Red Oak Structural Properties
(Load Bearing)

Introduction
Lumber Grading for Structural Application
Yield on Re-grading
Structural Properties
Design Values for American Red Oak
Species Durability

The guidance and recommendations given in this information should always be reviewed by those using it in the light of the facts of their particular case and specialist advice should be obtained as necessary. Although every care has been taken in the preparation of this information, no liability for negligence or otherwise in relation to this work and its contents is accepted by Ove Arup and Partners Ltd or the American Hardwood Export Council.

Introduction

The visual merits of American red oak have long excited the imagination of architects who have used this species, with its fashionable colour and grain patterns, to great aesthetic effect in building projects large and small. Traditionally within Europe, the use of American red oak species has been largely limited to non-load bearing applications. But now a shift in fashion towards wood solutions coupled with a growing interest in temperate hardwood species is fuelling a desire amongst specifiers to combine structural performance with aesthetic design.

The American Hardwood Export Council teamed up with Arup Research + Development and commissioned the Building Research Establishment (BRE) in the UK to undertake testing of American red oak to determine its characteristic values for structural design. These tests uncovered some surprising data and established that red oak has the potential to be more widely used in load bearing applications.

Lumber Grading for Structural Application

Red oak exported from America to Europe is graded by reference to the rules of the National Hardwood Lumber Association (NHLA). The two grades of relevance are FAS and No.1 Common. FAS will provide boards with a minimum of 83 1/3% clear faces (free of all knots), while the No. 1 Common will provide boards with faces with a minimum of 66% clear wood (free of all knots). Unfortunately, these are appearance grades and no limits are placed on the size of knots when they occur, or on the slope of grain, the two principal parameters of any structural grading system.

To use red oak with confidence in structural applications, it is necessary to have design data which applies to material graded in accordance with a structural grading standard complying with EN 5181 (shortly to be replaced by EN 14801-12 ).

One such standard that does comply with EN 518 is BS 57563. It gives rules for visual strength grading hardwood into two grades, TH1 and TH2. The upper grade, TH1, is more appropriate to the American red oak stock, maximising the quality of the individual pieces without producing unduly low yield rates. THUS THE FOLLOWING DESIGN DATA APPLIES TO AMERICAN RED OAK PROVIDED IT BHAS BEEN RE-GRADED TO BS 5756, GRADE TH1.

Notes:
  1. EN 518 Structural timber. Grading. Requirements for visual strength grading of hardwood.
  2. EN 14081-1 Timber structures – Strength graded structural timber with rectangular cross-section.
  3. BS 5756 Specification for visual strength grading of hardwood.

Yield on Re-grading

American red oak is exported as NHLA1 grades FAS and No. 1 Common, but these need to be re-graded for structural use in according to BS 57562, grade TH1. For red oak, the approximate yield on re-grading FAS material is 80%. The material which fails to make visual strength grade TH1 is not wasted as it is still FAS under the NHLA grading rules so can be put back into stock.

Notes:
  1. NHLA National Hardwood Lumber Association
  2. BS 5756 Specification for visual strength grading of hardwood.

Structural Properties

Strength, stiffness and density properties are given for red oak in both limit state and permissible stress formats. The species fits into the strength class profile of D40 as defined in EN 3383. However, both Eurocode 51 and BS 5268-22 allow design to be carried out using properties which have been derived from testing, and this option will obviously optimise the potential of a particular species.

Table of Design Values for use with Eurocode 5 and BS 5268-2

Notes:
  1. Eurocode 5 (EN 1995-1-1) Design of timber structures. General. Common rules and rules for Building.
  2. BS 5268-2 Structural use of timber. Code of practice for permissible stress design, materials and workmanship.
  3. EN 338 Structural timber – Strength classes

Species Durability

Species EN 350-21
American red oak 4 (slightly durable)
Notes:
  1. EN 350-2 Durability of wood-based products – Natural durability of solid wood. Part 2: The natural durability and treatability of selected wood species of importance in Europe.

Further Information

For more complete information on using this structural data please refer to the AHEC technical brochure “Structural Design in American Hardwoods” which can be ordered on line free of charge.

Links to addition information: -

 



English :: French :: German :: Italian :: Spanish

© Copyright 2006-2007 AHEC Europe. All rights reserved.