Design model for slabs strengthened against impact
Table of contents
Project data
| Titel | Title Promotionsprojekt A5/III: Bemessungsmodell für Entwurf, Konstruktion und Berechnung von gegen Impakt verstärkten Platten als Teilprojekt des GRK 2250 | Doctoral projekt A5/III: Engineering model for calculation, design and construction of RC slabs strengthened against impact loading as part of the RTG 2250 Förderer | Funding Deutsche Forschungsgemeinschaft (DFG) / GRK 2250 Zeitraum | Period 05/2023 – 04/2026 (3. Kohorte | 3rd cohort) Projektleiterin | Project manager apl. Prof. Dr.-Ing. Birgit Beckmann Bearbeiter | Contributor |
Report in the annual report 2024/25
Model development for strengthened concrete plates
3D scan of the backside of a strengthened RC plate after impact loading
Existing reinforced concrete structures typically provide limited protection against impact loads. Therefore, the Research Training Group (RTG) 2250 “Mineral-bonded composites for enhanced structural impact safety” is intensively working on developing solutions to optimize the behavior of components under impact loads. In doctoral project A5, the focus is on thin, rear-applied strengthening layers made of mineral-bonded composites, whose fundamental mode of action was already investigated in the first cohort of the RTG. The focus in the second cohort was more on precise experimental quantification of the achieved increase in bearing resistance, also considering the influence of shear reinforcement in greater detail. The third and final cohort is dedicated to the development of an engineering model that incorporates both a rear strengthening layer and a front side damping layer for reinforced concrete slabs under impact loading.
To achieve this goal, plate tests were conducted throughout the year, featuring novel strain sensors developed in another RTG’s doctoral project of the second cohort, which were applied along the two carbon reinforcement textiles in the strengthening layer. By alternating the arrangement of sensors with different lengths, the local strains induced by the vertical movement of the punching cone could be approximately measured. The global and local deformations of the plate matched well with the measured deformations, as soon as the strains in the textile plane agreed both analytically and experimentally. The reinforcement configurations of the tested plates are intended to allow for a direct transfer to strengthened plates with varying longitudinal reinforcement configuration.
Further development of the engineering model will involve the analytical consideration of the top-applied layer of infra-lightweight concrete with a cover layer of strain hardening cementitious composite (SHCC), which was experimentally explored in doctoral project A6 of the second cohort. As a sacrificial layer between the impactor and the reinforced concrete slab, it converts a large portion of the impact energy and ensures reduced damage to the base slab.
Report in the annual report 2023
Strengthening on every front
Impact test on a plate with a combination of damping system on top and rear side strengthening layer
In general, existing reinforced concrete structures only have limited resistance to impact loading. For this reason, the Research Training Group (RTG) 2250 “Mineral-bonded composites for enhanced structural impact safety” focused on developing solutions to optimize the behavior of components under impact loading.
In the first two cohorts of doctoral project A5, the research focus was on thin mineral-bonded strengthening layers applied to the rear side of reinforced concrete slabs which were designed both with and without shear reinforcement. In the current third cohort, the research approach is complemented by the consideration of an additional mineral-bonded damping layer applied to the impacted plate side. This research should result in an engineering model that describes the behavior of such reinforced concrete slabs.
At the end of the second cohort, a final series of tests was conducted in the institute’s drop tower facility to combine the research of several doctoral projects of RTG 2250. For this purpose, specimens with a rear side carbon-reinforced concrete layer (topic in projects A5/I and II) as well as plates with additional top side damping layer (topic in project A6/II) were tested. It was shown that the multi-layer damping system developed in project A6/II effectively reduced the impact load applied to the test specimen and completely prevented spalling on the top side. Fragmentation on the rear side due to scabbing was also reduced. In this respect, the strengthening layers showed their efficiency, as they were able to completely prevent the detachment of the fracture body due to their membrane effect. The combination of these two positive effects led to a significant reduction in plate damage in the velocity range tested and to the successful completion of the work of the second cohort.
In the third cohort, the system of plates strengthened on both sides is considered using a three-mass oscillator. Individual springs within the model describe the global bending properties, the local punching characteristics and the (damped) effect of the impactor. The behavior of the simplified dynamic model will be verified and improved by further tests.