IES VisualFoundation User's Guide
Foundations
Concrete foundations (also know as boundaries, slabs, footings, mats, etc.) are the primary elements modeled and designed in VisualFoundation. Foundations with a wide variety of shapes and sizes can be modeled in the program. Piles, Grade Beams, and Walls are used to add stiffness to the foundations. A single concrete material is used for all slabs in the project and is defined in the .
In the Model and Load view, circular, rectangular, polygonal, or custom slabs can be drawn using the buttons in the ribbon. Slabs are defined by the vertices at boundary points. Slabs can be drawn on grids or existing vertices and snap points can be used to create slabs. The number of snap points along each edge of the slab is specified in the in the tab. Any arbitrary geometry can be constructed by drawing multiple slabs connected to or overlapping each other. Adjoining slabs are modeled as continuous, with common displacements and flexural rotations at the boundaries. Each individual slab boundary can have a different thickness and Subgrade Modulus. At locations of overlapping slabs, the thickness and soil modulus are specified using the Thickness Overlap and the Soil Modulus parameters in the tab. Note: Disconnected slabs are not allowed in VisualFoundation and expansion-joints or other discontinuities in the slab cannot be modeled.
A selected slabs can be turned into a hole by setting Hole? = Yes in the tab. Loads that exist within holes are not included in the analysis. If portions of Area Loads lie partially over holes, only the loading lying over slabs are considered (i.e. the loading that occurs over holes is not distributed to adjacent plate elements).
The reinforcement parameters for each slab are defined by selecting the slab from the Model and Load view and editing the Reinforcement Details section in the tab, as described below.
Foundations may be loaded with Full Area, Circular, Rectangular, Ring, and Tubular area loads. Loads can also be transferred to the slab by Piers, Grade Beams, and Walls.
Finite element analysis is approximate and numerical. Use mesh refinement and examine the analysis results carefully, before trusting design checks.
Slabs in VisualFoundation are meshed into triangular FEA plate elements with displacement springs used to model the slab-soil interaction. See the Analysis page for more information on the FEA mesh density, including the available settings and options. For a better understanding of the FEA model that is built by VisualFoundation, use the feature to create a VisualAnalysis project and examine the FEA model in more detail. More information on integration between VisualFoundation and both VisualAnalsyis and VAConnect can be found in the Integration section of the Help File.
The results from the finite element analysis can be displayed graphically in the Analysis Results view. The tab displays the numerical results that correspond to the colored graphics. With nothing selected, the results displayed in the are a summary for the selected result case, whereas if one or more individual plates are selected, the shows the result range for the selected plates. The various Result Cases that were included in the finite element analysis can be selected using the Result Case drop down from the tab. The Result Type displayed graphically in the Analysis Result view is specified in the .
VisualFoundation checks and designs concrete slabs according to the following design specifications:
Slabs that experience two-way action have both bending moments (MX and MY) and twisting moments (MXY). The twisting moments may cause the maximum bending demand to not coincide with the X or Y reinforcing directions. To ensure that the slab has adequate strength in all directions, VisualFoundation uses the method by Wood and Armer as explained by MacGregor and Wight1,2 to design the reinforcement. The following equations are used to calculate the design moments which are obtained from Wood and Armer when k=1.0. According to MacGregor and Wight,2 k=1.0 is the best choice for a wide range of moment values. VisualFoundation takes the critical flexure section as the face of Grade Beams, Piles, Piers, and Walls. Plate nodes that fall within these objects are not checked for flexure.
MX+ = MX + |MXY| ≥ 0
MX- = MX - |MXY| ≤ 0
MY+ = MY + |MXY| ≥ 0
MY- = MY - |MXY| ≤ 0
The bending moment capacity of the slab is a function of the compressive strength (f'c), thickness, and the area of steel reinforcement provided. Reinforcing is placed in both plan directions (X & Y) and in either one or two layers. This results in up to four reinforcing quantities at every point in the slab (X, Y, Top, Bottom). VisualFoundation performs moment and steel demand calculations at the finite element model node points. When the slab's reinforcement is set to Optimize (as discussed above), the reinforcement required to meet factored demand is selected by the program based on the list of available rebar patterns. The rebar pattern with the smallest area (As) is selected from this list that meets the required flexural and minimum steel demands. If the slab's reinforcement is set to Specify, the reinforcement pattern defined for the direction and layer in question will be used when performing the design checks.
The critical section for one-way shear (i.e. beam shear) is taken at the face of Piles, Piers, Walls, and Grade Beams. If, however, a Pile or Pier introduces compression in the slab, the critical section is taken at "d" from the face of the object.
Plate shear checks are reported graphically from the Foundation Design view by selecting Shear Unity from the under the Slab Details category (red plate colors indicate a failing unity value). Shear checks can also be reported as numerical results using the programs's Test Reports.
Two-way (punching shear) checks are performed at locations where concentrated loads are introduced into the foundation slab, such as at piles, column piers, and walls. Additional information regarding punching shear design checks and punching shear reinforcement can be found in the Punching Shear page of the Help File.
The software can detail bar patterns by plate element, by column lines or by slab boundary. Use the tab from the Foundation Design view to display the different results. Note: The By Column Line display is not available if the Design Approach is set to Specify.
Reports can include both text-based and graphical information. Graphical information from the Analysis Results or Foundation Design views or from the plate diagrams can be inserted into a report using the and commands.
Plate result diagrams for moment, shear, displacement, and bearing are available in the Analysis Results view and plate design diagrams for shear unity and area of steel required are available in the Foundation Design view. Left-click and drag a line across the slab to view the diagrams at the line's location or right-click and select Show Plate Result/Design Diagram from the context menu to launch the respective diagram dialog box. The slice direction and location can be adjusted within the dialog along with the number of plots displayed and the plot type. Note: The slice direction and location along with the plot settings will persist within one session of VisualFoundation. This allows the dialog to be closed to select a different result case or to modify the model without losing the adjustments that were made in the dialog. To include graphs in the report, use the copy plots button to copy the plots to the clip board which can then be pasted into the report.
Analysis and design results can also be viewed in text form using the Report View tab. Once in the Report View, a list of available deign tables is shown on the tab and can be added to the text report by double-clicking an individual table or dragging and dropping a table into the report. Plates can also be reported on an individual basis by selecting one or more plates from the Analysis Results or Foundation Design view, and using the right-click context menu to Report Selected. Note: The reinforcement settings are included in the Slabs table located under the Structure Tables category.