In building and slab-on-ground construction, unbonded tendons are typically prefabricated at a plant and delivered to the construction site, ready to install. The tendons are laid out in the forms in accordance with installation drawings that indicate how they are to be spaced, what their profile (height above the form) should be, and where they are to be stressed. After the concrete is placed and has reached its required strength, usually between 3000 and 3500 psi (“pounds per square inch”), the tendons are stressed and anchored. The tendons, like rubber bands, want to return to their original length but are prevented from doing so by the anchorages. The fact the tendons are kept in a permanently stressed (elongated) state causes a compressive force to act on the concrete. The compression that results from the post- tensioning counteracts the tensile forces created by subsequent applied loading (cars, people, and the weight of the beam itself when the shoring is removed). This significantly Increases the load-carrying capacity of the concrete. Since post-tensioned concrete is cast in place at the job site, there is almost no limit to the shapes that can be formed. Curved facades, arches and complicated slab edge layouts are often a trademark of post-tensioned concrete structures. Post-tensioning has been used to advantage in a number of very aesthetically designed bridges.