Study On Bearing Capacity And Digital Sectional Analysis Of RC Column Strengthened By Increasing Section Area Based On Strain Control

It is sophisticated to unify the calculation formula of the bearing capacity of common reinforced columns due to its numerous cross-section forms and the phenomenon of "stress-lag".For these hard-quantified factors,the current code adopts the method of simple reduction of the strength of new reinforcement in structural design to improve safety redundancy,simplifying the calculation formula of bearing capacity,which may also bring hidden danger to the actual project.Based on the proposed design method of the limit strain state of the reinforcement column,this paper develops the analytical software of the normal cross-section bearing capacity of the strengthening column,systematically analyzes the influence of the main factors on the bearing capacity,draws the corresponding PM curve,and studies the rationality of the formula in the code.The specific work of the paper is as follows:(1)Finishing the theoretical system of the limit strain state design method.By dividing the strain distribution of each stage in the process of column destruction,the cross-section bearing capacity is integrated and the PMM surface is drawn.Under this theoretical framework,a new perspective is presented on some of the concepts in code,including:pure bending situation,the distinction between large and small eccentric pulling damage,and the definition of pulling damage,which show us the first step of “strain design”instead of “force design” in code.(2)Completing the theoretical structure of strengthening column in the limit strain state design method.On the basis of the previous design theory,the initial strain of the strengthening column is superimposed and the strain lines are drawn.Besides,PMM is not only an envelope surface,but also contains strain information under a variety of internal forces,which means in the case of known axial forces through iterative difference algorithm can also calculate the initial strain.By setting the parameter "load ratio",structural safety is measured and the proofing design is completed(3)Developing the software of cylinder cross-sectional auxiliary analysis.Based on the design method above,the PMM surface of the strengthening column considering the initial strain is finally drawn,with base class library defined,architecture of the software completed,module design of material definition realized,and internal force calculated.(4)Quantifying the level of influence of different elements on the bearing capacity of strengthening column by orthogonal analysis method,the phenomenon that the initial strain also has a significant effect on the bearing capacity is found,although the degree is not as significant as that of other elements.(5)By setting different initial strain combinations,the results from software are compared with the ones from code.The differences show that: 1)the initial strain has little effect on the large eccentric compression,but the bearing capacity of small eccentric compression decreases with the increase of initial strain;2)When the level of initial strain is low,the results of code have significant safety redundancy,but with the increase of the initial strain level,the results tend to be unsafe in reverse.