Rhode Island Demonstration Project: Replacement of Frenchtown Brook Bridge No. 435
Project Overview and Lessons Learned
The project consisted of replacing a bridge on Davisville Road over Frenchtown Brook in East Greenwich, RI, just north of the East Greenwich–North Kingston boundary. The existing bridge suffered from constant weight reductions. The replacement structure was designed to increase the structural capacity of the bridge, improve roadway conditions, minimize disturbance to the Frenchtown Brook, and minimize inconvenience to users by limiting road closure to less than a third of the period required for conventional construction.
The focus of this demonstration project was the innovation of combining precast bridge elements and incentives to reduce road closure and construction periods. Lessons learned on this project can help guide similar projects in the future. Featured in the project are prefabricated culvert-like three-sided bridge elements (two legs and roof) that span 28 feet (ft) over Frenchtown Brook and are placed on precast concrete footings. Each element is 6 ft wide and 7 ft high at its centerline. The four prefabricated wingwalls consist of wall stems that are also placed on precast concrete footings.
The technologies incorporated into this bridge project have been used successfully around the United States on a limited basis, such as a HfL demonstration project in Washington, DC, featuring a prefabricated substructure and steel and concrete modular superstructure system¹. Furthermore, the New Hampshire Department of Transportation presented a project that used techniques similar to this project, and its success set the stage for the all-precast method for the Rhode Island Department of Transportation (RIDOT). The fact that several diverse structural systems have been assembled and incorporated into a single project reinforces the concept that innovation does not necessarily mean creating something completely new, but rather facilitating incremental improvements in a number of specific bridge details to fully leverage previously successful work.
Under traditional construction methods, RIDOT estimated the bridge would have been closed for 6 months to accommodate cast-in-place construction. Central to the ABC approach adopted on this project was condensing the bridge closure to only 65 days, which was eventually reduced to 33 days by a $3,000-per-day contractor incentive capped at $90,000. This was enough time to facilitate both removal of the old bridge and construction of the new bridge.
Preliminary analysis of alternatives for the replacement bridge showed that the bridge with precast elements would be competitive with a conventional bridge at the site. The conventional bridge would have been a butted prestressed beam superstructure on cast-in-place abutments.
Construction on the project was completed without delays because of offsite fabrication and no handling, transportation, or erection difficulties. Also, user delay costs from roadway closure were reduced by more than 80 percent.
Encouraged by the success of this project, RIDOT announced that it will evaluate all future bridge projects to determine if they can be built using ABC techniques, taking into account factors such as the impact of total road closures that projects of this type normally require and the complexity of utility relocations.
HFL Performnace Goals
Safety, construction congestion, quality, and user satisfaction data were collected before, during, and after construction to demonstrate that innovations can be an integral part of a project while simultaneously meeting the HfL performance goals in these areas.
- Work zone safety during construction—As expected, no incidents occurred during the entire construction period including the full closure period, which meets the HfL goal of achieving a work zone crash rate equal to or less than the preconstruction rate.
- Worker safety during construction—No workers were injured on the project, so the contractor achieved a score of 0 on the OSHA Form 300, meeting the HfL goal of less than 4.0.
- Facility safety after construction—Normally, 3-year crash rates after construction are determined and compared to the preconstruction crash rates. With no change in roadway width (44 ft) before and after construction, the crash rate attributable to roadway width should be the same. However, traffic volume and flow are likely to affect facility safety after construction. The pre-construction Davisville Road consisted of two lanes and two shoulders carrying one-way traffic north toward Frenchtown Road and the on-ramp to Route 4 North. Post-construction, Davisville Road will no longer be part of Route 403 under the relocated Route 403 project and will serve as a two-way local road with less than 75 percent of its preconstruction traffic volume.
- Construction Congestion
- Faster construction—Compressing the time it took to replace the bridge from an estimated 6 months to only 33 days under the ABC approach drastically reduced the impact on motorists and went beyond the HfL goal of a 50 percent reduction in the time traffic is impacted compared to traditional construction methods.
- Trip time—Considering the cumulative trip time over the 33-day detour compared to 6 months of detour estimated for traditional construction, motorists experienced a substantial reduction in trip time, meeting the HfL goal of no more than a 10 percent increase in trip time.
