A typical hopper railcar was selected for the case study in this thesis. The solid model of the railcar was created using CATIA, and a preliminary stress analysis was conducted to illustrate the highly stressed areas of the railcar body. Material selection process was done using CES Software, and a third generation aluminum-lithium alloy, i.e. Al 2099, was selected as an alternative to conventional steel. The new material led to 66% weight reduction on the body as compared to conventional steel railcar bodies. Then, a sandwich panel was developed and optimized for the floor panel made of the newly selected material. By that, a 12.5 % weight reduction can be achieved on the body made of Al 2099. Finally, the proposed design was validated using finite element simulations and by comparing their results with the exact analytical solutions.