This dissertation focused on developing a new High-Performance Steel Plate Shear Wall system (HPSPSW) with an innovative Gusset Plate Moment Connection (GPMC). This research and development work has resulted in the innovative concepts, the modeling methods and interim design procedures of the new connection and the system.
Among the design issues for the current fully connected steel plate shear wall (SPSW) system, three of them are fundamental: (1) the tension field anchor force of the infill plate makes the columns very large, heavy, and expensive; (2) the complete joint penetration (CJP) field-welded moment connections used in the current system are not cost effective and require field-welding and on-site ultrasonic testing; and (3) the thin infill wall is susceptible to buckling under wind loads and small frequent earthquakes. The proposed new HPSPSW system incorporates two major modifications that are targeted at solving these root problems: (1) detaching the infill wall from the boundary columns but providing side stiffeners on the two vertical free edges; and (2) replacing the CJP welded moment connection by the innovative GPMC.
The GPMC utilizes the ductility of gusset plate as the main ductile energy dissipation element, enabling the beams and columns to remain essentially elastic. The entire connection configuration is proposed to minimize the field CJP welds, doubler plates, and continuity plates, resulting in potential savings in terms of fabrication costs. The GPMC offers several configurations and finds applications in a variety of lateral force-resisting systems. Extensive nonlinear finite element (FE) analyses were conducted to examine the appropriate range of gusset plate materials, strengths, thicknesses, free gusset lengths, gusset flange thicknesses, and bolt strengths, with the aim of achieving both the desired ductile behavior and a reduction in fabrication costs. With the gusset plate acting as the fuse, the “strong-column–weak-beam” criteria for special moment frames can be suspended, resulting in greater design flexibility and cost savings. In addition, a simplified rotational hinge model was calibrated for the GPMC for use in global analysis models. An interim step-by-step design procedure was proposed, following the format of pre-qualified moment connection design procedures and was developed based on desirable objective performance criteria and limit state hierarchy.
Through nonlinear FE parametric studies, the new HPSPSW system is shown to solve issues related to the tension field action anchor force with comparable or better performance compared to the current fully connected SPSW system; it is cost-effective, flexible and versatile. The infill wall thickness and the column sections are no longer strongly dependent on each other, allowing thicker walls to be used for drift or service performance goals, and lighter and more forms and orientations of the columns to be employed. In addition, the reduction of the two vertical welds increases the reparability as well as the ease of retrofit and modular construction of the system. After a study of various shapes, the T-shaped side stiffeners were found to be the most efficient and practical for use in the HPSPSW system. Design equations for establishing the strength and stiffness of the infill wall were derived based on the collapse mechanism of plate girders, followed by design recommendations for the infill wall and its side stiffeners. An equivalent brace (EB) model was developed and verified for the new HPSPSW system both as an analysis and a design tool.
Finally, the system performance was evaluated using realistic site and prototype buildings, including a series of 3-, 9- and 20-story prototype buildings that conform to the SAC building specifications. The model used the simplified rotational hinge model for the GPMC and the EB model for infill wall with side-stiffeners. Two seismic design procedures were proposed for the new HPSPSW system: a prescriptive code-based procedure and a performance-based procedure. The performance-based procedure adopts the code-based procedure to initiate the preliminary design and uses design iterations to achieve multiple enhanced performance objectives at different seismic hazard levels. It was found that the preliminary code-based designs generally satisfy the deformation controlled performance objectives (i.e., story drift, residual drift, and connection rotation) at the median level. All designs met service-level performance goals even without explicit consideration in the design process. Some code-based designs experienced a soft-story mechanism at the maximum considered level hazard. Column yielding other than the base of the first story was also observed in some of the code-based designs, indicating a need for improvement. The performance-based designs met all deformation-controlled objectives on the 84-percentile level, and satisfied the column axial-moment interaction objective on the median level with no column yielding other than the base of the first-story columns. A comparison between the current AISC SPSW system and the new HPSPSW system showed that the new HPSPSW system effectively reduced the column over-stress and structural weight, eased the design iterations, and improved the material-utilization ratio and economy of the system efficiently while exhibiting enhanced seismic performance.
In addition to the main findings, various design, detailing, and fabrication considerations were also discussed. Recommendations for future experimental and analytical research are suggested. A test program is proposed aiming to verify, validate, and refine the proposed concepts, analytical model, and design procedures.