The purpose of this study is to propose calculation formula of maximum deflection and the maximum bending moments of arbitrary shape of slabs, and we treat fixed end quadrilateral slab such as tangential quadrilateral, isosceles trapezoid and right-angled trapezoid subjected to uniform load in this paper. In our previous paper, we proposed the calculation formula of arbitrary triangle slab, where we found out main variables and their compositions of the calculation formula from FEM solutions and we assumed FEM solutions to be the targeted values. In the triangle slab, the main variable was found to be inradius of inscribed circle, because the maximum deflection generally occurs at the further point from the sides and the point is the incenter. So in first half of this paper, we consider whether the calculation formula of tangential quadrilateral slab can be formulated by the same variable. Furthermore, we consider that trapezoid slab is more practical shape, and formulate the calculation formula of that.
