Source: http://steel-ncci.co.uk/Clauses/BS-EN-1993-1-1-2005
Timestamp: 2019-04-26 00:05:36+00:00

Document:
Resistance tables are available in the Blue Book. The publication covers S275 and S355 steel, and provides section properties, effective section properties, including compression, bending, tension, combined axial load and bending, web bearing and buckling, bolt and weld resistances. This article in New Steel Construction describes the buckling tables.
The buckling length Lcr of a compression member is the length of an otherwise similar member with 'pinned ends' (ends restrained against lateral movement but free to rotate in the plane of buckling) which has the same elastic critical buckling load. In the absence of more accurate information, the theoretical buckling length for elastic critical buckling may conservatively be adopted. An equivalent buckling length may be used to relate the critical load of a member subject to non-uniform loading to that of an otherwise similar member subject to uniform loading. An equivalent buckling length may also be used to relate the critical load of a non-uniform member to that of a uniform member under similar conditions of loading and restraint.
This NCCI sets out the basis for the calculation of αcr, the parameter that measures the stability of the frame.
For the following common cases, torsional and flexural torsional buckling will not give a lower mode than flexural buckling: Doubly symmetric I and H sections (provided that both flanges are restrained at positions of lateral restraint); Hollow sections. However, in some particular cases, the torsional buckling mode or the flexural-torsional buckling mode of an axially loaded member may correspond to a critical load lower than the one corresponding to the flexural buckling mode, especially for open sections. This document gives rules to determine the critical load for such cases.
This NCCI provides the rules for checking the resistance of a beam section notched near the support. The rules are limited to beams of symmetrical I section with one or both flanges notched at the end to facilitate its attachment to a support. The support is usually a beam web but may be the web of a column.
Bracing is required to resist lateral loads, principally wind loads, and the destabilising effects of the imperfections defined in §5.3 of EN 1993-1-1. This bracing must be correctly positioned and have adequate strength and stiffness to justify the assumptions made in the analysis and member checks. It is essential to provide bracing that is both sufficiently strong and sufficiently stiff at all the points that are assumed to be restrained in the design calculations. This is especially true where the inner flange of the portal frame is in compression. Consequently, this document can only give general guidance, not detailed advice. The design criteria given in EN 1993-1-1 are summarised within this document.
The traditional analysis of a truss assumes that all loads are applied in the joints and that all joints in the truss are pinned. Even though this is generally not the case, since the upper and lower chords are normally continuous and the web members are often welded to the chords, it is still a common and acceptable procedure to determine the axial forces in the members. In a situation when the dimensions of the upper chord is very large and the overall depth of the truss is small the moments due to continuous upper chord has to be considered. However, this is rarely the case for roof trusses in industrial buildings that is treated here. Bending moments have to be considered in other cases, which will be explained here.
This NCCI presents structural design rules, compatible with Eurocode 3, for hot-finished elliptical hollow sections (EHS).
In many buildings, the structure and services zones beneath the floors are integrated, i.e. they share the same zone, in order to reduce the height between floors. In such integrated construction, various types of sizes of openings in the webs of the downstand beams are often provided. These openings may be in the form of regular circular openings in cellular beams or isolated rectangular openings in rolled or fabricated beams. This NCCI presents three approaches to the design of beams with openings in the web, in ascending order of refinement and complexity.
The method presented in this NCCI is applicable to steel framed buildings modelled as 'simple' according to EN 1993-1-8 §5.1.1 (2), in which the joints may be assumed not transmit any bending moment from the beams into the columns. The lateral stability of the frame must be provided by a system of bracing or by lift shafts and stair wells. Stability is not provided to any degree by the stiffness of the beam-to-column joints. The columns in this type of structure will primarily be loaded in axial compression, but 'nominal' moments due to the eccentricity of the beam-to-column joints should also be considered in design.
This NCCI presents values for the effective length parameter k and the destabilizing parameter D for beams and cantilevers with or without intermediate lateral restraints, for use with NCCI document SN004.
This NCCI gives guidance on the determination of the effective length of columns in truss and column construction. It also provides rules to calculate the effective length for chord and bracing members in truss and column construction. In a welded lattice girder, chord and bracing members are partially fixed at the nodes, although the static calculation of the internal forces in the members is usually carried out assuming the joints to be pinned. As a consequence of this partial restraint, the value of the system length L may be reduced to obtain the effective buckling length Leff. The rules given below are partly based on EN1993-1-1 Annex BB.1 (Buckling of components in building structures). Detailed information about the structural stability of hollow sections is given in CIDECT publications and the relevant information is summarized in section 3. Rules for special cases taken from DIN 18800 are presented within section 4.
This NCCI gives the expression of the elastic critical moment for doubly symmetric cross-sections. Values of the factors involved in the calculation are given for common cases. For a beam under a uniformly distributed load with end moments or a concentrated load at mid-span with end moments, the values for the factors are given in graphs.
This NCCI provides information for dealing with cantilever beams satisfying the following conditions: The beam has a uniform and doubly symmetrical cross-section; The beam is unrestrained except at support; The beam is torsionally restrained at support; Loads are applied normal to the beam to cause bending about the major axis; The line of action passes through the shear centre (applied at, above or below the shear centre); Favourable effect of the in-plane deflection not accounted for (beam assumed straight in the plane of loading at buckling); Normal force negligible.
