Comparación de la rotación interna del hombro en grados de amplitud articular

Specimen SS-8 was designed and detailed according to the conventional design. In addition, a partial hinge was provided to the beam section at a distance equal to twice that of the beam depth away from the beam-column interface. The intention of providing the partial hinges was to increase the rotational capacity of the RC beams and trigger the catenary action stage at a smaller middle joint displacement.

In the partial hinge regions, an additional T10 bottom bar was added and bent up at a distance of 345 mm away from the beam column joint interface and one of the top layer T10 bars was bent down at the same distance. The two bent bars levelled off at the bottom and top reinforcement layers, respectively. Finally, the pin of the partial hinges was formed at a distance 440.0 mm from the beam-column joint interface, as shown in Figure 3-5.

Figure 4-36 shows deflection curves along the length of the beam at different stages of loading. It can be seen from Figure 4-36 that the beam deflected symmetrically and the final deflection was 664 mm, which is larger than the other specimens. Also, it can be seen that the deflection increased uniformly from the initial stage until the maximum axial compressive force developed. The middle joint travelled vertically about 313 mm from the first top bar fracture until the end of the test which is approximately twice the distance from the first bottom bar fracture to the first top bar fracture. This can be explained by the presence of partial hinges, in which the steel bars forming these partial hinges enhanced the ductility of the beam after the fracture of the top bars.

Figures 4-37 and 4-38 show the relationships of applied load vs. MJD and axial force vs. MJD for specimen SS-8. Table 4-8 summarises forces and their corresponding middle joint displacements at critical stages of the load-deflection history.

The general trend of the non-linear behaviour of specimen SS-8 was similar to those for specimen SS-2 and SS-3, and the load-deflection history can also be divided into three stages as stated for SS-2 and SS-3. Flexural capacity was attained at a deflection equal to 31.7 mm, which is the smallest deflection compared to other specimens. At a relatively small deflection of 86.7 mm, the maximum applied load of 35.8 kN was attained at CAA.

After first and second bar fracture, catenary action started to develop at a deflection equal to 250.5 mm. At the catenary action stage, the applied load increased to 54.9 kN, which is larger than the applied load at CAA by about 53%. At a deflection of 550 mm, top bars forming the partial hinges at the ends of the specimen fractured simultaneously, which caused a large reduction in the applied load. At that point, the specimen was deemed to have failed, but it could still carry a reduced load until a total collapse at a deflection of 664 mm occurred.

Figure 4-38 Axial Force vs. Middle Joint Displacement Relationship of Specimen SS-8 The maximum axial compressive force was 53.4 kN attained at 90.6 mm of deflection, and the maximum tensile force was 85.7 kN attained at 431.8 mm of deflection. Compared to specimen SS-7, the axial compressive force developed was smaller and the deflection at which the axial tension was attained was also smaller.

Table 4-8 Forces with their MJD’s at critical stages for SS-8

Specimen Calculated flexural capacity with MJD Max. load at CAA 𝑃𝑐𝑜𝑚 Max. Axial compression Force Max. Axial Tension Force Max. Load at Catenary Action 𝑃_𝑓 (kN) MJD (mm) 𝑃_𝑐𝑜𝑚 (kN) MJD (mm) 𝑁_𝑐𝑜𝑚 (kN) MJD (mm) 𝑁_𝑡𝑒𝑛 (kN) MJD (mm) 𝑃_𝑐𝑎𝑡 (kN) MJD (mm) SS-8 29.8 31.7 35.8 86.7 53.4 90.6 85.7 431.8 54.9 437.1

Figure 4-39 shows the converted non-linear static behaviour to the Pseudo-Static behaviour for specimen SS-8. The first peak of progressive collapse resistance was 32.3 kN and the corresponding deflection was 252.2 mm. The second peak of progressive collapse capacity was 38.1 kN with a corresponding deflection 550.2 mm. Similar to specimen SS-7, the first peak was within the catenary action stage, while it was within the compressive arch action stage for the other specimens. Progressive collapse capacity for specimen SS-8 was larger than the capacity for specimen SS-7 by about 7%.

Figure 4-39 Non-linear Pseudo-static response for the specimen SS-8

Figure 4-40 and 4-41 show crack development at different stages of loading. There is no difference in crack pattern and failure mode compared to other specimens. Severe crack and concrete spalling occurred at the left side of the specimen after point “D”. Points A, B and C occur at flexural and compressive arch action, point “D” was the transition point from CAA to catenary action, and points E and F were at catenary action. In addition, the large axial tension caused a crack penetrating the section of the beam, which is shown in the points E and F.

Figure 4-40 Crack Development at different stages for right beam end of specimen SS-8