A large percentage of New Jersey residents live in coastal and inter-coastal communities. Oftentimes, the primary routes to and from these communities are over navigable waterways spanned by movable bridges. The majority of these structures are bascule bridges (single leaf or double leaf), although there are also vertical lift and swing span structures. Typically constructed 50 to 70 years ago, many of these bridges have undergone significant deterioration due to their age, the surrounding harsh marine environment, heavy use of deicing salts during winter months, high traffic volumes and numerous bridge openings.

The New Jersey Department of Transportation's (NJDOT's) inspection program requires that each bridge receive a structural inspection every two years and an in-depth mechanical/electrical inspection every four years, including testing of the machinery and electrical components. In between these four-year inspections, the movable span's mechanical operation is given a cursory visual inspection concurrent with the two-year structural inspection.

Common Problems

Our Princeton office has inspected and evaluated many of these bridges in the past 20 years. During that time, we noticed a pattern of similar problems at many of the movable bridges, including:

• Deterioration of the supporting superstructure in the movable span(s) under an open grid deck
• Incremental movement of the approach spans towards the movable span (particularly bascule spans), which can affect functionality of the bearings, damage the end diaphragms or floorbeams, and jam the deck joints
• Jamming of the bascule span in extreme hot weather (particularly the side that is exposed to southern sun)
• Improper seating and inadequate locking at the toe of the bascule span's live loading bearings
• Jamming of the center lock in double leaf bascules
• Overstressing of the end floorbeams under live loads.

In many instances, our inspectors uncovered deficiencies that required immediate attention, so we had to prepare emergency or high-priority repair details quickly-usually within two to three days after the inspection. Often, the information we needed was not available on plans, so it was critical that we recognized the severity of defects in the field, understood the reason for their occurrence, made the right judgment, and obtained adequate information in the field for proposing the appropriate solutions.

We take several factors into consideration when preparing repair details:

• Simplicity of the details
• Adverse effects of adding weight to the bascule span(s) where further balancing of the counterweight(s) is not feasible
• Age of the bridge, its remaining service life, and known previous rehabilitation or planned replacements
• Party responsible for performing the repairs (in-house maintenance staff or outside contractors).

A few examples of the emergency/high priority structural repairs that have been performed on several New Jersey bridges are presented below.

Route 47 Over Grassy Sound

The steel expansion bearings in this multi-span bridge had tilted excessively due to the movement of the superstructure into the bascule span. An unusual feature was the inclination of the first pier from the south toward the south abutment.

Late in 1990, a review of the construction plans determined that this tilting was the result of the pier foundation having moved away from the abutment. The south stub abutment is supported on short piles that may have moved toward the span due to their inadequate anchorage in a firm stratum. The fill supporting the abutment may have slid and pushed over the adjacent pier's foundation, which was built at the toe of the abutment fill.

Our recommendation was to take no corrective action because no change had occurred in the tilt of the pier or the bearings for more than a decade. The excessively tilted bearings were reset, however. The bridge was rehabilitated in late 1998/early 1999.

Figure 1: Steel shim blocks prevent further loss of bearing support area. Figure 2: Spalled concrete pedestals

Route 35 Over Shark River

One of the busiest movable bridges in New Jersey (handling a high volume of both marine traffic and vehicular traffic), this single-leaf bascule bridge showed excessive movements of the approach spans and bearing top plates toward the bascule span (Figure 1). The bearings consist of pinned op shoe elements sliding over bottom castings.

At the time of our inspection in the early 1980s, the top plate had moved up to 150 mm (6 inches) toward the span with respect to the bottom casting. Note that the approach span superstructure for this bridge consists of a three-girder system. To prevent the top casting from further loss of bearing support area and potential of catastrophic failure, our repair scheme consisted of extending the bottom casting by installing galvanized steel shim blocks on the concrete pier cap under the excessively expanded top castings.

During our 1998 inspection, we discovered that the supporting concrete pedestals under some of the excessively expanded bearings had spalled off (Figure 2), resulting in the loss of the previously installed shim blocks. Keeping in mind that the bridge was due for replacement in the near future, we proposed building steel column sections with welded cap plates at their tops to support the overhanging top bearing plates. These columns were attached to the pier columns with drilled and grouted anchor bolts.

Route 70 Over Manasquan River

This double leaf bascule bridge had a history of jamming in hot summer weather. Our 1985 inspection uncovered severe deterioration of one of the support piers. Repeated tidal flows, differential settlement of foundations and abnormal movements of the approach spans had all contributed to the deterioration of this lightly reinforced concrete pier. These effects resulted in wide through full-height vertical and diagonal cracks in the pier wall and severe erosion of the concrete at each nose. Our team informed the state immediately of a potential emergency situation and prepared the required repair plans in three days (over a weekend).

