The work presented in this study is concerned with the development of a knowledge-based system for the design of hybrid structural steelwork connections. hybrid connections are connections that combine the use of different types of fastener, namely bolts and welds. an important research programme into the behaviour of hybrid connection was carried out by the structural assessment group, umist. although this research programme produced a large body of expertise, a direct application of the research findings remains difficult for the non expert. a knowledge based system, called hycon, is proposed to serve as a vehicle for the transfer of this expertise and assist structural designers in the design of hybrid connections. in particular, the program allows one to investigate the feasibility of using hybrid action to strengthen existing bolted connections. the system is also intended to be used by researchers from the hybrid connections research programme as a research tool and allow them to access and easily modify knowledge encoded in the system. a novel knowledge-based system design approach is proposed for the development of the system. it combines in the framework of an object-oriented design the use of two programming techniques, namely, procedural programming and rule-based programming. the system was implemented using the golden common lisp programming environment and goldworks il, a development tool for knowledge-based systems. the system architecture and functionality are described in this work. the system validation is presented and results obtained by the system are discussed and compared with existing experimental and theoretical results concerning the different types of hybrid connection considered in the hybrid connections research programme.