Study On Bond-slip Properties And Anchorage Length Of Prestressing Strand Used In Nuclear Power Plant

The nuclear power plant containment is the last critical safety barrier of the nuclear island.Therefore,the integrity and tightness of the containment vessel are very important.In China,the nuclear power plant containment vessel adopts bonded prestressed concrete structure.If the fracture or partial fracture of individual prestressing strand is found in operation,it can not be replaced.It is necessary to consider the impact of this situation on the integrity and tightness of the containment vessel.In the process of nuclear power technology export,foreign nuclear safety supervision departments have been paying close attention to this problem.In fact,the prestress is not completely lost after the fracture of individual prestressing strand in the containment vessel.With the support of relevant topics,bond-slip properties and anchorage length of prestressing strand are experimentally and theoretically studied in this paper.The main content and conclusions are as follows:（1）According to a standard test method given by ASTM-A1081A for the bond properties between the cement mortar and prestressing strand.Using 1860 grade prestressing strand of seven wires with low relaxation,6 sets of 36 pull-out specimens are fabricated and tested.The specimens are casted with high strength grouting material,the bond length of steel strand is400mm and 50mm,and the curing time is 1d,7d and 28d.The results show that the bond strength of steel strand and grouting material increases with the growth of age.Under the same age,the average peak bond stress of the standard specimen is smaller than that of the short specimen,and the bond stress-slip curves of the standard specimen do not decrease significantly after the peak stress.（2）Three large post-tensioning prestressed concrete specimens are made and tested.One specimen uses 15 steel strand（7 wires）with a bonding length of 2m.Two specimens use 37steel strand（7 wires）,while bond length is 2m and 5m respectively.The fabrication process is exactly the same as the actual containment vessel.The test shows that the degree of fullness of grouting material in the casing pipe directly affects the bond properties of the prestressing strand,which is the focus of the selection of casing pipe and grouting in the construction of the containment vessel.The three specimens all show the overall bond-slip properties.After reaching or approaching the peak stress,the bond stress changes little with the increase of displacement.（3）The ABAQUS finite element software is used to simulate the specimens in the bond properties test of prestressing strand used in nuclear power plant,and the parameters of local bond-slip model are determined.The finite element model of 55 prestressing strand（7 wires）with the same section but different length is established.The relation between the maximum pull-out force and the length of the specimen is obtained,and the anchorage length of 55prestressing strand（7 wires）with 95%reliability is determined.The results show that when the bond-slip model which based on interface interaction in ABAQUS finite element software is used as the local bond-slip model of prestressing strand and concrete,the model parameter of prestressing strand are:μ=0.3,τ_crit=4.7MPa;the anchorage length of 55 prestressing strand（7wires）for nuclear power plant with 95%reliability is about 12.4m.