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The thesis discusses how to design the plastic hinge relocation of New RC beams. The method of hinge relocation referred basically in according with New Zealand Standard (NZS 3101 2006). The study performed the cyclic load testing on the New RC cantilever beams to verify the validation of the plastic hinge relocation design specified in NZS 3101. Meanwhile, this verification is also to check the application to the New RC beams.
To relocate the plastic hinge a distance away from column face toward the beam middle span, an extra beam bar setting at the beam end will be used. That is, the extra steel bars anchored in both beam and into beam-column joint with t-head bars. The extra t-headed bars extended a length normally equal to beam depth (h_b) from column face. The extra flexural strength according to the detailing of the section is increased up to 40%. Then, the plastic hinge can move away a distance of beam depth (450mm). Totally four 350 mm wide x 450 mm deep New RC are tested, in which two are 2.4 meters and the other two are 1.9 meters long. The longitudinal bars are arranged with three SD690 #8 in the top section and three SD690 #10 in the bottom. Three extra t-headed bars (3-SD690 #8) are placed at the top lower and bottom upper layers, respectfully. The transverse bars are arranged with SD790 #3 and SD790 #4. The concrete compressive strength is about 60 MPa. One beam with 2.4 meter long is control specimen RC beam, called as HR-Y0-L. The other with 2.4 meter long, having plastic hinge relocation of 450 mm away from beam end, is called as HR-Y450-L. The other two beams with 1.9 meters long are control specimen (HR-Y0-S) and hinge relocation specimen (HR-Y450-S).
Test results indicated that all the specimens (HR-Y0-L, HR-Y450-L, HR-Y0-S, and HR-Y450-S) satisfied the minimum seismic performance required by ACI 374.2r-13. The load degradation of all specimens happened at the drift ratio of 6%. Because HR-Y450-L and HR-Y450-S arranged more bars (40% increase in flexure) at the column face, it was observed this two specimens increased 20% in shear strength. Thus the design of the hinge relocation can force the plastic hinge exert in the desired region and prevent the joint failure from occurring. However, plastic hinge length (l_p) and and diagonal shear cracks in plastic hinge relocation beams are longer than control beams. The shear crack pattern at the hinge region presented non-smear x-shape and sliding shear like in the plastic hinge zone when the specimens were loaded until drift ratio reached 6%. So, the bent-up extra bars instead of t-headed bars may be used to prevent the non-smear diagonal shear cracks develop. It is also recommended for New RC beams a more conservative design shear of 1.15M_n/l_(n,R) shall be considered to obtain a higher shear demand, where M_n is nominal flexure strength of prototype beams, and l_(n,R) is a beam structural length accounting from new relocated hinge zone. | en_US |