Anchor head is a functional component of post-tensioning tendon system in construction and mining industry.
It is also called wedge block or anchor block. However, the formal term is wedge plate by PTI definition. According to the definition of Post-Tensioning Institue, it is a device that houses the post-tension wedges in the tapered cavity and transfers the prestressing force to a bearing plate for multistrand tendons.
Anchor Head Material and Manufacturing
Anchor head is an anchoring component of a bonded multi-strand tendon system. The design material is varied by application field demand, and ductile iron or casting steel is the most common choice. In either case, attention must be paid to the casting defects, such as internal porosity or sand inclusions. In general, castings are capable to meet construction field requirements. As such, casting manufacturing is the priority choice because of its cost-competitive.
However, If necessary, foundry supplier must take X-ray or magnetic powder detection to sort out anchor that has internal casting defects.
Read more: sand casting: the manufacturing craftmanship that shapes the world to learn inside of casting process and quality control.
Because of the inherent disadvantage of unstable quality, therefore it has the trend to make anchor block from hot rolled steel bar through CNC machining process. As result, manufacturing cost will rise, but it is affordable with considering the improved application performance.
Quality and Inspection
Anchor head casting quality has an important effect on the quality of construction tendon system. In severe conditions, casting defects, such as porosity or sand inclusion, may lead to disaster failure of construction projects.
Therefore, foundry suppliers need to take strict control of each step of sand casting process. Mold design has to consider air ventilation, iron water chemical composition has to be tested before pouring mold cavity. In addition, independent test specimen has to be cast for mechanical property test. If necessary, all casting has to do internal defect detection test to make sure that there has no defect parts pass to outgoing shipment.
Finally, shipment certification must be provided for each furnace batch to show customer quality assurance.
How does Anchor Head Work
In construction site field, anchor casting holds wedge in tapered hole once hydraulic jack releases tensioning force. As wedge serration will hold steel strand back, it will transfers prestressed force from strand to the concrete member through anchor head.
In conclusion, anchor head is a functional post-tensioning anchoring component. The specific application may affect not only the selection of its material, but also manufacturing process and its structure profile.
Read more: Post tensioning tendon system in construction and mining industry to get an overall and further view on how it work.