8.4.5 Rigid or Articulated

The most common forms of four wheeled trolley have the wheels arranged on fixed side plates and are known as rigid trolleys. This makes them suitable for use on straight runway beams or those with a generous radius. Articulated trolleys are also available. These have four or more wheels and are designed so that each pair or set of wheels is free to pivot relative to the others in plan. (See Figure 8.4.5-1 )

Trolleys are available to suit a wide range of beam widths. Most modern trolleys are designed to suit a limited range of sizes and must be set to suit the specific beam onto which they are to be mounted. Some types, particularly older trolleys and those for special applications, may be suitable for mounting on one width of beam only.