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`Carbon Fiber Reinforcing
`Making Double Tees in Parking Siruciures lighter and Sironger
`iii}! Harry A. Gieiofi. RE” FACI. FPCi
`
`As a lightweight. non—corrosive "enabling teclmology," car—
`bon fiber grid reinfirtcement allovvs double tees to be lighter.
`more durable and often less costly in the long run than
`conventional precast products that rely on steel reinforce-
`ment. Exceptionally strong, carbon fiber delivers 6,000 lbs;Ir
`lf of strength {comparable with steel reinforcement used in
`reinforced concrete design} and has tensile strength over five
`times that of steel. (Diil’iErent strengths are available, though
`the strength is consistent throughout the same sheet.) A car-
`bon fiber grid displays linear elastic behavior until failure.
`Epoxy coating chemistry and small—aperture grid design pro—
`vide excellent bonding to concrete and superior crack control.
`
`Carbon Fiber Reduces Concrete Cover
`'12.! minimize corrosion of steel reinforcement, double tee
`
`into the flange to
`manufiicturers incorporate concrete cover
`protect
`the steel mesh From water and corrosive chemical
`compounds.
`In Fact. most pretopped double tees have a
`minimum Hange depth ol‘l’i inches to provide ample cover for
`the steel mesh. In many cases, manufacturers put more concrete
`in the flange than is necessary to support expected loading. The
`extra concrete protects the reinforcement. it also adds weight,
`which until now has been largely unavoidable.
`it allows precast
`Because carbon fiber is corrosion-resistant.
`manufiicturets to reduce the amount of concrete cover in each
`
`double tee flange by up to 3% inch. Conventional prestl'essed
`strands in the stems are protected by more than 12 inches of
`concrete as measured fitom the top oFthe flange.
`Reducing the Flange thickness by 5/3 inch remiwes 9 pounds
`per square foot of dead load, which can either provide more
`reserve capacity or reduce the amount ofprestress required. And
`by eliminating the need to add cover over the reinforcement
`to resist corrosion. precastcrs can optimize the position of
`the reinforcement. moving it closer to the top surface of the
`flange to maximize performance and provide even better crack
`control. By moving the reinforcement toward the top of. the
`flange, precasters have been able to provide up to 2 'fr inches of
`
`E—GHID Reinforcing
`Concrete
`
`i---------------------4
`
`C :
`
`I
`
`.._ Presttessmg Strand
`
`arising structures represent one of the most demand-
`ing applications For concrete. They're exposed to the
`weather 24 hours a day. seven days a week. They’re
`expected to support hundreds or even thousands of vehicles.
`including today's heavyweight SUVs. And they‘re constantly
`exposed to corrosive agents such as salt used to clear roads
`during winter and chloride—laden air and ntoi5ture along the
`coastlines, or both in places like Boston and New Yorlc City.
`
`
`
`.
`t
`£9 rein!” in dc'iiiuiidin I re riuiu iii-r rouse near nmrine environments.
`grin-cg: declining is sim'ryiriiir’r m ju‘niiirim trim-(i in tire ammo».-
`nfiriaifiirrmrur
`
`Regardless of their source. chlorides have the potential to
`cause corrosion in some of the steel reinforcing. generally the
`secondary flange reinforcement. When the steel cortodes.
`it [Here than doubles 11-1 VDl'LUTlC and C311 Cause Cracking Dr
`spalling as well as unsightly staining — problems the building
`or garage owner would like to avoid. Corrosion isn't a problem
`everywhere, but in geographic areas where it
`is common, it has
`die potential to be a garage owner's Worst nightmare.
`A new approach to reinforcing double tee flanges involves
`die use of carbon fiber grid as a replacetnent for conventional
`steel mesh reinforcement. Carbon fiberis non-corrosive which
`
`virtually eliminates the problems noted above. as well as the
`cost of admixtures and barriers used to inhibit corrosion. Pit
`die same time, carbon fiber reinforcement can reduce the
`
`amount of concrete necessary in the flangewleading to a 12
`percent reduction in double tee weight—without compromising
`structural performance: the flanges have been tested For both
`point loads and un iform loads to meet the test load requirements
`of'both [BC and AC1.
`
`High—Tech Fibers Come to Precast
`Say the words “carbon fiber" and most people thinlc of
`items such as
`jet
`fighters,
`tennis racquets. bicycles, golf
`clubs and motorcycle components. Within the past decade.
`manufacturers have developed lower cost.
`industrial—grade
`carbon fiber For broader use in demanding construction
`applications. As a result, the precast concrete industry has been
`able to benefit from the same outstanding strength—to-weight
`ratios and durability characteristics that have made carbon
`fiber an ideal material to take a jet fighter to Mach 2 or propel
`Lance Armstrong through the French Alps.
`
`Cross Sectlon
`
`Double Tee—Narrow Leg
`
`Hermite mrimn fiber is corrosion resistant. irniinriopri'ritrrrrr to reduce
`die anterior dft‘tiiifit‘i'fft‘ {'QLI’P‘iH weir dntrbie reefbngr by up to Mind;
`
`STRUCTURE mogozine
`
`July 2006
`
`Metromont Ex-1003, p.1
`
`Metromont Ex-1003, p.1
`
`

`

`
`
`stnictural concrete below the mesh reinforcement, compared to only 2
`inches of concrete in typical precast double tees — important because
`the flange is designed as a prop cantilever.
`
`Strong and Durable Reinforcing
`Protecting the steel mesh reinforcement in conventional concrete
`double tees costs money. A number of chemical
`treatments are
`typically used during double tee Fabrication and after installation to
`inhibit and delay the corrosion of steel mesh in the flange.
