5. MARCO REFERENCIA
5.2 Marco Conceptual
5.2.7 Macroinvertebrados acuáticos
Chapter 11
Sign Conventions
The individual objects in Building Designer use the same sign conventions as for the individual object designs. These are clearly indicated on the various design object’s analysis result graphics.
Building Designer always takes account of an object’s orientation when displaying analysis results for objects in your model, rather than showing a single object’s analysis results. This means that to correlate the two sets of results you need to know which is the start and which the end of the beams in your model, and that you also need to know which is Face A of the columns.
If you switch the option to show the Element Direction on, then Building Designer shows an arrow on all beams, columns and braces. This arrow points from the start to the end of beams and braces, and up columns along Face A.
General beam sign conventions
The following diagrams show the sign conventions used for general beams, and are provided to help you understand the details that Building Designer presents.
End 2 End 1
Action Reaction Action Reaction
Chapter 11 : Sign Conventions Building Designer Documentation page 65
Simple beam sign conventions
The following diagrams show the sign conventions used for simple beams, and are provided to help you understand the details that Building Designer presents.
Beam end moments
End 2 End 1 Action Reaction Action Reaction End 2 End 1 Action Reaction Action Reaction
Building Designer Documentation page 66 Chapter 11 : Sign Conventions
General column foundation sign conventions
The following diagrams show the sign conventions used for general columns, and are provided to help you understand the foundation loads that Building Designer presents.
Vertical force at base
Action Reaction
Face A Face C
Major axis shear at base
ActionReaction
Face B Face D
Minor axis shear at base
Action Reaction
Chapter 11 : Sign Conventions Building Designer Documentation page 67
Major axis moment at base
Face A Face C
Compression side
Action Reaction
Minor axis moment at base
Face B Face DAction Reaction Compression side
Building Designer Documentation page 68 Chapter 11 : Sign Conventions
Building Designer shows Foundation Loads in its graphical windows, and not base reactions. However the Base Reactions given in reports, and in the export to Excel are the reactions and not foundation loads.
Simple column foundation sign conventions
The following diagrams show the sign conventions used for simple columns, and are provided to help you understand the foundation loads that Building Designer presents.
Building Designer shows Foundation Loads in its graphical windows, and not base reactions. However the Base Reactions given in reports, and in the export to Excel are the reactions and not foundation loads.
Vertical force at base
Action ReactionFace A Face C
Major axis shear at base
ActionReaction
Face B Face D
Minor axis shear at base
ActionChapter 11 : Sign Conventions Building Designer Documentation page 69
Supplementary supports sign conventions
The following diagrams show the sign conventions used for supplementary supports, and are provided to help you understand the foundation loads that Building Designer presents.
Global Axis System
X
Y
Z
Vertical force at support
Action ReactionForce in X direction
Action ReactionForce in Y direction
Action ReactionMoment about X axis
ActionReaction
Moment about Y axis
ActionBuilding Designer Documentation page 70 Chapter 11 : Sign Conventions
Column orientation effects
The foundation loads that Building Designer presents are based on those present in the column. These obviously depend on the column orientation. The diagram below shows the effects on the column action and reaction base shears as the column is rotated.
For General Columns there is an identical effect for moments1.
Effect of column orientation
Face A Face A Face B Face B Face C Face C Orientation 0° Orientation 90° Face D Face D
Action major Reaction major
Action minor Reaction minor Action minor Reaction minor
Action major Reaction major
Designing for Second-order Effects : Chapter 12 : Summary Advisory Note for Fastrak Building Designer page 71
Building Designer Advisory Note – Designing for Second-order Effects
Chapter 12
Summary
With the advent of BS 5950-1: 2000(Ref. 1)the treatment of second-order effects particularly in
relation to the susceptibility of buildings to ‘sway’ has come to the fore. Many buildings, even conventionally braced structures, have been shown to be ‘sway sensitive’ when the clarified rules of BS 5950-1: 2000 are applied.
In addition, the layout of multi-storey structures has changed over recent years,
•
longer spans,•
shallower construction (affecting connection depth),•
architectural preference for little or no bracing,•
minimization of heavy masonry walls that can be assumed permanent.All of these has lead to more reliance on the steel framing to resist lateral loads with much less assistance from non-primary elements that have traditionally not been taken into account and yet nevertheless significantly contributed to providing overall stability.
With all these changes, the likelihood of having to take account of second-order effects has increased significantly. There are codified methods for taking these into account based on modification of first-order analysis (linear elastic) – the ‘Amplified Forces Method’ being the preferred one. There are a number of implementations of rigorous second-order analysis but these are not a panacea(Ref. 2). For most buildings it is probably better not to allow the structure
to have such low sway stiffness (λcr < 4) for such techniques to be obligatory. The clearer and equally effective simple methods given in BS 5950-1: 2000 are entirely adequate for the majority of buildings.
The majority of this document is devoted to an explanation of the automated process of applying the ‘Amplified Forces Method’ that is included in Fastrak Building Designer1. This process is guided by just three choices.
The document first provides some reminders of the terminology with which you need to be familiar when considering second-order effects. It leads you through making the choice of whether to carry out first-order or second-order analysis and if so which formula you should adopt to calculate the ‘amplifier’ that is an intrinsic part of the ‘Amplified Forces Method’. There is also information on the ‘best’ amplification factor to use and to which of the loads this should be applied. The impact of the method on member design, base reactions, beam end reactions etc. is covered.
Footnotes
1. Portal frames have their own methods to allow for second-order effects and a comprehensive range of these is included in Fastrak Portal Frame.
Advisory Note for Fastrak Building Designer page 72 Designing for Second-order Effects : Chapter 12 : Summary
The default settings have been sensibly chosen so that most times you will not need to make any changes but options are given so that you can make rational decisions about your particular building based on your engineering judgement. The whole process is automated, simple to understand and nothing is ‘hidden’ from you.