Delegated Design in Specs for Glazing Systems

We've been asked to review several engineering company’s calculation packages and found engineers
stamping calculations that don’t meet specifications and code requirements.  Please check your calculation packages to be sure.

We found:

1. DL of the frame was not taken into consideration (flexure/axial load interaction) Typical C-Beam Calculations did not include axial load interaction with flexure required by the Aluminum Design Manual
2. Corner location analysis (75% WL acting simultaneously). Bite loss or movement into glazing pocket was not checked. Analysis of corners for 45 degree orthogonal loading was not considered as required by ASCE 7. Important for bite loss at the glazing pocket.
3. No Jam/perimeter mullion deflections to check caulking requirements. Deflections at Jamb perimeter joints were not checked for appropriate joint design. Important for preventing leaks at curtain wall interface to the structure.
4. LL movement was not taken into consideration at all.  Building structural live load movement and system thermal expansion was not accounted for in joint design, splices and glazing pockets. This is required by contract specifications as part of the delegated design.
5. Analysis of local buckling modes and lateral torsional analysis was omitted but is required by the Aluminum Design Manual.

“If undone, you are buying calculations half done                                                and not according to code requirements.”

It may be tempting to overlook it and we understand some contractors will simply say, "It's not worth the effort."  Just keep in mind that these calculations are a part of the “delegated design” required by contract documents. If left undone, glazing contractors, general contractors, AEs and the building owners are buying a design half done and not according to code requirements.

“Half done calculations may result in glass breakage, joint leakage, system failure or other liability.”

Half done calculations may result in damage such as glass breakage, joint leakage, system failure or other liability that quality service providers choose to steer clear of.

Let’s work together to design systems fast, affordable and correct.

Info@ JEIstructural.com 

816-505- 0987

FAST | CLEAR | FRIENDLY | RIGHT

Info@ JEIstructural.com 

816-505- 0987

Codes Changes Creating a Cladding Mess

If you’re a glazing contractor or a building envelop contractor; an estimator or project manager, you’ve probably tried to size your storefront and curtain wall members off of a wind design pressure.  

The wind design criteria are usually given on the contract structural drawings.   Sometimes design wind pressures for components and cladding are given as well.  However, the changes with the 2012 IBC have created much confusion regarding the actual design pressures to be used.

Many times the components and cladding pressures listed on the structural drawings are given in terms of “Ultimate strength design”, which is not used in any of the wind load charts given by manufactures.   Using these pressures will ultimately lead to overly conservative design.

Designers need to be able to calculate the allowable strength design loads from the information given off of the structural drawings.

If you have a question about what is on a structural drawing, give us a call.   

Stewart Jeske

816-734-8345

www.JEIstructural.com

 

Updated UFC 4-010-01 (2012) - Impact to Glazing Contractors

Based on a quick review, here are the major changes/impact that I see:

1) The biggest change – Conventional Construction Stand-Off Distances. This is a huge change!

They have re-identified the conventional construction stand-off distances in Table B-2 based on the wall type construction. I anticipate the net effect will be a moving to wall construction which minimizes the construction stand-off due to spacial constraints associated with military bases. So for reinforce masonry and concrete and wood studs w/brick that means about 30 feet and 16 feet and 36 ft respectively! Glazing systems with these requirements will not likely be able to have static equivalent calculations performed – They will be forced to dynamic analysis. I anticipate that these types of installations will start showing up late summer to fall of this year.

2) Another major impact – Testing Requirements. This is also huge! The requirements state that the testing must meet the appropriate pressure and impulse from the applicable standoff and explosive weight. So, given the changes with the Conventional Construction Stand-Off Distances most all of the manufacture’s blast testing (at 82′ Ex weight II and 144′ Ex weight I) will be obsolete! I feel badly for all of the manufacture’s who have invested a great deal of effort and resource to testing in the past 5 years.

3) Dynamic analysis is pushed. Under paragraph B-3.1.3 ASTM F 2248 Design Approach (This is the 3-second static equivalent method) they state, “In order to reduce the conservatism associated with using the ASTM methodology, the window systems may be designed using dynamic analysis or tested …”

4) Framing calculations under the static equivalent method is changed. Framing must now be shown adequate with a design load of 2x the glazing resistance instead of the 3-second equivalent blast load. In some cases (with small glass lites governing – Its usually the case that the Architect is unaware) this will be the difference between 50psf (typical 3-sec load) and 400 – 1200 psf! L/60 is used as a deflection limit now instead of L/160, but I don’t think that will help much – sections will need to be much stronger using this method.

