ICC-ES AC427 Cast Connex High-Strength Connectors™
Public Review comments from AISC / TC 9 Members
March 1, 2011
ICC-ES
Attn: Brian Gerber
5360 Workman Mill Road
Whittier, CA 90601
These comments are in response to the proposed acceptance criteria for structural cast
steel connectors for use as bracing connections in accordance with AISC 341. The
acceptance criteria and our comments are written with respect to AISC 341-05. The
acceptance criteria and our comments will still be valid using AISC 341-10. References
to Sections 13.3b and 14 would change to Chapter F2 6(b) and F1 6(a).
The acceptance criteria being considered is titled “Proposed Acceptance Criteria For
Structural Cast Steel Connectors For Use as Bracing Connections in Accordance with
AISC 341 Sections 13.3 and 14.4.” The letter from ICC-ES principal structural engineer
Brian Gerber, dated February 1, 2011, discusses a number of braced frame design
concepts in AISC 341 which do not relate to any proposed product. For moment frame
connections, AISC 341 establishes test requirements, a load protocol, and acceptance
criteria; AISC 341 does not do the same for brace frame connections, although it does
have provisions relating to brace frame connections. It is not within the purview of ICCES to establish performance standards for braced frames. Instead, the purpose of
acceptance criteria established by ICC-ES is to determine whether an applicant’s
product complies with the relevant provisions in the existing specifications.
The material used to cast the connection is an important characteristic of the connector
and should be considered in accepting the product for use. AISC 360 lists ASTM A216
for cast steels. Commentary to AISC 360 goes on to discuss the use of materials not
listed in the AISC specifications with steel structures, and states that strength, ductility,
toughness, and weldability are four of the properties to be considered when using
unlisted materials. This commentary can be used as guide when approving the use of
unlisted materials. For instance, in the course of approving the Kaiser Bolted Bracket,
the AISC Connection Prequalification Review Panel evaluated ASTM A958 SC8620
Class 80/50. Provisions related to the casting and testing of cast steel products are
shown in Appendix A of AISC 358. Therefore it is appropriate for ICC acceptance
criteria to contain material requirements, and appropriate to allow the use of unlisted
materials such as ASTM A958 with supplemental requirements.
The ICC letter states that acceptance of ASTM A958 material in the Kaiser bolted
bracket may not be a valid comparison to the cast steel connector. The claim is that the
Kaiser Bolted Bracket need not be designed to sustain plastic deformation, but the
braced frame connection is different because a plastic hinge may occur within the cast
steel connector. However, like the Kaiser Bolted Bracket, the brace connection is
designed not to be the yielding element in the frame. Circular HSS braces, the only type
of brace accommodated by this connector, will buckle out of plane because the in-plane
stiffness of the connection is much higher than the out of plane stiffness, and the
stiffness of the brace itself is the same both in and out of plane. In that sense it is similar
to the Kaiser Bolted Bracket and similar material requirements would be appropriate for
the connectors in question. The ICC letter goes on to suggest that the supplemental
quality provisions in Appendix A of AISC 358 Supplement No. 1 may not extensive
enough in relation to the application of complete joint penetration welds. The only
material requirement associated with complete joint penetration welds is a requirement
for toughness in heavy sections. That requirement is not intended for this application,
but it is of note that the material proposed by the applicant has a toughness in excess of
the aforementioned AISC requirement.
The ICC letter cites AISC 341 Section 13.3b, which requires a connection flexural
strength and provides an exception to this requirement. The exception exempts the
connection from the flexural strength requirement as long as it can accommodate
inelastic rotation. A method to achieve that inelastic rotation capacity is explained in the
commentary, which requires a 2t space in the gusset, thereby moving the hinge location
to within that 2t space. In practice, this exception is routinely used in braced frame
connection design, which means that the connector is not the element which forms a
plastic hinge. This detailing would also be used in designs with the proposed cast steel
connectors.
