Codes & Standards

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Portal Frames and liner of built-up systems becoming further for the proposed cladding system and apart and all forms of roof cladding becoming insulation thickness. heavier. With the insulation thickness now reaching a point where further increases will result b) Position of purlin flange – With the air leakage in diminishing improvements in performance, requirements becoming ever tighter, accurate greater emphasis is now being placed on air installation of the cladding is essential. The tightness with the promise of strict enforcement of quality of the installation will naturally depend the regulations through on-site testing. There are in part on the care with which the contractors two issues that designers should be aware of: carry out their work, but it can also be influ- enced by the condition of the supporting steel- a) Purlin restraint – It is common practice in the work. In particular, excessive sag of the purlins United Kingdom for designers to select the in the plane of the roof slope can present dif- required purlin size from the manufacturer’s ficulties when it comes to fixing the cladding. load/span tables. The capacities presented To avoid any such problems, it is important that in these tables are usually based on the consideration is given at the design stage to assumption that the purlins will be fully the method of working on the roof and that the restrained in the gravity load case and partially assumptions made at this time are realised on restrained against wind uplift. The load site. For example, operatives should not walk capacities have in the past been determined on unrestrained purlins unless they have been by full-scale tests. However, the increase specifically designed for this loading. in insulation thickness in recent years has reduced the level of restraint offered to the The SCI is currently engaged on research in this purlins by the cladding system and designers area and further guidance on the specification and should check with purlin suppliers that their installation of purlins and cladding will be pub- test results and calculations remain applicable lished later this year. Codes & Standards New and Revised Codes and Standards (from BSI Update March 2004) BS EN PUBLICATIONS BS EN 1991:- CEN EUROPEAN Accidental actions STANDARDS The following are British Standard BS EN 1991-1:- implementations of the English Eurocode 1. Actions on EN 1994:- language versions of European structures Eurocode 4. Design of composite steel Standards (ENs). BSI has an obligation NA to BS EN 1991-1-2:2002 and concrete structures to publish all ENs and to withdraw any Actions on structures exposed EN 1994-1-1:2004 conflicting British Standards or parts to fire General rules and rules for of British Standard. This has led to a BS EN 1991-1-7 buildings series of standards, BS ENs using the Accidental actions EN number. EN 10292:- Continuously hot-dip coated strip BS 4:- and sheet of steels with higher yield Structural steel sections strength for cold forming. Technical BS 4-1 (Revision) delivery conditions. Specification for hot-rolled sections AMENDMENT 2: December 2004 to Will supersede BS 4-1:1993 EN 10292:2000 NSC May 2005 27


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