Strengthening Buildings for Earthquake Resistance with New Concrete
A. Wyllie, Jr.
Appears on pages(s):
concrete jackets; infilled walls; shear walls
Many buildings built in the 19.50s and 1960s in regions of high seismicity are extremely vulnerable to extreme damage or collapse in future earthquakes. The most vulnerable and hazardous of these buildings are the unreinforced masonry buildings, with non-ductile concrete frame buildings considered the next most hazardous class. Concrete is a logical choice to strengthen these buildings, either with new shear walls or infilled walls or sometimes with jacketing. The most common and probably the best system is to add new reinforced concrete shear walls. It makes a building much more rigid, reduces seismic drifts or deformations and thus reduces damage and prevents the potential of collapse. A variation of adding shear walls is adding infilled walls, which are wall panels of reinforced concrete (or sometimes masonry) added between floor beams and columns. Concrete jackets consisting of a layer of concrete, usually about 4 inches (100 mm) thick, containing closely spaced ties, can also provide confinement and add shear capacity to concrete frame members. This paper will summarize the pros and cons of the application of these three seismic strengthening techniques.