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The Base Plate connection is used to design column base plate type connections for open I-sections and rectangular, square or circular hollow sections. It is also possible to be design simple (non-moment) base plate connections, by setting the applied moment to zero. This connection is also capable of being used to design bases in axial uplift with symmetrical bolt arrangements.
A typical layout of the Base Plate Connection is shown below.
The inputs for the Base-plate type connection are controlled by the input area of the connection property grid. For a stand-alone connection, the forces and geometry are controlled fully by the connection property grid, whereas for a linked connection (linked to a Masterframe model) the section sizes, forces and geometry will be read from the Masterframe model.
The General area displays the titles of the current connection and current loadcase. title for the connection can be entered in the Title by selecting the input area and typing in the required title. The title will also display in the Connection design screen and in the connection design output. The load case title can be similarly input by selecting the input area and entering the required text. The load case title will display in the design output screen and in the load case selector drop down.
For a standalone connection design, the required forces are input in the Force area of the connection property grid. The required forces inputs are the bending moment, shear and axial force in the load case under consideration. Multiple force combinations can be considered by entering multiple load cases. For a connection linked to a Masterframe model, the forces are taken from the Masterframe analysis for all the Ultimate Limit State load cases in the Masterframe model.
The default layout for the Forces area is shown below. In the case of a stand alone connection the default forces values are zero. A linked model will default to the first ultimate limit state load case.
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Moment - the major axis bending moment in the connection in the current loadcase
Shear - the horizontal shear on the connection
Axial - the vertical axial force on the connection
Fire case - is the current load case a fire boundary condition
Forces from support - for a linked Masterframe connection, controls whether the forces used are member forces or support reactions
Print Case - sets the current load case to print or excludes it from printing
Note: In a linked connection design, for columns where other members connect to the base node, for example in braced bays, the member forces will only be the forces in the column member. Thus the support reactions, which will be the total resolved forces, will include the forces from the other members. Which forces should be used will depend on the connection geometry as per the on site construction and needs to be determined by the design engineer.
The column properties are allows the column section to be selected for standalone base pale connections, the column section being taken from the Masterframe model in the case of a linked connection. When the base plate design brief is first set-up for a standalone connection, the default column section is set as a 457x191UB74.
To set a column section, the Column Properties area is expanded by clicking on the arrow to the left of the Column row. The layout of the expanded Column area is shown below.
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Each property can be amended by selecting each row. For the Steel Grade, Section Type and Section rows, this will activate a drop down indicator, which can be selected to expand the drop down to allow the required property to be selected. The cell depth input controls the beam depth for castellated or cellular beams. Using the mouse pointer, clicking in the right hand part of this row will allow the cellular beam depth by be manually input. This option is not used for Column Sections. User defined steel section can be added from the Section Type drop down option, by selecting the "BuiltUp & ASB" option. This will display additional rows. To input the dimensions of a user-defined section, select the Built-UP option and input the required dimensions in the addition rows.
When the Built-up option is selected, the Column Properties area will expand to include the built-up section inputs. These are shown below.
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Note: Base plate design cannot be carried out for asymmetric sections. Thus the top and bottom flanges must be identical in both width and thickness.
The base plate area provides parameters to control the dimensions of the base plate. A typical layout of the Base Plate area is shown below.
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Breadth - the width of the base plate. A value give a default breadth based on the attached section dimensions
Length - the base plate length. A value of zero gives a default length based on the column section
Thickness - the base plate thickness. A value of zero uses a default thickness value
Left Projection - the distance from the left hand edge of the left hand flange from the left hand side of the baseplate. A value of zero results in the column being centrally located on the base plate
Flange Weld - the weld thickness for the welds to the flange. A value of zero will result in a default weld size
Web Weld - the weld thickness for the web. A value of zero will result in a default weld size
Plate Grade - defines the grade of the base plate
Col-Plate Bearing - defines the bearing condition of the column to base plate connection in the compression zone. If direct bearing, no check is carried out on the weld in the compression zone as the column is assumed to bear directly on the base plate
The bolt details area provide control over the bolt grade, diameter, bolt spacings/centres and the numbers of bolts within a base plate. Using this area it is possible to define multiple bolts per row and define up to two rows per left and right side of the connection.
