DEFORMATION MONITORING OF THE BRIDGES BY CONVENTIONAL AND GPS METHODS

points (reference network) which are established on stable ground out of deformation zone (Caspary 2000). A more routine monitoring process can be employed to monitor the short-term behaviour of bri dges by simply confining observations to trends at selected points along the bridge . There are various theoretical hypotheses on the behaviour of the structure and therefore diffe rent tests have to be done. In this paper some of the results of static load test which was carried out on three different bridges in Croatia, obtained by conventional and GPS methods, are presented.

1 A static load test of the bridge According to national standard HRN U.M1.046, after construction is complete and before putting bridges into operation, a static load test has to be done. The purpose of static load test is to empirica lly quantify the load capacity of the structure, i.e., to verify the predicted load deformation response of a bridge. The amount of the expected deformations may be predicted using either de terministic model, for instance, the finite or boundary elements methods, or empirica l prediction model. The finite element method (FEM) is the most commonly used method in structural and geotechnical engineering (Bathe 1990). The basic concept of the FEM is that the continuum of the body is replaced by the small elements which ar e connected together only at the nodal points, so that the theoretical deformations can be computed using linear equations. In static load test the position changes (displ acements) of selected points are measured. There are recoverable (elastic) and non-recoverable (residual) deflections. The question of the order of magnitude of elastic and residual deformations is the primary interest of this test. In order to obtain the vertical displacement of the bridge, the elevations of the selected points are measured, relative to the stable reference point located off the bridge.