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3 CHAPTER ONE INTRODUCTION BACKGROUND With the popularity and rapid growth in the use of cable-stayed bridges in the United States and worldwide, issues related to inspection and maintenance of stay cables are taking on added significance. Examples of problems that could affect stay cable performance include excessive vibrations, corrosion, fatigue, and the general inability to reliably ascertain the internal con- dition of the cables, especially in the critical anchorage zones. Many of the assessment and repair methods are still in early development and information on reliable, proven techniques is not readily available. Bridge owners and engineers are faced with selecting and using a number of new technologies or approaches for cable assessments without the benefit of know- ing their degree of effectiveness. Although some valuable data are available, they are generally not readily accessible. There- fore, this synthesis project aims to collect and synthesize such information into a single document. FIGURE 1 Bridge systems envisioned by Navier (Gimsing 1999). Cable-stayed and suspension bridges are the two promi- nent types of cable-supported bridges. In both systems, cables are supported on pylons. In cable-stayed bridges, the cables The early bridges all had only a few stay cables, which pro- are inclined and directly support the deck on the pylon(s). In vided support at locations where piers would have otherwise suspension bridges, vertical suspender cables transfer loads existed (Walther et al. 1999). This concept of using cables with from the deck to the main catenary-shaped cables. The main large spacing did not fully realize the structural (and economic) cables in suspension bridges are typically anchored at massive potential of cable-stayed bridges. In 1967, H. Homberg used anchorages at the two ends of the bridge, whereas stay cables closely spaced stays (or the multi-stay system) on the Friedrich are anchored to the deck itself. Ebert Bridge in Germany (Walther et al. 1999). The Brotonne Bridge in France used closely spaced stays, and the cable In their basic form and concept, cable-stayed bridges have system was based on post-tensioning technology in which existed for centuries. In 1823, French engineer C.L. Navier parallel seven-wire strands were encased in steel pipes and presented some of his concepts for bridges supported by grouted (Gimsing 1999). The ZarateBrazo Largo Bridges in wrought iron chains, as shown in Figure 1 (Gimsing 1999). Argentina were the first cable-stayed bridges designed to carry Although these sketches strikingly resemble the modern railroad and automobile traffic. As will be discussed later, one cable-stayed bridges, Navier envisioned ground-anchored of the Argentine bridges had a complete failure of one of the backstays only. stays after fewer than 20 years of service. The next phase involved design of combined suspension The oldest cable-stayed bridge in the United States is the and stayed systems. A prominent example is the Brooklyn Sitka Harbor Bridge in Alaska, built in 1970 (see Figure 2). Bridge, designed in the 19th century by John A. Roebling. The oldest cable-stayed bridge in North America is believed The first modern cable-stayed bridge was the Strmsund to be the North Romaine River railroad bridge in Qubec, Bridge built in 1955 in Sweden, which was designed by Franz Dischinger. It had a main span of 182.6 m (599 ft) Canada, which was built in 1960. The oldest highway cable- (Gimsing 1999). stayed bridges in Canada are the Longs Creek #1 and Hawk- shaw bridges in New Brunswick, built in 1966 and 1967, The first major cable-stayed bridge made of concrete pylons respectively. Other early and prominent cable-stayed bridges and girders was the Maracaibo Bridge in Venezuela, built in in North America include the Papineau Bridge in Montreal 1962. As will be discussed later in this report, the cables of this (1969) and the PascoKennewick Bridge in Washington bridge were subsequently replaced as a result of corrosion. State (1978).