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5 - Matters from the Board, Review and Feedback on the Broadway Reconstruction Project CEAP Appendix (8)BROADWAY RECONSTRUCTION PROJECT APPENDIX A TECHNICAL MEMO ON BRIDGE REHABILITATION ALTERNATIVE ~ Appendix A Technical Memo on Bridge Rehabilitation Altemative Broadway (State Hwy 93) including the bndge over Boulder Creek are owned and maintained by the Colorado Department of Transportation (CDOl). As part of a federally mandated bridge inspection program CDOT is required to inspect all bridges every two years Due to the condition of the Broadway Bndge CDOT has increased its inspections of this bridge to every year. These inspections as well as the analysis performed for this project have shown the following problems wdh the existing structure: A. Deck and girder deterioration. B Undermining of bridge pier due to scour C. Bridge railing has insufficient strength and ability to expand and contract D. Insufficient hydraulic opening Description of Rehabilitation Alternative: Proposal to address Problems A and B(deck and girder deterioration and undermining of bridge pier) r ~,,,,, 1. Exterior fascia beams and bridge railing would be temporanly supported by using shonng into the river. 2. Sidewalk adjacent to the exterior fascia beam would be cut away from the fascia beam. This cut would be one foot ftom the face of the bridge rail through the sidewalk 3. Bndge deck would be cut along the center of the bridge. 4. The deck and girders befinreen the two cuts would be removed. 5 A ramp down from Broadway to Boulder Creek would be constructed. 6. Construction equipment would use the ramp to get into the creek. They would then remove the bridge pier and abutments. 7. Dnll and place concrete for the pier and abutment caissons 8 Construct new pier and abutments on caissons. 9. Place new girders and a new bridge deck 10. Transfer the exterior fascia beam from the temporary supports to the replaced bridge. ~ ~ Repeat the above 10 steps for the second half of the bridge. ~ 11 Carefully remove the ramp from under the bridge. 12. Repair of fasaa beams and light supports. Difficulties Involved with this Option: The fasaa beams are constructed of very slender and minimally reinforced concrete sections. In order to investigate the strength of the existing bridge railing, it was x-rayed on June 26, 2001. The resufts of this test show that the reinforcmg in the rad system consists of approximately %2" diameter smooth reinforcing bar in each element This reinforcing is not continuous or adequately embedded The combination of the finro factors makes the rail very brittle and sub~ect to breakage due to thermal forces and potential sign~cant damage due to vibration; construction movement and vehicle impact. #2 Cut Sidewalk from Fascia Beam. #3 Cut Bridqe Deck Alon4 Center of Bndae. #4 Remove Deck and Girders Between Two Cuts. The process of cutting 8 inch thick concrete and removing steel girders with cranes wdl cause significant vibrations of the fascia beams. It would be impossible to completely isolate the fascia beams from this disturbance. It is likely that the vibrations would cause damage to the fascia beams. .^° L.- #7 Drill and place concrete for the aier and abutment caissons. The process of drilling caissons ad~acent to the temporary supports for the fasaa beams will cause sign~cant vibrations in the temporary supports. This is likely to damage the fascia beams. Proposal to address Problem C(Bridge Railing Strength): Bridge railings have numerous requirements as determined by AASHTO, FHWA and CDOT. The railing on the Broadway Bridge fads to satisfy 3 of these criteria Its height is 3'-1" vs. the required 3'-6". 2 Bridge rads are required to have a smooth face on the traffic side This keeps automobiles from catching their bumpers and spinning out of control. 3. The railing must have sufficient strength to withstand vehicle crashes. The current railing doesn't meet these standards. Discussions have taken place with CDOT on the possibility of relaxing these criteria due to the historic nature of the bridge. As a result of these discussions CDOT has mdicated that critena #1 and #2 above could be relaxed for this project due to the load speed urban nature of Broadway CDOT will not relax the strength and safety cntena #3. ~"- 2 As described above, there is minimal reinforcing in the concrete bridge rail. The ~ reinforcing was placed in a configuration that provides minimal stability of the rail but very little capacity for crash protection To satisfy the strength criteria, a separate railing would have to be constructed on the sidewalk, adjacent to the existing rad to provide the reqwred strength. Proposal to address Problem D(insufficient hydraulic opening) To increase the flood carrying capacity and address pro~ect needs related to the Boulder Creek path crossing under Broadway, a second bridge would be built north of the existing bridge. This bridge would be separated by 25 feet to minimize the visual impacts to the existing bridge. This would increase the disturbance to ad~acent park land ~ 3 ,,^^ `...