Flexural tests on pre-tensioned lightweight concrete beams

Abstract

Eight pre-tensioned beams made using lightweight concrete with a design compressive strength of 35 MPa were tested under two symmetrical third-point concentrated loads. The main variables investigated were the eccentricity and effective prestress of the strands and the partial prestressing ratio. The flexural capacity of the beam specimens was compared with predictions obtained from simple equations using the equivalent stress block combined with different formulas proposed for the stress of bonded tendons at the ultimate strength of beams and from non-linear strain compatibility analysis. Test results showed that the normalised flexural capacity measured from pre-tensioned lightweight concrete beams with a reinforcing index below 0 . 15 was comparable to that of pre-tensioned normalweight concrete beams with a similar reinforcing index, while that of a pre-tensioned lightweight concrete beam with a reinforcing index of 0 . 207 was lower than that of pre-tensioned normal weight concrete beams with a reinforcing index of 0 . 2. As a result, the increasing rate of normalised flexural capacity against the reinforcing index in pre-tensioned lightweight concrete beams was slightly lower than that observed in pre-tensioned normal weight concrete beams. The flexural capacity of pre-tensioned concrete beams predicted using an equivalent stress block was marginally influenced by the values determined from different formulas for the stress of bonded tendons at the ultimate strength of beams, although the ratio of the measured and predicted flexural capacities was commonly lower in pre-tensioned lightweight concrete beams than in pre-tensioned normal weight concrete beams.

Flexural capacity and ductility of lightweight concrete T‐beams

“…Compared to normal‐weight concrete (NWC) at similar compressive strength ranges, LWAC exhibits a lower modulus of elasticity and more brittle fracture characteristics 7,8 . Thus, larger deformation and more rapid crack propagation are typically observed in LWAC members than in NWC members 9 . Moreover, LWAC displays a faster slope of stress decrease at the descending branch of the stress–strain curve than that of NWC with the same compressive strength 10 .…”

“…For example, most current code provisions 11,12 do not specifically differentiate the distributions of compressive stresses in LWAC from those in NWC when realizing the equivalent stress block for determining the flexural capacity of reinforced concrete members, even though the actual area under the stress–strain curve decreases as the unit weight of concrete decreases 13 . In addition, it is frequently pointed out 9 that LWAC members reveal lower flexural ductility than NWC members because of the reduced fracture energy and more localized failure zone caused by the cracks passing through the aggregate particles. As a result, it is still controversial how to reasonably evaluate the flexural performance of LWAC members.…”

Editorial

“…The first paper, by Yang et al (2014), presents a series of physical experiments on pre-tensioned lightweight concrete beams. The authors carefully selected a good combination of lightweight concrete and prestressing technique to achieve a sustainable construction system.…”