To　investigate　the　influence　of　structural　spatial　constraints　on　the　yielding　mechanism　of　frame　structures,reinforced　concrete　(RC)beam　models　with　different　boundary　conditions　were　established　using　a　multiscale　numerical　method.　A　quantitative　analysis　was　conducted　on　the　influence　of　end　constraints　and　the　addition　of　cast-in-place　floor　slabs　on　the　stiffness　and　flexural　capacity　of　RC　frame　beams,i.　e.,the　peak　bending　moment　that　the　specimen　can　withstand.　The　influence　mechanisms　of　end　constraints　and　cast-in-place　floor　slabs　on　the　bending　mechanism　of　RC　beams　were　revealed.　Furthermore,comparative　analyses　were　conducted　with　the　calculated　flexural　capacity　of　various　national　standards.　The　results　indicate　that　structural　spatial　constraints　affect　the　failure　modes　of　RC　frame　beams.　The　stiffness　and　flexural　capacity　of　fixed-end　beams　are　significantly　higher　than　those　of　simply　supported　beams,with　the　flexural　capacity　and　stiffness　of　fixed-end　beams　reaching　up　to　3.　06　and　4.　10　times　those　of　simply　supported　beams,respectively.　The　addition　of　cast-in-place　floor　slabs　significantly　enhances　the　flexural　capacity　and　stiffness　of　the　beams.　National　standards　can　accurately　calculate　the　flexural　capacity　of　simply　supported　beams.　However,　for　fixed-end　beams　and　floor　beams,the　calculated　flexural　capacity　is　extremely　conservative.　For　example,　the　simulated　values　of　fexural　capacity　for　the　fixed-end　beam　with　a　shear　span　ratio　of　5.　0　are　6.　25,6.　76　and　6.　06　times　the　calculated　values　according　to　Chinese,American,and　Canadian　standards,respectively.　©　2024　Southeast　University.　All　rights　reserved.