Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

[SEAOC] LA County position on Welded Moment Resisting Frame

[Subject Prev][Subject Next][Thread Prev][Thread Next]
The following letter was emailed to me by an employee of LA county. This
letter will also be available in our FTP area on our WWW server.


August 14, 1996									




This memorandum supercedes a March 26, 1996 memorandum on the same subject.  

The publication of SAC Interim Guidelines(FEMA 267) in August 1995 was a
major milestone in the Northridge Earthquake recovery effort for steel
moment frames and provided recommendations on engineering procedures for
modification and design of WMRF structures.  We continue to support the SAC
effort and consider the SAC Interim Guidelines the best document to date on
the WMRF issue, however, clarification and amplification is necessary for
the County's current and future projects.  The SAC Interim Guidelines
cautioned users that research "results may invalidate or suggest the need
for modification of recommendations."  

This memorandum is to provide up-to-date information as the result of the
County?s continuing and active effort to resolve the WMRF crisis.  It shall
apply to County capital projects and may be used for any new buildings in
Los Angeles County.  A Technical Advisory Panel(TAP) consisting of experts
in the design, research, and quality assurance of welded steel construction
was invited to assist County engineers in meeting the WMRF challenge.
Members of this panel are identified in the attachment (Attachment I). 


Welded moment resisting frame systems (special or ordinary) are not
permitted unless the connections proposed meet the following requirements
and are submitted to and approved by the County:

 1.	A minimum of three full size prototype specimens of the configurations
to be used shall have passed full-scale cyclic loading tests and
demonstrated plastic rotational capacity equal to or greater than 0.03
radians.  More than three specimens may be required if any of the first
three tests demonstrated "rapid deterioration" behavior described in ATC-24,
"Guidelines for Cyclic Seismic Testing of Components of Steel Structures",
Chapter 4 and Commentary.

a.	All tests using the same concept must be reported, regardless of the test
results.  Information required for the report is listed in the attachment
(Attachment II).

b.	The requirement of 0.03 radian plastic rotation capacity is subject to
modifications based the strength of the beam material, the location of the
plastic hinge, the basis for which this location is determined, and to
account for behavioral uncertainties of the connection assembly.  Therefore,
the applicability of this requirement to each connection system will be
evaluated accordingly.

2.	Nonlinear finite element analysis, e.g. MSC-NASTRAN, ANSYS, NISA-II,
NIKE-3D, etc. to demonstrate that the behavior of prototype test specimens
can be rationalized by known engineering principles and properties.

3.	A clear and complete design methodology for all the components of the
joint assembly and their effect on other components.  Describe, based on
engineering principles and material properties, how each specific design
attribute and/or parameter is determined, designed and controlled to achieve
predictable and repeatable connection behavior.  These attributes should
include geometry, types of materials, doubler plates, continuity plates,
cover plates, side plates, ribs, notches, drilled holes, welds, bolts,
shaved flanges, slotted webs and/or flanges etc. 

The County?s and TAP?s extensive review of all connection systems is
required.  This review will consist of examining the submitted documents and
test results, meeting with the proposer, and TAP issuing recommendations and
reports to the County.  The TAP?s reports are issued by the Construction
Quality and Contracting Division as TAP SMRF-Bulletins.  The TAP
SMRF-Bulletins will be used to complement and interpret the SAC Interim
Guidelines when necessary. 


A number of issues need to be considered in the design, analysis and testing
of connections.  It should be recognized that each of these issues affects a
specific connection type in different ways and to different degrees.  These
issues should be considered when evaluating the performance qualification of
any connection system: 

1.	Major Contributing Factors to the General Behavior of Connections:

· Through-thickness Strength of Column Flange
· Participation of the Column Panel Zone in the Required Plastic Rotational
· Location of Plastic Hinge
· Shorter Spans/Amplified Rotation Angle
· Axial  Load on Column
· Plastic Moment Interaction with Significant Beam Drag Force.
· Beam Material Strength (Yield and Ultimate)
· Column Material Strength
· Column  Depth
· b/t Ratio  of  Column  Flange
· b/t Ratio  of  Beam  Flange
· Connection Plate Thicknesses
· Rolling Direction of Connection Plates
· Weld Materials, Weld Sizes, Configurations and Fit-up
· Stress Concentrations in Connection Elements, Including welds
· Control of Strain Levels in Critical Connection Elements
· Beam Moment Demand at Each Critical Section

2.	Configuration of Connection:

· Two-sided Strong-axis
· One-sided Strong-axis
· Dual-strong-axes
· Weak-axis and Skewed-axis
· Effect of Bracing Members
· Restrictive Effect of Concrete Slab on the Formation of  Plastic Hinge
· Effect of Perpendicular Gravity Framing

3.	Testing:

· Extrapolation of Test Results to Member Sizes Not Tested - Methods and
· Test Setup to Reflect Significant Service Conditions
· Test Protocol
· Location of Instruments on the Prototype Test Specimen

4.	Construction and Quality Assurance:

· Construction Sequence
· Erection Fit-up
· Welding Materials and Methods
· Size of Welds
· Notch-toughness of Weld
· Weld Finishing (e.g. Grinding, Removal of Backing etc.)

