The 87-year-old Cincinnati Union Terminal in Ohio has undergone a comprehensive, $228-million restoration and renovation led by GBBN Architects. As part of that project, which included extensive historic preservation and structural repair work, Silman, a structural engineering firm, was part of the team that performed a methodical restoration of the grand art deco building's exterior facade. THP Limited Inc., also a structural engineering firm, was part of the team that renovated the terminal's interior and replaced the waterproofing for the underground structure beneath the terminal's east lawn. And TrueScan, a division of the Kleingers Group Inc., performed a full 3-D laser scan of the building's interior and exterior. In three articles on the following pages, Silman, THP, and TrueScan share the work they performed on the project .
Building A Better Envelope
BY LIZZIE OLSON, P.E., S.E., AND DEREK TRELSTAD
After a $228-million restoration and renovation, Cincinnati Union Terminal in Ohio, at 87 years old, looks as stunning as the day it was built. Silman, headquartered in New York City, was among the team of designers and contractors who methodically restored the exterior facade and site features of the vast complex. For more than three years, the company worked closely with project architect GBBN Architects, headquartered in Cincinnati; preservation architect John G. Waite Associates (JGWA), headquartered in Albany, New York; and construction manager Turner Construction Co. (Cincinnati office) to investigate existing conditions, diagnose deficiencies, and implement comprehensive repairs to the building envelope and underlying structure. Silman also collaborated with local firm THP Limited Inc., the structural engineer for the concurrent interior renovation, to document the building's structural systems and ensure that work on the exterior was appropriately coordinated with the interior work.
The existing terminal—a National Historic Landmark since 1977 and a touchstone of art deco architecture—was constructed from 1929 to 1933. After a relatively short period of use that lasted into the mid-20th century, the building was largely abandoned because of declining passenger train travel and subsequently slated for demolition. Fortunately, the wrecking ball only made it to the terminal's rear train concourse that extended out over the rail yard until the early 1970s. By then, that portion of the concourse had to be demolished because it was too low to accommodate double-stack freight cars. Despite attempts to repurpose the complex, Union Terminal remained underutilized until 1990 when it reopened as the Cincinnati Museum Center—a joint venture among several local museums and historical organizations.
The terminal complex is monumental in scale and in its 1930s streamline moderne design. The prominent arched limestone facade is buttressed by stepped north and south towers, each adorned with a carved bas-relief representing transportation and commerce. Outstretched curved "wings" extend from the towers and draw visitors into the main entrance under a decorative aluminum-clad marquee. A central half-domed rotunda connects the north and south blocks with the portion of the train concourse that still extends west toward the active rail yard at the rear of the building. The interior dome spans 180 ft and has a clear height of 106 ft. The station's former control tower, Tower A, at the eastern end of the rear train concourse, provides an aerial view of the active rail yard below.
An extensive promenade at the front of the building features a plaza and a whimsical cascading fountain. This plaza is bounded by a series of ramps originally intended to enable trolleys, buses, and cars to discharge passengers in a protected environment. Retaining walls raise the promenade from Kenner Street to the north and Hopkins Street to the south, while Dalton Avenue, at the same elevation as these roads, crosses beneath the plaza through limestone and aluminum-clad portals.
The terminal's primary structure comprises steel columns and beams that support short-span, draped-mesh, cinder concrete slabs. The building facades are a hybrid of load-bearing and non-load-bearing masonry intertwined with steel columns and spandrel beams—a common system referred to as "cage" construction found in early 20th-century steel-frame buildings. The outer finish layer of masonry, either stone or brick, depending on the location, is self-supporting and continuous from the foundation to the parapet, while the inner backup layers are interrupted at the floors and roof and supported on the building structure. This differs from contemporary curtain wall systems in which both finish and backup materials are supported on building structures.
