The use of basalt composites in modern construction offers a 75-year service life of the object.
The University of Miami deliberately chose to construct a pedestrian bridge using concrete elements solely reinforced and prestressed with fiber-reinforced polymer (FRP) composites to demonstrate its commitment to innovation and sustainability.
In addition to showcasing concrete reinforcing bars made of basalt and glass FRP (BFRP and GFRP), the bridge features unique BFRP forms such as continuous close stirrups used in the pier-caps and curbs as well as prefabricated BFRP cages for the auger-cast piles.
The main load-carrying members of the bridge are two prestressed concrete girders of double-tee shape (as used in parking garage structures) with shortened flange overhangs. Each girder stem was prestressed with nine CFRP strands.
Elements of the bridge were instrumented with vibrating-wire gages to monitor performance over time and during two load tests conducted on one of the prestressed concrete girders at the precast yard and on the completed structure, respectively. In addition to strain data, deflection measurements obtained during and after construction show field performance of the bridge to be in accordance with the predicted behavior.
Even though this pedestrian bridge named “Innovation Bridge” is a simple, single-span, 70 ft.-long construction, it offers a number of striking features intended to ensure a 75-year service life to its owner, the University of Miami. The bridge consists of the following concrete elements: auger-cast piles; cast-in-place pile caps and back walls; precast prestressed girders; and, cast-in-place deck topping and curbs.
This simple structure combines novel materials [Basalt-, Glass-, and Carbon-FRP (BFRP, GFRP and CFRP)] and novel composite manufacturing technologies (continuous close stirrups and preassembled cages) to ensure that degradation due to steel corrosion no longer undermines the longevity of the bridge.
The eight, 16-in. diameter, 40 ft.-long auger-cast piles were reinforced with prefabricated cages made of six #6 BFRP rebars and spirals. The cages (in the shape of an octagon) were prefabricated at the BFRP manufacturer’s plant and delivered to the site, ready for installation.
The pile caps and back walls were built of concrete reinforced with straight bars, bent bars and close (continuous) stirrups made with BFRP and GFRP. The application of close BFRP stirrups takes advantage of performance efficiency of the composite reinforcement when continuity of the fibers is assured.
The two prestressed girders have the shape of double-tees (as used in parking garage structures) with shortened flange overhangs. Each stem was prestressed with nine 0.6-in. diameter, seven-wire CFRP strands. Each tendon was tensioned to a load of 41.25 kip corresponding to 68% of its guaranteed capacity.
The reinforcement grids for both stems and flange were made of pre-assembled interwoven BFRP bars (#3 and #4, respectively). Finally, the cast-in-place, 3-in. concrete deck topping was reinforced with a grid of BFRP bars (#3 in both directions). The reinforcement for the curbs consisted of a combination of close #4 BFRP stirrups (integral with the double-tee flange) and straight BFRP bars.
Reinforcing bars, tendons and concrete at various locations were instrumented with a total of 16 vibrating wire gages to allow for monitoring of the bridge elements over time and, in the case of the girders, during construction to measure effective strain and transfer length.
One of the two double-tees was load-tested at the precast yard with concentrated loads up to a maximum mid-span load of 27 kip (the girder remained un-cracked under this load). A second load test along with strain and deflection measurements was conducted after bridge completion to confirm expected structural behavior.
This project intended to demonstrate lower labor and equipment costs because of the reinforcement lightweight and pre-assembly. The expected low maintenance costs are the primary benefit to the owner.
Guillermo Claure (1),Marco Rossini (2), Thomas Cadenazzi (3), Carlos Morales (4), Omid Gooranorimi (5), Saverio Spadea (6), Francisco De Caso (7), and Antonio Nanni (8)
1 – Post-Doctoral Associate, Civil, Arch & Environ. Engineering;
2 – Garduate Student, Civil, Arch & Environ. Engineering;
3 – Graduate Student, Civil, Arch & Environ. Engineering;
4 – Graduate Student, School of Architecture;
5 – PhD Candidate, Civil, Arch & Environ. Engineering;
6 – Fulbright Scholar, Civil, Arch & Environ. Engineering;
7 – Research Asst. Professor, Civil, Arch & Environ. Engineering;
8 – Professor and Chair of Civil, Arch & Environ. Engineering.