With the recent undertaking of a new independent study into the way commercial tents are ballasted when staking is not an option, the Tent Rental Division(TRD) of the Industrial Fabrics Association International (IFAI) has stepped in to find answers to the questions once found “taboo” by most in our industry. At the recent IFAI Tent Expo, where the green light was given to fund and start the process of this study, there seem to be quite a bit of confusion about what this study will tell us and how the information will affect our businesses. Here we will try to discuss, at least from one manufacturer’s perspective, what this will all mean to us the manufacturer, and you the tent renter.

Structural Engineering: Why do we have it?
While most tent renters throughout the country have yet to be required to provide structural engineering documentation for their tent installations, a growing number and especially those in larger metropolitan areas are being asked for this documentation. If we avoid the inconsistencies of when and where they ask for this information and truly focus on the reason why they request this documentation we can better understand where code officials are coming from.

The primary need for this information falls within the International Fire Code (IFC) and ultimately in the hands of your local municipalities building department to provide safe environments for their population. The wording of the IFC requires that tents (temporary membrane structures) shall be “structurally sound”. In many circumstances the fire officials that would be supplying you a special event permit to install a temporary membrane structure, will request information about the tent you will be installing and its structural stability, i.e. drawings, flame retardancy certification, installation manuals, and often generic engineering data to show how the tent has been designed. In other instances, fire officials will simply defer to their counterparts in the municipalities Building and Safety department, as they are the “true experts” on building codes in your municipality.

Typically, once your permit application has been directed to Building & Safety for review, you’ll almost always need to supply specific engineering documentation for your tent installation. This is when you’ll need to contact the manufacturer of your tent/structure for assistance in getting the documentation that you will need.

The tent I purchased is engineered, but is it really engineered for every installation?
This is a question that is asked, but rarely fully understood. The fact is that every municipality has different requirements to meet their specific building codes and every installation site has its own specific characteristics that can change how the tent will need to be engineered. In layman’s terms a tent installed in a sheltered area in the middle of Chicago will have different requirements and loads when compared to the same tent installed in Miami right next to the ocean.

To prepare ourselves for a wide rage of requirements, we as the manufacturer have to constantly update our engineering documentation to meet ever changing requirements to the building code and be flexible when municipalities have internal modifications to currently accepted building codes.

Most often when you purchase an engineered tent system, the system is pre-engineered for a specific code, under specific exposure requirements, at a specific wind velocity. The engineering documentation and calculations that test the components of the design most often terminate with a series of reaction forces or loads at the point of the ground. This transfer point of the forces from the tent to the anchoring system is quite possibly the least understood aspect of the engineering process.

Although your tent system might be pre-engineered and you have gone the extra step of securing site specific engineering documentation for the tent installation from your manufacturer, you can still see failure of the system well below its designed rating if you do not also confirm the resistance/holding power of your anchoring system. The best way to do this and the only way to limit your liability is through the added step of engineering your anchoring system.

In most situations where you will be staking tents, the preferred testing method for your anchoring system will be to have a “pull test” preformed. This test is often conducted by a local testing laboratory. These types of companies can be independently hired well in advance of your installation to join you at the installation site where you will drive a series of stakes around the work site. They will perform actual failure testing of the anchors and document the different values of failure at different locations throughout your job site.

With this information you can then submit the failure loads back to the structural engineer that engineered the tent to certify an anchoring plan that will resist the loads of the tent to be installed. This process usually adds additional costs unless they are already included within the scope of work of your original engineering proposal.

Understanding your anchoring:
With the release of the 2006 study for “Pullout Capacity of Tent Stakes” performed by The University of Illinois and funded by IFAI, the industry was better able to understand how the physics behind anchoring a tent with tent stakes all works. The study covered six (6) different soil conditions ranging from “hard” to “very soft” and addressed the following and how they affect the performance of the anchor; stake diameter, stake penetration depth, stake driving angle, guy line tie off points, and several commonly used methods of multiple staking.

The study by no way guarantees how stakes will perform at your specific site location, but it does offer significant information on what methods work and which do not. The study also provided some helpful advice for gauging your soils capacity by assessing how deep the stake penetrates the soil with each blow of a 16lb sledge hammer.

With the recent undertaking of a similar study by the IFAI to understand the physics behind anchoring your tents with weighted ballast, we expect to clarify how weighted ballast performs when being used as an anchoring point. For years, tent rental companies have been using weighted ballast to anchor their tents when staking is not an option. For the most part, these installations are not engineered nor endorsed by the manufacturer of the tents. This puts a tremendous liability on the hands of the tent rental company performing the installation.

The new study will be addressing friction levels of different surfaces and how they affect different objects used for conventional ballasting. The study will also address how the performance of the ballast changes as you change the height of connection, change the angle of connection, and several other key elements.

When completed, this study will not tell you how much weight to use, but rather give you an approximate multiplier of how the ballast can resist the reaction forces of the tent system. The study will also provide a similar group of information of how different variables found on your installation can affect the performance of the ballast. The net sum of all of this information will make us all more knowledgeable of how ballasted anchoring works.

Safety Factors: Why they are needed?
One common misconception about engineers and the work that they perform is that many think that engineers add safety factors on top of safety factors and their finished designs and recommendations are too conservative. The true fact of this situation is that structural engineers use safety factors to account for the unforeseen, slight variances in component strengths, unexpected loads, and/or degradation. Essentially, the engineers do not want the design to fail when the wind blows 1mph over the design load.

Through the process of running the engineering calculations, the reaction forces on all of the components of the design are determined. These are the forces that each component will need to withstand to resist the loads of the design. At the point of checking each individual component of the design, the engineer will compare the reaction load on the component, to the individual components allowable strength. The difference between these tow numbers is the safety factor.

Although safety factors vary for different applications, you need to be aware that most tent engineering documentation provides only a reaction load at the point of connection to the anchoring system. If an engineer were to design you an anchoring system for a specific installation, they too would apply a safety factor in addition to the reaction load provided by the tent calculations.

What it all means:
With a better understanding of the needs and requirements of our local building officials we all can make better, more educated decisions when we are faced with the hurdles of pulling tent permits. We feel the better we and you can understand the needs of both the permitting officials and the engineers who sign and “stamp” their name to the designs they engineer, the safer and more efficient we can operate. One thing is certain, codes and their implementation will change over the years, but they will never cease to exist. The better you understand the code, the better suited you are to making good business decisions.