March 21, 2011
TO:
PARTIES INTERESTED IN PIN-CONNECTED OPEN-WEB
TRUSSES WITH WOOD CHORDS AND TUBULAR OR
ANGULAR STEEL WEBS
SUBJECT: Revisions to the Acceptance Criteria for Pin-connected Open-web
Trusses with Wood Chords and Tubular or Angular Steel Webs,
Subject AC306-0211-R5 (JS/RK)
Dear Colleague:
Enclosed is a copy of the subject revised acceptance criteria approved by the
ICC-ES Evaluation Committee on February 10, 2011, effective March 1, 2010.
The approved revisions to AC306 clarify testing and analysis procedures for pinconnected open-web trusses and their components.
Revisions were approved as described in the ICC-ES staff letter dated December
29, 2010, (available at http://www.icc-es.org/Criteria_Development/1102pre/10_AC306.pdf), with modifications as noted in the staff memo dated February
3, 2011, (available at http://www.icc-es.org/Criteria_Development/1102pre/Memos/10_AC306_Memo.pdf). The following additional modifications were
approved at the hearings:
1. The revision to Section C4.1 as noted in the staff memo dated February 3,
2011 – effectively limiting the applicable load duration factor to CD=1.33 under
Method A – was stricken.
2. The words “or angular” were added after “tubular” in the first sentence of
Section 1.1.
3. References to UL 263-03 have been added to Sections 1.3 and 4.7, as an
allowable alternative to testing in accordance with ASTM E 119.
ICC-ES evaluation reports issued on or after the effective date noted above, both
new reports and conversions of legacy reports, must comply with this criteria if
they fall within its scope.
AC306-0211-R5
2
If you have any questions, please contact Jason V. Smart, Senior Evaluation
Specialist, at (800) 423-6587, extension 5692. You may also reach us by e-mail
at es@icc-es.org.
Yours very truly,
Gary G. Nichols, P.E., SECB
Vice President
GGN/raf
Enclosure
cc: Evaluation Committee
www.icc-es.org | (800) 423-6587 | (562) 699-0543
A Subsidiary of the International Code Council ®
ACCEPTANCE CRITERIA FOR PIN-CONNECTED OPEN-WEB
TRUSSES WITH WOOD CHORDS AND TUBULAR OR ANGULAR
STEEL WEBS
AC306
Approved February 2011
Effective March 1, 2011
Previously approved April 2007, February 2006
PREFACE
Evaluation reports issued by ICC Evaluation Service, LLC (ICC-ES), are based upon performance features of the
International family of codes and other widely adopted code families, including the Uniform Codes, the BOCA National
Codes, and the SBCCI Standard Codes. Section 104.11 of the International Building Code® reads as follows:
The provisions of this code are not intended to prevent the installation of any materials or to
prohibit any design or method of construction not specifically prescribed by this code, provided
that any such alternative has been approved. An alternative material, design or method of
construction shall be approved where the building official finds that the proposed design is
satisfactory and complies with the intent of the provisions of this code, and that the material,
method or work offered is, for the purpose intended, at least the equivalent of that prescribed in
this code in quality, strength, effectiveness, fire resistance, durability and safety.
Similar provisions are contained in the Uniform Codes, the National Codes, and the Standard Codes.
This acceptance criteria has been issued to provide all interested parties with guidelines for demonstrating
compliance with performance features of the applicable code(s) referenced in the acceptance criteria. The criteria was
developed and adopted following public hearings conducted by the ICC-ES Evaluation Committee, and is effective on
the date shown above. All reports issued or reissued on or after the effective date must comply with this criteria, while
reports issued prior to this date may be in compliance with this criteria or with the previous edition. If the criteria is an
updated version from the previous edition, a solid vertical line (|) in the margin within the criteria indicates a technical
change, addition, or deletion from the previous edition. A deletion indicator (→) is provided in the margin where a
paragraph has been deleted if the deletion involved a technical change. This criteria may be further revised as the need
dictates.
ICC-ES may consider alternate criteria, provided the report applicant submits valid data demonstrating that the
alternate criteria are at least equivalent to the criteria proposed in this document, and otherwise meet the applicable
performance requirements of the codes. Notwithstanding that a product, material, or type or method of construction
meets the requirements of the criteria proposed in this document, or that it can be demonstrated that valid alternate
criteria are equivalent to the criteria in this document and otherwise meet the applicable performance requirements of
the codes, ICC-ES retains the right to refuse to issue or renew an evaluation report, if the product, material, or type or
method of construction is such that either unusual care with its installation or use must be exercised for satisfactory
performance, or malfunctioning is apt to cause unreasonable property damage or personal injury or sickness relative
to the benefits to be achieved by the use of the product, material, or type or method of construction.
