Welding in the World

, Volume 63, Issue 2, pp 421–433 | Cite as

Fillet welds around circular hollow sections

HENRY GRANJON PRIZE 2018 winner Category C: Design and Structural Integrity
  • Kyle TousignantEmail author
  • Jeffrey A. Packer
Research Paper


An experimental and numerical research program was conducted to evaluate the safety of North American design rules for fillet welds around the perimeter of steel circular hollow sections (CHS). This assessment was performed in the context of the current American Institute of Steel Construction (AISC) steel building specification, AISC 360. Specifically, the appropriateness of the fillet weld directional strength-enhancement factor in AISC 360-16 Clause J2.4b was investigated for fillet welds to CHS branches, and the effect of non-uniform connection flexibility on the strength of welds in CHS-to-CHS connections was studied. A total of 24 large-scale, weld-critical experiments were tested, and a further 290 non-linear finite element models were used to parametrically expand the database. It was found that if the directional-strength factor is used, the target reliability (or safety) index prescribed by AISC for connectors, even when the welds are fully effective, is not achieved; hence, a recommendation to prohibit this factor for all fillet welds around the perimeter of CHS is made. With this restriction, it is then shown that AISC 360-16 Clause J2.4a fillet weld design provisions meet AISC’s target safety index for welds in CHS-to-CHS X-connections, where a weld effective length phenomenon exists. It is therefore recommended that AISC advocate 100% weld effective lengths for fillet welds in CHS-to-CHS X-connections, provided that the directional strength-enhancement factor (1.0 + 0.5sin1.5θ) is not used.


Circular hollow section Fillet weld Effective length Connection Experiment Finite element 



The authors would like to acknowledge the laboratory contributions of Ms. J. Lu and Mr. F. Wei (summer research students) to this work. Hollow structural sections for this project were donated by Atlas Tube, Harrow, Ontario, and fabrication services were donated by Walters Inc., Hamilton, Ontario. The financial support of the Natural Sciences and Engineering Research Council of Canada (NSERC) is greatly appreciated.


AwEffective throat area of weld (= twlw)

DOverall diameter of the CHS chord

DbOverall diameter of the CHS branch

FEXXElectrode ultimate strength

FuUltimate stress of the CHS; ultimate stress of the plate

FyYield stress of the CHS; yield stress of the plate

PApplied force

PFEFailure load in the finite element model

PaActual (experimental) load at weld rupture

PaGreatest actual (experimental) load sustained by the weld

PnNominal/predicted weld fracture load

VRCoefficient of variation of ρR

ZWeld throat dimension when full root penetration is achieved

lLength of the CHS chord member

lbLength of the CHS branch member

lhWeld leg measured along the plate; weld leg measured along the CHS chord

lvWeld leg measured along the CHS branch

lwTotal weld length

tWall thickness of the CHS chord member

tbWall thickness of the CHS branch member

tpPlate thickness

twWeld effective throat dimension

αRCoefficient of separation (taken to be 0.55)

βRatio of overall branch diameter to chord diameter

β+Safety index

δChord deformation

εEngineering strain

εTTrue strain

εeEquivalent (von Mises) strain

εefEquivalent (von Mises) strain at rupture for failure criterion

εef,plateEquivalent (von Mises) strain at rupture for plate failure criterion

εef,weldEquivalent (von Mises) strain at rupture for weld failure criterion

θBranch inclination angle; angle of loading measured from the weld longitudinal axis for fillet weld strength calculation (in degrees)

ρSubtended angle around the branch, measured from heel

ρRBias coefficient for the resistance

σEngineering stress

σTTrue stress

τBranch-to-chord thickness ratio

ϕResistance factor (associated with the LRFD method)

ϕβ+Adjustment factor for β+

ΨLocal dihedral angle (angle between the base metal fusion faces)


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Copyright information

© International Institute of Welding 2018

Authors and Affiliations

  1. 1.Department of Civil and Resource EngineeringDalhousie UniversityHalifaxCanada
  2. 2.Department of Civil & Mineral EngineeringUniversity of TorontoTorontoCanada

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