Frozen in Time: Structural Analysis in a Historical Renovation

Frozen in Time: Structural Analysis in a Historical Renovation

We recently started work on the renovation of a 100-year-old structure in the city as the Construction Manager for The Lyric Theatre, a project which has proved interesting for many reasons. One  is the history lesson we are getting about construction practices in 1913.

The foundations, rebar and structural steel have proven particularly interesting. We called in Bhate Geosciences, an associate we have trusted for years, to perform specific material inspections of key structural components. A few of the findings that Uday Bhate shared with me follow.

Bhate Layer Image

Amphitheater Excavation and Foundations Under the Stage Area: We found that the depth of the amphitheater excavation and foundation construction under the stage area were likely affected by the depth of upper limestone bedrock and pinnacles in the dressing room level under the stage. The exposed rock pinnacles above subgrade were apparently excavated or crushed and spread onsite, then overlaid by large aggregate concrete of variable thickness. This likely depended on the extent of rock protrusions. The surface was leveled, then topped by a grout slurry mix approximately 1 ½” thick.

No clear footing dimensions could be delineated, and it appeared that adjustment in the footing sizes was made during the progression of construction, based on presence of localized shallow rock or clay zones in response to minimizing the rock excavation at the site.

Bhate--Reinforcing BarsReinforced Concrete and Reinforcing Steel: The first steel-reinforced concrete construction systems were used in the mid-19th century. These early systems used square twisted bars. Plain round and square bars were typically used in reinforced concrete buildings built before 1920. Plain bars began to be phased out during the 1910s and early 1920s in favor of deformed bars.

The first materials specifications for steel reinforcing bars were developed in 1910. These bars were precursors to the modern deformed bars. The reinforcing bars at the Lyric were square twisted bars, as shown in the photograph. 

Bhate Structural SteelStructural Steel: During the early to mid 20th century, structural steel connections were either welded or riveted. High-strength bolts have largely replaced structural steel rivets. The latest steel construction specifications published by AISC no longer covers installation of rivets. The reason for the change is primarily due to the expense required to install high strength structural steel rivets vs high strength bolts used today. The Lyric Theatre structural roof frame is primarily constructed of riveted connections that still maintain a high level integrity after all these years. The chemical testing of a structural steel member indicated that the steel used was hot rolled low carbon steel.

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