To clarify the acceptance criteria in regards to the desired location of the plastic hinge, it
may be appropriate for the acceptance criteria to require that the Engineer of Record
specifying the use of these cast connectors comply with the requirements of the
exception listed in AISC 341 Section 13.3b or alternatively provide a rationale for using
an alternate design method to ensure that the plastic hinge at a brace end forms within
the gusset plate and not the connector or the brace.
Finally, in comments 1 and 2, the ICC letter implies that the use of the applicant’s
connector may cause the frame to behave in a way that is not in keeping with the overall
global response of a special or ordinary concentrically braced frame, and hence suggests
that full-scale frame testing may be required. If the applicant’s connectors meet the
AISC provisions relating to brace frame connections, and all else in any given frame has
been designed and detailed pursuant to the AISC provisions for special or ordinary
concentrically braced frames, the frame would be considered a special or ordinary
concentrically braced frame in accordance with the code.
Thank you for this opportunity to participate in the ICC-ES process.
This letter has been reviewed and supported by the following members of the AISC
Committee on Specifications Seismic Task Committee (TC 9):
Timothy P. Fraser
Keith Landwehr
James O. Malley
Bonnie E. Manley
Rafael Sabelli
Thomas A. Sabol
C. Mark Saunders
From:
To:
Subject:
Date:
tfraser@anvilcorp.com
Rosalind Fazel
AC427 Comments
Friday, March 04, 2011 8:51:24 PM
Comments on Criteria AC427.
Tim Fraser
Anvil Corporation
360 937-0448 (direct)
tfraser@anvilcorp.com
Comments:
The following comments address concerns about welding
requirements for the Cast Connex connections. 1) Section 2.6.1 of
the Proposed Acceptance Criteria indicates where heat treatment of
connectors includes quenching and tempering that a weld procedure
specification be prepared in accordance with AWS D1.8. This implies
that where there is no heat treatment that weld procedures are not
required. However Weld Procedures shall be prepared per AWS for
all cases of welding between the connection and the HSS member.
2) The casting material is not a prequalified base material per AWS
D1.1. Therefore a qualified weld procedure is required per AWS D1.1
for any welding of the casting material. Welding of structural steel to
castings is not a common practice in the structural steel fabrication
industry. It would be prudent for the report to indicate that weld
procedure qualification is required for the welds of the structural
steel to the casting material. The procedures shall be in accordance
with requirements of AWS D1.1 and AWS D1.8. Note that AISC 341
does not require Demand Critical welds for connections of ends of
diagonal braces of OCBF and SCBF systems. 3) The configuration of
the weld joint between the casting and the HSS is an unusual one. It
does not appear to conform to prequalified Complete Joint
Penetration configurations per AWS D1.1. Due to lack of access
there is no possibility of backgouging from the far side to ensure
complete penetration. There is no definitive root opening in the joint
where the casting could be definitively considered a weld backing.
Perhaps the requirement for the weld joint could be considered to
be a complete penetration weld without weld backing or
backgouging. (This should be confirmed with a welding expert (or
perhaps by AWS)) AWS D1.1 requires that such CJP welds made on
tubular connections without weld backing or backgouging be made
by a welder qualifed for such. This is not a common welded
qualification in the structural steel fabrication industry. If a more
restrictive welder qualification than the norm is required, it would be
prudent to note this in the ICC report. Please note that neither AWS
D1.1, AWS D1.8, AISC 360 nor AISC 341 preclude the welding of
the HSS material to the casting material. My concern is that there
are requirements beyond the use of prequalified weld procedure
specifications and perhaps common welder qualifications.
The experts in cast steel structural connections
March 1, 2011
Attn: Evaluation Committee
ICC Evaluation Services, Inc.
