Mid last year, Smith Crane and Construction was approached by Naylor Love Construction to undertake the lift of a new canopy for BP Rolleston in Christchurch.
The canopy was 37 metres by 17 metres and weighed 23 tonnes. And because the jobsite was a fuel station, the canopy was assembled off site in a vacant lot.
Ideally, the canopy would be tandem lifted into place, but there was not enough room to do this, so it had to be placed using just one crane.
Smith Crane and Construction chose its 250 tonne, all terrain crane, rigged with a 25.9 metre boom at 84 degrees with 28 metres of luffing fly, to undertake the lift, as the lift was to be 23 tonnes at a 24 metre radius.
The engineer confirmed that a single crane lift could be done by a 10 point lift maximum, providing that all 10 points were equally loaded with maximum sling angles of 50 degrees.
Then the client called with a weight change – from 23 tonnes to 29 tonnes – and with a new radius of 37.5 metres. It became obvious that the 250 tonne all terrain crane could not undertake the lift as the weight had increased too much. Problem was, Smith Crane and Construction’s 250 tonner was the biggest mobile crane in the South Island.
So the company decided to look at other options.
There were two. Option one was a tandem lift for the initial pick up. Option two was to mobilise the company’s 250 tonne crawler crane, an expensive, and the crane was not available for four weeks. This left the first option as the only option.
The company designed a 40 tonne, three metre transfer triangle for the lift, which gave the cranes a radius gain of 1.5 metres each in their safe working loads, and provided the capacity to do the lift.
Once the weight and radius had been confirmed, the canopy had to be moved closer to the site. This meant removing 320 cubic metres of dirt and undertaking a single lift to shift the canopy the necessary four metres to enable the cranes to perform the tandem lift. This shift also confirmed the weight and confirmed the size of the transfer triangle was correct.
There were 10 points that had to be evenly loaded. This was done by using six equalizing triangles and a load cell on one sling, and five tonne lever hoists to fine tune each leg.
With the 40 tonne transfer triangle it enabled the cranes to keep within five percent safe working load (SWL) and split the weight 50/50 of whatever was needed to keep them safe.
After getting the cranes set up and ready to lift, the next challenge was to lift the canopy over BP’s car wash and the vents of the fuel tanks, and this meant boom lengths were very critical, as a short boom was needed to get the capacity but also had to allow for height.
On the initial pick up the 220 tonne crane took 47 percent of the load and the 130 tonne crane took the rest, still with only five percent SWL between them. The 220 then started to reduce its radius until it was safe to carry the total weight – luffing up mainly to take the load off the 130 as its capacity lowered.
Both crane movements were very slow so they didn’t overload each other when using the triangle. Then the 130 was remotely released, and the 220 placed the canopy in its desired position.
To save time, so the service station could open at its earliest, the crane was derigged in its placement position, with minimal clearance.
Smith Crane and Construction used two supervisors, taking control of one crane each to keep them within five percent of their SWL.
The lift was successfully completed and all equipment removed within six hours, leaving the service station clear and able to open for business.
Contractor Vol.32 No.8 September 2008
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