Figure 3: Galvanized steel sections used to strengthen disintegrating concrete.

Galvanized steel plates that were to be left in place were bolted to the remaining portions of the pier, including the noses at each end, and repair concrete was pumped into the form work. Galvanized channel sections were strapped around the steel plates and pulled together at each nose to contain the concrete unit (Figure 3). Prior to the installation of the forms:

• All medium to wide cracks were pressure injected with epoxy resin.
• Low viscosity epoxy resin was used in some wider cracks, filling them by gravity flow.
• Long anchor rods were installed as stitches between separated concrete portions to hold them together.

After 14 years, the repaired pier has not deteriorated further and is still functioning.

Route 50 Over Tuckahoe River

This single leaf bascule bridge also had a history of jamming in hot weather. The NJDOT had cut off portions of the bascule span's end floor beam flanges in an attempt to alleviate the problem. Our inspection of the bridge determined that this was not a desirable solution because of the reduced flange section, even though the structural capacity of the end floor beam was not yet compromised.

Our repair details included removal and reconstruction of the deck joint because the existing steel finger-type joint had been cut back significantly over the years. Next, the span lock bar castings were removed and reset to accommodate the reconfigured deck joint and anticipated movements. These repairs were performed about eight years ago. No jamming problems have been reported since.

Figure 4: Corrosion of the supporting members.

Route 30 Over Beach Thorofare, Route 35 Over Cheesequake Creek, and Route 130 Over Raccoon Creek

The Route 30 and Route 35 bridges are bascule; the Route 130 structure is a vertical lift bridge. All three have open grating decks on the movable spans. The grating is typically supported by steel purlins spanning longitudinal stringers that, in turn, are supported by floor beams that are framed into girders. The open grating deck allows roadway dirt and debris to accumulate on the supporting members, causing unabated corrosion (Figure 4). The common deterioration in each of these movable spans was extensive corrosion of the deck purlins and stringers, with large areas of holed-through webs and/or flanges.

In recommending appropriate repair measures, a nagging problem was whether the weight of the repair material would affect the span balance. On the bascule bridges, there was not a lot of room in the concrete counterweights for placing additional steel billets.

After evaluating the additional steel weight required for the repairs along with their moment arm effects on the counterweight trunnion, it was clear that a significant portion of the existing deteriorated steel had to be removed to reduce the overall weight and resultant force on the trunnion shafts. After installing new elements, the old ones had to be cut out and removed.

All work was accomplished from underneath the spans while traffic continued to flow across these heavily traveled bridges. The new purlins had to be slightly shallower than the existing ones so that they could be threaded through the space between the existing purlins and the grating. The new purlins were then shimmed up and bolted to the top flanges of stringers. Repair plates and angles were bolted directly onto the deteriorated stringers.

Figure 5: Steel columns cracked at there bases.

Route 49 Over Salem River

This single leaf bascule bridge does not operate currently, except for regularly scheduled test openings for the Coast Guard. During our 1983 inspection, divers uncovered severe undermining at one of the approach span piers. The scour, which was caused by the very fast flow (4.5 m/sec or 15 feet/second), was so significant that they could walk underneath the pier through the timber piles. [Ed. note: For more information about scour on movable bridges, see "In-depth Scour Evaluations of Three Movable Bridges" by Tom Anella, Rama Krishnagiri and Tim Stanford.]

We proposed driving permanent steel sheet piling around the pier and pouring a tremie seal concrete to fill the void. Riprap was added to the outside of the permanent sheeting to prevent scouring at the sheet piles. To install the sheeting, the contractor removed portions of deck slab, drove the sheeting through the superstructure, and then reconstructed the deck slab.

Years later, during another inspection cycle, we found that the steel columns that support the approach span girders adjacent to the bascule span were cracked at their bases (Figure 5). This cracking was attributed to the movements of the approach spans toward the bascule span. Such movement in bascule bridges tends to be due to a longitudinal discontinuity of the superstructure, frequent opening of the movable span, longitudinal forces generated by traffic and lateral earth pressures behind the abutments.

Emergency repair details were developed after our analysis indicated that the cracked columns could support only the dead loads. The repair details consisted of tee-sections bolted onto the support columns to transfer the live loads and dead loads to the substructure supporting these columns.

Route 52 over Beach Thorofare

This single leaf bascule bridge had jamming problems at the toe of the main span. Several deck joints on the approach spans had also completely closed up. As an interim rehabilitation measure, we developed details to remove part of the concrete end diaphragms at the approach spans and reconstruct the deck joints.

More Inspections Planned

We have seven bridge inspection contracts with the NJDOT currently. One of them is a two-cycle contract to inspect seven complex/movable bridges. This upcoming inspection (at the time of writing) in April/May 2000 should prove to be interesting, particularly at the bridges we flagged during the last cycle for high priority repairs.