PS=Ø® 101: Everything You Need To Know About Pour Strip Zero

Part 1 - Eliminating Pour Strips

This is Part 1 of a four-part blog series about PS=Ø® . Part 1 focuses on why we need pour strips, what PS=Ø® is and how it eliminates pour strips. We will also cover typical slab elimination of pour strips, with and without a temporary stressing strip. Part 2 will focus on eliminating wall leave-outs, Part 3 will explain how PS=Ø® can be used to eliminate expansion joints, and Part 4 will address the installation process of PS=Ø® .

PS=Ø®

Did you know that PS=Ø® stands for pour strip zero? PS=Ø® is a mechanical reinforcing splice system that eliminates pour strips, wall leave-outs, and expansion joints while maintaining structural integrity and allowing for volume change. It utilizes proven coupler technologies recognized worldwide, featuring a thread on one end and a grout-filled sleeve on the other. The system is an ACI 318 code compliant full-tension mechanical Type 1 and Type 2 rebar splice, is ICC approved, and is made in the USA. PS=Ø® can be used to eliminate pour strips in both reinforced (RC) and post tensioned (PT) concrete. It can also be used to eliminate expansion joints in both concrete construction and composite steel frame buildings where the floor system consists of steel beams, profiled metal decking, and reinforced concrete slabs.

Why Pour Strips?

When a concrete floor slab cures, it undergoes significant volume change. If restrained (connected to shear walls, columns, etc.), it will be restricted from its natural volume change. The longer a floor slab is, the more volume change it will experience. Geometry also plays a significant role in restraint because a building’s configuration determines where stiff elements are placed. The larger, more complex a footprint is, the more restraint will be present.

Engineers refer to the volume change/restraint problem as restraint to shortening (RTS): concrete shrinks (shortens) and anything it’s connected to will restrain it, causing it to crack. To solve this RTS problem, pour strips (Figure 1), otherwise known as leave-out strips, delay strips, pour-back strips, etc., have been used by engineers for decades to solve the RTS problem.

Figure 1. Pour strips minimize restraint and allow for volume change but create scheduling issues and safety concerns. Furthermore, delayed pour-backs have a trickle-down effect for other trades.
Pour strips are great for solving restraint problems, but they are the first thing contractors question because of the schedule delays, increased costs, and safety hazards they cause. Pour strips are, at a minimum, left open for 28-days, but often required to be left open longer because at 28-days only 40% of the volume change has occurred. Many engineers specify leave-out times closer to 120-days when 70% of the volume change has occurred.

Why PS=Ø®?

PS=Ø® was developed by structural engineers to solve the RTS problem in a similar, but different way to a traditional pour strip. Just like a traditional pour strip, PS=Ø® allows for concrete to undergo its natural volume change, but doesn’t require problematic leave-outs. PS=Ø® is a simple mechanical reinforcing splice that allows for volume change by placing a loose piece of rebar into its sleeve (Figure 2). The rebar moves freely while the concrete shrinks until it’s grouted, creating structural integrity just like pouring back a lap splice in a traditional pour strip.
Figure 2. PS=Ø® Mechanical Reinforcement Splice System.

Reduce Costs

Closing pour strips is the most expensive concrete pour on a job. Formwork, shoring, and backshoring must stay in place for weeks, and crews must reassemble for small pours. The PS=Ø® system eliminates this costly and time-consuming step.

Accelerate Construction

Pour strips are a drag on any construction schedule. They not only require re-pouring the leave-out, but also restrict worker access. By eliminating pour strips, the PS=Ø® system can cut weeks or even months from construction schedules.

Improve Safety

An open leave-out in a floor is a major safety hazard. Pour strips are particularly hazardous because they run the entire width of the slab and are impossible to avoid. The PS=Ø® system replaces dangerous leave-outs with a narrow, grouted joint.

Quality Concrete

Without the need for an open pour strip leave-out, engineers can now achieve higher quality concrete by specifying longer leave-out times without causing delays or increasing cost.

Win-Win

It’s not often in construction that both engineers and contractors get what they want. Engineers are held to the high ethical standard of keeping the public’s safety paramount and must design structures that meet the minimum building code standards. Even though engineers are simply following their ethical and code requirements, there is a perception in the industry that they are conservative. Specifying long pour strip leave-out times for higher quality concrete is perceived in this manner and is not contractor-friendly. Solving the pour strip problem is something that both engineers and contractors alike want to do, so it is not surprising that a structural engineer came up with the idea of PS=Ø® . Now, engineers don’t have to sacrifice high quality for the sake of schedule and cost, making PS=Ø® a win-win for engineers and contractors.

Slab to Slab Application

In this application (Figure 3) either side can be poured first but if it’s PT, stressing of the second pour must happen at the outside slab edge. To see our installation video of this application Click Here.

Figure 3. Typical Slab to Slab Application

Slab to Slab with a Temporary Stressing Strip Application

What if you can’t get at the outside edge of the second slab to stress the tendons in PT? We have a solution for that, which is commonly used in subterranean conditions. In this application (Figure 4) either side can be poured first but after both pours are done and tendons stressed, the third pour (the stressing strip) can be placed right away. The joint will always open up next to the coupler

Figure 4. Typical Slab to Slab With a Temporary Stressing Strip Application.

Grouting the PS=Ø® Relief Joint and Couplers

The length of time between placing the slabs and grouting the joint and couplers is still specified by the Engineer of Record (EOR), although we recommend waiting as long as possible to achieve the highest level of quality. There will be a time when grouting the system is critical, but it’s typically beyond standard pour strip leave-out times. Trades can easily work across an ungrouted system with no issues, i.e., mechanical, electrical, plumbing, wood-framing, cold-formed-metal-framing (CFMF), etc. can be installed with ease (Figure 5). However, the system should be grouted prior to installing any rigid materials across the joint. For instance, grouting should take place prior to the installation of exterior wall systems consisting primarily of glass, precast concrete, or concrete masonry units (CMU) that are connected to the slab and are not designed for horizontal movement.

Figure 5. PS=Ø® Relief Joint prior to grouting.

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