The teaching building of a middle school has three stories, 3.0 m in height, 3.0 m in staircase ( room ) bay ( width ). The minimum depth ( length) is determined by yourself. The entrance and exit are required on the ground floor. The four walls of the staircase ( room ) are ordinary 240mm (wall thickness) bearing brick walls. The height difference between indoor and outdoor is 600mm. 2. Design requirements 1). According to the above conditions, design the width, length, step size and step number of stair flight. 2). Determine the width of intermediate platform and floor platform. 3). Determine the reasonable structural support mode. 4). Determine the form and size of railings.