Research On Local Stability Of FRP Axial Compression Member

Regarding the application of fiber reinforced Polymer materials(polymer-based composite materials or fiber reinforced thermoplastic resin Polymer materials,(FRP)for short),the progress of related research has been relatively slow,the main reasons are:(1)High initial cost;(2)Lack of high-performance FRP nodes;(3)FRP axial compression bar lacks relatively accurate prediction formula;(4)Lack of full FRP structural design.There is also insufficient research on the basic mechanical properties of FRP materials,which leads to the slow research of the basic mechanical properties of FRP components,which is also one of the important reasons why FRP materials have not been promoted in the construction industry.In this paper,the author has studied the local stability of FRP axial compression members.The main analysis methods and research results are as follows:(1)The database is used to compare the six existing explicit calculation methods of local buckling critical force of FRP members,and a finite element model is established to verify the accuracy of the equation accuracy,and the following conclusions are drawn:The equations proposed by the American Society of Civil Engineers(ASCE)and Creative Pultrusions and the empirical formulas proposed by scholars such as Pecce are relatively conservative,and are likely to cause waste of materials in structural design;The equation proposed by Strongwell is close to the experimental data compared with other explicit equations,which improves the utilization rate of materials.It can be used as a general formula to predict the local buckling critical stress of FRP members.Because the predicted value underestimates the experimental data of the database by 36.7%,the equation proposed by Strongwell Company is used to predict the critical stress of fiber reinforced polymer columns.There is room for improvement;After studying the influence of theb_f t_f ratio on each equation,it is found that when theb_f t_f ratio is greater than 15,the prediction error of the equation becomes larger and the prediction accuracy will decrease.When the b h ratio is in the range of 0-1.0,as the b h ratio increases,the prediction error of the existing explicit equation decreases,and the prediction accuracy will be improved.(2)Based on the use of ANSYS finite element analysis software,the finite element model was established through the APDL command flow,and the accuracy and applicability of the models of different bar sections were verified through the database.The difference between the critical force of the numerical simulation of the finite element model of different rod lengths and the existing explicit equations to predict the local buckling critical force of FRP rods are studied,and the following conclusions are obtained:The numerical simulation predicts that the critical force is close to the actual experimental data,and the finite element model almost restores the experimental results,indicating that the model is accurate and applicable,and can be used as an important reference for studying the local buckling critical force of FRP members;After changing the length of the member,the local buckling critical load calculation method proposed by Strongwell in the 1998 design code was analyzed and studied.It is found that this method has the highest accuracy in predicting the local buckling critical force of FRP members with wide flange I-shaped,rectangular and I-shaped sections.(3)Based on the calculation method of local buckling critical load proposed by Strongwell's 1998 design specifications,After using regression analysis of ORIGIN software and collected database experimental data,new explicit equations are obtained,and the prediction accuracy of the new equations is compared through the finite element numerical simulation results.And the effect of theb_f t_f ratio and the b h ratio on the prediction deviation caused by the equation is analyzed,and the following conclusions are obtained:The prediction accuracy of the new equation has been greatly improved.The mean is only 109.6%.The critical load prediction value underestimates the finite element numerical simulation result of 9.6%.The prediction result is very close.The average absolute deviation(AAE)and standard deviation(SD)are 8.1%and 9.3%,respectively.The deviation of the predicted value of the equation is low,indicating that the new equation is stable as a general formula to predict the local buckling critical force of FRP members with different cross sections;When theb_f t_f ratio of the new equation is greater than 15,the prediction error of the equation becomes larger,and the prediction accuracy will decrease.When the b h ratio is in the range of 0-1.0,as the b h ratio increases,the prediction error of the new equation decreases,and the prediction accuracy will be improved.This article also gives the FRP columns local buckling experiment database,so that the experimental parameters are needed for verification.