huangyhg

brittle fracture of structural steel
are there any guidelines for designing structural steel to be suitable in cold climates? i'm speaking primarily to the issue of brittle fracture. i know the asme pressure vessel code has a lot of brittle fracture criteria for vessel design, but i'm trying to find similar design information for structures?
i have a steel lattice tower going into canada, and can not seem to find any information (us or canadian) on how to address the brittle fracture concern on the structural members.
both the american welding society and the canadian welding society have fracture critical criteria for welding, that could be at least considered for the base material. also, check the cold regions research and engineering laboratory of the us army corp of engineers....
several considerations related to toughness come to mind:
1. last requirements---cvn at lowest anticipated service temperature. what is the last...what cvn value are you specifying..20 ft-lbs?
2. wps developed by qualification testing which takes cvn into account
british code bs5950-1 (section 2.4.4 brittle failure) deals with this issue and sepcifies minimum temperatures for steel subgrades.
i also have a textbook called cold region structural engineering by e eranti and g c lee. you might be able to cover borrow a copy from the library.
i realize that there are materials and welding processes that are suitable at low temperatures, and using these materials would definitely ensure that the structure is good for the low temperature; however, i think this is the easy way out and not necessarily the most economical solution.
in the pressure vessel code (asme sec. viii div. i, fig. ucs 66.1) it gives a way that you can rerate materials to a lower design temperature, based upon the stress level that you have in the part. in order to have a brittle fracture, you need tensile stress, if your tensile stress is low then it is less likely that you will have a brittle fracture. therefore, lets say you are at 50% of the allowable tensile stress, the curve lets you derate the minimum design metal temperature for the material x degrees.
are there any similar methods available for structural applications? pressure vessels are usually governed by tensile stress, but many components in structures are governed by compression and buckling, so is brittle fracture always considered when designing structures in low temp environments? other than throwing money at the problem with more exotic materials, are there other more economical methods to design the structure for low temp?
are the towers and other structures built in canada, built using structural steels rated to lower temperatures?
astm a 709 steel ordered to meet aashto temperature zone 3 requirements isn't all that exotic. it comes in both fracture-critical and non-fracture-critical varieties.
hg

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