Alternative Lifting Methods - Integrated Lifting Equipment
Lifting and rigging equipment can often be tied into the existing framing of a structure to provide the most efficient and safe installation. The following projects on which 2DM Associates provided engineering services illustrate successful applications of this practice.
Air Hoist Support for Digester Lifts
2DM Associates designed a support beam system that was tied into the building structure to carry a 100-tonne air hoist used for the lift and change-out of a series of digester vessels at a Louisiana paper mill. A structural analysis of the building revealed that only minor modifications were required to safely carry the loads for this lift. Specifically, the floor that carries the support beams and the floor below were braced together to form an 11-foot deep truss. One of the diagonal truss members is visible at the right side of the photo.
This integrated design eliminated the need to install shoring in the plant from grade up to the level of the air hoist support, a height of 180 feet, thus saving the contractor significant time and money and greatly reducing the impact of this work on other contractors working in the mill.
The design of the digester vessel lifting cover was also performed by 2DM Associates.
Air Hoist Trolley and Bridge
2DM Associates designed a 120-ton capacity crane bridge system (the yellow steel in the photo at left) to work with the client's air hoist and beam trolleys and to fit up to existing crane runway beams. This equipment, installed at a refinery in south Texas, was used to lift cooler bundles during plant maintenance. The structural design of the crane bridge was performed in accordance with the Crane Manufacturer's Association of America (CMAA) Specification #74.
Replacement of Feedwater Heater
2DM Associates analyzed the floor structure of this power plant to assess its ability to support the weight of this 56,000-pound feedwater heater. The heater was to be skidded on rollers from its installed location to this open area, where it was to be lifted by crane for removal. A replacement heater (shown at left) was installed by reversing the removal procedure.
The structural analysis showed a number of overstressed members, for which 2DM Associates designed improvements to allow the feedwater heater replacement to proceed without the use of extensive and difficult-to-install shoring.
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