The J.F. Kennedy Boulevard Bridge at Journal Square Station in Jersey City, N.J. was constructed in 1924 over a major east-west rail line contained in a partly natural, partly artificial cut that traverses the Palisades Ridge adjacent to the Hudson River. The bridge is a two- span, reinforced-concrete open-spandrel rib arch with each main span having a length of 140 ft and a rise of 23 ft.
When originally built, the bridge was known as the Columbus Bridge and carried a wide avenue--Hudson County Boulevard--over a train station consisting of two 54-ft wide roadways with a 35-ft wide parking area in the center. The bridge was modified in 1971 with the construction of the Port Authority Trans-Hudson (PATH) Transportation Center. The center was constructed on columns through the deck on top of the eastern third of the bridge. This combined with the addition of a center median, reduced the roadway width to a minimum of 35 ft in each direction.
Today, the bridge spans the PATH train station and is surrounded by small retail stores and food establishments in an urban setting. It has been deemed eligible for inclusion on the National Register of Historic Places by the New Jersey State Historic Preservation Office.
Age and heavy traffic volume gradually took its toll on this entirely reinforced concrete structure. An inspection performed by A.G. Lichtenstein & Associates Inc., Paramus, N.J. in 1978 revealed it to be in poor condition. The top of the concrete deck slab was saturated by surface water penetrating the asphalt overlay due to a lack of a proper drainage system and an inadequate cross slope and profile. In addition, water seeping through the deteriorated deck joints was causing the supporting longitudinal beams and arch ribs to deteriorate. Large pieces of concrete falling from the underside of the deck and supporting members were presenting a hazardous situation for the pedestrians utilizing the PATH station and trains below.
It was recommended that immediate precautions be taken to protect the public, and railroad personnel and facilities from the danger of falling concrete. Furthermore, a complete rehabilitation including deck repairs, installation of a drainage system and concrete repairs to the arch ribs also was recommended.
In 1985, the New Jersey DOT (NJDOT), the Federal Highway Administration and the Port Authority provided funds to Hudson County, owner of the bridge, to implement a two-stage rehabilitation of the structure. First, a protective netting system designed by Lichtenstein to catch falling debris was installed in order to protect pedestrians and facilities below the bridge. Concurrently, deteriorated concrete from the underside of deck and arch ribs was removed. Upon completion of this work, the second stage of the plan, which included a partial deck replacement from above was to be implemented.
Additional work required
During the course of the repair work, increased deterioration of the deck and supporting beams was revealed. In addition, cracks were discovered on several of the short columns near the crown of the arch. The underdeck concrete repairs were halted and steel braces were placed around the cracked columns as a temporary measure.
To get a better assessment of the current condition of the concrete deck, a deck study was done by Lichtenstein in 1988. This study revealed the deck to be in poor condition with a high chloride content and recommended complete replacement. The study also determined that the columns were over stressed causing cracks to form. Because of these severe deficiencies, the scope of the project was changed to a more comprehensive rehabilitation of the structure.
In 1989, the NJDOT selected Lichtenstein to design the repairs and prepare the construction contract documents. The revised project scope included complete replacement of the deck and longitudinal beams in the roadway area for the main spans and north abutment, replacement of the west sidewalk, installation of a complete bridge deck drainage system, concrete column repairs and concrete spall repairs to the deck under the PATH Transportation Center.
Various issues had to be addressed and overcome in developing the design. The bridge is located in a heavily traveled urban retail and commercial area. Pedestrian and vehicular traffic had to be maintained, and unimpeded access to all store properties and driveways was essential. Furthermore complete protection from falling and flying debris had to be maintained for the trains and pedestrians utilizing the PATH station below the bridge.
There were a number of independent agenciesÑNJDOT, Jersey City, Hudson County, the Port Authority of New York/New Jersey and ConrailÑthat had concerns regarding the bridge construction and close coordination was required.
The bridge has an overall width of 212 ft and is supported by 13 reinforced-concrete, 5-1/2 ft sq arch ribs spaced at 17-1/2 ft, with a span of 140 ft each. Varying-height concrete columns bear on the ribs, which in turn support longitudinal concrete beams and a concrete deck. At the approaches, the abutments have a bin chamber configuration with the deck supported by longitudinal beams and columns, similar to the main spans. The south and north abutments have a length of approximately 90 ft and 30 ft respectively.
As mentioned the first consideration in design development was maintenance of vehicular, pedestrian and rail traffic. A major disruption of any of these was not acceptable to the county, Port Authority and Jersey City businesses in the vicinity of the bridge. Due to the heavy volume of vehicular traffic in the area, a minimum of two through lanes during construction was mandatory.
Deck replacement on the bridge was to take place curb-to-curb between Ribs No. 2 and 8. The rib spacing of 17-1/2 ft would allow for one lane of traffic in each bay between ribs. Therefore, rehabilitation of two bays at a time would allow for two lanes of traffic to be maintained during construction. This led to the development of a four-stage construction plan.
