FEMA
SPECIFICATIONS AND STRUCTURAL MANAGEMENT
New
FEMA guidelines will change the way steel-framed buildings are constructed.
By
MICHAEL J. MAYES
Mayes Testing Engineers
Blue
comments from Ed.
Steel
buildings and structures have been designed and built for over 200 years. With
improvements in steel making and joining technologies, such as welding, it has
been possible to build taller buildings with longer spans between supports.
Get the FEMA reports
Order a free copy of FEMA's steel moment-frame
reports by calling (800) 480-2520. Find them online at www.fema.gov/library/lib06.htm.
A 31-page nontechnical summary for owners and tenants is also available online
at www.fema.gov/library/354final.pdf.
The ductile and toughness properties
of steel also have made it an ideal material to resist earthquake forces. Ductility
is the ability of a material to stretch and deform without breaking or cracking.
Brittle materials, like glass or cast iron, would exhibit poor ductility and will
crack when overloaded. Toughness, a property related to ductility, is the ability
of a material to resist fracture in the presence of a notch or defect.
In
1995 Lincoln recommended the E70T- 4 weld wire for structural joints designed
for seismic applications. This wire was known to have poor ductility and required
no AWS impact requirements that would indicate weld toughness.
Since
the 1960s structural engineers have used welded steel moment-frame designs in
seismic zones such as the Puget Sound. This configuration utilizes steel beams
welded to steel columns with complete-penetration welded connections designed
to fully transmit stresses from the beam to the column. These structures were
thought to be earthquake-proof, or at least incapable of collapse during a seismic
event.
The
structural components typically would have been able to with stand the loads and
stresses if welded with the common E7018 stick electrodes or E70T-1 gas shielded
flux cored wires, but had no chance with the E70T-4 wires, the selection of which
was an incredable management and engineering blunder.
Brittle
fractures
The 1994 Northridge California earthquake changed this perception.
A large number of steel moment-frame buildings were found to have cracks at or
near the welded connections. These cracks were brittle fractures instead of the
expected ductile behavior that was expected. These findings alarmed designers,
building officials and contractors. While there were no collapses of steel frame
buildings at Northridge, the damage compromised structural systems and created
significant economic losses as a result of repair and relocation of building occupants.
Why
were designers, building officials and contractors alarmed? It appears the design
of the structural components was sound while the welds which means weld consumables
were the primary cause.
After
the Northridge earthquake, the Federal Emergency Management Agency (FEMA) provided
funding to the SAC Joint Venture, which was formed by the Structural Engineers
of California, the Applied Technology Council and California Universities for
Research in Earthquake Engineering to provide research and testing to solve the
welded moment frame fracture problems.
If
you read the first section you will know what a joke this last paragraph is.
New
beam-to-column connections were developed and tested. Procedures for welding,
testing and inspection were extensively reviewed. Welding and steel products were
analyzed and tested.
ALL
THE WELDING QUALIFICATIONS TESTS AND PROCEDURES HAVE BEEN DONE SUCCESSFULLY WITH
EXISTING STANDARDS AND CODES THAT HAVE PREVAILED SINCE THE SECOND WORLD WAR.
Now we have new
structural steel weld recommendations driven from an inept political organization
that should retain its focus and resources in assisting the victims of disasters.
The
result of this $11 million effort was four publications:
FEMA-350, "Recommended
Seismic Design Criteria for New Steel Moment-Frame Buildings";
FEMA-351,
"Recommended Seismic Evaluation and Upgrade Criteria for Existing Welded
Steel Moment-Frame Buildings";
FEMA-352, "Recommended Post earthquake
Evaluation and Repair Criteria for Welded, Steel Moment-Frame Buildings";
FEMA-353: "Recommended Specifications and Quality Assurance Guidelines
for Steel Moment-Frame Construction for Seismic Applications"; and FEMA-354,
"A Policy Guide to Steel Moment-Frame Construction."
These
documents are written as recommendations. Structural engineers may incorporate
them into designs and specifications or may provide other justifications, such
as connection testing, to support alternative structural systems. While the recommendations
are written for moment frames, many engineers have adopted FEMA welding provisions
for other earthquake-resisting lateral systems, such as steel brace frames.
Engineers,
designers and building management will
love this stuff, lets face it this is what they want, someone to hold their hands
while they make a complex decision on a fifty year old, two control, simple weld
process.
