b'FEATUREinteractionpropertiesaredefinedforthese surface-to-surface interactions. Contact details(b)between the elements are also shown in Fig. 2. (a)Column behaviour: To represent the gravity load, an axial load equal to 30 per cent of the column capacity was applied as an axial compression. For uniaxial monotonic loading, a lateral drift of 10.6 per cent was applied along the strong axis direction of the column, whereas for bi-axial loading, additional 4.9-per-cent drift was introduced towards its weakFig. 3: Column stress (Von mises) along (a) weak axis and (b) strong axis under uniaxial loading axis direction in addition to the axial compression.FIGURE 3 : Column stress (Von mises) along (a) weak axis and (b) strong axis under uniaxial loadingThe column subjected to bi-axial loading suffered considerable out-of-plane local buckling near its base, compared to uniaxial loading. This occurred due to localized compression, as well as not having sufficient thickness of the web and flanges to resist weak axis bending. In Fig. 3, it can be seen that the(a) (b)stresses are concentrated near the column base when subjected to uniaxial loading. However, for bi-axial loading (Fig. 4), the stresses are spread along the columns height up to half of its total length due to an angular resultant displacement causedbysimultaneousbidirectionalloading. Maximum stress of the column is found to be three per cent higher for bi-axial loading compared to the uniaxial loading.FIGURE 4 : Column stress (Von mises) along (a) weak axis and (b) strong axis under bi-axial loadingFig. 4: Column stress (Von mises) along (a) weak axis and (b) strong axis under biaxial loading Base plate behaviour: Identifying yield lines in the base plate of deformed base connections is important and can be a difficult task. The current AISC design guideline assumes the yield line forms in parallel with the flange of the column. A detailed experimental program conducted by Gomez et al. (2010) revealed that yield lines develop in inclined patterns under uniaxial bending. Similarly, the FE model showed development of inclined yield lines on the tension side of the base plate (Fig. 5a) under uniaxialloading.Thiscanbeattributedtothe resistance to the tensile force by the anchor rods(a) (b)causing a curve-shaped deflection at the tension end. A straight yield line is formed beneath theFig. 5: Base plate behavior under (a) uniaxial and (b) biaxial loading column flange on the compression side of the plateFIGURE 5 : Base plate behaviour under (a) uniaxial and (b) bi-axial loadingAfter the 1994 Northridge Earthquake, design of steel connections has been significantly revamped across North America.26|SUMMER 2020 ADVANTAGE STEEL'