【作者】 李莹；

【导师】 黄侨；

【作者基本信息】 哈尔滨工业大学 ， 桥梁与隧道工程， 2008， 博士

【摘要】 我国公路钢桥发展较晚,疲劳研究相对滞后,设计规范比较陈旧。早期修建的为数不多的公路钢桥,大部分参考国外规范和我国铁路钢桥规范,许多钢桥已状态不佳。改革开放后我国公路钢桥发展很快,但由于缺少规范的科学指导,对公路钢桥疲劳问题的特殊性认识不足,以及细节构造处理不当等因素,造成疲劳破坏的事例屡见不鲜。因此开展针对公路钢桥抗疲劳设计和疲劳寿命评估方面的研究是十分必要、急迫和有意义的。本文主要针对我国公路钢桥疲劳方面存在的若干问题开展了研究工作。在钢桥抗疲劳设计方面,针对我国公路钢桥现行规范的不足之处,提出可供我国公路钢桥抗疲劳设计参考的方法,并通过实例分析证明该方法的可行性与适用性。在钢桥结构中,由于构造不当及对具体情况分析的欠缺,次内力和扭曲应力已成为复杂构造细节疲劳破坏的主导因素,针对这一问题,开展对复杂疲劳细节的受力特点研究,以焊接钢桥疲劳开裂的首要原因——腹板小间隙处的出平面变形为例进行分析,寻找导致这种破坏的根源,提出针对这一细节的改进措施,并对这些改进措施进行比较、分析,可供工程实际参考使用,同时这种分析思路也可为其它复杂构造细节的疲劳评估提供参考。在钢桥疲劳寿命评估方面,开展对适用于钢结构桥梁的两种确定性疲劳寿命评估方法,名义应力法和断裂力学方法应用于公路钢桥结构的实用方法的研究。对名义应力法评估钢桥疲劳寿命中的关键因素应力集中系数进行研究,采用有限元方法对公路钢桥常见的两种结构形式的焊趾应力集中系数随结构参数变化的情况进行分析,得到应力集中系数回归公式,可为工程中的使用提供方便。通过研究结构参数对应力集中的影响,可以为改进设计和加工工艺,降低应力集中提供理论依据,同时还可以提高名义应力法评估结构疲劳寿命的精度。另外,还对断裂力学方法评估钢桥疲劳寿命中的关键因素应力强度因子进行研究,采用有限元方法计算了两种含裂纹的公路钢桥常见结构形式的应力强度因子,并得到了形状函数关于裂纹长度和结构宽度的拟合公式,为工程中的实际使用提供了理论依据。我国现行的公路钢桥规范尚未对疲劳荷载形式进行规定,基于我国公路钢桥疲劳设计和疲劳寿命评估的需要,对疲劳荷载模型的建立方法进行研究,分别对车辆荷载调查、模型车辆建立和Monte-Carlo方法模拟随机车辆荷载的方法进行了分析评述。对国外的一些疲劳车模型和我国桥梁规范强度设计车辆荷载模型,在不同桥型和跨径造成的疲劳损伤进行了分析比较,有助于我国公路钢桥疲劳设计、评估时选用合适的车辆模型,这方面的研究在我国公路钢桥疲劳车的制定方面也具有一定的意义。另外,还开展了对公路钢桥实测应力谱的特点和分布形式的研究。在疲劳可靠性方面,分别基于传统的疲劳理论和近年来发展起来的断裂力学理论,建立了适用于公路钢桥结构的疲劳可靠性模型,对模型中的随机参数进行分析,对公路钢桥疲劳目标可靠指标的取值进行研究。将两种模型应用于实际钢桥结构,对实际钢桥的疲劳寿命进行评估并验证了模型的可行性与适用性。更多还原

【Abstract】 The development of highway steel bridges in our country is very late, and the fatigue study is comparative lag, at the same time, the design criterion is relatively old. Foreign criterions and the criterion of railway steel bridges in our country were taken as reference in the building of few highway steel bridges in early time, and the states of these steel bridges are almost bad. Highway steel bridges in our country have developed rapidly after reform, but these bridges sometimes destroy accidently by fatigue because lack of sience guidance of criterion, the deficiency in particularity of highway steel bridges fatigue, and the improper management in details. Fatigue design and fatigue life evaluation of highway steel bridges have become very necessary, imminent and meaningful. The issues in highway steel bridge fatigue of our country are discussed in this dissertation.In fatigue design of steel bridges, a fatigue design method that can be the reference for highway steel bridges in our country is proposed, according to the defects of current code. Feasibility and applicability of the method are proved by a case study. In steel bridges, secondary internal forces and distortion induced stresses have become the dominant destroying factors because of bad structure and minus analysis of specific conditions. Aiming at this problem, stress characteristics of complex fatigue details have been analyzed. Out-plane distorsion at webgap which is the first cause of welded steel bridges’destroying is studied as an example. The sourse causing this kind of destroying is analyzed and different improving measures are proposed. The comparison and analysis of different improving measures are carried on. The analyzing method used can also be the reference when studying other complex details.In fatigue life evaluation of steel bridges, the methods applied to highway steel bridges of two applicable deterministic fatigue life evaluation methods, nominal stress method and fracture mechanics method, are analyzed. Stress concentration factor which is the key factor in fatigue life evaluation using nominal stress method is studied. Changes of stress concentration factors at wed toes of two common structures in highway steel bridges with different structure parameters are analyzed, and the regressive formulas are achieved for the convenience of enginnering use. Study on the influence of structure parameters to stress concentration can be the theory basis of improving design and processing technology, decreasing stress concentration, and at the same time, the precision of fatigue life evaluation by nominal stress method can be increased. Stress intensity factor which is the key factor of steel bridges’fatigue life evaluation by fracture mechanics method is studied. The stress intensity factors of two common structures containing cracks in highway steel bridges are calculated. The regressive formulas about crack length and structure width of geometry functions are achieved, and can be the theory basis of engineering application.There are no fatigue load models in current code for highway steel bridges in our country. The establishing method of fatigue load model is studied, according to the needs of fatigue design and fatigue life evaluation of highway steel bridges in our country. The aspects of vehicle load survey, model truck establishment and random truck load simulation by Monte-Carlo method are analyzed and reviewed. The fatigue damages in different bridge type and span caused by foreign fatigue trucks and strength design truck models in other bridge codes in our country are analyzed and compared. It is helpful to the truck selection in fatigue design and evaluation, and is meaningful to fatigue truck establishment of highway steel bridges in our country. In addition, the features and distribution forms of highway steel bridges in measured stress spectrums are studied.At the aspect of fatigue reliability, fatigue models based on traditional fatigue theory and fracture mechanics applicable to highway steel bridges are established. The random parameters in the models are studied. The target reliability index of highway steel bridges is studied. The models are applied in actual steel bridges to estimate the fatigue lives of these bridges, the feasibility and practicability are also validateed.更多还原