Welding and testing - A36 backer with A572 plate at base plate - CJP

[ATSE]

Consider a bent plate pole section, 16 sides, 36" in diameter.
Pole plate is 1/2" wall
Base plate is 2" thick
Pole and base plate are A572-50ksi
Welded joint is similar to TC-U4a-GF (AWS prequalified CJP, GMAW)
Application is telecom / utility pole, where wind governs (TIA 222-G and ASCE 7-05 are governing codes)
Cyclic vs. non-cyclic: for some reason, TIA 222-G does not address whether poles and towers should be considered static structure or cyclically loaded structures, even thought the testing and detailing requirements are quite different. I believe most design-build fabricators treat these structures as statically loaded for purposes of AWS requirements.

1. Is it acceptable to use ASTM A36 (36 ksi) backer. Backer is permanent (left in place).

2. Does the AWS code require NDT? It appears like the AWS code leaves NDT completely up to engineer - correct? Seems like visual inspection + UT is appropriate, even if "static" structure.

 

[gtaw]

The basic premise of AWS D1.1 is that all welds are subject to VT as the baseline inspection. Additional NDT is at the discretion of the Owner (typically exercised through the Engineer).

Only welds subject to tension and classified as fatigue categories B and C are required to be subjected to volumetric testing.

You may want to review AWS D1.1-2010, Part D Specific Requirements for Design of Tubular Connections to determine if the conditions of the “Stress Range Threshold” require fatigue to be considered in your design.

Considering the diameter of most cell phone towers at their base, a CJP double bevel groove should be considered.


Best regards - Al

 

[ATSE]

Al - Thank you for your response. The base plate is mostly continuous, with a moderately small hole in the middle (25% to 50% of the pole diameter), so a double sided weld is not possible without specialized welding equipment.
The base plate center hole can be enlarged, up to the outside diameter of the pole above (sleeve or socket connection), but unless the plate is very thick (over 3") the flexibility of the plate creates large secondary moments in the pole wall - something many tower engineers ignore until they see the results of a detailed FEA analysis.

 

[gtaw]

Most of the cell phone towers I've seen have man-ways cut through the lower end of the tower. Access is not usually the problem with those installations.

The question is whether you meet the criteria where fatigue is a consideration. If the design parameters require fatigue as a consideration, the backing will have to be removed.

An alternative to the backing bar is to place a backing weld on the ID using GMAW, FCAW, or SMAW, back gouge from the outside, and weld from the outside using the process of your choice.


Best regards - Al