Over the past few years, codes, wood values, and column sizes have evolved significantly and Perma-Column, Inc. has stayed in step every bit of the way. All these change have been incorporated into a new Perma-Column Design and Use Guide authored by Brent Leatherman P.E. and Dimitry Reznik, P.E. of Timber Tech Engineering, Inc.
The updated design guide is intended to be used by post-frame building engineers and designers as a companion document to the test results document for Perma-Columns by David R. Bohnhoff Ph.D. The new Perma-Column Design and Use Guide includes code updated from the American Concrete Institute (ACI), The American Institute of Steel Construction (AISC), and National Design Specification for Wood Construction (NDS).
Structural analysis was performed using both the load and resistance factor (LRFD) and the allowable stress/strength design (ASD) methodologies. This was done so the laboratory results from the Perma-Column Test Report, which is based on LRFD, could be used, while also expressing the expected column performance in terms of maximum allowable capacity as is customary in the wood industry.
A design chart is presented for the Perma-Column assemblies with varying heights and boundary conditions (see Table 7.1). The design limitations and failure modes of each Perma-Column assembly are listed. An example is provided showing a straight forward design approach, which can be applied to all Perma-Column assemblies.
Note in Table 7.1, a standard 3 ply x 6” #1 mechanically laminated column is capable of supporting 17,400 lbs of vertical load, but connect it to a Perma-Column, and it will support 24,500 lbs of vertical load at 12’ interior clearance under the same boundary conditions. This represents a 41% increase in vertical capacity! The new PC8500GL for a 5 ply x 8” Glulam column can hold a whopping 41,700 lbs at 20’ interior clearance with a 90 mph wind pushing on the building. Similar load capacity increases are observed in posts, nail-lam and glu-lam column assemblies. The increase in load capacity offers economy and value by extending the capability of smaller columns.
Each Perma-Column component can be modeled using a structural analog with properties corresponding to the results of the laboratory testing, and can be used to simulate the Perma-Column performance in post-frame buildings of various spans and heights. The Design Guide contains the necessary tools and assumptions needed to create a structural model.
The calculations used to produce the design chart indicate that the Perma-Column assemblies are limited primarily by overall deflection, and by the strength of the laminated wood members. There are several foundation detail options including concrete collars, steel uplift angles, and foundation extenders that can be used with a Perma-Column to achieve adequate resistance for lateral, gravity and uplift loads for most applications.
The Perma-Column assemblies perform significantly better than standard mechanically laminated wood columns under the same boundary conditions primarily because no wet service reduction is required for the concrete component, and the maximum bending moment is resisted by the concrete portion below grade. The Perma-Column is a permanent foundation solution for the post-frame building market.
The new Perma-Column Design and Use Guide can be downloaded from https://www.permacolumn.com/pc-design-guide.pdf. You may also receive an e-copy by requesting one at sales@permacolumn.com.