Adventures in Renovation: The Historic Courthouse and the Stair and Elevator Tower Conundrum

By: Andrea Righi

The Theodore Levin US Courthouse in Detroit, built in 1934, is a beautiful example of Federal Post Office and Courthouse architecture of the early 20^th century.  After 80 years of continuous operation the building required significant upgrades to provide tenants with code compliant, state-of-the-art facilities and Class A office space. 

In 2014, Page began work on a phased modernization project for the 770,000 SF occupied historic courthouse.  A building-wide life safety analysis determined that the two existing egress stairs were insufficient to meet the population based on current building codes. To remedy this, the design team was tasked with adding a new egress stair that discharges to the exterior of the building.  This element, along with new service and passenger elevators, form a new vertical transportation tower for the building.  This article will specifically discuss the tower design process and complexities encountered during construction. 

What happens when you need to add a new stair and elevator tower to a landlocked historic building?

Additions are commonly made to the side of a building, which simplifies the structure and creates one plane where the new interfaces with the existing.  In the case of the Theodore Levin US Courthouse, however, the existing building occupies an entire city block and the upper floors are arranged in a “donut” shape with offices and courtrooms surrounding an interior light court.  The only option was to figure out a way to route a new stair through the existing building. The solution needed to solve the code compliance issues in a manner that limited the impact of the stair on the existing building, preserved historic materials, minimized impact on existing circulation, and allowed continuous building operation.  

Ultimately, a location in the center of the building was selected that allowed a narrow connection to the historic interior courtyard face but otherwise allowed the tower to be an object within the light court.  What worked well for the upper floors to minimize disruption became challenging on the interior of the building.  A significant number of MEP systems, some active and some abandoned, needed to be demolished and moved out of the footprint of the tower just under the second floor roof.  On the first floor, the location meant that the tower would go through the middle of the existing arraignment courtroom.  Since the other benefits to this location were so compelling, the US Courts and the General Services Administration determined it was worth moving the courtroom to a new location and relocating the MEP infrastructure to make way for the new structure.  The design and construction team worked through the phasing challenges to sequence the work in a manner that coordinated with the project schedule. 

While the tower program was relatively simple, the structure itself is complex. Early on, it was determined that the new structure could not be connected to the loads of the historic building. The structural engineer of record, Ruby + Associates, designed a completely freestanding 200-ft tall tower with slip connections to the existing structure.  New micropiles were drilled to support the tower foundations and massive structural steel columns were set in place to support the tall tower.  Locations of historic elements and existing structure left a very narrow footprint available for the new tower structure within the existing building.  Once the tower clears the 2^nd floor roof and extends into the light court, the upper floors cantilever over the building and allow a slightly larger floor plate. 

Here, another unique solution was developed to deal with the construction conditions.  On the upper floors, the back span is approximately the length of the cantilever.  With the asymmetrical loading of the tower elements, the steel structure was erected out of plumb so that once it was fully assembled and loaded the tower would right itself and become level.  Dead loads were recalculated multiple times as the design team worked through various options for the exterior envelope materials to precisely engineer the system.

Why is a building in Michigan built to seismic design criteria?

Code analysis determined it needed to be designed to meet seismic design criteria per the American Society of Civil Engineers (ASCE). The soil conditions, footprint of the tower, wind loads, and materials all figured into the seismic drift calculations. Because the tower is not square, the maximum drift in the north-south direction is different from the east-west direction.  With no appreciable movement at its base, the top of the tower is calculated to move up to 5-inches in each direction (which translates to a 10-inch seismic joint).  Joint sizes were regularized throughout the building for uniformity and ease of installation. Instead of changing sizes for each floor, nominal 4-inch, 6-inch, and 10-inch joints were specified to minimize the number of products purchased.

The tower exterior has a large 10-inch exterior metal joint cover integrated into the exterior façade. The joint cover is a hinged door with magnets that hold the door in place under normal conditions but release during a seismic event. The infill panel was color matched to the adjacent metal panel allowing the joint to completely blend in with the exterior façade. Most of the interior joints were concealed between two walls so exposed cover plates could be minimized. At doors and other isolated areas, a narrow joint cover with an aluminum or plate was used to blend in with historic metals.  

How were materials brought to the site and installed if the building takes up a full city block and is occupied?    

A critical requirement of the project was to allow the building to remain operational during construction.  Page worked with GSA and teams from The Christman Company as the CMc,  Jacobs as the CMa and the US Courts to execute a phased renovation project.  Impacted tenants and infrastructure had to be cleared out in the footprint of the tower early on to install the structure while the rest of the floor remained operational, including utilities, services, and emergency egress.   

Most tower elements needed to be lifted from the street over the top of the building and into the project site, including 528 tons of steel (over 1,400 individual pieces).  A 275-ton crane with a 340-foot boom was used to hoist materials from street level, 11 stories over the building and into the courtyard. The crane operator communicated with the steelworkers by radio due to lack of visibility into the project site. This work needed to be precise, at times the steel would need to be lowered through a 40 x 60-foot roof opening to be installed inside the existing building.  To make it more complex, work with the crane was done primarily at night and off schedule with building operations.  While the overall building modernization was done in phases, the tower construction occurred throughout the entire 5 year, 7 phase construction process.  

It was critical to work closely with manufacturers to specify materials and systems that could be installed with these constraints in mind. Early on limestone or precast were ruled out as the cladding for the tower due to the weight and size of the material. Ultimately, structural steel, insulated metal panels, and a unitized curtain wall system were selected as the most lightweight and practical.  Allowing as many items as possible to be fabricated in a shop off-site improved the quality of the overall product.  Even with multiple high-wind days that stopped work, these elements saved time and positively impacted the schedule.

How is water and weather infiltration managed with a hole in the building during construction?  

The cardinal rule of architecture is to do everything you can to keep water out of a building–except when you can’t. While the micropiles and foundations were installed in the basement with the exterior envelope of the building intact, the building had to be opened to install the structural steel with the crane. Once portions of the first and second floors were removed along with the second-floor roof, the building was open to the sky and all the elements. This “hole” was temporarily finished to create a waterproof funnel that directed water down to the basement and then pumped it out of the building through the stormwater system, similar to rain falling on the roof and going down through the building’s drainage system. New temporary exterior perimeter walls were installed, insulated, and waterproofed to direct the water. Insulated walls were critical to protect people working in adjacent interior space and to prevent existing interior piping and utilities from freezing during the cold winter months.

Conclusion

A significant number of buildings in the United States from the same era as the Theodore Levin US Courthouse will be undergoing renovations in upcoming years.  Modernization projects and existing building renovations present a Tetris-like challenge. There is never just one solution; the process is highly collaborative.  Project decisions require working through existing constraints while discussing a myriad of other important considerations like programming, cost, constructability, tenant disruption and systems integration.  

The success of this project was largely due to a passionate team that worked collaboratively across all professions.  The team faced a multitude of challenges in working within the existing building.  When items came up, roundtable discussions and working sessions were held with everyone involved to develop a path forward.  It was necessary to have a group that could turn on a dime and develop new options considering new information discovered during the process.  As designers, we spend a lot of time looking at systems, calculations and developing technical details within a computer model.  It’s necessary to take this knowledge and adjust the design or thinking with input from the construction team, suppliers, and the understanding of building occupants in order to create successful real-world solutions.  

Andrea Righi, AIA, is a Senior Project Architect and Associate Principal at Page in Washington DC.  She can be reached at arighi@pagethink.com