Post-yield Hardening Behavior Of FRP-strengthened Members And Bearing Capacity Of Structures Incorporating Them

Post-yield hardening member is the topic of this paper.The paper presents a new method for post-yield stiffness calculation for reinforced concrete beams strengthened in flexural with fiber reinforced polymer(FRP)and suggests a practical formula.The theory of designing the ultimate limit state of post-yield hardening member in a structure is proposed and verified through member analysis,structural finite element modeling,parameter analysis,mathematical justification and expansion.The main work and achievements of this study are shown below:(1)On basis of former experiments of fiber reinforced RC beams,the post-yield tangential stiffness is proposed and applied.A calculation formula is obtained by theoretical analysis and regression method.(2)Fixed-fixed beam under uniform load,fixed-pinned beam under point load at midspan,fixed-fixed beam under non-uniform settlement are analyzed.It is shown that for a single indeterminate member,the states on the connecting line of elastic limit state and elasto-plastic limit state(of equal structural ultimate bearing capacity)are the equal bearing capacity states.(3)The theory on the limit state of post-yield hardening member is proposed and frames are modeled and loaded in finite element software.Frames of different sectional heights,different load distributions are drawn and pushed over in SAP2000.The pushover results(120 results in total)show that if the post-yield hardening member could reach the states on the connecting line of elastic limit state and elasto-plastic limit state(of equal structural ultimate bearing capacity),the structure with post-yield hardening member would have greater bearing capacity than before(the capacity amplification factor is in the range of 1 to 1.009).That means the theory is applicable in frames.Parameter analysis is conducted for the post-yield hardening member's strength and ductility.(4)Serial and parallel spring systems are analyzed and verified.It is mathematically proved in the spring systems on the applicability of the proposed theory.The relationship between spring systems and structure is pointed out.(5)The theory is extended to multiple post-yield members in a structure.Parallel spring systems and frames are analyzed and checked.The application of the theory in structural strengthening and designing is proposed,followed by instances.