To　investigate　the　torsion　behavior　of　concrete　composite　box　sections　with　corrugated　steel　webs　and　steel　truss　webs,　the　torsion　bearing　capacity　experiments　were　carried　out.　It　is　found　that　the　diagonal　cracks,　perpendicular　to　the　principal　tensile　strains　of　concrete,　first　appeared　at　the　bottom　plate.　Then　the　cracks　spirally　developed　at　both　the　top　and　the　bottom　plates,　and　the　angle　between　the　cracks　and　the　longitudinal　axis　of　the　main　girder　was　approximately　45　degrees.　Eventually,　some　larger　diagonal　cracks　were　observed　at　the　bottom　plate,　and　the　specimens　failed　by　torsion　damage　after　steel　rebar　yielded　in　tension.　The　nonlinear　finite　element　analysis　(FEA)　for　torsion　test　specimens　was　simulated　using　finite　element　software　ANSYS,　and　the　results　obtained　by　FEA　agreed　well　with　test　results.　The　cracking　torque　formula　of　composite　box　sections　was　proposed　with　reference　to　the　formula　of　concrete　box　girders.　Using　the　variable-angle　spatial　truss　model　for　concrete　box　girders,　the　formula　of　the　ultimate　torque　for　composite　box　sections　was　established　according　to　the　three　probable　torsion　failure　modes.　In　comparison　with　the　results　of　model　test　and　finite　element　analysis　for　actual　structural　size,　the　proposed　formulas　of　torsion　bearing　capacity　of　concrete　composite　box　sections　with　corrugated　steel　webs　and　steel　truss　webs　had　high　accuracy,　and　the　maximum　error　was　less　than　10%.　The　proposed　formulas　can　be　applied　in　practical　bridge　calculation.　©　2016,　Engineering　Mechanics　Press.　All　right　reserved.