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There were design flaws as well as insufficient design reviews during planning and construction. Nothing wrong with the steel.

https://www.osha.gov/sites/default/files/2019-12/2019_r_03.pdf

The design criteria prepared by TY Lin for FIU recommended avoiding non-redundant structures and encouraged a steel superstructure. The design criteria stated that “The bridge superstructure should be primarily structural steel with concrete walking surface. The design should avoid use of non-redundant, fracture critical members.” (Emphasis ours.) The selection committee was swayed by the graphics and rendering of the bridge and did not consider the non-redundancy of the structure. During interviews with OSHA following the incident, FIGG engineers stated that because there were multiple PT bars and tendons in the structure, it could be classified as a redundant structure. This statement does not lend itself to the non-redundancy of the structure.

As a result of the investigation, OES concludes that:

1. FIGG Bridge Engineers (FIGG) ,the Engineer of Record (EOR) failed to recognize that the bridge was in danger of collapsing when he inspected it hours before the collapse. The concrete truss had developed numerous wide and deep structural cracks jeopardizing the integrity of the bridge. The EOR should have immediately instructed that the bridge be shored at appropriate locations and SW 8th Street be closed. At the time of collapse, the post-tensioning bars were being re-tensioned at the specific instructions of the EOR.

2. The bridge had structural design deficiencies that contributed to the collapse during construction stage III. The cracks on the bridge occurred due to deficient structural design.

3. The morning of the incident, EOR held a meeting with project participants after evaluating the cracks over the course of the previous two days. At that meeting, the EOR acknowledged that his computations could not replicate the cracks and therefore, he did not know why the cracks were occurring. The Construction Engineer and Inspector (CEI) of the project advised the EOR at this meeting that the cracks were lengthening daily. Despite these admissions and the knowledge that the cracks were growing in size, EOR stated more than once that the cracks did not present any safety concerns.

4. The magnitude of the cracks warranted that SW 8th Street be immediately closed, and the concrete truss be shored and supported at multiple intermediate locations to reduce the loads in the north diagonal and the node until final evaluations were done and remedial measures implemented.

5. Networking Engineering Services, Inc. dba Bolton Perez and Associates, Inc. (BPA) was retained by FIU to be the Construction Engineer and Inspector (CEI) of the project. BPA failed to classify the cracks, which were structural in nature, in accordance with the FDOT requirements. BPA, as a CEI, was expected to exercise its own independent professional judgement in accordance with their contract with FIU and Florida Department of Transportation (FDOT) requirements. With intimate knowledge of extensive cracking on the bridge, BPA failed to recognize that the bridge was in danger of collapsing, and did not recommend to FIU, MCM or others to close the street and shore the bridge, regardless of the opinion held by the EOR.

6. Munilla Construction Management, Inc. (MCM), the design-build contractor, was aware that the cracks were “getting larger” as reported by MCM superintendent and quality control personnel on March 12 and 14, 2018. On March 13, 2018, EOR stated in an email to MCM, among the list of facts, that “since Saturday (March 10, 2018), MCM has been monitoring the cracks and they have not grown in size.” MCM should have immediately informed EOR on March 14, 2018 that this assumption was not valid. Despite this oversight on the part of MCM, the EOR was provided with photographs and measurements of the cracks in the days leading up to the collapse and was specifically informed by BPA during the morning meeting on March 15, 2018 that the cracks were lengthening.

7. MCM, the design-build contractor, deferred to the decision of EOR and failed to exercise its own independent professional judgement, as a constructor of the bridge, to close the traffic on SW 8th Street until the cause of the cracks were conclusively determined by EOR and peer reviewed. MCM had extensive construction experience in concrete structures and had intimate knowledge of the magnitude of cracks which were growing in size daily. MCM’s deference to EOR in light of the conclusion No. 6 above, and failure to exercise their own independent judgment with regard to implementing necessary safety measures were unreasonable.

8. The evaluations of the cracks by the EOR, and his recommendation to re-tension the post-tensioning bars of diagonal 11, were not included in the original design and therefore should have been subject to peer review.

9. The consultant retained by EOR to conduct independent peer review of the EOR’s design, as per FDOT requirements, did not check the structural integrity of the bridge under different construction stages, a violation of the FDOT requirements. The independent check was performed only under the final design stage when all segments of the bridge were constructed and completed.

Note: This page has been amended by deleting the following sentence from the June 2019 report: “EOR failed to provide construction documents to Louis Berger at 30%, 60% and 90% of completion of construction documents, in accordance with the FDOT requirements.” 10. The EOR should have known that the consultant who conducted the peer review did not check the structural design of the truss design at stage III, as required by FDOT, meriting extra safety precautions by EOR.

11. EOR should have known that the truss was a non-redundant structure and if one diagonal member failed, the entire bridge could collapse. Given the nature and extent of the cracking and the non-redundancy of the bridge design, necessary safety precautions should have included closing the roadway below the bridge and immediately providing shoring to the bridge at suitable locations until a complete evaluation was done.

They were actually in the middle of adjusting the tension on the bridge supports to address the cracking (and this tensioning had not been reviewed by engineers) when the bridge collapsed. One member of the construction crew was killed and another critically injured; and five motorists whose cars were under the bridge waiting for a traffic light were killed when it fell.