Changsha University of Science and Technology, China
*Corresponding author:Lei Wang, Changsha University of Science and Technology, No. 960 Wanjiali Road, 410114, Changsha, Hunan, China
Submission: August 1, 2018;Published: August 13, 2018
ISSN: 2640-9690Volume1 Issue2
Strand corrosion is one of the main causes for the deterioration of Pre-stressed concrete structures. Corrosion decreases strand cross-section, causes material deterioration, induces concrete cracking, degrades bond strength and deteriorates the capacity of PC beams. As the high-stress level of prestressing strand, strand corrosion causes a brittle failure of PC beams without warnings. The potential dangers of corrosion in PC beams would be much more severe than that in reinforced concrete members. The structural behaviors should be thoroughly investigated to insure the serviceability and safety of corroded PC beams.
Keywords: Pre-stressed concrete beams; Strand corrosion; Concrete cracking; Bond strength; Structural behaviors
Pre-stressed concrete (PC) has been widely used in engineering structures due to its superior performances and high durability. Unfortunately, some failure cases raise concerns over the safety of existing PC structures. For example, the Ynys-Y-G was Bridge in the United Kingdom collapsed in 1985 due to corrosion of posttensioning tendons after only 32 years of service. Italy’s Saint Stefano Bridge failed in 1999, after 40 years of service, due to pitting corrosion of the pre-stressing steel [1,2]. Strand corrosion is one of the main causes for the deterioration of PC structures. Corrosion decreases strand cross-section, causes material deterioration, induces concrete cracking, degrades bond strength and deteriorates the capacity of PC beams [3-5], as shown in Figure 1. AS the highstress level of pre-stressing strand, strand corrosion can cause a brittle failure of PC beams without warnings. The potential dangers of corrosion in PC beams would be much more severe than that in reinforced concrete members. The structural behaviors should be thoroughly investigated to insure the serviceability and safety of corroded PC beams.
Strand corrosion can induce concrete cracking. A considerable number of studies have been undertaken on corrosion-induced cracking in reinforced concrete (RC) structures [6-8]. However, very few works have been reported on corrosion-induced cracking in PC structures. Concrete around the strand would be under a biaxial stress state during the corrosion process; horizontal expansive pressure, and pre-stress in a longitudinal direction . Additionally, a strand consists of several outer wires spiraled around a core wire and has a flower-like cross-section. The high stress level and geometric properties of the strand may lead to the corrosion-induced cracking process in PC structures different from that in RC structures . The strand corrosion-induced cracking mechanism in PC structures has not been clarified, which needs to be investigated further.
Corrosion leads to the cracking of the concrete cover and decreases the cross section of strand. These changes deteriorate the bond strength between strand and concrete. For pre-tensioned concrete structures, the effective bond strength is particularly important as compared to other structures. Many studies have been performed to investigate corrosion’s effects on the bond strength between steel reinforcements and concrete in the past few decades [11,12]. However, the material and shape of the pre-stressing strand are very different than those of the steel reinforcements . Thus, corrosion’s effects and the existing bond strength models for steel bars may not be suitable for the twisted pre-stressing strand.
Strand corrosion expansion can induce concrete cracking and degrade bond strength, which would further cause the prestress loss in corroded PC beams. Numerous studies have been undertaken to assess the effects of concrete creep and shrinkage, and the stress relaxation of pre-stressed strands on long-term prestress losses [14,15]. As compared with researches on long-term pre-stress losses, studies regarding corrosion-induced pre-stress loss have been afforded little attention. The evaluation of corrosioninduced pre-stress loss is a complicated issue. Except for the crosssection reduction of corroded strand, concrete cracking and bond degradation can also cause pre-stress loss. Additionally, posttensioned concrete beams use the anchorage systems to transmit the pre-stress, while the pre-stress in pre-tensioned concrete beams is built through the bond stress at the strand-concrete interface. The pre-stress loss in pre-tensioned concrete beams may be different from that in post-tensioned concrete beams. How to evaluate the pre-stress loss in PC beams caused by corrosive cracking still needs to be studied further.
Corrosion can deteriorate the flexural capacity of PC beams by decreasing strand cross-section, causing material deterioration, inducing concrete cracking and degrading bond strength . Some experimental studies have been undertaken to investigate the flexural behaviors of corroded PC beams [17-19]. Based on the load testing, corrosion effects on concrete cracking, stiffness, ultimate strength, ductility and failure mode of PC beams have been evaluated. However, very few analytical studies have been undertaken to predict the flexural capacity of corroded PC beams. Cavell et al.  neglected the effect of bond degradation, and used a strain compatibility theory to study the residual flexural capacity of deteriorating PC beams caused by tendon failure. Wang et al.  proposed a strain-incompatibility analysis method to evaluate the flexural capacity of corroded PC members, but it failed to consider the effect of concrete cracking. The effect of strand corrosion on structural behaviors has not been clarified. More studies are needed to explore the capacity deterioration mechanism in corroded PC beams. The structural behaviors of corroded PC beams are the complicated issues. This paper is intended to provide a brief summary of information needed by researchers to understand the challenge in the structural behaviors of corroded PC beams. Hopefully, much effort will be made to identify this topic and to find better solutions to address the existing issues.
© 2018 Lei Wang. This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and build upon your work non-commercially.