Wood Structural Panels

CE A433 – Spring 2008T. Bart Quimby, P.E., Ph.D.

University of Alaska AnchorageCivil Engineering

Wood Structural Panel Uses

• Structural panels are used for a wide variety of uses including– Sheathing of roofs, floors, and walls to

• Transfer pressure loads normal to the surface to supporting framing

• Carry shear loads in structural diaphragms

– Structural Components such as• Lumber-plywood beams• Various types of panel components

– Gusset Plates– Concrete Formwork

Sheathing Applications

• See figure 8.1 from text• The required panel thickness is a

function of the loads applied normal to the surface

• Attachment of sheathing is a function of the loads in the plane of the panel (i.e. diaphragm shears)

Types of Wood Panels

• The principle types of wood panels used in timber construction include:– Plywood– Oriented Strand Board (OSB)– Waferboard– Composite panels– Structural particle board

Plywood• Made by gluing veneers together

– Plys have different names• Face• Back• Crossband• Center

– Grain direction is alternated by layer• This creates different strengths in each

principle direction

– Veneers come in different qualities • Dependant on number and types of

imperfections

Section Properties by Principle Direction

• See text figure 8.6

Face Grain

More Plywood

Plywood comes in many different thickness and plys.

Species Groups

• Species are grouped together by similar strengths.

• See text for the five plywood species groups.

Veneer Grades

• Veneers come in different levels of quality, based on imperfections.

• See text for different grade specifications.

Exposure Durability Classifications

• U.S. Product Standard PS-1 – Construction and Industrial Plywood Specification– Interior– Exterior

• APA Performance-rated panels– Exterior– Exposure 1: Interior plywood with

exterior glue– Exposure 2: Interior panels

Plywood Grades• There are a large number of grades• Most SHEATHING applications use

– C-C Exterior– C-D Exterior 1– C-C STR I– C-D STR 1

• The “STR I” grades have added strength properties and are more expensive.

• Span ratings give the maximum recommended span lengths for roof and subfloor applications– Assumes strong direction over two or more spans– Must satisfy edge support requirements– Different thickness can result in same span rating

Plywood Grade Stamps

• See examples in the text (pgs 8.15, 8.18, 8.19, 8.29)

• Also see…

From APA Website

Oriented Strand Board• Made of wood

strands or wafers directionally oriented, compressed and bonded by a resin.

• Two different surfaces

• Grade designated by Performance-based ratings and PS 2

Combined Sheathing-Siding

• T1-11 is commonly used.• See text figures

Two Layer Floor Sheathing• Two Layer System

– See text Figure 8.28– Subfloor

• The structural support for the floor

– Underlayment• Provides a smooth surface for floor• Non Structural

– Need to make sure the panel edges don’t align with adjacent layer.

– Second number is span rating when used as subfloor

Drawing from APA

One Layer Floor Sheathing

• Must have some means of connecting edges of panels so that they move together– Tongue & Groove– Blocking– Offset underlayment– Lightweight concrete– Thick wood finished flooring

Selection of Floor Sheathing

• “typical wood structural panel applications for floor sheathing are not controlled by uniform load criteria, but instead are based on deflection under concentrated loads and how the floor feels to building occupants.” (text pg 8.27)

• Can use span ratings to select the flooring• See “Guide to Panel Use” (ASD/LRFD Manual for

Engineered Wood Construction, Table M9.1-1), and Table M9.2-1 for usage and typical span ratings.

Wall Sheathing

• All edges must be blocked• See text Figure 8.16• Architectural panels can be used that

are combined sheathing and siding• Details for preventing water

infiltration are shown in text figure 8.19c

Structural Calculations

• Not normally done for sheathing applications– Use span ratings.

• The ASD/LRFD Design Manual for Engineered Wood Construction

• APA Documents: http://www.apawood.org/– Load-Span Tables for APA Structural Use

Panels– Panel Design Specification

APA Load-Span Tables

Sample Allowable Uniform Load Calculations

Should also make shear spreadsheet