Two-way reinforcement of cast-in-place slab is to arrange reinforcement in X and Y directions, which is two-way.

Double-layer, because the board has a certain thickness, so use a layer of steel bar at the top of the board and a layer of steel bar at the bottom of the board, which is double-layer.

Double-layer two-way reinforcement, the short-term reinforcement at the bottom of the plate should be placed in the lower part and the long-term reinforcement should be placed on it; For surface reinforcement, short-direction reinforcement should be placed at the top, and long-direction reinforcement should be below short-direction reinforcement. When setting double-layer bidirectional reinforcement, it is generally not necessary to set negative slab reinforcement.

-Quoted from Baidu know.