5) Connections and anchors under static equivalent method is changed. The connections and anchors must be designed for either 1x or 2x the glazing resistance instead of the typical loop holes that we have seen 2x the 3-second load (usually 100psf). Anchors and connections at these loads will be difficult if the controlling glazing lite in an elevation is small. I think anchors into masonry and wood and light-gage steel will not be workable with this method.

6) We are now able to Use ultimate strength design instead of allowable stress, but again this helps little in light of the major changes above.

 Stewart Jeske, PE
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Kauffman Performing Arts Center - Built for snow

JEI Structural was honored to do a small part of the glazing calculations on the lower portion of this structure.    We didn't work on the roof, but we're happy to see that the Kauffman Performing Arts Center performs well with snow loads.
http://www.kmbc.com/news/26577116/detail.html

How experience for design calculations saves time and money

Some glazing contractors don’t budget enough for appropriate engineering calculations (structural calcs) on projects. Those who do, understand the value of industry expertise. Some glaziers brag, “I’ve got a guy that does it on the side.” The truth is, a structural engineer with industry experience will save you time and money.

Structural engineers with glazing system experience are familiar with industry manufactures and have worked with their components and framing, so you’ll end up with system components and anchors that will work. An experienced engineer will always look at the boundary joints to make sure that excessive movement will not compromise the joint water barrier. In addition, years of experience usually results in a quick turn around using better software, specifically for aluminum curtain wall and storefront design.

Experts in aluminum code won’t over design your project. Aluminum design is specialized and requires adherence to the complex 2010 Aluminum Design Manual. This 469 page book larger is larger than the steel code! Few engineers ever pick up aluminum design, due to it’s specialization. University curriculums for structural engineers focus on steel, concrete and CMU. Aluminum is never used in the design of building or bridge structures so most structural engineers just don’t come across it in their everyday work. This type of experience is essential if you want your glazed system to work without problems for years to come.

So next time you need design calculations, hire experience. You’ll save money in the end.

Antiterrorism: Blast-resistant Glazing Systems

The environment of rapidly evolving antiterrorism codes has left estimators and manufacturers in a whirlwind of confusion asking themselves, “Why do blast resistant requirements seem to be a moving target?” It’s important for us to understand what is driving this part of the glazing industry. A great emphasis has been placed on protecting the inhabitants of government buildings from flying shards of glass due to explosion. The U.S. government will be investing great amounts of capital into protective glazing systems during the next 10 to 15 years to make the changes necessary to their existing buildings and for all new construction. The two major codes driving the changes are GSA/Interagency Security Committee Security Design Criteria and the U.S. Department of Defense Unified Facilities Code UFC 4-010-01, Minimum Antiterrorism Standards for Buildings. The UFC code requires all future DoD programming beginning in 2004 to include blast resistant glazing systems. Over the last couple of years we have begun to see many of these projects entering into construction and it’s essentially the same story for the GSA’s programmed projects.

For more insight on this topic see:

http://www.glassmagazine.com/article/commercial/antiterrorism-blast-resistant-glazing-systems-and-moving-target

Government Bid Lists - glass & glazing specific

Do you want the best industry specific government bid list?

Checkout: http://www.jeistructural.com/web/govt-bids

Recovery money is starting to flow into the glass and glazing industry. Now is the time to position your company to recieve business.

Misinterpretations of UFC Requirements

Are the anchors for your blast resistant glazing systems appropriately designed?

There are many misinterpretations of UFC requirements for blast resistant design among engineers. Some engineers solely design anchors for two times the static equivalent blast load determined from ASTM F2248.

However, UFC 4-010-01 (2007) also requires a minimum anchor design equivalent to the resistance of the glass determined from ASTM E1300.

Many engineers miss this requirement, but UFC, under section B-3.1.1.4 Connection Design, state, "The actual connection design load is dictated by the glass type and thickness determined by ASTM E 1300."

Therefore, the correct design load is the maximum of either two times the static equivalent blast load from ASTM F2248 or the resistance of the glass from ASTM E1300. The intent of UFC is to design anchors such that they will not fail before the glass.At JEI Structural, we stay up-to-date on the latest codes and offer many value-added services.

Let's build together,

Stewart P. Jeske, P.E.
President
www.JEIstructural.com

"Expert engineers for commercial glazing calculations."