During Stage 1, the deck and beams would be replaced in the middle portion of the bridge with traffic placed on the existing outer portions. Concurrently, half of the 8-ft-wide west sidewalk was to be replaced with pedestrian traffic maintained on the other half. A temporary traffic signal erected at the north end of the bridge would accommodate modified turning movements onto Pavonia Avenue and the entrance to the parking garage. A statue of Christopher Columbus located on the existing median was to be removed and stored.
For Stage 2 construction, the southbound traffic lanes were now to be shifted to the reconstructed deck completed during Stage 1. Northbound traffic would be maintained on the existing outer portion of the bridge. It would be necessary to close the entrance to the parking garage during this stage; however, vehicles were to be diverted to another entrance at an adjacent street. The deck and beams in the western third of the roadway area would now be replaced.
The other half of the west sidewalk was to be completed with pedestrian traffic shifted to the newly reconstructed portion during Stage 1. The temporary traffic signal heads at the north end of the bridge would be adjusted to accommodate proposed turning movements.
For Stage 3 construction, the northbound and southbound traffic lanes were now to be shifted to the reconstructed western two-thirds of the bridge. The deck and beams could now be replaced in the eastern third of the roadway area. Again, the temporary traffic signal heads would be adjusted to accommodate the proposed turning movements. The parking deck entrance was to be reopened during this stage.
Finally, for Stage 4, traffic would be shifted to the newly constructed outer portions of the bridge deck to accommodate construction of the center median. The temporary traffic signal system was to be adjusted and maintained. The statue of Christopher Columbus would now be remounted on the newly constructed center median.
The time required for project completion utilizing the staging scheme was estimated to be 30 months. Elimination of the staging and complete bridge closure would have substantially decreased this time but this was considered secondary to maintaining vehicular and pedestrian traffic.
Construction in this busy transportation center raised concerns about protection of the vehicles, pedestrians and trains. A large amount of concrete demolition was required creating the potential for falling and flying debris. To address this, a shield surrounding the work area was called for. Below deck, the existing netting would remain; however, a solid shielding system was needed to catch any falling debris and contain dust. Walls also were to be created at the ends of the shielding system to prevent dust or debris from escape.
The first consideration in the structural design was the choice of concrete to use for the deck and beam replacement. Prestressed elements were considered but rejected due to the varying member dimensions, vertical column connections and staging requirements. A Class A (4000 psi) cast-in-place concrete was selected to be used for all the elements.
Next, the existing concrete arch ribs and columns to remain had to be analyzed. Finally, a complete service load analysis of the 5 1/2-ft sq ribs and 2-ft-sq columns was undertaken to ascertain if the maximum allowable capacity of these elements would accommodate the proposed dead load and HS20+10% design live loading.
Computer models using the STAAD structural analysis program were developed for the entire structural system including the deck, longitudinal beams, columns and the arch ribs. Portions of the plans from the original date of construction were available and revealed the reinforcement steel configuration of the arches and columns.
The result of this in-depth analysis yielded two completely different conclusions regarding the arches and columns. The arch ribs possessed almost double the necessary capacity for the proposed dead and live loading; however, the existing column capacity was significantly below the minimum required. The arch rib shear capacity was satisfactory, but the column shear capacity was also below the minimum required.
As mentioned previously, several columns had developed cracks. The structural analysis confirmed that the columns were over stressed and strengthening was necessary. The problem was how to accomplish this.
Removing the concrete and rebuilding the column would have involved the use of a temporary column support system and was deemed not feasible due to maintenance of traffic requirements. Therefore, it was decided to encase the existing 2-ft x 2-ft column with a 1-ft-thick concrete jacket creating a new column 4-ft sq. New No. 9 longitudinal and No. 5 shear reinforcement steel was placed inside the new concrete and was designed to act together with the existing reinforcement steel. At the staging lines (Ribs No. 2, 4, 6 and 8), the entire column was constructed up to 2 ft below the longitudinal beam. Above this, half the column was constructed at a time to facilitate construction of the longitudinal beams. Cracks and spalls on the columns were repaired and the surface was roughened to create a stronger bond with the new concrete.
Analysis of the proposed column configuration considering a fixed condition at the joint between the column and rib revealed the column still to be over stressed for the service loads. To remedy this, an articulated hinge was introduced at the base of the column on the arch rib to eliminate the fixed connection.
This was accomplished by placing a 1/2-in. neoprene pad between the new jacket and the top of the arch rib. The existing column would now effectively be allowed to crack and act as the pin of the hinge. The neoprene pad allows the new concrete to rotate and not crush into the arch rib. The longitudinal steel in the existing column anchors the column and hinge to the arch rib and accommodates the shear loads.
This was done to each of the columns under the portion of the deck being replaced (a total of 77 columns). The stress levels in the rehabilitated columns are reduced to below maximum allowable service load levels once the hinge has formed. Essentially, a pinned connection is created at the column arch joint.
The design of the longitudinal beams was complicated by the staging requirements. The beam is 5 ft wide and 2 ft deep and has a span of 15 1/2 ft with 7-ft cantilevers near the deck joints at the center pier and abutments. Because the beams would be poured prior to the deck, the beam had to be designed non-composite for dead load. Live load also was put on the non-composite section as an added safety factor.
