APA - IRC Allowable Design Values for OSB Wall Bracing = 175 PLF

Originally published by the following source: SBC MagazineMarch 6, 2019
by Sean Shields, with contributions by John Fredrick, Larry Wainwright and Kirk Grundahl

   

APA provided a report written for the National Institute of Building Sciences' Building Seismic Safety Council, which evaluated available IRC-compliant braced wall line test data. This data was then compiled, organized, and publicly reported.

Report to BSSC Bracing Committee

May 2007
©2007 APA – The Engineered Wood Association

The APA report states the following purpose:

A REVIEW OF LARGE SCALE WOOD STRUCTURAL PANEL BRACING TESTS

By Zeno Martin, P.E., Tom Skaggs, Ph.D., P.E., Ed Keith, P.E., Borjen Yeh, Ph.D, P.E.
APA – The Engineered Wood Association

1. OVERVIEW AND PURPOSE

This report summarizes available large scale test data for wood structural panel conventional construction wall bracing. Several 4-ft long wall tests are included, but the majority of test data is taken from tests where wall lengths are at least 12-ft. The purpose of assembling this information is to help evaluate and determine the strength of wood structural panel wall bracing.

This APA-BSSC report documents the OSB tests in a series of tables. Copied from this report, Table 1 below documents testing of wall assemblies with IRC-compliant OSB braced wall line segments. For this sampling of tested wall assemblies, representing single story walls using traditional anchor bolt restraint, OSB (i.e. wood structural panels (WSP)) provided an average ultimate lateral resistance capacity of 351 pounds per lineal foot (plf) with no interior gypsum wallboard (GWB) applied. This means that OSB has an IRC allowable design value of 175 plf (351 plf divided by 2 per Special Design Provisions Wind and Seismic (SDPWS) section 4.3.3).

Summary of test results for isolated wood structural panel wall bracing without gypsum finish.

Row
#

Description

Load at
0.5% drift

Peak Load

Total
Length of Wall

Total Length of Bracing

Gyp

Bracing

Test Protocol

Segment Width

Test #
in Ref.

Reference

(plf)

(plf)

(ft)

(ft)

--

--

--

(ft)

--

 

 

Average =

187

351

 Allowable lateral resistance design capacity is 175 plf.

Minimum =

115

180

Maximum =

307

582

Table 1: Large scale wall bracing tests APA-BSSC report. See appendix B for the full table.

Additionally, the APA-BSSC report shows that IRC-compliant OSB braced wall lines with GWB attached, in accordance with the IRC (i.e. screws spaced 16:16), provides an average ultimate lateral resistance capacity of 383 plf. As can be seen in Table 2 below, OSB with GWB has an IRC allowable design value of 192 plf (383 plf divided by 2 per SDPWS).

Summary of test results for isolated wood structural panel wall bracing with gypsum finish.

Row
#

Description Load at
0.5% drift
Peak
Load
Total
Length of
Wall
Total
Length of
Bracing
Gyp Bracing Test
Protocol
Segment
Width
Test #
in Ref.
Reference
  (plf) (plf) (ft) (ft) -- -- -- (ft) --  
Average = 255 383 Allowable lateral resistance design capacity is 192 plf.

Table 2: Isolated bracing with GWB APA-BSSC Report. See appendix C for the full table.

The APA-BSSC report of IRC-compliant braced wall line assembly tests suggest that the application of GWB is only adding 32 plf (383-351= 32).

The Structural Building Component Research Institute (SBCRI) also undertook IRC code compliant OSB braced wall line testing without interior GWB. This testing yielded the results¹ found in Table 3 below.

Full-Scale Monotonic Lateral Wall Testing in a 12' x 30' Building: 3/8" WSP 6' from End Wall, No Interior GWB (with Load Path to the Foundation) 2 1/2" x .131 Nail 6:12 371

Allowable lateral resistance design capacity is 187 plf.

Note  [1] These are proprietary tests and proprietary intellectual property, which is being provided herein to increase decision-making knowledge regarding IRC-compliant braced wall line performance

374

Table 3: SBCRI testing of IRC Compliant (i.e. anchor bolt hold downs) OSB Braced Wall Lines. See appendix D for full table.

In the IRC code compliant OSB braced wall testing, the SBCRI test minimum was 334 plf and averaged 374 plf. This testing confirms the APA-BSSC report generated OSB capacity of 350 plf. Please see appendix A for photos of the SBCRI testing.

