Post-Tensioning — Safe Work Method Statement

Post-tensioning (PT) puts large forces into a structure. Each strand is stressed by a hydraulic jack to a very high load and locked off at the anchorage. If a strand, wedge or anchorage fails during stressing, the strand and jack components can be thrown out from the slab edge with lethal force. PT work is High Risk Construction Work because stressing crews work at slab edges and on decks with a fall of more than 2 metres, and because the work is done in an area with cranes, pumps and other powered mobile plant. A SWMS is required, and it must address the stressing exclusion zone as well as the usual deck hazards.

The key control is the exclusion zone. No one stands behind the jack, in line with the tendon, or below the anchorage during stressing, and the zone is barricaded on the deck and at the levels or ground below where an ejected strand could land. Stressing only starts once the engineer or PT designer confirms the concrete has reached the specified transfer strength, usually from test results. Hydraulic hoses, couplings and gauges must be in good condition and rated for the jack's working pressure. Gauges and jacks must be calibrated so the recorded elongations and pressures can be checked against the design.

Other PT-specific hazards include strand recoil when uncoiling strand from packs, cutting strand tails with oxy-acetylene or abrasive discs (hot work, burns), cement grout injected at pressure into ducts, and working at the slab edge from hung stressing platforms. Once tendons are stressed, the slab is a live PT structure. Any later coring, drilling or saw cutting must be scanned and approved by the engineer, because cutting a stressed tendon can release it violently and weaken the slab. Mark the slab and record tendon locations on the as-built drawings.

PT installers and stressing operators must be trained and competent with the specific system and jack. Anyone slinging crane lifts of strand packs or jacks needs a dogging licence. The PT designer's stressing sequence and records are part of the structural design and must be followed exactly.

Customise this template with: the PT system and supplier; the structural drawings and stressing sequence reference; the concrete transfer strength required and how it is confirmed; the jack and pump models and calibration dates; the exclusion zone layout at deck level and below; the stressing platform or edge access method; the tail cutting method; the grout specification; and who keeps the stressing records.