Project: Granite Cladding Repairs at Chase Tower
>>> Designed by I.M. Pei, Chase Tower (formerly known as the Texas Commerce Tower) was completed in 1981 and contains almost 2 million square feet of office building space in downtown Houston. The office tower is clad in Barre Grey granite, stainless steel and gray glass. At 1,002 feet tall, the 75-story building is the tallest building in Texas and noted as being the tallest “5-sided” building in the world.
Now forty years old, the Barre Grey granite clad skin of the Chase Tower was in need of attention. Camarata Masonry Systems, Ltd. (CMS) was selected to address the stone cladding windload anchors that were now also being subjected to gravity loads. This work was to be completed with the building occupied and without removing the stone panels. Wiss, Janney, Elstner Associates, Inc. engineered a through-face anchor system that met the needs of the project. The 15,610 stone panels on the building skin would require 46,626 anchors. The quantity and size of the anchors varied depending on the location, size and thickness of the panel. After installation of the anchors, the through-face holes were sealed with stone plugs (below Level 12) and sealant plugs (above Level 12). In addition to the new anchors, it was necessary to ensure that all horizontal stone to stone and stone to window joints were “opened”, eliminating any transfer of deadload weight to the element below. This required the removal and replacement of 42,000 linear feet of sealant and the cutting of approximately 20,000 linear feet of stone to open the joints to the minimum joint width of ¼”.
Because of the dangerous nature of the work, occurring 1,000 feet above active sidewalks and the prominent downtown Texas and Travis Streets, public safety was addressed first. Sidewalk overhead protection was designed and built to remain in place for the entire 22-month duration, including two hurricane seasons. Measures were also taken to minimize the chance of dropping any tools or stone anchorage components. The swing stages were fitted with an extended horizontal surface to close the gap between the stage and the face of the building, while the perimeter of the stages was wrapped with fabric mesh to further minimize the chance of falling material.
To help keep the duration of the project to a minimum, work was performed simultaneously on all elevations of the building using fourteen crews, six swing stages and the building’s maintenance unit stage. A detailed swing stage plan was developed to provide enhanced worker safety (by not having adjacent stages working in close proximity) and for ease in moving to the next drop without disrupting the other stages.
In performing all of the work from swing stages, wind and rain were expected to be the most problematic elements; as such we allowed for an anticipated loss in time due to the weather. Wind protocols were established to determine what elevations and stages were safe to work or if it was safe to work at all. As expected, significant time was lost due to wind and rain. The majority of this additional lost time was made up with extended daily work hours and weekend work, enabling us to complete the project within its original 22-month scheduled duration.
While very effective, the through-face anchor installation process was time consuming and required a very high degree of quality control. The anchor installation process itself is deserving of a detailed step by step description to fully appreciate the complexity. To best describe this process, we have included the details and photos to illustrate the process in the supplemental material section of this entry. The complexity of the anchor and the installation method was the reason that CMS chose to implement a detailed training program at our main office prior to mobilizing on site. The training involved all personnel that were selected to work on the project. With the exception of the swing stage, we built numerous work stations that mocked the building façade (the concrete substrate, cavity and the granite cladding); we even restricted the work area to reflect the same constraints as would be encountered on the swing stages. It is estimated that each worker installed in excess of two hundred anchors (the complete assembly) in these mock up stations. While very costly at the outset, we believe that this training and familiarization of the anchorage assembly was invaluable.
As the tallest building in Houston, it is important that the Chase Tower maintain its prominence in the downtown business sector. The first step in keeping up with the downtown growth was the cladding repairs. While the work had significant risk of physical damage and personal injury, CMS completed the work with no recordable or lost time accidents and is proud to have met its goal of providing an efficient and safe installation which led the way to continued modernizing of the building interior and site; assuring that the building would remain as the benchmark standard for the City of Houston.