Civil Engineering Reference
In-Depth Information
• “Principles of Mechanics Model for Wood Structural Panel Portal Frames.”
8
This report presents a principles of mechanics model to predict the in-plane
lateral racking strength of a wood structural panel portal frame using semi-
rigid joints. The method used accurately predicts the strength to within 5 percent
of tested portal frame assemblies.
Since the early 1970s to middle 1980s, there has been a concerted effort to utilize
built-up plywood-lumber beams in the construction of residential and commercial
structures in Australia, New Zealand, Brazil, and Europe. Field-glued composite sec-
tions were considered to be somewhat impractical due to the high fabrication require-
ments and lack of quality control. For this reason, nailed-only sections have become
more appealing. Recent research and testing in those countries have been conducted on
nail-glued and nailed-only composite beams, with a greater emphasis on nailed-only
assemblies. The objective of the tests and research was to establish a method of design-
ing nailed-only composite plywood-lumber beams, taking into account the effects of
nail slip. The testing and research conducted in those countries have been focused on
simple span beams, continuous beams, and portal frames.
14.2 Method of Analysis
The method of analysis outlined in this section applies to all moment-resisting wall
configurations. A frame wall similar to the one shown in Fig. 14.4 is broken down into
piers, headers, and/or sill sections, as they occur, similar to examples that will be pre-
sented later. Composite beam section properties are calculated using lumber flanges
and plywood or OSB sheathing web members, as detailed in Sec. 14.3. Once the section
properties are determined, they are transformed into equivalent solid rectangular wood
sections of equivalent stiffness for easy input into a computer model at their respective
neutral axis (N.A.) locations, as shown in Fig. 14.5. The resulting shears, moments, and
axial forces from the computer output are applied to the ends of the panels, as shown in
Fig. 14.6 for visual reference only. The frame members are then designed as plywood
beams with lumber flanges. The joints (panel zones) of the frame are designed as rigid
connections, which are developed to fully resist the applied moments, shears, and axial
forces. The advantages of the method are that:
• The distribution of forces is determined by a computer analysis.
• Multiple load combinations can be used, which allows a more detailed exami-
nation.
• The computer output can be used to verify the design at any point in the frame.
• All frame members and connections are designed, not just the shear capacity, tie
strap size, and hold-down anchors.
Computer Model (See Fig. 14.5)
The calculated total moments of inertia of the composite sections are converted to
equivalent solid rectangular wood beams, where the equivalent depths of the sections
are calculated by using the following equation:
12
I
d
equiv
=
x
3
b
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