Archive for October 2007
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No Mixing, No Welding
Posted by Geoff Weisenberger on October 1, 2007 at 9:37 AM. | No Comments »
I would like to augment the answer that was given to the first
question in the August Steel Quiz, which asked about the difference
between “filler metal” and “weld metal.” The term filler metal refers
to the chemistry and physical properties of the welding metal by
itself. The term weld metal refers to the chemistry and physical
properties of the weld deposit. This metal is a combination of the
effects of the welding process, the chemistry of the filler metal, and
the chemistry of the base metal. The answer, as given, did not include
the effect of the base metal. If there is no mixing of the filler metal
and base metal, the joining process is either brazing or soldering, not
D. Robert Lawrence II, CWI, CWE
On a Misleading Note?
Posted by Geoff Weisenberger on October 1, 2007 at 9:36 AM. | 1 Comment »
Zoruba and Liddy did an excellent job of outlining the specifications relevant to current structural steel (SteelWise, March 2007). But in one of their listed items, namely Direct-Tension-Indicator Washers, ASTM F959, they offered a note "e" to their table that stated: "Washers that express colored dyes when compressed are not covered by ASTM."
This note may be misleading because our Squirter DTI washers are produced to the requirements of ASTM F959 and installed according to the corresponding procedures in the RCSC specification. The orange silicone itself is not covered by ASTM, but a DTI having this feature can still be approved on jobsites and used exactly as a non-squirting DTI is used.
We believe the squirt feature, when calibrated on Skidmores on bolts at jobsites, as the manufacturer recommends, can enable the bolt installers and inspectors to be better and more efficient, and therefore improve the constructability of steel structures.
Chris Curven, Applied Bolting Technology Products
Posted by Geoff Weisenberger on October 1, 2007 at 9:35 AM. | No Comments »
Most contractors will agree that cost is designed in. Customer requirements and site conditions, blended with architects’ willingness to surpass themselves, often result in projects that seem to be reaching new heights in cost. That said, as steel detailers we recommend that the customers not only discuss their projects with the architects, but also with the structural engineering group. Get a sound structural design recommendation first and then walk it though with the architectural firm in order to get the body and shape onto the skeleton.
I really enjoyed "Banking on Sustainability" (July MSC, p 26). This is exactly what we recommend: a fresh look at the dynamics of doing things. I congratulate Mr. Christensen on his approach and I hope that it confirms a trend in the industry. I’d like to add that you can bank on the experience of the structural engineering group every time.
As steel detailers we are quite far down the food chain and have little say in major projects. We leave this to the structural engineering group, but in many cases they too have their hands tied. Let’s change that.
Mario Lapointe, North American Steel Detailing
The Numbers Don’t Add Up
Posted by Geoff Weisenberger on October 1, 2007 at 9:28 AM. | 1 Comment »
A few months ago, I saw a press release with renderings of the Grand Canyon Skywalk and was very impressed. When I read through the release and saw the 71 million-lb, “71 fully loaded Boeing 747s” statistic, I punched a couple of buttons on my calculator and dismissed these claims as unfounded early Internet blab. To see the same stats in MSC (July 2007, p. 74), a respected industry publication, astounds me. I don’t know where those numbers came from, but they are undoubtedly false. I would be very surprised if the walkway’s live and dead loads totaled over two million lb past the edge of the cliff. Run a few quick numbers yourself.
David Soulier, P.E., Baton Rouge, La.
Not in the Spec?
Posted by Geoff Weisenberger on October 1, 2007 at 9:17 AM. | 1 Comment »
The article “Above-Grade, Below Estimate” (March, p. 55) describes a project in which hybrid girders have been used in a horizontally curved bridge. However, the AASHTO Guide Specifications for Horizontally Curved Steel Girder Bridges does not provide for hybrid girders, probably due to lack of related research.
Apparently, this hybrid bridge has been designed as a conventional bridge on a curved alignment. In your opinion, is this an appropriate design?
Andreas Paraschos, P.E.
Durability Zone Map for Parking
Posted by Geoff Weisenberger on October 1, 2007 at 9:15 AM. | 1 Comment »
I am president of a national engineering firm that specializes in parking structure design and restoration. With offices in many geographic regions, we are very aware that different exposure conditions exist on concrete slabs and structural frames in various areas of the country. However, we believe the AISC map of durability regions shown in the article “Are You Next?” (September 2006, p. 35) and also included in Steel Design Guide 18: Steel Framed Open Deck Parking Structures in Figure 2-1 is overly simplistic. The AISC map has only three durability regions:
Region A applies to the majority of the United States; it covers the southern two-thirds of the country and the West Coast.
Region B applies to the northern one-third of the country, but excludes most of Washington and Oregon.
Region C applies to areas within one-half mile of a salt water body.
This regionalization lumps areas subject to harsher exposure conditions (e.g., Colorado, Kansas, Missouri, Kentucky, Virginia, and much of Illinois, Indiana, Ohio, West Virginia, and Delaware) into the same durability design category as dry and warm weather states such as New Mexico and Florida. We believe this is unrealistic. Durability design considerations for structures exposed to snow, ice, and the use of de-icing salts can not be ignored. We’ve restored many deteriorated parking structures in these states that succumbed to the harsh exposure conditions. AISC Region A is too varying in atmospheric exposure conditions for the purposes of defining a single, one-size-fits-all durability design strategy.
We highly recommend that AISC adopt by reference the durability zone map included in ACI 362, Design of Parking Structures published by the American Concrete Institute. This map more reasonably depicts the country divided into four regions. Also, the industry does not benefit from having two separate maps apply to the design of parking structures—one for the concrete and one for a steel frame.
Gary Cudney, P.E., President, Carl Walker, Inc., Kalamazoo, Mich.