Summaries for Steel Conference Toronto Canada...
Transcript of Summaries for Steel Conference Toronto Canada...
Summaries for Steel Conference Toronto Canada
Chris Hahnel
Wednesday:
We did not make it to the conference in time to attend any of the sessions. We could not skip
class on Tuesday so we spent all day Wednesday driving to the event.
Thursday:
Perforated Plate Shear Walls
I have had only a little exposure to steel plate shear walls in my schooling, so this lecture
seemed like a great place to learn something new. First off, the idea of perforated walls seemed illogical
to me for however, the lecture showed that when these perforations are slanted at a 45° they can
improve the wall as well as impacting the wall price due to less steel. I also learned that shear walls cost
more to fabricate and are more complex to design than conventional bracing but, are cheaper to erect
have a cheaper foundation and have a better seismic performance.
Seismic Design of Steel Structures
This session reinforced much of what I have learned this semester in my earthquake engineering
course. Damping in structures are initially considered about 5% but steel structures usually have about
2-3% damping. The fundamental equation which involves the input energy, stored kinetic energy, the
stiffness, and the dissipated energy were talked about in depth. It was also pointed out that drifts must
be tracked mode by mode and combined with the SRSS method.
Shanghai Tower
This was a case study into the hurdles in the design of the Shanghai tower. This talk was
amazing to see the insight and creativity that went into that structure. The first interesting thing was
that the building code there requires shelter zones every 10-15 floors. So the shelter zones are used as
mechanical floors and each mechanical floor serves the 15 floors above and below. Amazingly, the
rounded shape of the building was twisted at 120° which allowed the wind load to be reduced by 24%.
To combine engineering practicality and architectural beauty, the interior core is actually just a cylinder
that gets smaller as you go up like a wedding cake, and the exterior glass curtain wall is what twists and
slants. This building incorporates green technology by collecting water in the cone on the roof to use in
gardens and toilets while there are wind turbines built into the top that can power all the lights at night!
Lastly, an outrigger system is used to activate the whole width of the building to resist overturning
moments.
Student Session
The conference provided a student session in which two speakers spoke to only us students and
then we had a job fair session in which we got to speak with about 40 companies. The first speaker was
actually a well-known architect from Canada but her focus was on brining architects and engineers
together. Her research as a professor revolves mostly around Architecturally Exposed Structural Steel
(AESS) and its application. I have seen such steel in the past but I did not know there was a special term
for it (AESS) and that there were specific guidelines. It was a very interesting as well as informative talk.
The second speaker was from a small company that uses BIM software in their design and he simply
showed some examples of the software’s application. I have heard of BIM but I have never used it so
this was very interesting to see how it can be applied, though I did not learn really HOW to implement it.
Friday:
Iconic & Economic – Can you have both?
This was actually a bridge symposium seminar but I have experience in bridge design and it was
very interesting. This session took a short look at several bridges that were of unique design. First, was
the Vancouver Port Mann Bridge with is a cable stay bridge with a 163m tall center pylon. To connect
the cables to the spans two main options were available, the fin-type and external bucket option. The
first of which has a critical weld that you can’t see to inspect while the bucket option is bolted on and
easily inspected. The new New York Bridge was addressed in particular because it is the first design
build that NY has ever done so those hurtles were addressed. Lastly, the Shenandoah River Bridge
posed complications because they had to maintain pier locations so as to not disturb the valley. A delta
frame was used which I am not familiar with but looks very interesting. Also, such a frame is not
explicitly covered in the code so that caused some problems that were addressed.
25 Years of North American Retractable Roofs
This session was especially interesting as a sports fan to see how these roofs are designed and
the history behind them. The speakers started with the Rogers Center which was the first retractable
roof around and then moved on to discuss this likes of all sporting venues from baseball to football.
Some roofs are fully enclosing while other function only as an “umbrella.” The talk circled back to the
Rogers Center and the updates that are needed. It was interesting to hear that they have found one of
the reasons the roof struggles to open now is that because of creep in the columns over the years, the
structure is bowed inward and the roof is basically stretching the structure out every time it opens.
Also, in some places the rails on which the bearing ride is <25cm when the bearing itself is 25cm.
Seismic Innovation: New Beam Column Connections
This interests me because my master’s research is actually in seismic response of beam column
reactions. The new connection that was presented involves heat treating a portion of the end of the
beam which softens the metal and overall lowers the yield stress. They call this a HBS connection. The
heat treatment leaves the material still isotropic but the grain size increases. Compared to RBS
connections, they have found the HBS to be “just as good.”
