Experimental and numerical studies of concrete beams prestressed with unbonded tendons

Numerical study on the flexural performance of precast segmental concrete beams with unbonded internal steel tendons

“…Tao and Du [16] tested monolithic beams with unbonded internal tendons and found that increasing f'c led to increasing the tendon stress increment, strength, and deflection capacity of the beams. Similar results were observed in the study by Tanchan [7]. Furthermore, when f'c increased, beams loaded under four-point loading exhibited greater increases in the ultimate moment capacity and stress increment in the tendons compared to the beams under three-point loading.…”

“…Moreover, the increment of stress in the tendons was also affected by Aps. When Aps increased from 161 mm 2 to 742 mm 2 , fps considerably reduced by 35% as observed in the study by Tanchan [7]. Lou et al [17,18] conducted a numerical study on beams prestressed with unbonded fibre-reinforced polymer (FRP) tendons and observed that the ultimate deflection decreased consistently with the increase of prestressing reinforcement ratio.…”

“…However, no explanations for this contradictory observation were provided by the authors. Tanchan [7] conducted a numerical investigation and found that L/dps ratio greatly affected the ultimate moment capacity of the member while only a slight effect was observed for the change in fps. For instance, the ultimate moment capacity decreased by 50% for both four-point and three-point loadings when L/dps increased from 10 to 45.…”

“…The beams with low fpe developed two or three widely spaced cracks and only one of which continued to widen under the applied loads. Tanchan [7] conducted a numerical analysis on beams with unbonded tendons with span-to-depth ratios L/dps varying from 10-18.5 and observed that fpe slightly affected the ultimate moment capacity Mu, but significantly affected the stress increment in the tendons, fps. As fpe increased from 827 MPa to 1241 MPa, the ultimate moment capacity increased by 10% for both four-point loading and three-point loading while fps decreased considerably by 35%.…”

“…In case of monolithic beams with unbonded tendons, it was found that as the area of prestressing steel increased, the ultimate strength capacity of the structure increased, but the deflection capacity decreased. In other words, the beam is less ductile with the increase of the area of the prestressing steel [7,[16][17][18]. All the beams tested by Tao and Du [16] with low values of combined reinforcement ratio were very ductile as they underwent large deflections of 90 to 120 mm (1/47 to 1/35 of the effective span) at failure while that for beams with higher values of combined reinforcement ratio was about 40 to 50 mm (1/105 to 1/93 of effective span).…”