Long-tern field test and numerical simulation of foamed polyurethane insulation on concrete dam in severely cold region

摘要

The environmental temperature is the key factor for cracking failure of mass concrete structures in severely cold regions. In this paper, field test and numerical calculation of long term insulation are carried out to prevent thermal cracks, and ensure the durability and safety of concrete arch dam. Firstly, an equivalent simulation element for concrete-polyurethane composite structure and its calculation method is proposed, based on the equivalence idea of heat emission coefficient for concrete layer and surface insulation layers with different thickness. Secondly, field tests are demonstrated on an 87.5 m height concrete gravity-arch dam, named Xianghongdian dam, from January 1, 2001 to May 30, 2017. Distributions laws, change laws of temperature field and horizontal displacement of the dam, before and after setting polyurethane insulation layer, are compared deeply. Then, the insulation effects of different thicknesses of foamed polyurethane layer are investigated upon the establishment of a FEM model of a concrete arch dam in northwest China. Consequently, stress fields under different broken conditions of polyurethane insulation layer with different typical temperature loads in severely cold region are calculated and analyzed. The results show that the polyurethane insulation layer generally decreases the temperature change range of concrete dam body over 30% in all conditions and even 90% at some locations. Accordingly, the horizontal displacement component, caused by dam temperature, decreases greatly from 10.80 mm to 2.34 mm and its contribution ratio to yearly horizontal displacement decreases from 75.11% to 36.23%. The insulation layer broken would result in a sharp increase of tensile stress of the corresponding area, with the combination influences of low temperature and cold wave. Under small broken condition, the tensile stress increases from 3.69 MPa to 7.57 MPa among broken area; while under large broken condition, the tensile stress increases to 8.68 MPa, which exceeds the maximum tensile stress of concrete material. In this case, a cracking failure of concrete structure would happen. As the dam concrete is an insulation material in some degree, the stress filed doesn't change a lot in areas the insulation layer is unbroken. (C) 2019 Elsevier Ltd. All rights reserved.