Creep and shrinkage of HPC in prebended composite structures. Part II: in situ case study

Abstract

A prefabricated, prebended and prestressed railway bridge deck was instrumented in June 2000 with strain gauges and vibrating wire extensometers. It is a kind of structure in which large time-dependent stress redistributions between steel and concrete are expected to occur. The purpose of this paper is to report on the comparison between strains recorded in situ on an instrumented bridge deck of this kind up to four years after its construction with values computed within the framework of four different time-dependent analyses: (a) a pseudo-elastic analysis with variable modular ratios for concrete used for the design of these bridge decks; (b) a step-by-step method applying the principle of superposition; (c) a step-by-step method incorporating a recovery function; and (d) an original modelling method. This final analysis is presented in Part 1 of this paper, which is based on the evolution of three fundamental local parameters: the temperature, the degree of advancement of reaction of hydration and the water content in concrete.

Creep and shrinkage of HPC in prebended composite structures. Part I: modelling

“…adjustment parameters C free water content C eq water content at the equilibrium with the external relative humidity C ini initial water content in concrete C ì stiffness of the ìth Kelvin unit c o initial cement content C 1 water content owing to the drying process and the water consumption by the cement hydration reaction C 2 water content owing to the internal water consumption by the cement hydration reaction C 100 water content corresponding to a relative humidity of 100% @C/@h slope of the desorption isotherm D diffusion coefficient E a activation energy E 0 p c j delayed modulus of the jth concrete phase at time t p ECH exchange coefficient f c, 28 average compressive strength at 28 days h internal relative humidity J compliance function K slope k coefficient of hydrous contraction m i ratio between the mass of each anhydrous compound and the total mass of cement N number of Kelvin units n normal to the boundary of the volume element P 0 initial mass (˜P/P) relative mass loss (˜P/P) 0 threshold of the relative mass loss p index of the time step p i mass of water which is needed for a complete hydration of each cement anhydrous compound per unit mass of the anhydrous compound Q activation energy with the influence of the temperature on the kinetics of drying ¼ 4700 K À1 q water content which is consumed per hydrated cement unit R gas constant S surface T temperature of concrete at a given time…”

“…temperature of concrete at the initial time T 1 ultimate temperature during the adiabatic calorimetric experiment t time w…”