Los Angeles Business/Regional Office
5360 Workman Mill Road
Whittier, CA
90601
Dear Colleagues,
Re:
Request for comments on AC427, Proposed Acceptance Criteria for Structural
Cast Steel Connectors for Use as Bracing Connections in Accordance with AISC
341 Sections 13.3 and 14.4
Cast Connex Corporation engaged ICC Evaluation Services, Inc. to report on the code compliancy of our
Cast ConneX® High-Strength Connectors™, which are intended for use at round HSS or Pipe brace
member-to-gusset plate connections in seismic-resistant braced frames designed pursuant to the
provisions of AISC 341-05 for Special or Ordinary Concentrically Braced Frames. It was deemed the
development of a new ICC-ES Acceptance Criteria was necessary and that development of the criteria
would follow ICC-ES’ “alternate criteria process” as precedent for the acceptance of our products exists in
various AISC codes.
We are providing comments herein pursuant to ICC-ES’ request for public comment as written by Brian
Gerber, Principal Structural Engineer at ICC-ES and dated February 1, 2011.
In the second paragraph of the above noted letter, ICC-ES asserts that neither AISC 341 nor AISC 360 is
clear with respect to the acceptance of non-referenced grades of steel, such as ASTM A958, the material
standard to which our High-Strength Connectors are produced. Actually, the Commentary on Section
A3.1a of AISC 360-05 clearly defines which material properties should be considered when determining
the suitability of a non-listed ASTM material for use in a particular structural application. Further, the
grade of steel from which High-Strength Connectors are produced (ASTM A958 Grade SC8620 Class
80/50) has already been evaluated by the AISC Connection Prequalification Review Panel, and this cast
steel grade, pursuant to the casting and non-destructive examination requirements of Appendix A of
Supplement No. 1 to AISC 358-08, was deemed to be appropriate for use in a similar structural
application – namely for the production of Kaiser Bolted Brackets for use in seismic-resistant moment
resisting frames.
The letter goes on to suggest that the comparison in regards to material suitability between the connector
of the present application and the Kaiser Bolted Bracket is inappropriate because welding to the Kaiser
Bracket is achieved using fillet welds, whereas welds to High-Strength Connectors are complete joint
penetration welds. However, we would like to point out that the weldability of a material and welded joint
configuration are separate matters. Clearly, ASTM A958 Grade SC8620 Class 80/50 is a weldable grade
of steel, considering its approval for use in the case of the Kaiser Bolted Bracket, which as ICC-ES noted,
Cast Connex Corporation – 203 College Street, Suite 301A – Toronto, ON Canada M5T 1P9
The experts in cast steel structural connections
can be used in conjunction with fillet welds. Welded joint configuration, on the other hand, is addressed
in AWS D1.1 and AWS D1.8, and once a material is deemed weldable, any joint type can be welded
pursuant to the provisions of the aforementioned specifications.
On the second page, the letter incorrectly asserts that plastic hinging may occur within the cast steel
connectors. When employed in an SCBF, Cast ConneX High-Strength Connectors are intended to be
used in conjunction with the exception listed in AISC 341-05 13.3b. With the 2t free length provided in the
gusset plate beyond the ends of the connectors, the brace will buckle out-of-plane of the gusset, forming
plastic hinges within the free length of the two gusset plates and at the center of the brace. For clarity,
the moment of inertia and plastic moment capacity of the brace and connector are both larger than that of
the gusset plate, and the in-plane stiffness of the connection is much higher than its out-of-plane stiffness,
so the brace will physically only buckle out-of-plane in such a way as to form plastic hinges in the 2t free
length of the gusset plate. This behaviour is dictated by the structural mechanics of elastic and inelastic
buckling phenomena, which are very well established and which in fact form the basis of the exception
listed in AISC 341-05 13.3b.
The incorrect assertion that plastic hinging may occur within the connector is then used as further
evidence that the adequacy of ASTM A958 Grade SC8620 Class 80/50 for use in the production of the
Kaiser Bolted Bracket does not imply that the material is adequate for use in the manufacture of the
connectors of the present application. This logic is obviously faulty. The remaining comments on page 2
of the letter are therefore irrelevant to the discussion.
