It’s almost impossible to imagine building construction without concrete.
Steel and concrete have been used together in construction since at least the middle of the 19th century. Concrete and reinforcement can work together because there is a sufficiently strong bond between the two materials.
It is known that concrete has high compressive strength, but it has low resistance to tension but steel copes with it very well. Concrete reinforcement is utilized not only to prevent the concrete from cracking but to take up the tensile force. When the concentrated load influences on the concrete, it reaches the limit of its strength; in the reinforced concrete beam reinforcing bars take up tension after the concrete has cracked. Only when the concrete reinforcement approaches ultimate strength, the deflection and the crack become large enough to make the beam to break down. The failure of the beam is characterized by the crushing of the concrete in the compression zone.
There are three methods of calculation of reinforced concrete structures: allowable stress method of design (it’s not possible to determine the actual stresses and failure load), failure load method of design (it does not allow to evaluate the performance of the structure before the failure, for example at working load), limit stage method of design (it is widely used today). The main idea of the limit stage method is that even in those rare cases when the construction is exposed to maximum load, the strength of concrete and reinforcement is minimal, and under the most unfavorable operating conditions the construction would not be destroyed, and would not accept invalid deflections or cracks. In many cases it is possible to obtain more economical solutions than in the calculation of the previously used methods.
But reaching the limit stage the reinforced concrete structure does not crash immediately, there is some time during which it continues to resist. Nowadays there are no methods that would take this into account.