5. MARCO REFERENCIA
5.2 Marco Conceptual
5.2.5 Índices de Calidad del Agua
Chapter 9
Connections Integration
Introduction
Note For a more comprehensive description of the engineering within Fastrak Connections see: Building Designer Advisory Note – Integrated connection design
Fastrak Connections is design software that allows you to analyse and check a wide range of connections in Fastrak Building Designer. Connections can be,
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simple connections - transfer vertical shear only,•
moment connections - transfer vertical shear and major axis moment•
column splices - continuity splices in simple construction•
tubular connections - principally for use in truss work•
column bases - simple and moment resisting bases including soil bearing pressure and concrete base design.The definition and check of connections is an intrinsic part of Fastrak Building Designer - all data associated with a particular connection is held within the building model. All
connections can be 'opened' within Fastrak Building Designer where they can be modified and refined before saving the data back to the model. Alternatively one or many connections can be passed out to Fastrak Connections where, again, they can be modified and refined and then passed back to Fastrak Building Designer. Note that certain data cannot be modified since it would affect other parts of the building model e.g. sections size of the connecting members. As a further alternative Fastrak Connections can be run as a 'stand alone' application and the connection data entered in isolation.
Whilst all data is held in the building model, the source of such data is several fold. This includes,
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attributes - certain data can be set to be used during the definition of the connections e.g. beam to beam simple connections are to be fin plates,•
derived data - the building model already holds such items as the section size and grade of the members that are to be connected and the design forces,•
default data - when the connections within the building model are set up by Fastrak, intelligent defaults are used that can establish a part or full solution to the connection configuration,•
added data - any individual connection can be edited to improve or add to the connection configuration e.g. stiffeners can be added to moment connections.Unless otherwise stated all calculations are in accordance with the relevant sections of BS 5950-1: 2000 and the design models for connections draw heavily on the series of publications from the Steel Construction Institute that cover the design of connections - the so-called 'Green Books'.
Building Designer Documentation page 60 Chapter 9 : Connections Integration
Simple Connections
Simple connections are by definition pinned connections and transfer vertical shear only. Fastrak will attempt to configure a simple connection at the end of any Simple Beam, Composite Beam or General beam that is pinned. The word "attempt" is used since there are some configurations of member and connection that are beyond the scope of the current release e.g. if the supporting beam is not an I-section or the supported beam frames in at a steep angle.
Simple connections can be end plates, fin plates and (double) angle cleats. During definition of your building model a set of Connections Attributes can be established such that in preference, for example, beam to column web connections are end plates and are designed for the
minimum tie force requirement of 75 kN. The defaults for these attributes are,
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beam to beam - fin plate with one line of bolts,•
beam to column flange - end plate,•
beam to column web - end plate,•
beam to hollow section column - fin plate.When a particular type of connection is established by Fastrak in the building model e.g. fin plate for beam to beam connections, the default settings for bolt size and number, fin plate thickness etc. are such that the subsequent check of this connection should under normal circumstances give a Pass. This is because simple connections are more about detailing than design i.e. a well detailed simple connection will usually be adequate in design. This has been underpinned in Fastrak by careful selection of the defaults to ensure that the 'Recommended Details' and standard connections contained in the 'Green Book' on simple connections are followed.
This all means that as a designer, once you have selected the type of connecting element for a particular situation e.g. fin plate for beam to beam connections, Fastrak will provide robust and well detailed simple connections for the majority of the building. It is likely then that only a few connections will not be adequate. These can be displayed to you on the main building graphic and you can then interactively adjust the connection type or configuration to establish an adequate detail. Examples might be a heavily loaded beam that might require two lines of bolts or a shallow beam where the default bolt pitch has to be decreased in order to increase the number of bolts.
General Limitations
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If a simple connection exists on one or more faces and a moment connection exists on another face, they will be treated as separate connections - no influence on the strength or detailing will be taken into account.•
In a double sided connection, either side of the web you are limited to the same connection typeeg. angle cleat to angle cleat, end plate to end plate or fin plate to fin plate.
The one exception to this is if you have an angle cleat or an end plate on one side you are permitted a fin plate on the other.
Chapter 9 : Connections Integration Building Designer Documentation page 61
Note For a more comprehensive list of assumptions and limitations you are directed to : Building Designer Advisory Note – Integrated connection design
Moment Connections
Moment connections are by definition able to transfer moment as well as vertical shear. The design is also able to deal with axial force in the beam member if present. Fastrak will attempt to configure a moment connection at the end of any General Beam that has a 'Moment Connection' or is 'Fully Fixed' at the appropriate end. The word "attempt" is used since there are some configurations of member and connection that are beyond the scope of the current release e.g. if the supporting column is not an I or H-section or the supported beam frames into another beam.