Acceptance criteria are developed for use solely by ICC-ES for purposes of issuing ICC-ES evaluation reports.
Copyright © 2011
ACCEPTANCE CRITERIA FOR PIN-CONNECTED OPEN-WEB
TRUSSES WITH WOOD CHORDS AND TUBULAR OR ANGULAR
STEEL WEBS (AC306)
1.0
1.3.12 ASTM D 5055-05, Specification for Establishing
and Monitoring Structural Capacities of Prefabricated Wood
I-Joists, ASTM International.
INTRODUCTION
1.1 Purpose: The purpose of this criteria is to establish
minimum requirements for recognition of pin-connected
open-web trusses with wood chords and tubular or angular
steel webs in ICC Evaluation Service, LLC (ICC-ES)
evaluation reports under the 2009 and 2006 International
®
Building Code (IBC), the 2009 and 2006 International
®
®
Residential Code (IRC), the BOCA National Building
®
Code/1999 (BNBC), the 1999 Standard Building Code
(SBC), and the 1997 Uniform Building Code™ (UBC).
1.3.13 ASTM D 5456-05a, Specification for Evaluation
of Structural Composite Lumber Products, ASTM
International.
1.3.14 ANSI/AF&PA NDS National Design Specification
(NDS) for Wood Construction, 2005 edition, American
Forest and Paper Association.
1.3.15 AISI S100-07, North American Specification for
the Design of Cold-formed Steel Structural Members,
American Iron and Steel Institute.
The reason for the development of this criteria is to
provide information in regard to a combined analytical and
empirical approach to qualify the trusses, since the current
codes do not provide such information.
1.3.16 UL 263-03, Standard for Fire Test of Building
Construction and Materials, Underwriters Laboratories Inc.
1.2 Scope: This acceptance criteria applies to
proprietary pin-connected open-web trusses with wood
chords, consisting of sawn lumber or other wood-based
material, cold-formed tubular or angular steel webs, steel
pins and bearing hardware (e.g., bearing clips), used as
structural members. The chord members are continuous, or
are fabricated with finger joints, or proprietary connections,
as required by design. The steel web members are
fabricated from flat coil stock which is cold-rolled to form the
tube or angle member and then die-stamped to the lengths
required by design. The web members are pin-connected to
the chord members. The trusses are used as floor or roof
framing members.
1.3
2.0
2.1
®
1.3.2 2009 and 2006 International Residential Code
(IRC), International Code Council.
®
®
1.3.3
BOCA National Building Code/1999 (BNBC).
1.3.4
1999 Standard Building Code (SBC).
1.3.5
1997 Uniform Building Code™ (UBC).
General Information:
2.1.1 Product Description: The top and bottom
chords consist of visually graded or machine stress rated
(MSR) sawn lumber, or structural wood-based lumber
complying with the ICC-ES Acceptance Criteria for
Structural Wood-based Products (AC47) and recognized in
a current ICC-ES evaluation report. Chord members are of
either single-chord or double-chord configuration. The
minimum thickness of top and bottom chord members is a
nominal 2 inches (51 mm). Web members consist of coldformed steel tubing or angles having various steel
thicknesses and sizes, which are die-stamped to the lengths
required by design, with a flattened end profile that is
punched or drilled with the proper hole size. The web
members are connected to the chord members with steel
pins. The trusses are connected to bearing supports through
proprietary bearing hardware (bearing clips), connected to
the trusses at either the top or bottom chord locations, in
order to transfer bearing loads from the truss bearing pins to
the supports, as required by design. The trusses are
manufactured in either parallel chord, tapered chord (single
slope), pitched chord (double slope), or other shapes with
and without cantilevers, as needed to fit the end use. The
chord members, steel webs, steel pins and bearing
hardware are as specified in the manufacturer’s approved
quality control manual and manufacturing standard. The
proprietary trusses evaluated as per this acceptance criteria
shall be recognized in a current ICC-ES evaluation report.
Codes and Referenced Standards:
1.3.1 2009 and 2006 International Building Code
(IBC), International Code Council.
BASIC INFORMATION
©
1.3.6 ASTM D 2559-10, Specification for Adhesives
for Structural Laminated Wood Products for Use Under
Exterior (Wet Use) Exposure Conditions, ASTM
International.
1.3.7 ASTM E 73-83 (2007), Practice for Static Load
Testing of Truss Assemblies, ASTM International.
