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The Structural Engineer

Full-scale precast prestressed hollow-cored flooring slabs have been tested under fully reversible horizontal shear loading to determine their suitability as horizontal diaphragms in multistorey buildings. No structural topping screed was used, but in situ reinforced end beams were used to reproduce the presence of beams in a frame environment. A hypothesis is presented which describes the shear transfer mechanism between two adjacent slabs. This is based on the shear friction mechanism appropriate to this type of construction. The critical plane is the longitudinal joint between the slabs. An analytical model is derived to predict the shear failure load. The results are within 10 % of the experimental values. The results show that, under working load conditions, the deformation at the interface between the slabs is fully recoverable. Under ultimate load conditions, although some permanent damage occurs by abrasion of the asperities of the cracked matrix, the shear resistance of the joint is in excess of BS 8110 design values by between 1O % and 63 %. Design guidance for the use of hollow-cored slabs as horizontal floor diaphragms is offered. K.S. Elliott, G. Davies and W. Omar

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Author – Elliott, K S;Davies, G;Omar, W

Price – £9

The Structural Engineer

Preservation of structural timbers On 20 August last year, we included a letter from Mr P. A. Campbell of the State of Victoria, Australia, questioning dependence simply on 'prorecess control’ for the treatment of structural timbers (as opposed to direct sampling of degree of penetration), with particular reference to radiata pine. In our column for the following 15 October, correspondents with firms concerned with carrying out such treatments (Mr G. O’Brien of Permacrib, Cheltenham, and Mr G. J. Cavanagh, of Pinex Timber Products, Auckland, NZ) responded, claiming reliability for the procedures concerned. On 18 February this year, we included a letter from Mr M. Connell, of Hickson Timber Products, advocating the benefits of a process-type specification for timber products as against a results-type specification. Mr Campbell has now sent us two further letters on the subject, including also a copy of a letter to him from John Falloon (Minister of Forestry, Wellington, New Zealand). Mr Campbell explains his receipt of the latter following our October correspondence: I wrote to the Director of the NZ Forest Research Institute (NZ FRI) asking for details of its treatment procedures that ensured ‘the full penetration of CCA preservative through the heartwood of radiata pine’. They did not reply, so after 2 months I wrote to their Minister. Verulam

Publish Date - N/A

Author – N/A

Price – £9