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.