A　total　of　12　geometric　similar　stirrup-confined　circular　reinforced　concrete　(RC)　columns　subjected　to　axial　compression　were　designed　and　tested.　In　the　tests,　two　stirrup　ratios　of　1.26%　and　2.89%　were　utilized.　The　structural　similarity　ratio　of　the　columns　was　1:1.5:2.25.　The　maximum　cross-sectional　diameter　was　576　mm,　and　the　slenderness　ratio　was　3.　The　confinement　effect　on　the　failure　patterns　and　the　axial　compressive　strength　of　the　stirrup-confined　columns　was　explored.　Moreover,　based　on　the　basic　theory　of　the　Size　Effect　Law　(SEL)　proposed　by　Baant,　a　modified　formula　for　evaluating　the　bearing　capacity　of　stirrup-confined　RC　columns　was　developed,　which　can　reflect　the　effect　of　structural　size.　Good　agreement　between　the　theoretical　results　and　the　test　results　indicated　the　reasonability　of　the　modified　formula.　Finally,　a　3D　meso-scale　numerical　method　for　the　simulation　of　the　failure　behavior　and　size　effect　of　RC　members　was　established.　The　simulated　results　were　consistent　with　the　tested　ones,　and　the　meso-scale　simulation　method　was　then　extended　to　model　the　failure　of　circular　RC　columns　with　larger　structural　dimensions.　©　2018,　Engineering　Mechanics　Press.　All　right　reserved.