Unreinforced concrete structures perform poorly in which scenario?

Unreinforced concrete structures are particularly vulnerable during earthquakes due to the lack of tensile strength reinforcement commonly found in other concrete designs. Unlike reinforced concrete, which contains steel bars or mesh that can absorb and distribute forces, unreinforced structures are rigid and brittle. When an earthquake occurs, the ground shakes in unpredictable ways, causing dynamic loading conditions that can lead to collapse in unreinforced structures. This is especially true for taller structures or those with intricate designs that introduce stress concentrations. The failure mechanism often involves cracking and shear failures at corners and joints, which are unable to withstand the torsional forces generated by seismic activity.

In contrast, while unreinforced concrete may experience some challenges during flooding, wind storms, or extreme heat, these scenarios do not exert the same immediate and intense dynamic forces that earthquakes do. Flooding typically impacts the integrity through erosion, wind storms can exert lateral forces but often do not exceed the capacity of even unreinforced structures, and extreme heat primarily causes thermal expansion issues rather than the severe structural failures linked to seismic events.