A seismic design method for one-piece gusset plate connections

Abstract

In multi-story Special Concentrically Braced Frames (SCBFs), there are bracing nodes where two braces associated with two sequential adjacent stories of a similar bay intersect each other at beam-to-column joints. In these bracing nodes, under loading, one of the braces is in tension and the other is in compression. Consequently, maximum vertical force is imposed on the column. Note that in these bracing nodes, force distribution at a gusset plate affects the force distribution at the other gusset plate. Generally, two separate gusset plates are considered for the bracing nodes with two braces at the beam-to-column joints and designed according to Uniform Force Method (UFM). While the UFM proposed for corner gusset plates with one brace does not consider the force distribution effects at both gusset plates. To resolve this problem, the current study proposes a one-piece gusset plate for the bracing nodes with two braces at the beam-to-column joints. The one-piece gusset plate involves the gusset plate of the tension brace, the gusset plate of the compression brace, a part of the beam web whose length is equal to the interface of the gusset plate to the beam, and finger stiffeners. The finger stiffeners are considered in the connection region on both sides of the one-piece gusset plate to simulate the presence of the beam flanges removed in this region. Note that in this connection, the beam is extended to near the one-piece gusset plate and thereafter is connected to it. The aims of this study are as follows: (1) considering the force distribution effects on both gusset plates, (2) calculating the force and bending moment demands of the gusset plates in the bracing nodes with two braces at the beam-to-column joints via proposing a new method, and (3) determining the gusset plate dimensions in the bracing nodes with two braces at the beam-to-column joints through presenting a new procedure. Five one-bay, two-story SCBFs with the brace angles of 37−37, 45−45, 59−59, 37−59 and 59−37° (the first number is the lower story brace angle and the second number is the upper story brace angle) were designed in accordance with the method and procedure proposed in this study. These specimens were simulated in ABAQUS and subjected to a monotonic loading. The accuracy of the proposed method was confirmed via comparing the results of ABAQUS and UFM with those of the proposed method.