Cook County, Chicago, Illinois, FAU Route No. 3730
The HBM scope of improvements included the Phase II analysis, design, structural final plans, special provisions, quantity calculations, specifications, and Quality Assurance / Quality Control (QA/QC) for the south and north abutments, wingwalls, cofferdams, south and north Conspan precast arches.
Main Span Bridge (Tied Arch Bridge):
The existing structure is a bascule bridge, 301.2ft long and 60ft wide. The existing superstructure is steel grating supported by steel truss (on movable portion of the bridge) and reinforced concrete deck slab and steel deck beams on the fixed spans. Substructure is reinforced concrete wall piers and reinforced concrete abutments. Existing bridge superstructure is to be removed and replaced with new structure. Existing substructure is to be strengthened and reused for the approach spans. New reinforcement concrete abutments on steel piles are to be built in canal to support the main span. In reviewing the existing drawings from the original bridge plans, the existing abutments are supported on timber piles. The plans do not specify the tip elevation of the existing timber piles.
The length of the proposed bridge is 156″ -8″ back to back of abutments with no skew. The proposed superstructure is a simply supported tied arch bridge with 10″ deep structural deck slab. An HPS 70W 42″ composite bolted, built-up steel tie box girders, welded, built-up steel box arch ribs, welded, built-up steel box rib bracings, welded, built-up steel composite box floor beams, and an AST
M A586, class C structural strands. The width of the deck is 80″ -4″ out to out deck, 54″ -0″ face to face of curbs with two 9″ -6″ sidewalks.
The abutments will be closed abutments supported on piles driven to bedrock. The bottom of the abutments will be constructed at 17″ below the water surface. This will require the construction of temporary cofferdams to construct the abutments “œin the dry”. Based on the loads anticipated and soft soil conditions encountered near the river bottom surface, the abutment and piers will be supported on steel HP-piles extended to refusal on bedrock. This issue and the existence of the applied loads from the tie arch bridge at two locations close to the ends of each abutment, and the lateral loads behind the abutments and surcharge, requires the use of a 3-dimensional finite element analysis to find the applied axial loads, moments, and shears on the abutment , stem, pile cap and piles. The bridge seismic performance category (SPC) is A. The horizontal alignment is straight.
South and North Conspan Pedestrian Tunnels:
The portion of the existing abutments interfering with the Conspan prestressed foundation mat will be removed. Concrete Counter weights will remain in their pits. The existing and remaining portions of abutments will be extended to cover the area between the wingwalls. The Conspan prestressed foundation mat will be dowelled and supported on the top of the remaining abutments and their extensions.
All wingwalls are designed as Cantilever Retaining Wall with footing supported on Steel H-Piles. The proposed length of Northeast wingwall is 63″ -1″ with maximum height of 16″ -7 آ½” , while the proposed length of Northwest wingwall is 79″ -10 3/8″ with maximum height of 18″ -7 آ½” . The proposed length of Southeast wingwall is 84″ -1″ with maximum height of 18″ -6 آ½”, and the proposed length of Southwest wingwall is 84″ -1″ with maximum height of 18″ -6 آ½”. The minimum footing depth is 3″ -0″.
A temporary cofferdam system will be installed at Both North and South Abutments. The cofferdam height shall be designed according to Estimated Water Surface Elevation (EWSE) which can be used to evaluate the need for underwater structure excavation protection. Depending on Loading Conditions, the use of walers and/or seal coats shall be included in the design.
Subconsultants: HBM Engineering Group, LLC