# Experimental Testing of Reinforced Concrete Deep Beams Designed by Strut-And-Tie Method
## 6 Conclusions  
In this paper, the results of experimental testing of three reinforced concrete deep beams with openings designed by the Strut-and-Tie method are presented. Specimens have the same geometrical and mechanical characteristics of the material and monotonic increasing load is applied on them until failure. Each of the specimens is reinforced by a different reinforcement layout which is determined by the analysis in the software \"ST method\". As suspected, the first cracks were influenced by the arrangement of the spacers for fixing the reinforcement, which is confirmed by the FEM analysis in program Abaqus. Since the appearance of the first member cracks was suspected to be influenced by the arrangement of the spacers for fixing the reinforcement, numerical model FEM B was developed to further examine this possibility. In the model FEM B on location of the spacers, the discontinuity of concrete volume was modeled so it can resemble the experimental setup. The model FEM B will provide opportunity for extrapolation of data on other, untested geometries of the members in future research. The following conclusions are derived from the test results:  
* Strain values in concrete and reinforcement, for the maximum load intensity in the test, did not reach the ultimate limit values of the strains for concrete in compression and for reinforcement in tension. This indicates that the maximum load intensity in the test is greater than the ultimate limit load for design. One of the reasons for this is the conservativeness of design of the members according to the Strut-and-Tie method, which is implemented in the program \"ST method\", and which uses in the analysis the constant cross-sections of the rods in the replaced truss member. In contrast, the generated Strut-and-Tie models in the tested members have bottle-shaped struts with rigid connections and cross sections that are realistically larger than the calculated ones. Also, the conservativeness of design is affected by the neglecting of adhesion between concrete and reinforcement in the zone between cracks. In addition, the stiffness of the steel frame also affected the reduction of stresses and strains in the tested specimens. * For all three tested deep beams, the shapes of the proposed Strut-and-Tie models, obtained from the software \"ST method\", correspond to the crack patterns of the tested specimens. This indicates that various Strut-and-Tie models can be applied to one member. Based on this it can be concluded that the program \"ST method\" can be used for obtaining the Strut-and-Tie models. * Although the member is designed in a static simple beam system, numerical simulations (models FEM A and FEM B) of experimental testing have shown that the interaction between the wall, frame, and floor base, as well as the existence of spacers significantly affected the numerical results. The model FEM B can be used to simulate the nonlinear behavior of the tested specimens for displacement estimating. Such complex simulations can significantly contribute to the reduction of material costs of experiments and savings of research time in the initial stages of scientific research designing. * As the Strut-and-Tie method does not provide an unambiguous solution, the choice of an optimal model represents an engineering assessment, following specific criteria. According to experimental tests, member W3 has shown the best behavior under load based on the comparison of crack widths and deflection values with the remaining test specimens. Future research will include the analysis of the optimal Strut-and-Tie models for various reinforced concrete member geometries. Since the experimental research is limited in the number of the members, the presented model FEM B analysis could provide opportunity for extrapolation of data on other, untested geometries of the reinforced concrete members and reinforcement layouts. **Author Contributions:** Conceptualization, A.S.-C. and A.R. ; methodology, A.S.-C., M.M., and V.R. ; software, A.S.-C., A.R., and D.Z.