For comments or questions regarding the contents of this memorandum and/or
TAP SMRF-Bulletins, please contact Y. Henry Huang, Supervising Civil
Engineer III at (213)738-2832 or by fax at (213)386-4818.

Very truly yours,

Director of Public Works

THOMAS V. SCHRIBER, Division Chief
Construction Quality and Contracting Division					 



Mark Saunders, SE (Chairman)

· Vice President, Rutherford and Chekene Consulting Engineers, San
Francisco, CA.
· Director, Structural Engineers Association of California, 1993-1995
· President, Structural Engineers Association of Northern California, 1992-1993
· Vice President, Applied Technology Council 
· Chairman, Technical Sub-committee 6 on steel, "National Earthquake Hazard
Reduction Program (NEHRP) Recommended Provisions for the Development of
Seismic Regulations for New Buildings"

Karl Frank, Ph.D.

· Member of Executive Committee, Research Council on Steel Connections
· Professor of Civil Engineering, University of Texas at Austin

Egor Popov, Ph.D.	

· Professor Emeritus of Civil Engineering, University of California, Berkeley
· Member, National Academy of Engineering
· Distinguished Teacher Award - University of California, Berkeley
· Recognized by the Berkeley Citation - University of California, Berkeley
· President (1984), Structural Engineers Association of Northern California
· Member, Specification Committee, American Institute of Steel Construction

Bob Schwein, CE	

· Principal, Schwein/Christensen Laboratories, Inc., Lafayette, CA. 

Additionally, valuable contributions were made by:

Chia-Ming Uang, Ph.D.

· Associate Professor, Department of Applied Mechanics and Engineering
Science, University of California, San Diego


1.	Test location

2.	Test date

3.	Investigator(s)

4.	Details of the specimen (in graphical form), including any specific
attributes of the connection design, such as doubler plates, continuity
plates, cover plates, side plates, ribs, notches, drilled holes, shaved
flanges, slotted webs or flanges.

5.	Design methodology: describe, based on engineering principles and
material properties, how each specific design attribute in item 4 is
determined and controlled to achieve predictable and repeatable connection

6.	Material Properties:

· Member Size, ASTM Specification and Grade, Mill and Location, Heat Number,

· Certified Mill Test Report for All Base Metal
?	Complete Mechanical Properties Showing Yield Method, Specimen Type &
Location of Test Coupon in Shapes
?	Complete Chemical Analysis
?	Compliance with Astm Specifications and Grade

· Shop or Lab Coupon Tests
?	Mechanical Properties (Flange & Web)
?	Yield Strength & Method
?	Tensile Strength
?	Elongation
?	Stress/strain Diagram
?	Flange & Web Locations
?	CVN at 70oF on Column Material

· Weld Metal
?	Manufacturer's Technical Data Sheets
¨	Chemical Analysis
¨	CVN at 0o F
¨	Mechanical Properties

7.	Shop and Field Fabrication:

· Welding Procedure, Process and Electrode Specifications

· Qualification of the Welders

· Quality Control Procedure
·  · Quality Assurance Procedure

· Ultrasonic Testing Reports

8.	Testing Procedure: 

· Loading Protocol 

· Location of Instruments on the Test Specimen

· Failure Criteria

9.	Test Results:

· Force Versus Deflection Relationships

· Elastic Rotation Based on Test Specimen Column Centerline Dimensions

· Plastic Rotation Based on Test Specimen Column Centerline Dimensions

· Actual Plastic Rotation at the Assumed Plastic Hinge Location

· Basis for the Selection of the Location for Establishing the Plastic
Rotation Capacity

· Actual Flexural Capacity of Test Specimen Beam Based on Laboratory Coupon
Tests of Flange and Web

· Actual Strain Hardening Ratio at the Plastic Hinge Location

· Description of All Plastic Deformation and Rapid Deterioration Exhibited
by the Test Specimen, I.e., Weld Metal, Beam and Column.

· Photographic Documentation of the Testing Sequence