Structural behavior of reinforced concrete slabs subjected to uniform and concentrated loads
Final Report Abstract
As part of an ongoing research project, tests were conducted on 8 full-scale reinforced concrete cantilever slabs (w/l/t = 3.25/4.5/0.25 m) without stirrups. The test specimens were loaded mainly by a concentrated load. The influence of the amount of reinforcement and, for the first time, the influence of additional uniform loads on the load-bearing capacity were investigated. Essentially, the acting forces, the deformations of the slab and the supports and the crack widths and crack patterns were measured. The stress in the longitudinal and transverse reinforcement were recorded continuously during the tests using fibre optic methods. After the tests, the slabs were dismantled into individual parts to determine the crack pattern inside the slab. Furthermore, all relevant building material parameters were determined experimentally. All tests went well. An increase in the upper bending reinforcement from the usual ρl ≈ 1.1 % (Ø 16-800) to ρl = 1.83 % (Ø 20-80) resulted in a slight increase in load-bearing capacity of ∆ = 1.7 % compared to the reference test. Even a reduction of the upper and lower transverse as well as the lower longitudinal reinforcement from Ø 12-100 to the structurally required minimum dimension of only Ø 8-300 had hardly any effect on the limit load (∆ = 11.4 %). Contrary to expectations, both cases resulted in load capacities that hardly differed from the assumed scatter of the tests. In the second part of the test series, the entire cantilever surface was subjected to a uniform load in addition to a concentrated load. For this complex test setup, the load was applied with an additional 18 force-controlled individual jacks. The load positions av = 3d - 5d were considered, for which no significant influence of a direct load transfer to the support is to be expected. For a comparison of the tests with and without additionally applied surface loads, the linear-elastic internal forces at a distance of 1d from the edge of the load plate of the concentrated load v1dL were considered in addition to the maximum concentrated single load Fu. Only for load position 3d with an additional surface load of 33.70 kN/m² resulted in a significant reduction in the ultimate load Fu (∆ = 23 % of the reference test). If normalized bearing loads (Fu/fc1/3) and internal forces (v1dL/fc1/3) are considered, all other tests are in the scatter range of ±10 % to the reference tests. Further numerical and statistical investigations are currently being conducted to draw conclusions about the load-bearing behaviour and the decisive verification section. The use of continuous, fibre-optic measurements of the strains in the reinforcement provided new insights into the load transfer of reinforced concrete slabs under concentrated individual loads. In addition, the research work was accompanied by non-linear FE calculations, which were already used for the design of the test series. Good results were achieved in the calculation of the bearing loads before the tests began as well as in the modelling of the failure after conducting the tests.
Publications
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Modelling aspects of non-linear FE analyses of RC beams and slabs failing in shear. Computational Modelling of Concrete and Concrete Structures, 669-678. CRC Press.
Harter, M.; Jauk, V. & Rombach, G.A.
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Versuche zur Querkrafttragfähigkeit von Stahlbetonplatten unter Gleich- und konzentrierten Lasten: Versuchsbericht. Technische Universität Hamburg
Rombach G., Harter M., Henze L. & Finger H.
