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13 R E L A S T ® D E S I G N M A N U A L Figure 11 Forcedisplacement diagrams of shear tests with installation of concrete screws from the upper side and the lower side of the beam respectively [1] Figure 13 Influence of the installation depth of bonded RELAST ® 22 M20 to the maximum forces [1] Results seen in Figure 12 also show the advantage of using injection mortar to bond the screws to concrete as specimens with both RELAST ® sizes 16 and 22 showed a higher shear load capacity when bonded More specifically specimens with RELAST ® 22 achieved 60% higher loads in comparison to nonbonded samples while specimens with RELAST ® 22 achieved 30% higher loads in comparison to the same nonbonded samples Accordingly the technical approval only covers bonded screws due to their higher performance With respect to the installation depth it can be seen from figure 13 that load capacity is directly correlated to the installation depth of the screws The investigated depths were 1 290 mm so that the tip of the screw is at the top level of the upper flexural reinforcement bars 2 260 mm so that the tip of the screw is below the lower level of the upper flexural reinforcement bars Figure 10 Shear test setup [1] 6 x RELAST ® 22 M24 8 x RELAST ® 22 M24 6 x RELAST ® 22 M24 12 x RELAST ® 16 M16 Figure 12 Force-Displacement diagrams of shear tests with and without injection mortar for RELAST ® 22 and RELAST ® 16 screws [1] To achieve smaller crack widths in the shear area a torque was applied at the nuts of several screws to generate axial prestress For dynamic loading the specimens were precracked with a load of 160 kN Afterwards 1 25 and 5 million load cycles between 70 kN and 140 kN were performed respectively No specimen failed during cycling loading and hence the ultimate load was determined by static loading [1] The test setup is shown in Figure 10 below Acomputer controlled hydraulic jack was used to apply a maximum load of up to 630 kN The load was applied gradually following a pathcontrolled method with a 1 mm min displacement Six inductive displacement transducers were used to record beam deformation and further measurement equipment was used to determine more parameters such as screw strain and concrete strains in the shear area 3 1 1 Shear test results With reference to the forcedisplacement diagrams in figure 11 it can be clearly shown that specimens with nonbonded 6 or 8 RELAST ® screws achieved a signifi - cant load increase with respect to the reference specimens without RELAST ® reference bottom unbonded top unbonded reference bottom unbonded top unbonded reference unbonded bonded reference unbonded bonded reference 230 mm bonded 260 mm bonded 290 mm bonded