Welding reinforcing plates to stressed members 1

[dlew]

Hello!

I am working in the reinforcement of an existing steel structure to carry additional loads. We are planning to add reinforcing plates to those members that need them. The existing dead load stress in those members is approximately 15 to 20 ksi. Live load is relatively small.

The current AWS D1.1 tells the Engineer to determine if the member to be reinforced should be permitted to carry loads while heating and welding is performed, and to consider the effect of the elevated temperature in the stability of the member.

Previous editions of AWS D1.1 specifically mentioned that the level of existing stress should not exceed 3 ksi, and that the proportioning of the reinforcement should take in consideration the existing stress.

Given the vague requirements of the current D1.1, what is the standard practice to determine if the members have to be relieved of the dead loads?

Since the yield stress in the steel does not start dropping until the temperature reaches 650F, and the temperature during welding generally does not exceed 700F on a very small portion of the cross section. Is there an actual concern about the stability of the member/structure? Or is the distortion of the member by unsymmetrical welding what the code wants to eliminate?

Is there any book, article or other information that treat this subject in more detail?

Thanks in advance!

 

[metengr]

I don't have a copy, but I would check the AISC - the American Institute of Steel Construction manual. They may address the issue of adding weld reinforcement to existing members.

 

[unclesyd]

USACE TI 809-26 1 March 2000

STRENGTH REDUCTION EFFECTS AND OTHER CONCERNS WHEN WELDING UNDER LOAD.
a. Elevated Temperature Effects. Elevated temperatures in steel reduce both the yield strength (F ) y
and the modulus of elasticity (E). At approximately 300 C to 400 C (600 F to 800 F), F and E are
reduced approximately 20%. Preheat temperatures at this level are rarely used, but localized
temperatures near the weld region will exceed these temperatures for brief periods. As a general guide,
steel during welding, within the weld region, will exceed these temperatures approximately 25 mm (1 in.)
to the side of a weld, and a distance of approximately 100 mm (4 in.) trailing the weld puddle. Steel
further from the weld region will remain at temperatures that will not significantly reduce the steel’s
properties.
b. Welding Direction and Sequence. When welding under load, consideration should be made for the
temporarily reduced strength of localized areas of the steel. When welding parallel to the applied stress,
the affected area is typically small compared to the area of the unaffected steel. When welding
transverse to the load, additional caution is needed. It may be necessary to stagger welding operations,
use shorter sections of weld and then allow cooling, or use lower heat input procedures.

 

[AlohaBob]

We generally require shoring or bracing stressed members to remove the question of failure during welding.

 

[dlew]

Hey Guys,

Thanks for your fast response. Your comments and references were very useful and are appreciated.