Moving materials on the job site in an efficient and safe manner is often the prime driver of the project schedule. The selection and placement of hoisting equipment is critical to our success. Whether we are renting and operating the crane directly or turnkeying the entire structure package, we, as the controlling contractor, must conduct a detailed study of the proposed equipment.
None of us can afford idle hooks on a job; it is an intuitive notion that an idle crane wastes money. The cost of not enough crane for the job can be difficult to calculate, but undoubtedly it is equally if not more costly. The obvious effect of too little crane for the job is schedule impact. The not so obvious costs include extended hours, tired operators, cutting corners on rigging in the name of speed, and safety-related issues from trying to do too much with too little, not to mention unhappy subcontractors, poor morale, and back charges that can follow.
A simple way to study a subcontractor's crane choice is for you and your sub to draw a scale drawing of the crane at the first and last elevated deck with a typical load in place.
Using this process I've identified numerous potential issues. One such example follows: I've found with the scale drawing that a mobile crane that safely moved 100-foot tables at lower elevations is boom blocked by its own load at top floors. It was physically possible to set these tables, but with the boom angle so steep and load so close to the tip of the boom, the tables could rotate and strike the boom in windy conditions.
Another easy mistake is charting a crane for building height with standard rigging, then failing to consider the longer rigging required for precast, glass and other building skins. When this happens, contractors have to take the materials over the building perimeter and roads, as opposed to the relative safety of traveling over the structure. These drawings, charts and studies should be kept in the JHA (Job Hazard Analysis) section of your Job Safety Files.
It is imperative that all superintendents and project managers get involved in a subcontractor's choice of cranes. While we don't want to mandate all means and methods, we can and should mandate that enough crane is supplied to complete the job safely.