High-Performance Composites

NOV 2014

High-Performance Composites is read by qualified composites industry professionals in the fields of continuous carbon fiber and other high-performance composites as well as the associated end-markets of aerospace, military, and automotive.

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Page 64 of 67

N O V E M B E R 2 0 1 4 | 6 3 angular columns, slab construction, etc.) and condition, and compared to the origi- nal construction drawings, if available. A key step is locating and mapping the re- inforcing steel inside the concrete, which is accomplished with ground-penetrating radar (GPR) equipment. Other nonde- structive testing methods (e.g., pin test- ing) are used to measure the concrete's resistance to penetration. Typically, cores extracted from the concrete are subject to microscopic examination and compres- sive strength tests in the laboratory. The goal is to identify, quantify and evaluate compression strength problem areas. The investigative team uses the site in- spection data to build a virtual layout of the building, using modeling software de- veloped for repair/strengthening applica- tions. SAP2000 from Computers & Struc- tures Inc. (Walnut Creek, Calif.) is one of several programs used. "What the model- ing ultimately helps determine is, can the building withstand the load requirements desired by the customer? Are required upgrades constructable and cost-effec- tive, when compared to replacement?" says Thomas. Answers to these questions help the team develop and cost a specifc repair or rehab strategy. "Carbon fber is one of several solu- tions we can implement," he points out. If the modeling shows that the required actual load demand exceeds the exist- ing capacity by more than 40 percent, the strengthening options must be able to carry signifcant primary loads. Op- tions include bonded steel plates and enlargement of existing concrete struc- tural members. However, if the increase in load conditions is less than 40 percent, the most cost-effective solution, he con- tends, is Structural's trademarked carbon fber/epoxy V-Wrap material. Made with a proprietary unidirectional fabric of inter- mediate-modulus carbon fbers supplied by Toray Industries Inc. (Tokyo, Japan, and Decatur, Ala.), the material can be used alone or in combination with the options listed above. Labor costs typically drive strengthening projects, so the cost of the carbon isn't a factor, Thomas claims, and the relative ease of application can actu- ally help reduce project costs. "Composite" action V-Wrap works because it becomes an integral part of a concrete member via bonding, resulting in what Thomas calls "composite" action. The term is a refer- ence to the fact that the carbon/epoxy laminate and the concrete column or slab to which it's applied act together to bear applied loads. To achieve this effect, however, surface preparation is crucial, Thomas stresses. Grit-blasting and grind- ing with specialized abrasive disks (with the dust and debris vacuumed away) ensure a clean surface on undamaged concrete. "The concrete is like a big, hard sponge," he explains. "You've got to open the pores and get the resin to fully pen- etrate to achieve an effective bond." Dry V-Wrap fabric sheets are wet-out at the job site, using Structural's in- house-designed feld saturators. (A satu- rator dips fabric in a resin bath and then passes it through precisely gapped roll- ers and/or scrapers, to yield a wet layup with a precise — and project-specifc — resin content, without air bubbles that could result in voids.) Where and how V-Wrap is applied is guided by Structural's extensive experi- ence, the modeling results and, in Reinforcements for rehabilitation projects When Courthouse Square (Salem, Ore.) was in need of repair and strengthening, to address design and construction errors, V-Wrap carbon was part of the solution. The V-Wrap on this column in the Salem parking garage (inset) was combined with a bigger column footer and a cast-in-place capital (square casting around column top) that increases punching shear capacity. Source: Structural COST-CONSCIOUS REHAB by sara black illustration / karl reque and upgrades of reinforced concrete.

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