THE BS NEVER ENDS IN THE WELDING INDUSTRY:
BECAUSE OF APATHETIC STRUCTURAL MANAGEMENT, ENGINEERS AND DESIGNERS WHO WOULD
NOT ACCEPT PROCESS MANAGEMENT RESPONSIBILITY AND HAVE TYPICALLY ALWAYS RELIED
ON WELD SALESMANSHIP FOR ADVICE, WE NOW HAVE THE BLOODY GOVERNMENT LEADING THEM
DOWN THE WELDING PATH.
The
FEMA recommendations, while not mandatory, have become the state of the art for
new construction. Efforts are currently under way by the American Welding Society
and American Institute of Steel Construction to incorporate the FEMA provisions
into codes and standards.
What's new for contractors
Welding procedures:
New welding procedures may require qualification testing. Welder qualifications:
Welders welding on steel moment-frame connections need to demonstrate competence
on special weld joint mockups.
For
the fifty years those of us interested in quality welding called this Weld and
Procedure Qualification.
New connection designs: Structural
engineers are incorporating new connection configurations. Base metal: New steels
are specified for seismic applications. Welding wire: Many welding products are
no longer suitable for seismic work, especially the self
shielded weld wires recommended by Lincoln.
Welder training:
New seismic welding wires will require training and practice for welders. Weld
testing: New requirements for testing and inspection. (Every
weld company needs to do this fundamental function). Contractors
need to provide access and allow time for increased inspection. Specifications:
New recommendations are being incorporated into project specifications and structural
notes.
Contractors need to review these documents to properly qualify subcontractors
and suppliers.
FEMA-352 evaluation procedures were used to evaluate several
existing steel moment-frame buildings after the Nisqually earthquake. At this
time there doesn't seem to be any of the brittle fracture-type damage detected
in Puget Sound structures. Since the design and construction of Puget Sound moment-frame
buildings is similar to the damaged California buildings, it is likely that recent
earthquakes have not been strong enough to cause brittle fracture. (again
please remember a simple point frequently not emphasized. The great percentage
of brittle fracture issues was with the poor weld wire selection ).
FEMA-351
provides methods to evaluate probable performance of existing structures in future
earthquakes. Owners of existing buildings can use these procedures to evaluate
safety and financial factors when considering upgrades to higher seismic performance
standards. FEMA-354 provides a nontechnical overview of the of the steel moment-frame
issue.
FEMA-350
and FEMA-353 apply to design and construction of new buildings. Recent or current
buildings under construction, which incorporate the new FEMA provisions, include
the Sea-Tac Airport terminal expansion, Sea-Tac air traffic control tower and
the new federal courthouse project.
Changing practices
The
new FEMA recommendations have required the entire construction team to adopt new
practices and procedures. Structural engineers are incorporating new FEMA details
and connections into drawings and specifications.
Most structural engineering
curriculums do not include welding metallurgy or weld joint design. Many engineers
are attending seminars or are using welding engineers as subconsultants to review
welding procedures on their projects.
For
gods sake read a
book.
Steel
fabricators and erectors have had to write, and qualify by testing, new welding
procedures that produce weld joints with good ductility and toughness. Welding
product manufacturers such as Lincoln, Hobart and ESAB are now producing "FEMA"
wire with special packaging in controlled lots.
FEMA
WELD WIRE MEANS YOU WILL NOW HAVE ACCESS TO AN OF THE SHELF REGULAR QUALITY WELD
WIRE THAT PROVIDES WELD AND MECHANICAL PROPERTIES SUITED TO NUMEROUS QUALITY WELD
APPLICATIONS.
The
certified lots of welding material are tested by the manufacturer or user using
maximum and minimum welding variables. This is the way
reputable weld consumable manufacturers have always made normal weld consumables
.
Steel
mills are now providing steels with tighter control of chemical and mechanical
properties.
The new FEMA recommendations place much more emphasis on tighter
quality control, by both contractors and the owner's inspector. There is increased
nondestructive examination such as ultrasonic and magnetic particle testing. Ultrasonic
testing technicians must be trained in new evaluation techniques and must demonstrate
that they can accurately detect weld flaws. Good luck.
This will put many contractors out of business when the numerous weld defects
become evident.
Fabricators
and erectors need to set up quality-control systems which monitor welding variables.
Welders must weld special weld joint mockups to demonstrate their ability to weld
the configurations that will be used for construction.
Once systems and
procedures have been set up, projects are proceeding without delay or significant
cost impact. The lessons of past earthquakes are providing better and tougher
structures AND HOPEFULLY WELD WIRES
for future earthquakes.
