Posey Tube Retrofit

REPAIR AND REPLACEMENT OF SIDEWALK WITH GUARDRAIL REPLACEMENT AND NEW CONDUIT

The guardrails in both the Posey and Webster tubes are in poor condition and will be replaced. For the installation of a replacement pedestrian guardrail in the Posey tube, the old railing will be removed. The existing edge of sidewalk will be repaired, loose concrete removed and replaced, corrosion of reinforcement cleaned and painted for a length of 4,750 linear feet to restore the sidewalk to its former dimensions. New angle plates will be installed and the vertical section bolted at the transit side and the horizontal at the pedestrian/ bicycle concrete path to receive the new guardrail posts. This new railing will be very similar in appearance to the original existing railing, but will have tensioned cables added to meet current safety standards and placed flush with the edge of the sidewalk. New 4’-0” tall stainless-steel tube rails with horizontal tensioned cable spaced at 4” on center will be installed in the sockets. The railing will be adapted to accommodate the following irregular conditions: (a) existing metal plates and grates which intrude on the edge section to be replaced, (b) fire extinguishers and call boxes, (c) existing toe-hole stairs in lower wall and chained emergency exits which allow pedestrian access from vehicle lanes onto walkways which will be replaced with gates.

For installation of 4,750 linear feet of replacement guardrail at the maintenance-use walkway in the Posey Tube, and 3,520 linear feet of new guardrail at the maintenance-use walkway in the Webster Tube, the design and construction will be the same as for the pedestrian guardrail in the Posey Tube, except that no tensioned cable will be installed. When forms are constructed over the removed concrete, a 3”-diameter PVC conduit will be placed in the form for the entire length of the removed concrete. At both ends of the conduit installations in each Tube, an additional 6”-wide section of walkway pavement will be removed using jack hammering without disturbing the reinforcing and/or utility pipes and a conduit will be placed through this cut to the wall of the Tube, where it will be led up the wall to the new electrical safety panels. Panels will be affixed to the Tube wall by drilling holes for bolts which will be affixed in place. The panels will then be bolted to the wall.

Spalls in the sidewalk of the Posey and the Webster Tubes and at the pedestrian entrances to both Tubes will be filled with PCC and finished to match the original surfaces, existing expansion joints on the concrete path will remain, and existing plate covers will be replaced; as suggested in the 2009 Estuary Crossing Study. Hooks that were left protruding from the Posey Tube wall from an earlier project will be removed.  Warped expansion joint plates and conduit covers on the sidewalk will be repaired or replaced.

INSTALLATION OF CCTV CAMERAS

CCTV cameras with telecommunication lines will be installed at the Posey Tube (Alameda side) and Webster Tube (Oakland side) entrances. A bracket will be mounted into the upper side wall on the maintenance-walkway side of each Tube entrance, to which a CCTV camera will be affixed. Half-inch-diameter metal conduits will be led up the wall from the new safety panels to the CCTV camera installations and attached to the cameras. The camera will be approximately 13”x7’x12” in size.

INSTALLATION OF NEW LIGHTING

Most of the existing cobra head lighting on both sides of the Posey Tube approach structures’ balustrades will be removed. The cobra head light standards were added in the 1960s and are not original to the historic structure. Reproductions of historic light fixtures lit with high pressure sodium bulbs will be installed on the second, fourth, sixth, and eighth pilasters (counting from the Tube mouth) on both balustrades of the approach structure on the Alameda side, and the existing first and third pedestals (counting from the Tube mouth) on both balustrades of the approach structure on the Oakland side. One side of each approach will be constructed at a time to provide continuous lighting to the facility. Minor concrete work will be used to patch and replace bolts as needed to receive the new fixtures. At locations where no existing fixture will be removed, minor concrete work will be used to prepare the base for the replacement fixtures. Conduits exist at all locations for new and replacement reproductions of historic lighting, but may not be usable. If necessary, new 1” metal conduits will be laid on top of existing architectural molding on the approaches, and flexible ½” conduit will be laid from it to the fixture bases. New reproductions of historic lighting will be installed on the new and renovated bases. The reproductions of historic lighting will be as close as possible in overall style and scale to the historic light fixtures using the original plans and historic photos as a guide. On the existing second, fourth, and sixth pilaster on the pedestrian side of the Oakland approach and the first, third, and fifth pilaster on the pedestrian side of the Alameda approach to the Posey Tube, modern LED wall luminaires will be installed. Wall luminaires will be unobtrusive lamps. Fixtures will be connected via flexible conduit to either existing conduits or new lighting conduit installations described above.

RESTORATION OF LANTERNS

Lanterns atop the east and west pylons of the Alameda approach structure will be removed and restored to their original condition. No lanterns have survived on the Oakland approach due to the overhead construction of I-880. Metal on the lantern will be checked for corrosion. If the metal is slightly corroded, it will be replaced with stainless steel and welded together to match the existing shape and dimensions. Grinding and polishing the surface is needed after the welding job is done. If the lantern is completely immured from corrosion, the metal will be ground until resurfaced, then anti-corrosive paint will be applied. The condition of the glass surrounding the lantern will be examined. Any broken glass will be replaced with glass matching the existing material, including color and thickness. The anti-corrosive paints shall demonstrate a minimum classification of 2B, according to ASTM D3359-90 Method B. Corrosion resistance will be under the salt-fog test, the traditional method for measuring corrosion resistance, which has many limitations. The anti-corrosive paints will be formulated to not exceed 250 VOC. The VOC concentrations are measured in grams per liter of product, minus the water. The color of the paint will be matched to the original color. The new base of the lantern will be rebuilt to accommodate the new electrical components: the ballast, the capacitor, the ignitor, and the lamp socket (to hold a 70 watt high pressure sodium lamp). One-half-inch rigid steel conduits with adapters and #18 TWN wires will supply power to these lanterns. The cobra head lights in front of the Alameda approach pylons will be removed.

