How to calculate the axial force when the internal force of bent

1. 1. Load: vertical, roof snow load, ash load, roof equipment and roof weight; Self weight of roof truss; Dead weight of column, dead weight of crane beam and track, wheel pressure of traveling crane, etc; Horizontal direction, wind load, trolley braking force (transverse), etc. And the required load combination< Shape: section size of upper and lower column, height of column top, height of corbel, ratio of upper and lower column height, lateral stiffness ratio of side column to middle column, etc
3. When the superposition is the most unfavorable, the bending moment, axial force and shear force of the column foot section, corbel section and crane beam flange elevation section.

2. Multi story frame is a high-order statically indeterminate structure. It is very difficult or even impossible to calculate its internal force and displacement by hand according to the accurate method. Therefore, approximate analysis method is usually used in engineering structure calculation. Next, we will introce several common approximate methods, that is, the reverse bending point method and D-value method under horizontal load, and the secondary distribution method of bending moment under vertical load< Calculation of internal force and displacement of frame under horizontal load
internal force calculation
1. Reverse bending point method
under horizontal load, the joint will proce rotation and lateral displacement at the same time. According to the analysis, when the ratio of the linear stiffness of the beam to that of the column is greater than 3, the rotation angle of the joint will decrease θ It has little influence on the internal force of the frame. Therefore, in order to simplify the calculation, it is usually ignored, that is, assumed θ= 0 In fact, this is equivalent to simplifying the frame beam into a rigid beam with linear stiffness KB = ∞. In this way, the calculation can be greatly simplified, and the error is generally less than 5%
with the above assumption, the section bending moment is zero at 1 / 2 of the column height. The elastic curve of the column changes the concave convex direction at this place, so this place is called the reverse bending point, and the distance from the reverse bending point to the bottom of the column is called the height of the reverse bending point
after the reverse bending point of the column is determined, if the shear force of the column is obtained, the bending moment diagram of the frame can be drawn
2. Improved reverse bending point method - D value method
the above reverse bending point method is only applicable to the case that the linear stiffness ratio of beam to column is greater than 3. If this condition is not satisfied, the lateral stiffness and the position of the reverse bending point of the column will change with the small angle of the frame joint. At this time, using the reverse bending point method to calculate the internal force of the frame will proce large errors
the improved reverse bending point method is introced below. This method approximately considers the influence of the rotation of the frame joints on the lateral stiffness and the height of the anti bending point. The improved reverse bending point method is a simple and accurate approximate method for analyzing the internal forces of frames. Therefore, it is widely used in residential engineering
the lateral stiffness of the column can be obtained by the improved reverse bending point method, which is expressed by D in engineering, so the improved reverse bending point method is also called & quot; D-value method & quot< br />

3. The calculation of concrete bent structure is the stress analysis of single story instrial building columns. Calculate the bending moment mmax + corresponding axial force N and the bending moment M corresponding to axial force nmax + for each possible most unfavorable section. The most disadvantageous sections are the section at the top of the column, the section at the elevation of the crane beam, the section under the bracket and the section at the base of the column. The basic load combination value is used as the design value.

4. Cut a knife at any place between CDs, then keep the upper section and discard the lower section, and substitute a force FCD at the section of the reserved section. Finally, the balance equation is listed as follows:
∑ f = 0, fcd-f2 + F1 = 0, FCD = f2-f1 = 20-20 = 0 (KN)
four word formula of section method (four steps): cutting, discarding, replacing and leveling

5.

It's a hinged bent with unequal height. The calculation of concrete bent structure is the stress analysis of single story instrial building columns. Calculate the bending moment mmax + corresponding axial force N and the bending moment M corresponding to axial force nmax + for each possible most unfavorable section. The most disadvantageous sections are the section at the top of the column, the section at the elevation of the crane beam, the section under the bracket and the section at the base of the column. The basic load combination value is used as the design value

in order to obtain the most unfavorable internal force of the control section of bent column under various loads, which can be used as the basis for column design; At the same time, the most unfavorable internal force of the column bottom section is also the basis of the design foundation, and the bending moment diagram, axial diagram and shear force diagram of the bent column are drawn

extended data

principle: under the action of dead load and live load, the midspan can be approximately replaced by the midspan. Under the representative value of gravity load and horizontal earthquake, the maximum bending moment in the span is calculated by analytical method: first determine the position of the maximum bending moment in the span, and then calculate the bending moment at the position

after the internal forces of the frame under various loading conditions are obtained, the internal forces are combined according to the most unfavorable and possible principle. When considering the favorable effect of redistribution of plastic internal force, the internal force under vertical load should be increased before internal force combination. The combination of dead load and live load controlled by variable load effect and the combination controlled by permanent load effect are considered respectively, and the internal force of the two combinations is compared, and the most unfavorable one is selected. Because the internal force value of the control section of the component should be taken from the edge of the support, the internal force value of each control section (at the edge of the support) should be calculated before the combination

6.

