Xdisp – Building damage results are sensitive to the spacing of displacement points along a displacement line. Why?
To define accurately the location of the points of inflection, it’s important to state sufficient number of displacement calculation points along the displacement line where a building is specified. Xdisp will calculate and propose the locations of the points of inflection based upon where it calculates the displacements. The locations of the suggested points of inflection are derived by differentiating the curve of the vertical displacement calculated along a given line and finding where the gradient of the resulting function changes from positive to negative. In general, the spacing of displacement calculation points at 1 to 2m spacing is sufficient. If very close spacing is specified (less than 0.5m centres), there is a risk that a significant number of points of inflection may be identified, due to the complex form of equation that is developed to curve-fit the data displacement points. When this is differentiated more points of inflection may be derived than are necessary. The program does include a facility to ‘combine segments’, therefore ignoring selected points of inflection that the program has derived. It may, however, be time consuming for the user to have to combine segments after each analysis due to the specification of too many displacement calculation points.
The building damage assessment method also has a function to specify a trough width limit. The reason for this facility is to enable appropriate deflection ratios and horizontal tensile strains to be calculated in the hogging section of a settlement trough. Usually a limit of 1 to 0.1mm is specified depending on when displacements are considered to be of little concern. If this value is set at zero, smaller deflection ratios and horizontal tensile strains will be calculated than may be appropriate. This is due to the settlement trough extending many metres beyond the 1 or 0.1mm limit to become 0mm (to the many decimal places that Xdisp will calculate results to).