According to the following conditions and requirements, design a reinforced concrete parallel double running stair ( dogleg stair ) of a middle school teaching building. 1. Design conditions
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.

3、 Drawing requirements
1). Draw three plans of the bottom floor, the second floor and the top floor of the staircase (specify the dimensions of the stair flight, platform, elevation, etc.)
2). Draw the stair’s section, scale 1:50
The reference drawing of stair design is attached at the back

3. (20 points) Draw the roof waterproof methods of accessible roof and non -accessible roof respectively.