The east facade, the north and south towers, and the ramp wings are clad with carved and multidimensional ashlar limestone. The side and rear facades are buff-colored face brick laid in a Flemish bond pattern, with decorative soldier coursing and profiled panels. The backup masonry is a combination of common brick and hollow terra-cotta block. Most of the masonry cladding is built tightly around the steel columns and beams, though in some areas where the steel structure is close to the exterior the face brick does not extend the full depth. These partial-depth face brick "soaps" are so-called because they are similar in size to a bar of soap. In these areas, the backup masonry is loosely placed behind the soaps and provides little protection for the embedded frame.
Evaluating the Past
By the turn of the 21st century, the terminal was in need of a complete programming, infrastructure, and materials overhaul, having undergone only fragmented renovations and maintenance over time. The building envelope had reached a critical state of decline, and stopgap repairs performed over the prior three decades were starting to fail.
The most recent phase of work on the building began in 2015, although Silman's involvement with the building extends to an initial master plan and pilot project in 2004 that restored the exterior facade at the southwest block of the building. The pilot project provided an opportunity to investigate the terminal's as-built conditions, test proposed treatments, and establish quality controls and standards for the full restoration. The pilot project also revealed critical details about the building, including information about the performance of the unique coping and parapet construction, the adequacy of connections between the double-height window frames and adjacent structure, and the condition of the embedded steel framing. This initial work helped guide the team's approach toward planning and design for the entire building.
The full restoration campaign began with extensive hands-on surveying and targeted probes to pinpoint the root causes of the exterior damage and deterioration. Layers of the cracked and displaced masonry enclosure were locally peeled back, which revealed corroding steel framing just below the surface. Union Terminal was constructed before the integration of air cavities, weep holes, impermeable membranes, and other measures that are now commonly used to keep building facades watertight. Because of this, the steel began to corrode and forcefully expand over time, pushing out the surrounding masonry through "rust jacking." Cracking and damage caused by corrosion were most severe at the upper stories and protruding corners of the building.
Similarly, the building was constructed before expansion joints, relieving angles, and other accommodations for structural and thermal movement were incorporated into common design practices. When subject to environmental stresses, the vast fields of confined masonry cladding had nowhere to release but out, with few lateral ties to the substrate behind. Cracking and displacement caused by this outward expansion were most noticeable along the curved facades of the north and south ramp wings and the drum walls beneath the dome.
The design proceeded with three overarching objectives:
- restore and, in some cases, strengthen the structural capacity of damaged and deteriorated elements
- improve the performance of the facade against environmental factors such as water and extreme temperatures
- maintain the overall character and appearance of the iconic exterior
Architectural and structural design drawings from the 1930s provided reasonably accurate and detailed information about the original construction and materials. Subsequent alterations were less well-documented, creating a challenge for evaluating and developing fixes for those areas. At the west facade, for example, a masonry wall with embedded steel columns and beams had been installed to enclose the building after the original structure extending over the rail yard was hastily cut off in the 1970s. Supplemental "wind columns" and modifications to the original roof structure, which helped support the rear wall, were made when the Robert D. Lindner Family OMNIMAX Theater was installed in the remains of the concourse in the 1990s. Only limited design drawings for this later work were available.
Preparing for a Second Century
The exterior restoration encompassed a range of materials and conditions, some typical and some unique. Displaced limestone and brick cladding were carefully removed and either reset or replaced. Corroded steel framing was repaired within the walls and inside the aluminum-clad marquee, the Tower A sunshade, and the portal entries to the underground portion of Dalton Avenue. Spalling concrete was patched throughout the roof slabs and at the west concourse smoke shelf, a feature originally intended to protect the overhead structure from smoke and cinders emitted by steam locomotives.
Silman and JGWA coordinated closely on detailing repairs that maintained the appearance and integrity of the building, introducing new materials and methods only where justified to improve long-term performance. At the curved parapets that had begun to severely lean outward along the north and south wings, for example, damaged backup masonry was replaced with new reinforced masonry, and salvaged face brick was reinstalled with lateral ties and expansion joints to mitigate the potential for future displacement.
