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Tension cable structures: concerns over connectors

Cable connection integrity under the spotlight following out of court settlement in Doha airport dispute.

A leading structural engineer said this week that a dispute about manufacturing quality at Doha International airport in Qatar has highlighted more widespread problems with tension cable structures.

Manufacturer Macalloy settled the dispute with subcontractor Stressed Structural last week after problems had been encountered with a tension cable structure at New Doha International airport (NDIA).

The dispute followed the discovery of defective end pieces that connect the cables to the structure. This meant the manufacturer had to rework or replace some of the structural elements supplied to subcontractor Stressed Structural (see box).

Confidential Reporting on Structural Safety (Cross) director Alastair Soane told NCE that the dispute had underlined on-going concerns about the manufacturing quality of critical structural connecting elements. He expressed fears that defects could lead to a major collapse.

Number of reports

“Irrespective of the manufacturer we have had a number of reports that show termination pieces have not been as inspected or specified,” said Soane. He stressed that concerns were directed toward generic elements rather than any specific manufacturer’s products.

Tension cable structures are now commonplace in large buildings often supporting glass curtain walls or suspended ceilings. They are also often used as light weight alternatives to heavy steel trusses in the building envelope. Soane said that exposure of this problem and dispute added more justification to the structural experts’ fears.

He pointed out that the scale of concern prompted the Standing Committee on Structural Safety (Scoss) to issue an alert in July. This came after Cross had received several anonymous reports relating to the problem.

“These are safety critical components,” said Soane. “Once one goes then you risk a collapse.”

Soane added there was a “whole range of issues” to do with tension cable structures including material quality. He said engineers had to be vigilant when specifying cable tension structures to ensure that what has been specified was actually delivered and to ensure that quality control checks are rigorously made.

Dispute fuels concern

Macalloy was forced to replace or repair work at Qatar’s New Doha International airport after concern was expressed about the manufacturing quality of connections used within a cable tension structure.

Macalloy last week settled a dispute with its subcontractor Stressed Structural hours before the case was due to heard in court.

Sources close to the project said the dispute centred on unpaid work to repair defects in the cable structure.

It is understood that the defects were found in the swaged ends of the stainless steel cables.

Stressed Structural was originally employed by Macalloy to tension the cable structure supporting a glass façade at the airport in

Qatar after it had been installed by local labourers.

The cables form part of a complex structural system designed by consultant Buro Happold. They link the building’s columns with the wind truss, which in turn supports the terminal building’s glass façade. Macalloy provided 12mm and 16mm diameter cables to support the glass wall that forms the perimeter of the building.

But it is understood that inspections by Italian glazing contractor Permasteelisa Gartner - Macalloy’s client - revealed cracking in the swaged end pieces which connect the cables to the structure.

“Over time the crack would propagate until it eventually could break the cable,” said the source. Stressed Structural was, he said, then called in to rework or replace the defective areas three times on Phase 2 of the terminal building contract.

Permasteelisa Gartner worked for main contractor Sky Orxy on the terminal building. Sky Orxy is a Japanese firm owned by engineering giant Taisei.

Following discovery of the defects Stressed Structural revisited the site twice to grind down cracks or replace them with like-for-like components.

Macalloy completed its work on the project about six months ago. The firm declined to comment.

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