Abstract:Cracking damage influences the stiffness of the girders. Many articles in the literatures have studied the development of stiffness of the scale-down model; however, full-scale model testing cannot be completely replaced by scale-down testing because of material component characteristics and boundary effects. This paper deals with the effects of cracking damage on the structural static and dynamic stiffness based on three prestressed concrete (PC) girders which were removed from an old bridge. First, the equiv… Show more
“…The bending stiffness of the cracked section is reduced by γsEI (γs is the degradation coefficient of the bending stiffness), whereas the bending stiffness in the uncracked sections does not change under a load, as shown in Fig. 1(b) 19 .…”
Section: Bending Stiffness Of Beam With Cracksmentioning
Precast, pretensioned concrete girders are extensively used in bridge engineering to prevent damage to concrete girders, such as the loss of prestress and the corrosion of strands. Existing studies of the mechanical performance and failure characteristics of bridge girders had shortcomings, resulting in potential safety hazards. This study conducted a full-scale model experiment and theoretical analysis of the bending performance of a 35-m long precast, pretensioned concrete I-girder with pretensioned double broken strands. The cracks and bending damage were investigated. The results showed that the maximum vertical displacement of the composite girder was much lower than the required standard value, with a crack factor and bearing capacity factor of 1.31 and 1.54, respectively. The bending stiffness of the composite girder decreased by 70%. Many cracks occurred in the concrete, resulting in excess stress of the steel bars and prestressed strands. The crack width during loading was much smaller than the theoretical one in the Specifications for Highway Reinforced Concrete Prestressed Concrete Bridge Culverts(JTG 3362 − 2018). Therefore, the girder exhibited optimum bending stiffness, sufficient crack resistance, acceptable ultimate bending capacity, and ductile failure performance. The mechanical behavior and failure mechanism during loading were investigated. This study provides recommendations for the design, maintenance, and damage assessment of this bridge type to improve the service lives of bridges.
“…The bending stiffness of the cracked section is reduced by γsEI (γs is the degradation coefficient of the bending stiffness), whereas the bending stiffness in the uncracked sections does not change under a load, as shown in Fig. 1(b) 19 .…”
Section: Bending Stiffness Of Beam With Cracksmentioning
Precast, pretensioned concrete girders are extensively used in bridge engineering to prevent damage to concrete girders, such as the loss of prestress and the corrosion of strands. Existing studies of the mechanical performance and failure characteristics of bridge girders had shortcomings, resulting in potential safety hazards. This study conducted a full-scale model experiment and theoretical analysis of the bending performance of a 35-m long precast, pretensioned concrete I-girder with pretensioned double broken strands. The cracks and bending damage were investigated. The results showed that the maximum vertical displacement of the composite girder was much lower than the required standard value, with a crack factor and bearing capacity factor of 1.31 and 1.54, respectively. The bending stiffness of the composite girder decreased by 70%. Many cracks occurred in the concrete, resulting in excess stress of the steel bars and prestressed strands. The crack width during loading was much smaller than the theoretical one in the Specifications for Highway Reinforced Concrete Prestressed Concrete Bridge Culverts(JTG 3362 − 2018). Therefore, the girder exhibited optimum bending stiffness, sufficient crack resistance, acceptable ultimate bending capacity, and ductile failure performance. The mechanical behavior and failure mechanism during loading were investigated. This study provides recommendations for the design, maintenance, and damage assessment of this bridge type to improve the service lives of bridges.
