Journal of Performance of Constructed Facilities

The Specific Pavement Study–1 pavement test section on US281 in south Texas comprise the largest Strategic Highway Research Program experimental site in the United States. The project was opened to traffic in 1997, and performance has been poor. Three of these test sections developed deep rutting within 1 year. Their surfaces were milled to restore ride quality. Three years after construction, 14 of the sections had 10 mm or more rutting. A forensic study was initiated by the Texas Department of Transportation to identify the cause of the problem. Nondestructive testing was conducted with both the falling weight deflector and ground penetrating radar. No structural problems were detected with either device, both indicating that the base and subbase layers were strong. A field investigation was initiated; the original plan was to cut nine trenches, however, after four trenches were cut, the problematic layer was identified and the trenching operation was terminated. Dynamic cone penetrometer, stiffness gauge, seismic pavement analyzer, and nuclear density gauge tests were then conducted on top of the base and subgrade layers. The trench profiles indicated that the rutting was coming primarily from the top 50-mm (2-inch) asphalt-concrete layer. Asphalt cores were taken from both rutted and nonrutted sections and bag samples of the base were tested in laboratory. The binder was recovered, and the asphalt content and penetration, aggregate gradation, and type were determined. The cause of the problem was traced to a change in aggregate screening, and also an excess of asphalt in the top layer.

This is the first of two papers that present the results of a comprehensive and systematic study into the effects of false flooring on the vibration serviceability of long-span concrete floors. In this paper, advanced modal testing technology was utilized to determine modal properties of long-span concrete floors (natural frequencies, modal damping ratios, and mode shapes) before and after the installation of false flooring. It was found that false flooring had the capacity to change modal properties significantly, particularly modal damping ratios, which had increases of up to 89%. Parametric studies using updated finite element models were also performed, which showed that the false flooring contributed also to floor stiffness. However, changes in modal properties were not consistent across all modes of vibration and it was not possible to predict easily which modes would be affected beneficially by the installation of false flooring.

This is the second of two papers that present the results of a comprehensive and systematic study into the effects of false flooring on the vibration serviceability of long-span concrete floors. In this paper, controlled pedestrian response measurements were utilized to determine the effects of the installation of false flooring on the vibration serviceability of long-span concrete floors. It was found that, in most cases, the installation of false flooring tended to reduce the measured vibration response of the floor under controlled pedestrian excitation. This was more significant for false floors with a relatively high finished floor height (FFH) than for floors with a lower finished floor height. It is tentatively proposed that the effects of false flooring be incorporated into existing design procedures by multiplying calculated responses by a vibration response reduction factor. This factor would be 0.9 for false flooring with FFH less than 500 mm or 0.8 for false flooring with FFH of 500 mm or greater.

This case study considers the question of whether settlement or heave is the principal cause of damage to a school building near Denver. The building, which was underlain by engineered fill in the center and shallow claystone bedrock beneath the outer wings, experienced progressive deformation and significant damage during a 15-year period. With several millions of dollars of rebuilding costs at risk, the most likely cause of failure needed to be ascertained to arrive at an optimum mitigation solution. The investigation described herein considers the regional geology and its known effect on various types of engineered structures in terms of characteristic damage patterns. The focus progressively narrows to concentrate on the geology and damage patterns of the local area and the site. The findings indicate that the major cause of damage to the building is associated with differential heaving of steeply dipping, expansive bedrock layers. This conclusion was adopted as a basis for subsequent remedial planning and design.