10.5.2 Selection of Jib Crane
The design of jib crane selected will depend much on its location and the task it is to perform. Careful consideration must be given to its location as relocation may be costly.
If wall or column mounted designs are selected, a qualified engineer must be consulted and approval obtained as to the suitability of the structure to accept the increased loadings that will be imposed on it.
If free standing designs are selected, a prepared foundation will probably prove necessary. This must take into account the type of mounting of the column together with any plating or bracing, i.e. surface mounted or cast in, the turning moments, the permissible soil loadings and the loads that will be imposed. A suitably qualified person should be commissioned to design the foundation.
Consideration must also be given to the style of the jib, i.e. over-braced or underbraced. This must take into account the available overall height, the required effective height, the required length of travel along the jib arm, i.e. the effective travel and the required area of coverage taking into account any obstructions which may impede the facility to slew.
Over-braced jibs give the greatest effective travel and therefore area of coverage, but as the bracing is above the jib arm, they require a lot of clear height. They are therefore unsuitable for use in low buildings or where there are overhead obstructions.
Underbraced jibs give the maximum lifting height, but as the bracing is to the underside of the jib arm, they offer a reduced effective travel and area of coverage. They are therefore unsuitable where the load is to be placed near to the support column or wall.
In order to gain the advantage of lifting height and maximum effective travel, it is possible to have an underbraced jib with the bracing spaced to allow the hoist and trolley to pass between the bracing legs. This has the disadvantage of adding to the width of the jib assembly and can severely restrict the available slewing angle.