Issue 35

W. Xu et alii, Frattura ed Integrità Strutturale, 35 (2016) 481-491; DOI: 10.3221/IGF-ESIS.35.54 483 axial compressive strength of concrete , c r f (refer to Table 1); c d refers to concrete single-axial compressive injury evolutionary parameter;  refers to compressive stress of concrete;  refers to compressive strain of concrete; c E refers to elasticity modulus of concrete. Degeneration of mechanical property of corroded steel reinforcement mainly reflects on decrease of yielding strength, ultimate strength and elongation ultimate of concrete. With the increase of corrosion rate, ultimate deformability weakens and yielding platform shortens and even disappears. Based on the feature, we propose stress-strain relationship model for corroded steel reinforcement as shown in Figure 1. When corrosion rate of steel reinforcement is small and yielding platform has not disappeared, Figure 1 (a) is used; and when corrosion rate exceeds certain critical point and yielding platform disappears, Figure 1(b) is used. yc f and uc f refers to nominal yield strength and nominal ultimate strength of corroded steel reinforcement respectively; sc  and sc  stands for stress and strain of corroded steel reinforcement respectively; syc  and suc  stands for yielding strain and hardening strain of corroded steel reinforcement. Figure 1: Constitutive relation curves for corroded steel reinforcement before and after disappearance of yielding platform [8]. Finite Element Model and Grid Generation Cruciform frame joints of reinforced concrete is taken as the finite element model (Figure 2). Size of test beam (simply supported beam) used for modeling is b×h×l = 120×200×1900 mm. Span of the beam is 1.7 m. Two concentrated forces are applied on midspan and the distance between two forces is 50 mm. Concrete cover of main reinforcement is 2.5 mm thick. Detailed size of the beam and reinforcement are shown in Figure 3. Figure 2: Frame joint model.