Presentation on Safety Issue - Steel Portal Frame Erection

8/4/2019 Presentation on Safety Issue - Steel Portal Frame Erection

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Safety during erection ofsteel portal frame

Rajalakshmi NagarajanSeptember 15, 2011


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ISSUE

Project involved construction of a large span steel framed portal framebuilding.

Longitudinal stability was provided by triangulated vertical side bracings andtriangulated bracings in the plane of the rafters.

The erection method statement had been based upon the principle that the

first bay to be erected would be the bay containing the side and rafterbracings. There would be temporary wire rope guys until the permanentbracings has been installed and fully bolted.

A delay occurred in the delivery of the permanent bracing to the site but itwas decided to progress with the construction using the temporary wire rope

guys to achieve longitudinal stability. After erection of several bays, purlins were lifted on to the roof.

Longitudinal wire rope guys could not take up the eccentric loading, buildingcollapsed.


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WHAT WENT WRONG ???

They did not stick to the construction sequence. Only after the agreement of the originator or any competent authority , the

construction sequence can be altered.


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Truss erecting and bracing

A truss rafter roof system, if properly designed fabricated erected and bracedwill be a strong and economical way to frame a building roof.

There are some design assumptions which should be taken care duringerection.

Trusses have very little strength in the lateral direction


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Erection of truss by lifting them upside down onto the wall plates. Then tip into theupright position.


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Temporary truss and wall bracing will be required until the bracings are secured.These temporary braces supports the trusses against wind from either direction

Wallbracing

Temporarytruss


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The permanent bracings are to be installed with bolts and subsequent construction ofbays.


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After the erection of bays, the purlins are lifted to the roofs.

Cross bracings are also provided for tension web members for stress reversals(e.g. Wind uplift)

The trusses should not be used as a working platform until they are permanentlybraced.

The building site should not be left without all temporary and permanent bracing

being installed.

Web member


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CDM duties that will ensure safety

The main designer must ensure that they take buckling of compression members intoaccount and specify in the drawings wherever stiffeners are required for lateralsupport.

The temporary work designer should ensure stability of the temporary works

In words of CDM,

Eliminate Taking care of buckling action of compression members

Reduce By providing temporary supports and stiffeners

Inform Giving notes in the drawing. about providing temporary supports.Informing the contractor through construction sequence.

Control - The contractor should ensure that the construction sequence isbeing followed properly.


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THANK YOU


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DISCUSSIONS, QUERIES,COMMENTS????

Documents

Presentation on Safety Issue - Steel Portal Frame Erection