Steel Buildings in Europe

Part 4: Detailed Design of Portal Frames 4 - 1 1 INTRODUCTION Steel portal frames are very efficient and economical when used for single-storey buildings, provided that the design details are cost effective and the design parameters and assumptions are well chosen. In countries where this technology is highly developed, the steel portal frame is the dominant form of structure for single-storey industrial and commercial buildings. It has become the most common structural form in pitched roof buildings, because of its economy and versatility for a wide range of spans. Where guidance is given in detail elsewhere, established publications are referred to, with a brief explanation and review of their contents. Cross-reference is made to the relevant clauses of EN 1993-1-1 [1] . 1.1 Scope This publication guides the designer through all the steps involved in the detailed design of portal frames to EN 1993-1-1, taking due account of the role of computer analysis with commercially available software. It is recognised that the most economic design will be achieved using bespoke software. Nevertheless this document provides guidance on the manual methods used for initial design and the approaches used in software. The importance of appropriate design details is emphasised, with good practice illustrated. This publication does not address portal frames with ties between eaves. These forms of portal frame are relatively rare. The ties modify the distribution of bending moments substantially and increase the axial force in the rafter dramatically. Second order software must be used for the design of portal frames with ties at eaves level. An introduction to single-storey structures, including portal frames, is given in a complementary publication Single-storey steel buildings. Part 2: Concept design [2] . 1.2 Computer-aided design Although portal frames may be analysed by manual methods and members verified by manual methods, software is recommended for greatest structural efficiency. Bespoke software for portal frame design is widely available, which will:  undertake elastic-plastic analysis  allow for second order effects  verify members  verify connections. Generally, a number of different load combinations will have to be considered during the design of a portal frame. Software that verifies the members for all load combinations will shorten the design process considerably.