Hearst Greek Theatre Seismic Retrofit - UC Berkeley

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• published: 29 May 2012
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The retrofit scheme for the colonnade primarily comprises four new, large reinforced concrete columns cast into existing void spaces near center stage and at the ends of the return walls. These columns connect at the base to new concrete rafts supported by drilled piers. At the top, the existing unreinforced concrete ridge was demolished and replaced with a new reinforced concrete ridge that is much wider along the back wall of the colonnade. This new ridge beam ties the tops of the new columns to better stabilize the colonnade. New glass-fiber reinforcement (GFRP) was epoxied along the back façade of the colonnade to prevent the existing unreinforced wall panels from falling out during an earthquake and to add in-place shear strength. Reinforcing bars were doweled into the existing concrete in various places to prevent large chunks of unreinforced concrete from falling and endangering life safety during an earthquake. Under each round column, new underpinning elements were placed to improve soil-bearing stability. The soil near the back of the colonnade was likely disturbed during the placement of the basement backstage, and the new underpinning should mitigate any compromising effects that may have then occurred. Other retrofit work was designed for the auditorium end walls, which are unreinforced-concrete gravity-retaining walls showing significant cracking and signs of settlement and distress. The footings of these walls did not have adequate embedment into the soil. The retrofit approach underpinned the footings with new grade beams supported by drilled piers; new prestressed tiebacks were then be placed to laterally stabilize the walls.