Integrated Monitoring System for Carbon Composite Strands in Cable-Stayed Bridge, Penobscot Narrows, Maine

Abstract

An integrated monitoring system for carbon fiber composite cable (CFCC) strands recently implemented in the Penobscot Narrows Bridge in Maine is presented. This cable-stayed bridge features a cradle-stay system in the pylons that provides a continuous cable stay between the main span bridge deck anchorage and the back span bridge deck anchorage. The cradle-stay system allowed for replacing epoxy-coated steel strands with CFCC strands. The monitoring system installed in the bridge is composed of a set of sensors and devices that provide complementary structural information: (a) load cells supported on steel anchorage chairs, (b) linear voltage differential transformers (LVDTs) mounted on the steel anchorage chairs, (c) fiber-optic strain (FOS) sensors embedded in composite sleeves, and (d) temperature sensors. The monitoring system was designed to detect variations over time in individual carbon fiber strand force and strains at the anchorage locations and to correlate the measurements with ambient temperature. Laboratory tests were conducted to proof-load the steel anchorage chairs and to calibrate the LVDTs and embedded FOS strain measurement systems. The baseline response of the CFCC strands that was based on load cell, FOS sensors, and LVDTs measurements after the strand stressing operation is presented. The CFCC strands experienced changes in tensile force between +3% and −5% over the first 4 months in service, which were consistent with ambient temperature fluctuations. The FOS measured strand strains and the LVDT deflections of the anchored chair exhibited trends consistent with the variations in CFCC strand force.