Table 4 below provides data from SBCRI testing of IRC-compliant OSB braced wall line with interior GWB installed. The OSB testing yielded a 102 and 141 plf contribution for the GWB when screws are spaced 16:16. Testing was also performed on proprietary engineered fiberboard sheathing where the GWB contribution was 110 plf. SBCRI testing confirms the APA-BSSC report generated capacity of 383 plf when OSB has interior GWB attached.

30 foot Wall Experimental Testing to Determine Contribution of 1/2" GWB 16:16 PLF on a 30' basis to define GWB contribution Contribution of GWB
7/16" 8d 6"/12" IRC Test 4_1 WSP@ each corner; full roof dead; NO wall gyp; ultimate ave of two walls; anchor bolts 114  
7/16" 8d 6"/12" IRC Test 4_1 2- WSP@ each corner; full roof dead; 30' wall gyp; ultimate ave of two walls; anchor bolts 215 102
7/16" 8d 6"/12" IRC Test 2; WSP 2 @ 6' from corner; full roof dead; NO wall gyp; ultimate ave of two walls; anchor bolts 110  
7/16" 8d 6"/12" IRC Test 2; WSP 2 @ 6' from corner; full roof dead; 30' wall gyp; ultimate ave of two walls; anchor bolts 251 141

Table 4: SBCRI testing of IRC Compliant (i.e. anchor bolt hold downs) OSB Braced Wall Lines with Interior GWB (screws 16:16)

Given the testing performed, it is reasonable for SBCRI to use an interior GWB contribution of 100 plf, when attached using screws spaced 16:16. This GWB addition to OSB is for code compliant IRC braced wall lines where OSB is applied as isolated panels (i.e. non-continuous 4x8 sheets using anchor bolts as hold downs). 

Given the foregoing set of undisputed facts, IRC code compliant walls are using a systems effect factor (i.e. a "standard factor for equivalency") of roughly 1.8 for walls sheathed with OSB only. (600/334 using the minimum OSB performance to be conservative is 1.8).

Additionally, IRC code compliant OSB walls with interior GWB attached are using a "standard factor for equivalency" of roughly 2.19 (840/383) if APA-BSSC report generated numbers are used and 1.8 (840/450) for walls tested by SBCRI. It is an SBCRI opinion that 450 plf most accurately reflects the lateral resistance for a braced wall line sheathed with OSB and interior GWB (840/434 as the minimum OSB performance is 1.9).

For proprietary products that compete with OSB sheathed walls, it is critical to know the "standard factor for equivalency" as defined by APA. SBCA created an IRC code change proposal to reflect APA and SBCRI testing. This 2013 code change proposal, which provides what SBCRI believes are reasonable “standard factors for equivalency,” is provided in Table 5 below:

This item is on agenda for individual consideration because a public comment was submitted.

Public Comment:

Larry Wainright, Qualtim, representing Structural Building Components Association, requests Approval as Modified by this Public Comment.

Modify the proposal as follows:

TABLE R602.10.4.4
SIMPLIFIED SHEAR VALUES FOR WIND LOADING BRACED WALL PANELS

Sheathing
Material
Bottom plate connection to foundation Fastener Fastener Spacing Any Species Stud Framing
Tested Capacity System Effects Factor IRC Lateral Design Capacity
3/8", 7/16" or 15/32" WSP @16" and 24" o.c framing Anchor bolts in accordance with code requirements 6d (2" x 0.113" nails) or 8d (2 1/2 x 0.131") 6:12 335 350 1.80 600
3/8", 7/16" or 15/32" WSP @16" and 24" o.c framing (with 1/2" gypsum on interior face of wall. Anchor bolts in accordance with code requirements 6d (2" x 0.113" nails) or 8d (2 1/2 x 0.131") nails and Types S or W drywall screws 6:12 WSP & 16:16 for GWB 465 450 1.80 840

a. The lateral design capacity of braced wall panels is based on full scale wall assembly tests using the minimum restraint provisions of the IRC, further adjusted by the partial restraint/systems effect factor.

Note: the change from 335 to 350 plf for the walls without GWB changed the system effect factor to 1.7 and similarly for walls with GWB so that a common “standard equivalency factor” could be used. This change accurately reflected tested performance well.

Table 5: Proposed 2013 IRC Code Change Proposal table showing “standard equivalency factors”, which APA acknowledges exist in APA’s bracing spectrum analysis which can be read in the APA-BSSC report.

