This　paper　discusses　theoretical　and　experimental　investigations　of　the　planar　nonlinear　vibrations　and　chaotic　dynamics　of　a　beam　structure　composed　of　two　beams　with　right-angled　L-shape.　Differential　equations　of　motion　for　the　L-shape　beam　structure　with　two-degree-of-freedom　are　derived　firstly　by　application　of　the　substructure　synthesis　method　and　the　Lagrangian　equation.　Then,　the　method　of　multiple　scales　is　utilized　to　obtain　a　four-dimensional　averaged　equation　of　the　structure.　Based　on　the　averaged　equations,　numerical　simulations　are　presented　to　analyze　the　nonlinear　responses　and　chaotic　dynamics　of　the　L-shape　beam　structure.　The　bifurcation　diagram,　phase　portrait,　amplitude　spectrum　and　Poincare　map　are　plotted　to　illustrate　that　the　periodic　solutions　and　chaotic　motions　occur　in　the　planar　nonlinear　vibrations　of　the　L-shaped　beam　structure　under　certain　conditions.　Finally,　the　experimental　apparatus　and　schemes　for　measuring　the　amplitude　of　nonlinear　vibrations　for　the　L-shape　beam　structure　are　introduced　briefly.　Then,　the　detailed　analysis　for　experimental　data　and　signals　which　represent　the　nonlinear　responses　of　the　beam　structure　are　given.　Copyright　©　2009　by　ASME.