1.3.10 ASTM D 4442-07, Test Method for Direct
Moisture Content Measurements of Wood and Wood-Base
Materials, ASTM International.
2.1.2 Installation
Instructions:
Installation
instructions, truss design drawings and truss placement
diagrams shall accompany the product to the final jobsite.
The instructions shall include any special instructions
required for the product, as well as weather protection and
handling requirements. Where attachment requirements,
lateral support details, framing details and bearing or
connection requirements are not adequately covered by
general notes, standard details and charts shall be included
with the installation instructions, or specific job drawings
shall cover these requirements.
1.3.11 ASTM D 4444-08, Standard Test Method for
Laboratory Standardization and Calibration of Hand-Held
Moisture Meters, ASTM International.
2.1.3 Identification: The trusses shall be clearly
identified by the evaluation report number, product name,
company name, plant location or identifier, inspection
1.3.8 ASTM E 119-07, Test Method for Fire Tests of
Building Construction and Materials, ASTM International.
e1
1.3.9 ASTM D 2395-07a , Test Method for Specific
Gravity of Wood and Wood-Based Materials, ASTM
International.
2
ACCEPTANCE CRITERIA FOR PIN-CONNECTED OPEN-WEB TRUSSES WITH
WOOD CHORDS AND TUBULAR OR ANGULAR STEEL WEBS (AC306)
bearing deformation around the pin hole, the test results
derived under Sections 3.3.1(a) and 3.3.2(a) are permitted
to be combined for the purposes of determining R.]
agency name or logo, and a means of establishing the date
of manufacture.
2.2 Testing Laboratories: Testing Laboratories shall
comply with Section 2.0 of the ICC-ES Acceptance Criteria
for Test Reports (AC85) and Section 4.2 of the ICC-ES
Rules of Procedure for Evaluation Reports.
2.3
b. The allowable compression load based on
analysis of the web member’s pinned-end connection
configuration, in accordance with AISI S100 Section E3.3.2.
c. In cases where the evaluation report will specify
maximum allowable web lengths corresponding to allowable
web compression design values, the allowable axial
compression strength calculated in accordance with AISI
S100 Section C4.1. (Note: If the web members are attached
to the pin connections in such a manner that the resultant
compressive load on the member is not applied directly
through the centroid of the effective section, the allowable
compressive strength shall be calculated in accordance with
AISI S100 Section C5.2.1.).
Test Reports: Test reports shall comply with AC85.
2.4 Product Sampling: Product sampling for tests
under this criteria shall be in accordance with Sections 3.1
and 3.3 of AC85. Specimens for qualification testing shall be
representative of production.
3.0
TEST AND PERFORMANCE REQUIREMENTS
3.1 General: Testing and analysis shall be performed in
accordance with Sections 3.2 through 3.8 for trusses and
their components. The test program and analytical approach
shall be approved by ICC-ES prior to the commencement of
any testing. Calculations shall be sealed by a registered
design professional.
For calculations in accordance with AISI S100
Section C4.1, the effective length factor, K, shall be taken as
1.0. The laterally unbraced length, L, shall be taken as the
distance from centerline to centerline of the pin holes in the
web member. For cases where the evaluation report will not
specify maximum allowable web lengths corresponding to
the allowable web compression design values, see Section
6.0 of this criteria.
3.2 Chord Members: Qualification and development of
design properties for chord members shall be in accordance
with ASTM D 5055 Sections 6.3.1.2 through 6.3.1.6, or
ASTM D 5456. An analysis of the stresses within chord
members at pin holes and other critical locations shall be
performed in accordance with NDS Section 10.1.2. Where
chord members contain finger joints, joint qualification shall
be performed in accordance with Section 6.4 of ASTM D
5055.
3.4 Pin Connections: Allowable lateral loads for pin
connections shall be derived in accordance with Appendix
C.
3.5 End Reactions: Allowable truss end reaction values
for proprietary bearing hardware shall be derived in
accordance with Appendix D.
3.3 Web Members: For qualification of web member
design values, testing of web members shall be in
accordance with Appendix A. Test values from Appendix A
shall be adjusted in accordance with Appendix B. Also, web
members shall be analyzed for tension and compression in
accordance with AISI S100. The steel used to fabricate test
samples shall be within the tolerance limits specified within
the manufacturer’s quality documentation.
Allowable
tension and compression design values for web members
shall be derived in accordance with Sections 3.3.1 and
3.3.2, respectively.
3.6 Confirmatory Full-scale Truss Tests: Confirmatory
full-scale truss tests shall be conducted to verify the
assigned design capacities and design assumptions of the
truss components, as derived, in Sections 3.2 through 3.5.