Responding to the varied conditions across the building required an equally measured treatment strategy; most areas were addressed through surgical repairs. These included local removal of masonry cladding to facilitate cleaning, assessment, and, where required, reinforcing or replacement of the embedded steel structure. The tight-knit assembly of masonry cladding and steel frame made it unrealistic to expose, let alone document and detail, exact repair locations and quantities on drawings before the start of construction. A robust menu of typical repair details was developed instead, based on representative conditions. This enabled work to proceed according to unit prices and quantity allowances. Most of the building envelope work—including roofs, parapets, and window and door openings—was captured through this approach.
Certain conditions warranted more invasive demolition and rebuilding to correct irreversible damage and shortcomings inherent in the original design. For example, at the drum walls beneath the dome, extensive cracking and displacement of the facade allowed excessive moisture to seep into the perimeter corridor directly behind the historic rotunda murals. The original brick and terra-cotta were no longer performing their most basic function of protecting the building structure and interiors. Restoring the capacity of the exterior facade in this area required more wholescale replacement of the masonry cladding and treatment of the embedded steel structure. The original steel structure was repaired in place and enclosed with a new cavity wall assembly of reinforced-concrete masonry units (CMUs) and carefully salvaged brick.
The facade was bulging outward and on the verge of failure at the portion of the west wall that had been cobbled together after the demolition of the rear train concourse. A structural analysis of the steel frame revealed a poorly defined load path and undersized members for current load and deflection requirements. A new steel structure was installed and meticulously integrated with the existing structure and, like the drum walls, enclosed with a new cavity wall assembly of reinforced CMU and brick.
The planning and sequencing of the work between Silman, JGWA, Turner, and the subcontractors were critical to minimizing the impact of replacing the building's outer skin at the drum walls and at the west wall—logistically more so than aesthetically. As masonry was removed and steel structure exposed, Silman visited the site frequently to observe progress, identify discrepancies between the design details and field conditions, and provide final direction. Access to the west wall also had to be approved by, and tightly coordinated with, the active freight railway that was feet away from the face of the building.
The restoration and renovation of Cincinnati Union Terminal has reversed the physical marks of age, environment, and abandonment, securing the building's future as an icon of its namesake city. That Silman's mark on the building is essentially hidden to visitors makes it all the more gratifying—as structural and preservation engineers, the most thoughtful solution to a problem is often that which cannot be detected once our work is complete.
Lizzie Olson, P.E., S.E., was an associate at Silman's New York City office during this project. She is now a project manager in the capital projects department at the Frick Collection, a museum in New York City. Derek Trelstad is an associate at Silman's New York City office.
BY ANTHONY METTE, P.E., S.E.
When Cincinnati Union Terminal was built in 1933, public transportation dropped off passengers in the terminal via the north and south wings, but private vehicle parking and individual passenger and luggage drop-off occurred east of the main building on a lower level that was built beneath the terminal's front lawn and fountain. To create this additional space, more than 2.5 acres of structured building was constructed below the lawn and fountain. This space is now occupied by the Cincinnati Museum Center, which comprises the Museum of Natural History & Science, the Cincinnati History Museum, the Duke Energy Children's Museum, the Robert D. Lindner Family OMNIMAX Theater, and the Nancy & David Wolf Holocaust & Humanity Center. The terminal also remains true to its heritage as a train station, however, and is a stop for the Cardinal—Amtrak's thrice-weekly train service between New York City and Chicago—as it has been since 1991.
There were multiple phases and design packages for the terminal project over the 28-month construction schedule. THP Limited Inc. had previously completed renovations in the terminal and applied that experience to the various design packages of the new project: the temporary lobby, which created a secure entrance to maintain a portion of the museum exhibits while construction began in other areas of the building; the interiors; and the plaza waterproofing above the underground portion of the building.
