Steel bridges with orthotropic decks are a common construction method for long-span bridges. The type of construction was developed in the 1960s, and the early structures in particular show increasing crack damage. The reasons for this are, on the one hand, design deficiencies and, on the other hand, massively increased traffic loads. Therefore, there is a need for rehabilitation methods that neither weaken the cross-section, like bolted solutions, nor introduce thermal stresses, like welds, but so far there are no reliable and economic alternatives. This paper summarizes the state of the art on possible damage categories of orthotropic bridge slabs and presents a new rehabilitation alternative using bonded steel patches for crack rehabilitation. It is reported from an ongoing research project how to determine numerically the effectiveness of the bonded steel patches. For this purpose, simple analytical calculations are first used to determine the determining factors and to record their influence. Subsequently, nonlinear numerical calculations with the Drucker-Prager material model are used to identify the stress distributions in the bonded joints in order to optimise the patch geometries. To this end a stiffness factor is presented that can be used to classify such patch bonds and categorize them in terms of their effectiveness.

Structural bonding of batch hot-dip galvanized components poses a particular challenge against the background of the build-up of the zinc coating in the form of different zinc-iron phases. As part of a research project, parameters influencing the zinc coating, the pre-treatment of the zinc substrate, and the adhesive were investigated with regard to the load-bearing capacity of a bonded joint. The variation of the zinc coatings was achieved by using four different steel grades in combination with four batch galvanizing processes. Therefore, small-scale, thick shear tensile specimens were uniformly fabricated, galvanized, bonded in pairs, and mechanically tested. A second series of tests was aimed at the feasibility of an adhesive bond of batch galvanized, medium-scale components under realistic boundary conditions. The test specimens were produced by varying the surface preparation and the adhesive and tested mechanically to shear failure. The results of both test series show that zinc-coated components can be adhesively bonded well and reliably, and, by this, a high load-bearing capacity can be achieved in the bonded joint. The small-scale tests clearly show that the type of zinc coating and its structure obviously have a significant influence on the load-bearing capacity. In summary, it can be stated that the relevant material and process-related influences on the shear load-bearing behavior of bonded joints of batch hot-dip galvanized components were demonstrated by means of the two test series, and the basis for implementing such joints on real load-bearing structures was laid. The presented procedure (small-scale tests and component tests) can be used as a suggestion for a later application in practice.

This paper presents the development of a monitoring system using acoustic emission (AE) analysis for the prediction of micro- and initial cracks in fatigue-stressed steel structures such as bridges, cranes, offshore, or industrial constructions. Initial experimentation suggests a relationship between microscopically observed crack length and AE intensity, further data is required to establish a definitive correlation. As part of an ongoing research project, AE measurement techniques and evaluation are to be further developed to create a monitoring concept for micro-crack prediction in more complex fatigue-stressed steel components. The focus of this research is not on the localization and detection of crack growth or structural changes but on micro-crack detection using AE. Existing acoustic emission analysis systems can thus be extended to measure and detect micro-cracks for the earliest possible identification of damage events. This paper describes the first results of the innovative research idea.