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Interstate bridge on the Sava River near Gradiška: Test Load

May 30, 2022

In the period 23 -26 May, 2022, the company “Institute IGH” a.d. (JSC) Zagreb performed the test load of the bridge structure, which was constructed as a steel box girder bridge over three spans l=128+170+128=426 m with support on two abutments. The middle of the main span is in the range of l=170 m.

The aim of this test is to determine the response of bridge at the test load in relation to the designed load, and in this regard, to determine the ability of the bridge to take over the loads foreseen by design.

The test included static and dynamic testing of the bridge structure.

A. Static testing

Static testing is the testing of the stiffness of the bridge span structure under static load. Static load was achieved by symmetrical and asymmetrical positioning of trucks on the span structure. 

As part of the static testing of the bridge structure, the following measurements were performed:

  • Measurement of vertical displacements during static truck loading, by modified method of high accuracy geometric levelling in the middle of each span, and on all bearings.
  • Measurement of residual vertical displacements after unloading at the same measuring points.

A. Dynamic testing 

Dynamic testing is the measurement of oscillations of the bridge structure during dynamic excitation in order to determine the basic dynamic parameters of the structure (natural frequencies and attenuation). The following measurements are planned within the dynamic testing:

  • Measurement of natural frequencies and attenuation of the span structure at a point in the middle of bridge, based on the measured function of response of the span structure due to dynamic excitation (truck crossing over an obstacle on the bridge pavement).
  • Measurement of the dynamic coefficient in the middle range due to the excitation of the transition of a full truck (mass 30 – 35 tons) at speeds from 30 to 70 km/h.

This is the last test before the technical acceptance and issuance of the exploitation permit.