Discussion on The London Ark, Hammersmith by Mr. R.H. Jackson and Mr B. Leidner

Self-certification of structural design Under the heading ‘Serving and protecting the profession’, our column for 7 December last included an invitation from Allan Lowe for information on the progression, since its introduction in Scotland, of ‘self-certification’. Mr A. C. Aiken, of Glasgow, ofsers his experience: Mr Lowe asks for feedback on self-certification of structural design in Scotland. Well, when the hated Forms 4A and 4B were first introduced a year ago, there were screams of protest. Since then there has been almost complete silence on the subject. Verulam

The influence of compressive axial load on the shear capacity of reinforced concrete elements is investigated, using results from tests on 15 external reinforced concrete beam-column connection specimens. Shear stresses in the connection zones of these specimens are compared with values predicted by the design equations in BS 8110 and observations made concerning the applicability of these equations. The revised eqns. (6a) and (6b) in BS 8110 are presented and recommendations made for assessing shear stresses at initial joint cracking and specimen failure. Bearing stresses within bends in the reinforcement in the connection zones are also evaluated and compared with the recommendations of BS 811O.

The actual flexibility of nominally ‘rigid’ connections and the actual stiffness of nominally ‘pinned’ bases can have a major effect on the accuracy of prediction of structural deflections under service load conditions. Connection flexibility tends to increase deflections, but base stiffness usually will reduce deflections. Both can be important factors in the acceptability of calculated predictions, particularly for large-span, lowrise portal frame structures for which end wall and roof sheeting and bracing stiffness play a minor role in providing lateral stiffness. Professor R.E. Melchers and G. Maas, BE