AISC LRFD 1.pdf

Comm. J2.] WELDS 235When longitudinal fillet welds parallel to the stress are used to transmit the load tothe end of an axially loaded member, the welds are termed “end loaded”. Typicalexamples of such welds would include, but are not necessarily limited to, longitudinallywelded lap joints at the end of axially loaded members, welds attaching bearingstiffeners, and similar cases. Typical examples of longitudinally loaded filletwelds which are not considered end loaded include, but are not limited to, weldsthat connect plates or shapes to form built-up cross sections in which the shear forceis applied to each increment of length of weld stress depending upon the distributionof shear load along the length of the member, welds attaching beam web connectionangles and shear plates because the flow of shear force from the beam orgirder web to the weld is essentially uniform throughout the weld length, that is, theweld is not end-loaded despite the fact that it is loaded parallel to the weld axis. Neitherdoes the reduction factor apply to welds attaching stiffeners to webs becausethe stiffeners and welds are not subject to calculated axial stress but merely serve tokeep the web flat.The distribution of stress along the length of end loaded fillet welds is far from uniformand is dependent upon complex relationships between the stiffness of the longitudinalfillet weld relative to the stiffness of the connected materials. Beyondsome length, it is non-conservative to assume that the average stress over the totallength of the weld may be taken as equal to the full design strength. Experience hasshown that when the length of the weld is equal to approximately 100 times theweld size or less, it is reasonable to assume the effective length is equal to the actuallength. For weld lengths greater than 100 times the weld size, the effective lengthshould be taken less than the actual length. The reduction coefficient, , provided inSection J2.2b is the equivalent of Eurocode 3, which is a simplified approximationto exponential formulas developed by finite element studies and tests preformed inEurope over many years. The criterion is based upon combined consideration ofnominal strength for fillet welds with leg size less than 1 4 in. (6 mm) and upon ajudgement based serviceability limit of slightly less than 1 32 in. (1 mm) displacementat the end of the weld for welds with leg size 1 4 in. (6 mm) and larger. Mathematically,the application of the factor implies that the minimum strength of anend-loaded weld is achieved when the length is approximately 300 times the legsize. Because it is illogical to conclude that the total strength of a weld longer than300 times the weld size would be less than a shorter weld, the length reduction coefficientis taken as 0.6 when the weld length is greater than 300 times the leg size.Fillet weld terminations do not affect the strength or serviceability of connectionsFig. C-J2.4. Restraint of lap joints.LRFD Specification for Structural Steel Buildings, December 27, 1999AMERICAN INSTITUTE OF STEEL CONSTRUCTION