This　paper　focuses　on　theoretical　and　experimental　investigations　of　planar　nonlinear　vibrations　and　chaotic　dynamics　of　an　L-shape　beam　structure　subjected　to　fundamental　harmonic　excitation,　which　is　composed　of　two　beams　with　right-angled　L-shape.　The　ordinary　differential　governing　equation　of　motion　for　the　L-shape　beam　structure　with　two-degree-of-freedom　is　firstly　derived　by　applying　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　L-shape　beam　structure.　Numerical　simulations,　based　on　the　mathematical　model,　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　the　periodic　and　chaotic　motions　of　the　L-shape　beam　structure.　The　existence　of　the　Shilnikov　type　multi-pulse　chaotic　motion　is　also　observed　from　the　numerical　results.　Furthermore,　experimental　investigations　of　the　L-shape　beam　structure　are　performed,　and　there　is　a　qualitative　agreement　between　the　numerical　and　experimental　results.　It　is　also　shown　that　out-of-plane　motion　may　appear　intuitively.