Studies on Post Buckling Strength (Thursday 3-4p)
Three presenters talked about their research on post buckling strength in steel. The first, Basaglia,
looked into the influence of cross-section geometry on the distortional post buckling strength of
columns. He had three cross-sections (a “lipped” channel, a “hatted” channel, and a “Z”-shaped column)
that were tested to measure their deflections after buckling and apply a modal analysis to compare
with. He quickly noticed some differences that were unexplained by General Beam Theory and the
effects of typical measures of geometry (moment of inertia, for one) and plans to continue his research
to determine what is causing the difference.
The second presenter, Subramanian, talked of her research on post buckled stiffened web plate
girders. She particularly was focused on how the necessary stiffness was based on a depth to thickness
ratio, but not the post-buckling strength. Various I-girders were tested in four-point bending with lateral
torsional buckling being blocked and focusing on the center of the girder. Using these results, eight
parametric studies were conducted and found that the constant Rb used in Eurocode was close to that
measured, while the constant for AASHTO was very conservative.
The third presenter, Safar, presented on his experimentation with strengthening end web panels by
adding CFRP strips to the web. The strips allowed post-buckling strength to form in the web but would
stop the web from fully failing.
Shanghai Tower – Design and Construction Challenges of the Tallest Building in China (2,074 ft)
(Thursday 4:15-5:15p)
This was a presentation by the building’s designer, Dennis Poon, where he describes the difficulties of
designing a super high rise building. He talks on how the taper and twist design were selected to
significantly reduce the wind loads and also for architectural reasons. The building also has “amenity
floors” every 30 stories that were described as a “city in a city” with atriums and shops. The building was
designed with a shell and a core, so that the shell is doing the twisting, allowing the core to be designed
in a more traditional circular structure. The funnel formed at the top of the building collects rainwater
that can then be used for water for toilets and other water. Wind turbines are also on some of the
higher floors to generate electricity for the building. The outer skin insulates the building to help with
energy costs as well. To deal with lateral forces (seismic, wind, etc.) the building was designed with an
“outrigger” system that fights overturning. Chinese code is very strict when it comes to high rise
buildings and a lot of convincing was needed to allow some of the designs (though they would be
conservative by American standards). The overall lateral resistance was the core, outrigger, and a
megaframe truss between supercolumns bracing everything up. The foundation is made with 955
concrete friction piles because of the very deep depth to bedrock.
Field Fixes: Common Problems in Design, Fabrication and Erection – Solutions and Prevention (Friday
8-9:30a)
This presentation by Larry Kloiber covered various field fixes for common problems that arise on
jobsites. The basic message was that material is cheap, labor is not and most of the fixes involved this.
The fixes covered things such as anchor rods and specifying camber.
Case Study: Canadian Museum of Human Rights (Friday 10-11:30a)
The presentation by the designers and steel supplier of the project (in Winnipeg, Canada) covers the
design and some of the construction process. The project was a design competition that the government
hosted. The design was based on natural elements with sprawling sections to look like roots, a glass and
steel shell to look like clouds, and a mountain rising in the center core. They did a wind tunnel test on a
model of the building to determine its wind load and seismic loads were not necessary due to location.
Multiple different software programs were used in the design, with BIM software allowing them to
communicate the design quickly and across long distances. The BIM models also allowed them to
discover constructability problems while still in the design process, which allowed for a cheaper final
cost. The foundation included 141 caissons and 400 precast piles.
Seismic Innovation: New Beam-Column Connections (Friday 2:15-3:15p)
This presents the experimental results on a new type of beam-column connection. They proposed an
alternative to the typical RBS connections by heat treating the ends of beams instead, which lowers the
yield point by about 37% without changing its plasticity. The Heated Beam Section (HBS) caused no
flange distortion and reduced the residual stresses throughout the beam depth. An analytical model was
also created and agreed with experimental results. The beam was heated heat pads that are typically
used in mechanical engineering applications. The heat increased the steel’s grain size, which makes the
metal weaker.
