Wednesday, July 2, 2014

Tower Cranes

Most tower cranes have to be assembled and erected on site prior to use and can be equipped with a horizontal or luffing jib. The wide range of models available often make it difficult to choose a crane suitable for any particular site but most tower cranes can be classified into one of four basic groups thus:-

1. Self Supporting Static Tower Cranes † high lifting capacity with the mast or tower fixed to a foundation base - they are suitable for confined and open sites. (see page 194)

2. Supported Static Tower Cranes † similar in concept to self supporting cranes and are used where high lifts are required, the mast or tower being tied at suitable intervals to the structure to give extra stability. (see page 195)

3. Travelling Tower Cranes † these are tower cranes mounted on power bogies running on a wide gauge railway track to give greater site coverage - only slight gradients can be accommodated therefore a reasonably level site or specially constructed railway support trestle is required. (see page 196)

4. Climbing Cranes † these are used in conjunction with tall buildings and structures. The climbing mast or tower is housed within the structure and raised as the height of the structure is increased. Upon completion the crane is dismantled into small sections and lowered down the face of the building. (see page 197)

All tower cranes should be left in an `out of service' condition when unattended and in high wind conditions, the latter varying with different models but generally wind speeds in excess of 60 km p.h. would require the crane to be placed in an out of service condition thus:

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