the competitive turn-key solution that Metrostroy needed to stand a chance in winning the race for the job," said Andrey Chukichev, JSC GRPM equipment supplies director.
One of the initial constraints identified in the feasibility study involved the height at which the crane would be working. At least three tie collars are generally fitted to the CTT 331-16 to ensure the required stability.
It was decided to erect the crane inside the cooling tower to take advantage of the structure's protection against extreme weather conditions. A solution had to be found to avoid the potentially labour-intensive and costly process of setting-up and dismantling the crane's 65 m boom and telescopic cage within the confines of the cooling tower wall.
A traditional anchoring technique using steel bracing rods was first considered, but this was not feasible since the rods proved to be too long to withstand estimated forces without buckling. Analysis also gave evidence of a further constraint - the cooling tower's walls were not strong enough to serve as an anchor to the tie-in braces
Tests proved that by erecting the crane inside the cooling tower, reduced wind forces made it possible to employ two tie-in collars instead of three, resulting in reduced equipment costs and time saved during set-up and dismantling.
Based on this evidence, a system using eight pairs of 40 mm thick pre-stressed steel cable anchors, attached in two stages as the cooling structure's wall grew higher, would be fixed on two separate levels of the crane's tower. Tests showed that the cables would need to be pre-stressed to compensate for stretching, and then rigged at a tension of 17 tonnes per cable to withstand the increased pressure induced by their length and inclines.
To overcome the insufficient strength of the cooling tower's walls, there was no other solution than to fix the cables' tie-in braces into the base perimeter of the cooling structure directly.
An innovative jib dismantling device was also specially designed for the job. The result would save valuable time in shortening the jib length during set-up and dismantling, and make work safe and more comfortable within the restricted cooling tower perimeter.
"The Terex Cranes team's recommendation corresponded exactly to what our company needed," said Paul Kolpakov, OAO Metrostroy. "We asked for a full "turn-key" crane proposal including the purchase of the crane, plus the skilled, responsive support of applications specialists and local sales and service teams from start to finish. This is what we got, and working together for seven months on this project was a good experience."
Between March and September 2010, the CTT 331-16 worked 24 hours a day, using a self-climbing framework to adjust to the structure's increasing height, steadily lifting and placing the steel reinforcements and liquid concrete used to form the tower's wall. "The CTT 331-16 performed perfectly - completing the job on schedule, and is now being employed to lift heavy elements inside the cooling tower at ground level," added Chukichev.