Research On Meso-scale Modeling And Size Effect Of Concrete

Concrete has been the most widely used building material because of their moderate price,wide range of resource and construction convenience.As a kind of quasi-brittle material,concrete shows size effect in its mechanical properties,of which the compressive strength is a typical representation,decreasing with the increase of the size.However,according to the existing design codes of concrete structure,the design strength of concrete members is based on small-size specimens.Therefore,the actual strength of large-size concrete members cannot be reflected,leading to different safety margin.This could be an unsafety factor for the design of concrete structure.Previous researches on size effect of concrete were mainly limited to experimental studies,and the specimens were mainly of small sizes.The classical theories regarding size effect cannot be fully calibrated to wide-range sizes.The mesoscale modeling of concrete,as a novel analytical method,breaks through the limit of laboratories’ restriction.Applying this method to the researches of size effect of concrete is able to reduce experimental tests,obtaining more valuable data,and make it convenient to analyze the cause of size effect through meso scale.This research including the three parts below:(1)An analysis was conducted on the design strength of concrete in several codes of different countries and areas(including the USA,Europe,Canada and China)to figure out whether these codes take size effect into consideration.And the influence of size effect of concrete on reliability was studied by comparing the design strength stipulated in the codes with the experimental data collected from the literature.(2)A kind of random aggregate model was established by regarding concrete as a three-phase heterogeneous composite comprised of the aggregates,mortar and the interfaces.The destruction of concrete under axial compression was simulated with the meso-scale model.(3)An effective method that can simulate the size effect of concrete was proposed based on meso-scale modeling.The viability of the model was identified by comparing the simulation results with experimental data.Parameters that influenced the simulation results were analyzed.Moreover,the compressive behavior of concrete columns confined by constant stress was studied with the meso-scale model.The influences of constant confining stress on size effect of concrete columns were also analyzed,paving the way for research on FRP reinforced concrete and concrete-filled-steel-tubular concrete by meso-scale modeling.