Author: C. O'Regan (AECOM)
3 September 2018
First published: 3 September 2018
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C. O'Regan (AECOM)
This Technical Guidance Note addresses the design of timber elements that are unrestrained against lateral torsional buckling. It explains how such beams are analysed and designed. The impact of notching the supports of beams is also considered with respect to the shear capacity of the beam.
For clarity and brevity, this note only covers solid and glued laminated (glulam) timber elements; compound and composite beams, such as flitch beams, are not considered. The connections within timber frame assemblies will be addressed in a future note.
Readers should also be aware that this note forms part of a trio of Technical Guidance Notes leading to the design of bespoke timber trusses – assemblies made from unrestrained timber beams and posts. Notes on the design of timber posts and bespoke timber trusses will follow later in the series.
This Technical Guidance Note concentrates on the design of reinforced concrete columns to BS EN 1992-1-1 – Eurocode 2: Design of Concrete Structures – Part 1-1: General Rules for Buildings. It covers the design of columns of all cross section proﬁles, which are typically square, rectangular and circular.
Portal frames are a simple and very common type of framed (or skeleton) structure. Steel portal frames, in particular, are a cost-effective structural system to support building envelopes (such as warehouses and shopping complexes) requiring large column-free spaces. In general, the loads and consequent deformations for these frames are in the plane of the structure, and hence these are a 2D (or plane) frame structure. Due to the practical requirement of having a clear space between the supports of a portal frame, providing in-plane bracing is generally not feasible. Consequently, these frames undergo larger deflections and are prone to sway laterally, even under the vertical loads. The concept of sway frames is addressed in more detail in Technical Guidance Note No. 10 (Level 1) Principles of lateral stability. Thus, in spite of the inherent simplicity of portal frames, many aspects of their analysis, design and detailing require careful consideration.
Portal frames can be made from concrete, timber and even glass but the vast majority, in the UK certainly, are constructed from steel. This Technical Guidance Note gives an introduction to steel portal frames and their preliminary analysis. Steel portal frames usually have pinned bases and moment connections at the column/rafter interface and mid-span apex splice in the rafter. Although there are other forms of portal frame (described in Elastic Design of Single- Span Steel Portal Frame Buildings to Eurocode 3), for the sake of brevity and clarity this note will be dedicated to this particular form.
(This article was updated in October 2016 to reflect errata issued since its original publication.)