Structural design and performance of composite wall-foundation connector elements

Kristin Anne Duchateau

Field observations following extreme earthquake events and laboratory testing identify a key area to improve upon in wood-frame shear walls as maintaining sill plate structural integrity. Due to current load paths through the sill plate when resisting overturning, coupled by construction misalignments, traditional sill plate designs split along the line of anchor bolts and lose lateral resistance. In addition, this location in a structure is susceptible to moisture infiltration. Therefore, structural member degradation from moisture and the required use of potentially hazardous preservative treatments makes it advantageous to develop durable wood thermoplastic composites (WPCs) as structural members for this location. This paper presents an experimental investigation and proof of concept of the utilization of WPC members as sill plates in wood shear walls. Connection and component testing of one polypropylene hollow section (PP10) identified weakness in the perpendicular-to-extrusion direction, though with the use of reinforcement, performance was improved. Final design configurations showed an improvement of 27-31 kN (6000-7000 lbf) in uplift resistance over traditional end stud-to-sill connections without hold-down hardware. As well, improvements in section design have eliminated rotation and cross-grain bending in sills (forces that have caused brittle splitting of wood sills). Full scale shear wall tests were performed on one wood sill wall configuration (as the control) and three wall configurations with WPC sills, none of the four configurations used conventional hold-down hardware. Changes in capacities, ductility, and energy dissipation resulted from different sill plate materials and configurations. Cyclic response exceeded monotonic response for walls with WPC sill plates. One WPC section was shown to be a feasible equal substitution to wood sill plates, obtaining similar performance parameters. Another WPC sill plate wall configuration had substantial improvements in capacities and exhibited racking behavior and associated failure modes, developing a completely different load-deformation response. Stiffness degradation for this section was the most gradual, allowing more than a two-fold increase in energy dissipation and retention of its ability to resist deformations in a plastic state.

Structural design and performance of composite wall-foundation connector elements

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