First, let's take a look at how the specification performs this internal force adjustment:
According to high regulations and anti-regulation regulations: in seismic design, the number of shear walls in the frame-shear wall structure must meet certain requirements. This means that the shear wall takes most of the horizontal force as the first line of defense during an earthquake. But this does not mean that the frame part can be designed very weakly. On the contrary, the frame part as the second line of defense must have a certain lateral resistance capability, which requires adjustment of the shear force undertaken by the frame part during calculation. In high regulations, to Vf
Second, understand why the internal force adjustment of the frame part is necessary
I think almost all structural engineers probably know that this is to ensure that the frame serves as a second line of defense for the structure. So what does a detailed analysis look like? First look at the internal force distribution diagram of a typical frame shear wall (this figure is an analytical derivation, and there is a way out from the actual situation. You can refer to the assumptions derived from the theory, but the basic rules are suitable).
The bottom shear wall of the structure needs to bear most of the internal force. The deformation is that the shear wall is small and the frame is large. Therefore, the shear wall plays a leading role in this part, that is, the first line of defense. If the shear force is under the action of external force The wall yielding will transfer a lot of internal force to the frame. At this time, the frame designed based on the elastic analysis will not be able to bear the part of the wall transferred and destroyed, so we need to increase the design internal force of the bottom area frame to achieve its Two lines of defense. Is this still the case for the upper area of ​​the structure? That's not the case, the frame in the top area may bear the effect of shearing forces above the layer and the internal force of the shear wall is reverse to the same as the external force. Therefore, in the upper (especially the top) area, the frame shearing force = external force + wall shearing force! On the other hand, the frame with small deformation and large shear wall is large. At this time, the frame plays a leading role. The frame is helping the shear wall. Then the concept of two lines of defense has shifted, so the top area of ​​the frame shear wall structure The framework needs to be strengthened.
Third, for ordinary frame shear wall structures, what will happen if the rules of the code are implemented?
It should be discussed in two cases. In the first case, when 1.5Vf, max0.2V0, the internal force adjustment of the bottom area of ​​the frame shear wall structure is controlled by 0.2V0, the middle area does not need to be adjusted, and the upper area is controlled by 0.2V0. At this time, there is also a case where the internal force adjustment coefficient is too large for the top area. In this case, the internal force of the adjustment frame is not clear in the structural concept, so HiStruct recommends that if the adjustment coefficient is very high If it is large, the adjustment factor of "2" can be directly used, but in general, since 1.5Vf, max> 0.2V0, it means that the frame part is not too weak, that is, the adjustment factor of 0.2V0 on the top is generally not too large, and can be designed Down. When V0 can not be adopted in the specification, it is also considered that the top area of ​​the frame shear wall structure needs to be strengthened. Therefore, from the perspective of safety, the provisions of the specification should be implemented honestly.
Fourth, some internal force adjustment measures under special circumstances
There are some special situations in actual structural design. HiStruct gives some examples for your reference. In fact, as long as the frame shear wall structure is truly understood, then the conceptual design and seismic measures need to be strengthened naturally. (1) Frame tube structure with reinforced layer, in this case, the internal force of the frame near the reinforced layer generally has a large abrupt change, Vf, max need not be adopted according to this, but should be grasped from the overall concept, but due to the specification The design of the office is not specified, because it is recommended to strengthen it appropriately. (2) For mixed structures, see the requirements of the code, and raise the requirements appropriately. (3) Frame limb column, see specification requirements. (4) The structure has obvious regular segments, such as vertical component reduction, elevation indentation, conversion, etc., segment adjustment can be considered, but the overall grasp should be emphasized. (5) A small number of large frame columns may have fewer frame columns due to architectural layout and other reasons. If you want to break through the code, you must propose a program review. You can refer to the internal force adjustment regulations or stronger measures for a small number of frame limb columns.
Finally, the conclusion
In fact, only if you really understand the structure system of the frame shear wall, on the basis of theoretical basis and structural concept design, you can deeply understand the rules and regulations. When faced with the ever-changing special situations in structural design, the specific problems are analyzed specifically, then the design ideas and strengthening The measures will come naturally.
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