Lattice boom crawler cranes are very common on most types of construction projects. They are versatile in that many attachments to perform many different types of work such as draglines and clamshells for excavation, pile drivers, dynamic compactors, ‘‘wrecking’’ balls for demolition, augers for drilling holes, and magnets for moving metal objects can be easily attached and used. There are several boom configurations that can be used.
|Figure 1 Parts of a lattice boom crane.|
A guy derrick crane uses a back boom as a derrick that can be anchored temporarily to other structures to counterweight the load as it is lifted and placed. The lifting cable comes from the back of the cab of the crane, over the derrick boom and then through the lifting boom to the load, thus transferring the compressive force of the load to the derrick. This crane can boost capacity 800% over a basic crawler crane.
A crawler tower crane is less costly than a true tower crane. The main boom is vertical with a luffing boom attachment. The compressive load is transferred to the crane cab and counterweights down this vertical boom. Maximum boom and jib combination are approximately 4800.
The sky horse configuration is similar to the guy derrick, except the back boom is shorter than the lifting boom. It is not temporarily secured during the lift. This crane can approximately triple the capacity of a standard crane.
A ringer lift attachment at the base of a crawler crane is used for heavy lifting. The ring helps to stabilize the crane to the lifting surface. The crane can have a sky horse boom configuration with a luffing jib attachment. Typically a great amount of counterweight is attached for balance. The counterweight is supported on the structural ring. Ringer lift cranes can lift and swing mega-heavy loads.
Figure 1 is adapted from an illustration in the Mobile Crane Manual published by the Construction Safety Association of Ontario and shows the basic parts of a lattice boom crane. Because of the crawler tracks and the instability caused by the moment created at the end of the boom by the load, these cranes move slowly and must travel on a level stable surface. If necessary, the crane can build its own road as it moves forward. This portable surface must be level and stable enough to support the crane’s weight and also the weight of its load. When planning a lift, how and where the crane travels to its lifting position with its load must be planned. Provision for avoiding obstacles and having a stable travel surface must be made.