Research on Concrete-Filled Steel Plate Sandwich Walls (Friday 3:30-4:30p)
Michel Bruneau presented his research on these walls. He started by talking about Concrete Filled
Steel Tubes which were tested for seismic and blast resistance. The CFSTs are great at blast resistance
since the steel and concrete help each other out. Just having a concrete column jacketed is not
equivalent since the steel does not go down into the foundation. Next, he talked about Concrete Filled
Double Skin Tubes (CFDST) that performed similar to CFSTs in seismic. It performed very well in blast,
where only the outer skin failed during an extreme blast. The concrete also fireproofs the inner steel
tube. For the sandwich walls, two steel plates were connected by bars and concrete was filled in
between them. He looked at a sandwich wall with and without boundary CFSTs (circular CFSTs were
used to avoid creating corner weld fractures). Concrete sandwiching SPSWs (Section H6 of the Seismic
Provisions) is not the same as Concrete Filled Steel Sandwich Plate Walls (CFSSPW)and they need their
own section, which he recommends as Section H7 for the next Provisions with his proposed design
method.
2014 NASCC Session Summaries Derek Marucci
Graduate Student University of Cincinnati
Thursday 8:00am: What Every Engineer Needs to Know About Performance-Based Design
Ronald Hamburger –
The goals of performance-based design are to protect life safety, minimize potential
repairs, and minimize disruption time for those occupying the buildings. Performance-based
design generally results in more economical solutions than code-based design. Buildings are
designed for “essential conformance” to the building code while using new detailing not
covered by the code and avoiding capacity-based design requirements. Designers need to check
with the building official to determine if consideration will be given to a performance-based
designed building. Performance-based designs need to demonstrate that the structure exhibits
a stable and predictable response to the maximum considered earthquake. Resources available
for performance-based designs include ASCE 41 and FEMA P695.
Thursday 10:00am: Students Connecting with Industry Sessions
Terri Meyer Boake –
This speaker is the main entrepreneur for developing a standard for Architecturally
Exposed Structural Steel (AESS). When using AESS, each structure should be evaluated
independently when comparing costs to aesthetics. The proposed standard will categorize the
needs, goals, and complexity of a project to streamline the design process for AESS.
Sean Smith –
This speaker discussed the use of BIM software to simplify the complexity in unique
building designs and included some of the methods used in the design of the Ripley’s Aquarium
in Toronto. The use of BIM software in this project enabled improved collaboration between
the engineers, the architect, and the contractors, which helped to simplify the complexity of
the project. The speaker stressed the advantage of using 3D modeling to visualize problems and
form solutions.
Thursday 3:00pm: Tips for Successful Delegation of Connection Design
Clifford Schwinger –
To delegate connection design, designers need to differentiate between connection
design and member design. Designers need to follow sections 3.1.1 and 3.1.2 in the Code of
Standard Practice and remember to show member reactions at the connections.
Constructability and designability need to be considered, with designability being the ease by
which economical connections can be designed for given frame configurations. Engineers
should always remember to permit consideration of alternative connection details in order to
make connections more designable and constructible.
Thursday 4:15pm: Seismic Innovation: New Beam-Column Connections
Tasnim Hassan and Machel Morrison –
New beam-column connections have been developed at North Carolina State University
to enhance the seismic performance of moment connections. A new connection type called a
Heated Beam Section (HBS), which has similar details to an RBS, involves heating a section of
the flanges to form a weaker section of a beam and the location for a plastic hinge. Another
new connection design type uses a modified bolt layout for the Extended End-Plate connection
where the bolts are positioned in an oval-shaped pattern which results in a more even
distribution of stress in all of the bolts. A third new connection design type, based on the
Welded Unreinforced Flange-Welded Web, employs the use of a modified bolt pattern in the
shear tab which results in increased yielding in the web. The end goal of this research is to have
these new connection types added to the list of moment connections prequalified in AISC 358.
Friday 8:00am: Design Tips for Constructible Steel-Framed Buildings in High-Seismic Regions
John Hooper –
The concepts that engineers can use to improve the constructability and economy of
steel moment frames include; increasing column sizes, using bay widths of 25 ft. or less, and
considering column fixity at the base. For braced frames, this means; using bay height to bay
length ratios less than or equal to five, avoiding the use of 30° fans in gusset plates, and
employing the use of modified workpoints in gusset plate design. It is highly recommended to
hold pre-fabrication and pre-erection meetings to greatly reduce the amount of errors and
issues encountered for each project that includes seismic design.