The default layout of the Bolt Details area is shown below.
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The Bolt properties such as bolt grade, bolt diameter and type can be set by expanding the bolt details area. This is done by clicking on the arrow to the left of the Bolt Details row. The expanded bolt details area is shown below.
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The number of bolts in the outer and inner, or "exterior" and "interior" row of bolts, on the left hand side of the base plate are defined under the Left side bolts. This area can be expanded by clicking on the arrow to the left of the Left Side row. The default layout of the expanded area is shown below.
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The Exterior Bolts area controls the leftmost row of bolts on the left hand side while the Interior bolts controls the interior row of bolts. Interior bolts do not need to be "interior" to the column section, so both the Exterior and Interior rows of bolts can lie outside the column section. The Exterior and Interior refer to the arrangement of the bolts relative to the baseplate. The interior bolts need not be located further to the right than the exterior bolts, the software determine the bolt forces on the actual bolt positions.
To set up the Exterior Bolts, expand the Exterior bolts row. The layout of the expanded Left Side Exterior and Interior areas are shown below.
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Number of bolts - the number of bolts in the bolt column
Edge Distance - the distance to the centre line of the bolt column from edge of the base plate
Inner Cross c/c - the spacing of the inner bolts in the bolt column
Outer Cross c/c - the spacing of the outer bolts in the bolt column
Where values of zero are input for any of the edge distance or bolt centre inputs, the software will use a default value based on geometric rules based on the bolt diameters. Where only two bolts are specified, either the inner cross or outer cross can be used to determine the bolt spacings.
Where a CHS column has been specified, an additional input appears in the Bolt Details area. This additional option allows pitch circle diameter bolts to be specified. By setting the PDC Bolt input the "Yes" the Bolt Details inputs modify, as shown below.
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The PCD option will place the bolts in a circular arrangement around the column. The number of bolts is controlled by the CHS Bolt Number input. The Pitch Circle Diameter controls the radius the bolts are arranged on.
When bolts have been specified as a Pitch Circle Diameter arrangement, it is then possible to use a circular baseplate rather than a rectangular or square baseplate. This is done by setting the Breadth and Length inputs in the Base Plate area to zero. The circular baseplate is then sized based on the pitch of the bolts and the minimum required edge distance of the bolts which is based on the bolt diameter
The Stiffeners input area provides options to include addition base plate stiffeners. Stiffeners can be added to reduce the bending in the base plate in both the tension and compression zones. Stiffeners can be added for both rectangular and circular base plates.
The layout of the Stiffeners area is shown below.
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Stiffener type - controls the arrangement of the stiffeners to be added. The drop down contains different options depending on the base plate shape.
Thickness - the thickness of the stiffener plates. All stiffeners are taken to be the same thickness.
Support height - the height of the stiffener plates at the junction with the column member (the inside edge)
End Height - the height of the stiffener plate at the outer edge
Stiffener welds - notes the currently selected weld size.
Flange-Toe Weld - notes the currently selected weld size for the toe of the flange to the stiffener interface
Both the Stiffener Welds and Flange-Toe weld areas can be expanded by clicking on the arrow at the left of the row. This gives additional options for setting the weld for the selected area. The additional rows displayed are controlled by the Weld settings in the Design Options area - see the Options Menu section for more details on the available options.
With Partial Penetration butt welds selected in the Weld Type, the expanded options are as shown below.
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With Deep Penetration fillet welds selected, the expanded options are as follows.
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When stiffeners are added to a connection, the graphics display updates automatically to indicate the stiffener arrangement and the design calculations also update to include the additional calculations relevant to the stiffener arrangement selected.
When stiffeners are added, these are extended from the section, in the selected arrangement, to the edge of the baseplate. It is not possible to add stiffeners which only project part way over the end plate, since it is then not possible to determine the distribution of forces in the baseplate or in the stiffeners.
The Washers area provides options to control the dimensions of the washer plates which anchor the holding down bolts and also provides control over the size of the void former around the bolt. The layout of the Washers area is shown below.
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Thickness - the thickness of the washer plate
Width - the washer plate size. The input length in the length of one side. Washer plates are always taken to be square, with a single washer per bolt
Void Former Width - the diameter of the void former around the bolt.