The test program shall be in accordance with Sections 3.6.1
and 3.6.2.
3.6.1 Material Properties Verification: Tests to verify
material properties of the components within the tested
trusses, such as mill certification, or specified quality control
tests or checks at the component manufacturing location or
the truss manufacturing location, shall be required for the
chord material, steel web members, steel pins and
proprietary bearing hardware.
3.3.1 Allowable tension design values for web
members shall be the least of the following:
a. The allowable design strength, R, derived in
accordance with Appendix B using tension test results from
Appendix A. [Note: When the observed failure mode from
both the tension and compression tests is limited to bearing
deformation around the pin hole, the test results derived
under Sections 3.3.1(a) and 3.3.2(a) are permitted to be
combined for the purposes of determining R.]
3.6.2 Full-scale Truss Test Program: A full-scale
truss test program shall be developed and conducted in
accordance with ASTM E 73, or an equivalent test method,
for verification of the assembled truss performance and
representative failure modes, and to confirm applicability of
the design values derived for the individual components
described in Sections 3.2 through 3.5. A minimum of three
trusses of each selected configuration shall be tested. The
tested truss configurations shall be selected based upon the
following:
b. The allowable tension load based on analysis of
the web member in accordance with AISI S100 Sections
C2(a) and C2(b).
c. The allowable tension load based on analysis of
the web member’s pinned-end connection configuration in
accordance with AISI S100 Sections E3.1 and E3.2
(Appendix A of AISI S100) and E3.3.2.
a. Size of chord members (extreme capacities,
minimum and maximum dimensions)
b. Chord member configuration (single or double
3.3.2 Allowable compression design values for web
members shall be the least of the following:
chord)
c. Moment capacity
a. The allowable design strength, R, derived in
accordance with Appendix B using compression test results
from Appendix A. [Note: When the observed failure mode
from both the tension and compression tests is limited to
d. Shear and reaction capacity
e. Deflection
3
ACCEPTANCE CRITERIA FOR PIN-CONNECTED OPEN-WEB TRUSSES WITH
WOOD CHORDS AND TUBULAR OR ANGULAR STEEL WEBS (AC306)
truss chord members consisting of sawn lumber or structural
composite lumber. Repetitive member factors may not be
applied to allowable pin bearing values.
f. Creep recovery
g. Duct chase (if included within truss designs)
h. Multiple spans
4.6 Notching and Holes: Not permitted in any truss
component members.
3.7 Special Details: Special details, such as
concentrated loads, blocking, and bracing, shall conform to
accepted engineering practice, and shall be acceptable to
ICC-ES.
4.7 (Optional) Fire-resistance-rated Construction:
When recognition is sought for use in fire-resistance-rated
construction, tests shall be conducted in accordance with
ASTM E 119 or UL 263.
3.8 Moisture Content and Specific Gravity: The
moisture content and specific gravity shall be measured and
reported for representative samples of the truss chord
members from the trusses tested as per Sections 3.2 and
3.6. Measurements of moisture content shall be in
accordance with ASTM D 4442 or ASTM D 4444, and
measurements of specific gravity shall be in accordance
with ASTM D 2395.
4.0 DESIGN
PROPERTIES
CONSIDERATIONS
AND
5.0
QUALITY CONTROL
5.1 The trusses evaluated under this acceptance criteria
shall be manufactured under an approved quality control
program with inspections by an inspection agency
accredited by the International Accreditation Service, Inc.
(IAS), or otherwise acceptable to ICC-ES.
OTHER
5.2 Quality documentation complying with the ICC-ES
Acceptance Criteria for Quality Documentation (AC10) shall
be submitted.
4.1 Truss Design Properties: Allowable moment, shear
and reaction capacities shall be determined using
appropriate analytical and statistical methods based on the
established truss component properties. Design properties
shall be derived and verified from the testing and analysis
required in Sections 3.2 through 3.6.
5.3 Sections 3, 4, 5, 7, 8 and 10 of Appendix A of AC14
(the ICC-ES Acceptance Criteria for Prefabricated Wood Ijoists) shall be covered in the quality control manual.
6.0
EVALUATION REPORT RECOGNITION
6.1 The evaluation report shall include a statement
indicating that the installation instructions, truss design
drawings and truss placement diagrams must accompany
the product to the final jobsite, along with any special
instructions, as noted in Section 2.1.2. The statement shall
indicate that the truss design drawings must include, at a
minimum, the information specified in 2009 IBC Section
2303.4.1.1 or 2006 IBC Section 2303.4.1.2, as applicable.
4.2 Stiffness: Truss stiffness shall be determined
analytically and verified by the deflection data obtained
during the tests required in Section 3.6.2.