- Queue length during construction—There were no traffic backups observed along the detour routes. The project, therefore, met the HfL goal of less than a 0.5-mi queue length in a rural area.
- Smoothness—Because of the new asphalt surface on the bridge, motorists will notice a smoother ride.
- The quality of the products used was superior because the contract required that the manufacturing plant furnishing precast bridge members be certified by the Precast/Prestressed Concrete Institute (PCI) Certification program at a minimum of B3 category. Furthermore, it required that dimensional tolerances not exceed those recommended in the latest edition of the PCI manual for quality control for plants and production of precast and prestressed concrete products. This assessment is based on the products meeting all specifications and the belief that disciplined procedures enforced at certified plants audited by external personnel are likely to yield better quality control than those at a construction site where quality control of concrete cast in place is dispersed among several entities and individuals. These personnel range from those at batch plants proportioning aggregates, cement, and water to drivers transporting the mixes in concrete trucks to inspectors responsible for ensuring that placing, compacting, and curing of concrete conforms to specifications.
- User satisfaction—A formal user satisfaction survey was not conducted on this project. It is, however, evident to the project team that with reduction in roadway closure time by more than 80 percent compared to conventional construction, users are likely to be very satisfied and their responses would easily meet the goal of 4 or more points on a 7-point Likert scale.
In a similar study on the use of ABC on U.S. 6 over Keg Creek² in Iowa, where the roadway closure was reduced from 6 months to 2 weeks through the use of prefabricated bridge elements, user satisfaction was quite positive. 92 percent of respondents to the survey considered using prefabricated components to speed construction as important or somewhat important and 100 percent of the respondents found condensing closure to 2 weeks to be important.
The costs and benefits of this innovative project approach were compared with those of a project of similar size and scope delivered using a more traditional approach. A comprehensive economic analysis that accounted for construction and road user costs revealed that RIDOT’s innovative approach realized a cost savings of about $1.5 million, or 38 percent of the total project cost, over conventional construction practices. A significant amount of the cost savings stemmed from avoiding delay costs to road users through the use of ABC techniques.
Through this project, RIDOT gained valuable insights on the innovative techniques and materials—both those that were successful and those that need improvement in future project deliveries. The following are some of the lessons learned on using prefabricated elements:
- The 65-day bridge closure allowed in the contract was adequate for demolition and construction of a bridge of this size. In fact, the contractor completed the work in 33 days, qualifying for the incentive of $3,000 per day capped at $90,000. This was enough time to completely remove the existing bridge and set the precast elements in place despite a significant rain event that disrupted operations. The contractor typically did not have to work past dusk during this period.
- A muddy job site would have made moving the heavy bridge elements difficult, but this did not occur.
- By reducing the construction time at the site with accelerated construction using prefabricated elements, the amount of time construction crews and motorists were exposed to the dangers of the work zone was also reduced.
- Onsite construction time is often limited by weather and environmental permitting requirements. Because of prefabrication and accelerated construction, limited available construction time was not a factor and the project was easily completed during the construction season.
- While precast concrete produced at a certified plant has the advantage of being constructed in a controlled environment with higher production and curing standards than normally found in the field, there is debate on the impact this has on costs and the need to evaluate this requirement for simple elements. The positive side of plant certification is that internal quality control is apt to be at least satisfactory, but the negative aspect is that all elements must be shipped from a certified facility that may be a long way from the construction site, increasing transportation cost. Transportation also involves restriction on the size and weight of individual elements. The option of allowing near-site fabrication versus fabrication at a certified facility should be considered on future projects that involve prefabricated elements.
- The incentives in the actual contract helped offset some of the risk in the contractor's bid decision making process.
RIDOT gained valuable insights on this project on the use of innovative ABC techniques. These innovations were key to successfully achieving the HfL performance goals of increasing safety, reducing traveler inconvenience from construction, and increasing quality at a lower cost.
¹Reconstruction of Eastern Avenue Bridge Over Kenilworth Avenue in Washington, DC, August 2011, Federal Highway Administration, www.fhwa.dot.gov/hfl/summary/projects_summary.cfm.
²Iowa Demonstration Project: Accelerated Bridge Construction on U.S. 6 Over Keg Creek, March 2012, Federal Highway Administration, www.fhwa.dot.gov/hfl/summary/projects_summary.cfm.