Lamellar Tearing and Built-up Angles 4

[RFreund]

I'm trying to get some feedback on built-up angle joints. For some reason I just don't like the look of these. It doesn't seem like you will develop the full capacity of the steel before cracking of the joint, but hopefully I am wrong. Below are some welded joint details for built-up angles where the joint is in bending.

Are these more or less what you would use to achieve a full penn weld at the joint in order to use the full yield strength of the plate?

EIT

http://www.HowToEngineer.com

 

[WARose]

What is the thing in red......and how do the blue plates attach to it?

 

[dhengr]

RFreund:
On all three welds, you would want to make 3 or 4 (several) passes in the groove, then go to the backside of the weld, back gouge it and reweld it with some (maybe small) reinforcing fillet weld. Then move back to the main groove and complete that weld. In case 1, on the “F” pl. weld, I would make that a larger reinf’g. fillet weld. On the “V/R” pl. weld I would use a smaller reif’g. fillet weld on the inside. In case 2, I would do as above with a larger reinf’g. fillet on the reentrant corner. You have put the grooves in the right places to minimize the potential of any lamellar tearing at the raw edge of a pls. You should show the straight “grind flat” or circular arc shape over your groove weld symbol to show that it shouldn’t be only .75% filled.

 

[JAE]

How thick are these plates? I always understood lamellar tearing to only apply to > 1 1/4" or thicker.

 

[RFreund]

dhengr:
Thank you, very helpful.

@WARose:
I did a poor job of posting this. I was going to discuss a specific situation, but then wanted to talk about a more general idea. Which is lamellar tearing and if there a concern or check and if the thickness starts to get large, does there start to become more of an issue?
The specific case (fyi): The red is a concrete beam. It needs to support a new load on the side of it which sits on an angle.

Thanks again.



EIT

http://www.HowToEngineer.com

 

[RFreund]

@JAE
Not sure yet, but that is what I was wondering - is there an issue at a certain thickness?

EIT

http://www.HowToEngineer.com

 

[JAE]

In your AISC manual there is a discussion on lamellar tearing in Section 1 I believe. Thinner plate sections aren't usually subject to it and I think they discuss this there.

 

[Ingenuity]

...but that is what I was wondering - is there an issue at a certain thickness?

AISC DG#21 states: "...that while there is no distinct thickness below which a guarantee can be made that lamellar tearing cannot occur, AWS D1.1, clause 2.7.3, advises that the concerns increase..."

“…especially when the base metal thickness of the branch member or the required weld size is 3/4 in. (19  mm) or greater… .”

 

[dhengr]

RFreund:
It is not some specific thickness where the problem starts, but the thicker the stl. pls. the more likely there could be a lamellar tearing problem. Generally, thinner pls. do not cause a problem. It has to do with the thicker pl. being stiffer, more restrained, through the thickness, that the through thickness mechanical properties are not quite as good as those in the direction of rolling (in the plane of the pl.), and finally that the rolling process induces/causes some weak planes parallel to the rolled surface of the pl., exactly where the lamellar tearing might take place. Finally, with thicker pls. the welds are invariably much larger and cause substantially larger weld shrinkages and residual stresses caused by that welding, and these combined, is what causes the lamellar tearing. Over the years, AISC has had some good journal articles, and the like, on lamellar tearing. That might be a good place to continue your search.

 

[dauwerda]

For those interested, here is a response that we received from Larry S. Muir with AISC regarding lamellar tearing:

I cannot provide a date when lamellar tearing became a less significant issue in our industry, but your general perception is correct. It is much less of an issue than it once was. I have worked in the steel industry for over twenty years, and I have never personally been involved with a project where lamellar tearing occurred. I have only heard of a couple potential instances of lamellar tearing over that time period.

The following statements in AISC documents support the idea that lamellar tearing is less of an issue today than it once was:

• Section 5.4 of AISC Design Guide 21 (a free download for members from

http://www.aisc.org/dg)

addresses lamellar tearing and states, “Current steel-making practices have helped to minimize lamellar tearing tendencies. With continuously cast steel, the degree of rolling after casting is diminished. The reduction in the amount of rolling has directly affected the degree to which these laminations are flattened, and has correspondingly reduced lamellar tearing tendencies… The incidence of lamellar tearing today is significantly reduced as compared to the past, due mostly to proper joint selection and better steel chemistry.”

• The Manual states, “Although lamellar tearing is less common today, the restraint against solidified weld deposit contraction inherent in some joint configurations can impose a tensile strain high enough to cause separation or tearing on planes parallel to the rolled surface of the element being joined… Dexter and Melendrez (2000) demonstrate that W-shapes are not susceptible to lamellar tearing or other through-thickness failures when welded tee joints are made to the flanges at locations away from member ends.”

Neither the 2016 Specification nor its Commentary mentions lamellar tearing. There is no requirement in the Specification to UT the base metal. There are requirements to UT CJP welds in Section N5.5. There are also toughness requirements in Sections A3.1c and 1d.
Section J6.2c of the Seismic Provisions includes requirements to UT base metal in some instances. There are no pre-fabrication UT requirements and the post-welding requirements apply only to specific conditions. It states, “After joint completion, base metal thicker than 1½ in. (38 mm) loaded in tension in the through-thickness direction in T-and corner-joints, where the connected material is greater than ¾ in. (19 mm) and contains CJP groove welds, shall be ultrasonically tested for discontinuities behind and adjacent to the fusion line of such welds. Any base metal discontinuities found within t/4 of the steel surface shall be accepted or rejected on the basis of criteria of AWS D1.1/D1.1M Table 6.2, where t is the thickness of the part subjected to the through-thickness strain.”


While the Specification for Safety-Related Steel Structures for Nuclear Facilities does not contain UT requirements for base metal, it does acknowledge that the engineer of record may wish to impose project-specific requirements. Section NA3.1d states, “The project specification covering material for structural components that, as a result of proposed welding procedures, design details, etc., are susceptible to lamellar tearing shall, as determined by the engineer of record, include the requirement that the material shall be either ultrasonically examined in accordance with ASTM A578/A578M, Level C, or tested in tension in the through-thickness direction (z-direction). The resulting percentage reduction in area in the z-direction shall not be less than 90% of that in the direction of material rolling.” A User Note states, “In determining the need for prefabrication inspection and the inspection acceptance level, the engineer should consider the geometry of the joint, the material type and grade, the anticipated quality of the material, and other experience factors. See Chapter NN. Lamellar tearing is generally caused by the contraction of large metal deposits with high joint restraint; lamellar tears seldom result when weld sizes are less than ¾ in.”

I also recently worked with a colleague and an individual working at a U.S. mill to write the following for an article that may be published in the near future:

“Lamellar tearing is one consideration related to this anisotropy. Several factors play a part in lamellar tearing, including joint configuration and steel chemistry. The manufacturing process itself also plays a role. The current steel making practice of continuous casting places demands on the producer that have the benefit of controlling the shape of inclusions and improving through-thickness strength. Therefore current continuous cast products have less likelihood of lamellar tearing than older ingot cast product did. Engineers can reduce the likelihood of lamellar tearing through good design practice, as described in Design Guide 21. Material specifications define some aspects of chemical composition, such as limits on sulfur, which can be objectively evaluated assuming the proper expertise, but the details of the manufacturing process may be more difficult to know and to evaluate.”

ASCE 48 (the standard for steel transmisison poles in the US) addresses the issue by limiting the maximum allowable through-thickness stress for all grades of steel to 36 ksi. This is done by adding reinforcing fillet welds over the groove welds as dhengr mentioned.