Friday 10:00am: Becoming a Results-Oriented Structural Engineer
John Miller –
To become a results-oriented engineer means to transform from being task-oriented to
results-oriented. Aim to be familiar with all structural project types and materials that your
employer uses. Becoming familiar with the AISC Code of Standard Practice will aid in the
development of complete and thorough contract documents and drawings. Before agreeing to
work on projects, evaluate the risk and keep in mind that sometimes walking away from a
project is the best option. Keeping promises and commitments with clients, as well as
developing relationships with them, will lead to higher project satisfaction.
Friday 2:15pm: Northridge: Twenty Years Later, The Changes that Resulted in Fabrication
and Erection
Robert Hazleton –
The lack of understanding of welders in the shop and in the field was a contributor to
the damage experienced in welded moment-resisting frames in Northridge. Another key issue
involved applying multiple and conflicting references from AWS and AISC in the designs of the
connections. One of the first responses to Northridge was AISC Technical Bulletin 3 which
established upper yield limits for 65 ksi steel and a maximum yield-to-tensile ratio of 0.85. Also,
new systems have been developed including proprietary moment frame connections, buckling
restrained braces, and steel plate shear walls for use in seismic force resisting systems.
Northridge has also led to the development of performance-based design practices that have
enabled engineers to design more economical and better performing structures.
Richard Kennedy
Graduate Student
University of Cincinnati
Summaries on seminars attended at NASCC 2014, presented to SEAoO for student travel
funding.
S6. Studies On Post Buckling Strength. Thursday 3:00 – 4:00 p.m.
1. C. Basaglia summarized research on the effect of unique geometric shapes on post-buckling
strength. The shapes were (1) channel with tails bent inward, (2) channel with tails bent
outward, and (3) zee with tails bent inward. Computational GBT-based analyses assumed
linear elastic material properties with initial imperfections up to 10%. Buckling modes for
all shapes were calculated, and the modes could be added together (linear elastic) to get the
analytically derived buckling curve. The local buckling is very similar between the three
shapes. Global buckling was about the minor axis for the channels, and major axis, minor
axis and torsional for the asymmetric zee. The channel with tails bent inward showed higher
post-buckling strength.
2. L.P. Subramanian presented the impact of longitudinal stiffeners on flexural resistance of
plate girders. The test was run by finite element analysis, putting the specimen under
uniform moment. Initial imperfections were chosen by first running analyses to find the
failure shape, then scale the failure shape down to initial imperfections for the next run.
Results showed that Rb = Mmax/My was larger for the finite element analyses than predicted by
AASHTO and the Eurocode. Also found that you get diminishing returns when increasing
stiffener width.
3. S.S. Safar presented the influence of beam slenderness, a/h ratio (deep beam influence), and
number of CFRP strips. When used, CFRP strips acted in the direction of the tension field.
All tests were designed to fail in shear. Beams with small slenderness (more compact) and
small a/h (deep beams) showed the best strength gain when CFRP strips were used. Current
equations find the nominal shear strength by Vn = Vcr + Vpb, where Vcr is from Timoshenko
and Vpb is from AISC for intermediate web panels. This study showed that strips are good
for elastic end web panels.
N62. Shanghai Tower—Design and Construction Challenges of the Tallest Building in
China (2,074 ft). Thursday 4:15—5:15 p.m. Dennis Poon.
I found this presentation most interesting from what I saw. Shanghai Tower is still under
construction, and for a short time will be the second tallest structure in the world. The lateral
system is perimeter mega columns tied to the fuse coupled core wall by outriggers at several
mechanical levels. The floor plan is constant for a zone, which is about 14 to 16 stories between
mechanical levels, and floor diameter decreases with height. 55% taper at the top was chosen to
balance sexiness, useable floor space, and reduced vortex shedding. The exterior curtain wall
(the building has 2 sets of curtain walls) has a shape that will reduce wind loads (tested in wind
tunnel with 8 m tall model) by twisting the guitar pick shape 120° over the height. Poon shared
difficulties in dealing with the Chinese government. First mode Tn = 15 s was unacceptable to
gov’t who wanted Jin Mao Tn = 7.6 s, so they negotiated Tn = 9 s. Earthquake laws are very
stringent, one requirement being the entire structure must remain elastic for a 60 year EQ.
Interstory drift limits included both shear and axial overturning, which is unfair to such a slender
building. One advantage to the Chinese gov’t was closing surrounding streets to speed
construction, especially the foundation mat which required a 60 hour continuous pour.
