基于拉拔试验钢筋与全轻混凝土的黏结破坏模型分析

Analysis on bonding failure model between reinforcing steel and all-lightweight concrete based on pull-out tests

为了探讨热轧月牙肋钢筋和热轧光圆钢筋在全轻混凝土(ALWC)中的黏结滑移性能,进行了不同工况下的拉拔试验,得到了拉拔力-位移曲线(F-S曲线),并观察了破坏形态。结果表明:光圆钢筋只发生拔出破坏,而月牙肋钢筋则会出现拔出破坏或劈裂破坏2种形式;通过对2种破坏形式分析,以及对F-S曲线进行黏结应力-位移曲线(τ-S曲线)的变换分析发现,其黏结破坏机理和黏结滑移曲线特征均与普通混凝土(NWC)相似,并据此给出了全轻混凝土的τ-S拟合曲线;虽然黏结应力随混凝土强度和钢筋直径增大而增大,且对于月牙肋钢筋而言,月牙肋与混凝土之间的机械咬合力对黏结应力的贡献率一般在95%以上;当直径为20 mm时,拉拔力出现倒缩现象;根据月牙肋钢筋的月牙肋特征,提出了月牙肋钢筋的物理-力学分析模型;并按不同受力阶段分别导出了相应的力学模型。最终得到了月牙肋钢筋直径与等效半径之间的关系式,并通过试验验证了模型的正确性。

In order to investigate bond-slip( BS) behaviors of hot rolled crescent-shaped bars( HRCSB) and hot rolled plain steel bars( HRPSB) in all-lightweight concrete( ALWC),the pull-out( PO) tests were carried out under different conditions in the paper. PO force( F)-displacement( S) curves were gained and failure modes were observed. The results show that the PO failure( POF) is found in PSB,while the POF and splitting failure( SF) are found in CRB. Based on the analysis of the above failure modes and the transformations of bond stress( BS) with( τ)-displacement( S) curves by F-S curves,the bond failure( BF) mechanism and the BS curves are found similar with normal weight concrete( NWC). Therefore,the classic τ-s curves adapted for ALWC are given. Although the BS increases with the strength of concrete and the diameter of reinforcement increasing,and for the CRB,the contribution of mechanical bite force between the crescent rib and concrete to BS is more than 95 percent. However the PO force will generate retraction when the diameter is 20 mm. A physical-mechanical analysis model on CRB is put forward based on the characteristics of crescent rib and the corresponding mechanical models are also derived according to different stress stages. The relations between the diameter of CRB and equivalent radius is given,which is verified correct by test data.