SEISMIC STABILIZATION OF HISTORIC ADOBE STRUCTURES
WILLIAM S. GINELL, & E. LEROY TOLLES
8 8. ASSESSMENT OF THE RETROFIT MEASURES
Both systems used on the retrofitted model had significant impacts on the structural performance of the model. The first requirement of a retrofit system is to reduce (or eliminate) the collapse hazard of the building, and each method proved very successful in this regard.
8.1 8.1 STRAPS AND CABLES
The advantage to the strapping system is that the installation has minimal impact on the historic fabric and is also, to some extent, reversible. The retrofit method using vertical straps is most effective for reducing the risk of out-of-plane collapse but had little or no effect on the initiation and early development of crack damage. When displacements or offsets become significant, the strapping system controls the relative displacement of cracked sections of walls that could otherwise lead to instability. When coupled with anchorage to the roof and/or floor system, the out-of-plane overturning or midheight collapse can be prevented.
In-plane damage is much less affected by vertical straps generally, because in-plane offsets are of smaller magnitude and more likely to remain after the dynamic motions are completed. Straps can prevent large displacements but not small crack offsets, and they can prevent piers between doors and windows from becoming unstable.
8.2 8.2 CENTER CORE RODS
The center core rods were found to be particularly effective. The initiation of cracks was delayed, and some cracks in the in-plane walls that started at the corners of the door and window propagated to the center core rod and then stopped for one or two more tests. The cracks never became severe.
In the out-of-plane walls the center core rods acted as reinforcing elements. The adobe-epoxy grout provided effective shear transfer between the adobe and the steel rods. The epoxy unevenly soaked into the adobe especially at the mortar joints and therefore provided a positive attachment between the steel rods and the adobe wall. The walls with center core rods were then able to act as structurally reinforced elements in the vertical direction.