Historically, suspended footbridges have been built from ropes (i.e., cables) constructed of a variety of
materials including iron and natural fibers. However, contemporary suspended footbridges are typically
constructed with steel rope. One exception, a 64 m span polyester-rope footbridge completed in 2013,
demonstrates the potential for alternative rope materials in contemporary footbridge design and construction.
The first goal of this paper is to support the idea that polyester rope has promise in future footbridge
applications by comparing minimum rope volume and self-weight results for polyester-rope and
steel-rope footbridges with spans ranging from 15 to 64 m in two multi-objective optimization problems.
In both problems the competitive objective functions are span which is maximized and rope volume
which is minimized. The results are minimum volume systems for spans in the defined range.
Minimizing volume reduces rope cost and eases material transport and handling. To provide an alternative
measure of rope quantity, volume results are scaled to find the equivalent self-weights. This study
focuses on in-plane structural behavior and investigates two-dimensional rope systems with or without
prestress and with or without under-deck stays. A combination of static and natural frequency constraints
is considered in the optimization problems. The second goal of this paper is to describe the novel
methodology developed to evaluate these optimization problems. This methodology combines a
non-dominated sorting genetic algorithm for searching the design space with dynamic relaxation and
eigenanalysis algorithms for the structural analysis. Results indicate that polyester-rope systems have
higher volumes, but lower self-weights than steel-rope systems. This observation supports the premise
that polyester-rope footbridges are potential alternatives to steel-rope footbridges. The presented
methodology can be adapted to evaluate how other unconventional materials compare to more conventional
counterparts that are well established in bridge applications.