The first is to ensure the integrity of the main girder: ready-mixed commercial concrete is used now, which is very mobile. Pouring concrete along the beam will cause a certain flow in the beam groove template. When the flow rate is large or the material is stopped in the process, it is easy to produce cold joints in the beam. The primary and secondary beams are generally vertical, and the lesser of the two evils is taken. So choose to pour concrete along the beam direction to ensure that the main beam concrete is basically formed at one time.

The second is to ensure the compliance of the construction joint position: the code requires that the beam construction joint should be located at the position with the minimum relative shear, simple force and convenient construction, and the construction joint of the primary and secondary beams should be located at 1/3 of the secondary beam span, so it is necessary to pour in sequence according to the beam direction.

The beam bearing on the column is the main beam, and the bearing on the main beam or the secondary beam is the secondary beam. In the code, the main beam and frame beam are marked with "KL" and the secondary beam with "L", but there are some irregularities in the design of the main beam and secondary beam.

It can be considered from two aspects: mechanical characteristics and structural characteristics: the load is transferred from the plate to the secondary beam and then to the main beam, and then from the main beam to the column. So generally speaking, the main beam overlaps the column and the secondary beam overlaps the main beam.

The main beam of extended data is the main skeleton to undertake the safety of the whole building structure, and it is a necessary component to meet the requirements of strength and stability, paying more attention to the strength requirements. The secondary beam is a secondary skeleton designed to meet the building requirements and the effective connection of the main beam and column, and pays more attention to the structural requirements.

Secondary beam reinforcement should be anchored on the main beam.

Principles for adding secondary beams:

(1) In order to support the partition wall, a secondary beam with a width greater than 250mm is set at the position with the partition wall, and the beam height is calculated by span: h >；; l/ 18~ l/ 12 .

(2) When there is no partition wall:

One-way slab, and the ratio of long side to short side is greater than or equal to 3, no secondary beam is required. Two-way slab, when the slab in any direction is longer than 5m, the secondary beam shall be set. (If it is between 5m and 6m, no secondary beam is needed. )

Baidu encyclopedia-primary and secondary beams