Methods of Constructing Tower Crane Foundations

For base-frame fixed self-erecting tower cranes, a block-type reinforced concrete foundation is most suitable. On foundations with relatively high soil bearing capacity, the dimensions of such concrete foundation blocks may be taken as 200 cm × 200 cm × 50 cm, and both the top and bottom of the blocks should be reinforced in two directions. If the tower crane must be installed near a deep foundation pit, a bored cast-in-place pile cap foundation should be used to ensure the strength and stability of the tower crane foundation, and measures should be taken to prevent collapse of the foundation pit slope.

The conventional method for rail-mounted tower crane foundations is as follows: first compact the ground or make a 3:7 lime-soil cushion layer, then spread crushed stone ballast, then place wooden sleepers, and lay steel rails on the wooden sleepers. This method consumes a large amount of wood and has a short service life, and is extremely unsuitable for heavy tower cranes. The method recommended today is as follows: on the compacted ground, erect a reinforced concrete base slab or reinforced concrete sleeper beam; on the base slab or sleeper beam, fixedly install I-beams with embedded parts; and then install steel rails on the I-beams. To improve rail-laying efficiency and save rail-laying costs, reinforced concrete sleeper beams, I-beam supports, and steel rails are often assembled together to form a 12.5 m long prefabricated reinforced concrete rail foundation. This type of rail foundation is very suitable for heavy self-erecting tower cranes such as FO/23 B, HK40/21B, and H3/36 B.

The foundation of a tower-body fixed self-erecting tower crane must meet two requirements: first, it must uniformly transmit the upper loads of the tower crane to the ground and must not exceed the soil bearing capacity; second, it must enable the tower crane to maintain overall stability under various unfavorable working conditions without overturning. Therefore, the foundation of this type of tower crane is quite large in volume, and the foundation weight must be equivalent to the ballast weight of the tower crane. The foundation weight of this fixed-type tower crane is closely related to the free-standing height of the tower crane; the higher the free-standing height, the greater the foundation weight. Taking the FO/23 B tower crane as an example, when its free-standing height is 59.8 m, the concrete foundation dimensions must reach 6.5 m × 6.5 m × 1.7 m. If the tower crane needs to be erected near a deep foundation pit during the foundation construction stage and the surface soil conditions are relatively poor, this foundation must also be supported by bored cast-in-place piles. Therefore, to save foundation construction costs, it is advisable to decompose this whole mass concrete foundation into several precast concrete strips or blocks, thereby forming a prefabricated reinforced concrete foundation, so that it can be used repeatedly many times and the tower crane foundation cost allocated to each engineering project can be minimized.