Seismic Retrofit of a Historical Building Using Cored and Internal Grouted Reinforcing

Abstract

The building, constructed in 1929, was an airport terminal, and included a 2,322 m2 two-story structure and a four-story tower. The building sustained damage from the 1994 Northridge earthquake and was mothballed in accordance with Department of Interior standards. An extensive inspection and testing program was developed for evaluating the strength of the in-place materials and for the development of retrofit solutions. To preserve the historical fabric of the building, grouted reinforcing was selected to strengthen the existing masonry walls to act as shear walls. The reinforcing system consisted of removal of a wall core from near the center of an existing unreinforced wall and installation of stainless steel reinforcing. Coring/reinforcing was from the top continuously into the existing footing. To meet the requirements for an intermediate reinforced masonry shear wall, horizontal cores were also provided. The horizontal cores were off-center from the vertical cores to avoid intersection. Drilling was dry, to minimize effect on the heritage walls, with debris handled by a vacuum and filtration system to keep minimum dust. Reinforced walls were designed to resist both out-of-plane forces from wind and seismic as well as in-plane seismic shears. The advantages of internal reinforcing included minimal site/interior disturbance and preservation of historic building fabric, in addition to supplying resistance to future earthquakes. Voids in the existing walls identified early during construction, apparently due to poor workmanship, were subsequently injected with a flowable, compatible material. Success was confirmed by performing pre-injection and post-injection scanning using microwave radar and borescope examination.