Research On Mechanical Performance And Detailing Design Of UHPC Anchorage Zones

Ultra-high performance concrete(UHPC)is a new type of cement-based material with ultra-high strength and excellent durability.The application of UHPC can simplify the details of the anchorage areas,reduce the consumption of steel,and effectively prevent various diseases caused by uncompacted vibration of concrete in construction of post-tensioned prestressed anchorage areas.In this paper,the mechanical performance and design method of the UHPC anchorage area are studied through model tests and theoretical analysis.Details of this study are summarized as follows:(1)Local compression experiments are designed to discuss the influence of some factors on local performance of UHPC specimens such as fiber ratio,local area aspect,indirect reinforcement forms,indirect reinforcement ratio and anchor plate forms.Two expressions to determine UHPC local bearing capacity are proposed from different angles.The first expression is based on constraint enhancement theory.With a simple form and strong applicability,the first expression takes the contribution of steel fibers into account,which endows itself significant advantages over existing calculation formulas;The other expression is based on the plastic upper bound analysis of ideal wedge failure mode.It has a clear mechanic background and a more precise result,but its form is too complex and it cannot consider the contribution of indirect reinforcement.(2)End anchorage zone tests are conducted to study the mechanical performance and design method of UHPC end anchorage zone under loading case of single anchor,two anchors with small spacing and two anchors of large spacing,respectively.On the basis of load-path model(LPM),the cracking load calculating method of splitting crack and spalling crack are proposed,in which the Mohr–Coulomb failure criteria linearised by plastic analysis is adopted to consider the biaxial strength of UHPC under anchors.Then through comparative analysis of 3 alternatives,a reasonable division method of support area is obtained.Finally a conservative calculation method for the tensile capacity of splitting and spalling is suggested using the residual tensile strength of UHPC.(3)The lightweight design method of UHPC anchorage zone is studied.In case of no indirect reinforcement,the finite element analysis of UHPC local compressison specimens with deeply buried bearing plate and flat bearing plate are carried out respectively.Results indicates that if using the flat bearing plate instead of using deeply buried bearing plate in UHPC anchorage zone,following conclusions could be drawn: 1)in local region,the maximum local compressive will increase by 34,which is still in a reasonable range;2)in general region,the increasement of splitting force depends on the height of anchorage section(expressed by “h”).If the h value of specimen is small,the splitting force would increase significantly.If not,the splitting force would not change much.