# Experimental Study of Steel Reinforced Concrete (SRC) Joints
## 2 Methodology  
The tests were conducted using cycles of loading and unloading. Tests were performed on a joint between two beams and a column, in which a cyclic loading-unloading test, with no load in the opposite direction, was carried out on the column in order to obtain an understanding of the joint's behavior. The test was repeated with different sections: reinforced concrete and steel reinforced concrete. The embedded cross-section was only in the joint (see Figure 1).  
Tests were carried out in the loading framework of the laboratory, which can apply a maximum load of 300 kN (Figure 2).  
Specimens were designed with steel cross-sections to reinforce the joints of the singular points of the structures subjected to strong earthquakes. Under earthquake action, an asymmetric and cyclic bending moment diagram takes place due to the dynamic effect of loading and unloading. The bending of a framework against horizontal forces are distributed according to Figure 3.  
The tested joint corresponds to a T-joint of a conventional framework with a point load in the center, which may correspond to a horizontal or vertical load. Given the test frame's characteristics, the T-shape was chosen, which corresponds a T-joint that belongs to a conventional building structure frame.  
Figure 1: Detail of the steel cross-section reinforcement only in the joints.  
Figure 2: Loading framework.  
Different constructive solutions of the framework's representative beam were subjected to a cyclic loading and unloading process to obtain an understanding of its real behavior in the elastic and plastic phases up to breakage, which was achieved only in less ductile assemblies. Load is introduced as a displacement imposed at the center of the beam. The displacement values obtained are repeated twice in the load-unload cycles. They increased and progressed in a parabola until the maximum displacement of 330 mm (Figure 4).  
The arrangement of supports and the produced rotation do not allow larger deflections in the center. The tests that were run corresponded to a symmetrical bending distribution in Figure 5A. The asymmetric distribution in Figure 5A corresponds to tests similar to those run by [PERSON] et al. [7].  
Figure 4: Loading history in displacement control.  
Figure 3: Typical bending arrangement in the event of an earthquake.  
However, the absorbed energy is the same for bending in the same direction throughout the length of the bar (Figure 5A), which is the tested case, and also the same for bending with the inverted sign from the joint (Figure 5B). Therefore, both cases are valid for simulating the real behavior of a structure affected by an earthquake.  
The absorbed energy is calculated as:  
\[\mathrm{W}=\lambda\cdot\int_{e}^{l}\cdot\mathrm{M}\left(x\right)\cdot\chi\left(x \right)\cdot\mathrm{d}x \tag{1}\]  
where W: total energy absorbed.  
\(\lambda\): elastic coefficient, \(\lambda=1/2\) in the elastic phase and \(\lambda=1\) in the perfect plastic phase.  
\(l\): length.  
\(\mathrm{M}(x)\): bending moment.  
\(\chi(x)\): curvature.  
The curvature \(\chi\) and bending moment \(\mathrm{M}(x)\) have the same sign in each section regardless of the direction of bending, which always results in a positive value.  
Figure 6 shows the hysteretic behavior of the specimens tested without (6A) and with (6B) load inversion.  
Figure 5: (**A**) Symmetric distribution in the joint. (**B**) Asymmetric distribution in the joint.  
Figure 6: Graph with the tested hysteretic behavior without load inversion (**A**) and with load inversion (**B**).  
The force-displacement graphs obtained in the tests of the load form part of those that can be obtained with load-unload cycles. The results are comparable to a bilinear behavior with a linear elastic section and another plastic curved section. The loss of stiffness in (**A**) is less in the tests as the damage caused when the load moves in the opposite direction (**B**) increases when the concrete at the other end of the section is fractured by pulling.