Crane types, terminology, major components and stability principles of self-erecting tower cranes
Types and terminology
Self-erecting tower cranes are designed to be erected and dismantled quickly, often without a separate mobile crane. They may be trailer-mounted, truck-mounted, or static with a concrete base. Key components include the mast, jib, counter-jib, slewing unit, hoist, trolley, and outriggers/base. Terminology: rated capacity, radius, load moment, and stability.
Stability principles
Stability depends on the load moment (load × radius) not exceeding the crane's rated capacity for that configuration. The counterweight and base provide resisting moment. Ground bearing pressure must be adequate; outriggers must be fully extended on stable ground. Wind can affect stability; never exceed the manufacturer's wind speed limit. The load chart must be consulted for every lift, considering radius and configuration.
Traps in questions
A common trap is assuming a crane can lift its maximum capacity at any radius; capacity decreases as radius increases. Another trap is ignoring the effect of wind or dynamic loads. Also, the term 'self-erecting' does not mean it can be erected by anyone; it requires a competent person and adherence to the manufacturer's manual.
Worked example / rule of thumb
Example: If the load chart shows 2 t at 10 m radius and 1 t at 20 m, lifting 1.5 t at 20 m is unsafe. Rule: always check the load chart for the actual radius and configuration.