This NCCI clarifies the general method presented in §6.3.4 of EN1993-1-1 for verifying out-of-plane buckling of members in portal frames for which the methods given in § 6.3.1 to § 6.3.3 do not apply. The guidance is of particular relevance to non-uniform members or members with particular lateral restraint conditions.
This document provides design graphs for the selection of Universal Beam profiles to be used as secondary beams (non composite beams). These graphs give the maximum span length versus the slab span, for various section ranges and steel grades. The lightest section is used for each range.
This NCCI provides information for dealing with mono-symmetrical uniform members subjected to bending and axial compression satisfying the following conditions: The verification is restricted to the elastic behaviour of the member; The cross-section is symmetrical about the weak axis; The flanges and the web are made of the same steel grade; The loads create bending moments about the strong axis only; The axial load is expected to be applied at the centroid of the cross-section; The web is made of a solid plate of constant thickness; The effects of the fillet welds are not taken into account. Note 1: Such a mono-symmetrical cross-section is susceptible to torsional-flexural buckling. Note 2: This kind of cross-section can be found, for instance, in composite structures where the upper flange of the beam is connected to a composite slab by means of shear connectors. Then, the following calculations are required in the non-composite stage when the fresh concrete acts only as an external load. In this case, the smaller flange is generally mainly in compression. This kind of cross-section can be found also in welded cross-sections when a higher resistance to torsional-flexural buckling is needed for the member. In this case, the smaller flange is generally mainly in tension. Note 3: Cellular beams or beams made of two different hot-rolled profiles are not covered by this NCCI.
Portal frames verified by plastic design are commonly fabricated from hot-rolled I sections. It is generally most economic to have haunches to deepen the rafters at the columns as shown in Figure 1.1 below. It is essential that the section classification is Class 1 at all plastic hinge positions and so it is most common to use Class 1 sections throughout the columns and rafters. It is common to use Class 3 webs and Class 1 flanges for the haunches, provided that in the Class 3 portion of the web either the stress distribution remains elastic or the requirements of EN 1993-1-1 §6.2.2.4 are satisfied and no plastic hinge occurs.
No specific deflection limits are set in Eurocode 1993-1-1. According to EN 1993-1-1, §7.2 and EN 1990 – Annex A1.4, deflection limits should be specified for each project and agreed with the client. The National Annex to EN 1993-1-1 may specify limits for application in individual countries. Where limits are specified they have to be satisfied. Where limits are not specified, the following might be helpful when deciding relevant deflection limits.
Second-order effects occur due to sway of the frame. The sway causes eccentricity of vertical loading that generates second-order moments in the columns. The effects of the deformed geometry (second-order effects) shall be considered if they increase the action effects significantly or modify significantly the structural behaviour, see EN 1993-1-1, section 5.2.
All structures contain imperfections and for steel structures EN 1993-1-1 §5.3 explicitly defines the allowances in structural analysis to cover their effects. The treatment of imperfections in EN1993-1-1 is very general, in order to be applicable to all forms of steel construction. This NCCI provides a simplified approach to these effects that focuses on the appropriate treatment of imperfections for low and medium-rise multi-storey buildings. It proposes horizontal force coefficients that are simple to apply and will be familiar to experienced users of previous national design standards.
This NCCI provides design graphs for the selection of Euronorm H profiles to be used as columns in simple construction. The document may be used to make an initial selection of column sizes for internal and external columns over the full height of a building. The selection is based on estimated axial forces in the columns, the storey height and the chosen steel grade (S235, S275 or S355).
The document may be used to make an initial selection of column sizes for internal and external columns over the full height of a building. The selection is based on estimated axial forces in the columns, the storey height and the chosen steel grade (S235, S275 or S355).
Design of steel to BS EN 1993 need not be complex - and the physics has not changed since BS 449. This article in New Steel Construction suggests how design to the Eurocode may be made simple.
This NCCI provides guidance about the verification of a member subject to torsion. When a member is loaded by transverse forces whose resultant does not pass through the shear centre of the cross-section, the member is subject to stresses due to torsion. These stresses should be combined with those due to bending and shear forces. This NCCI gives some guidance for the verification of a member in torsion. It contains the equations to calculate the stresses due to torsion, and expressions for the calculation of the torsional properties concerning common profiles. References are given for more complex cases. This document deals with uniform members only.
Clause 6.3.1.4 describes torsional and torsional-flexural buckling. In some circumstances, these are the critical modes of buckling, for example for cruciform sections, or asymmetric sections with different restraints to each flange. This article in New Steel Construction describes the phenomena, and gives background to the checks.
This NCCI proposes a new expression for the verification of columns that will avoid the calculation of k factors in Annexes A and B of EN 1993-1-1. For the design of columns in the following situations The column is a hot rolled I or H section, or rectangular hollow section; The cross section is class 1, 2 or 3 under compression; The bending moment diagrams about each axis are linear; The column is restrained laterally in both the y and z directions at each floor but is unrestrained between floors. Relates to: Simple Connections.
No specific deflection limits are set in EN 1993-1-1. Instead it states in §7.2 that the serviceability criteria, including deflection limits, should be specified and agreed with the client for each project. Furthermore, the verification should be based on criteria concerning deformations that affect appearance, comfort of users, functioning of the structure or that cause damage to finishes or non-structural members. In some countries, the National Annex to EN 1993-1-1 specifies the limits. Where limits are specified they have to be observed.
This NCCI gives rules for the consideration of vibrations by simple (and thus conservative) approaches for verification.

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