In　order　to　simulate　the　real　load-carrying　capability　of　strengthened　components　in　practical　engineering,　the　original　concrete　components　were　strengthened　and　cured　with　self-compacting　concrete　while　continuously　under　load.　Flexural　testing　was　carried　out　on　7　RC　beams　strengthened　with　self-compacting　concrete　under　secondary　load　and　2　beams　without　strengthening.　Different　initial　forces,　different　strengthening　thicknesses　and　different　methods　of　interface　treatment　were　studied　to　find　the　corresponding　effects　on　the　flexural　capacity　and　section　stiffness　of　the　strengthened　beams.　Crack　distribution　patterns,　load-deflection　curves　and　development　law　of　steel　strain　were　measured　in　the　test.　The　results　show　that　strengthening　RC　beams　with　self-compacting　concrete　can　significantly　improve　the　flexural　capacity,　section　stiffness,　and　crack　resistance　of　the　RC　beams.　The　flexural　capacity　of　the　RC　beams　strengthened　with　self-compacting　concrete　under　secondary　load　was　reduced　with　the　increase　of　the　initial　load.　Based　on　the　test　results　and　the　plane　section　assumption,　formulae　predicting　the　lagged　strain　and　the　flexural　capacity　of　the　beams　strengthened　by　self-compacting　concrete　were　proposed,　and　the　calculation　results　were　in　good　agreement　with　the　test　results.　©,　2015,　Tsinghua　University.　All　right　reserved.