FRP versus Steel Beams
FRP versus Steel Beams
(OP)
I am looking at replacing some galvanized steel beams (W8x18 and W8x24) with something more corrosion resistant. The specific application is for a cooling tower walkway/laydown area. The beams support FRP grating around the perimeter of the tower. The galvanized coating is failing rapidly on the metal that gets tower spray (already plan to replace the galvanized handrails with FRP). I believe the design firm didn't account for as much water/evap with chemicals getting on the walkway, thus after a few years in service it is heavily corroded.
I have never designed a structure with FRP and in general my experience with FRP in field use hasn't been great (failed joints, beams shearing under impact, etc.). I have read some of the available internet info on FRP versus steel and it appears that FRP tensile strength is used as the design limit versus yield for steel. That said, it looks like the FRP design strength is nearly equal to steel (which will vary some by actual manufacturer of the FRP beams). Does anyone have any guidance in replacing steel beams with FRP to ensure loading is appropriate?
I have never designed a structure with FRP and in general my experience with FRP in field use hasn't been great (failed joints, beams shearing under impact, etc.). I have read some of the available internet info on FRP versus steel and it appears that FRP tensile strength is used as the design limit versus yield for steel. That said, it looks like the FRP design strength is nearly equal to steel (which will vary some by actual manufacturer of the FRP beams). Does anyone have any guidance in replacing steel beams with FRP to ensure loading is appropriate?






RE: FRP versus Steel Beams
RE: FRP versus Steel Beams
RE: FRP versus Steel Beams
W8x18 and W8x24 are not proportioned correctly for extended life in a corrosive environment. Like all wide flange sections their dimensions are optimized for use as beams - "thick" flanges and "thin" webs (1/4" webs in both cases). The webs are often the first site of structural failure.
Consider replacing the W8s with HP8x36, used as beams. Both the webs and flanges are 7/16" thick.
The original design may not have required a "thick" zinc coating in the hot-dip galvanizing process. Make sure the specification requires an average zinc coating thickness of, say, 4.5 mil (2 1/2 ounces / square foot).
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RE: FRP versus Steel Beams