The figure shows the connection in a common node of the frame rafter, column and ribs.
In multi-storey buildings, columns have a variable cross-section in height. The cross-section is changed at the height of the transom or the floor slab. Details of the column reinforcement when changing the cross-section are shown in Fig. b.
The ribs located perpendicular to the frame transoms ensure the building's stiffness in the longitudinal direction, this is especially true for ribs along the axis of the columns, because they together with the columns form a multi-span frame system.
The floor slab transfers the load from the floor to the ribs, it is one-way reinforced and the main reinforcement is located at the bottom of the slab and above the ribs at the top (support) perpendicular to the ribs. In the longitudinal direction, parallel to the ribs, the distributive reinforcement is assumed. Rods with a diameter are used to reinforce the plates 6-14 mm. Bars with smaller diameters are used for thinner plates.
Mullion-transom system; a) view, b) slab reinforcement; 1 – pole, 2 - transverse bolt, 3 - longitudinal bolt, 4 - plate, 5 - main bars of the bottom reinforcement, 6 - main bars of the top reinforcement (over the crossbars).
Another mullion-transom structure is shown in the drawing. There are transoms in the axes of the pillars in both directions of the building, which are connected by rigid nodes to the columns. As a result, transverse and longitudinal frames were obtained, ensuring the stiffness of the building. The poles in this type of system are placed on grids similar to a square with dimensions 5,0-7,0 m. A plate with a thickness of approx. 16-20 cm. The slab is reinforced with the bottom in the span and the top above the supports. The bottom reinforcement of the slab consists of bars arranged in both directions (cross reinforcement), while the upper ones (Lynx. b) they are the main bars arranged above the ribs perpendicular to the ribs, which are connected by separating bars arranged parallel to the ribs.
The thickness of the cross-reinforced plates is assumed within the limits 1/45 l(l— shorter spread) and no less from 15 cm. These ceilings are used where the service loads are less than 3,0 kN/m2. For larger spans of transoms and loads greater than 3,0 kN / m2, a much greater board thickness and transom height are required.