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854 Suspended ceiling partial collapse

Report ID: 854

Published: Newsletter 57 - January 2020

Report Overview

A suspended ceiling formed from a lay-in grid partially collapsed in a school classroom.

Report Content

A reporter was asked to investigate the partial collapse of a suspended ceiling formed from a lay-in grid with medium weight acoustic tiles in a school classroom. Fortunately, although the room was in use, nobody was harmed.

The building and ceiling were less than 10 years old. The ceiling was fixed to the underside of a timber joisted roof by wire hangers. The underside of the roof had a layer of plasterboard attached for airtightness such that the joists were not visible.

For supporting the suspended ceiling, eye bolts were screwed into some joists. In other locations, short lengths of inverted ceiling grid were used to bridge between joists, and these were fixed back to the timber joists with two or three 32mm long drywall screws at each end. The effective embedment of the screws into the joists was approximately 10mm having passed through the inverted grid and the plasterboard.

The failure of the suspended ceiling was initiated at a location where the screws to fix the inverted grid to the joists had missed the joist and were only screwed into plasterboard at one end of the inverted grid. The failure progressed along two other fixing points for the inverted grid and stopped where the suspended ceiling was supported by an eye bolt screwed into a joist.

The specification did not directly state how the suspended ceiling was to be fixed to the roof, but did refer the installer to BS8290-3 (already superseded at the time - now replaced by BS EN 13964:2014 Suspended ceilings - Requirements and test methods), which did require a minimum screw embedment of 38mm into the underside of a joist, says the reporter.

In the view of the reporter, errors in workmanship caused this failure but contributory causes were both the lack of a clear specification and effective supervision of the work.

Comments

Failures of ceilings are a recurring problem. In addition to the example in this report, there was a recent failure of a ceiling at a theatre in London and another collapse at a shopping centre in Paisley. The CROSS database contains a number of other ceiling collapses (enter “ceiling” as a key word into the Quick Search box on the website).

In 2015, the Best practice guide - selection and installation of top fixings for suspended ceilings was developed by the Finishes and Interiors Sector (FIS), the Construction Fixings Association (CFA), the Standing Committee on Structural-Safety (SCOSS) and other industry experts, as a guide to best practice on the choice, installation and testing of fixings for suspended ceilings.

The 2014 SCOSS Alert on Tension systems and post-drilled resin fixings listed further CROSS reports on ceiling failures and provides guidance on the design of new ceilings and for the checking of existing ceilings. A 2019 article in The Structural Engineer on the Safety of hanging systems: lessons from CROSS reports is another useful reference. It appears that ceilings do not receive the level of attention, both in design and construction, that the potential consequences of failure deserve.

The failure in this report follows a familiar pattern; a progressive collapse initiated by a single hanger failure, with that initial failure precipitated by connection failure. Self-evidently, the hanger loads were uncertain and using wire hangers would not permit any meaningful control of hanger loads. A division of design responsibility and an inability to inspect also appear to be contributing factors to this failure.

Designers should also remember to check Contractor's Design Portion (CDPs) listed in the contract to ensure there is clarity about design responsibility and what liaison is required.

 

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View other CROSS reports published in Newsletter 57


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