What are the reasons for the splayed cracks at the junction of primary and secondary beams of frame structure? Most of the primary and secondary beam joints in the whole building are like this.

What you said is probably caused by insufficient shear strength of beam members, and the possible reasons are as follows:

1, design defect (at present, it is all software calculation, so this possibility is the least)

2, the concrete strength is insufficient

3. The steel bars are not set according to the design or specifications, especially the hanging bars and the encrypted stirrups.

4, unauthorized replacement of masonry materials.