The terminal, including the building under the plaza and fountain, is steel framed with reinforced cinder concrete slabs, masonry walls, and a limestone facade. The steel Carnegie beams that support the lawn and fountain are 30 to 36 in. deep, weigh 138 to 275 lb/ft, and span between 34 and 43 ft. The girders are built-up riveted steel-plate girders that weigh more than 800 lb/ft and span 40 ft to the steel columns.
The first design package was the 33 ft deep, 106 ft wide, 25 ft tall temporary lobby in the rotunda. This lobby protected visitors from work occurring on the curved ceiling and maintained access to the children's museum and space dedicated to traveling exhibitions.
The temporary lobby was freestanding (unanchored to the historic terrazzo floor in the rotunda), constructed around the main ticket kiosk, and structured to bear over the existing Carnegie floor beams. It was framed on three sides with 4 by 7 ft scaffolding towers to match the 7 ft spacing of the rotunda beams. The temporary lobby roof comprised a 1.5 in. metal deck anchored to W12X14 beams that were welded into yokes at the scaffolding towers. Wood sheathing was anchored to the sides of the scaffolding to create a three-sided box for lateral stability, with steel columns and beams on the fourth side of the box that provided a pathway through the main building entrance for visitors. Steel plates, which acted as dead weight, were anchored to the scaffolding with cables to resist overturning from internal wind pressures on the walls. Windows were installed in the temporary lobby walls to allow visitors to view construction activities in the rotunda.
The interior renovation focused on reconfiguring the museum space for long-term flexibility; modernizing the building's mechanical, electrical, plumbing, and information technologies systems; and providing long-term protection of artifacts and collections. Upgrades included new elevators in the rotunda and exhibit spaces to improve access between the levels. Additionally, new structured stairs and ramps were added in exhibit spaces throughout the building, including a new landing and grand staircase.
Creating a 3-D model of the existing historic building was critical for the project's multidisciplinary team and its wide scope of work. THP used existing drawings to model the entire structure—all 10,238 elements—in Revit software by Autodesk, of San Rafael, California. Accurately modeling the built-up riveted columns and girders, as well as the concrete encasement around the steel framing, was critical for coordinating with new architecture and mechanical systems to minimize their visibility from the exhibit areas. THP's structural modifications to the building added almost 600 new elements to the initial model.
One interior structural modification was made to improve the functionality of the lower level's exhibit areas: the orientation of the diagonal bracing that supported the longest-spanning steel roof truss of the rotunda was reversed between two building columns. THP designed a new horizontal brace and the reversed diagonal brace to replace an existing double-channel diagonal brace. Because the existing double C12X25 braces provided lateral stability for the main rotunda structure, the challenge was to design a new brace that could be installed while the existing one remained in place. The new braces were connected to built-up riveted columns that had a total flange thickness of 5 in. Interestingly, it was discovered during field excavations that the diagonal bracing connection to the column base was offset by more than 2.5 ft from the top of the baseplate, which created an eccentricity in the brace connection. The new double-channel bracing was anchored to the column at the baseplate work point to remove the eccentricity and more efficiently transfer the force.
Support for the new columns for the exhibit areas and stairs was complicated because of the building's original siting. The original foundation system comprised driven steel piles with concrete caps to support the building columns. This deep foundation system was necessary because of the 20 to 40 ft of fill used to raise the building's pad elevation, which was necessary to protect the building from flooding. Because of concerns with the original uncontrolled placement of the fill material, the geotechnical engineer, the Cincinnati office of Geotechnology Inc., recommended new shallow foundations with a bearing capacity of 1,000 psf and a possible settlement of 0.75 to 1 in. Chemical soil grouting was added under the new shallow foundations to increase the soil density to minimize long-term settlement.
