Abstract
Background/Objectives: To professionally meet bridge load demands, hollow PC-girders are recently considered for bridge construction, particularly in Japan. Hollow girders are pretensioned girders, which can be a good alternative for ordinary PC-girders by having lightweight, using less material than other beams, and spanning long distances. Hollow PC-girders can be vulnerable to horizontal end cracking at the time of prestressing strand release. Methods: In this study, a nonlinear finite element analysis was performed to investigate the occurrence of horizontal cracks at the time of prestressing at the ends of hollow PC-girders. First, the selected hollow girder was miniaturized to a span length of 4 m required for sufficiently prestressing; then, a standard static prestressing analysis was performed using a finite element analysis software Midas FEA. This software is an analysis tool with standard FEM analysis functions in the construction field and can perform detailed analysis for reinforcements and concrete crack analysis. The software was used to model the girder and investigate the temporal changes of principal stresses at hollow PC-girders’ ends. Findings: The study showed that placing only end-zone reinforcements cannot reduce principal stresses to the level to be less than the concrete’s tensile strength. However, debonding four PC-strands at the ends of the girder alongside the placement of end-zone reinforcements could sufficiently reduce principal stresses to the level to be less than the tensile strength of concrete, and consequently, horizontal cracks were eliminated at the ends of the hollow PC-girder. Keywords: Horizontal cracks; pretensioned girders; hollow PCgirders; finite element analysis; Midas FEA
Highlights
In the 1930s, with the advent of the prestressed concrete industry by French engineer Eugene Freyssinet[1], high strength concrete and high strength steel became economically usable
In Case #2, debonding two PC-strands in the half model reduced principal stresses to the level to be less than the tensile strength of concrete even in the stage of 100% prestressing as shown in Figure 12, and horizontal cracks are not likely to occur in this case
In Case #3, all PC-strands were fully bonded, and one end mesh was placed at each end of the girder; the magnitude of principal stresses was reduced compared to the stresses in Case #1 but not to the desired level to become less than the tensile strength of concrete as shown in Figure 13, and horizontal cracks are likely to occur in Case #3
Summary
In the 1930s, with the advent of the prestressed concrete industry by French engineer Eugene Freyssinet[1], high strength concrete and high strength steel became economically usable. To meet the bridge load demands effectively, pretensioned PC-girders are prestressed heavily in most cases [2]. Several possible sources may increase or decrease the likelihood of horizontal cracking at the ends of pretensioned girders: method of detensioning, the release of the top straight or draped strands before the bottom straight strands, the order of release of bottom strands with the flame cutting method, length of the free strand in the prestressing bed, friction with the bottom form of the prestressing bed, heat concentration during flame cutting, lifting the precast member from the bed, Hoyer effect, use of large strands, unacceptable design of end zone reinforcement, concrete type, low concrete release strength, and strand distribution [3,4,5,6,7,8,9,10]
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