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Southern Pine Design Values

  
 

 

The History
Why, Where and When
 

 

1

 

 

Small Clear Specimens             

 

  • Since the 1920’s, assigned stress values for lumber properties have been developed from data collected from small clear specimens.

 

  • In the 1960’s the lower 5% exclusion was used to develop stress ratings.

 

  • The 5% exclusion was further adjusted for species grouping, normal duration of load, safety, size, strength ratio, end use moisture content and short term load duration.

 

2

 

 

Questions On Properties           

 

  • In the mid-60’s , some allowable properties for lumber began to be questioned as full size data became available.

 

  • In 1968 ASTM D245 set tension values at 55% of bending values.

 

  • A width adjustment for stress in bending was also added.

 

 

 

3

 

 

Tension Questions           

  • In 1976 the technical advisory committee of the National Forest Products Association recommended a cooperative effort with the major rules writing agencies to review available data on tension parallel to grain.

 

  • There were indications that tensile stress values for some sizes and grades of lumber should be reduced.

 

  • In 1977 the rules writing agencies, together with the NFPA reduced the allowable stress in tension parallel to grain for wider widths of structural lumber.

 

4

 

       

       Broad Questions on Design Values

 

  • During this time there was a noticeable increase in product liability cases.
  • A Canadian study on full-size in-grade lumber indicated that design values could be 25%-30% overstated. An American study seemed to confirm this.
  • In 1977 the major grading agencies, in cooperation with the USDA Forest Products Laboratory, began to formulate the North American In-Grade Testing Program

 

 

 

  

 

5

 

 

              Implementation

 

  • The program was split into phases.
  • Phase 1 was to determine the extent of the problem by sampling 2x8 No.2 and 2x4 Stud
  • Phase 2 began in 1981 in the US and 1988 in Canada and consisted in sampling in all four regions of the major species groups. Testing included bending, tension and compression parallel to grain.
  • Phase 3 consisted of lesser species.

  

6

 

             
            Results

  • In-grade values were close to the D245 values
  • Design values for wides were found to be overstated and specific width values were published
  • SPIB developed, with assistance from the FPL, and as recommended in D1990, a resource monitoring program

 

7

 

 

    ASTM Standards

  • ASTM standards were modified as a result of the in-grade
  • Some new standards were written to document the process for future design value determination.
  • SPIB documented our specific process in “Determination of Design Values for Southern Pine”
  • The result is a detailed procedure for evaluating and developing stress rating

 

 

8

 

   

      ALSC Lumber Properties Task Group

 

  • Formed to provide ASTM D1990 Guidance
  • Produced a history of in-grade testing
  • Currently developing resource monitoring guidance for ASTM

 

  

9

 

        

         DESIGN VALUE PROCESS

 

 

  • Design Values are Determined by Regional Agencies Accredited by the ALSC
  • ASTM Standards provide the procedures
  • DV Sampling Plans are approved by the ALSC BOR after USDA-FS review
  • Test Results are certified by the ALSC-BOR after USDA-FS review

 

  

10

 

      Both ALSC & ASTM have a balance of types of members

 

  • Producers - produces or sells materials, products, systems or services
  • Users - purchases or uses materials, products, systems, or services, other than household and cannot be classified as a producer
  • Consumers - purchase products and services for household use 
  • General Interests - cannot be classified as producer, user, or consumer 

 


 

 

 

11

 

        ALSC CERTIFIED DV PUBLICATION

 

  • Design Values are Published by the Regional Agency  
  • American Wood Council publishes the Design Value in the National Design Specification as a Supplement (NDS is an ANSI Publication) 
  • Design Values are referenced in the International Building Code and local codes 
  •  Builders are required to use the applicable Building Code

 

12

 

 

       Why Revise Design Values

 

  • June 2010 SPIB was notified by a subscriber of low Fb values in testing by SBCA and a large lumber producer
  • SPIB considered this information in conjunction with trends in our annual resource monitoring
  • SPIB Board of Governors directed an expeditious investigation based on tension, bending and MOE testing of full size 2x4 No.2 lumber

 

 

13

 

 

    Initial Test Protocol

 

  • Based on In-grade Test Procedures in ASTM D1990, a consensus standard  
  • Technical Committee formed to develop a test plan 
  • Test Plan submitted to the ALSC Board of Review, with 30 days notice 
  • Test Plan approved and implemented 
  • Data reviewed by the Technical Committee 
  • SPIB Board of Governors considered all available information and submitted proposed interim design values to the ALSC BOR 30 days prior to their meeting. 

 

  

 

14

 

     

                  SAMPLE MAP

   

 

15

 


MOE and BENDING

 

  • Modulus of Elasticity is measured on edge  
  • MOR, used to develop Fb is tested edgewise 
  • Testing in Pensacola, Fl by SPIB 

 

   

16

 

       

              Tension Testing

 

  • 100,000 lb Tension Tester for Tension Parallel  
  • Timber Products Inspection did the initial 2x4 No.2 testing 
  • Testing in Pensacola, Fl by SPIB 

 

 

   

17

 

 

         Compression Testing

 

  • Timber Products Inspection is conducting the compression testing in Conyers, Ga. Wide pieces will be tested at the Forest Products Laboratory in Madison, WI  
  • Compression testing was not done on the initial 2x4 No.2  

 

18

 

 

 

 

19

 

 

 

 

20

 

 

Were all of the weakest pieces from one or two mills or regions?  

  • The 17 weakest pieces in bending came from 9 different regions and 13 different mills. 
  • The 18 weakest pieces in tension came from 8 different regions and 14 different mills 

This material is widespread and not due to isolated “low-pockets”. 

    •  
    •  

     

    21

FACTORS CONSIDERED TO MAINTAIN 1991 DV'S

  • Rings per Inch  
  • Percent Summerwood 
  • Presence or Absence of Pith  
  • Unable to maintain the 1991 DV’s without significant waste of resources  

22

 

What Has Changed

 

  • Maturing of Significant Acreage of Improved Pine  
  • Sawmill Technology 

 

23

 

The Wood We Grow Has Changed

 

24

 


25

 


 Where Are We

 

  • January 11, 2012 ALSC BOR issues decision on SYP Design Values  
  • January 18, 2012 SPIB BOG issues Supplement 9 that implements the ALSC BOR decision effective June 1, 2012 
  • Effects No.2, No.2D, No.2N, No.3, STUD, Construction, Standard, Utility, No.2 Prime of all species groups of pine, 2-4” thick, 2-4” wide 
  • ALSC-BOR has approved the Supplement 9  

26

 

 

 WHERE ARE WE GOING

Completion of testing for minimum cells for a full In-grade

  • No.2 and SS  
  • 2x4, 2x8, and 2x10 sizes 
  • Bending, Tension, Compression Parallel and MOE 
  • Almost 7,000 pieces to be tested 

Testing at SPIB Pensacola, FL and Timber Products Conyers, GA

 

27

 

 

               WHEN

 

  • Physical Testing complete late spring/early summer  
  • Staff review of data  
  • Distribution of data to Technical Committee Technical Committee Review
  • SPIB Board of Governors action to approve proposed design values   
  • Submission to ALSC-BOR 30 days prior to their meeting  
  • Decision by ALSC-BOR  
  • Publication of New Design Value Tables 

 

28

 

 

   
2013 Volume 72:


May/ June 2013

  
March/April 2013
 
Jan/Feb 2013
2012 Volume 71:

  
Nov/Dec 2012

  
Sept/Oct 2012

  
July/Aug 2012
 
May/June 2012
  
March/Apr 2012
2012 Volume 70:
 
Jan/Feb 2012
    

 

 

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