中文摘要：

假设材料为黏弹性材料时,带缝混凝土结构在荷载作用下,缝岸相对位移将逐渐增大,如果采用位移直接法计算缝端应力强度因子,该应力强度因子将逐渐增大,甚至可能大于混凝土的断裂韧度。基于信息熵理论对黏弹性材料的断裂问题进行了研究,分析表明,如果结构为黏弹性体,那么结构在流变过程中不涉及到能量的耗散和释放,结构信息熵为一常数,裂缝并不会失稳,即位移直接法不适用于流变断裂问题。对钝裂缝带模型进行了研究,认为裂缝扩展单元开裂时,将引起结构能量的释放,该释放能等于外力功与总弹性应变能的差值,也近似等于裂缝扩展单元开裂前后的总弹性应变能的差值。对于线弹性断裂力学问题,这2个能量差值与裂缝前沿的虚拟扩展长度（平面问题）或虚拟扩展面积（空间问题）的比值,通过简单的转化即可以获得缝端应力强度因子。分析还表明,钝裂缝带模型一定程度上不依赖于网格粗细,且相对分离裂缝模型而言,其剖分网格较方便。

英文摘要：

Assume the material of concrete structure with crack is viscoelastic material,the relative displacement of crack side increases under load.If stress intensity factor is calculated by displacement direct method,the stress intensity factor will increase and may be even bigger than the concrete’s fracture toughness.The fracture problem of viscoelastic material is studied based on Entropy theory.It is showed that if the structure is viscoelastic material,there is no energy dissipation and release during the rheological process;the entropy is a constant and the crack remains stable,which means the displacement direct method is not feasible to rheological fracture problem.The blunt crack band model is preliminarily studied as well.It is believed that when fracture expanding element cracks,the structure energy will release,which is equal to the energy difference value between external work external work and total elastic energy and also approximately equal to the difference value between the total elastic energies of fracture expanding elements before and after cracking.As to linear elastic fracture problem,the stress intensity factor can be obtained by simply transforming the ratio of the energy difference value and virtual expanding length（plane problem） or virtual expanding area（spatial problem）.It is also indicated by the analysis that blunt crack band model is independent of mesh size partly and its mesh can be obtained easier comparing with discrete crack model.