Ground Beam Design
Once column and wall loads have been calculated, Tribli provides a range of functions to assist engineers in the sizing and design of ground beam footings.
Ground beams are used where walls are to be supported on piles rather than on soil. The beam sits beneath the wall chain and distributes the wall load evenly to the pile group along its length. Ground beams are always assigned to a wall chain; the beam geometry follows the wall above automatically.
Note
Tribli applies an additional factor of safety to all loads prior to being used in any of Tribli's design functions including; column, wall, pad footing, column transition and punching shear design. This value defaults to 1.20, but can be changed by the user in settings or by clicking on the text in the bottom right hand corner of the screen.
Prerequisites
- Loads must be calculated before design checks or optimisation can be run. Follow the load calculation workflow before proceeding.
- At least one pile type must be defined in the Edit menu before a ground beam can be created. Pile types define the pile diameter, depth, working capacity and ultimate capacity used in the design.
Creating a Ground Beam
From the Draw Menu
Select "Ground Beam" from the Draw menu, or click the Ground Beam icon in the toolbar. Then click on the wall to which the ground beam is to be assigned. The wall must be the lowest wall in its chain and must belong to a wall chain.
To create ground beams one after another without re-selecting the tool, enable "Repeat Draw" before drawing.
To set the default ground beam properties before drawing, hold Ctrl while selecting "Ground Beam" from the Draw menu. This opens the default properties dialog where the pile type, spacing, dimensions and reinforcement can be configured. New ground beams will be created with these defaults.
From the Context Menu
Right-click on a wall and select "Add Ground Beam" from the context menu to assign a ground beam directly to that wall's chain.
From a PDF Markup
Ground beams can be defined in a PDF markup file and imported into Tribli along with the rest of the structural model. See the PDF Formatting guide for details on how to mark up ground beams.
Note
Although ground beams can be specified in PDF markups, it is generally easier to add them manually in Tribli once the PDF has been imported. Only a limited number of properties can be set via markup.
Ground Beam Properties
Double-click a ground beam, or right-click and select "Properties", to open the properties dialog.
| Property | Description |
|---|---|
| Pile Type | The pile type used to support this beam. Pile types are defined in the Edit menu and control the pile diameter, depth, and capacities used in the design. |
| Pile Spacing | The maximum centre-to-centre distance between piles in mm. Piles are distributed evenly along the wall so the actual spacing never exceeds this value. |
| Depth | The depth of the concrete beam in mm. |
| Pile Clearance | The clear distance from the pile face to the nearest edge of the beam in mm. The overall beam width is derived automatically from the pile diameter. |
| f'c | Characteristic compressive strength of the beam concrete in MPa. |
| fy | Yield strength of the reinforcing steel in MPa. |
| Cover | Nominal cover to reinforcement in mm. |
| Top Bar Diam. / No. Top Bars | Diameter and number of longitudinal bars in the top face of the beam. |
| Bottom Bar Diam. / No. Bottom Bars | Diameter and number of longitudinal bars in the bottom face of the beam. |
| Ligature Diam. | Diameter of the shear ligatures in mm. |
| Ligature Spacing | Longitudinal spacing of the shear ligatures in mm. |
| No. Ligature Legs | Number of vertical legs in each ligature set. |
Checking Ground Beams
Checking an Individual Ground Beam
Right-click on a ground beam and select "Inspect Capacity" (or Alt-double-click) to open the design summary dialog. This shows:
- Pile load utilisations at working and ultimate limit states
- Beam bending and shear utilisations at the hogging (over-pile) and sagging (mid-span) critical sections
- Detailing check results
- A full text design report
Checking All Ground Beams
Select "Check All Footings" from the Design menu to perform design checks on all footings in the model, including ground beams. Once complete, turn on utilisations in the element visibility settings to view results in the graphics window. Utilisations greater than 1.0 are shown in red.
Optimising Ground Beams
Optimising Pile Spacing
Right-click on a ground beam and select "Optimise Pile Spacing" to reduce the pile spacing to the maximum value permitted by the pile capacity for the current wall loads.
Optimising Pile Type
Right-click on a ground beam and select "Optimise Pile Type" to automatically test all pile types defined in the model and select the one that results in the lowest total pile cost. Pile costs must be entered for each pile type in the Edit menu for this function to produce meaningful results.
Exporting the Ground Beam Schedule
Select "Ground Beam Schedule" from the Design Summaries menu to export an Excel schedule summarising all ground beams in the model. The schedule includes the wall chain name, pile type, beam dimensions, number of piles, pile utilisations, beam strength utilisation, and detailing status for each ground beam.