Abstract
Due to their high cost efficiency and flexibility, semi-precast concrete slabs with lattice girders are widely used in constructions all over the world. Prefabricated concrete slabs, combined with in situ concrete topping, exhibit a quasi-monolithic structural behavior in which lattice girders serve as vertical shear reinforcement and ensure the transfer of longitudinal shear within the interface, acting in combination with concrete-to-concrete bonding mechanisms. To be applicable in industrial and bridge construction, semi-precast slabs need to have sufficient resistance against fatigue failure. To improve and expand the limits of application, theoretical and experimental investigations are conducted at the Institute of Structural Concrete (IMB), RWTH Aachen University. To investigate the fatigue behavior of lattice girders, small size tests with lattice girder diagonals were carried out. These test results have been used to derive an S–N curve (S: stress, N: number of load cycles) for lattice girders for a more refined fatigue design. Subsequently, the fatigue behavior of semi-precast slabs with lattice girders was investigated by fatigue tests on single-span slab segments. The fatigue design regulations of lattice girders according to technical approvals can generally be confirmed by this test program; however, they tend to be conservative. The use of the derived S–N curve leads to significantly improved agreement of fatigue behavior observed in tests and design expressions.
Highlights
Lattice girders are prefabricated reinforcement systems to be installed in semi-precast concrete elements, e.g., in semi-precast slabs or in semi-precast walls
In the ultimate limit state, lattice girders serve as interface reinforcement and can fulfill the function of shear reinforcement to ensure adequate resistance against vertical shear depending on type and disposition [1]
In order to extend the range of application by deriving S–N curves for lattice girders, small-size fatigue tests with lattice girder diagonals cast in concrete cubes have been conducted at the Institute of Structural Concrete (IMB), RWTH Aachen [43,56], using the procedure of the interactive method [57,58] (Figure 5b)
Summary
To extend the limited data basis and to verify the investigations from literature, 14 test specimens with two sub-tests have been conducted with semi-precast slab sections under cyclic loading [43,61,62]. In order t vestigate the effect of untreated interfaces, concrete surfaces were tested without mec ical post-treatment to be very smooth and oiled or left as cast with a roughness dep Rt = 0.4 mm. Since the applied lattice girders KTS and EQ may be accounted as shear forcement, the shear capacity has been investigated during the research program. Since the applied lattice girders KTS and EQ may be accounted as shear reinforcement, the shear capacity has been investigated during the research program. The test results considering the shear resistance can be found in [43]
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