## 2 Incremental Hole-Drilling Method  
Residual stresses introduced by the welding operations for an orthotropic steel deck are evaluated with the incremental hole-drilling method. A small hole is drilled into the test material through the center of a strain gauge rosette [10]. These strain gauge rosettes are used to measure the relieved surface strains caused by the introduction of a hole that is formed by drilling in a series of small steps. Residual stresses can be calculated with the measured strains and calibration coefficients according to the calculation principles specified in ASTM E837-13a. Reliable measurements are only achieved by limiting the residual stresses to 80% of the material's yield stress [11]. However, the residual stress values can reach the material's yield stress by drilling of the hole and the elastic limit of the material can be reached. This plastic region is present near the lower circumference of the hole and spreads out towards the strain gauges of the strain gauge rosette by increasing of the hole depth [10]. The black zones in Figure 1 indicate this plastic region where a hole drilled up to a depth of 1 mm is simulated for a quarter of a steel plate of quality S235 with 6 mm thickness using a linear-elastic material law. Two strain gauges of a strain gauge rosette are also indicated in the figure. Residual welding stresses introduced by the weld connection of the deck plate with a longitudinal stiffener of an orthotropic steel deck are evaluated with the RS-200 Milling Guide (Figure 2). For the installation of the strain gauge rosette, a smooth surface is required. However, the surface preparation prior to bonding the strain gauge rosette should not induce significant residual stresses [10]. The paint layer of the orthotropic steel deck was removed with a grinding tool. After processing the first measurements, it was noticed that the near-surface stresses were very large. By using a grinding disc with less coarse abrasive paper, the near-surface stresses could be reduced. To expose the surface material, it is necessary to drill only through the material of the strain gauge rosette and not trough the material of the test specimen in order to establish the correct zero depth [10; 12]. In practice, this zero depth is established by very slowly advancing the cutter by 0.02 mm and rotating the drilling machine all the way around. The strains of the strain gauge rosette are recorded and remain constant when the cutter has not yet reached the test surface. When the recorded strains are changing, the cutter has  
Figure 1: Plastic zone introduced by hole drilling. drilled through the material of the strain gauge rosette and reached the surface of the test material. This depth of the cutter indicates the first measurement of the strain gauge rosette. The zero depth is the depth of the cutter before this first measurement. Only one type of strain gauge rosette is used for the measurements on the orthotropic steel deck. Therefore, only this type of strain gauge rosette will be considered in this paper. A strain gauge rosette with the Rendler and Vigness [13] geometry. Strain gauge rosette type CEA-06-062 UL-120 is used for the experimental measurements on the orthotropic steel deck. The geometry is schematically presented in Figure 3a with a detail of one strain gauge on the rosette in Figure 3b. The dimensions of the used strain gauge rosette are shown in Table 1 and it has a hole diameter of 2 mm and a maximum hole-drilling depth of 1 mm [10]. Figure 3: Schematic geometry of a strain gauge rosette (**a**) and detail of one strain gauge (**b**). Figure 2: RS-200 Milling Guide (**left**) and hole-drilled strain gauge rosette (**right**). Bigger strain gauge rosettes can be used to obtain residual stresses more into the depth of the test surface. In this way, the uncertain near-surface residual stresses due to the surface preparations for the strain gauge rosettes can be eliminated.