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Design Plans, Wind Eyed in M1 Collapse

Friday, July 15, 2016

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The official inquiry into a 2015 fatal bridge collapse in South Africa has called out potential causes ranging from material quality and workmanship to a gust of wind.

The Oct. 14 accident left two people dead and another 19 injured when a temporary bridge at a Johannesburg construction site collapsed onto the M1 highway, the city’s busiest roadway.

As reported previously, the bridge was a support structure erected to enable the construction of a pedestrian and cycling bridge project connecting the neighborhoods of Sandton and Alexandra over the M1, project contractor Murray & Roberts explained.

The fallen structure trapped several vehicles in the debris. The driver of a minibus taxi and a man in an SUV were killed during the collapse, station News24 said.

The proceedings, set up by order of the Department of Labour immediately after the collapse, are investigating whether the accident was a result of negligence under the Occupational Health and Safety Act, MSN reported.

The inquiry is also attempting to identify who should be held responsible for the collapse, according to the South African Broadcasting Corporation (SABC).

Analyzing Structural Movement

The inquiry, which resumed this month after experiencing delays since May, has been calling expert witnesses to testify since July 7.

Professor Roelof Mostert, who testified on behalf of contractor Murray & Roberts, stated that when viewing security video footage of the accident, he noted separation of the girders that held the structure together, Times Live reported.

“The structure didn't show any noticeable movement until the time of collapse‚” he said.

"A combination of still photographs and video demonstrates that the initiation of the collapse was a significant displacement of the girders in an actual direction, together with the separation of the eastern and western assemblies at a later stage, followed by a downward rotation of the two assemblies and the collapse," he stated, according to News24.

As head of the University of Pretoria's Materials Science and Metallurgical Engineering Department‚ Mostert based his testimony on analysis of the materials used to build the bridge structure.

He stated that the failure could have been caused by unexpected pressure on the structure, but that Murray & Roberts could not have predicted the collapse, according to a local news station.

Design, Construction and Wind

While Murray & Roberts had indicated that it was responsible for constructing the support structure‚ including scaffolding and super beams, it later clarified that a subcontractor brought on board for the project, Form-Scaff, was responsible for its design.

A second expert witness, civil engineer Richard Beneke, indicated that Form-Scaff’s design drawings lacked relevant proprietary information such as guidance on sequence of construction and the materials used.

According to Beneke, without that information, there was no way Murray & Roberts could effectively analyze the structure to ensure its stability, business news site Moneyweb reported. He also claimed that the subcontractor should have clearly indicated that the drawings were not intended to be used for construction purposes.

Beneke, who has 40 years’ experience in designing temporary works, was selected by the contractor to check the design after the accident. This usually occurs before construction, he admitted.

During his analysis, he said he identified nine instances of minor concern, 29 of inadequate information and 61 instances of “structural risk” in the subcontractor’s drawings, which could have prohibited the structure from transferring load and caused it to give way as a result of wind force.

A third witness for Murray & Roberts, Ric Snowden, further testified on the role wind may have played in the structural collapse, the South Africa Department of Labour said in a statement released Wednesday (July 13).

According to Snowden, a high wind speed of 10.1 meters per second (almost 23 miles per hour) was recorded six minutes before the collapse.

As of Wednesday, the agency is reporting that a wind gust coupled with other weaknesses in the temporary structure were responsible for the collapse.

Materials vs. Workmanship

While Beneke noted that connections between major elements were not adequately considered, Mostert also suggested that the subcontractor provided couplers that did not adequately connect components of the metal structure, Eyewitness News said.

Using photographs of the fallen metal structure to illustrate his points, Mostert stated that in his opinion it is clear the collapse resulted from what he described as “material failure.”

Form-Scaff has not yet testified on the purpose of the drawings; however, it disagrees with the material findings. The subcontractor reportedly contends, by way of its own commissioned analysis, that poor workmanship by the contractor is to blame.

A report from Australian engineer AMOG, reported to be experts in collapse analysis who performed the analysis for the subcontractor, pointed to poor workmanship by the contractor in terms of under-tightening of swivel clamps.

However, Beneke argued that it is normal by South African work practices to tighten clamps like these with a hand wrench and not a torque wrench. He claimed the engineers preparing the report for Form-Scaff did not take local conditions and practices into consideration.

Additional expert witnesses for Murray & Roberts will be called for testimony as the inquiry continues.

   

Tagged categories: Accidents; Asia Pacific; Bridges; EMEA (Europe, Middle East and Africa); Fatalities; Government; Infrastructure; Latin America; North America; Quality Control; Roads/Highways; Safety; Scaffolding; Transportation

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