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

 

Can you break me down the difference in Explosive Weight I and Explosive Weight II?

Explosive Weight I and Explosive Weight II?

Question

Can you break me down the difference in Explosive Weight I and Explosive Weight II?

 Answer

This is the criteria from the 2012 UFC:

Explosive weight I is associated with a larger weight of TNT for a van or truck bomb outside of the base perimeter.   Its based on the assumption that a vehicle bomb will not be able to penetrate the base perimeter and/or will be detected at the gate.  If we have a facility that is less than 200 feet from the base perimeter/fence, then we must consider explosive weight I in addition to explosive weight II and its pressure/impulse may govern over the explosive weight II.

Explosive weight II is associated with a smaller weight of TNT simulating a back-pack or smaller bomb that gets past the base gate.  The standoff for this explosive weight is no longer the 82 feet typical of the 2007 criteria.  Now it is based on the new conventional stand-offs that are listed in the tables based on construction type and load bearing/non-load bearing walls.  The actual stand-off must be used which is from the parking lot to the window/wall in question.

Hope this helps.  Please call if you have any questions.

Stewart P. Jeske, P.E.

JEI Structural - Glazing Systems Engineering

www.jeistructural.com

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."