Calculating constraint reactions

In summary, the conversation discusses calculating constraint reactions on 6 pads using FEM calculations and how to solve statically indeterminate systems. It suggests lumping the constraints together and distributing the forces and moments equally among the pads.
  • #1
Andrea Vironda
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TL;DR Summary
Constraint reactions on a 6 pads system
I would be interested in calculating the constraint reactions on the 6 pads in yellow in the figure, about 300mm apart among them and loaded with F=12500 kN in blue. Since the system is highly hyperstatic, I don't know how to calculate the constraints. Can you give me a hand?

I've made a FEM calculation using Ansys Workbench v18. Do you think it's possible to read those data from there?
Schema RAM.jpg
 
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  • #2
https://en.wikipedia.org/wiki/Statically_indeterminate#Mathematics said:
To solve statically indeterminate systems (determine the various moment and force reactions within it), one considers the material properties and compatibility in deformations.

But if one wants to assume that the forces are well distributed between the different constraints, one can lump the constraints together.

First, find the centroid of the six pads by averaging Xs and Ys to simulate a single reaction pad. The vertical reaction force on that pad will be ##F## and there will be a moment ##M## created to be in equilibrium.

Then draw a line from that pad to each pad. These are your lever arms and the reaction force to the moment for each pad will be perpendicular to these lever arms of length ##R_n## (where ##n## varies from ##1## to ##6##).

Now assume the vertical force and the moment reactions are distributed equally to each pad, thus each pad will have a reaction force that will be a vector composed of ##F/6## and ##M/6/R_n##.
 
  • #3
Thanks, it helped me a lot
 

FAQ: Calculating constraint reactions

What are constraint reactions in mechanics?

Constraint reactions are forces and moments generated at points of contact or supports in a mechanical system. These reactions ensure that the system remains in equilibrium by counteracting external loads and maintaining the prescribed constraints.

How do you determine the types of constraints in a mechanical system?

The types of constraints in a mechanical system can be determined by analyzing the supports and connections. Common types include fixed supports (which prevent all movement), roller supports (which allow movement in one direction), and pinned supports (which prevent translation but allow rotation). Each type of support imposes different constraints and generates different reactions.

What is the process for calculating constraint reactions in a static system?

To calculate constraint reactions in a static system, follow these steps: 1) Draw a free-body diagram of the system, 2) Identify and label all external forces and moments, including constraint reactions, 3) Apply the equilibrium equations (sum of forces and moments equal to zero), and 4) Solve the resulting system of equations to find the unknown reactions.

Why is it important to calculate constraint reactions accurately?

Accurate calculation of constraint reactions is crucial for ensuring the structural integrity and safety of a mechanical system. Incorrect calculations can lead to underestimating or overestimating the forces and moments, potentially causing failure or inefficient design. Accurate reactions also help in predicting the behavior of the system under various load conditions.

Can software tools be used for calculating constraint reactions?

Yes, various software tools and finite element analysis (FEA) programs can be used to calculate constraint reactions. These tools automate the process by creating detailed models of the mechanical system, applying loads, and solving the equilibrium equations. They are especially useful for complex systems where manual calculations would be too time-consuming or prone to error.

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