Finite Element Bond Modeling for Indented Wires in Pretensioned Concrete Crossties
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2016-04-12
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NTL Classification:AGR-INFRASTRUCTURE-Railroads;AGR-SAFETY AND SECURITY-SAFETY AND SECURITY;NTL-RAIL TRANSPORTATION-RAIL TRANSPORTATION;NTL-RAIL TRANSPORTATION-Rail Safety;
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Abstract:Indented wires have been increasingly employed by
concrete crosstie manufacturers to improve the bond between
prestressing steel reinforcements and concrete, as bond can
affect several critical performance measures, including transfer
length, splitting propensity and flexural moment capacity of
concrete ties. While extensive experimental testing has been
conducted at Kansas State University (KSU) to obtain bond
characteristics of about a dozen commonly used prestressing
wires, this paper develops macro-scale or phenomenological
finite element bond models for three typical wires with spiral or
chevron indent patterns. The steel wire-concrete interface is
homogenized and represented with a thin layer of cohesive
elements sandwiched between steel and concrete elements. The
cohesive elements are assigned traction-displacement
constitutive or bond relations that are defined in terms of normal
and shear stresses versus interfacial dilatation and slip within the
elasto-plastic framework. A yield function expressed in
quadratic form of shear stress and linear form of normal stress is
adopted. The yield function takes into account the adhesive
mechanism and hardens in the post-adhesive stage. The plastic
flow rule is defined such that the plastic dilatation evolves with
the plastic slip. The mathematical forms of the yield and plastic
flow functions are the same for all three wire types, but the bond
parameters are specific for each wire. The adhesive, hardening
and dilatational bond parameters are determined for each wire
type based on untensioned pullout tests and pretensioned prism
tests conducted at KSU. Simulation results using these bond
models are further verified with surface strain data measured on
actual concrete crossties made with the three respective
prestressing wires at a tie manufacturing plant.
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