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Research Activities: 2006
Design, Construction, Laboratory and Field Testing of the Bridge on the Arnault Branch, Washington County, Missouri
Matching Research Agency
Washington County and Missouri Department of Transportation
|One graduate student|
Two innovative FRP technologies will be employed for the rapid and effective replacement of different portions of the structure with a safer and more functional slab type bridge. The design strategies consist of a) helicoidal FRP helixes integrated with longitudinal FRP rebars as slab reinforcement, and b) prefabricated pultruded FRP panels as stay-in-place (SIP) formwork and structural reinforcement.
Washington County, Missouri, has made available an overpass located on Pat Daly Road, over Arnault Branch, that is in critical need of replacement with a more efficient concrete slab bridge. The overpass consists of a 1.52 m (5 ft) thick unreinforced concrete slab-on-ground, with a total length of 12.19 m (40 ft) and width of 4.57 m (15 ft). The approach roadway is 4.88 m (16 ft) wide. Two 0.91 m (3 ft) diameter corrugated steel pipes run parallel through the concrete underneath the roadway and allow water flowing. The current slab-on-ground is structurally and functionally inadequate, and poses the primary issue of safety. Specifically:
It is herein proposed to replace the slab-on-ground overpass with a rapidly constructed FRP reinforced concrete slab bridge with open-post railing, using two innovative FRP reinforcement concepts. The bridge will have three 8.23 m (27 ft) long spans, for a total length of 24.69 m (81 ft), and out-to-out deck width of 6.10 m (20 ft).
The increased length and clearance between roadway and water level will allow to minimize the risk of flood, while the increased roadway width will provide a functional mean to improve safety under normal traffic conditions.
The proposed project will be designed by the University of Missouri-Rolla (UMR)/ University of Miami, reviewed by MoDOT, and constructed by crews from Washington County. The inspection/evaluation will be conducted by the three agencies.
Specifically, the innovative strategies for bridge design and accelerated construction:
The idea of using GFRP helixes as shear reinforcement would be implemented for the first time in the present project, with relevant implications from both the structural and constructibility standpoints.
GFRP helixes would provide improved shear reinforcement in a concrete slab type bridge, and allow reduction in thickness. In addition, helicoidal reinforcement is more efficient than discontinuous ties because the continuity fulfils the need for anchorage. In addition, continuous helicoidal reinforcement enhances the pseudo-ductility of the concrete it confines, thereby increasing the concrete core ultimate strain and compressive strength. This results in less brittle failure modes that may justify an increase in the design strength reduction factors. Constructibility of a reinforcement cage is significantly improved by the use of a coil, which can be simply stretched to attain the desired constant pitch of the helix, thereby rationally and easily providing the shear reinforcement needed.
The availability of helicoidal FRP reinforcement allows for a simple pre-assembly of the cages that can then be installed at the site with obvious and significant construction time savings. Furthermore, the helixes provide for the first time an economical and effective mean of shear reinforcement that would result in the concrete slab thickness reduction. These cages (of high strength-to-weight and stiffness-to-weight ratio) could have a length equal to the length of the deck (ensuring the continuity of the main longitudinal reinforcement) and be installed side-by-side (male-female type intersection) for transverse reinforcement continuity. The intellectual merit of the proposed solution lies in truly exploiting the inherent advantages of FRP materials by means of a rational design strategy, breaking the tie with typical steel-reinforced schemes.
A new pultruded GFRP stay-in-place formwork and internal reinforcement for concrete bridge decks, referred to as gridform, will be implemented. The system is comprised of prefabricated large-size FRP panels composed of a reinforcing grating and a pultruded plate acting as a formwork. The system will be complemented by an integrated FRP reinforced open-post concrete railing. Design and detailing of the FRP SIP panels aims at competitively combining structural efficiency with speed of installation and constructibility, together with providing the durability ensured by the use of advanced composite materials. The large-size FRP SIP panels will be designed to meet prescriptive material and performance specifications.
The newly implemented GFRP deck system, comprised of helicoidal GFRP reinforcement (span 1) and large-size pultruded SIP panels (span 2) selected for the rapid replacement, will be complemented with a fully integrated, modified GFRP reinforced open-post concrete rail. Experimental validation of the design assumptions, as well as definition of the performance characteristics with respect to typical steel RC railing counterparts, will represent a fundamental step in the transition of this innovative solution from the laboratory to the field.
The conventional design and construction approach will serve as a benchmark.
The Bridge will also be instrumented with embedded sensors to monitor the strain at critical locations, and with a remote flood alarm device. The device will have a periodical auto-test feature (“heartbeat”) with some telemetry data (fuel gauge, temperature, some local sensors such as strain gauges) and remote software upgrading capabilities.
The project will include the following phases:
Rapid construction of bridge decks thanks to the implementation of FRP composite technologies.
|Bridge design, construction and assessment|
Relationship to other Research/Projects
Technology Transfer Activities
Use of composite materials for the rapid construction of bridge structures
Transportation Research Board Keywords
Bridge Design, Construction and Assessment; FRP Technologies; Rapid constructions; NDT/NDE Evaluation