East Lawn and Fountain
More than 200,000 sq ft of museum exhibit area exists below the terminal's fountain and front lawn, known as the east lawn. The east lawn building is structurally isolated from the main terminal building and is separated into three structures by expansion joints extending east to west. As originally built, the structure was protected with coal tar waterproofing and a lead pan liner under the fountain. A large part of the project was removing this original waterproofing as well as all hardscapes, lawn areas, and the fountain. The new THP-designed, hot-applied waterproofing system was installed continuously under the rebuilt fountain. Historic preservation work by John G. Waite Associates, headquartered in Albany, New York, included detailing the reconstruction and waterproofing of the fountain above the slab.
Severe corrosion of the steel beams below the plaza expansion joints was discovered as sections of the old waterproofing were removed. THP analyzed the reduced steel sections and, after exploring various options, determined that two girder spans and the associated beams below and along each east-to-west expansion joint needed reinforcement. A pair of steel girders placed below the bearing of the plaza beams did just that. The two W36X302 girders were installed parallel to the existing girder and below the plaza's wide-flange beams and welded to the existing beams at one end. To maintain the expansion joint at the other end, the new girder supported the beams with a new slide-bearing connection. Four of the columns were plated to create box columns to support the new girders with 44 in. deep gusset plate connections. Additionally, two new columns were installed adjacent to two existing columns to increase the load capacity. This reinforcement solution limited impacts on the museum exhibit areas, minimized redesign of mechanical ducts, and maintained the underground building's ceiling heights.
Plaza waterproofing at the expansion joints was replaced to prevent future water infiltration after all steel reinforcement work was complete. Improved detailing at these joints included the following:
- a concrete curb along both sides of the joint
- neoprene flashing embedded into the waterproofing system over the joint opening
- a stainless-steel plate-protection cover
- a winged, compression-seal, expansion joint set at the plaza hardscape level
Rehabilitation of the terminal was supported by the citizens of Hamilton County (which encompasses Cincinnati) through passage of a fixed-term, five-year sales tax. In addition, private donations, state grants, and state and federal tax credits were used to fund the $228-million rehabilitation project.
Anthony Mette, P.E., S.E., is the senior restoration project manager at THP Limited Inc., in Cincinnati.
Scanning The Terminal
BY DAVID L. COX, P.S.
GBBN Architects of Cincinnati led the design efforts for the renovation and restoration of Cincinnati Union Terminal. The terminal is a complex space, spread out over nine levels totaling more than 530,000 sq ft. The facility was not constructed exactly in conformance with the original design drawings and had been renovated at various times over the years. GBBN determined early in the project that an accurate 3-D model of the facility would be key to determining the best course of action for this historic preservation project.
TrueScan, a division of the Kleingers Group Inc., headquartered in West Chester, Ohio, worked with GBBN to understand the scope of the proposed renovation and assist with recommendations for building documentation services. TrueScan is unique in that the entire management team holds professional surveyor licensure and oversees all reality capture projects.
TrueScan's final project scope required 3-D laser scanning of the entire interior and exterior of the building. This included color imagery of historic interior areas, such as the rotunda, as well as the entire exterior facade and the iconic plaza fountain leading to the entrance of the building.
The interior scanning included all public spaces and exhibit areas, offices, storage areas, and mechanical rooms as well as the structural steel in the plenum between the rotunda ceiling and the exterior of the dome. Above-ceiling scans were also performed within limited office spaces to locate various overhead utilities, including fire protection lines and ductwork. Additional services included a boundary and topographic survey of the roughly 24-acre site along with identification of the underground utilities.
TrueScan began work in late June 2015 with a horizontal and vertical control survey. Tied to state plane coordinates, the control established the foundation for the boundary and topographic survey and provided georeferenced scan-control points at numerous locations, including doorways and rooftops. Upon completion of the control survey, scanning began, first on the exterior (the top priority) and then the interior. Because of the tight schedule, two two-person scan teams worked back-to-back shifts for six weeks. The day-shift scan team concentrated on the behind-the-scenes areas, while the evening-shift team handled the public areas and offices when human traffic was at a minimum. Both teams used a Leica P40 long-range scanner by Leica Geosystems, headquartered in St. Gallen, Switzerland, for its range, accuracy, data quality, and high-dynamic-range color-imaging capabilities.
