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以往的工程设计习惯用安全系数来表示结构的安全度,只要结构的抗力大于荷载效应(由于外力引起的弯矩、轴向力、剪力、应力等),就认为结构百分之百安全了。这是一种定值概念,很容易使人们误认为构筑物的设计满足了规定的最小安全系数要求,结构就绝对可靠、不会有任何潜在风险了。其实不然,任何工程无论设计施工做得多么完善,结构总是不能完全排除失效的可能性,结构安全性之所以成为问题,正是由于客观世界里种种复杂的不定性的存在。实际上,结构的安全问题是和概率紧紧连系的。例如图1中的f(Q)和f(R)分别为荷载和抗力的概率分布曲线,按以往的安全系数表达
In the past, engineering design used the safety factor to express the safety of the structure. As long as the structural resistance is greater than the load effect (bending moment, axial force, shear force, stress, etc. due to external force), the structure is considered 100% safe. This is a valuation concept and it is easy for people to mistaken that the design of the structure meets the required minimum safety factor requirements, and the structure is absolutely reliable without any potential risks. In actual fact, no matter how well the design and construction of any project are done, the structure cannot always completely eliminate the possibility of failure. The reason why structural safety becomes a problem is precisely due to the existence of various complex ambiguities in the objective world. In fact, the structural safety problem is closely linked to the probability. For example, f(Q) and f(R) in Fig. 1 are the probability distribution curves of load and resistance, respectively.