In comment number 1, ICC-ES notes that AISC 341-05 requires full-scale testing for other lateral forceresisting systems, however, we do not see how that is relevant to the discussion of the code compliancy
of the connectors of the present application, as AISC 341-05 has provisions for the brace connections in
SCBF and OCBF, and those provisions do not require full-scale testing. Any concern with the adequacy
of the existing provisions should be dealt with via the ANSI process as administered by AISC, and is
outside of the scope of ICC-ES’ evaluation of our product against the existing codes.
Comment number 2 suggests that an SCBF or OCBF equipped with our connectors may not behave as
an SCBF or OCBF, and goes on to suggest that testing of full-scale braced frames would be required to
ensure the structural design of the system using our components adequately predicts the system’s
performance. Research has shown that the response of concentrically braced frames is a function of the
brace member’s overall slenderness (KL/r) and cross-sectional slenderness (which for round HSS or pipe
members is computed as D/t). The use of High-Strength Connectors, or of any other one-off designed
and fabricated connection meeting the requirements of AISC-341-05 13.3 or 14.4 for that matter, would
have no bearing on either of these controlling parameters, and hence this concern is unfounded. Further,
the provisions of AISC 13.3 and 14.4 ensure the desired brace and system response through the
“capacity design” approach for the connections, and as High-Strength Connectors clearly meet those
provisions, additional requirements for full scale testing are unnecessary and are clearly beyond the code
intent.
In response to comment number 4 which notes that AC427 does not currently provide for proof that
inelastic rotation out-of-the-plane of the brace can be achieved, we suggest that the Acceptance Criteria
or the eventual Evaluation Report simply require that the Structural Engineer of Record specifying the
connectors for use in an SCBF comply with the requirements of the exception listed in AISC 341-05 13.3b
Cast Connex Corporation – 203 College Street, Suite 301A – Toronto, ON Canada M5T 1P9
The experts in cast steel structural connections
or provide rationale for using an alternate design method to ensure the plastic hinge at the brace end
forms within the gusset plate and not the connector or the brace.
Comment number 5 asks whether the welding of the cast steel connector to the brace element should be
limited to approved fabricators as defined by IBC Section 1704.4. We suggest, as an alternative to
limiting the use of the connectors to approved fabricators, that users of High-Strength Connectors could
be advised to weld the connectors to the round HSS or pipe member braces in a shop environment,
pursuant to a duly approved Welding Procedure Specification.
Based on the rationale presented above, one can only come to the conclusion that the draft Acceptance
Criteria presented, which focuses on the material and non-destructive examination requirements for the
connectors and which is based on the requirements of Appendix A of Supplement No. 1 to AISC 358-08,
is adequate for the application of Cast ConneX High-Strength Connectors in SCBF and OCBF designed
and detailed pursuant to AISC 341-05.
Sincerely,
Carlos de Oliveira, M.A.Sc., P.Eng.
Chief Executive Officer
Cast ConneX Corp.
Cast Connex Corporation – 203 College Street, Suite 301A – Toronto, ON Canada M5T 1P9
STRUCTURAL ENGINEERS ASSOCIATION
OF CALIFORNIA
555 CAPITOL MALL, SUITE 755
SACRAMENTO, CA 95814
916.447.1198 • 916.442-0812 FAX
info@seaoc.org • www.seaoc.org
PRESIDENT
STEPHEN PELHAM*
PRESIDENT-ELECT
DOUGLAS HOHBACH*
SECRETARY
JANAH RISHA
TREASURER
BRADLEY LOWE*
DIRECTORS
KELLY COBEEN
MICHAEL COCHRAN
JEFF CROSIER*
JOYCE FUSS*
BRADLEY LOWE*
PETER LEE
JEFFREY MARCHANT
JANAH RISHA
RAFAEL SABELLI*
ALI SADRE*
MICHAEL WEST*
PAST PRESIDENT
WILLISTON WARREN*
EXECUTIVE DIRECTOR
LEE ADLER*
(*EXECUTIVE COMMITTEE)
March 18, 2011
Bohdan N. Horeczko, P.E.
