# Experimental Testing of Reinforced Concrete Deep Beams Designed by Strut-And-Tie Method
## 1 Introduction  
Strut-and-Tie is one of the methods that can be used for designing reinforced concrete members in which geometric and static discontinuities (D-regions) occur, and where the conventional design method does not apply, as it is the case with the whole or parts of the member, the so-called, B-region [1], Figure 1.  
The advantage of this method is reflected in the simplicity of its design application, while one of the main disadvantages is that there is no single solution for the Strut-and-Tie model form. This disadvantage is a consequence of the possibility to form valid Strut-and-Tie models in many variations. The Strut-and-Tie model can be adapted to follow main stress trajectories, it can be conditioned by the reinforcement layout, and it can be determined intuitively, i.e., based on engineering assessment. Typical examples of the members where Strut-and-Tie models can be successfully applied are: pile cap, stiffening cross-sections diaphragm, wall members with and without openings, places with sudden static or geometrical changes (e.g., sudden reduction in a cross-section at the end of the member, places where large concentrated loads are applied), short elements, etc. So far, a significant number of experimental studies have been carried out regarding the application of the Strut-And-Tie method for the design of a part or the whole of reinforced concrete members. In general, the objectives of this research relate to the verification of the method from the aspect of the Strut-and-Tie model and member strength, [2; 3; 4; 5; 6]. The testing of deep concrete beams, designed by various methods, including the Strut-and-Tie method, is shown in the paper [7]. Analytical predictions of the member strength were made and then compared with the results obtained by the experiment. Twenty members were tested, in two series of ten. The specimens had the same geometry, mechanical properties, and low shear span-to-depth ratio \(a/H=0.27\). The load was represented by two forces that were positioned at the thirds of the span length. The member supports were positioned symmetrically. Variations within specimens were made with respect to the position of the circular hole, the layout, and the quantity of reinforcement. Following the experimental investigations, [PERSON] and [PERSON] [7] came to the conclusion that the members' failure shapes and the load values at the moment of the first crack appearance were dependent on the existence and position of the opening. When the hole was set in the region of the shear span, the load reduction was in the range of 18-30%, while the hole in the center of the member did not affect the behavior of the deep beam. The existence of vertical stirrups increased the load limit value by approximately 15% in the case of a solid member and in the member with an opening in the central part, while there was no significant impact when the opening was set in the region of the shear span. Horizontal reinforcement increased the member strength by approximately 20% in the region of the shear span, whereas there was no impact if the opening was in the center of the member. By comparing analytical and experimental results, similar strength values were obtained. [PERSON] and [PERSON], [8], experimentally examined two different types of wall members. One wall member featured ordinary reinforcement, while the other, besides reinforcement, had steel fibers added to the concrete mixture [8]. The amount and arrangement of reinforcement for all wall members was determined using the Strut-and-Tie method. The wall members were loaded with one concentrated force. Two members had dapped heights and two members had constant heights. Each of the specimens had a rectangular opening positioned on the load transfer path from the application location to the support. The amount of reinforcement of the wall members with the addition of steel fibers was smaller when compared to the amount of reinforcement for the ordinary reinforced concrete wall members.