INSTALLATION OF NEW SPOTLIGHTING

New spotlighting with wires, rigid conduits, brackets, and safety protection devices will be installed on both portal buildings of the Posey tube. The spotlights will be located at the balcony level of the portal buildings. Each spotlight comes with a bracket which can be adjusted to a specific angular position, then secured with a wrench. The two spotlights will be fastened with anchors and will be pointed up to the twin towers on each portal building. The towers will be illuminated during the night. A 3/4" rigid conduit and #8 THW wires are connected between the spotlight and the safety protection device.

REHABILITATION OF POSEY PORTAL BUILDING EXTERIOR

The existing cementitious coating and paint will be removed from each Posey Tube portal building which will be surrounded with scaffolding and a lead-containment system employed to contain construction debris. The existing cementitious coating will be removed by hand, and the contained debris treated as hazardous material. Where continuous cracks and spalls exist on concrete walls, cracks and spalls will be removed and/or repaired. Any exposed structural steel will be cleaned and treated with rust preventative product. The concrete will then be patched with highly-adhesive non-shrink concrete patching compound and finished to match the existing surface.

The original Art Deco style relief panels on the portal towers were removed in the 1960s. At locations where ornamental panels originally existed but were removed, new cast-concrete panels copied from the original designs will be installed by bolting the panels to structural members.  A new flexible ter-polymer coating will be applied so as to mimic the original historic surface texture, still in evidence on the Alameda portal building.

The new exterior finish will be painted using the original color palette on file with the District 4 Office of Cultural Resource Studies.

The arched opening between the two portal towers and the smaller windows at the side of the arched opening and lower level in each Posey portal building originally were glazed with clear glass but have since been painted over or had glass replaced with plywood and asbestos cement boards. Existing glass and plywood in window frames will be replaced with new clear, non-glare, non-yellowing impact-resistant, laminated glasspanels. This will recreate the original appearance of each portal as two towers surrounding a central arched window. All the steel window frames will be repainted.

Existing handrails on landings and at the stairs to the entrances to the Posey Tube, and existing metal-clad doors and steel window frames on the Posey portal buildings will be stripped and cleaned using the gentlest means possible, as outlined in National Park Service Preservation Brief #6 while the lead-containment system is in effect. These will be repainted using the original color palette on file with the District 4 Office of Cultural Resource Studies.

REPAIR OF POSEY PORTAL BUILDING INTERIOR

Where continuous cracks and spalls exist on concrete walls, cracks and spalls will be removed and/or repaired. Any exposed structural steel will be cleaned and treated with rust preventative product. The concrete will then be patched with highly-adhesive non-shrink concrete patching compound and finished to match the existing finish. Existing asbestos will be contained and removed following the development of an Asbestos Containment Plan. The interior will then be painted.

OVERFLOW ROOF DRAINS AND REPAIR OF ROOF SLOPE OF THE POSEY PORTAL BUILDING

Decayed wooden structural members around the existing roof drains will be repaired or replaced. New overflow drains of the same size as the existing roof drains will be installed with the inlet 2” above the low point of the roof.  The overflow drain will have an independent downspout to discharge to an exterior location close to the primary drain piping. New flashing and tapered insulation will be applied to the roof to direct water away from the walls and towards the existing drains and new overflow drains. The entire affected area will be patched and receive a new coating. These drains are located on the mezzanine roof area of the portal buildings. This work will not alter the exterior appearance of the portal buildings

SIGNAGE

New signs that read "Pedestrian Walkway" will be placed on the Oakland and Alameda sides at the commencement of the Posey and Webster Tube approach structures. All new signage will be designed to be consistent with the refined, monumental appearance of the portals. Existing signs on the Posey Tube approach structures will be removed or relocated so as not to block pedestrians’ or motorists’ views of the rehabilitated structures: 

• “Watch for Stopped Traffic” – will be relocated 100’ south of its present location.
• “Historic Bridge – Posey Tube 1927” – will be relocated 125’ south of its present location.
• The two electronic message signs will be removed.
• “Pedestrians Bicycles Motor-Driven Cycles Prohibited” – will be relocated directly northeast of its present location.

ORDER OF WORK

Due to high traffic volume, most work near the roadway will be done during non-peak hours. The guardrail replacement will require at least one lane closed. An additional lane may be closed, which will result in closing the Tubes completely, if during construction a safe lane width cannot be provided. While the Tube(s) is (are) closed, a detour will reroute the traffic via I-880 and the Park Street Bridge. This project has state funding through SHOPP program 201.110 Structure Rehabilitation. The total project cost is $8,000,000. The project requires no additional right-of-way.