The Design of Steel Structures: Questioning the Code

Settlement cracks and cavity wall insulation Andrew Shaw, from Wakefield, W Yorks., writes: My practice investigates inter alia building movement, frequently subsidence-related. I wonder whether the pages of Verulam can be used to air a matter that somewhat perplexes me?

The Bann River Bridge is located on the M1 Motorway in Northern Ireland. The bridge was assessed as part of the National Assessment Programme. Localised durability problems were identified in the areas of the expansion joints, which had failed, allowing deicing salt contamination to parts of the bridge soffit and parts of the substructure. The bridge fniled the loading requirements of the National Assessment Programme, achieving 45% of the required HA loading. The preferred repair and strengthening option involved the repair of the contaminated areas. However concrete replacement repairs could not be applied economically to some of the contaminated areas owing to access problems and the extent of the contamination. Electrochemical repair techniques were therefore regarded us the only viable repair option. The Department of the Environment Roads Service (NI) decided to carry out an electrochemical chloride extraction demonstration on purt of the bridge, to ascertain the effectiveness of the technique. The University of Ulster was commissioned to provide independent assessment of the success of the treatment. During the autumn of 1997 the demonstration was carried out by Martech Services Ltd, and the range of tests performed by the team from the Universily of Ulster proved its success. J.A. Cromie, A.I. Abu-Tair and J.F. Lyness

This paper provides an overview of the design of external, reinforced concrete beam-column joints for monotonic 1oading.There is little consensus over the variables that influence joint behaviour. Existing test data are analysed to determine the influence of factors, including concrete strength, column loading, joint aspect ratio, reinforcement detailing, and joint stirrups, on joint shear strength. The most significant conclusions are that joint shear strength reduces with increasing joint aspect ratio and is increased by joint stirrups, but by less than is commonly assumed. The conclusion that joint shear strength is dependent on joint aspect ratio is at variance with many design recommendations, including EC 8 and ACI/ASCE Committee 352. A new design method is proposed for external beam-column joints based on a comprehensive analysis of all existing test data. The proposed design method is compared with other design methods and is shown to be more realistic. R.L. Vollum and J.B. Newman