The behaviour of beam-column joints is discussed in the context of current design procedures for reinforced concrete ductile frames subjected to severe earthquake motions. As plastic hinges are expected to develop in beams, the beamcolumn joints must be capable of transferring large shear forces across the joint cores. The mechanisms of shear resistance of joint cores comprise a diagonal concrete strut mechanism and a truss mechanism. A considerable amount of joint core shear reinforcement is necessary to sustain the truss mechanism if bond failure of longitudinal bars is avoided. The diameter of longitudinal beam reinforcement in joint cores needs to be restricted to ensure adequate anchorage in joint cores. The significant differences in detailing requirements of beam-column joints that exist between various concrete design Codes led to an international collaborative research project involving the testing of full-scale beam-column-slab joint subassemblages under quasi-static cyclic loading. The three subassemblages designed to New Zealand practice performed very well. P.C. Cheung, Professor T. Paulay and Professor R. Park
A study of the strength development of concrete made with blends of rapid-hardening Portland cement (RHPC) and pulverised-fuel ash (PFA) is described and compared with ordinary Portland cement (OPC) and OPC/PFA concretes. It is shown that RHPC/PFA blends can be used as alternatives to OPC in concrete construction, without incurring any loss of early strength, particularly with the limited moist curing that is normally applied on site, and with distinct economic advantages. While the study was in the main concerned with RHPC/PFA blends with up to 25 % PFA, test results from a parallel study presently in progress indicate that the use of blends with PFA content up to 45 % show similar benefits. Professor R.K. Dhir, E.A. Byars and S.A.A. Amir-Latifi
Partial underpinning of semidetached houses In our column for February, Mr V. T. Brierley invited comments on a situation in which the local authority was threatening action against a client for contravention of Building Regulation requirement A.1 para. (b) because her house-one of a semidetached pair on a raft foundation - had been repaired by being piled. A number of readers have responded, including Eric Skilton of Waltham Abbey, Essex: The question of foundation repair to half of a pair of semidetached houses is one which has, in the past, raised a wealth of issues and opinions. The DOE determination to which Mr Brierley refers was by no means the first on this issue; they invariably stem from an objection from the Building Control Department under Regulation A.l (1) (b). Verulam