侧爆作用下浅埋钢筋混凝土拱形结构破坏机理与防护对策研究

In the current codes for design of national defense and civil air defense engineering, the top of arch framed structures is deemed as the most dangerous location under blast load. The blast resistance design is based on single degree of freedom models subjected to equivalent uniformly distributed loads. The level of structural resistance is measured by ultimate bearing capacity. However, considering the penetration point of conventional weapons exerted in a certain angle, it is evident that the quarter point instead of the top is the most dangerous point and the straight wall end is the most vulnerable part of straight wall arches. As the load-bearing capacity of arches under asymmetric loading is smaller than that under symmetric loading conditions, the design of arches against lateral blasts following conventional methods will put it on the unsafe side, especially for the large span arch. Therefore, this project aims to put forward a suitable analysis and design method for shallow buried reinforced concrete arches subjected to lateral blast loads by investigating the failure mechanism of the arch. These include: (1) the asymmetric temporal and spatial distribution of the blast load model; (2) failure evolution rule and sections criteria of arch; (3) ultimate state analysis method and protection measures for shallow buried reinforced concrete arch.

现行国防和人防工程设计规范视拱形结构顶部为最危险受爆点，基于单自由度体系、按等效均布荷载进行抗爆计算, 按极限承载能力确定抗力级别。但常规武器侵入点多呈一定偏角，且现阶段研究表明，圆拱的最危险受荷点不是拱顶而是1/4跨附近，而直墙拱的直墙端是最易受损部位，且拱形结构在不对称荷载作用下的承载能力小于对称荷载作用下的承载能力。特别当拱形结构跨度较大时，偏压效应尤其显著。按原有方法设计过高地估计了拱形结构的承载能力，结构将偏于危险。本课题针对该工程安全问题，探讨侧向受爆浅埋钢筋混凝土拱的破坏机理，提出合理的抗爆分析方法与防护对策。具体研究内容包括：（1）构建不对称时空分布荷载模型；（2）拱的塑性演化规律和截面破坏准则；（3）拱的破坏极限承载力分析方法与防护对策。

本课题针对目前工程中常用的圆拱结构在炸药侧向爆炸荷载下的弹性动力响应和塑性破坏特征开展研究。理论研究分别以空气介质和土体介质中两端固支圆拱结构为研究对象。当点爆源位于结构侧向时，圆拱结构受到非对称、不均匀的局部荷载。在空气介质中，考虑结构表面正反射、规则斜反射和马赫反射区域与爆炸偏角间关系；在土体介质中，基于介质和结构的相互作用理论，考虑结构曲率半径影响。确定圆拱结构在两种介质中侧向爆炸下的受荷范围，并建立结构表面荷载函数。其次，基于振型函数，求解圆拱结构在上述荷载函数作用下的振动方程，从而得到结构在弹性阶段的位移、速度、加速度和弯矩、轴力、剪力的函数解析式。再次，基于理想塑性铰假设和结构四铰破坏理论，引入截面弯矩和轴力共同作用下的截面塑性破坏准则，利用MATLAB软件建立了圆拱结构塑性破坏简化计算方法，判断不同爆炸偏角下圆拱结构塑性破坏时截面的受力模式，确定结构塑性铰的分布位置、顺序和塑性极限承载力。此外还进行了两端固支圆拱结构抗爆试验研究，即针对爆炸偏角为0度、45度和90度的情况下的圆拱结构，设置不同比例爆距，研究结构在弹性阶段、弹塑性阶段和破坏阶段下的响应。基于试验研究，验证了本课题理论和方法，考察了圆拱结构在爆炸作用下的弹性动力响应特点，明确了塑性破坏特征。