“…The reason for this is that the tensile strength of UHPC is much greater than that of ordinary concrete, and after a crack is created, the energy to create a new crack is greater than the energy to continue the development of the crack, which is called the “energy-based crack development principle”.Figure 4.Schematic diagram of cracks in prestressed UHPC composite beams: (a) Cracking load stage, (b) Pre-ultimate load stage, (c) Failure stage.Figure 5.Diagram of crack development in the field.Figure 6.Diagram of main bending cracks.Figure 7.Diagram of penetrating cracks.Figure 8.Schematic diagram of cracks in prestressed ordinary concrete: (a) The maximum crack width is 0.6 mm, (b) The maximum crack width is 1.0 mm, (c) The maximum crack width is 1.3 mm. (Zhou et al, 2020). …”
“…Schematic diagram of cracks in prestressed ordinary concrete: (a) The maximum crack width is 0.6 mm, (b) The maximum crack width is 1.0 mm, (c) The maximum crack width is 1.3 mm. (Zhou et al, 2020). …”
“…The stiffness of the beam can be expressed by the curvature of the load-deflection curve. Referring to the research literature (Gong et al, 2007; Yu et al, 2021; Zhang 2004; Zhou et al, 2020) on ordinary concrete beams and prestressed concrete beams, it can be found that the development process of the load-deflection curve of the prestressed UHPC-RC composite beam without web reinforcement is more full compared with that of the prestressed concrete beams as shown in Figure 10, which indicates that the beam stiffness is significantly improved compared with that of the prestressed concrete beams, and the stiffness folding is significantly reduced to approach that of the ordinary concrete beams, which have a more excellent structural performance.Figure 10.Comparison of load-deflection curve diagram.…”
Ultra-High Performance Concrete (UHPC) is a new type of engineering material with high compressive strength, high tensile strength, and high fracture toughness. Its bending failure mechanism is different from that of traditional concrete beams, which requires a new computational model to describe the bending failure phenomena of the prestressed ultra-high performance concrete - reinforced concrete (UHPC-RC) beam without web reinforcement. Therefore, this paper, through full-scale tests on a 30m prestressed UHPC-RC beam without web reinforcement, captures unique bending failure phenomena, including initial cracking, development of local cracks, and rupture of prestressed steel strands. Considering the tension-compression constitutive relationship of UHPC material, an innovative computational model for bending bearing capacity is proposed. Based on this model, a study on the minimum reinforcement ratio of full prestressed-ordinary steel bars is conducted. The results show that in the bending failure of the prestressed UHPC-RC beam without web reinforcement, excessive tensile strain of steel strands will occur at the local crack location. At this time, the structure does not satisfy the assumption of plane sections, and the introduction of the calculation model of the limit state of external prestressed tendons can effectively match this model, which is highly consistent with the experimental results. The minimum reinforcement ratio of full prestressed-ordinary steel bars is revised to the auxiliary reinforcement ratio of full prestressed-ordinary steel bars, quantifying the minimum reinforcement requirements of ordinary steel bars. The research results of this paper can provide reference for the next step of theoretical research.
“…At the beginning of the 21st century, Chinese scholars gradually began to use full-scale model tests to conduct research on the evaluation and maintenance of concrete bridges. A full-scale model test study on three 30 m prestressed concrete box girder was carried out [8], and the results show that the initial damage condition infuences the statistical distribution characteristic parameters of cracks in the box girder after loading. Te stifness decay law of the full-scale test and the scaled-scale model test is not the same.…”
Due to the simple design and convenient construction of prestressed concrete box girder bridges, it is widely used in bridge construction in China. At present, the load test of bridge is the most direct and effective method to evaluate the actual bearing capacity of the structure. However, this method has barriers including high cost, long time, and unfriendly to the damaged structure. Besides, the calculation method of the ultimate bearing capacity of damaged structures is relatively subjective and uncertain. Therefore, this study combines the full-size model test results of a newly built 30 m prestressed concrete box girder, and the mechanical properties of the test beam under three different working states (elastic, elastic-plastic, and plastic stage) are obtained. The stiffness degradation and bearing capacity change law of precast prestressed concrete box girder during failure are investigated. Two different stiffness damage reduction coefficients are defined. Combined with the structural characteristics of this kind of precast prestressed concrete box girder and the calculation formula of flexural rigidity of cracked members given by the code, the calculation formula of the actual residual bearing capacity of members is proposed based on the stiffness damage reduction coefficient. The results show that the reduction coefficients of flexural stiffness defined by the two methods have the same variation trend. The stiffness reduction effect of the box girder after damage is evident. The stiffness reduction of the box girder from the cracking damage to the ultimate bearing capacity state is about 40%, and the stiffness reduction of the two adjacent sections can be approximately linear distribution. The deviation between the residual bearing capacity calculated based on the stiffness damage reduction coefficient and the test value is less than 5%. Combined with the distribution law of the stiffness reduction coefficient along the longitudinal section of the box girder, the distribution law of the actual residual bearing capacity along the longitudinal section of the box girder after the damage occurred in the midspan section can be calculated. This calculation method changes the previous assessment method of structural technical condition from qualitative assessment to quantitative assessment, which can be the reference for evaluating the technical condition of damaged bridges and the calculation of residual bearing capacity in engineering.
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