Actions during service
Concrete structures or structural elements are designed to take up external mechanical loading. In modern design codes based on ultimate limit state design, it is considered that concrete in tension will crack, leaving only the reinforcement to carrying the tensile loading. This does not mean that concrete structural elements under service load will always show cracks. However, it does mean that if cracks occur in concrete structures, the structural load-bearing capacity of the structure is not immediately at risk. Of course, excessive cracking in concrete structures is neither generally expected nor accepted. And even small cracks could impair long-term concrete durability because of the accelerated ingress of aggressive substances.