One of the many things to consider when sizing a crane for a job is the site that the crane will be located at and its surrounding conditions.  

This can be done prior to knowing all of the project details because there are many times where the existing site conditions may limit you on the crane selection versus the actual loads lifted.  The location of the site, access around and to the crane, existing soil conditions, undergrounds, overhead lines, existing buildings, prevailing wind conditions, and other limiting factors all play major role in the selection of a heavy lift crane.

The location of the site may limit the size and type of crane for the job.  Heavy lift cranes cost significant amounts of money and time to mobilize and demobilize and it is ideal to limit those costs by finding a rental house close to the job site.  By limiting the number of rental houses due to distance from site, usually the types and availability of heavy lift cranes are also limited. This factor becomes less and less as you select larger and larger cranes because fewer rental houses will have these larger cranes.  Also, as the cranes get bigger there may only be one or two of them in the whole country.

Another important site constraint is the actual location of the crane on the site and the area surrounding it.  Access around and to the crane brings up a variety of questions:

• Can the modules or pieces that are to be lifted be brought directly to the crane?
• Are the modules being fabricated right next to the crane, or being brought in on a trailer?
• If the modules cannot be brought or built near the crane, how far does the crane have to reach to pick up the module and how does it relate to the radius of the final setting location?

This last question is very important.  

If the crane is sized based on just the weight of the module and how far its final location is from the crane, then there could be a major issue if the initial pick location of the module is farther away than the final location.  One particular item to watch out for is the minimum radius. If you are setting modules at a radius of 250ft, then you need a large amount of boom and/or jib. This usually creates a minimum radius of say 75ft. With that, you need to be sure that you do not need to pick anything in that minimum 75ft.  Or you need to create a walkway to back the crane up to allow you to make picks within that minimum radius. Each crane chart will show you the minimum and maximum radii based on the crane setup.

Another item dealing with access around is the amount of space available to build the crane.  Heavy lift cranes usually do not require a significant amount of room to build their superstructure, but they do need a significant alley way to assemble their boom and jib attachments.  There are ways to build the boom and jib attachment in the air, but in terms of safety, cost and schedule it is preferred to lay out the boom on the ground and build it. Therefore, for however long the boom and jib attachment are, that is the length of room required to build the boom.  This area to build the crane usually requires an assist crane to help build the boom and the crane itself. Also, the boom may need to be laid down periodically during the job whether due to high winds, inspections, or repair needs. Therefore, a boom laydown area should always be available to a heavy lift crane within a reasonable amount of time.  Each manufacturer gives the wind speeds for when and how a crane boom should be laid down. You should also consider whether or not an assist crane is needed to help raise the boom from a flat position. This is usually only required when very long lengths of boom and jib are installed on the crane.

Existing soil conditions and undergrounds can also steer the direction of the crane size or type.  It is important to find out where the major undergrounds, especially electrical duct banks, during a site walkdown.  If the soil conditions are rather poor or there are a lot of undergrounds, then it may be prudent to select a crane that puts down a lower ground bearing pressure such as a ringer.  If this is impractical or unavailable, then it will be necessary to improve the ground conditions and/or move undergrounds. This will then lead to trying to find a crane with a small footprint that will do the job.  This may make using a large crane more practical than a smaller crane with a wheeled counterweight or hanging counterweight due to the smaller footprint. It is always prudent to obtain the underground information around where the crane will be located and the allowable ground bearing pressure in that area.  Both items are important when selecting a crane and vital when designing the matting to go beneath the crane.

Other existing site conditions like overhead power lines or existing buildings will likely set the type of boom and jib attachment configuration.  Overhead power lines will either limit the location of the crane, or how far it can rotate. OSHA 1926.1409 gives the minimum clearance distances based on voltage.  This part of OSHA also gives requirements if operating near power lines. If near power lines, make sure all safety procedures are in place to limit the rotation or boom angle to keep the crane out of the power lines.  If the crane has to lift over buildings, it may make using a luffing jib more appealing and/or necessary. Also, if these building are occupied and/or house critical equipment, then this may lead to developing critical lift plans for all lifts made depending on your lift planning procedures.  There may be another location on the site that could eliminate or at least limit these types of lifts.

Wind can be a factor in the selection of a heavy lift crane.

Heavy lift cranes come with tables which state the allowable operating conditions for a specific boom and/or jib combination.  This may limit the decision of how much boom or jib to add if the heavy lift crane is to be operating in a high wind area.

We want to make sure you have a successful lift and that starts with proper planning and selecting the correct crane for the job.  We can assist in this process by helping to create a lift plan and help size the correct crane for the job. Here at The Dothea Group, we will do our best to meet your schedule needs and we will provide efficient, engineered solutions to better your project, improve safety, and increase your bottom line.

If you are interested in learning more about our engineering services, contact us today.  We can partner with you to ensure a successful bid or project.