In modern construction heavy W-shape beams, deep W-shape columns, and column shapes other than the traditional W-shape are often preferred as components of welded steel moment frames because moment-resisting frames designed with such components can provide better drift control and may be somewhat more economical. Practical design guidelines, published in a series of FEMA documents, starting with the seminal FEMA-350 design guide for new steel moment-frame construction, both gave designers new tool to design special steel moment frames and provided a portfolio of new connection solutions. However, FEMA-350 connections are pre-qualified only for W12 and W14 columns. There is not enough test data upon which to base a performance evaluation or develop retrofit solutions for the connections to box or to deep W-shape columns. The main objectives of this study are to investigate the seismic performance, identify the key design variables, and present design recommendations for such connections.; To achieve the objectives three phases of work were conducted. First, three factors that influence the ductility of welded steel moment connection were identified. They are: brittle fracture, inelastic instability, and residual rotation capacity. The effect of these factors on the performance of moment connections were investigated and strategies to evaluate the severity of these effects were proposed. Second, steel moment connections in a building built before the 1994 Northridge earthquake were selected to evaluate the pre-Northridge type moment-resisting connections to box or deep W-shape columns. Standard pre-qualification tests were conducted for the connection specimens. The observed performance of these pre-Northridge connections was poor. In parallel with the test program the connections were analyzed using nonlinear finite element models. These analytical models were used to augment and interpret the test results. Third, key design variables were identified: column shapes, continuity plates, column plates, and loading directions for box column connections; and column boundary conditions, connection types, and beam lateral bracing for deep W-shape column connection. A series of parametric finite element studies for these design variables were conducted to formulate design recommendations.
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