4.3 Design Details: Where applicable, design details for
wood products noted in the NDS are applicable to trusses
evaluated to this acceptance criteria.
4.4 Duration of Load: Code-prescribed adjustments for
duration of load, CD, with sawn lumber are applicable to the
truss chord members. Allowable pin bearing loads in chord
members may be adjusted for duration of load where
permitted under Appendix C. Load duration factors shall not
be applied to allowable web tension or compression design
values, or allowable end reaction (bearing hardware) design
values derived in accordance with Appendix D.
6.2 In cases where the evaluation report will not specify
the maximum allowable web lengths corresponding to the
allowable web compression design values, the evaluation
report must include a statement indicating that the web
compression design values must be further limited by long
column buckling, as determined by analysis in accordance
with AISI S100. ■
4.5 Repetitive Member Factor: Code-prescribed
adjustments for repetitive members, Cr, are applicable to the
4
ACCEPTANCE CRITERIA FOR PIN-CONNECTED OPEN-WEB TRUSSES WITH
WOOD CHORDS AND TUBULAR OR ANGULAR STEEL WEBS (AC306)
APPENDIX A
A1.0 INTRODUCTION
The purpose of this appendix is to specify the test protocol to be used for tension and compression testing of tubular and angular
steel web components of the open-web trusses addressed in this criteria, for the purpose of determining design values in
accordance with Appendix B.
Scope: This appendix details the procedures to be used to determine the ultimate load and proportional limit test values for web
tension and compression. The web tension test procedure described herein includes consideration for pin bearing on the web
member, end shear and net section failure. The web compression test procedure described herein includes consideration for pin
bearing on the web member and buckling in the flattened portion at either end of the web member. Long column buckling
limitations shall be determined by analysis in accordance with AISI S100 specifications using the specified Fy of the web member.
The intent of the confined test procedure is to replicate as closely as possible the conditions found in a truss with web members
pinned and the flattened web profile confined in the routed chord of the truss in the case of a single chord member, or between two
chord members in the case of double chord members. The steel pins used for testing shall be in compliance with applicable openweb truss manufacturing standard. The web members used for testing shall be in compliance with and shall be manufactured as
per the specific open-web truss manufacturing standard.
A2.0 TEST PARAMETERS
The final test program shall be approved by ICC-ES prior to the commencement of any testing. A minimum of 10 tests shall be
conducted on each critical combination of tube wall thickness or angle thickness, tube diameter or angle size, and connecting pin
diameter for tension tests and for compression tests. The web member length used for the tension tests may be any length
suitable for use with the test setup. The web length used for the compression tests shall be selected to avoid long column (Euler)
buckling failures. The load rate shall be set at a uniform rate to cause failure in two to three minutes. Load versus deformation of
the total assembly (i.e. cross-head movement) shall be continuously recorded during the tests by use of an LVDT or similar device.
Plots of the load versus deformation curves up to the point of failure shall be included in the test report. The actual thickness, t, of
the steel tubes or angles used in the web member tests shall be measured and recorded for each test specimen. The actual yield
stress, Fy, and ultimate tensile stress, FU, of the steel tubes or angles used in the web member tests shall be documented on the
submitted mill certificates. The mode of failure shall be recorded for each test specimen.
A3.0 WEB TENSION TEST
A3.1
The test setup shall be as depicted in Figure A1, with the approved pins inserted through the web holes.
A3.2
No preload shall be applied.
A3.3
The pins shall be loaded in double shear adjacent to the web-pin interface placing the web member in tension.
A3.4 For single or double chord member truss application, the test web member and dummy web member shall be pinconnected between two sections of wood or steel members as part of the load application apparatus (see Figure A1). The load
application apparatus shall not interfere with the web failure mechanisms at or near the web-pin interface. If the truss
manufacturer’s standard allows a gap between the flattened portion of the web member and the side or face of the rout within the
chord, this condition shall be duplicated in the test setup by leaving the same gap between the face of the test web and the face of
the wood or steel spacer for each combination of web steel thickness, pin diameter and rout width used. The diameter and location
of the pin hole in the web member shall be as specified in the open-web truss manufacturing standard, using the maximum gap
specified for each combination of web gauge and diameter.
A3.5 The average value of test results, Rn (see Appendix B), shall be taken as the average of the ultimate loads, adjusted in
accordance with Section B3.0 of Appendix B where necessary. If the plots of load versus deformation have more than one peak,
Rn shall be taken as the average of the lesser of a) the load values at the first peak, or b) the proportional limit load offset by 5
percent of the pin diameter.
