A new version of STAAD Foundation Advanced (Version 7.0) has just been released. As a matter of fact, it was a much-awaited version for its content-rich, new features. Improvements include a new foundation module as well as adding advanced features to existing modules. The focus was to improve productivity and to enhance user experience. The most important addition is the introduction of dynamic analysis of vibrating equipment foundation. The other equally important enhancement is the addition of real time graphics in the popular calculation sheet. This version is packed with features and includes more than fifty major and minor enhancements.
Detailed discussions on all new features are beyond the scope of this post, but we will briefly discuss a few items which are the cornerstones of this release. For a complete list of new features and enhancements, “What’s New” document can be downloaded from the link below.
A proper analysis of vibrating machine foundation can be challenging. Several important steps are involved which can be broadly categorized as follows:
A good software program should offer tools to automate the significant components and integrate those to create an engineering workflow. The New version of STAAD Foundation Advanced (SFA) simplifies the design steps of a vibrating machine foundation to achieve this goal.
Finite Element Modeling:
Many authors and practicing engineers recommended use of solid (brick) elements for modeling a block foundation. With very few basic inputs, the program generates block foundation with solid elements. Meshing parameters are internally controlled by the program to accommodate pedestal(s) and to ensure proper load distribution. Depending on machine configurations, there are three types of block foundations to choose from. It can be single block, combined block or combined block with a gear box. The program supports both rotary and reciprocating machines for single block and reciprocating machine for combined block.
Soil spring stiffness and damping calculation
Soil spring stiffness and damping calculation for a machine foundation is considered as the most critical segment of the analysis process. It depends of several parameters and different methods. Fortunately, SFA 7.0 can automate the process with very few inputs. There are three methods to choose from. The engineer can directly input soil spring values or choose either Veletsos or Richart Whitman method. Program can calculate complex soil spring values involving equivalent foundation Radius (Ri), footing coefficients (βi), damping constants (ci), damping ratios (Di) etc. Engineers do have the option to include or exclude the effect of embedment (embedment impedance) and material damping.
Dynamic loading and analysis
Proper input of dynamic loads is an essential component for a successful machine foundation analysis. The forcing function of a rotary machine can be described as:
Where, F0 is known as machine unbalanced force and often supplied by machine manufacturer. In case it is not known, an approximate value can be chosen from a table for the machines meeting ISO 1940 or ANSI standards. When a manufacturer supplies mass unbalance (or eccentricity) the resulting amplitude can be calculated as below:
Ref. ACI 351.3R-04
STAAD.Pro’s analysis engine is used to perform dynamic analysis. It is a Time History analysis for harmonic forcing function. All necessary parameters including mass modeling, time step calculation and forcing function definitions are automatically done by the program. An option for out-of-phase loading can be used for combined block foundations. It will create harmonic forcing functions on the second pedestal with a 180 degree phase angle.
Output and calculation sheet
The final step is to interpret dynamic analysis results to ensure foundation safety and comply with industry standards. Two checks must be performed to ensure foundation safety. First check is resonance criteria and then check for severity and permissible displacement.
Check for resonance
Modal calculation is an integral part of dynamic analysis. Number of desired mode shapes can be user specified. By default 10 mode shapes are requested. Frequency associated to each mode is then compared with the machine operating frequency to ensure there is no resonance. Normally modal frequency should not be within ±20% machine operating frequency. The program automatically checks resonance condition and display message in calculation sheet.
Check for severity
Several charts are in use for vibration severity check. These charts are typically machine frequency versus displacement graphs. The program uses two such charts from ACI 351.3R-04 (figure 3.9 and figure 3.10) to report machine severity condition.
Finally a permissible displacement check is performed based on ACI 351.3R-04, figure 3.11
Variable bearing capacity is an advanced feature for isolated and combined footing design. Bearing capacity is a function of foundation shape, size, depth and geotechnical conditions. So, a pre-calculated bearing capacity may not be the most accurate parameter for foundation design. The best option would be to pick allowable bearing capacity from a list of bearing capacities based on foundation shapes, sizes and depths. The program now has the option to input a bearing capacity table and while optimizing foundation sizes, it will automatically pick the right value.
Often engineers need to design a combined footing with column eccentricities. Generally, engineers can design it as a mat foundation, but when eccentricities are not large enough engineers prefer to design it as a regular combined foundation.
So far, STAAD Foundation Advanced didn’t have an option to include columns which are not collinear. Now the program includes a new input to define column eccentricities. Length of the footing is in the longitudinal direction and column offset (or eccentricity) needs to be defined in the transverse direction. A column can be offset by positive or negative value. It follows the right hand rule where X-axis is the parallel to the length of the footing and Z-axis is parallel to the width of the footing.
As discussed earlier, this module is meant for small eccentricities. For large eccentricity users are advised to perform a full FEA based mat foundation analysis.
One of the most popular features in SFA is its calculation sheet. It mimics a hand calculated design sheet with design steps, code clauses and even exact equations. It displays sketches to clarify axis system conventions, diagrams and nomenclatures. But until version 6.2, those were static images and didn’t represent the actual footing to the scale. So, a rectangular footing with a higher L/B ratio might not get a good visual representation if the sketch is meant for a square foundation.
This sketch is now greatly improved with the introduction of “dynamic sketches”. Now, all the sketches are drawn to the scale with actual dimensions and even a detailed drawing at the end. For a combined footing design, it draws Shear Force and Bending Moment diagram for critical load cases which helps engineers to compare results. It even includes soil pressure contour which was a frequent request.
In conclusion, new version of STAAD Foundation Advanced (version 7.0) is content rich, it is definitely one step closer to replace manual or legacy workflows in design offices. Machine foundation design is an advanced module and will certianly benefit users. We are planning to put more advanced features for future release, such as Table Top machine foundation which we expect to make available soon.
How to calculate reinforcement bars in Vibrating machine foundation. This option is not currently available with machine foundation using wizard to create block foundation. Reinforcement calculation of foundation available for static load considering isolated footing. please advise.
Hello Vo and Pravin - the best place to ask questions about STAAD is to post on the Structural Analysis Forum:
Is it Indain machine foundation code is added in this version?
Vibrating Machine Foundation: I need 3 examples of each type of foundations (single block, the combined block, combined with GEARBOX) for customers. *.sfa files or reports. thanks a lot. My email address is firstname.lastname@example.org
Thank you for the STAAD Foundation Advanced Ver. 7.0 overview. This was very informative!