APA, the American Wood Council (AWC) and NAHB opposed this code change proposal, and the IRC committee denied it.  The  APA-BSSC report stands undisputed by APA and confirmed by SBCRI testing, which means that the testing is correct. This also means the IRC still has “standard factors for equivalency” embedded in the building code and codified into law. However, these "standard factors for equivalency" are not explicitly defined by the IRC, instead they are implicitly used.

On January 3, 2013, SBCA attended a meeting with APA to address OSB design values and “standard factors for equivalency,” which clearly exist in the law. Mr. Ed Elias, president of APA attended the meeting and responded with via letter to SBCA, where he discusses the concept of “standard factors” for “product equivalency.” Specifically, he wrote:

"APA staff has reviewed the information that was shared with us and we have the following comments and concerns:……….

We believe that a major goal for the SBCA position is to provide a cost-effective engineering solution to their membership and as such this goal serves the SBCA membership well. However, by establishing standard factors in which product equivalency or system performance are applied generically, an unintended consequence may be that non-wood products (e.g. foam sheathing) gain an advantage and supplant traditional OSB market share.

This is not in our Association member’s best interests."

…………

SBCA fully understands APA’s desire to have a competitive advantage codified into the law (i.e. IRC). All sheathing manufacturers would like this to be the case for their products.

SBCA has provided, and will continue to provide transparency to the market with respect to “standard factors of equivalency.” By law, these factors can be used to establish IRC compliant OSB equivalency for any braced wall line product including OSB.

Knowledge of the APA-BSSC report test data, and how OSB braced wall line lateral resistance is codified, provides code officials and manufacturers with the knowledge and tools needed to use IRC “standard factors of equivalency.” The goal of any free, fair and competitive market is to use accurate design values and any known “standard factors of equivalency” so that a fair playing field is provided. In their 2007 report to the BSSC, APA acknowledges this should be done through their "bracing spectrum" concept generated through their own analysis.  

SBC Magazine appreciates your input, and continually seeks to improve the value it provides to the market. If you have any comments or corrections on this article, please email us and we can publish your comments.

Related Articles and Information

OSB as a Raw Material (background information on OSB testing and engineering analysis)

Appendix A

Photos of SBCRI OSB Testing

Appendix B

Table 1: Large scale wall bracing tests- APA- BSSC Report

Summary of test results for isolated wood structural panel wall bracing without gypsum finish.

Row
#

Description

Load at
0.5% drift

Peak Load

Total
Length of Wall

Total Length of Bracing

Gyp

Bracing

Test Protocol

Segment Width

Test #
in Ref.

Reference

(plf)

(plf)

(ft)

(ft)

--

--

--

(ft)

--

 

25

4-ft wall isolated bracing segment

131

180

4

4

No

Isolated

mono.

4

718&719

Simpson, 2007a

30

20-ft wall isolated bracing segments, "Cabo"

136

204

20

8

No

Isolated

mono.

4

713&714

Simpson, 2007d

19

4-ft wall isolated bracing segment

210

225

4

4

No

Isolated

SPD

4

7

APA, 2006

31

20-ft wall isolated bracing, "Cabo" with 2x10 rim joist

158

238

20

8

No

Isolated

mono.

4

721&722

Simpson, 2007d

43

3D - NW: Cabo, NE: Cabo, SW: Cabo, SE: Cabo (+45)

177

256

20

32

No

Isolated

mono.

4

2006744

Simpson, 2007o

47

3D - NW: Cabo, NE: Cabo, SW: Cabo, SE: Cabo (-45)

168

265

20

32

No

Isolated

mono.

4

2006732

Simpson, 2007s

28

20-ft wall isolated bracing, "IRC Center"

115

294

20

4

No

Isolated

mono.

4

702&709

Simpson, 2007c

40

3D - W: Cabo, E: Cabo, N: Cabo, S: Cabo (90)

222

363

20

16

No

Isolated

mono.

4

2006715

Simpson, 2007l

39

3D - W: IRC Center, E: IRC Center, N: IRC Center, S: IRC Center (90)

181

394

20

8

No

Isolated

mono.

4

2006700

Simpson, 2007k

32

20-ft isolated bracing segment "IRC Side"

147

401

20

4

No

Isolated

mono.

4

710&711

Simpson, 2007e

46

3D - NW: IRC Center, NE: IRC Center, SW: IRC Center, SE: IRC Center (+45)

177

420

20

16

No

Isolated

mono.

4

2007001

Simpson, 2007r

29

20-ft wall isolated bracing, "IRC Center" with 2x10 rim joist

172

467

20

4

No

Isolated

mono.

