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

different earthquake excitations but depends on the earthquake characteristics, themodal properties, and mass distribution.2. Although less obvious, time history analysis generally confirms the conclusiondrawn from the modal properties of the bridge that the bridge is most flexible invertical direction and then in transverse direction.3. All cables behave elastically under a design earthquake. Their factor of safety islarger than 2.35 at all times. On the other hand, the cable subjected to least stressis always in tension, ensuring no slack occurrence during the earthquake.Therefore, cables can be simplified as linear elements for seismic analysis.4. The solid section of both towers at the lower portion is generally more criticalthan the hollow section of the upper portion of the towers above the cap beams.The in-plane behavior of two towers is always in elastic range under the designearthquake with a wide margin of safety. For out-of-plane behavior, the upperportion of the towers above the cap beams remains nearly elastic with asignificant margin of safety. The lower portion of the towers, however, issubjected to moderate yielding out of plane during the design earthquake thoughthe bridge safety is not a concern.92