Analysis And Optimization Design Of Long-span Prestressed UHPC-NC Continuous Hybrid Box Girder Bridge

With the increase of service life,the long span PC girder bridge has two major diseases,the cracking of beam body and the continuous deflection in span.Based on Hongyan River Bridge,a new technology and new technology of UHPC-NC continuous hybrid beam are put forward in this paper.The span of UHPC-NC hybrid bridge,the curve of beam bottom,the ratio of middle to high span of fulcrum span and the bundle arrangement of UHPC section of UHPC-NC hybrid bridge are studied in this paper.The continuous beam bridge is more reasonable and the creep deflection is smaller.The main conclusions are as follows:1)the preliminary design of the UHPC-NC hybrid bridge is compared with the original bridge.It can be seen that the stress and deformation of the hybrid bridge in the construction and service stages are better than the original bridge.The deflection caused by shrinkage and creep in 10 years is only 4.35 cm,which is 33.2% lower than that of the original bridge,and 6.20 cm in 20 years,30.8% lower than that of the original bridge.The stress deformation of hybrid bridge is superior to that of the original bridge under the condition of loss of prestressing force of steel beam and the decrease of stiffness of ordinary concrete.It shows that UHPC-NC hybrid bridge has obvious advantages in improving the disease of long span PC beam bridge,which is worthy of further study.(2)The reasonable side principal span ratio of UHPC-NC hybrid beam bridge is0.55 ≤ k 1 ≤ 0.65.In the range of the side principal span ratio,the bending moment of the main beam on both sides of the pier top is approximately equal.The unbalance bending moment of the main pier is smaller.When the length ratio of UHPC segment is 0.3 ≤ k2 ≤ 0.4,the moment and shear force of UHPC-NC connection section are small.The optimal solution of recommended UHPC length ratio by comparison is 0.35.Finally,the ratio of side to main span is reduced to 0.4 by applying the weight of side span cast-in-place section,which makes the bridge more suitable for the construction of canyon area.(3)The way of bunching in the UHPC section of the main pier is recommended to adopt the third method: the UHPC section sets Internal steel bundle and anchored at the fulcrum.The stress value of the key section of the whole bridge with this method is not different from that of the original design,and the stress at the UHPC-NC joint issmaller than that of the other methods.The shear strength of the UHPC-NC hybrid bridge and the position of the main pier are much smaller than that of the original bridge.The shrinkage and creep value of the span in 10 years is 18.9% less than that of the original bridge,20-year shrinkage and creep deflection decreased by 21.7% and the resultant force of all supports of the whole bridge is 96.7% of that of the original bridge.(4)In the optimum design of the height of UHPC-NC hybrid bridge,it is found that when the span ratio of the fulcrum is 1 / 16.4 and the ratio of middle to high span is 1 / 50,the internal force,stress and deflection of each section of the main beam are smaller,the bending strain energy is relatively low,and the stress of the whole bridge is more reasonable.In the optimization of parabola exponent,it is found that when the number of parabola is 1.5,not only the bending strain energy is small and the Internal force and stress at the cross section with high standard deviation rate are both small,the stress of the whole bridge is better.