Gerald Desmond Bridge – Challenges and Solutions for Vibration Control

Gerald Desmond Bridge replacement is a 305m mainspan cable stayed bridge which is under construction and will become California’s first long span cable stayed bridge, and form a distinctive landmark in Los Angeles with its elegant mono-pole towers with a unique section transforming from an octagon to a diamond. The total length of the replacement is about 3km long including 2km elevated approach viaducts built with prestressed concrete box sections.

The cable stayed main bridge carries six lanes of traffic and a bikeway attached to the edge girder with cantilever beams. The challenges of a durable solution for dynamic effects induced by seismic events, winds and traffic have been resolved by an intelligent solution with dampers and fuses. This paper focuses on the issues of aerodynamic instability during construction and in service, wind induced and vehicle induced vibrations and pedestrian comfort. Wind tunnel studies are discussed for the free standing tower during construction, full-cantilever erection stage, in-service with traffic, post-earthquake damages and behaviours with traffic. Rain and wind induced and vehicle induced stay cable vibrations, bikeway vibrations due to traffic on main girder and people running and jumping on the bikeway are also studied. The design covers a full checking of the bridge vibration and control for various stages and loading conditions, and proves the sustainable design for a high performance bridge.