October 2011 NHI Innovations webinar, I-93 Fast 14 Project
MassDOT Responses to Outstanding Questions
- Paul mentioned that there were some quality control issues with Jersey Pre-Cast. Can you elaborate?
There were isolated incidents of honeycombing in the units, which were discovered by contractor QC inspectors, and were repaired with corrective action approved by the owner.
- Regarding the closure pours, could you provide any details regarding the performance characteristics of the concrete to used?
- Water-cement ratio <=0.4 by weight
- Minimum compressive strength 2,000 psi within 4 hours of final set
- Minimum 28-day compressive strength 4,000 psi
- Inclusion of shrinkage reducing admixture (immediately after placement, curing compound was applied, and concrete covered with polyethylene sheeting)
- When precast concrete modular units were used to replace existing steel beams, what consideration was given to the capacity of the substructures to account for the heavier dead loads from the concrete beams?
The superstructures were replaced with modular units consisting of two steel plate girders with a precast deck. The units were shipped to the site, erected, and connected to adjacent units with concrete closure pours. The existing vs. proposed superstructures were similar in weight and the existing piers and abutments were analyzed for proposed superstructure loads during the preliminary design. The piers were found to be acceptable for the proposed superstructures.
- How much was this project?
The total project value is $98,127,600.00
The breakdown is: (includes $4.7 Million for Sound barrier)
Contractor Bid $78,450,100 Project Contingency $7,000,000 Traffic Police $3,800,000 Fire Services $720,000 Deck/Substructure Repairs $1,100,000 mat’l cost adjustments $57,500 Incentives $7,000,000 Total $98,127,600
- Who managed the traffic within the project corridor and also, off-site?
Responsibility for designing and implementing traffic management plans on the project belonged to the Design-Build entity. This not only included I-93, but also any of the local roads that were used as detour routes (e.g. Fellsway West). The D-B entity was also responsible for having a traffic engineer and traffic signal contractor available to monitor and provide changes to area signals, if necessary. Although these provisions were put into the contract, MassDOT recognized the need early on to monitor traffic conditions and provide assistance to the D-B entity in order for the project to succeed. During the procurement process, the Massachusetts State Police (MSP) offered the use of their mobile command post each weekend of bridge construction to centralize all communications, which proved invaluable. Provisions for the various monitoring systems (RTTM, HAR, EarthCam, etc.) were included in the D-B entity’s contract, which greatly assisted MassDOT in its supportive role. As explained during the webinar, MassDOT traffic engineers as well as two traffic consultant engineers were onsite during the weeks and weekends of bridge work doing various tasks from participating in review meetings with the D-B entity to assisting with field location of signs/devices to developing PCMS messages and traffic advisories. Of particular note is the fact that the traffic management plans, although designed and reviewed quite intensely, were dynamic, evolving from week to week based on the bridge work occurring and on traffic issues encountered. Therefore, it was critical that the D-B entity and MassDOT worked together continuously to minimize traffic impacts to the extent possible.
In addition, MassDOT Maintenance forces were called upon each weekend for further assistance to provide additional traffic control (lane closures, ramp closures, specialized messages, etc.). And, of course, the assistance of the MSP and local police, fire and emergency services was absolutely critical to the success of the project. It was truly a collaborative effort between the parties involved. In the end, we all managed on-site traffic together.
With regard to managing off-site (regional) traffic – this responsibility fell to MassDOT and the MSP. MassDOT had initially identified area projects during procurement that would need to adjust their work hours to accommodate the Fast14 project. Outside of this, however, MassDOT knew there would be a need to address incidents on roadways outside of the project area that would have impacts on the Fast14 Project. Therefore, MassDOT Maintenance forces were also at the ready to assist the MSP in this endeavor.
- How is ride quality/smoothness? Were the decks overlaid with AC/HMA?
The decks were sealed with a methylmethacrylate membrane waterproofing system which consisted of a primer, membrane coat, and an aggregated key coat. A tack coat was applied immediately before paving. The pavement design consisted of Superpave HMA in the form of a 1.5” bridge protective course followed by a 1.5” bridge surface course. An as-built survey was conducted prior to paving from which paving work plans were developed. Approaches were milled/shimmed in areas to provide a smooth roadway profile. MassDOT is very pleased with the ride quality along the corridor.
- Were any contract specification waivers given to the contractor?
MassDOT did not issue any specification waivers.
- From the photos it appeared the prefabricated panel consisted of two simple-span steel beams with a precast deck. Were these beams made continuous over the piers, if so how was this done?
The modular units were designed as single spans. Link slab technology was employed at the pier locations where the reinforcing in the deck is designed for the strain caused by live load rotation. Each span has its own bearings and due to the variable height of the girders from one span to the next a full continuity connection was avoided.
- Any changes to the final grade elevations and the clearances due to the use of new superstructure elements?
At the beginning of the project, the need for improvement to the vertical under clearances of the roadways below was made one of the project objectives. This project was designed using LRFD and improvements to substandard vertical under clearances were made using “thinner” plate girders and in some cases raising the roadway profiles for I-93.
- What was the overall percent of contract change orders verse original bid price?
The project is not complete, but the total value of approved change orders to-date is $234,220.24, which constitutes 0.3% of the Contractor’s original bid of $78,450,100. At the request of MassDOT, The Contractor is finalizing a proposal to install snow fences atop the parapets of the bridges which cross roadways. At this time the proposal is valued at $1.1 million.
- When were the parapet and barrier walls constructed? Were there light poles constructed on parapets?
Due to erection weights, the parapets were cast in place following bridge construction. There is no highway lighting incorporated into the bridge median or parapets. The existing system is located in the median off the bridges, and some of the system had to be relocated and eventually restored at the north and south crossovers.
- This question is related to shrinkage during thawing and warming cycles in Winter & Summer. How were the concrete panels and joints performed? Is there any deterioration?
The completed bridges have not been subjected to a full seasonal cycle, but will be fully inspected in the spring/summer as part of final project acceptance. The bridges will also be monitored periodically as part of normal MassDOT freeze/thaw inspection.
- How were seismic issues treated in the piers and foundations in those bridges were the steel superstructure was replaced by the precast concrete units?
The superstructures were replaced with modular units consisting of a two steel plate girders with a precast deck. During the preliminary engineering phase of the project, a seismic analysis was performed using the newer maps found in the LRFD Code. In all cases SDC A was used for a force based analysis. With the exception of the Rte. 16 bridge which has a significant skew, the substructure elements had sufficient capacity to resist the seismic forces through shear keeper blocks constructed as part of the substructure rehabilitation. At the Rte. 16 structure, seismic blocks were not constructed at the piers and the entire seismic force (lateral and longitudinal) was resisted by the abutments. This required a check of the entire deck to act as one element to transmit all of the forces to the abutments.
- Can this pre cast system be implemented in the poor states?
We believe Accelerated Construction Processes offer savings over conventional techniques, both in terms of actual construction costs and economic costs associated with the duration of traffic impacts. MassDOT intends to evaluate the economic viability of this project upon its completion.
- What kind of overlay used? How to deal with the joints over the piers?
The design paving consisted of Superpave HMA in the form of a 1.5” bridge protective course followed by a 1.5” bridge surface course. Joints over the piers were eliminated by link-slab detailing in the bridge deck, and depending on calculated expansion, eight of the 14 bridges had only saw & seal joints at the abutments. The remaining bridges feature strip-seal joints with elastomeric headers at abutments.
- Was OSHA involved in this project?
OSHA was involved in the project in their normal oversight role.