Technology | Retrofitting & Reinforcement
Restoring LA’s Italian Hall Building and its iconic mural
By Chukwuma G. Ekwueme, PhD, PE, SE, LEED AP,
Principal at Thornton Tomasetti
The Italian Hall Building that serves as the Italian American Museum of Los Angeles was constructed between 1907-1908. The ground floor of the two-story unreinforced brick masonry building, which is listed on the National Register of Historic Places, was home to several shops. The second floor hosted numerous banquets, weddings, meetings, and concerts. Located on historic Olvera Street, the building is part of the El Pueblo de Los Angeles Historic Monument, a historic district that is the oldest section of Los Angeles.
In 1932, the noted Mexican artist David Alfaro Siqueiros was commissioned to paint a mural on the building’s exterior second-floor wall. Expecting an image that celebrated the beauty and romance of Latin America, civic leaders were shocked by Siqueiros’ massive 180 by 80-foot, politically-charged painting (América Tropical) that included a peasant tied to a cross and an eagle—representing American imperialism—hovering over him. The mural was soon whitewashed and Siqueiros was deported from the United States when his visa expired.
Decades later, as the whitewash began to fall off and the painting began to reappear, efforts to restore the iconic mural began. In 2012, the City of Los Angeles and the Getty Conservation Institute funded a plan to restore the mural. As part of the restoration, the wall needed to be strengthened to reduce the likelihood of damage to the historical monument during earthquakes that often occur in the Los Angeles area.
As with buildings of its era, The Italian Hall was constructed with unreinforced brick masonry walls and wood-framed floors and roof. Such buildings are highly susceptible to damage and collapse during large earthquakes. The building already had been strengthened in accordance with the local ordinance for seismic retrofit of unreinforced masonry buildings. This type of strengthening primarily involves life safety protection by providing positive anchorage of the unreinforced walls to the roof and floor diaphragms to prevent collapse during large earthquakes. While this improves overall seismic performance, it is based on a philosophy that a building will be severely damaged but remain standing to allow occupants to exit safely after a major earthquake. Such performance would destroy the mural and render the conservation efforts useless. In addition, the previous strengthening does not consider the building during smaller earthquakes, which could lead to cracks that are large enough to damage the mural. As a result, further strengthening of the wall was recommended to reduce likelihood of damage to the mural during earthquakes.
The strengthening of the mural wall was based on a performance-based design approach using the criteria outlined in a technical standard published by the American Society of Civil Engineers (ASCE)—Seismic Rehabilitation of Existing Buildings, ASCE 41-06.
With a performance-based framework, structures are designed to achieve specific performance levels when subjected to earthquake shaking due to selected hazard levels. New (or seismically rehabilitated) buildings typically are designed to achieve “life safety” performance during the Design Earthquake, which has an approximate return period of 475 years. The strengthening of the mural wall was designed to achieve “immediate occupancy” performance during the Maximum Considered Earthquake (MCE), which has an approximate return period of 2,475 years. This means that the performance level for the mural wall is more stringent and the earthquake ground motion being considered is more severe. Figure 1 illustrates the target performance level for the mural wall in comparison to the target performance level typically used for the design of new buildings.
When a building achieves life safety performance, damage is expected to be moderate with no out-of-plane wall failures, but with some permanent drift. Extensive cracking is expected in unreinforced masonry and noticeable in-plane offsets and minor out-of-plane offsets likely will occur at the mortar joints. For immediate occupancy performance, damage to the building is expected to be light and masonry walls are expected to receive minor cracking with no observable offsets at the mortar joints.
The strengthening of the mural wall was achieved by increasing the stiffness and strength of the walls in out-of-plane and in-plane directions. This would decrease the deformation of the walls during earthquakes and reduce damage since the size of cracks that will occur is directly related to the amount of wall deformation.
In the out-of-plane direction, damage likely will occur in the form of horizontal cracks along the continuous bed joints on the wall exterior. Increased out-of-plane stiffness will be achieved by attaching steel tube strong-backs to the interior surface of the mural wall at a spacing of about four feet on center. The steel tubes will be connected to the wall with anchor bolts installed in epoxy and transfer loads to the rest of the building by spanning between the roof and second floor. The strengthening will reduce the out-of-plane deflection of the wall to about one-fifth of the current expected displacement. Simplified estimates indicate that the maximum crack size that can occur in the mural wall will be reduced from about 1/16-inch to about 1/80-inch.
To reduce the number of holes that need to be drilled in the mural wall to install the steel tubes (and to minimize the possibility of damage to the mural), testing was performed to justify the use of higher bolt capacities than values stated in the City of Los Angeles Research Reports. The best performance will be achieved if the anchor bolts are installed deeply enough to engage the exterior wythe of the masonry. However, it is acceptable to stop the bolts short of the exterior wythe if it is found that drilling to this depth has the potential to damage the mural. No strong backs are required at the first floor of the south wall since horizontal cracking at the level below will not propagate to the second floor and damage the mural.
In the in-plane direction, possible damage will be in the form of diagonal, “stair stepped” cracks that occur due to large in-plane shear stresses. The in-plane shear strength of the wall will be increased by applying fiber-reinforced polymers (FRP) to the interior surface of the wall. FRP is a composite material that consists of high-strength carbon or glass fibers that are embedded in an epoxy and adhered to the wall. The FRP will be applied prior to the installation of the tubes and will help form a bedding surface for the tube-to-wall connection. Holes for the epoxied anchor bolts can be drilled through the FRP. Since diagonal shear cracks have the potential to propagate from the first floor, the FRP will be applied to both the first and second floor of the south wall.
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