Quantitative Approach to Bridge Aesthetics for the 21st Century

Many important qualities must be considered for the proper aesthetic design of bridges to develop harmony with their environment. Methodologies for segmental bridge design that create bridges that preserve the existing landscapes and complement, and even enhance, their settings are examined. Bridges considered have received 123 design awards in the past 21 years, including 3 Presidential Awards through the National Endowment for the Arts. Proper scale and proportions of various bridge members to create balanced and slender appearances are quantified, including proper span-to-depth and pier width-to-height ratios for graceful structures. The design methodology for aesthetics includes a quantitative and qualitative sorting of natural site features to determine appropriate shapes for the superstructure and substructure. Criteria for selecting and evaluating the visual effects of shape, shadows, vistas, color, textures, and the use of native materials are addressed. Quantification of the cost of aesthetic decisions and determination of aesthetic value are addressed for different elements of these bridges. Case studies are used to quantify aesthetic features for such bridges as the Natchez Trace Parkway Arches [first precast concrete arches with 177-m (582-ft) main arch span], Tennessee; Sunshine Skyway Bridge, Florida; Linn Cove Viaduct, North Carolina; Hanging Lake Viaduct, Colorado; and Wabasha Street Bridge, Minnesota.

Tolerance of Loblolly Pines to Fusiform Rust

Loblolly pines (Pinus taeda L.) that were 8 to 17 yr old tolerated one to three fusiform rust (Cronartium quercuum [Berk.] Miyabe ex Shiraif sp. fusiforme) galls in their stems. Families with four or more galls in their stems lost 25% or more of the trees by age 17. In living trees with less than four stem galls, diameter growth was comparable to that of trees with no galls. Tolerance was indicated by the ability of loblolly pines to maintain the rust fungus in stems that had dbh's similarto asymptomatic trees on the same site. In plantations, the number of galls in the stem was generally one to two per infected tree. This was also true for mature trees (12 to 38 in. dbh) along the Natchez Trace Parkway. These trees have been infected with fusiform rust for nearly 100 yr. On the other hand, the presence of four or more stem galls seems to be a reliable indicator of mortality rather than tolerance. South. J. Applied For. 19 (2): 60-64.