The beams at the staging lines (Ribs No. 2, 4, 6 and 8) were to be constructed half at a time. At the curbline (Ribs No. 2 and 8), the new half beam (2 1/2 ft wide) was to remain permanently. Additional longitudinal and shear reinforcing steel had to be added to the proposed half beam to accommodate the torsional stresses. At Ribs No. 4 and 6, the two half beams were joined together with dowels and threaded inserts to create one beam acting compositely.
During staging, the existing 5 1/2-ft-wide longitudinal beams were to be cut in half. An extensive analysis was done on the existing half beam to determine if it was capable of supporting the proposed traffic loading. Because this would be a temporary condition, an ultimate strength analysis method was used to ascertain the beam capacity. Moment, shear and torsional effects had to be accounted for. The result of this analysis concluded that the capacity of the half beam would be adequate to accommodate the proposed staging traffic loads.
The proposed deck was designed to span between the longitudinal beams a distance of 12 1/2 ft. Conventional reinforced concrete was chosen due to the staging requirements, the varying cross slopes required and the long span. A 1-ft- thick deck was required with threaded inserts and splicer reinforcement bars used at the staging lines to achieve continuity.
Deck drainage system
The proposed drainage system presented some unique challenges. Scuppers were to be located at the curblines both at the sidewalk and center median. However, at most areas along the curbline, a longitudinal beam is directly underneath. This presented a conflict and a fit problem for the placement of the proposed bridge scupper. In addition, due to the caustic environment of the train station and urban area, there was concern that metal drainage pipe may deteriorate rapidly.
To address these issues, a specially designed narrow scupper was called for connecting to a fiberglass pipe system via a flexible rubber connection. The scupper did not conflict with the reinforcing steel of the longitudinal beam and the fiberglass pipe was well suited for the corrosive environment. This was tied into the existing storm sewer system at the bridge approaches.
Throughout the design process, meetings were held with all the various agencies involved to address their concerns. The NJDOT was very interested in the constructability of the project, which would affect overall costs. This included the choice of materials and the structural design. Jersey City was concerned about maintaining traffic flow for both pedestrians and vehicles to accommodate the needs of the businesses and commuters in the area. Hudson County, responsible for maintenance of the bridge, wanted a design which would yield a structure as maintenance free as possible. The Port Authority and Conrail's primary concern was protection of trains and pedestrians from the possibility of falling debris during construction. The Port Authority requirements dictated the loads and construction constraints for the temporary shielding system to be used during construction.
After almost two years of design and coordination, the final construction plans were complete by February 1991. These plans incorporated the concerns of each agency involved and NJDOT initiated the process to begin construction.
Bids were received on May 23, 1991. The low bidder was Bellezza Co. Inc., Kearny, N.J., with a bid of $4,308,000, 35% lower than the engineer's estimate. The sluggish nature of the construction industry at that time allowed for highly competitive bidding with prices significantly lower than previous years. The contract was awarded and construction began in August, with the completion of the project scheduled for August 1994.
Before demolition work could begin, the temporary shielding system was constructed. The system consisted of channel beams spanning between the arch ribs with a plank and plywood floor. Plywood walls were built at each end to prevent the escape of debris. Traffic control and pedestrian shielding were set up on the bridge deck to prepare for demolition operations.
Stage 1 construction began with the removal of the existing deteriorated deck. This was done by jack hammering around the perimeter of large sections and then cutting the rebar. The section was then lifted out by crane, which kept the construction debris to a minimum.
Once the existing deck and beams were removed, the surface of the existing columns were roughened and the new column forms set. The column concrete was placed and the forms vibrated. Superplastizer was used to decrease the slump and increase the workability of the concrete. This was necessary to eliminate the possibility of voids at the base of the long narrow column.
After the columns had cured, the form work was placed for the longitudinal beams. The extremely dense placement of the reinforcing steel in the beams complicated the placement of the concrete. Extreme care was taken to vibrate the concrete to achieve proper placement around the rebar.
Upon completion of the beams, the deck forms were constructed and the drainage system erected. Deck concrete was placed according to a sequence provided on the plans. In cold weather, heaters were provided and the curing temperature carefully monitored.
This was repeated for Stages 2 and 3 and construction proceeded smoothly. Concurrently with the deck replacement, concrete spall repairs were being performed on the deck under the PATH building and on the arch ribs.
The new median was constructed, approach paving finished and all traffic control removed by the beginning of 1995. The project was completely finished by early spring of that year. Severe weather conditions during the winter seasons had slightly delayed the completion date but the project cost was still significantly under original estimates.
The successful completion of this rehabilitation project was the result of years of studies and coordination between concerned public agencies. Complicating this was the unique structural challenges and construction staging requirements of the rehabilitation. The use of approximately 2,500 cu yd of cast-in-place concrete, innovative structural design and construction techniques allowed for a cost- effective, complicated staged construction with minimal disruption to vehicle, train and pedestrian traffic. Furthermore, the aesthetic appeal of this 70-year-old historically significant graceful arch structure was maintained with little visual alteration.