Now, of course, since all of the supports are settling to some extent in this example, the support at point C is not pulling down on the beam with a full effective displacement of $\Delta_C$ relative to the other two supports. So, this support effectively pulls down on the beam at point C, inducing bending in the beam. It seems that the middle support at point C settles rather more than the others. In Figure 8.23 an indeterminate beam is shown that has some support settlement at all three vertical support locations. there are more restraints than the minimum required for stability.įigure 8.23: The Effect of Support Settlement on Indeterminate Beams This is because an indeterminate structure is effectively over-constrained, i.e. On the other hand, for indeterminate structures, settlement of structural supports can induce internal shears and moments as shown in the middle of Figure 8.23. This situation is shown at the top of Figure 8.23. Although this movement may be undesirable, the settlement cannot cause any internal forces in the structure itself. Supports could also potentially heave due to frost effects (this could be considered a negative settlement).įor externally determinate structures, support settlements will simply cause a rigid body rotation of the structure. Support settlements may be caused by soil erosion, dynamic soil effects during earthquakes, or by partial failure or settlement of supporting structural elements. The latter two will only be discussed in terms of their effect on indeterminate structures we previously discussed and analysed their effect on determinate structures in Section 5.7.
The force method may also be used to determine the effect of support settlement, temperature changes and fabrication errors on indeterminate structures. >When you're done reading this section, check your understanding with the interactive quiz at the bottom of the page.
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