Director, Professional Services
ICC Evaluation Service, LLC
Los Angeles Business/Regional Office
5360 Workman Mill Road
Whittier, CA 90601
RE: AC427, Proposed Acceptance Criteria for Structural Cast Steel Structural Engineers Association of California (SEAOC) Recommendations
In response to ICC-ES’s request for recommendations regarding AC427,
document entitled “Proposed Acceptance Criteria for Structural Cast Steel
Connectors for Use as Bracing Connections in Accordance with AISC 341-05
Sections 13.3 and 14.4.,” dated February 1, 2011, the SEAOC Evaluation
Report (ER) Committee and Seismology Committee (SC) have reviewed and
had an approval vote for the recommendations presented herein for this AC.
We credit Dr. Scott Adan, the Chair of the Steel Subcommittee of SEAONC SC,
for providing background material on this topic, and we note that he was the
primary author of Chapter 9 and Appendix A provisions of the AISC 358-05
supplement No. 1 design standard. We also note that our deliberations
included input from representatives of Kaiser Bolted Bracket™ moment
connection (KKB) and Cast ConneX Corporation, makers of cast high-strength
connectors.
The reviewed documentation included the following:
1. ICC-ES five-page introduction letter written by Brian Gerber, Principal
Structural Engineer with ICC-ES for parties interested in
structural cast steel connectors.
2. Cast ConneX High-Strength Connectors three-page ICC-ES AC427
Public Review Primer.
3. ICC-ES eight-page Proposed Acceptance Criteria for Structural Cast
Steel Connectors for Use as Bracing Connections in Accordance
with AISC 341-05 Sections 13.3 and 14.4.
AC427
Background – As provided primarily by the proponents
The Cast ConneX® High-Strength Connectors™ (www.castconnex.com/HSC) are an off-the-shelf
brace connection solution for use in seismic-resistant concentrically braced frames. On one end,
the connectors accommodate a welded connection to round tubular braces (which would
include both ASTM A500 round HSS and ASTM A53 Pipe members), and on their other end, the
connectors accommodate a double-shear bolted connection to an appropriately designed and
detailed gusset plate (use of “2t” free length in the gusset plate beyond the end of the
connector to accommodate out-of-plane buckling of brace via formation of plastic hinges in the
gusset plate). The connectors were developed at the University of Toronto by Professors Jeffrey
Packer (tubular steel connections expert; author of AISC Design Guide 24) and Constantine
Christopoulos (professor of dynamics and earthquake engineering at University of Toronto) to
meet AISC requirements for SCBF/OCBF brace connections. The development process was
intended to simplify SCBF/OCBF connection design, detailing, fabrication, and erection; to
eliminate the necessity to weld braces to the gusset plates in the field (connectors are shop
welded to round HSS/pipe brace members and the brace-connector assembly is bolted to the
gusset plate in the field); and to provide for substantially more compact field-bolted connections
than would otherwise be possible with a bolted connection using splice plates (half the number
of bolts, half the number of holes to drill, and half the number of bolts to install and pretension
in the field).
The connectors are joined via complete joint penetration groove weld to the hollow section
brace – a joint that can be shown to meet the strength requirements of AISC 341-05 Sections
13.3 and 14.4. On their other end, the connectors are joined to a gusset plate via double-shear
bolted connection or fillet welded connection – connections which can be detailed by the
Engineer of Record using provisions in AISC 360-05 to meet the strength requirements of AISC
341-05 Sections 13.3 or 14.4. Further, as outlined in AISC 341-05 Section 13.3b, the “2tp rule”
can be used to accommodate the requisite out-of-plane end rotation of the brace in SCBF
assemblages (the free length of gusset plate is to be left beyond the end of the connector). The
connector’s solid steel “body” is analogous to a cap plate. It transitions within the distribution
slope of 2.5:1 described in AISC 360-05 Section K1.6 (refer to AISC Design Guide 24 page 83 for
the cap-plate-to-round HSS case), thereby eliminating shear lag.
