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Sloped Connections and Connections with Fillet Welded Continuity Plates for Seismic Design of Special Moment Frames

  • Author(s): Mashayekh, Adel
  • Advisor(s): Uang, Chia-Ming
  • et al.

Steel Special Moment Frames (SMF) are one of the most popular lateral force-resisting systems for multistory building construction in high seismic regions due to their architectural versatility. With a significant amount of research that was conducted after the 1994 Northridge, California earthquake, AISC has published design guidelines (AISC 341 and AISC 358) to avoid brittle fracture of beam-to-column welded moment connections that occurred in more than 100 steel buildings. This dissertation addresses two issues related to the moment connection design of SMF.

Unless the column flanges are sufficiently thick, AISC 341 requires that continuity plates be installed, and that expensive complete-joint-penetration (CJP) groove welds be used to connect the continuity plates to the column flanges; the conservative nature of this requirement stems from a lack of procedure that the designer can use to quantify the required seismic forces in the continuity plates such that more economical welds (e.g., fillet welds) can be used. The first objective of this research was to investigate a design procedure and to verify it with full-scale testing of two Reduced Beam Section (RBS) moment connections. It was shown that the proposed design procedure could result in a more economical weld design while developing the ductile response of the moment connection.

AISC seismic design codes implicitly assume that beams are orthogonal to the columns in elevation, but in real-life construction beams are sometimes connected to the columns with a slope. To fill this knowledge gap, both experimental and analytical studies were conducted. Full-scale testing of two additional moment connections with a 25° angle of inclination showed that sloped connections are vulnerable to brittle fracture at the “heel” location, where the beam flange and column form an acute angle. Fracture would initiate from the end of beam web CJP weld and the weld access hole. Guided by finite element simulation, a truss analogy model was proposed to predict the force concentration at the heel location. A Force Concentration Factor was introduced to evaluate when the effect of inclination can be ignored. When such effect needs to be addressed, a solution that introduces a curved slot in the beam web was proposed. The effectiveness of this solution was verified by nonlinear finite element analysis.

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