Advisory Desk: AD 297: Disproportionate collapse regulations - Advisory Desk: AD 298: Guidance on the use of Quicon slotted hole connections

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Advisory Desk AD 297 Disproportionate collapse regulations This AD is to advise engineers how Scotland control body when buildings are Northern Ireland hot-rolled steel they might account for the differ- In Scotland, the Building Standard less than five storeys. framed buildings with five or more ences between the disproportionate 1.2 of the Building (Scotland) Regu- storeys should comply with Clauses collapse regulations in England lations 2004 states: Northern Ireland 2.4.5.2 and 2.4.5.3 of BS 5950-1: 2000. and Wales, Scotland and Northern ‘Every building must be designed The obligation to limit disproportion- Buildings with less than five storeys Ireland. The regulation for each and constructed in such a way that ate collapse currently applies only should comply with Clause 2.4.5.2 of country has slightly different limits in the event of damage occurring to buildings of five or more storeys. BS 5950-1: 2000. defining when disproportionate col- to any part of the structure of the The next amendments to BS lapse should be considered. building the extent of any resultant England & Wales 5950-1 (expected summer 2006) will The requirements for the Building collapse will not be disproportionate Although no storey limit is given in include the building classification Regulations of England and Wales to the original cause.’ Regulation A3, Approved Document system from Approved Document A. regarding disproportionate col- Despite this, the Technical Hand- A defines four classes of building Therefore, buildings designed to BS lapse are detailed in SCI publication books for domestic and non-domes- and the structural provisions re- 5950-1 will follow the classification P341. On page 2 of P341 there is a tic buildings states that progressive quired for each class to comply with system even though they may not be note that suggests in Scotland and collapse should be considered only the regulations. Further guidance is covered by the England and Wales Northern Ireland disproportionate if the building is five or more sto- provided in SCI-P341. Building Regulations. collapse only needs to be consid- reys. ered for buildings of five or more In view of this uncertainty, it is How to comply Contact: Andrew Way storeys. This AD shows why this is recommended that agreement is It is advised that to comply with Telephone: 01344 623345 an over simplification for Scotland. reached with the relevant building the regulations in Scotland and in Email: a.way@steel-sci.com AD 298 Guidance on the use of Quicon slotted hole connections This AD presents guidance on deflect by more than its theoretical applications. Where the supporting • As the studs in a Quicon con- the use of the Quicon slotted simply supported value for a given beam is susceptible to twist (e.g. an nection are not tightened against hole connection system based magnitude and distribution of load. edge beam), it may be advisable to the cleat (only against the beam on experience gained during a Designers should note that there increase the precamber to the full web), there is sufficient slack in recent application of the system. has been a tendency in recent years dead load deflection. However, all the connection to permit a small This guidance is supplementary to to place the concrete in floor slabs of the secondary beams, including amount of twist between beam the design information presented to the required level, irrespective those that connect directly to and cleat. This could contribute in P338, which is still valid. The of the slab thickness. When deflec- the columns, will need to be to the twist experienced by the following issues have been tions in the metal decking, second- precambered by the same amount to primary beams when Quicon con- identified as needing additional ary beams and primary beams are avoid potential difficulties on site. nections are used between the guidance: taken into account, the additional primary beams and the columns. • Deflections weight of concrete can be very Twist • Precamber significant, leading to deflections Where a primary beam supports a Designers are advised to consider • Twisting of primary beams well in excess of those based on a secondary beam on one side only, the use of flexible end plates for uniform slab thickness. This is the it will be subjected to torsion due to the connections between the edge Deflections case irrespective of the connection the unbalanced loading. The result- beams and the columns in cases The moment-rotation behaviour of type. ing twist in the primary beam will where significant twist is expected. a Quicon cleat when connected to depend on the magnitude of the tor- Where the construction a column is very similar to that of a Precamber sion and the torsional rigidity of the programme calls for the concrete fin plate, exhibiting significant rota- It is common practice to precamber primary beam and its connections slab to be poured on one side of a tional stiffness compared to a true long span secondary beams to to the supporting columns. In this line of primary beams before the pin. However, when connected into either 2/3 or 3/4 of the simply respect, there are two issues that steel has been erected on the other the web of a beam that is itself free supported dead load deflection, could result in greater twist when side, the primary beams in question to twist, there is less end restraint which assumes that the supports using Quicon compared to other should be considered as edge and the mid-span beam deflections provide some stiffness to reduce simple connections: beams in the temporary condition. approach the predicted simply sup- the deflection. This approach is • Where a Quicon cleat with 2 col- It is important that twisting of these ported values. The SCI recommends still recommended where Quicon umns of studs is used in beam-to- beams is limited in order to facilitate that Quicon should be treated like connections are used, provided beam connections, the increased the erection of the adjacent any other type of simple connection that the support is sufficiently stiff eccentricity associated with the secondary beams when predicting beam deflections, to prevent rotation of the cleat. This second column of bolts results in allowing for any flexibility in the sup- will always be the case with beam- increased torsion in the primary Contact: Martin Heywood porting member. A beam supported to-column connections and should beam, thereby increasing the Email: m.heywood@steel-sci.com by Quicon connections cannot also be true for many beam-to-beam twist. Telephone: 01344 623345 38 NSC March 2006


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