Because they are an off-the-shelf, standardized, pre-tested connection solution, Cast ConneX et
al believe the connectors improve the quality and therefore safety of seismic-resistant
concentrically braced frames in which they are installed, and they provide a unique connection
aesthetic that is unachievable using fabricated connections.
There is currently no Braced Frame equivalent to AISC’s standard for Prequalified Moment
Frame Connections (ANSI/AISC 358-05) against which the connectors could be evaluated and/or
introduced through an ANSI process. As a result, Cast ConneX engaged ICC-ES to evaluate their
products for conformity to the International Building Code, 2009 Edition (IBC 2009) and
standards referenced therein. With a product evaluation report, this would assist with
implementing the relative new product in the construction industry. To this end, the connector
requires the development of a new AC, which in turn should cite the applicable provisions of the
AISC standards discussed in more detail below, and this AC is being developed through the
“Alternate Criteria Process”.
2
AC427
The ASTM A958 Grade SC8620 Class 80/50, used with the Cast ConneX system, is not explicitly
listed in AISC 360-05 or AISC 341-05; this is the only aspect of the connectors which does not
appear to be in accordance with the IBC and referenced standards. Furthermore, based on our
initial review, ASTM A958 Grade SC8620 Class 80/50 steel is not covered in AWS D1.1 (up
through the 2008 version). However, as acknowledged by ICC-ES, the same material grade has
been approved for use in Supplement No. 1 to AISC 358-05 for the Kaiser Bolted Bracket, subject
to the casting and non-destructive examination requirements listed in Appendix A of
Supplement No. 1 to AISC 358-05. Given that both the Kaiser Bolted Bracket and Cast Connex
Connectors are capacity-designed elements, Cast ConneX has proposed that the requirements in
Appendix A would also be suitable for the connectors.
The above discussion was provided primarily by the proponent as background and is not to be
construed as SEAOC’s endorsement of the product or any of the statements made. SEAOC’s
positions on the proposed AC language are elaborated in the discussion below as responses to
the questions raised by ICC-ES.
Responses to ICC-ES Questions
1. Is the proposed criteria adequate for a unique connector within a seismic load–resisting
system in that it specifies only material-related properties and quality control?
After debating this request, the consensus opinion is that the proposed AC should widen the
context of the requirements to more generic language, as discussed further below. This
recommendation is due to the wide variety of geometric shapes that could be proposed with
cast connections, and those may or may not be engineered accurately to prescriptive code
requirements.
Regarding the use of ASTM grade SC8620 class 80/50 (including compliance with appendix A of
ASIC 358-05 Supplement #1) which is a material not currently recognized in AISC 360-05, AISC
341-05, or AWS D1.1 (up through the 2008 version), SEAOC has reviewed the minimum required
tensile properties contained within that ASTM (yield strength, tensile strength, and elongation)
and found those properties to meet or exceed similar properties of other materials that are
recognized in the applicable standards. Therefore, except for the need to comply with the
ASTM and supplemental requirements for QA/QC as well as to require welding procedures
appropriate for the type of material and configuration, SEAOC is unaware of additional
requirements to be placed on the use of this material as proposed in a connection configuration
complying with AISC 341-05 sections 13.3 and 14.4.
Regarding the potential requirement for testing to validate the strength of the component
(required to comply with overstrength requirements in AISC 341-05 to preclude component
yielding prior to brace yielding), SEAOC’s position is that such validation testing should only be
required when the component’s strength (including both yielding and fracture mechanisms)
cannot be clearly quantified by design equations contained with the AISC standards. Since the
AC does not limit, nor should it limit, the geometric configuration of the component, it is
possible that a component could be configured in such a way that the existing AISC equations
regarding yielding on gross section, fracture on net section, and/or shear lag allowances are
appropriate for use to calculate the strength of that configuration, which would make validation
testing unnecessary. However, there could be a configuration for which there is no clear
3
AC427
existing AISC equation(s) that could be applied appropriately to determine strength based on
calculation, in which case validation testing and/or other robust analysis should be required.
