David G. Pollock

MEASUREMENT AND EVALUATION OF MOORING CABLE FORCES DURING STORM EVENTS ON THE EVERGREEN POINT FLOATING BRIDGE: LAKE WASHINGTON, WASHINGTON STATE

On January 20, 1993, the Evergreen Point Floating Bridge incurred structural damage at two mooring cables and at various other locations during a storm event of approximately the 20-year return period magnitude. The two mooring cables damaged were the shorter and stiffer cables located at the ends of the bridge and were likely damaged because of load attraction issues. To improve the performance of the floating bridge during storms, special replacement cables were installed after the 1993 storm near the areas where cable distress was noted. Measurements of cable forces were made during the winter season of 2001–2002 to evaluate the effectiveness of the replacement mooring cables. From the experimental measurements, it was found that the special replacement mooring cables have reduced the load attraction at the shorter end cables with respect to cable tension values reported for the pre-retrofit analysis. However, the measurements indicate that the replacement cables continue to attract loads between 65% and 80% higher than those measured at the longer and more flexible cables located near the midspan of the floating bridge during storm events of approximately the 1-year return period magnitude.

ULTRASONIC INSPECTION OF GLUED LAMINATED TIMBER FABRICATED WITH DEFECTS

FHWA set up a validation test to compare the effectiveness of various nondestructive inspection techniques for detecting artificial defects in glued laminated (glulam) members. The validation test consisted of a glulam beam fabricated with artificial defects known to FHWA personnel but not originally known to the scientists performing the validation tests. Ultrasonic inspection was effective in identifying voids within the glulam beam. The glulam was inspected across the width and through the depth. The inspections from each direction were combined to accurately detect and locate artificial voids in three dimensions. Wave travel time allowed identification of some of the voids, but signal amplitude parameters, such as root-mean-square voltage and peak voltage, provided more precise location of the voids. The three-dimensional image provided valuable insight into the internal condition of the glulam. However, through-thewidth inspection was able to locate voids in two dimensions along the length and depth of the glulam. For a field inspection, two-dimensional location of decay would provide sufficient information for judgments to be made on the future of the inspected specimen.

Reliability Indices for Bolted and Nailed Connections in Wood Structures

Recently published test data for bolted and nailed connections was evaluated to assess the structural reliability inherent in current allowable stress design procedures for connections in wood structures. Reliability indices were determined for timber connections using standard firstorder, second moment (FOSM) procedures. For the connections considered in this study, reliability indices range from 2.6 to5.1, generally providing higher levels of safety than the structural members in timber structures.