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View NCCI for Section 5: Structural analysis

Taken from BS EN 1993-1-1: 2005

Calculation of αcr  (SN004)
This NCCI sets out the basis for the calculation of αcr, the parameter that measures the stability of the frame.
Keywords:
frame stability; second-order effects; sway effects; imperfections; 5.2.1; 5.2.2
Valid until:
Feb 2015
Created by:
SCI
Created on:
Feb 2006
BSI Approval:
Not reviewed by BSI
Column base stiffness for global analysis  (SN045)
After a general discussion on connection classification, this document presents three approaches for determining values of column base stiffness for practical global analysis. The first, empirical, approach provides simple conservative ways of recognising that all practical column base arrangements have some rotational stiffness in practice. The second presents a more detailed analysis of the response of the column base steelwork. The third introduces a method for taking account of the interaction between the foundation and the surrounding soil.
Keywords:
modelling; baseplate; 5.1; 5.1.2; 5.1.3
Valid until:
Jan 2015
Created by:
SCI
Created on:
Apr 2006
BSI Approval:
Not reviewed by BSI
Design of out of plane and transverse restraint systems for portal frames  (SN046)
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.
Keywords:
5.3; 5.3.2; 5.3.3; portals
Valid until:
Jan 2015
Created by:
SCI
Created on:
Apr 2006
BSI Approval:
Not reviewed by BSI
Design of roof trusses  (SN027)
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.
Keywords:
trusses
Valid until:
Jan 2015
Created by:
SCI
Created on:
May 2006
BSI Approval:
Not reviewed by BSI
Design recommendations for hot-finished elliptical hollow sections
This NCCI presents structural design rules, compatible with Eurocode 3, for hot-finished elliptical hollow sections (EHS).
Valid until:
Dec 2015
Created by:
Imperial College
Created on:
Apr 2011
BSI Approval:
Not reviewed by BSI
Frame Stability
Frame Stability (sensitivity to second-order effects) is covered in section 5.2 of BS EN 1993-1-1. This article in New Steel Construction offers an overview of the Eurocode provisions.
Valid until:
Jun 2008
Created by:
NSC
Created on:
Jun 2008
BSI Approval:
Not reviewed by BSI
Modelling of portal frames - elastic analysis  (SN029)
The internal forces and moments in structures are usually calculated using a software programme. For common buildings, designers often prefer using, where relevant, 2D models whose data are easier to input and results are easier to deal with than 3D models. Portal frames can generally be calculated using a 2D model.
Keywords:
portal frame; 5.1; 5.2; 5.2.1; 5.2.1(4)
Valid until:
Jan 2015
Created by:
SCI
Created on:
Dec 2005
BSI Approval:
Not reviewed by BSI
Practical analytical models for portal frames (plastic analysis)  (SN039)
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.
Keywords:
haunch; portal design; 5.2.1; 5.2.2
Valid until:
Jan 2015
Created by:
SCI
Created on:
Mar 2006
BSI Approval:
Not reviewed by BSI
Simple Construction - Concept and Typical Frame Arrangements  (SN020)
Introduces the concept of 'simple construction' for multi-storey buildings. Lateral stability is provided either by stiff cores or by braced bays; global analysis is elastic and joints are nominally pinned.
Valid until:
Jan 2015
Created by:
SCI
Created on:
Oct 2005
BSI Approval:
Not reviewed by BSI
Simple methods for second order effects in portal frames  (SN033)
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.
Valid until:
Jan 2015
Created by:
SCI
Created on:
Mar 2006
BSI Approval:
Not reviewed by BSI
Simplified approaches to the selection of equivalent horizontal forces for the global analysis of braced and unbraced frames  (SN047)
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.
Keywords:
sway; imperfections; frame stability; braced frames; 5.3; 5.3.1; 5.3.2; 5.3.3
Valid until:
Jan 2015
Created by:
SCI
Created on:
Jun 2006
BSI Approval:
Not reviewed by BSI