|PROJECT MANAGER||Eassam Alameddine||(213) 897-0141|
|PUBLIC AFFAIRS OFFICE||Pat Reid||(213) 897-4432|
|CONTRACTOR||Traylor Bros Inc.||(714) 475-0444|
|NUMBER OF WORKING DAYS||472|
|CONTRACT AWARDED||March 31,1997|
The Vincent Thomas Bridge is located on Route 47 (P.M. 0.86) in Los Angeles County (see Figure 2.1-1 for basic particulars). It is a cable-suspension bridge, approximately 6062 ft long, consisting of a main suspended span of approximately 1500 ft, two suspended side spans of 506 ft each, ten spans in the San Pedro Approach of approximately 1838 ft total length, and ten spans in the Terminal Island Approach of approximately 1712 ft total length. The roadway width between curbs is typically 52 ft, and accommodates four lanes of traffic. The clear height of the navigation channel is approximately 185 ft.
The design of the bridge was completed by Caltrans in 1960. The bridge was constructed under two separate contracts, one for the substructure and another for the superstructure. The substructure contract was completed in 1962 while the superstructure contract was completed in early 1964.
Stage 1 seismic upgrading in the form of cable restrainers, shear keys abutment seat extenders and girder lateral supports was completed in 1980. Modifications to the vertical cross frames, and the lateral bracings near the bents, and inclusion of a full length cat-walk were also made in 1980 as part of the seismic upgrading contract. New elevators at Bents 9 and 15 were added in 1992.
Twenty-six seismic sensors were installed on the bridge to record ambient and seismic behavior.
FIGURE 2.1 - 1 GENERAL ARRANGEMENT
The suspended structure consists of two stiffening trusses spaced 59 feet apart, floor trusses with 31 feet center to center spacing and a lower lateral bracing system (K-truss type). The stiffening truss is 15 feet deep while the floor truss is 10 feet deep. The top edge of the roadway is 3 feet below the top edge of the stiffening trusses. A lightweight concrete deck is supported on rolled beam stringers, spaced transversely at 7 feet, which are in turn supported by the transverse floor trusses. The suspended spans are supported by the main cables through suspenders at each floor truss location.
The towers are 335 feet high and are supported on steel HP pile foundations. The towers consist of two shafts which are braced together through five struts. The tower shads, with a cellular cross-section, consist of four welded box sections (3/4 inch plates) that are field bolted with 1 inch diameter high strength bolts. The Moss section of each shaft tapers toward the top. Each tower shaft rests on a 3 inch thick base plate and is anchored to the underlying concrete footing by thirty nine 2.5 inch (in diameter) by 25 feet long prestressed rods.
The cable in the suspended spans consists of 4,028 cold-drawn galvanized, 6 gauge steel wires providing 121.5 in^2 of area including galvanizing. The suspenders are made of small diameter, high strength wires laid up into rope. The cable saddles are centered on the top of tower legs. This causes the cable to spread at the tower tops where the frictional resistance between the cable and the saddle to prevent the cable from slipping through the saddle.
The main span and the side spans are connected to the towers through truss links that provide vertical support and wind shoes that provide transverse support only. The end of each side span is supported on a reinforced concrete cable bent through truss links that provide vertical support and wind shoes that provide longitudinal as well as transverse support. The cable bents also support the last spans of the approach structures.
At the cable bents, the cables are deviated by a cable saddle towards the anchorages where they are attached to eye-bars embedded in the anchorages. These are massive reinforced concrete structures that are supported on heavily battered pile foundations.APPROACH SPANS
The approach superstructure consists generally of four rows of steel girders ranging in span from 132 ft to 230 ft. Two spans adjacent to the San Pedro abutment consist of five rows of girders. The built-up, stiffened plate girders are composite with the 8-3/8" thick lightweight reinforced concrete deck. All spans are simple spans, except the two spans adjacent to both cable bents, which consist of continuous haunched girders.Cross Frames and Bracings
End frames and intermediate cross frames consisting of structural tee-section members spaced 20 to 25 feet on center, are provided between girders. Tee-section bottom chord lateral bracing is provided between the interior girders along the approach spans. In general, the connections are made with 3/8" gusset plates and 7/8" highstrength bolts. The vertical frames were modified after construction to accommodate a walkway which runs the entire length of the approach spans.Bearings
Girders are supported at each end by built-up steel bearings approximately 2'0" in height. In general, the end of the girder nearest the abutment has a fixed bearing while the other end is supported on rocker type expansion bearing. The continuous spans adjacent to the cable bents have a fixed bearing in the center and expansion bearings at the ends.Typical Bents
The superstructure is supported on normal weight reinforced concrete bents which range in height from approximately 36' to 120' above bottom of footing. All bents are two-column bents except Bent 2 which has three columns. Bents 2,3,4 and 5 on the San Pedro approach and Bents 19, 20 and 21 on the Terminal approach have 7' x 4'4" solid columns; the remaining bents have 12' x 6' hollow columns. All bents have 8' deep solid rectangular bent caps. Concrete shear keys which provide lateral restraint to the girders were constructed as part of the seismic retrofit contract. These are cast on the top of the bent caps and secured with dowels drilled and bonded into the bent caps.Cable Bents
The cable bents ( Bents 11 and 12 ) are approximately 142' tall frames, each with two 16' x 8' hollow normal weight concrete columns and a 10' x 8' solid concrete bent cap. There are no intermediate braces. 8' x 3' concrete pedestals rise approximately 16'-6" above the girder seats on each end of the bent cap to serve as seats for the cable saddles. Steel brackets are embedded in the top of the bent concrete to support the truss links and to resist the forces from the wind shoes.Bent Footings
All bent footings are supported on piles. Footings for the typical bents are of normal weight concrete and range in size from 14' x 10' to 26' x 18' thicknesses range from 3'6" to 4'-9". There is no top reinforcement mat in these footings. The cable bent footings are continuous between the columns with an upstand spine beam. The cable bent footings do have a top reinforcement mat.Piles
The San Pedro Approach bent footings are supported on 14-BP-89 steel piles. These piles are embedded 6' into the bottom of the footing and do not have any hairpins or other type of anchorage. Both cable bent footings are supported on three rows of 14BP-117 steel piles, the outer row being battered 1:6. In this case, however, the outer rows of battered piles have #11 hairpins connecting the tops of the piles to the footings.
The Terminal Island Approach bent footings are supported on 16" octagonal reinforced concrete piles. These are embedded 3" into the bottom of the footings and have 8#9 dowels embedded 2'-6" into the concrete.Cable Restrainers
3/4" diameter cable restrainers are provided to longitudinally interconnect the deck segments at each typical bent. These are looped cables connected by tumbuckles at the ends. The total length of each loop is approximately 100'. Three banks of looped cables are provided at each bent. The interior banks consist of eleven cables while the exterior banks are eight cables each. The cables are looped around cross beams which were retrofitted during the seismic upgrading contract and which span between the deck girders.
The looped cable restrainers are not present either at the abutments or at Bents 10, 11, 12 and 13. Vertical restrainers are provided at these locations as hold-down devices. These vertical restrainers consist of 1-1/4" diameter high-strength bolts cast into new concrete pedestals constructed on either side of the existing deck girders.