4

723&724

Simpson, 2007c

34

3D - W: Cabo, E: Cabo, N: Cabo, S: Cabo (0)

281

469

20

16

No

Isolated

mono.

4

2006716

Simpson, 2007f

38

3D - W: IRC Center, E: IRC Center, N: IRC Center, S: IRC Center (0)

219

513

20

8

No

Isolated

mono.

4

2006703

Simpson, 2007j

33

20-ft isolated bracing "IRC Side" with 2x10 rim joist

307

582

20

4

No

Isolated

mono.

4

726&727

Simpson, 2007e

 

Average =

187

351

 Allowable lateral resistance design capacity is 175 plf.

Minimum =

115

180

Maximum =

307

582

Appendix C

Table 2: APA BSSC report- Isolated bracing with GWB.

Summary of test results for isolated wood structural panel wall bracing with gypsum finish.

Row
#

Description Load at
0.5% drift
Peak
Load
Total
Length of
Wall
Total
Length of
Bracing
Gyp Bracing Test
Protocol
Segment
Width
Test #
in Ref.
Reference
  (plf) (plf) (ft) (ft) -- -- -- (ft) --  
3 40-ft wall with isolated bracing 237 366 40 12 Yes Isolated mono. 4 E Dolan and Heine, 1997a
6 40-ft wall with isolated bracing 273 400 40 12 Yes Isolated SPD 4 E Dolan and Heine, 1997b
Average = 255 383 Allowable lateral resistance design capacity is 192 plf.

Appendix D

Table 3: SBCRI testing of IRC Compliant (i.e. anchor bolt hold downs) OSB Braced Wall Lines

Full-Scale Monotonic Lateral Wall Testing in a 12' x 30' Building: 3/8" WSP 6' from End Wall, No Interior GWB (with Load Path to the Foundation) 2 1/2" x .131 Nail 6:12 371
Full-Scale Monotonic Lateral Wall Testing in a 12' x 30' Building: 3/8" WSP 6' from End Wall, No Interior GWB (with Load Path to the Foundation) 2 3/8" x .113 Nail 6:12 391
Full-Scale Monotonic Lateral Wall Testing in a 12' x 30' Building: 3/8" WSP 6' from End Wall, No Interior GWB (with Load Path to the Foundation) 2 3/8" x .113 Nail 6:12 402
Full-Scale Monotonic Lateral Wall Testing in a 12' x 30' Building: 3/8" WSP 6' from End Wall, No Interior GWB (with Load Path to the Foundation) 2 3/8" x .113 Nail 6:12 339
Full-Scale Monotonic Lateral Wall Testing in a 12' x 30' Building: 3/8" WSP 6' from End Wall, No Interior GWB (with Load Path to the Foundation) 2 3/8" x .113 Nail 6:12 407
Full-Scale Monotonic Lateral Wall Testing in a 12' x 30' Building: 7/16" WSP 6' from End Wall, No Interior GWB (with Load Path to the Foundation) 2 1/2" x .131 Nail 6:12 334
Full-Scale Monotonic Lateral Wall Testing in a 12' x 30' Building: 7/16" WSP 6' from End Wall, No Interior GWB (with Load Path to the Foundation) 2 1/2" x .131 Nail 6:12 414
Full-Scale Monotonic Lateral Wall Testing in a 12' x 30' Building: 7/16" WSP 6' from End Wall, No Interior GWB (with Load Path to the Foundation) 2 1/2" x .131 Nail 6:12 410
Full-Scale Monotonic Lateral Wall Testing in a 12' x 30' Building: 7/16" WSP 6' from End Wall, No Interior GWB (with Load Path to the Foundation) 2 1/2" x .131 Nail 6:12 330
Full-Scale Monotonic Lateral Wall Testing in a 12' x 30' Building: Two 3/8" WSP Panels 6' from End Wall, No Interior GWB (with Load Path to the Foundation) 2 3/8" x .113 Nail 6:12 356
Full-Scale Cyclic Lateral Wall Testing, 3/8" OSB 4' From Corner, No Interior GWB, w/o Hold-Down 2 3/8" x .113 Nail 6:12 316
Full-Scale Cyclic Lateral Wall Testing, 3/8" OSB 4' From Corner, No Interior GWB, w/o Hold-Down 2 3/8" x .113 Galvanized Nail 6:12 321

Allowable lateral resistance design capacity is 187 plf.

Note  [1] These are proprietary tests and proprietary intellectual property, which is being provided herein to increase decision-making knowledge regarding IRC compliant braced wall line performance

374