scope:

This document provides a comprehensive description of the different processes that are required to create openings in PT slab systems. This includes a description of the required structural analysis as well as construction methods used to create openings. The most common PT system that is used for buildings in North America is with unbonded single-strand tendons. The system consists of prestressing strand protected within an extruded plastic sheathing and anchored by specially designed anchorages. Figure 2 shows the schematics and construction sequence of an unbonded PT system. The case study included in this document provides an example for making large openings in a slab constructed using unbonded single-strand tendons. Unbonded tendon systems generally fall within one of the following categories; the evolution of corrosion protection for unbonded tendons used in buildings is in Fig. 3.

• Single strand inside paper sheathing;

• Single strand inside loose-fitting plastic sheathing (oversized tubes or "cigarette wrapped" heat-sealed sheathing); or

• Single strand inside extruded plastic sheathing.

The methods described in this paper apply equally to all unbonded systems.

There are other types of PT systems that exist in buildings, including button-head wire systems (Fig. 4) and grouted (or bonded) PT systems (Fig. 5). Much of the analysis procedure used for creating openings in slabs with unbonded tendons can also be used for button-head wire systems. However, there are significant differences in the field procedures, hardware, equipment, and jacking forces for button-head systems; hence, these systems are beyond the scope of this guide. Grouted systems are also not considered in this guide.