A German contractor has developed a highly practical new post-tensioning system based on the use of flat, ribbed oval wires. For tensioning, the wires are located side by side in fours within sandwich plates which are clamped vertically together by means of four bolts. When these bolts are tightened the ribs on the wires bite firmly into the sandwich plates. A similar arrangement can also be used for coupling wires at intermediate points within the member being tensioned. By clamping vertically, the tension in all wires is equalized. This means uniform loading throughout the end block. The duct containing the tendon is connected to a wider, rectangular duct where the wires fan out to the anchorage within the end block. This portion is surrounded by a spiral or reinforcement, and is pierced by a vertical length of threaded pipe for pressure grouting. Alternatively, grouting can be accomplished through an opening in the end plate of the block. During tensioning the tendon passes between a twin cylinder, hydraulic jack. The font of this jack surrounds the anchorage sandwich of wires and bears against an end abutment plate. At the back of the jack a further sandwich plate is located and is vertically clamped tight to bear against the jack, the front sandwich remaining free. The tension is applied by forcing the sandwich at the end of the tendon outwards; the sandwich at the face of the end block can then be vertically clamped in place to retain the prestressing force within the tendon. The jack is then removed and grouting begun.