B17. Iconic and Economic—Can You Have Both? Friday 8:00 – 9:30 a.m.
1. David Goodyear. The Port Mann Bridge near Vancouver is a cable-stayed single pylon 10
lane bridge. A single pylon was deemed necessary because of tight ROW requirements. The
pylon tower uses shear walls and contains an elevator for maintenance. Vancouver being a
high seismic area, the soil-structure response was modelled using nonlinear soil springs.
Wind tunnel tests showed that chamfering the girders would reduce vibrations. Before
building the superstructure, the foundation design was tested by pre-jacking a pile to find that
compression was better than predicted and tension failed not by pull out but by pile fracture.
2. Ken Wright. The Tappon Zee Bridge near New York City is a cable-stayed bridge with 4
lanes in each direction and the ability to add rail between the girders at a future date. The
entire water crossing is approximately 3 miles. The owner wanted a structure that would not
require substantial repairs within 100 years, so the team had to use proven technologies.
Coupled with the required use of labor unions, the best choice was a steel bridge. This
allowed for rapid construction on shore, which is safer for workers, and a lighter
superstructure. Also aiding in the construction safety was the enormous crane that could
place the entire main span at once, as opposed to the standard practice of cantilevering from
the pylon.
3. Jason Fuller. The Shenandoah River Bridge near Washington, D.C. replaces a small 2 lane
bridge. The design started as a deck truss, but the owner was scared by the I35W collapse of
a deck truss, so design proposals were requested again with deck truss out of the picture. The
winning design is a delta frame, which would meet the pier placement requirement in a cost-
effective way. However, there is limited recent use of delta frames, so the design team had to
learn the system together. The most interesting part of the system is the knuckles—
connections between delta frame and either bridge girder or pier—which are extremely stiff
(CJP welds) which reduces wind loads, and have large stress concentrations.
S9. Beedle Presentation Session: Professor Sriramulu Vinnakota. Friday 10:00 – 11:30 a.m.
The Beedle presentation is unique in that the recipient, Dr. Vinnakota, is able to present any
subject of his choosing. He chose the gradual improvements in computational power and the
impact of these improvements on the ability to model structural stability. In the 1960’s, he used
a computer with the equivalent of 900 words of memory to model portal frames with members
that can spread plasticity. Shortly thereafter, he used a computer with 33,000 words to model a
larger test with P-∆ and P-δ. In 1972, the computer had 128,000 words, and he was able to
analyze more general members and load patterns. Continued improvements allowed more rapid
modelling of biaxially loaded columns to choose specimens for a test research program. In 1996,
Vinnakota had a student who modelled a 16 story, 8 bay frame with partially restrained
connections. He concluded by comparing the computers’ ability to model inelastic stability
(from very basic to very complex), and suggested that in 30 years we use our understanding of
inelastic structural stability (currently Appendix 1 of AISC 360) by placing it in a chapter.
N26b. Seismic Innovation: New Beam-Column Connections. Friday 2:15 – 3:15 p.m. Tasnim
Hassan and Machel Morrison.
This seminar described a new process that can be used to guarantee ductile hinging of beams in
seismic moment frames. Currently the best way to do this is with a reduced beam section away
from the weld and shear tab at the column. The proposed method involves heating the beam
flanges where hinging should occur, allowing the crystal structure to change, and slow cooling to
get larger crystals (lower yield strength). This reduces residual stresses, and when loaded it gets
similar stiffness as RBS, but maintains strength better. This process was applied to EEP and
WUF-B connections in AISC 358 to get a good hysteretic behavior (no brittle fractures) without
stress concentrations these connections typically see.
N29b. Research on Concrete-Filled Steel Plate Sandwich Walls. Friday 3:30 – 4:30 p.m.
Michel Bruneau.
The presentation began by explaining how research led from concrete filled steel tubes to
concrete filled sandwich walls. Under lateral loads (blast) a steel tube around concrete will help
it survive large shear and bending. With another tube inside, casting the concrete as a donut, the
column is able to even further resist fracture (the outside tube fractures, but inside tube is intact).
Putting this into wall form by “unrolling” the donut, it was found that round corners are better at
avoiding weld fractures. The walls behave very differently from steel plate shear walls, which
yield in shear. These are designed to yield in flexure, and ties in the wall are used to prevent
local buckling. Using “vertical boundary elements”, the walls are able to undergo larger drifts
before local buckling (after yielding) and fracture occur.