Assessment of the Bill Emerson Memorial Bridge - FTP Directory ...

Frequency (Hz)1.110.90.80.70.60.50.40.3Springs and dashpotsFixedHinge0 5 10 15 20 25 30 35ModeFigure 5.38 Natural frequencies with various pile foundation conditionsTo understand the role of dashpots at pile foundations, different energy terms of thebridge system are compared in Table 5.7 for two cases: piles on springs & dashpots andpiles all fixed. It can be seen that the input energy, kinetic and potential energy with thepiles on “springs & dashpots” case are relatively smaller than those of the case with allpiles fixed. This indicates that the soil-pile foundation system can dissipate to certaindegree the earthquake energy and reduce the responses of bridges. Note that the results inTable 5.7 are obtained under two earthquake excitations: D1 as the earthquake occurredon May 1, 2005, near the cable-stayed bridge and the 1971 Pacoima earthquake.Table 5.7Energy dissipation at the soil-pile foundation systemCaseEarthquakerecordInput(KN-m)Kinetic(KN-m)Potential(KN-m)Modal damping(KN-m)Springs &dashpotsD1Pacoima-49.08×1051.28×10-53.47×1042.57×10-52.98×1043.45×10-49.02×1051.26×10FixedD1Pacoima-49.50×1051.46×10-54.27×1042.31×10-54.34×1043.10×10-49.42×1051.46×105.4. Model calibration and verification70