7.11 : 混凝土的疲劳强度

In concrete, fatigue can lead to two distinct forms of failure. The first occurs under a consistent load or one that increases gradually; this is referred to as static fatigue or creep rupture.

The second form of failure happens under cyclical or repeated loads, called cyclic fatigue.

Compressive strength is typically measured in a short span of 2 to 4 minutes. As the loading rate decreases or the test duration increases, the measured strength dips below that observed in standard tests.

Conversely, if the load is applied rapidly or nearly instantaneously, the resulting strength is higher, yet the material's strain at failure, or strain capacity, is reduced.

At low loading rates, static fatigue in concrete happens when stress surpasses approximately 70 to 80 percent of the short-term strength. This level marks the beginning of swift microcrack formation, leading to failure.

Concrete becomes stronger as it ages, and its capacity to endure repeated loads, or fatigue strength, increases proportionally. This means concrete fails under fatigue at stress levels proportional to the ultimate strength, regardless of age.