【正文】 re and partitions and to add lateral shearresistance to the structure. These steelframe infill masonry buildings have generally performed better in past California earthquakes than the smaller bearingwall buildings. Noheless, these buildings were included in California legislation addressing the unreinforced masonry hazard. In the Loma Prieta Earthquake, many steelframe buildings with infill masonry walls performed quite poorly, although no collapses occurred. Several major structures of this type in San Francisco and Oakland experienced extensive damage including partial loss of the exterior masonry walls, shattering of interior clay tile partitions, and cracking and spalling of terracotta veneers. Concrete Buildings Many older reinforced concrete structures have very limited seismic resistance. These buildings tend to be quite heavy, resulting in large seismic forces. In addition, concrete itself is quite brittle and requires extensive amounts of reinforcing steel to perform properly in earthquakes. Most concrete structures designed prior to the mid1970s do not have adequate reinforcing steel to ensure good performance. Termed nonductile concrete structures by engineers, these structures have collapsed in past earthquakes. The Cypress Viaduct structure that dramatically collapsed was a nonductile concrete structure. Fortunately, there are relatively few nonductile concrete buildings in the region and no buildings of this type collapsed. Many midrise concrete structures did experience extensive damage, however. Damage typically consisted of large diagonal cracking of shear walls, occasionally acpanied by spalling of large pieces of concrete from the building A fifteenstory concrete shearwall structure in downtown Oakland was extensively damaged. The lightweight concrete shear walls at the first story literally shattered, exposing the reinforcing steel to view. The presence of a redundant steel frame within the building may have prevented the collapse of this structure. A sixstory concrete shearwall building in San Francisco also experienced substantial damage. This building had recently been seismically strengthened with the addition of steel braces on the building perimeter. Due to poor design and construction workmanship, the attachment of the braces to the building was inadequate and most of the bolts failed. Building deflections following failure of the bracing caused an interior column to punch through a floor slab. Extensive damage to shear walls above door openings also occurred. Tiltup Buildings Concrete tiltup buildings are the most mon form of modern lowrise industrial and mercial construction throughout California. They usually are constructed with plywood sheathed woodframe roofs supported by perimeter concrete walls. They are called tiltups because the perimeter walls are constructed lying flat against the floor slab and then tiltedup into position around the building. Extensive damage to these buildings has been observed in past earthquakes, including the 1987 Whittier and 1971 San Fernando events. Thousands of tiltup buildings are present in the affected region. Although some significant damage was experienced near the epicenter, the greatest concentrations of these buildings are located in areas that experienced very weak ground motion. Most of these buildings therefore had little damage. Several buildings in Hollister were investigated. Several tiltup building partially collapsed as the result of inventories of stacked cans containing tomato product impacting the walls during the earthquake. Damage was extensive. Much of the inventory was lost or severely damaged. This underscores the importance of addressing seismic issues relating to equipment and contents, as well as structural designThe buildings appeared to be late 1960s or early 1970s vintage and as such were observed not to have rooftowall anchors. These anchors were required following collapses of tiltups during the San Fernando Earthquake in 1971. Much of the roof of a half of one building occupied by the adjacent tenant also collapsed, causing extensive interior damage In Watsonville, several panels of a large tiltup owned by a food packager bowed outward at midheight and approached collapse. Concrete spalled off of several of the pilasters in the building wall, exposing the reinforcing steel, some of which buckled. In another, newly constructed Watsonville tiltup, interpanel connections at a skewed corner were damaged and roof sheathing was severely torn. Steel Buildings Modern steelframe buildings performed excellently in this earthquake, as they have in the past. Damage to these structures was typically limited to cracking of cladding and interior partitions and widespread disarray of contents. The nonstructural damage sustained by steelframe buildings may largely be attributed to their flexibility, which results in very large displacements. A steelframe building with corrugated metal siding in Hollister serves as a warehouse for a food pany. As with the concrete tiltup buildings in Hollister, this tomato packing pany experienced severe damage to its steelframe building and significant loss of inventory. Canned tomato products stacked over 30 feet high on standard pallets were mobilized by the earthquake. Most stacks collapsed, impacting and ripping through the corrugated metal side walls. Impact forces were so great that several tapered steel columns and beams were severely damaged. These steel members twisted, bent, and failed, taking down an entire section of the building. Much of the inventory was lost or severely damaged. As with concrete tiltup warehouses, this incident highlights the effect that stored inventory can have on the integrity of a building during an earthquake. Summary