Field-Measured Natural Frequencies of Delaware Memorial Bridge
The Delaware Memorial Bridge is a major suspension bridge that is critical to the tristate region of northern Delaware, southern New Jersey, and southeastern Pennsylvania. The Delaware Memorial Bridge consists of two nearly identical suspension bridges (hence, the nickname Twin Spans) that cross the Delaware River from southern New Jersey to northern Delaware. Field ambient vibration measurements of Structures 1 and 2 of the Delaware Memorial Bridge were conducted in June 2001 and September 2003. These measurements were used to derive the natural frequencies and modes of vibration for these structures. These field-measured frequencies and modes were then compared with each other and with computer-generated natural frequencies and modes of vibration derived for Structure 2 of the Delaware Memorial Bridge in 1997. Specifically, the 2001 seismometer-generated results for Structure 1 were compared with the 2003 accelerometer-generated results for Structure 1; the 2003 field-measured results for Structure 2 were compared with the 2003 field-measured results for Structure 1; and the 2003 field-measured results for Structure 2 were compared with the 1997 computer-generated results for Structure 2. Overall, these three types of comparisons indicated relatively good correlation for transverse motion but only fair correlation for longitudinal and vertical motion.
NATURAL FREQUENCIES OF CONCRETE BRIDGES IN THE PACIFIC NORTHWEST
Analyses of field ambient vibration were performed on 50 concrete bridge spans along Interstate highways I-5 and I-405 in Washington State. These 50 spans included 21 pretensioned concrete beam (PCB) spans, 19 reinforced concrete box-girder (CBOX) spans, and 10 reinforced concrete slab (CS) spans. Eight measurement transducers were used to record ambient bridge vibrations at three locations on each span: midspan, one-quarter point, and one support. These records of bridge motion versus time were each subjected to a fast Fourier transformation, and plots of amplitude versus frequency were generated for each record. The plots of amplitude versus frequency were used to determine the fundamental vertical and lateral frequencies for the bridge spans measured. These fundamental frequencies were used with the bridge design parameters to derive empirical formulas that will be used to estimate the fundamental vertical and lateral frequencies of other PCB, CBOX, and CS bridge spans along I-5, I-205, and I-405 in the Pacific Northwest.
Comparative study of the molecular species of chloropropanediol diesters and triacylglycerols in milk fat
In an effort to establish the origin of the fatty acid esters of 3-chloropropanediol, which recently have been isolated in small amounts from goat milk, we compared the molecular species composition of the chlorohydrin diesters and of goat milk triacylglycerols. The chloropropanediol diesters were found to be composed of molecular species containing C10−C18 fatty acids and corresponded closely in carbon number to those calculated for the long chain sn-1,2-diacyl-glycerol moieties of goat milk triacylglycerols. The molecular species of goat milk total triacylglycerols contained C4−C18 fatty acids. It is suggested that triacylglycerols and chloropropanediol diesters are derived from the same pool of long chain fatty acids. A molecular distillate of bovine milk fat did not contain chloropropanediol diesters, while the available samples of human milk fat were shown to contain alkyldiacylglycerols as the major components of a neutral lipid fraction corresponding in polarity to the chloropropanediol diesters.