Journal of Performance of Constructed Facilities

Forensic engineering investigations of residential structures often include measurements of elevation differences across the slab-on-grade floor as an indicator of movement (settlement or heave) of the underlying soil. Such assessments are predicated on an assumption that the slab was flat or very nearly so at the time of initial placement. Despite the relatively frequent use of such measurements in practice, confirmation of the underlying assumption is scarce in the archival literature. This paper describes a testing program to measure the deviation from level of a large number of residential concrete slab-on-grade floors in Phoenix, Arizona, within a few days of concrete placement. An average maximum elevation change of 13.5 mm was observed. Average and maximum slopes are also presented. The construction of the residential structure atop the slab was found to have no statistically significant effect on the levelness of the slab, nor did the season in which the concrete was placed. Residential slab-on-grade construction methods are reviewed, concluding that this degree of deviation from level is to be expected. Comparison of the data with recommendations in the literature suggests that caution must be taken in evaluation of cosmetic or structural impairment of residential structures based in large part on measurements of interior floor slab levelness.

In this paper a number of serviceability issues related mainly to excessive deflections of structural floor elements (beams and slabs) are discussed. Field data of serviceability damage caused by excessive deflections of structural floor elements have been collected from various sources and probabilistic models are developed. Current serviceability specifications for allowable deflection limits in Australian, U.S., and other concrete structure codes have been compared against these probabilistic distributions of damaging deflections. Preliminary results confirm that allowable deflection limits in these design codes represent realistic lower-bound values of damaging deflections.

A civil engineer performed a condition evaluation of an eight-story building of approximately 1,500 m² (16,000 ft²) per floor constructed in 1909 in downtown Milwaukee. Subsequent to the evaluation, a failed real estate transaction along with poor forensic engineering investigation and incomplete testing led to a lawsuit filed against the civil engineer. At a large cost for his defense, the civil engineer was exonerated in Milwaukee County Court.

This paper develops a probabilistic construction load process model for multistory reinforced-concrete building construction. This model considers loads causing peak structural actions on floor slabs for two widely used shoring procedures and includes probability distributions and temporal characteristics of slab self-weight, sustained construction live loads, “material stacking” loads, and “move-in” loads. Construction load statistics derived from Monte Carlo simulation show that the mean of maximum construction loads exceeds nominal (design) service (occupancy) loads whenever the nominal live-to-dead load ratio is less than approximately 1.0. A Type I extreme value distribution provided the best fit to the inferred distributions of construction live loads.