At Princeton University's Whig Hall, almost 100 years of weathering and a fire caused extensive damage to the masonry portico. Originally targeted for replacement, non-destructive testing techniques allowed isolated areas of damage to be evaluated and localized repairs conducted. Photo: Edmund P. Meade, P.E.

WHIG HALL,
PRINCETON UNIVERSITY
Princeton, New Jersey

    Whig Hall is located at Princeton University, in Princeton, New Jersey. An adaptation of a Greek Temple, the two story structure features an entrance portico with full entablature and a simple pediment supported on six fluted marble columns.

   Along with its adjacent twin, Clio Hall, Whig Hall was constructed of Vermont Montclair Danby Marble and completed in 1893. Designed by A. Page Brown, the buildings originally housed two rival, campus debating societies.

Problem

   The portico of Whig Hall is primarily constructed of unreinforced, load-bearing masonry. Weathering over the past 100 years and a major fire resulted in extensive cracking of the column bases and plinths; sugaring, erosion and pitting of marble surfaces; and erosion of mortar joints. Although initial reports commissioned by the university concluded that the portico substructure and columns should be replaced, less intrusive methods of repair were sought.

Evaluation of Whig Hall
Using NDE Techniques

   Robert Silman Associates, P.C., was retained in 1994 to evaluate repair alternatives rather than undertaking a total reconstruction. In order to perform a load analysis of the portico structure, it was necessary to document the effective cross section of the columns. A program utilizing NDE techniques was established for both Whig and Clio Hall, although only the results of Whig Hall are presented here. The purpose of this evaluation was to determine the depth, extent, and nature of masonry cracking. Column A of Whig Hall, which measures 22 feet in height and 2 feet, six inches in diameter, appeared to have the most significant cracking. There was considerable concern for the integrity of this column and the unknown nature of the cracks.

The column capital volutes were cracked and spalled. Photo: Edmund P. Meade, P.E.

   Initial condition investigations of the stone elements and the supporting structural members of the portico included a visual examination as part of the survey of the entire exterior of the building. All major elements were examined using "cherry-pickers," scaffolding, and ladders.

   The examination focused on the cracked pieces of stone at the entablature level; the cracked or spalled column capital volutes; the cracked stone columns; the cracked stone column bases and plinths; the deteriorated pieces of masonry that were immediately below or adjacent to the column plinths; and the deteriorated support structure                                                 below the portico floors.

The column base and plinths had extensive exterior cracks. The internal column cracks were detected by ultrasonic pulse velocity and impulse radar investigation techniques. Photo: Edmund P. Meade, P.E.

   At Whig Hall, Column A exhibited severe surface cracking, and an extensive internal crack pattern within the plinths. Additional cracking was noted at the bases of a number of other column shafts. Some deterioration of the masonry walls beneath the column plinths was also observed, although without signs of differential movement between different portions of the portico foundations.

   Following this initial evaluation, the project team, including a stone conservator and stone fabrication specialist, recommended that the column bases and plinths be replaced; the upper portion of the column foundation system be reconstructed; and that localized stone repairs occur where cracks and/or spalls existed.

   This repair and restoration plan would require in situ support of the columns and pediment while their bases and plinths would be replaced and repairs conducted underneath. To better establish a probable scope of work, a more thorough study of the column interiors was undertaken using ultrasonic pulse velocity and impulse radar investigation. It was hoped that these techniques could more accurately determine areas of failure, voids, or other indications of stress.

Solution (Test Results)

Impulse radar is being used to evaluate both the orientation and depth of cracks visible on the surface of the column shaft. Photo: Edmund P. Meade, P.E.

   NDE was undertaken by a firm specializing in the evaluation of older buildings, G.B. Geotechnics of Cambridge, England. They performed a survey of both porticos over a three-day period using a combination of ultrasonic pulse velocity and impulse radar. The Whig Hall project benefited from the previous NDE work at the New York State Capitol; however, here, only two tests were determined to be appropriate. Additionally, a single firm that offered a range of NDE services was used.

   Ultrasonic Pulse Velocity. The ultrasonic pulse velocities recorded for the marble were in the range of 0.157 to 0.256 inches per microsecond. In some areas of the column shafts, high amplitude internal reflections were noted, indicative of discontinuities or cracks within the column.

   The orientation of the various cracks, e.g., horizontal, was identified. The variable depths of the cracks were calculated, with the average maximum depth being about 2 inches.

Above: This impulse radar transducer emits and receives electromagnetic energy. The unit is attached directly to the equipment below. Below: Raw radar output was analyzed by the geophysicists. Correlations could then be made to provide qualitative and quantitative evaluations of the stone. Photos: Edmund P. Meade, P.E.

   Impulse Radar. The radar readings indicated that the column shafts were constructed of monolithic marble, with the same type of marble used for the column bases and capitals. The radar detected anomalies near the junctions of the column shaft with the base and the capital. The readings also indicated that there may be cramps or ties between the columns and the bases/capitals. It could not be determined whether the objects detected were metallic, or if they were possibly "Lewis holes" that had been used to maneuver the stone blocks during construction. Magnetic detection equipment with the ability to penetrate large diameter columns could have been used in conjunction with the radar to verify the nature of the internal anomalies.

Project Summary

   The consulting NDE firm provided a written report describing its methodology and findings; it also provided graphics to assist the engineer, architect and conservator in the interpretation of the results.

   To help maintain the integrity of the masonry during the repairs, it was recommended that Column A, as well as several areas of other stone elements be pinned. It was necessary to support the column shafts while the bases and plinths were removed. This could be accomplished by the use of high strength steel pins through the column shaft, or the placement of steel clamps around the column shaft to establish a friction hold around the column.

The non-destructive evaluation of Whig Hall allowed the diagnosis of the condition of the masonry and the specification of a relatively low impact repair. Photo: Edmund P. Meade, P.E.

   The NDE results indicated areas where pinning or clamping should be avoided, or if not possible, performed with great accuracy and using extreme care. This would limit the amount of drilling and pinning, techniques that could potentially weaken the columns further. An additional benefit of the NDE work is that it provided a basis of comparison for evaluating other stone elements on the building which exhibited signs of deterioration.

Conclusion

    The case studies provided different perspectives on the use of NDE. At the New York State Capitol, the primary purpose was to research nondestructive methods of locating and imaging hidden structure in a massive masonry building. The research project supplemented information acquired during a visual survey with destructive probe work. At Princeton's Whig Hall, the specification of NDE was part of a contract to assess structural capacities and design repairs, and to prepare construction documents.

    The point of the comparison is that there are techniques currently available and experienced firms to perform field investigations, but continued research is needed. Ways to improve the portability and simplify the use of equipment should continue in the manufacturing community. Additional applications and improvement of accuracy for the techniques should be researched through a combination of academic, non-profit research, and commercial organizations. Standards and guidelines need to be developed to aid the architect, engineer, or conservator in the specification of NDE in historic preservation projects.

   It is hoped that through the combined efforts of preservation professionals, researchers, and equipment manufacturers and operators, that NDE will become generally available and increasingly economical for use on landmark structures. For projects where these techniques should be implemented, the preservation professional must impress upon the client the need for NDE in conjunction with limited conventional probes before beginning project work.

Project Data and Credits

 

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