Global　bifurcations　and　multi-pulse　chaotic　motions　of　flexible　multi-beam　structures　derived　from　an　L-shaped　beam　resting　on　a　vibrating　base　are　investigated　considering　one　to　two　internal　resonance　and　principal　resonance.　Base　on　the　exact　modal　functions　and　the　orthogonality　conditions　of　global　modes,　the　PDEs　of　the　structure　including　both　nonlinear　coupling　and　nonlinear　inertia　are　discretized　into　a　set　of　coupled　autoparametric　ODES　by　using　Galerkin＇s　technique.　The　method　of　multiple　scales　is　applied　to　yield　a　set　of　autonomous　equations　of　the　first　order　approximations　to　the　response　of　the　dynamical　system.　A　generalized　Melnikov　method　is　used　to　study　global　dynamics　for　the　＂resonance　case＂.　The　present　analysis　indicates　multi-pulse　chaotic　motions　result　from　the　existence　of　Silnikov＇s　type　of　homoclinic　orbits　and　the　critical　parameter　surface　under　which　the　system　may　exhibit　chaos　in　the　sense　of　Smale　horseshoes　are　obtained.　The　global　results　are　finally　interpreted　in　terms　of　the　physical　motion　of　such　flexible　multi-beam　structure　and　the　dynamical　mechanism　on　chaotic　pattern　conversion　between　the　localized　mode　and　the　coupled　mode　are　revealed.　(C)　2017　Elsevier　Ltd.　All　rights　reserved.