Before the bridge is subjected to the test load, it is examined structurally so as to record its condition and to obtain a minimum of data (e.g. dimensions). The abutments must not give rise to suspected problems with the foundation, and the deck of the bridge must not exhibit any signs of damage indicative of overloading. Test loading determines the moment capacity of the bridge deck. Prior to test loading the shear force of the deck is worked out mathematically, based on geometry and status, to guarantee that it is not determinative during test loading.
By placing a load incrementally in the centre of the span, it is possible to cause a controlled moment in the bridge deck. This moment is compared with the moment in the bridge deck as a result of the normative load including safety factors whereby any reduction factor is determined. By measuring the deflection of the bridge deck with great accuracy at every incremental load, it is possible to determine whether the deck springs back to its original position after the load is removed from the bridge (elastic deflection). The bridge deck is then capable of taking the load safely. If during an incremental load it is observed that the deck no longer springs back in its entirety, it means that plastic deformation has occurred and the test is stopped. The incremental step is chosen in such a way that the plastic deformation has no adverse effects on strength and durability. In addition to the deflection, the abutments are monitored precisely, with a view to subsidence. If subsidence is observed, it again constitutes a reason to stop the test.