The slender steel and cold formed steel structures are normally prone to local buckling. The FRP is regarded to be a high strength and high stiffness material. Will it be cost effective to apply FRP on the highly slender steel or cold formed steel sections to prevent local buckling, so that overall sectional load carrying capacities can be enhanced.
Please have a look at recent Master's thesis at Queen's university.
STRENGTHENING SLENDER S-SECTION STEEL COLUMNS USING CFRP PLATES OF VARIOUS MODULI by Allison Christine Ritchie (Jan 2014)
This thesis investigates strengthening slender steel columns with carbon fibre reinforced polymer (CFRP) plates of various moduli. It was demonstrated that adding CFRP strips to steel columns does increase the strength of the column. . The gain in axial strength due to CFRP retrofitting ranged from 0% to 25%, depending on the various parameters.
https://qspace.library.queensu.ca/bitstream/1974/12258/1/Ritchie_Allison_C_201406_MASC.pdf
FRP composites do not perform well in compression members therefore I would not recommend this method for strengthening slender steel columns.
The FRP are strong in tension not compression. No point from using them in your case.
Thanks
Please have a look at recent Master's thesis at Queen's university.
STRENGTHENING SLENDER S-SECTION STEEL COLUMNS USING CFRP PLATES OF VARIOUS MODULI by Allison Christine Ritchie (Jan 2014)
This thesis investigates strengthening slender steel columns with carbon fibre reinforced polymer (CFRP) plates of various moduli. It was demonstrated that adding CFRP strips to steel columns does increase the strength of the column. . The gain in axial strength due to CFRP retrofitting ranged from 0% to 25%, depending on the various parameters.
https://qspace.library.queensu.ca/bitstream/1974/12258/1/Ritchie_Allison_C_201406_MASC.pdf
While FRP indeed has significant contribution to local (not global) buckling, encasing the slender steel section in concrete seems to be a wiser alternative in your case. Concrete encased steels have superior performance against both local and global buckling. Besides, they have significant long-term durability with an acceptable behavior against fire-induced demands. The concrete can be either of reinforced or unreinforced types depending on ductility demand of the element. Obviously, compared with FRP, concrete is much more preferable from an economical perspective.
Thanks. What about cold formed steel sections with very thin gauge webs of 0.9 to 1.2 mm? They are quite commonly adopted in lightly loaded roof purlins. Will FRP improve the local buckling prone sectional properties and enhance the load carrying capacities? Normally cold formed steel is not encased in concrete and shear studs can't be welded onto it.
If your intention is to avoid local buckling, no shear connector or shear stud is required as load transfer would occur through direct bearing. This technique has been successfully used in buckling restrained braces in which no shear transfer occur between the steel core and the surrounding mortar. Meanwhile, the steel core would not buckle (locally or globally), thanks to the provided direct bearing.
FRP strengthening the are definitely dedicated to the slender columns.
But cost effectiveness determines a lot of parameters and you can not forget about the cost of execution time, the social costs such as the bridge of exclusions of use, the cost of living an so on.
I used the CFRP at strengthen short concrete column at our researches.
I saw it is good for strengthen them, but it is costly.
FRP won't be effective to improve bucking behavior of clod form steel purlins. FRP is effective to resist tension capacity of the section and consequently it increases the ultimate load carrying capacity. However it has minor effect of the overall section stiffener for steel members which is the key factor for bucking capacity of the member.
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