SEAOC recommends that the AC should require the design criteria and approach be submitted
to demonstrate how the prescriptive code provisions are applicable, or provide methodology of
design validation through either numerical and/or physical cyclic testing to assess strength and
failure mode. The latter is required when an appropriate design equation(s) is not available for
the configuration. The review of this design validation, whether through prescriptive code
provisions or alternate validation methodologies, should be performed through a technical peer
review process. The makeup of the peer review should include a metallurgy specialist. SEAOC is
willing to participate in separate discussions regarding specific considerations for development
and implementation of such a validation testing program (extent of assemblage to test, loading
protocol, number of tests, extrapolation of results, etc), if required and which would be on a
case-by-case basis.
Given that AWS D1.1 and AISC standards have not explicitly considered the specific cast steel in
question, we recommend that AC stipulate that the proponent provide PQR/WPS requirements
in the ER. Again, these requirements should be vetted by a peer review panel, one with a
metallurgy specialist, and consider such items as preheat, maximum interpass temperature
requirements, etc. Furthermore, to assist the building official, EOR, and constructor of the
assembly, the full welding and connection requirements, such as the QC/QA/PQR/WPS, should
be specified in the ER.
We note that the round brace “connector” by Cast ConneX, like the KBB, is intended to be
designed to be the non-yielding element within the frame. The braces in this configuration will
buckle out-of-plane because the in-plane stiffness of the connection is always higher than the
out-of-plane stiffness due to gusset geometry, and the stiffness of the brace itself is the same
both in and out-of-plane. In that sense, the connector of discussion is identical to the KBB and
hence similar material and non-destructive examination requirements would, for code
equivalency, be appropriate for the connectors in question. We note, however, that the
connector should be checked and/or methodology provided by the proponent for out-of-plane
strength relative to the preferred mechanism of gusset plate bending, and this requirement
should be stated in the AC regardless of the product; again, this should be vetted by a peer
review at the time the ER is prepared.
2. …. we ask whether methods to confirm a rational analysis with validation testing needs to be
incorporated within AC427.
See response to item #1 above.
3. Is the proposed criteria sufficient to permit a registered design professional to apply the IBC in
determining performance of the connector due to tension, compression, and flexural loadings
through the connector, welds, and bolting?
See response to item #4 below. Additionally, the SEAOC position is that the following should be
specified by the applicant in the ER report (and that the AC should be modified to explicitly
require):
• Welded joint performance requirement of providing a full strength weld, one
that can develop the expected strength of the brace per AISC 341-05. To assure
4
AC427
•
this is achieved and given that this is a new material, the standards’ welding
requirements for non-prequalified weld should be cited in the ER. The welding
to the cast steel shall not be considered a prequalified weld. In stating so, clear
direction will be provided to the building official, the EOR, contractor, and IOR
regarding their scope in the construction process of this connector. Specifics
regarding the requirements and, as much as possible, the process for Quality
Control, Quality Assurance, Procedure Qualification Report, Welding Procedure
Specification, etc., should be outlined in the ER to assure the weld strength
performance objective is obtained.
The specific cross section and material specification for each brace that is
acceptable for use with each connector assembly (that complies with the
strength requirements of AISC 341-05)
4. Design details may need to clearly note this is needed to prevent in-plane rotations of the
assemblage.
