ASCE Met Section Spring Seminar - Session 3

Wednesday, May 27 - 5:00-6:30PM

Unionport Bridge – Twin Single-Leaf Bascules in a Constrained Urban Site

Speaker: William Nyman, PE

The new Unionport Bridge project in the Bronx includes two parallel single-leaf bascule spans constructed to replace the prior double leaf span which carries 60,000 vehicles per day on the Bruckner Expressway service road over Westchester Creek. The new wider bascule spans (north span at 58ft wide; south span at 56ft wide), carry six vehicular lanes along with an 8ft sidewalk and add a two-way bicycle path to the corridor. Both simple trunnion bascule spans measure 125ft from trunnion to toe and share a closed pit bascule pier. The local roadway tie-ins were also reconstructed with a revised geometry that eliminated many non-standard features and included fill-type retaining structures and load transfer platforms in lieu of the prior concrete cellular structures. The construction included extensive displacement and vibration monitoring, as well as the use of secant pile isolation walls to mitigate any effect on the adjacent foundations of the existing expressways that carry the Cross Bronx and Bruckner Expressways overhead.

The replacement bridges were constructed while traffic was diverted to two vertical lift temporary bridges nested below the overhead structures and the west end ramps were constructed using an innovative inside-out technique. This allowed for construction traffic impacts to be limited while accommodating the needs of the channel users. During the final stages of construction, a major ‘last-mile’ shipping facility was opened adjacent the bridge. This was accommodated by proactive adjustments to the project.

Wednesday, May 27 - 7:00-8:00PM

Progressive Collapse Behavior of Long-Span Cable Supported Bridges under Extreme Events

Speakers: Qian Chen, Ph.D., P.E and HongFan Wang, Ph.D.

Long-span cable-supported bridges are critical components of modern transportation infrastructure and are directly exposed to extreme environmental hazards, including floods, scour, hurricanes, earthquakes, and impact loads. Recent bridge failures have demonstrated that localized damage—particularly cable loss—can trigger disproportionate responses and, in some cases, progressive collapse. Understanding the system-level vulnerability of such structures under extreme events is therefore essential for ensuring structural robustness and resilience.

This study investigates the progressive collapse behavior of two prototype long-span cable-supported bridges: a suspension bridge and a cable-stayed bridge. Detailed finite element models were developed, including explicit dynamic models in LS-DYNA and complementary implicit models in Midas Civil and ANSYS to ensure modeling robustness and cross-validation. Progressive collapse scenarios were simulated through (1) sudden removal of a single cable at various locations and (2) sequential removal of multiple cables. Dynamic effects, as well as material and geometric nonlinearities, were fully considered.

To quantitatively evaluate structural response, four performance indices were introduced: demand-capacity ratio (DCR), dynamic increase factor (DIF), static increase factor (SIF), and dynamic amplification factor (DAF). Critical cable-loss locations were identified based on system response. Furthermore, pushdown analyses were conducted on both intact and damaged bridge configurations to assess residual capacity and identify critical limit states. The results provide insight into collapse mechanisms, vulnerability distribution, and robustness characteristics of long-span cable-supported bridge systems under extreme events.

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Host or Publisher ASCE SEI Metropolitan Section