`With non-corrosive carbon fiber reinforcing, manufacturers can
`avoid the cost of sacrificial barrier coatings on the steel and eliminate
`the need to add corrosion inhibiting admixtures to the concrete.
`Meanwhile. owners can forego the application of sealers to the precast
`deck surface after installation and also avoid re-applying these sealers
`every five to ten yea rs.
`From an initial cost standpoint, carbon fiber tends to be more
`expensive than steel mesh. However. when one considers the increasing
`cost of steel.
`the cost for corrosion inhibitors. potential reductions
`in substructure and site costs, and increased life span, carbon fiber
`reinforcing can lower life cycle costs dramatically, especially after the
`first decade of operation.
`Laboratory testing has affirmed the performance of double tees
`with carbon fiber reinforcement. Load testing demonstrates they can
`stand up to the heaviest sport utility vehicles. Fire tests confirm that
`they can meet ASTM E-ll9 fire rating for one-hour performance,
`and calculations show that. just like steel mesh reinforced tees, they
`can provide a two-hour fire rating with 4 5/3 to 4 3/3 inch thick flanges.
`'l'est reports are available.
`
`Practical Applications
`A 27fl.llflll-square-foot.
`four-level parking structure in suburban
`Milwaukee has carbon fiber reinforced double tees on the top deck.
`The owner. a developer that leases to a Fortune 500 company. opted
`for carbon fiber reinforced double tees because of their long-term
`durability and resistance to corrosion- The owners choice was especially
`important considering the top deck is exposed to Milwaukee's harsh
`weather. everything from ice storms and severe snow to summer heat
`waves. The 15-foot wide double tees have a two—hour lire rating to
`match the balance of the garage.
`Another precast project. designed to replace a badly corroded,
`condemned cast—in-place structure located near the New Jersey shore,
`is also being constructed with pre-topped carbon fiber reinforced
`double tees. Several odier projects are currently in the engineering and
`evaluation phases.
`
`A New Technology... A New Delivery Model
`The application of carbon fiber reinforcement heralds the first
`major advancement in precasr technology in decades—perhaps since
`
`
`
`A 270,000—5gome—flror. firrr—frodporl'rng structure in wombat: Mineral?“ om
`carborrfifurr reirrfirccd dam”: rm
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`_-‘.'d.
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`fkrbonfiéfl deft-wry 6.000 fésféfiofstrcrz‘g'tb and )5er tmrife strength oycrfitlc
`mm: dim ofrrrer’
`
`the introduction ofprecast itself: Several of the nation's leading precast
`companies have collaborated to develop,
`rest and market carbon
`fiber reinforced products such as pretopped double tees, architectural
`cladding panels. high perliirmance insulated wall panels and precast
`components for residential uses.
`Their partnership establishes a new model for the introduction
`of new technologies to the precast concrete industry. By pooling
`resources. expertise. and technical knowledge. and by working
`together to develop best practices. these companies have expedited
`the introduction of carbon-fiber reinforced precast concrete. The
`daunting cost and time to bring this technology to market could haVe
`been too much for one company to absorb. But as a collaborative
`unit. the partner companies' commercialized carbon fiber reinforced
`precast concrete in only two years.
`The use of carbon fiber reinforcement is an important innovation
`because it promises improved corrosion resistance by eliminating steel
`reinforcement
`in double tee flanges. Compared with conventional
`precast concrete, poured-in-place and other options, carbon fiber
`reinforced pretopped double ters can deliver reduced weight and life
`cycle improvements, especially in highly corrosive environments.
`[t is likely that the use of carbon fiber reinforcement will grow in
`popularity as its elfectiveness is validated by a variety of installations.
`With architects and engineers clamoring to be the “first one to be
`the second one in." carbon fiber reinforcement should gain a rapid
`following as the innovators give way to early adopters and the early
`majority — and possibly one day make this novel precasting technology
`the new industry standard.I
`
`Him)! Clark. VP ofEngincerirrgfor the Metromont Corporation. he:
`more taboo 20 years crazier-Emir: in rbeprcmsr concrete industry He is or:
`mine memo” 1'n the Promo/Betweed Concrete Industry (PCB, booing
`served on the rcvmdPCI Design Handéooil' Commizm and currentrlyar
`Charmer: ofrbc Parking Structure: Committee. He rir r: member ofrbc
`technology committee and boardof—dircdonfirfllmGroup, opal-rumba}
`ofpier-err concrete momfimramr that have collooomrcd to expertise the
`commercialization ofmroonfiocr rer'nfirccdprrcarr concrete.
`
`ALWSGROUP IS a CONSORTIUM OF Lemme PRECAST
`COMPANIES COILABORA'ITNG TO DEVELOP, TEST AND
`MARKET CARBON FIBER REINFORCED PRODUCTS-
`
`THIS COLLABORATION HAS ENABLED THE FIRSTeEVER
`NATIONAL ROLLOUT OF A NOVEL PRECAST BRAND,
`CARBONCAST. manuspmszcm
`
`PRECAST, HELDENFELS ENTERPRISES AND MORSE BROTHERS.
`
`NIEMBBRS OF THE Accuanouo INCLUDE: OLDCASTLE,
`HIGH CONCRETE GROUP, METROMONT Coaeonimon.
`GATE PRECAST, SHOCKEY PREcas'r GROUP, BLAKESLEE
`
`STRUCTURE mogozine m July 2006
`
`Metromont Ex—1003, p.2
`
`Metromont Ex-1003, p.2
`
`