TWM Contributor: David Holdener, PE, SE
Director of Structural Engineering
A Bridge Reconstruction Project in Champaign County IL
I-74 Bridge over the Illinois Central Railroad (ICRR)
TWM’s structural group was recently involved in a bridge replacement project for a crucial piece of Champaign-Urbana infrastructure. The I-74 bridge over the Illinois Central Railroad (ICRR) and Oak Street in Champaign County is a major thoroughfare and carries an average traffic load of over 63,000 vehicles per day.
After an inspection by structural engineer EXP, it was concluded that the bridge was in poor condition due to severe deterioration of Pier 3 under the deck expansion point as well as substantial loss of bearing support under a couple of girders. A protective shield system was installed under the deck and over the railroads to prevent damage to the tracks from deck spalls. After further evaluation and based on the extent of labor costs, future inspections, and repair maintenance, EXP recommended a complete superstructure replacement.
TWM’s structural group provided construction phase engineering services for Sangamo Construction as the bridge was replaced. As the contractor’s structural engineer, our structural team worked on the protective shield, slab demolition plan, steel demolition plan, and steel erection plan. Below is an outline of the work TWM performed:
Protective Shield Reuse & Strengthening Plan | The contract plans called for the removal and replacement of the existing timber protective shield before commencing demolition operations to protect the railyard below. The awarded price for this item was $308,686, but the project bid in April 2020 and lumber prices increased rapidly by approximately 2.7 times from April to the end of August 2020. Working with the contractor, our engineers visually inspected the existing protective shield and prepared plans to strengthen the existing protective shield in place, thereby saving time and materials during the most volatile time in the lumber market in recent history.
History of lumber costs. https://www.macrotrends.net/2637/lumber-prices-historical-chart-data
Slab demolition. Photo courtesy of Sangamo Construction.
Slab Demolition Plan | We analyzed and checked the existing plate girders, which included riveted girders from 1956 and welded girders from 1992, for the loading configurations needed for slab demolition. The concrete slab was sawn into pieces with maximum dimensions of 21’-6” x 6’-0”, each of which weighed approximately 11,500 pounds. CAT 330 Excavators, with operating weights of 68,000 pounds, used slab crabs to pick and handle the sawn pieces. CAT 950 loaders removed the sawn pieces from the deck. Working backwards, the excavators and loaders were able to quickly remove the existing deck concrete from the bridge. Slabbing the bridge out expedited construction and minimized impacts to the rail yard below.
Steel demolition. Photo courtesy of Sangamo Construction.
Steel Demolition Plan | The steel demolition removal was more complicated than steel erection plan because the contractor could not utilize conventional beam clamps due to flange widths. We developed a yoke rigging system that was like a clevis. A 2 ¼” diameter pin was installed through the web portion of the girders and portions of the existing flanges were cut to allow the system to be installed. Temporary bracing was installed between the last girder line removed and the adjacent bridge, eliminating the need for a hold crane during demolition. There were many benefits to eliminating this crane, including lowering costs, reducing site congestion, and avoiding additional conflicts with railroad tracks. We developed both single and double girder removal options and presented both in the plans for steel removal to give the contractor flexibility for removal. The longest piece removed was 148’-4” long and was removed two girders at a time using two crane picks with Manitowoc 999 cranes. The total pick weight was 164,000 lbs.
Steel Erection Plan | The field splices shown in the contract plans were well-placed. Our engineers worked with the contractor and drew from our erection plan experience to develop an erection plan that did not require temporary towers within the congested railyard below the bridge. To eliminate hold cranes and further reduce congestion, we detailed connection plates for the steel fabricator to add to the proposed girders. The connection plates served as temporary brace points for the first girder line installed. We prepared an MBrace model to perform erected and global stability calculations on the partially erected girders.
Additional checks included cross frames, rigging, lifting stability, local flange bending, temporary works wind analysis, and longitudinal restraint. The steel and demolition plans were reviewed and approved by both IDOT and the ICRR.
Steel erection photos, courtesy of Sangamo Construction.
About TWM’s Construction Phase Engineering Services
TWM’s structural engineers have provided construction phase engineering services for contractors in Illinois, Missouri, Arkansas, and Tennessee. Some of our most complicated and interesting structural projects are construction phase projects. We assist contractors in developing methods of construction that accomplish the desired intent, do not cause damage to structures, and are safe. Our work as structural consultants to contractors focuses on the items that are unknown during design and frequently involves partial structures. Our objectives are to provide strength, stability, and serviceability for the steps required to demolish and construct bridges. Typical construction phase projects include: