The Results of Experiments on Seated Beam Connections

Seated beam connections have been used for many years. They have historically been designed by tabular methods, and this tradition was recently continued in the new LRFD Manual. The derivation of these design tables are discussed elsewhere and will not be repeated here. It should be noted that the tables have historically considered local yielding of the beam web under edge loading, the strength of bolts or welds, the yielding capacity of the seat angle and the normal detailing dimensions. The new AISC LFRD Specification includes the new equation (K1-5) which checks the beam web for crippling or buckling. In this paper, the term buckling is defined to mean a vertical crimping or crippling of the web due to the application of a concentrated load on the flange. This is a stability mode of failure rather than a web yielding failure as presently considered in ASD design (8th Edition Manual). Unlike a web yielding formula, it includes the depth and the flange thickness of the beam as variables. Table 1 summarizes LRFD beam web capacities according to Eq. (K1-5) and a 3-½ in. bearing length. It can be seen that there are cases where the tabulated unstiffened seat capacities exceed the beam web buckling capacity. Therefore, AISC funded a research program at the University of Washington to study these connections. This paper summarizes some of the results of this experimental program.