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Title: Evaluation of parameters affecting thermal stresses in mass concrete
Authors: United States. Army. Corps of Engineers. St. Louis District.
Bombich, Anthony A.
Garner, Sharon B.
Norman, C. Dean.
Keywords: Aging-creep model
Concrete properties
Finite element method
Finite element analysis
Incremental construction
Mass concrete
Thermal stress
Concrete construction
Melvin Price Locks and Dam
Mathematical models
Numerical models
Publisher: Structures Laboratory (U.S.)
Engineer Research and Development Center (U.S.)
Series/Report no.: Technical report (U.S. Army Engineer Waterways Experiment Station) ; SL-91-2.
Description: Technical Report
Abstract: This report describes an investigation to evaluate parameters that affect thermal stresses in mass concrete. This investigation, conducted at the US Army Engineer Waterways Experiment Station (WES) was part of a cooperative effort conducted at Corps District Offices, Corps research laboratories, and several universities to support construction of the second lock in Melvin Price Locks and Dam (MPL&D). The investigation was based upon implementation of ABAQUS, a finite-element program capable of performing complete incremental construction analyses of complex mass concrete structures during and following construction. The report describes a user-defined aging creep material model, UMAT, used with ABAQUS to account for the changes in concrete material strength, modulus of elasticity, creep, shrinkage, etc. following placement in a mass concrete structure. UMAT also contains a smeared cracking model to evolve the onset and effects of cracking. In addition to material aging, ABAQUS includes the capability to simulate placement of incremental stages (lifts) of concrete in a structure, time-stepping, modeling of thermal and mechanical boundaries, model environmental conditions, and provides other user-defined subroutines to model parameters such as heat evolution of cement in the concrete mixtures. The report describes calibration of the UMAT aging creep material model for use in the overall research project. Initially, test data for MPL&D were not available; therefore, the initial UMAT calibration was based on properties of "similar" mixtures. Modulus and creep were predicted using two different equations, and the results compared with the test data for three mass concrete mixtures. Due to limited data available for shrinkage, a curve was assumed based on previous test results at WES. Upon completion of testing MPL&D concrete mixture C2-2 for modulus of elastic modulus, creep, and shrinkage, actual test data were compared with the predicted curves used in the model. The UMAT curve was in fairly good agreement with elastic modulus for the mixture. However, test creep strains were less than half of the UMAT creep equation. The UMAT shrinkage curve approximated the total test strains, but not the shape of the test shrinkage curves. Both shrinkage and creep depend on variables whose contributions to the final properties are not easily determined, such as volumes and properties of the aggregates and chemical composition of the cement paste. It is recommended that properties of mass concretes used in UMAT, especially those at early ages, should be based on test results rather than assumed properties. The report also describes the development of an incremental construction formulation to address aspects of nonlinear finite -element analysis of mass concrete structures that are not common in conventional structural analysis. Accurate computation of thermal stresses during incremental construction finite-element analysis is dependent upon accurate computation of thermal loads produced by variation in concrete temperatures during simulations of construction. The final section addresses requirements and methodologies needed for computation of thermal loads. Through a series of finite-element thermal analyses, grid size and time-step length sensitivity are examined. These analyses were performed using constant and varying ambient temperature boundary conditions. Evaluation of material, placement, and construction parameters were included. Multiple heat generation input curves were implemented, and boundary conditions were varied to simulate curing conditions, ambient conditions, surface insulation, and lift interface equilibration. The thermal analyses were conducted in a sequence of simple-to-more-complex conditions which finally simulated actual conditions. The analyses were based upon finite -element models of an instrumented, incrementally constructed model lock wall, the WES Test Wall, constructed for a related research program. In order to evaluate critical parameters for incremental analyses, computed results from thermal simulations with ABAQUS were compared with measurements made during construction of the WES Test Wall. The report discusses the sequence of analyses including problems and solutions relating to incremental construction methodology in computation of thermal loads. Based upon the results of the investigation, criteria are presented to be applied in the selection of certain parameters used in incremental construction analyses and to identify the state of the art.
Rights: Approved for public release; distribution is unlimited.
Appears in Collections:Technical Report

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