Existing Steel Structure with Low Toughness Resistance at 0°C 2

[Logan82]

Hi,

I have a situation where a Charpy test indicates less than 20 Joules at 0°C for the main beams of an old existing steel structure on which there is a hoist used to lift a single load of 30 metric tons. The crane members are not covered by an envelope, so therefore the structure can sometimes be at a temperature of -30°C. There are 2 main beams, with no redundancy.

Here are the things I worry about from what I understand of the situation when the temperature of the structure is below 0°C:
- Fatigue. However I believe I can calculate the number of fatigue cycles remaining using the Charpy value.
- Ductility of the structure, since it does not respect the minimums presented in the Handbook of steel Construction 10th Edition:

One solution is to limit the use of this building when the temperature is at 0°C or higher. However this is not feasible in reality.

In CSA S16-19, it says "Statically loaded structures that are subjected to low temperature do not normally require the use of notch-tough steel. In these structures, brittle fracture can normally be avoided by following the design and fabrication criteria provided in this Standard and CSA W59."
Source: CSA S16-19 31.1.1

Also:
"Dynamic loading shall be taken as a loading condition that creates strain rates greater than 10^–3 s^–1 but less than 1 s^–1. Impact loading shall be taken as a loading condition that creates strain rates greater than 0.1 s^–1. The impact of stress concentration shall be included in the evaluation of the strain rate."
Source: CSA S16-19 31.3.2

My questions are:
• How can I calculate the strain rate in my structure to know if the live load is an impact load or a dynamic load? In my case, I have a live load, seismic load, and wind load, however the live load is the most important load.
• Is there an other solution to this problem other than verifying if this structure can be classified as statically loaded?

 

[AUCE98]

You may want to consider reviewing ASME BTH-1. It addresses some of the concerns regarding dynamic loading, fatigue, and operational temps.

 

[EdStainless]

You can calculate stresses, so you can figure out the strains.
Getting a strain rate takes a bit of estimation but it isn't that difficult.
The cranes that I have worked with came in three varieties: Very carefully designed to minimize notch and fatigue issues, or so over designed that the stresses were low and not an issue, or death traps.
The biggest problems that we had was with rail supports and rail splices.
These are places where high local loads are inevitable and more difficult to address.

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P.E. Metallurgy, consulting work welcomed

 

[Logan82]

Thank you both for your answers, in my case the structure is built very close to 100 % of structural utilization. I used the lifting speed and the max stress to determine the strain rate. The strain rate looks close to 0.001 s^-1, but I have to confirm some estimates before finishing this project, so the live load would be in fact a dynamic load.

The live load of 30 ton is not very often lifted by the hoist, so the fatigue is not a big problem here.

My biggest issue is if the structure fails in a brittle manner instead of a ductile manner under 0°C.