Railway cars are provided with sidewalls having an optimum number of support posts formed from a first material such as, but not limited to, steel and an optimum number of support posts formed from a second material such as, but not limited to, aluminum to optimize empty car weight and service of life of each railway car. Endwall assemblies, roof assemblies, floor assemblies and other components associated with a railway car may be fabricated from different types of material and an optimum number of supporting structures to reduce manufacturing cost, reduce repair costs, increase service life and increase load carrying capacity. Self piercing rivets may be used to attach two or more layers of material, particularly two or more layers of dissimilar materials. The use of self piercing rivets may also reduce manufacturing and repair costs, increase service life and load carrying capacity of a railway car.