Issue 65

S. S. E. Ahmad et alii, Frattura ed Integrità Strutturale, 65 (2023) 270-288; DOI: 10.3221/IGF-ESIS.65.18

Figure 3: Beam details and loading.

Load cell

Spreader

LVDT

Tested Beam

Roller Support

Figure 4: Test setup.

E XPERIMENTAL TEST RESULTS AND DISCUSSION

ll beams are tested up to failure, and load-deflection data, crack patterns, and modes of failures were recorded for each beam. Three different stages during beam loading were observed. The first stage was the pre-cracking of concrete, in which there was a linear relation between the load and deflection of beams. The second stage was posting cracking of concrete in which the stiffness of beams was reduced up to tension steel yielding. After that, concrete crushing or shear failure occurred according to the beam case, as will be shown in the load-deflection curves. Fig. 5.a shows the load-deflection curve for beam ID of 20-20 Min as the control beam (concrete strength is 20 MPa for the two layers of the beam with minimum A s ). The strength of the compression zone in the other beams was 35 or 50 MPa. It can be seen that the load carrying capacity increased from 80.3 kN to reach 81.5 kN for beam of upper layer strength equals 35MPa, with an increment of 1.5%, and from 80.3 kN to reach 105.6 kN for beam of upper layer strength equals 50 MPa, with an increment of 31.3%. A similar behavior was found for the beam's deflection, where the deflection increased from 11.1 mm to reach 12.4 mm for the beam with upper layer strength of 35 MPa with an increment of 11.7%. While the A

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