The scanning process involves setting up a terrestrial or tripod-mounted scanner in strategic locations throughout the scan area. After setup and leveling, a high-intensity scan takes about 90 seconds and captures everything within its range and line of sight. The scanner is then moved to another position where the field of view includes a minimum of three targets that are in common with the previous scan, ideally with a minimum overlap of about 30 percent of the previous scan area. The scanning progression continues in this fashion throughout the building; individual spaces or rooms are connected by corridors, and individual levels are connected by stairways until the entire area has been scanned. Interior and exterior scans are connected by scanning through open doors and windows in as many locations as possible.
For this project, scans were performed from the ground around the exterior and the first floor in the interior and from several rooftop vantage points. All nine levels of the structure were tied together sequentially by data that went through four stairwells connecting each floor.
In total, the project consisted of more than 2,300 individual scans and captured every required space with one exception: the top of the half-dome structure. Drone-based photogrammetry was used to capture this area. Survey controls in the form of rooftop targets were included in the drone's flight path. The resulting color photography was converted to a point cloud, and then registered to and combined with the terrestrial point cloud to complete the exterior scan.
Raw scan data were imported twice daily. First-shift data were imported every evening, while data from the second shift were imported early the next morning. Office staff analyzed and registered data as they were captured and downloaded. As part of the quality-control process, any apparent discrepancies or uncertainties were immediately relayed to the field crews for clarification or acquisition of additional data.
Data management was by far the most challenging part of the entire project. The raw data for the project consisted of more than 2 terabytes of information that had to be processed, managed, stored, and transferred to the client. Pointcloud data were categorized by level and further segregated into 12 rectangular segments that were consistent throughout each level. By breaking down the data into bite-size chunks on a consistently segregated grid pattern, the client was able to load only those portions of the point cloud needed to evaluate the different areas of the structure.
One of the greatest benefits of having an accurate and comprehensive data set was the team's ability to check existing conditions and verify dimensions without making repeat trips to the site. This was especially efficient for the out-of-town consultants and team members. Even after construction began, time was saved by avoiding the 15-20 minute walk to ascertain an existing condition on-site every time a question arose. Additionally, the digital data were made available to the consultant and construction teams as well as the owner. The owner even used the scan data to verify conditions of the exhibits that were in place at the time of the scan.
In the five short years since scanning work began on this project, laser-scanning technology has seen huge advancements. If the same services were repeated on this project today, the data set would be of an even higher quality, delivered more seamlessly, and in half the time.
David L. Cox, P.S., is the director of geospatial services at TrueScan, part of the Kleingers Group Inc., headquartered in West Chester, Ohio.
PROJECT CREDITS Owner Union Terminal LLC Design and executive architect GBBN Architects, Cincinnati Historic preservation architect John G. Waite Associates, Albany, New York Structural engineer, exterior envelope Silman, New York City Structural engineer, interior renovation, and plaza waterproofing THP Limited Inc., Cincinnati Civil Engineer and landscape architect Kleingers Group Inc., West Chester, Ohio 3-D scanning TrueScan, part of Kleingers Group Mechanical, electrical, and plumbing engineer and fire protection engineer Arup, Washington, D.C. office, and Heapy Engineering Inc., Dayton, Ohio Geotechnical engineer Geotechnology Inc., Cincinnati office Construction manager Turner Construction Co., Cincinnati office Masonry contractors Lang Masonry & Restoration Contractors, Waterford, Ohio, and Lithko Contracting, West Chester, Ohio Signage and wayfinding Two Twelve, New York City
Civil Engineering, March 2020, © American Society Of Civil Engineers. All Rights Reserved