The Research On The Performance Of Reinforced Concrete Frame Structure During Construction

Studies about performances of reinforced concrete framed structures during construction provide research foundation for security during construction, and safety and durability during usage. Performances of concrete at early age, structural characteristics and reliability have played important roles in domestic and foreign studies about structures during construction. In this paper, performances of loaded concrete at early age, characteristics and dynamics of reinforced concrete framed structures during construction were experimentally and theoretically studied. The following research contents were mainly obtained:Time-variant rules about mechanical properties and constitutive relationship of concrete conserved with standard condition at early age versus conserved time were experimentally studied. Relationship functions between both compressive strength and elastic modulus of early-aged concrete and conserved time were established, whose fitting coefficients were gained by non-linear least squares fitting to experimental data. Dimensionless experimental relationship curves about uniaxial compression stress versus strain of early-aged concrete prism specimens were researched, and were compared with Z. H. GUO's empirical curves supplied in national concrete design code, whose parameters: a andαwere recommended.Time-variant rules about mechanical properties and constitutive relationship of concrete loaded from early age to 28 D versus conserved time were experimentally studied. At earlier age loading higher stress to concrete specimens of lower strength grade, compressive strength and plastic deformation ability of concrete loaded were decreasing more distinctly. Through analysis of test data, their affected range on loading time and stress continuously loading were gained. Dimensionless experimental relationship curves about uniaxial compression stress versus strain of concrete prism specimens loaded at early age were given, which were compared with Z. H. GUO's empirical curves and parameters of empirical formulas were recommended.Experimental studies were carried out, and focus on the effects of fly ash replacement content and water-to-cementations mass ratio on time-dependent compressive strength, elastic modulus and shrinkages of concretes cured for a period from curing to 180 day after curing. Fitting formulas about relationship of shrinkage versus compressive strength were given based on test data. Interactional mechanism about reinforced concrete framed structure during construction and temporary shoring frameworks were researched by experiments. Experimental results show that interactional systems of reinforced concrete framed structure and temporary shoring frameworks loaded less than cracked loading calculated by concrete properties at loading age was linear system, and to less extent, concrete's shrinkage and creep effected systems on the non-linear. Internal force on steel pipe supports had been decreasing with concretes'increasing age. It was at basic age of 15 d when internal forces and deformation of the system achieved stabilization.With numerical simulation, time-dependent characteristics about construction procedure of concrete framed structures were studied. Numerical computational formulas about concrete's time-dependent stress-strain coupled mechanism were deduced, in which the creep deformation of concrete was described in accordance with a trapezoid integral algorithm based on the expansion of a degenerated kernel of the compliance function. In addition, the finite element method submitted to the increment algorithm was established to analyze both non-mechanical deformations induced by the time-dependent deformations of concrete and mechanical deformations induced by external loads after long-term loads. They were illustrated with a reinforced concrete beam and a column, which of time-dependent behaviors by being loaded in early period had been tested. The numerical analysis results were in agreement with experimental data. Based on floor-by-floor superposition method and considering impacts of construction procedures, concrete shrinkage and creep, calculating models about concrete framed structures during construction were established, using which effects of constructional cycle, supporting stiffness, and concrete shrinkage and creep on cumulated vertical deforms of columns were calculated. The results show that 1) longer constructional cycle versus less cumulated vertical deforms of columns, 2) more supporting stiffness versus less deforms at the top of structures, and more deforms at the bottom, 3) concrete shrinkage and creep affects more on cumulated vertical deforms of inside columns than outsider ones.It was based on failure model of concrete cracks that limit-stated equations of reinforced concrete structures during construction were presented. Based on concrete time-dependent characteristics, both random model of time-variant resistance and probability model of loading effect were established. Monte-Carlo method in which essentially sampling procedures were numerically simulated was deduced, with which reliability analysis of dynamic structural model during construction was carried out. It was illustrated that crack reliability about reinforced concrete framed structure during construction was calculated,and some recommendation about construction were presented.The effects of concrete's time-variant elastic modulus, casting structural components, assembling temporary shoring framework system, and shock by operating construction equipments on dynamic characteristics of reinforced concrete frame structure during construction were experimentally investigated. Dynamic tests of an eight-storey reinforced concrete framed structure during full-scaled stages of the sixth storey and the housetop construction cycle were carried out by ambient vibration. Transfer functions of Structures were gained processing the testing signal data in frequency domain, with which natural frequencies, corresponding mode shapes and damping ratio were determined, and their rules at different construction stages were given.