What is the appropriate value of the ratio K of the longitudinal reinforcement in the tension zone o

There are many examples of asymmetrical reinforcement and segmented reinforcement. The asymmetric reinforcement mainly considers the compression area and the tension area, that is, the distinction between the inner side of the foundation pit and the outer side of the foundation pit; Segmented reinforcement can also be selected in the software of the deep foundation pit, and the segmented reinforcement is mainly to save the amount of reinforcement, usually the position of the bending moment changes greatly or 1m to start the section, and the segmentation can be divided into many sections, which is a comprehensive consideration of the difficulty of construction operation and the amount of steel bar. In our area, the length of the foundation pit support pile is not very long, and it can be used by butt welding or mechanical connection, without considering the stress concentration of the connection point.

1. Non-uniform reinforcement refers to the section because the section of the retaining pile is usually circular (bored pile), which is very similar to the general bored pile construction (the common bored pile is uniformly reinforced, and the main consideration is the axial bearing effect), but the enclosure pile is bent, because the contribution of the concrete and axial reinforcement to the resistance to the bending moment is very small, from the economic consideration, the steel bar is mainly distributed on both sides, rather than uniform reinforcement 2, the segmented reinforcement refers to the longitudinal force analysis, and the bending moment can generally be seen to change in the longitudinal direction. From economic considerations, for large bending moments with more reinforcements, small bending moments are less reinforced, but how to segment, generally to consider a certain excess, after all, the calculation is an ideal state 3, there is a point to point out, the kind of complete gradual reinforcement that the old hat hopes for does not exist in the construction, because there are only those types of steel bars, and the convenience of construction should be considered 4, as for the operation, I think you can choose a small diameter of steel bars with more matching, so that you can achieve segmented reinforcement 5, as for welding, Different diameters can be welded together, but why weld?

In the actual design, in order to reduce the difficulty of construction and prevent too many changes from causing mismatching, the longitudinal reinforcement is divided into 3 or 4 sections at most, and one is too idealized in design, and the second is that the construction unit will scold the mother The uneven cross-section reinforcement is generally used for digging piles and not for bored piles, mainly because the bored pile reinforcement cage is lifted, and may rotate during the placement process, and the azimuth accuracy required by the design is not reached, and the reinforcement cage of the excavated pile is tied within the pile and will not move. There are two main factors to consider: 1. Reasonably divide the interval of the bending saw; 2. Consider the convenience and feasibility of construction.

The construction of uneven reinforcement engineering, long spiral reverse insertion reinforcement cage, reinforcement cage is really not easy to control, compression, tension area position is difficult to control, digging cantilever pile, the force is relatively clear, can use cross-section uneven reinforcement, longitudinal uneven reinforcement is not recommended, 1, generally according to the bending moment envelope diagram using the same specification of steel bars in the longitudinal change quantity: such as the bending moment of the large place to use 30, the bending moment of the medium use of 20, the bending moment of the small place to use 10, no bending moment of the place you can only with the construction of the reinforcement. 2. Where the number of steel bars changes, the effective truncated length of the longitudinal steel bar should be considered

For example, when calculating the transition between medium and small, the length of the longitudinal reinforcement to be truncated according to the envelope diagram should exceed the envelope diagramThe main thing is that there are three problems: 1

The construction is inconvenient 2There is a risk in doing so: the strata and stresses revealed in the survey report used in the calculation are not necessarily the actual situation, so if the local actual stress is too large, will it lead to excessive bending moment and cause the slope protection pile to break?

3.The amount of reinforcement that is actually reduced by doing so is not very much construction error.

The distance from the resultant point of the longitudinal reinforcement in the tension zone to the compressive edge of the cross-section is h0

This is solved according to the mechanical equilibrium.

The relevant c represents the thick soil of the protective layer, and AS represents the distance from the resultant point of the longitudinal reinforcement in the tension zone to the tension edge of the cross-section, so h0=h-as