Frequently Asked Questions
Fortress Stabilization Systems Engineer and Contractor Resources
ENGINEER / CONTRACTOR
Q. How are Fortress Stabilization Systems grid straps different from other forms of carbon fiber?
A. Prior to Fortress grid strap, there were two types of carbon fiber commercially available: wet layup (tow sheet), and protruded plate. Both of these have pros and cons. After evaluating the strength and weaknesses of available products, Fortress developed the Carbon Fiber/Kevlar grid strap.
Wet layup: Must use more fabric for wall coverage to achieve desired strength and must be impregnated on the job site, which is messy. This also requires a much higher skill level in getting tows straight. Any misalignment of tows and carbon has no strength at all. If used on damp walls it may also fail to properly bond.
Protruded Plate is very strong. However, its is also very rigid and typically has very poor bonding capabilities. Epoxies do not bond well to epoxies or polyester resins. This can be a disadvantage on deflected surfaces. It also depends on a “sandwich” bond, where voids can be typical and unseen.
Fortress Stabilization Systems Carbon Fiber Kevlar Grip Straps has the advantages of both the wet lay up and protruded plate but eliminates the disadvantages related to both.
Q. Do I always need to install straps on 4ft. centers?
A. In compliance with A.C.I. #530 the maximum spacing for external reinforcement is four times the thickness of the masonry wall, translated is 4ft., this is with a 2.5 safety factor.
Q. Will carbon fiber straighten a wall?
A. The simple answer is no, and most ways of straightening walls require excavation.
Tie-backs may, over a period of time, straighten walls to a certain degree. Tie-backs tend to creep or loosen and may punch through and twist a masonry wall when tightened. So the required tightening of tie-backs every 6 months is adjusting the grip that can loosen. The lamination of carbon fiber will hold the wall in it’s current deflection or can be applied after straightening to hold the wall in place and strengthen the foundation.
Q. My walls move with the seasons. Cracks open in winter and close in the summer. How does this affect the carbon fiber?
A. By tuck pointing all cracks at the time of carbon fiber lamination, will assure a wedge when the wall attempts to hinge. Tuck pointing material goes into compression not allowing the wall to move outward, while the laminated carbon fiber will not allow the wall to move inward.
Q. A competitor is showing us that their carbon fiber is much stronger than Fortress, what does this mean?
A. We manufacture a 12k, 24k, 48k, 80k as well as a 100k. The 50k grid makes sense for higher wall and loads; however, it is overkill for an 8ft. high with 7ft. backfill. What they neglect to inform you is that you will never achieve 40,000 tensile or even close to 20,000 tensile before the bond will fail.
One manufacturer makes a 4″ steel beam and the other manufactures a 6″ beam. A 2″ beam is required. Of course, the 6″ beam is stronger. Or is it? Not really, because neither the 4″ or 6″ will ever load up. The connection will fail before the steel does.
Q. How does FRP perform in fires on interior installations?
A. Strengthening of a Structure Composite Design Guide ACI 440-F states:
A Class-A FRP system can be used as long as it is self-extinguishing. A Class-B can be made a Class-A by utilizing ¼ gypsum board or coatings.
Fire ratings can be misleading. Fire ratings are a timetable calculating the time a person has to leave a burning building. A Class-A fire rating is a measure of how much smoke is produced and how quickly the resin burns.
Painted on fire coatings such as in tumescent paints help by swelling and insulating the surface below. The reaction time of a coating and heat deflection of epoxy is far different. For example: heat deflection of Fortress 4020 is 175 degrees and foaming of coatings is around 300 degrees. Most epoxies are self-extinguishing after the fire source is removed.
FRP is a Reinforced Polymer or plastic. The kind of fibers used play little role in its performance in a fire. The fibers maintain their physical properties at high temperatures; they are actually produced at extreme temperature. Carbon Fibers are manufactured by cooking at roughly 1,900 degrees F.
It therefore is the bonding agent that is in question under fire. The most common bonding agent is a thermo set plastic, two-part resin: such as epoxies, vinyl esters and polyesters. It is Glass Transition Temperature Tg. where polymer begins to soften and how resin performs. Thermo-sets do not re-harden and lose any physical characteristics of hardened laminate.
Tg is a function of initial cure temperature. For example: many per preg plates and grids are cooked over 300 degrees. Therefore their glass transition is at or higher than 300 degrees. Epoxy resins in the field are usually cured at room temperature and have a Tg of roughly 120 to 175 degrees.
In conclusion the difference between 120 degrees Tg and 300 degrees Tg is simply the amount of time. Yet you will have a Class-A fire rating. A thermal barrier such as ¼ gypsum board will improve this. But like many of the compounds that make up a building, depending on the duration of heat and smoke, many components may be lost and in need of replacement.
Q. Why use Fortress Carbon Kevlar Staples for stitching concrete cracks?
A. Crack injection became less expensive with the introduction of dual cartridge tube sets, dual dispensing guns, etc. However, it also became too easy. Everyone with a pulse began shooting cracks with some kind of sealant.
Poured wall companies, when they are slow, will pull a guy off a crew and send them out for warranty repairs. Find a contractor today that doesn’t offer a warranty, but are they still in business 2 or 3 years later when the repair fails.
Very few crack repairs fail immediately. It is long-term creep and fatigue of material injected with the movement of foundation that can fail over time. By cross-stitching crack repair with staples this creep is eliminated, improving long-term performance of repair material. Think in terms of 3 roof repair options giving a 10 yr, 20 yr or 30 yr warranty vs. the cost for quality.
Q. Is Carbon Fiber Reinforcement in the Building Code?
A. Yes. However the original ICBO codes are and have been changing based on new codes and ACI 440 Technical Guidelines. Therefore only a very few manufacturers have across the board approval. This is actually a good thing as our systems have upgraded dramatically over the last seven years, so approvals are based on outdated systems. All Fortress products are manufactured and meet ACI Guidelines as well as ASTM Standards.
The most common test method is ASTM D-3039.
Q. How far out of plumb / bowing is allowable?
A. The code that covers the alignment on a wall is ACI 513.01. The code states that the maximum out-of-plumb is 1/4″ for a distance of 20ft. Any foundation contractor will say that this is like asking for a perfect wall. Regular tools would probably not measure this accurately.
The National Association of Home Builders (NAHB) has prepared their own guidelines to help resolve issues that arise in all types and kinds of construction, not just foundation walls. It is the Residential Construction Performance Guidelines (RCPG) 4th edition. This guideline says under, Basement and Crawl Space Concrete Block Walls, sections: “Observation” A concrete block basement wall is out of plumb “Performance Guideline” Block concrete wall shall not be out of plumb greater than 1″ in 8ft when measured from the base to the top of wall. This is what contractors use as guidelines when building foundation walls, provided that there is a contract signed by the owner and contractor agreeing to the guidelines. A true plumbed wall foundation that is built out of plumb to the 1″ in 8ft can stay that way for the life of the building, provided that there are no unusually high lateral forces action on it or cracking. Unusually high lateral forces can cause cracking and bowing even on a perfect aligned wall.