A4.0 WEB COMPRESSION TEST
A4.1
The test setup shall be as depicted in Figure A1, with the approved pins inserted through the web holes.
A4.2
No preload shall be applied.
A4.3 For single or double chord member truss application, the test web member and dummy web member shall be pinconnected between two sections of wood or steel members (see Figure A1). The diameter and location of the pin hole in the web
member shall be as specified in the open-web truss manufacturing standard. The load application apparatus shall not interfere
with the web failure mechanisms at or near the web-pin interface. If the manufacturer’s standard allows a gap between the
flattened portion of the web member and the side or face of the rout, this condition shall be duplicated in the test setup by leaving
the same gap between the face of the test web and the face of the wood or steel spacer for each combination of web steel
thickness, pin diameter and rout width used. The load apparatus shall be configured to prevent contact under load between the
ends of the compression webs and the load apparatus.
A4.4
The pins shall be loaded in double shear adjacent to the web-pin interface placing the web member in compression.
A4.5 The average value of test results, Rn (see Appendix B), shall be taken as the average of the ultimate loads, adjusted in
accordance with Section B3.0 of Appendix B where necessary. If the plots of load versus deformation have more than one peak,
5
ACCEPTANCE CRITERIA FOR PIN-CONNECTED OPEN-WEB TRUSSES WITH
WOOD CHORDS AND TUBULAR OR ANGULAR STEEL WEBS (AC306)
Rn shall be taken as the average of the lesser of a) the load values at the first peak, or b) the proportional limit load offset by 5
percent of the pin diameter.
FIGURE A1⎯FULL-LENGTH WEB TEST
6
ACCEPTANCE CRITERIA FOR PIN-CONNECTED OPEN-WEB TRUSSES WITH
WOOD CHORDS AND TUBULAR OR ANGULAR STEEL WEBS (AC306)
APPENDIX B
B1.0 INTRODUCTION
The purpose of this appendix is to specify the methodology to be used for the determination of the safety factor to be applied
to the results of steel web tests performed in accordance with Appendix A, and the determination of the web member design
properties to be recognized in the evaluation report.
Scope: This appendix uses the procedures of Section F1.1 of AISI S100 as the methodology to be used for the derivation
of the safety factors, Ω, to be applied to the results of steel web tests (performed in accordance with Appendix A), to
determine the allowable design strength (R) for allowable strength design (ASD) method of design.
B2.0 DETERMINATION OF SAFETY FACTORS
Ω
= Factor of Safety = 1.6/Ф, but not less than 1.75
Ф
= Resistance factor:
Ф
= CФ(MMFMPM)e , where:
A
2
2
2
2 1/2
A = (-1)βO(VM +VF +CPVP +VQ )
CФ = Calibration coefficient = 1.52
MM = Mean value of material factor = 1.10
FM = Mean value of fabrication factor = 1.0
PM = Mean value of professional factor = 1.0
βO = Target reliability index = 2.5
VM = Coefficient of variation of material factor = 0.08
VF = Coefficient of variation of fabrication factor = 0.05
CP = Correction factor = (1+1/n)m/(m-2) for n≥4, and 5.7 for n=3
m
= Degrees of freedom = n-1
n
= Number tests (minimum = 10 tests)
VP = Coefficient of variation of test results, but not less than 6.5% (0.065)
VQ = Coefficient of variation of load effect = 0.21
e
= Natural logarithmic base = 2.718
B3.0 ADJUSTMENT FOR ACTUAL STEEL STRENGTH
The adjusted average value of web member test results, Rn, adj, shall be calculated from the average value of test results from
Appendix A, Rn, for each set of tests as follows:
If FU > FUSPEC, then Rn, adj = Rn(FUSPEC/FU)
If FU ≤ FUSPEC, then Rn, adj = Rn.
where:
Rn
= Average value of test results from Appendix A (lbs).
Rn, adj
= Adjusted average value of test results from Appendix A (lbs.)
FUSPEC = Specified ultimate tensile strength of the steel (psi)
FU
= Actual average ultimate tensile strength of the steel (psi)
B4.0 ALLOWABLE DESIGN STRENGTH
The allowable design strength, R, shall be calculated as:
R
= Rn,adj/Ω
7
ACCEPTANCE CRITERIA FOR PIN-CONNECTED OPEN-WEB TRUSSES WITH
WOOD CHORDS AND TUBULAR OR ANGULAR STEEL WEBS (AC306)
APPENDIX C
C1.0 INTRODUCTION
The purpose of this appendix is to detail the test protocol to be used for pin bearing tests in the chord members, for the purpose of
determining allowable pin bearing design values.
