1 / 8

Resonance and Bridge Construction

Resonance and Bridge Construction. Engineers have always pushed the frontiers of bridge construction with both materials and design. Sometimes they push too hard with devastating results!.

dexter-bennett
Télécharger la présentation

Resonance and Bridge Construction

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Resonance and Bridge Construction Engineers have always pushed the frontiers of bridge construction with both materials and design. Sometimes they push too hard with devastating results!

  2. The Tacoma Narrows bridge was redesigned after World War II. Not surprisingly, there was extensive wind tunnel testing on models of the bridge before it went into the construction phase. This was a radical thing to do in the 1940’s

  3. Look at this view of the bridge. How does the construction of the road deck differ from that seen in the video clip?

  4. Here’s the old bridge again! When the twisting motion was at the maximum, elevation of the sidewalk at the right was 28 feet (8.5m) higher than the sidewalk at the left. The deck was built on a solid 8ft I-beam girder which split the airflow causing vortices to form. These swirling air currents pushed the bridge into a torsional or twisting motion. The frequency of this pushing matched the natural resonant frequency of the deck leading to large amplitude motion and failure of the supporting I-beam leading to collapse.

  5. LOMA PRIETA 1989 The Loma Prieta earthquake occurred on October 17, 1989 at 5:04 p.m. Pacific Daylight Time. It had a moment magnitude of 7.0. The duration was 15 to 20 seconds. The earthquake occurred due to slip in the San Andreas Fault. The epicenter was near Loma Prieta, which is a peak in the Santa Cruz mountains. This location is 10 miles northeast of the city of Santa Cruz. The earthquake caused damage throughout the San Francisco Bay area. Sources place the death toll between 63 to 68 people. The cost was 6 to 8 billion dollars. San Francisco had 22 structural fires during the seven hours from the time the earthquake struck until midnight.

  6. CYPRESS VIADUCT The earthquake caused the Cypress Viaduct to collapse, resulting in 42 deaths. The Viaduct was a raised freeway which was part of the Nimitz freeway in Oakland, which is Interstate 880. The Viaduct had two traffic decks. Resonant vibration caused 50 of the 124 spans of the Viaduct to collapse. The reinforced concrete frames of those spans were mounted on weak soil. As a result, the natural frequency of those spans coincided with the forcing frequency of the earthquake ground motion. The Viaduct structure thus amplified the ground motion. The spans suffered increasing vertical motion. Cracks formed in the support frames. Finally, the upper roadway collapsed, slamming down on the lower road. The remaining spans which were mounted on firm soil withstood the earthquake. In addition, a span of the San Francisco Bay Bridge collapsed.

  7. The cypress street viaduct before and after the earthquake. This was California’s first double-decker freeway

  8. Here’s the collapsed freeway from above!

More Related