The AC requires compliance with AISC 341-05 sections 13.3 (SCBF) and 14.4 (OCBF). For SCBF
configurations per section 13.3b, the connection is required to have a flexural strength in excess
of the expected flexural strength of the brace or, per the exception, be detailed in such a way to
accommodate the inelastic rotations (which is usually accomplished in gusset plate conditions
with ‘2t’ offset detailing). For the flexural strength condition, the AC already requires
demonstration of the capacity to meet the required strength. However, for the exception
allowing detailing to accommodate the rotations within the connector, the SEAOC position is
that the AC should require the proponent to demonstrate that the connector’s connection to
the gusset plate has the adequate strength and stiffness to force the inelastic rotations to occur
in the ‘2t’ space of the gusset plate rather than within the connector. The basis for this position
is that the traditional ‘2t’ detailing is for brace sections and connections to the gussets that
inherently have that strength and stiffness. With no limitation in the AC regarding the
configuration or section properties of the cast connector, it is prudent to require the applicant
to demonstrate this behavior can be achieved by the product.
5. Should welding of the cast steel connector to the brace element be limited to approved
fabricators as defined in IBC Section 1704.4 [sic, the correct reference is 1704.2.2]?
The intent of the connector application is to prefabricate, and to have this work performed by
those knowledgeable with the cast steel material and in a controlled environment. So, yes, we
should evoke the cited reference. If, however, a contractor seeks to perform this work on site,
which may occur as a remedial detail or the like in an extreme scenario, the responsibility is on
them to prove they provide a weld that meets the strength performance objective, as defined in
AISC 341-05 and the ER.
We note that for HSS sections, ultrasonic testing is difficult and somewhat unreliable for flare
bevel groove welds and proof by non-destructive methods is difficult to assess the full weld
depth. The intent of stipulating fabricator approval is to highlight the importance and
uniqueness of this weld, particularly with a material that is not addressed by the code and a
weld geometric type that is unknown at this time.
5
AC427
During our discussions on this topic numerous points have been brought to our attention. The
following items are SEAOC’s recommendations to ICC-ES for further consideration (during the
review of the AC or future requests for an ER under the AC), although formal positions on these
have not been vetted by SEAOC ER or Seismology Committees.
1. Inclusion size (defect size) distribution in rolled steels is fairly consistent. However, in
cast steels, this is part of the cast steel design process and is variable, depending on the
requirements. ASTM A958 does not cover this. A specification needs to be developed to
assure that inclusion size distribution is similar to that of rolled steel. Toughness tests do
not address this since toughness is a measure of the ability of cracks to not propagate
after initiation in an inclusion and not a measure of the inclusion density. The
requirements of AISC 358-05s1 App. A are being studied in more detail by a SEAOC
subcommittee for recommendations regarding this topic.
2. Endurance limit of structural steels is normally 0.5. Same for cast steels varies from 0.4
to 0.5, a variation of 20%. QC specs can insure that the number is 0.5 or greater.
3. Heat treatment beyond 400oF after welding is known to reduce the toughness of cast
steel. If this level of heat treatment is to be required or performed by the fabricator
after welding, the effects need to be investigated.
4. Should the maximum yield/tensile strength ratio be 0.85 (similar to ASTM A992)?
5. Specifications similar to roughness requirements for flange cuts (AISC 358.5.7) may need
to be considered as a potential requirement for transition regions of a cast shape.
When considering these additional items or while reviewing case-specific design and details
while in preparation to issue an ER, SEAOC is ready and willing to participate in more detailed
conversations.
Kind regards and on behalf of SEAOC,
Also on behalf of Ryan
Mark A. Moore, S.E.
Chair, SEAOC Evaluation Report Committee
Ryan A. Kersting, S.E.
Chair, SEAOC Seismology Committee
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snhchamb@centurytel.net
Rosalind Fazel
AC427 Comments
Tuesday, February 15, 2011 3:16:04 PM
Comments on Criteria AC427.
Harry Chambers
SNH Consultants
216-513-1500
snhchamb@centurytel.net
Comments:
The AWS/ANSI codes do not allow or adress cast steels. The
sections below should be taken off the criteria. 1.3.6 ANSI/AWS
D1.1-2004, Structural Welding Code ? Steel, American Welding
Society. 1.3.7 ANSI/AWS D1.8-2005, Structural Welding Code ?
Seismic