Production of Bearing Plate
Bearing Plate is a very important element in a post tensioning system. It serve the purpose of transfering prestressing force derived from the tendon (tensile element, eg. PC strand) to the concrete. And it is precisely in this, that explains what we want to achieve in prestressed concrete structures, and thus we take a special interest on the Bearing Plate.
In our earlier blog post we shared on the testing we conducted on ‘Load Transfer and Static Load Test of Anchors in accordance to European Technical Approval (ETAG 013)’, we posted some photographs of Bearing Plate casted into concrete blocks for Load Transfer Test. Well, this is to test the ultimate load bearing capability of the Bearing Plate (by means of a Stressing Jack) under a real-life situation. As ETAG 013 specification clearly states under Load Transfer to the Structure; “Post Tensioning systems shall be able to transfer a specified percentage of the tensile element ultimate strength from the anchorage into the concrete structure, of a defined strength class of concrete, without undue cracking of the structure, and at deformations which stabilise within a given time frame”.
However, we are not going in-depth on this test procedure and result. Rather we are taking an interest on the manufacturing of the Bearing Plate. Bearing Plate is generally manufactured with ductile iron (eg, ASTM A536, Grade 80-55-06) or grey iron (eg, HT200, GB/T9439-2010), casted in a steel foundry. There are numerous ways in the production of Bearing Plate. From an automatic production line (eg, DISA) to a brick & mottar method of using moulds, very much like how we produce precast concrete products.
We take a particular interest in a method we are familiar with, and that is, the usage of polyfoam to bring our Bearing Plate to life!
The polyfoam is produced to the exact same shape and size as the actual Bearing Plate. And then a layer of clay is coated over the polyfoam to form an ‘temporary’ mould over it. Molten iron is then poured into this temporary mould through a small opening, and the polyfoam inside will then be burnt away. With the disappearance of the polyfoam, the molten iron will then filled up the temporary mould. Once the molten iron cools down and harden, the removal of the exterior clay will then give us the Bearing Plate we wanted.
We posted some photographs of our Bearing Plate production process and we hope this will provide some insights of our daily production activities.