Bending-bearing capacity of UHPC-NC composite negative bending moment region of small box girder
The construction process of negative bending moment tendons of simply supported and then continuous small box girder beam bridge was complex and inefficient,and improper construction can lead to issues such as cracking of the bridge deck.However,the ultra-high performance concrete-normal concrete(UHPC-NC)composite negative bending moment region can effectively address these problems.A 3 × 30 m span small box girder beam bridge was taken as an example,a refined finite element model of the UHPC-NC composite negative bending moment region was established based on the concrete damage plasticity(CDP)constitutive model,and a 1∶2 scaled model test was conducted.Three key parameters influencing the stress performance of the UHPC-NC composite negative bending moment region were identified,UHPC thickness,UHPC layer steel bar diameter,and UHPC tensile strength.The variation in the cracking load and bending-bearing capacity of the negative bending moment region under different combinations of these parameters was studied.The results show that the cracking moment of the test specimen is 3 620 kN·m,the bending-bearing capacity is 9 611 kN·m,while the design value of negative moment for the background bridge example under normal serviceability limit state is 3 300 kN·m,and the design value of negative moment for the ultimate limit state is 5 838 kN·m.The crack resistance and bending-bearing capacity of the UHPC-NC composite negative bending moment region are both in accordance with the engineering requirements,and the experimental results are well consistent with the calculation results of the solid finite element model.For every 25 mm increase in UHPC thickness,the cracking load of the beam increases by approximately 10％and the bending-bearing capacity increases by approximately 9％.The change in UHPC thickness has a significant impact on both the cracking moment and bending-bearing capacity of the UHPC-NC composite beam.For every 2 mm increase in UHPC layer steel bar diameter,the bending-bearing capacity of the beam increases by approximately 6％,while the cracking load only increases by about 1.8％.The different diameters of UHPC layer steel bars primarily affect the residual stiffness and bending-bearing capacity of the beam after cracking,with a minor effect on the cracking load.On the other hand,for every 2 MPa increase in UHPC tensile strength,the bending-bearing capacity of the beam increases by approximately 10％,but the impact on the cracking load is limited.Increasing the UHPC tensile strength leads to an increase in the residual stress of the UHPC layer upon failure,contributing to the bending-bearing capacity of the UHPC-NC composite beam and thus enhancing the bending-bearing capacity of the beam.For a 30 m span small box girder beam bridge,it is recommended that a UHPC length of 2 m be provided on each side of the mid-support,with a UHPC thickness of 200 mm and a UHPC layer steel bar diameter of 10 mm.5 tabs,24 figs,29 refs.
bridge engineeringsimply supported and then continuous structuresmall box gird-ernegative bending momentfinite element analysisparameter analysis
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