Numerical studies on multistage strength degradation of notched concrete beams under sequential loading

Initial flaws and defects exist in all engineering materials and thus in all structural members; only the degree of imperfection varies. Under cyclic loading, the material weakening process in structural members inevitably involves multiple cracking originating from some of these spatially-distributed initial imperfections, and therefore diverse cracking behaviors are expected. As a threshold value of crack propagation is approached, new cracking behaviors can abruptly emerge and replace the previous ones, causing strength degradation. In the present study, by applying sequential loads at different locations of the same FE model of a notched beam, it is shown that this unique strength degradation mechanism can repeatedly occur amid a variety of cracking behaviors, leading to a multistage, periodic reduction of the load-carrying capacity.

Research highlights
► The maximum load remains constant until a critical value of crack growth is reached.
► Beyond it, new cracking behaviors abruptly emerge and the maximum load is reduced.
► This strength degradation takes place periodically amid multiple crack activities.
► The multistage strength degradations will ultimately cause abrupt structural failure.