FAQ >> Bottom-Slewing Tower Cranes Structure and Configuration

Bottom-Slewing Tower Cranes Structure and Configuration

The main parts of a typical bottom-slowing tower crane include:

  • Undercarriage. Unlike top-slowing cranes, which are often configured without an undercarriage, bottom-slowing cranes would always have an undercarriage to connect between the ground or any other supporting surface and the slewing crane. The undercarriage is commonly either sta- tionary (Figures 19.16a and Figure 19.17b) or rail-mounted. Light models may have a wheeled undercarriage, but this is used only for infrequent crane relocations on the jobsite, without loads, and not for operation. In truck-mounted tower cranes (see below), the truck replaces the conven- tional undercarriage. Another configuration, seen mainly in Europe, is that of a crawler under- carriage (Figure 19.16b). Whenever it is not in motion, the crane is stabilized by outriggers.
  • Slewing ring. The slewing ring of the top-slowing crane is located near the top of the crane, but the slewing ring of a bottom-slewing crane is located near its base, such that practically the entire crane-slewing platform, mast, and jib-can slew. For this reason, the mast cannot be braced to the building for increased stability, and its height is limited.
  • Slewing platform. The slewing platform carries, in addition to the mast, the entire ballast of the crane, as well as the motors. To balance the crane, the ballast blocks are located at the rear of the platform, always opposite the jib. To be most effective, the greatest possible distance between the ballast and the mast would be desired. On the other hand, the smallest possible projection of the rear end of the platform from the footprint of the crane (as determined by the undercarriage) is desired to allow crane setup in dose proximity to the building and for increased safety. Newer models, therefore, have a compact platform, compensated for by a high stack of ballasting concrete blocks.
  • Mast. Earning the bottom-slewing tower crane the name telescopic tower crane (to distinguish from the sectional top-slcwing crane), the mast of this crane is made of two to three telescoping parts. This type of structure is in line with the limited height of the crane and, even more so, with its rapid self-erecting concept. The operator cab is traditionally located at the top of the mast, or the crane can be operated from a control post at the lower part of the mast. Many new models now offer a dimbing cab that can move along the mast for optimal view (Figure 19.17b). Wireless radio remote control of these cranes is now offered on most models. Masts are either lattice (Figure 19.16) or hollow section (Figure 19.17). hollow-section masts used to be common only on smaller models but are increasingly being seen on larger models, as well. In smaller models, this hollow- section mast is often foldable instead of telescopic.
  • Jib. The lattice-type jib is similar to the main jib (i.e., no counter-jib) and trolley system of the top-slewing crane; however, it is foldable for fast erection and dismantling and, in many models for a shorter jib work option. Some models feature a telescoping jib. Unlike top-slowing cranes, where the horizontal jib and the luffing jib are two different crane configurations altogether, the jib of the common bottom-stewing crane can usually be raised, though not in a sharp angle (commonly up to 300), while maintaining trolley movement. This grants the initially height- limited crane an additional lifting height. Some models have an articulated jib, in which the part closer to the mast is horizontal and the outer part can be angled upward.

Relative FAQ