We have a large expansion project currently under construction. One of the new buildings is a large production building with an 18 gage metal roof deck, mechanically fastened to the steel framing with HILTI powder actuated fasteners. The roof framing is composed of Vulcraft steel LH joists, wide flange beams at column lines, and wide flange girders. Two different HILTI PAF's were specified, HILTI X-ENP-L15 for steel thickness greater than 1/4" (structural steel), and HILTI X-HSN 24 for bar joists. The contractor incorrectly installed the X-HSN 24 fasteners at wide flange steel at the deck laps. The special inspector, HILTI field rep, and contractor all missed this and the incorrect fasteners weren't noticed until roofers were placing roofing on the building and noticed a bunch of the fasteners laying on the deck and not holding. HILTI provided a letter and determined that the incorrect fastener heads were fractured during installation (due to 2 layers of deck and thick wide flange steel flanges), and the roofers noticed the loose PAF heads laying on the deck. As long as the contractor selects the appropriate fasteners, there shouldn't be any issue with specifying 2 different PAF's for a given building. I am now inclined to specify TEK screws or puddle welds for bar joists and PAF's for wide flange framing to avoid this issue in the future or use an all-welded deck for roof construction of this type. The tricky part is not knowing the top chord thickness for the bar joists. I guess a 1/4" min. thickness for joist top chords could be specified and the same HILTI X-ENP-L15 fasteners used on the entire roof, but this is not typically done and would make chords heavier than required.
What does HILTI recommend for specifying in this type of construction?
Shane,
To eliminate confusion with two different pins, sometimes all one pin is proposed if the joists and beams both fall under the thickness requirements of the X-ENP 19 nail which is ≥ ¼”. Sometimes the thickness of the beams and joists is too varied, and X-HSN 24 would be proposed for the joists section. To better show which pins go in which sections, our Technical Services Department can color code the roof framing plans to correspond with the different pin areas. Other than paying close attention while attaching the deck, there are not many other ways to ensure the correct pin is installed in the appropriate area.
Lisa