Half-joints in concrete bridges are known to exhibit an increased rate of degradation. Their main vulnerability is situated in the re-entrant corner, buried deep inside the joint. This makes visual inspection nearly impossible. A Structural Health Monitoring (SHM) system offers a promising alternative, but interpretation of the half-joint status from SHM data is not straightforward. The study presented in this paper is a case study of the SHM system on the Naardertrekvaart bridge in the Netherlands. Analysis of SHM data revealed a dependence of the movement of the bridge on a seasonal temperature cycle, presumably caused by hindered thermal contraction of the half-joints. This phenomenon offered no reliable estimation of the half-joint status. In addition, from the movement of the lower half-joint nibs under traffic loads, a stiffness parameter was devised, used as an estimation of the half-joint status. The study indicated that a high-frequency approach can increase effectiveness of the SHM system.

In the assessment of existing infrastructure performing only a desk study is often not sufficient to determine the structural reliability of a bridge or viaduct. For concrete structures gathering field data by performing a proof load test offers detailed information about the structural performance. However, the relation between the magnitude of the load and the structural reliability is not immediately clear. In the present study the challenges in determining the target load and the uncertainties that require attention are described. An approach is presented that addresses the time-dependent character of the structural reliability, the need for accurate stop-criteria, the knowledge level and spatial uncertainty. It is shown how both past trafic loads and a proof load test may contribute to the proven strength of a structure. The described methodology provides a starting point towards a flexible approach for proof load testing in which structure-speciic information and requirements are considered.

Proof load testing can be an interesting method to assess existing bridges for which analytical methods are unable to provide an accurate assessment. In a proof load test, a load representative of the factored live load is applied to the bridge. If the bridge can carry this load without distress, the proof load test is success-ful, and the bridge proves it fulfils the code requirements. Since large loads are applied, the structure or element that is tested needs to be carefully monitored during the test. This paper reviews the literature on reported load tests and the measurement techniques used during these tests. It also includes the test goals these techniques can address, and the advantages and disadvantages of the contact and non-contact techniques. The result of this re-view is guidance for the selection of appropriate monitoring and measurement techniques during load tests. This practical recommendation can serve engineers during the preparation of a load test, and will be extended in the future with stop criteria validated with experimental results.