You may have heard rumors that it was coming, and yes, they are true. ANSI/TPI 1-2007 is now in the final approval stages and is soon to be published. If you’ve been in the business for a while, you probably remember the drastic changes between TPI-1998 and TPI-2002. Have no fear, the changes in the new code are not major and will not leave you running for the hills. For most of you, it will be awhile before you are required to comply with the new code, but it is good to develop a feel for what is coming.
When the ANSI/TPI Project Committee set out to create the new code, they wanted to incorporate clarity wherever possible. They also wanted to update the code to work together with the International Building Code and International Residential code. To accomplish this, chapter two had to be completely rewritten.
Chapter two of the new TPI-2007 deals solely with the responsibilities in the design and application of metal plate connected wood trusses. This chapter starts off with definitions of various references (such as BCSI) and people involved in the design, manufacturing, and installation of trusses. Chapter 2 then breaks down different professional responsibilities for buildings that have a Registered Design Professional and for buildings that do not have a Registered Design Professional. Perhaps one of the bigger changes with responsibilities lies in the fact that TPI-2007 will now reference the appropriate BCSI detail with regards to bracing. One new requirement dealing with bracing is involved in cases with a 60 foot or greater clear span truss. Trusses with this great of clear span shall require a Registered Design Professional to design both temporary and permanent truss bracing. The owner of the building is responsible for making sure that these special cases are inspected by a Registered Design Professional for their temporary and permanent bracing. A clearer delineation of responsibilities helps all parties understand their respective roles and makes it less likely that anyone in the process will attempt to place inappropriate responsibilities on component manufacturers.
Chapter three, “Quality Criteria for the Manufacture of Metal Plate Connected Wood Trusses”, has a few changes which intend to simplify quality control and plate inspection methods. Basically, joints chosen for quality control inspection shall be inspected with a plate placement diagram (see Figure 1 below) that incorporates the use of polygons for checking plate center locations. Should the joint fail this inspection, the tooth count method of inspection shall be performed.
Another notable change is the exclusion of truss installation tolerances (truss bow or out of plumb). It was decided that truss installation is not a design consideration and should be left up to the appropriate BCSI document. Changes have also been made to allow for higher bearing perpendicular to grain values given various circumstances.
New compression member buckling calculations should allow for webs to carry more load before requiring a lateral restraint/brace. Other changes that deal with the computations of plate and lumber interaction have been made to provide for a more accurate design of metal plate connected wood trusses. These changes will take place “under the hood” in the software and should not have a drastic effect on truss designs.
Overall, the new TPI-2007 is nothing to be scared of. Clarifications have been made to define different people’s responsibilities, the plate inspection process has been simplified, and design value computations have been modified to model more closely real life conditions.