If the bearing section of the beam may have positive bending moment and the mid span section may have negative bending moment e to the action of load, the combination of the bearing section positive bending moment and the mid span section negative bending moment should also be carried out

Generally, two most unfavorable internal forces should be considered in the bearing section of

beam: one is the most unfavorable negative bending moment of the bearing section, and the other is the most unfavorable shear force of the bearing section. The former most unfavorable internal force is used to design the normal section of the bearing section, and the latter most unfavorable internal force is used to design the inclined section of the bearing section, so as to ensure that the bearing section has sufficient bearing capacity. Generally, the most unfavorable positive moment of the midspan section is considered

extended data:

precautions:

1. Bending moment diagram of bent column is obtained by bent analysis of various vertical loads and horizontal loads, and superposition of the most unfavorable combination of several important sections, which is used to calculate design column and reinforcement

Vertical load: reaction force of roof truss support (permanent and variable load), dead weight of crane beam, variable load transmitted by wheel pressure of crane through crane beam, etc; Horizontal load: wind load, trolley braking lateral force of bridge crane, etc

3. Important sections: column base section of top elevation of foundation, column section above and below bracket, column section of top elevation of crane beam, etc

The load acting on the structure is first transferred from the one-way plate to the secondary beam, then from the secondary beam to the main beam, and finally from the main beam to the column and wall. In order to rece the span of the integral one-way slab beam structure, the secondary beam should be set. In order to rece the span of the secondary beam, the main beam should be set. In order to rece the span of the main beam, the column or wall should be set

7. The most rigorous method is to calculate one reinforcement for each group, and then take the maximum reinforcement
this method is not very "practical" unless it is calculated by program
empirically, the most unfavorable combination of internal forces of columns often occurs in the group of maximum bending moment, maximum axial force (including minimum axial force, or tensile force), and maximum shear force. Therefore, the three combinations are selected for reinforcement, and then it is considered that all stress combinations can be satisfied. This is empirical, and the real "worst" may be missed. But the real most unfavorable, may also occur in the actual use of the probability is very small, the structure is generally safe.

8. Hello, I'm glad to answer for you. I hope I can help you
the combination of civil buildings mainly includes dead load, live load, wind load and seismic action, while the combination of instrial buildings mainly includes dead load, live load, wind load, seismic action, snow load, crane load and ash load
ast structure software team

9. In the basic man-machine input of jccad, the load input can be seen, which has the force under various working conditions

10. Bent frame structure is often used in reinforced concrete single story factory building. Bent structure is composed of roof truss or roof beam, column and foundation. Generally, the bent structure or roof beam is hinged, and its foundation is rigid structure. According to the actual engineering structure of the single story factory building, in order to simplify the calculation, the following basic assumptions are made when determining the calculation diagram: (1) the lower end of the bent column is fixed on the top of the foundation 2) The upper end of bent column is hinged with crossbeam (roof truss and roof beam). Crossbeams are usually prefabricated components, which are welded or bolted together by embedded steel plates at the top of columns. This kind of connection can transfer horizontal force and vertical force, but can not transfer bending moment reliably. Therefore, it is more reasonable to assume that the upper end of bent column and cross beam are hinged 3) The beam is a rigid link with negligible axial deformation. Under the action of load, the axial deformation of reinforced concrete or prestressed concrete roof truss is very small, which can be ignored. It is regarded as a rigid link. According to this assumption, the horizontal displacement of the columns at both ends of the beam is equal after the pylon is accepted. However, it should be noted that if the crossbeam is a composite roof truss with lower chord stiffness or a two hinged arch or three hinged arch roof truss, the influence of the axial deformation of the crossbeam on the internal force of the bent column should be considered