The rack assembly contains a number of vertical rail members and each rail member contains two or more column elements, a number of connection elements, and a number of fastening elements. Each column element has a number of connection grooves and sliding grooves. The connection elements are positioned between and connected to two adjacent column elements. Two vertically adjacent connection elements are locked together by a fastening element. The rack assembly allows a number of stretching members movably configured. Each stretching member contains a number of wheel elements and at least an elastic hook element. The wheel elements are embedded into the sliding grooves of a column element and the stretching members as such could slide along the column element to various positions and, by connecting the elastic hook elements to a curtain's various spots, the curtain is stretched from multiple directions.