Grounds for concern

In order to effectively transmit the forces from the crane column into the floor, dowel plates are designed both to keep the required dowel spacing and to limit the maximum admissible force to be transmitted by the dowel. In fact, the entire structure must be fully engineered taking into consideration all static needs.

However, current market reports suggest that suppliers and users tend to dowel the crane base directly on the floor surface - without using any type of anchor plate. This method of fixating the column is highly unsafe because the crane is in danger of tilting.

Potential risks associated with faulty mounting:

- The base plate/base flange of the crane column is not plain; the structure is subject to swinging movements - design fundamentals to calculate the lever arms are likely to be misleading

- Dowels are not properly sized and are not suited for dynamic loads

- Requirements on minimum dowel spacings are not met but limits are considerably below the admissible values

- The calculation is based on the misleading interpretation that, for example, a group of eight dowels can transmit eight times the tensile load because each dowel will transmit a defined tensile load. Actually, this is not the case. The forces transmitted by the dowels must be reduced. A group of dowels, set in-line, will never transmit the force of a single dowel.

Since dowels arranged in-line are affecting each other. Wrong calculations and faulty placing of dowels can be the reason for conical fractures in the floor enhancing the risk of the crane tilting.

For safety reasons, Vetter urges crane users not to dowel free standing slewing cranes on the floor surface without using an appropriate dowel plate.

Therefore, it recommends the use of dowel plates specially developed by manufacturers for crane mounting. Standard base plates/flange bases of free standing jib cranes are only suited for the fixation with anchor studs on the concrete slab or for bolted connections of steel structures - they are absolutely not suited for dowel fixation on the concrete floor.

Qualified specialists

Besides the engineering by qualified specialists, it is very important to properly set the dowels. In fact, faults also occur when fastening the dowels. Only the manufacturer’s experienced personnel provide the know-how and have the tools and equipment available which are needed to properly fix the dowels. It is important to use the recommended fixing material, developed and tested by the manufacturer.