The following link is to a technical note on the method used in MasterSeries to design and check the embedment required for a washer plate in a concrete base design:- Base Plate Washer Embedment and Bending Design.
The Concrete area of the connections property grid provides options to control the concrete elements of the base plate design. The parameters include the concrete and grout grades, the anchorage length of the cast in bolts and also the area and cover to any top reinforcement. These parameters control the compression zone of the base plate, the tension capacity of the holding down bolts and the pullout capacity of the bolts in the tension zone by controlling the pull out cones and/or the punching perimeter of the tension zone.
The layout of the Concrete area is shown below.
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Concrete Cube - concrete cube strength
Grout Strength - grout cube strength
Grout Gap - gap between the underside of the base plate and the top of the concrete base
Cast in depth - the depth from the top of the concrete to the underside of the washer plate. This is not the same as the embedment depth
Pullout Angle - the angle of the conic section used when calculating the shear resistance using pull out cones.
Cone shear stress - shear capacity of concrete for use when calculating the pull out resistance of a pullout cone
Top steel - the reinforcement in the top of the concrete base
Cover to Top Steel - the concrete cover to the top reinforcement
Concrete Edge Distances - the distances from the edges of the base plate to the edges of the concrete. A value of zero assumes the concrete edge is far enough from the base plate to not affect the design
Concrete depth - the foundation depth. Used to check the embedment depth of the holding down bolts.
Pullout punching - select between pullout cones or a punching perimeter
The area of reinforcement in the top of the base can be entered by expanding the Top Steel row. When expanded this row gives two additional options, as shown below.
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Diameter - the diameter of the top reinforcement
Centres - the centres of the bars in the top reinforcement
The reinforcement is assumed to be the same in each direction, so an average value and average bar spacing should be input. The reinforcement also assumes a single layer of reinforcement. The input of the reinforcement is used to determine the punching shear resistance for the punching perimeter checks. In addition, the presence of the reinforcement also affects the compressive strength of the concrete which has an effect on the bolt bearing capacity in the resistance of the shear force on the base.
BS EN 1992-4 Anchor Bolt checks have recently been implemented for the pry-out and edge shear of the bolts.
The Shear Key area provides option to specify a shear key to the base of the column to enhance the shear resistance of the base connection. The shear key can be formed from a plate or angle welded to the base of the base plate. Alternatively, the shear key can be formed from a stub member cut form an open I-section or from a hollow section. When using a shear key it is also possible to ignore the shear contribution from the base friction and holding down bolts.
The default layout of the Shear Key area is shown below.
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Shear Key Type - indicates the currently selected shear key type
Ignore bolts - indicates whether the shear contribution of the holding down bolts is being considered in the current brief
Ignore Friction - indicates whether the shear contribution of the base friction is being considered in the current brief
Recessed base plate - the depth of any specified recess. The sides of the recess are used to enhance the bearing of the baseplate
Dimensions - notes the dimensions any specified shear key
Shear key weld - indicates the input weld size
To select the shear key type, expand the Shear Key Type row dropdown. The available options are:
Plate or Angle - defines a plate or section of angle welded to the base underside
None - no shear key
Stub - a stub section welded to the underside of the baseplate
When "None" is selected, only the base recess option remains and the Shear Key area is then as shown below.
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With the Plate or Angle option is selected, the shear key dimensions are input by expanding the Dimensions row. This is done by clicking on the arrow to the left of the row. With the Plate or Angle option selected, the dimensions input area provides inputs to control the thickness, width depth and horizontal length of the plate or angle section. The layout of this area is shown below.
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Thickness - the thickness of the plate or angle to be used as a shear key
Depth - the vertical depth of the shear key
Width - the horizontal width of the shear key
Angle Horiz Length - for an angle section, the length of the horizontal element. An input of zero means the software will assume the shear key is formed from a vertical plate
When the Shear Key Type is selected as a Stub Section, the Sear Key area will include a Stub Section row. This row can be expanded to allow for the selection of the section type, section size. The stub section depth can also be input along with the weld to the shear key stub. The layout of the shear key area with the expanded stub section row is shown below.
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