中文摘要：

通过试验研究了二次受力条件下增大受拉区截面加固的梁的力学性能，主要考虑了增大截面的高度和初始荷载两个主要影响因素，对比分析了梁的极限荷载、荷载-挠度曲线及钢筋的应变变化。研究结果表明：采用增大截面法加固可有效提高梁的极限承载力和刚度，其极限荷载受初始荷载等级的影响较小，其荷载-挠度曲线包括混凝土开裂、上下层纵向受拉钢筋先后屈服及梁的破坏四个阶段。最后，认为二次受力条件下增大截面加固梁在实际使用中应避免产生过大的变形。

英文摘要：

An experimental program was carried out to study the behavior of the beams strengthened by enlarging the tensile area and subjected to secondary loading. Two main factors were considered in the test, which are the height of the enlarged section and the initial load. The ultimate load of the beam, the load-deflection curve and the steel strain were discussed in this paper. The results indicate that the section enlargement method can effectively improve the ultimate bearing capacity and the rigidity of the beams, the initial load has little effect on the ultimate load of the beam, the load-deflection curve consists of such four phases as the concrete cracking stage, respective yielding sta- ges of longitudinally tensile reinforcement at upper and lower layers, and failure stage. Finally, it suggests that the beam subjected to secondary loading should avoid excessive deformation for the practical application.