How to attached a part to a beam to determine a load it can handle

Hi,

        I am designing a construction elevator for a school project. I am try to do a stress simulation on the elevator car to determine what it can handle. The car is design using weldment structural components. I want to attach a fix point to the center of the car but I can't because it is a beam elements. Do anybody having any tips that can help me to solve this problem? In addition, I  am using a student edition and educational education for this project.

Ron

SolidworksSimulation