In order to aid design for environmental vibration, a simplified analysis for a floor slab is presented. The floor slab is supposed to be rectangular orthotropic Mindlin plates with Timoshenko beams. Then, the Rayleigh-Ritz method is adopted using Timoshenko beam functions with elastic restraint against translation and rotation as admissible functions. Since point supports are also considered, it is possible to create appropriate boundary conditions. Furthermore, a moving load and SMD (Spring-Mass-Dashpot) system are taken into account to stand for a moving body on the floor slab such as a forklift.