C2.0 TEST SPECIMENS
A minimum of 10 tests shall be conducted for each combination of pin diameter, chord width and depth, chord material and load
direction with respect to the wood grain of the chord members. All truss components of the tested assemblies shall be
manufactured and assembled per the approved truss manufacturing standard. If the manufacturer’s standard allows a gap
between the flattened portion of the web member and the side of face of the rout, this condition shall be duplicated in the test
setup. If the manufacturer’s standard specifies washers on the pin, this condition shall be duplicated in the test setup.
C3.0 TEST PROCEDURE
Tests for pin bearing in chord members shall be in accordance with either Section C3.1 (Method A) or C3.2 (Method B).
C3.1 Method A: Tests conducted in accordance with Method A shall be performed as shown in Figures C1 and C2 for loading
parallel and perpendicular to grain, respectively. Loads shall be applied at a uniform rate that will cause failure in two to three
minutes. No preload shall be applied. Load versus deformation of the steel member relative to the wood chord member(s) shall
be recorded for each test. Deformations shall be measured using an LVDT or similar device. The proportional limit load offset by
5 percent of the pin diameter, yield mode, ultimate load, and failure mode shall be recorded for each test. Yield modes shall be
reported as defined in Appendix I of the NDS.
C3.2 Method B: Tests conducted in accordance with Method B shall be performed as shown in Figures C3 and C4 for loading
parallel and perpendicular to grain, respectively. Loads shall be applied at a uniform rate that will cause failure in two to three
minutes. No preload shall be applied. Load versus deformation shall be recorded for each test. For parallel-to-grain tests
performed as shown in Figure C3, deformation shall be measured between each pin and its bearing attachment. For
perpendicular-to-grain tests performed as shown in Figure C4, deformation shall be measured at the center pin between the top of
the chord and the bearing surface. The ultimate reaction load at the center pin, R2, and mode of failure shall be recorded for each
test.
C4.0 DESIGN VALUES
The allowable pin bearing design value, Z, for each combination of pin diameter, chord width, chord material, and load direction
with respect to the wood grain shall be determined in accordance with Section C4.1 for pin bearing tests conducted in accordance
with Section C3.1 (Method A), or Section C4.2 for tests conducted in accordance with Section C3.2 (Method B). Allowable pin
bearing design values, Z, shall be determined using the same method for both the parallel and perpendicular to grain load
directions.
C4.1 Method A: The allowable pin bearing design value, Z, for each combination of pin diameter, chord width, chord material,
and load direction with respect to the wood grain shall be determined as follows:
Z = P5% / R
where:
P5% = The average proportional limit load, offset by 5 percent of the pin diameter
R
= 4.0 (for Yield Mode Im or Is, parallel to grain)
= 5.0 (for Yield Mode Im or Is, perpendicular to grain)
= 3.2 (for Yield Mode IIIs or IV, parallel to grain)
= 4.0 (for Yield Mode IIIs or IV, perpendicular to grain)
Allowable pin bearing design values derived in accordance with Section C4.1 (Method A) are permitted to be adjusted by the
load duration factor, CD, in accordance with the NDS.
C4.2 Method B: The allowable pin bearing design value, Z, for each combination of pin diameter, chord width, chord
material, and load direction with respect to the wood grain shall be the lesser of the following:
a.
The minimum ultimate reaction load at the center pin, R2, divided by a factor of 2.1,
b. The average ultimate reaction load at the center pin, R2, divided by a factor of either 3.0 for solid-sawn lumber
chords, or 2.8 for structural composite lumber chords.
Allowable pin bearing design values derived in accordance with Section C4.2 (Method B) are permitted to be adjusted by the
load duration factor, CD, in accordance with the NDS, up to a maximum value of CD = 1.33.
8
ACCEPTANCE CRITERIA FOR PIN-CONNECTED OPEN-WEB TRUSSES WITH
WOOD CHORDS AND TUBULAR OR ANGULAR STEEL WEBS (AC306)
FIGURE C1⎯METHOD A PARALLEL TO GRAIN TEST
FIGURE C2⎯METHOD A PERPENDICULAR TO GRAIN TEST
9
ACCEPTANCE CRITERIA FOR PIN-CONNECTED OPEN-WEB TRUSSES WITH
WOOD CHORDS AND TUBULAR OR ANGULAR STEEL WEBS (AC306)
9 in
12 in
30 in
9 in
.
FIGURE C3⎯METHOD B PARALLEL TO GRAIN TEST
P
b
a
Pin
1.5”
l
Rout
R2
Where:
P
l
a
b
R2
= cross-head load (lbs.)
