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News - 02 March, 2018

Salt barn roof structure


Voortman Steel Construction secured an order in the summer of 2016 to build six mobile hatches for a salt storage barn in the Botlek area of Rotterdam. In this article you can read why this is an unusual project for a number of reasons, requiring the necessary expertise.

It is a design and build contract, in which the contractor – TME Machinebouw & Engineering in this case – is charged with the design as well as build. TME outsourced the design and detailing of the steel structure to Voortman Steel Construction. One of the reasons for TME choosing Voortman is our ability to act fast, which is of prime importance in view of the tight project deadline.

ROOF SECTIONS

The salt barn consists of two concrete bunkers. Above them is a mobile roof structure consisting of two sets of three hatches: two low and one high on each bunker. Each hatch (or roof section) is capable of being moved as a unit in order to enable salt loading and unloading to proceed as efficiently as possible. The hatches are equipped on the underside with motorised wheels which run on rails laid on either side wall of the barn. The high hatches pass over the low one when being moved. Voortman Steel Construction designed the roof structure in close collaboration with TME Machinebouw & Engineering. Here, TME took responsibility for the mechanical engineering part, such as the drive and control systems. Cordeel, a construction company, provided the concrete shell for the salt barn.

COATING

Salt storage in the barn meant that all kinds of measures needed to be taken to prevent corrosion. Salt actually accelerates the corrosion process, which can result in a loss of strength in the steel structure. One of the anticorrosion measures consisted of applying a C5M coating, which protects against the highest corrosion risk. The use of this coating had an impact on all phases of the project, from design to assembly. Erik Baan (Detailing Engineer) sets out a number of examples of this: “Accumulations of salt on the roof sections must be kept down to a minimum in order to prevent the coating from being degraded. That is why all box sections in the trusses are positioned at an angle of 45° and all corners and edges rounded off. Furthermore, rubber pads were fitted between all joints. This was done to prevent damage due to friction brought about by movement. Finally, the assemblers were also required to go about their work with care in order to avoid damaging the coating as far as possible, because it is awkward to touch it up in situ.”

DESIGN

The working method during the design phase was also markedly different from that of regular projects. Jelle Meilink (Structural Engineer) explains why. “With most projects we get a complete package supplied by the contractor: a design comprising all the steel sections. In this project we, Voortman Steel Construction, were sitting in the lead designer's chair. We worked out all the sections in detail for the hatches based on the drawing of the previously existing barn.” Erik and Jelle are highly positive about the partnership with TME Machinebouw & Engineering. “There really was teamwork: both sides adopted a flexible attitude and devised designs collaboratively.”

PREPARATION GRADE

Stringent requirements were imposed on the manufacture of the steel structure because it had to be delivered in accordance with the highest preparation grade (P3). In order to meet this requirement, welds were finished smooth, weld spatter removed and cut edges rounded off. All this was done to guarantee a long lifecycle for the C5M coating. Jan Nijkamp (Production Manager): The first hatch we delivered was rejected by the coater because the preparation grade did not meet their requirements. That is why we devoted more care to the finish with the second hatch. The result was that this hatch was delivered with a mirror finish, however it cost us many more production hours than we had budgeted for. At that point we came to new agreements with the customer, the result being a product that met the customer’s wishes and requirements in full plus a more positive end result for Voortman.”

ASSEMBLY

After coating, the parts were taken by transport to the Port of Rotterdam, where our assemblers started preassembly at the end of December. Because the salt barn was built right on the edge of the water, the space for setting up the crane and steel storage on site was limited. The assembly team made special trestles first on which they were able to preassemble the parts into larger units. These units, some of which weighed as much as 16 tonnes each, were subsequently hoisted onto the concrete shell using a 250-tonne crane. The assembly team completed their work on the salt barn in a few weeks.