Prestressing and post-tensioning
Distinguish the systems and construction stages
Prestressing introduces force through designed steel and concrete arrangements. In pretensioning, steel is tensioned before casting and force is transferred through the approved release process after the concrete reaches the required condition. In post-tensioning, force is applied after casting when the specified stressing conditions have been met. The actual system details govern. Bonded tendons use a grouted duct system, while unbonded systems rely on their particular sheath, corrosion protection, and anchorage details. Neither system can be treated as ordinary loose reinforcing bar.
Tendon profile is part of the structural design. Preserve the required high and low points, support spacing, end geometry, and anchor-zone details. Construction access is not sufficient reason to change the route. Damage to a sheath or protection at an anchorage needs the approved repair or disposition before concealment. Drilling or cutting into an existing post-tensioned member requires reliable assessment of embedded tendons and an authorized location and method.
Verify force and elongation appropriately
Stressing readiness depends on the specified concrete strength and other acceptance conditions, not only age or a dry surface. Use the correct calibrated jack, gauge, and pressure-force relationship. In a simplified pressure calculation, force equals pressure times effective piston area, with units kept consistent. A megapascal is a newton per square millimetre. An elastic elongation estimate may use PL divided by AE when the problem explicitly defines that model and its inputs. Actual systems can involve effects not captured by that simplified expression.
Pressure and measured elongation provide related checks. If their results fail the project's acceptance criteria, investigate using the approved process. Do not increase force arbitrarily to make one value match, and never replace an actual reading with a predicted number. Record tendon identity, equipment, measurements, sequence, and acceptance information accurately.
Control stored energy and complete protection
A stressing operation can release substantial energy if a tendon or anchorage fails. Maintain the planned exclusion, positioning, and emergency controls. Follow the approved stressing order and do not cut tails before the required acceptance and anchorage conditions are satisfied. Bonded-duct grouting needs the qualified mix, vent and outlet sequence, and confirmation of filling. Unmeasured extra water or an unexplained leak can undermine the intended result. Restore specified corrosion protection at terminations. Existing tendons may retain force long after construction; de-stressing for repair requires a designed plan addressing both energy release and the changed structural condition.