= distance between bearings (in.) = 22.5 in.
= distance from outside bearing to load (in.) = 16.5 in.
= distance from load to center bearing (in.) = 6.0 in.
= reaction at center bearing (lbs.)
Dimensions may be adjusted to test other chord depths, provided all other dimensions are adjusted in proportionally.
FIGURE C4⎯METHOD B PERPENDICULAR TO GRAIN TEST
10
ACCEPTANCE CRITERIA FOR PIN-CONNECTED OPEN-WEB TRUSSES WITH
WOOD CHORDS AND TUBULAR OR ANGULAR STEEL WEBS (AC306)
APPENDIX D
D1.0 INTRODUCTION
The purpose of this appendix is to specify the test protocol to be used for the reaction testing of the bearing assembly of
open-web trusses, for the purpose of determining allowable design end reaction values of the trusses.
Scope: This appendix details the test procedures to be used to determine the reaction loads to determine the allowable
design strength for the allowable strength design (ASD) method of design.
D2.0 TEST PARAMETERS
A minimum of three tests shall be conducted on each critical combination of: (1) bearing hardware; (2) maximum distance
between the bearing pin and the edge of the truss bearing support; (3) minimum bearing length; (4) minimum distance from
the bearing pin to the end of the chord; and (5) any other special bearing conditions specified in the manufacturer’s
installation instructions (such as those requiring a bevel or shaped support plate for proper bearing). The diameter and
location of the pin hole in the chord and web members shall be as specified in the open-web truss manufacturing standard.
Dimensions and material properties of the pins, web members and chord members used in the tested assemblies shall be as
specified within the truss manufacturer’s quality documentation. If the manufacturer’s standard allows a gap between the
flattened portion or the web member and the rout or bearing hardware, this condition shall be duplicated in the test setup by
leaving the same gap between the web or strap and one face of the rout or bearing hardware for each combination of web
steel thickness, pin diameter and rout width used. The “B” distance shown in Figure D1 shall be the maximum distance for
which design values will be established. Tests shall be conducted on specimens with the minimum and maximum “PTE”
distances for which design values will be established. If the manufacturer’s standard requires the use of head and/or spring
washers on the pin, the same shall be used in the tested assemblies. The angle of the web members from vertical shall be
equivalent to the minimum web angle (from vertical) used within the truss.
D3.0 TEST PROCEDURE
D3.1 The load rate shall be set at a uniform rate to cause failure in two to three minutes. Load versus deformation of the
total assembly (i.e., cross-head movement) shall be continuously recorded during the tests by use of an LVDT or similar
device. Plots of the load-versus-deformation curves up to the point of failure shall be included in the test report. The
moisture content and specific gravity of the chord member shall be measured and recorded for each test specimen in
accordance with Section 3.8 of this criteria. The mode of failure shall be recorded for each test specimen.
D3.2 The test setup shall be as depicted in Figure D1 with the pins inserted through the hole in chord and bearing
hardware.
D3.3
No preload shall be applied.
D3.4 The pin shall be loaded in double shear adjacent to the chord-pin interface by placing the web or strap member in
tension.
D3.5
The load application apparatus shall not interfere with the bearing assembly failure mechanism.
D4.0 DESIGN VALUES
D4.1 The allowable truss reaction design value, RA, for each critical combination of test parameters described in Section
D2.0 shall be based on the lesser of the following:
a. The lowest ultimate load of three test replicates divided by 3.0 (provided none of the ultimate load values differs by
more than 20% from the average ultimate load) or the average ultimate load of six or more test replicates divided by 3.0.
b. The average load from all tests at a vertical deflection of 0.125 inch (3.2 mm), measured directly above the pin on
the top of the chord relative to the spacer block.
D4.2 Where the actual steel yield strength of the tested bearing hardware, Fy, test, is greater than the specified yield
strength, Fy,spec, the allowable reaction design value, RA, for truss bearing assemblies transmitting reaction loads through
bearing clips or other steel hardware shall be adjusted accordingly. The adjusted allowable reaction design value, RA, adj,
shall be as follows:
If Fy, test > Fy,spec, then RA, adj = RA(Fy, spec/Fy, test)
If Fy, test ≤ Fy, spec, then RA, adj = RA.
11
ACCEPTANCE CRITERIA FOR PIN-CONNECTED OPEN-WEB TRUSSES WITH
WOOD CHORDS AND TUBULAR OR ANGULAR STEEL WEBS (AC306)
FIGURE D1⎯TRUSS END REACTION TESTS
(Bearing hardware not shown, for clarity)
12