Uplift Testing for Induction Welded Systems

The induction welded attachment method, which uses RhinoBond or isoweld Plates and approved fasteners, is similar to a conventional mechanically fastened system. The difference is that the plates are coated with TPO or PVC and are installed using an induction welder. The fasteners and plates are installed on top of the insulation or cover board. Then, once the TPO or PVC membrane has been installed, the induction welder is placed on top of the membrane just above each fastener. The welder is then used to weld the membrane to the plate.

This system allows for fewer fasteners and plates than conventional mechanically fastened systems. The fasteners do not penetrate the membrane and the wind load is symmetrically distributed.

What tests have been performed for this system and how do they compare to conventional mechanically fastened systems?

Static Load Testing, ANSI/FM/SPRI 4474, is conducted by applying increasing pressure increments of 15 pounds per square foot (psf), holding each increment for one minute until failure of the system occurs.

Dynamic Load Testing is certified for Canada using the CSAS123.21 test standard. CSAS123.21 exposes the assembly to multiple cycles of increasing fluctuating pressures (from low to high) every 8 seconds. This subjects the assembly to 450 cycles per hour to simulate fatigue due to wind. The test has five levels (A to E) to be attained. Level A for mechanically fastened assemblies involves 2,200 gusts (cycles) of pressure and must be passed to obtain any uplift pressure rating. The dynamic test can take several hours if failure does not occur prematurely, versus the static test which lasts only six minutes for an assembly to be an FM 1-90 rated.

Two induction welded assemblies (PVC and KEE HP and TPO) using RhinoBond plates were tested per CSA A123.21 starting with a 55 psf test pressure, which passed Level D and ultimately failed in Level E. The passing pressure was 96.3 psf for the PVC and 105 psf for the KEE HP and TPO. The test duration was approximately 12 hours where the assemblies were subjected to 3,600 or greater cycles. A conventional PVC mechanically fastened assembly using 8’-wide sheets with fasteners placed 12” on center was also tested using this dynamic test method, which resulted in a pass at 81 psf.

For more information about the Canadian Standards Association Wind Uplift Test Results, click here. The report uses a safety factor of 1.5, so the uplift resistance number should be multiplied by 1.5 to obtain the actual pressure sustained.

What types of failure modes occur? Is there peel from plate, fastener pullout, plate bending, and/or tearing around the plate?

For induction welded systems, the mode of failure is typically delamination between the top and bottom ply of the sheet. If peeling occurs, it is a sign of improper welding.

For conventional mechanically fastened assemblies, the mode of failure is usually membrane tearing around plates.

Seam separation, if it occurs, is usually an indication of an improper weld. As far as fastener pullout, it is only experienced when testing an assembly over wood decks. The bending of plates is very rare in today's roofing assemblies, due to the heavier gauges and the profiled design.

For more information, check out the Guide Specifications on using induction welding for thermoplastic membranes:
Click here for TPO Guide Specifications
Click here for PVC/KEE HP Guide Specifications

Contact Craig Tyler at [email protected] with questions.