Pittsburgh City Council has awarded WSP a $1.5M (£1.25M) contract to inspect 150 structures in the US city in the wake of the collapse of the Fern Hollow Bridge in January this year, which injured 10 people.

Following the sudden collapse of the steel girder bridge, which is still under investigation by the National Transportation Safety Board, Pittsburgh mayor Ed Gainey ordered re-inspection of any bridges rated poor or below. However, the appointment of WSP extends the inspection process to all city-owned structures.

News of the appointment of WSP comes as work to rebuild the Fern Hollow Bridge reaches a major construction milestone with new concrete beams being lifted into place this week (see box) and an expectation for reopening the structure by the end of the year confirmed.

Gainey announced plans to appoint an independent firm to carry out inspections of a 150 city-owned bridges in June this year. Gainey confirmed that the city was in final negotiations with a consultant earlier this month after concerns were raised about the structural integrity of the Swindell Bridge – a major truss beam bridge – in the city. At the time of the Swindell Bridge closure due to falling debris from the structure, he said: “We take the safety and security of our bridges seriously and this programme is critical for us to make sure the bridges are safe.”

WSP is expected to deliver a final report on bridge condition by October this year, which will include a list of immediate and short term bridge repairs and cost estimates and timelines for the work. The work by WSP will also involve developing a comprehensive asset management plan for the city’s bridges and a specific plan for each bridge.

While the report is due to be filed in October, the procurement document for the contract suggests that WSP’s work with Pittsburgh City Council could last for up to two years.

The 136m long steel girder Fern Hollow Bridge, which carried up to 21,000 vehicles a day in four lanes of traffic on Forbes Avenue over Frick Park, collapsed suddenly at 6.40am on 28 January.

The structure fell over 30m onto the park below with four vehicles – including a bus carrying four passengers – on the deck. A fifth vehicle drove off the east abutment following the collapse. The incident injured 10 people.

The collapse came hours before US president Joe Biden was due to visit the Pennsylvania city to deliver a speech on his $1.2trillion infrastructure investment package for the US to address deterioration of assets. Biden took a detour to visit the site of the bridge collapse with Pittsburgh mayor Ed Gainey.

This morning, the Frick Park Bridge collapsed in Pittsburgh. This afternoon, I visited the site and met with local officials. Jill and I are keeping those injured in our prayers, and we’re grateful for the first responders. They deserve an incredible amount of credit. pic.twitter.com/s6JwRiFpRX

Speaking from the site of the incident, Biden said: "Across the country there are 45,000 bridges in poor condition. That is simply just unacceptable. That is why your governor, your members of Congress and your mayor has been saying for years.”

The National Transportation Safety Board investigation into the collapse is still underway, but despite a series of updates on the work, no insight has yet been shared on the possible cause of the collapse. However, investigators have pinpointed the collapse as having started from the western end of the structure.

What has emerged are more details on the design of the bridge, which the interim report describes as: “The bridge was an uncoated weathering steel, three-span, continuous rigid ‘K’ frame structure with two welded steel girders, welded steel floor beams, and rolled steel stringers. The ends of the structure rested on reinforced concrete caps on stone masonry abutments. Each girder was additionally supported by two inclined, welded steel frame legs, also made of uncoated weathering steel, which rested atop reinforced concrete thrust blocks. Although certain areas of the welded steel girders were identified as being fracture critical, no primary fractures were found in these areas.”

The new bridge is expected to be completed by the end of 2022

Although investigations into the collapse have yet to be concluded, reconstruction of the bridge has got underway. Pennsylvania Department of Transport (PennDOT) commended the partnership it had established with the Pittsburgh City Council and Federal Highway Administration for fast tracking the work to rebuild the structure with HDR Consulting and Swank Construction.

Design work started a week after the collapse and demolition of the failed structure was carried out in collaboration with the NTSB to aid its investigation. Construction of the new three-span structure started on site in April with four sets of columns now constructed and the first pre-stressed concrete beams scheduled to be lifted in this week.

A spokesperson for PennDOT said that it would normally have taken three years to get to the stage the project is currently at but added that the aim is to open the new bridge by the end of this year.

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