Moment connections can be established at beam to I- and H-section column flanges, and at beam to beam on end e.g. apex type connections. All are formed using bolted end plates in the current release. Beam to column moment connections can be single- or double-sided.
There are no Connections Attributes associated with moment connections in Fastrak Building Designer. Hence, during definition of your building model only the essential data and a number of basic defaults are set up for each moment connection. Essential data includes section size of the members joined and their design forces. Basic defaults include such items as one pair of M20 Grade 8.8 bolts top and bottom of the connection with 20 mm thick end plates. It is necessary therefore for you to 'open' each individual connection and enter such data as,
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"additional tension and shear bolts,•
"extensions to the end plate,•
"stiffeners,•
"haunches.Obviously at the same time you can also adjust the default values e.g. change from 20 mm thick end plate to 25 mm thick.
You may prefer to adjust the moment connections 'inside' Fastrak Building Designer or you can send one or more connections to the 'stand-alone' application. In either case the data you have added or modified is saved in Fastrak Building Designer. You can see whether your connection configuration looks sensible by right clicking on the connection in the
Connections window - this displays a 3D graphic of the connection in its own window. You can adjust each of the connections individually and design them as you proceed or once you are content with the layout of all of them you can click the Check Connections icon. You can use the Show/Alter State icon to view which have passed and which have not.
Fastrak checks only the strength of moment connections. Stiffness, ductility and rotation capacity can be important characteristics in some situations. Your attention is drawn to Clause 2.4.2.5 of BS 5950-1: 2000 and Section 2.5 of the Green Book on moment connections.
Note For a more comprehensive engineering description of moment connections you are directed to: Building Designer Advisory Note – Integrated connection design
Building Designer Documentation page 62 Chapter 10 : Issues and Limitations
Chapter 10
Issues and Limitations
Foundation loads
There can be some differences in the base load values between the Building Designer summary table and the individual column designs (General Column and Simple Column). This occurs if there is bracing coming in at the column base – the brace loading at the base of the column is not handled in the standalone applications – it is irrelevant to the column design. The foundation values in the Building Designer summary table are correct for foundation design these should be used and not the standalone values.
Vertical cross bracing
Foundation shear and vertical load
When vertical cross bracings are modelled, only one member is considered active, irrespective of lateral load direction. This means that at the base, only one of the two foundations has the correct shear and vertical load. If the load direction is able to be reversed (and hence the other brace should be active) then you need to allow for the correct shear and vertical load in the corresponding foundation loads.
Column axial load
When vertical cross bracings are modelled, only one member is considered active, irrespective of lateral load direction. The axial load in a column is only included into the column where the bracing is connected. This means that if the lateral load is able to reverse, one column of a braced pair will have some axial load that is not accounted for in the column design. The diagram below illustrates this. In the design model, the left-hand column will be designed without the axial compression that is actually present when the correct brace is active in tension only. Therefore great care must be taken when selecting active/inactive bracing members, and in cases where bracing loads are significant, additional checks on columns may be necessary. T T C T C
Chapter 10 : Issues and Limitations Building Designer Documentation page 63
Notional Horizontal Force Load Calculations
Gravity loads carried by braces not accounted for in NHF load calculations
Any gravity load carried between floors in a brace element is not picked up in the calculation of NHF forces - in a majority of structures this is not an issue as braces tend to carry very little gravity load. However just occasionally they can be used in a model where they do carry gravity load - see brace supporting cantilever beam/slab on the right in the figure below. (actually in this case the user should use a general beam and not a brace and then the calculation of NHF forces would be correct).
A quick look at the load case summaries in the design tree will advise the user of the relative size of the error in the NHF calculation: NHF = 0.005 x grav load.
Axial load in discontinuous columns used twice in NHF load calculations
If a structure has a transfer beam carrying a column, or if wall mid pier models do not align vertically in a wall (due to openings etc) then the NHFs for the axial load in the supported column are used twice in the NHF calc - once when they get onto the supported column and a second time when picked up in the level of the transfer beam. This is actually conservative as too much NHF is applied to the structure.
A quick look at the load case summaries in the design tree will advise the user of the relative size of the error in the NHF calculation: NHF = 0.005 x grav load