Reality Tests: The Real Strength Of Steel Structures & Components

By D.V. “Red Mc-1” McConnohie, Roof Hugger, Inc.

Roof Hugger, Inc. along with all other manufacturers of steel structures and components have spent large amounts of capital in research, design and testing of systems to assure maximum protection against the vagaries of nature and compliance to various engineering and building codes.

Florida product approval numbers 9561.1, 9352.1, and 9352.2 for IBC code compliant assemblies in higher wind load areas are the result of some of the extensive test series on Roof Huggers.

One can’t help but wonder however if we are not getting to the point of “over-kill”. If you examine the corner design loads in a typical South Florida roof, the first thing you notice is they approach 135 lbs./sq. ft. Thinking about that load…if the building corners are 10’ x 10’ or 100 sq. ft. that means corners must resist uplift of 13,500 lbs. If you apply the mandated safety factor of 2, that moves the load up to 27,000 lbs, keeping in mind of course, the maximum deflection allowed is L/240. In other words we are asking the roof to resist the upward force of EIGHT 3,300 lb. automobiles and not deflect over ¼” in 5’.

Such minimal deflection allowance is a major error in considering steel since the value of steel is that it gains its ultimate strength only under duress of tension or compression! Such an error in restrictive codes MUST BE ADDRESSED and corrected to stop the waste of public and private monies thrown away for no good purpose!

Typical test assembly. Click image to enlarge.

Testing as dictated by an ASTM protocol is necessarily limited to 10' x 20' or 20 x 20' "mock--ups" of roof and wall sections to fit the testing apparatus and the facilities space limits. Testing, by its nature, needs to be conservative and repeatable so the results can be relied upon. The testing analyses done today have certainly moved our industry significantly forward in providing the strongest and highest quality of roof available to our market.

Interestingly, in the case of retrofitting with a notched "Z" sub-purlin as designed and manufactured by Roof Hugger, there is no test protocol and no credit can be allowed for strength added by clamping the old roof panel down. This clamping increases the diaphragm strength of the existing building and increases the capacity of the existing roof structural support system. It is the old roof that will absorb the internal component of the total uplift loading.

The code writing authorities throughout the country are charged with finding a balance between the protection of the public, the potential losses to the insurance companies, and the cost of construction. That is always a tough job with many public and private interests having copious amounts of input. It is easy to fall on the side of becoming “over” conservative. The problem is that once adopted, codes are difficult or impossible to remove. If you have very conservative testing protocol, a very conservative safety factor, and a very conservative deflection limitation, soon we will all need tax subsidies to buy, build or rent the barest of buildings.

Reality Tests

Roof Hugger, Inc., therefore is offering herewith the “Reality” tests imposed by nature on the many retro-fitted, double roof structures in the direct path of the past 12 named hurricanes to hit Florida and/or the Gulf Coasts from 2004 through 2007. All of the buildings shown were retrofitted prior to the latest code revisions. Every other manufacturer of panels and buildings we have spoken with can provide similar testimonials. In actual Roof Hugger tests performed by Farabaugh Engrg. & Testing Co. under the direction of Tom Shingler, P.E., Design Dynamics of Dallas, TX, the addition of the Roof Hugger component in re-roofing, increased the existing load capacities by an average of 20% and lateral "stiffening" by some 30%, thus inferring significant increased torsional and lateral stability of the entire structure !

Guam. "Super Typhoon" with winds constant at 170 mph, hit a 160,000 sq. ft. shopping center with a new roof retrofitted only 6 weeks earlier. There was no roof damage, while there were severe roof losses everywhere in the vicinity.

Mobile, AL. State docks warehouse, 360,000 sq. ft. Directly on the waterfront, a retrofitted double roof completed only months prior to a major hurricane was hit at 120 mph and an 8 foot wall of water surge! No damage was reported by the contractor who further said, "Roof Hugger should show—and tell--about this in their advertising”. We agreed!

	Click image to enlarge.

Katrina! 140,000 sq. Ft. Warehouse—on the riverfront—a retrofit roof-over job was completed 4 weeks prior to Katrina, packing 160-mph winds! There was no roof or structure damage. Trim and roof vents were replaced, as reported by very happy contractor! Aerial pic shows several nearby structures -- demolished!

Results?

No retrofit, double roofs mounted over Roof Huggers were lost. None had any severe roof damage! Owners and contractors reporting in after such storms reported only that, quote, "some damage to gutters, ridge vents and trim flashings!”

Roof Huggers now support over 42 million sq. ft. of new "roof-overs”. The foregoing are typical of the "reality proof" of the old design criteria which plainly demonstrates a significant level of added strength. We are and always have been in favor of conservative design but, as shown below, there will always be unusual storm events such as tornadoes that simply cannot be designed for. Additionally, unlicensed contractor activity, poor field construction and lax code enforcement can also result in failures. These events however serious are not events that mandate design or code changes.

We should endeavor at all times not to be the cause of wasting public and private sectors monies by enacting realistic codes that protect, not punish, the purchasers of homes and commercial buildings.

One recently retrofitted structure in the West Palm Beach vicinity was struck directly in the endwall by a tornado out of hurricane Wilma. It hit with such force it separated the rigid frame rafter beams from the columns, purlins from rafters and picked up the entire end bay roof and deposited it upside down, on top of the roof of the adjoining bay. Note that the roof remained attached to the existing purlins.

Click images to enlarge.

I enjoyed my 84th birthday and my 43rd year in the metal building industry this last July. I have seen tremendous growth and countless changes over the years but each was based in a simple common sense approach to making this market and construction system the best in the world. Let’s not forfeit our common sense to the bureaucrats or insurance companies now.

Thanks to one and all in our industry for the combined--and successful--past efforts to bring to market the best of structures to provide shelter to the industries, recreational, institutional and educational needs of our USA! Roof Hugger, Inc. is proud to be a part thereof!

D.V. “Red MC-1” McConnohie, of Roof Hugger Inc., has more than four decades of experience in the metal construction industry. He is inventor of the Roof Hugger, used for reroofing over metal roofs. To contact Red, email to red@roofhugger.com.

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