Have you ever wondered what an L/360 or L/480 deflection limit feels like? Specifying floors with adequate floor performance (i.e., vibration) has challenged designers for many years. Builders and framing contractors want predictable costs with no callbacks. Homeowners want floors that meet their expectations. What most customers really want to know is “how is my floor going to feel” and “which is the most cost effective system”.
Weyerhaeuser’s solution? TJ-Pro™Rating.
What is the TJ-Pro Rating System?
The TJ-Pro Rating system is a sophisticated computer model designed to predict floor performance by assigning the floor performance a numerical value. Rating values typically range from 25 to 65 points; the higher the points, the more customers will be satisfied with the floor performance (see Figure 1 on right).
TJ-Pro Rating system is a robust analytical model based on extensive laboratory research and more than one million installations. The TJ-Pro Ratings give the designer a tool to predict the floor performance and evaluate the relationship between the cost and “feel” of any given Trus Joist® engineered wood floor system.
What Effects Floor Performance and the TJ-Pro Rating Value
The TJ-Pro Ratings are dependent upon the floor system assembly and components such as TJI® joist series and depth, member span, support conditions, on center spacing, thickness of the subfloor, ceiling, and partitions. Since the TJ-Pro Rating system is available in Forte® and Javelin® software, the designer can model various floor configurations to adjust the performance rating and see how system costs are affected. In many cases, the TJ-Pro Ratings will offer a system that improves performance while actually reducing cost.
The following example compares two similar floor systems with different assembly components to illustrate the floor performance difference:
Some of the best ways to economically improved floor performance is using a thicker deck, deeper joist and directly applying the ceiling membrane to the TJI® Joist. Although floor performance is highly subjective and selecting an appropriate rating level cannot guarantee 100% satisfaction, the TJ-Pro™ Rating System enables the designer to select an approximate level of acceptability.
For more detailed information regarding the effects of the floor assembly components on floor performance, see Weyerhaeuser Technical Bulletin TB-104.
Application of TJ-Pro Rating
TJ-Pro® Ratings give the designer a tool to have a pro-active approach to floor designs. Trying to stiffen a floor that a homeowner is unhappy with once the home is already built is costly and virtually impossible without the addition of beams or additional joists. Taking floor performance into account from the design phase is a much better option. Areas such as open kitchens and great rooms are often the causes of concern. For example if a great room is framed with both long and short span joists, the homeowner is more likely to notice the difference in the deflection in the longer span as he or she walks across the floor. Matching the floor performance ratings in these high traffic areas will help minimize the difference in the feel of the floor.
While the software can’t model every floor assembly, it does give the designer a good understanding of how floor assembly components can help or hurt the floor performance. For example, while a poured concrete topping can help the performance in short spans, in longer spans, the TJ-Pro Rating is actually reduced due to the difficulty in dampening the vibration of the added mass, thus causing one the need to compensate in other ways to get the floor rating back up to the level desired.
Also, protect your design of a floor system by including the TJ-Pro Rating number in your specification along with joist series, depth, and L over deflection limits. Add a sentence such as “When applicable, floor performance of alternate shall be substantiated as equivalent to TJ-Pro Rating of _____” to your general notes sheet.
A sample Trus Joist Product Specification General Notes word document is available at: http://www.woodbywy.com/document/as-tjgn/
For more information, see page 2 of the TJI® Specifiers Guide, our Fine Tune Your Floor brochure, or contact your Trus Joist Representative.