Chapter 37
Miscellaneous
Roof truss on column cap plate – If you place a parallel chord truss on top of a column and the side member is vertical, then the force in the side member is applied as an axial load to the top of the column (as expected). However, if the side member is not vertical then the load is applied as a reaction to one of the faces of the column (assuming an eccentricity of 100 mm from the face of the column web or flange as appropriate). The side to which the load is applied is determined by towards which face the side member leans. In both cases the vertical force at the end of the chord is applied as a reaction to the appropriate face, again with the standard eccentricity of 100mm from the face of the web or flange.
Tubular truss design – Hollow sections are very efficient in resisting both tension and compression – the latter particularly in comparison to other section types. It is all too easy therefore to construct a tubular truss in which the members are very efficient – small size and thin-walled. Later, it may be found difficult to justify the connections between such minimum weight members and stiffening may be required. Since most of the work and hence cost is in the preparation and welding of the member ends then attempting to minimise the section size can be counter productive.
Mixture of section types – A wide range of sections is available for both internals and chords. There is no restriction on the mixture of section types. Hence, for example you could use a different section type for each internal (!). More importantly you can select section types for internals and chords that would not be practical to connect. This could mean that there are no design models for such connections and/or they may very difficult (expensive) to fabricate. The choice of appropriate section sizes and types is entirely yours.
Chapter 38 : Introduction Wind Modeller Documentation page 139
Wind Modeller Engineer’s Handbook
Chapter 38
Introduction
This Engineer's Handbook describes Fastrak Wind Modeller. This is design software which allows you to load a Fastrak Building Designer model for wind in accordance with
BS6399-2:1997(Ref. 1). The wind loading assessment is performed on the walls and roofs which
are defined in your building model. The resulting wind loads are distributed back to the members for structural analysis and design.
You can use Fastrak Wind Modeller:
•
to determine site and effective wind speeds (standard or directional),•
to determine the zones of wind pressure on walls and roofs,•
to determine standard values of Cpe for each zone,•
to determine wind pressures on each zone,•
to determine wind loads and load cases for your structure.Unless explicitly stated all calculations in Fastrak Wind Modeller are in accordance with the relevant sections of BS 6399-2:1997 incorporating Amendment 1 and corrigendum No. 1. It is essential that you have a copy of this code with you while assessing wind on any structure. In addition, you may find the following books useful to enhance your understanding of wind loading and the software:
•
Wind Loading - a practical guide to BS 6399-2(Ref. 2),•
Wind and Loads on buildings: Guide to Evaluating Design Wind Loads to BS6399-2:1997(Ref. 3).Unless explicitly noted otherwise, all clauses, figures and tables referred to in this document are from BS6399-2:1997.
Fastrak Wind Modeller is a very powerful tool which has been developed to aid engineers in their assessment of wind loads on buildings. You will find that the determination of wind speeds, zones, pressures… is rigorous but the final wind loads adopted are your responsibility. Your attention is particularly drawn to BS6399-2:1997 – Clause 1.1. For building shapes which are not covered by the Standard you will need to seek specialist advice.
Wind Modeller Documentation page 140 Chapter 39 : Scope
Chapter 39
Scope
Fastrak Wind Modeller works from a Fastrak Building Designer model which has been
“clothed” in walls and roofs. Wind is “applied” intelligently to this building envelope within the scope below and the limitations clearly laid out in the next section.
In the main, BS6399-2:1997 addresses rectilinear buildings. In order to develop a tool for engineers, we have extended this capability to address non-rectilinear buildings using the standard method. For more information, please refer to reference 2 (section 2.5.3.2.4, page 82 and 2.5.4.3.3 pages 89-90).
It is assumed that the wind loads are developed to assess the overall stability of the structure and for member design. The wind loads have not been specifically developed for the design of cladding and fixings.
The scope of Fastrak Wind Modeller encompasses:
•
Enveloping the building with walls and roofs is undertaken in Fastrak Building Designer in the normal manner. There is only limited validation of the envelope defined (for example connected walls must have consistent normal directions). The onus is on you to model the building shape as completely and as accurately as you determine necessary.•
Choice of method:•
BS6399-2:1997 - Standard Method - Standard effective wind speeds with standard pressure coefficients,•
BS6399-2:1997 – Hybrid Method - Directional effective wind speeds with standard pressure coefficients.•
Basic Wind Speed or Dynamic pressure is determined using BREVe Active X Control(Ref. 4).•
Having defined walls and roofs (defaults are standard wall, flat or monopitch roof depending on the slope), you are able to specify the type in more detail e.g. multi-bay, monopitch / duopitch etc.).•
The main wind parameters, are calculated for you but conservatively, (for example Crosswind Breadth, B, is determined for the enclosing rectangle of the whole building). Wherever possible other attributes are determined conservatively, but you are able to override the values should you need to.•
Given the above, zoning is semi-automatic, (not attempted for roofs with more than 4 sides which are defaulted to single conservative coefficient), with full graphical feedback. Provision is made for you to modify the zoning. For example you can define a manual zone layout, you can override the coefficients… …•
Load decomposition is fully automatic where valid, (walls and roofs need to be fully supported in the direction of span). Please note that the decomposition for walls results in nodal loads rather than UDLs / VDLs.Fastrak Wind Modeller has been developed in order to provide you with a comprehensive design tool which can assess and apply wind loading to your Fastrak Building Designer model in advance of analysis and design.
Chapter 39 : Scope Wind Modeller Documentation page 141
Fastrak Wind Modeller is a very flexible tool that can, should you wish, be used purely for wind assessment – by setting up a model of consisting only of walls and roofs (no members) Fastrak