How Were the Prefabricated Panels in Old Houses?

The prefabricated panels used in old houses had many issues, but with reasonable design, good construction, and proper management, they could still have a relatively long service life.

Extremely Poor Earthquake Resistance

Prefabricated panel houses have poor integrity. There is a lack of firm steel bar connections between the floor slabs and the walls, similar to building with building blocks. During an earthquake, under the action of horizontal forces, the floor slabs and walls separate instantly and collapse suddenly. There is no crack warning or deformation buffering; the entire panel drops directly, leaving little chance for escape. In many past earthquakes, prefabricated panel houses have been the type of building with the most severe collapses and the highest casualty rates.

Vulnerable Connection Points

The connections between the prefabricated panels and the walls are mostly simple overlaps, and the gaps between the panels are simply filled. There is a lack of ring beams and structural columns, so the entire house has no rigid framework. Once the foundation settles or the walls crack, the panels will become misaligned and loose. Over time, factors such as wind, sun, and thermal expansion and contraction will weather the connections and cause the steel bars to rust, continuously reducing their strength. In some old houses, after living in them for two or three decades, the floor slabs are already on the verge of collapse. Even a slight increase in weight or knocking down a wall can trigger a chain collapse.

Substandard Material Quality

The steel bars in standard prefabricated panels are relatively thin. However, many small workshops, in pursuit of profit, use thin steel wires instead of steel bars, and the concrete grades do not meet the standards and are not thick enough. These prefabricated panels have the characteristic of brittle failure, unlike cast-in-place floor slabs which have toughness and can still support for a while even when cracked. Once the prefabricated panels exceed their load-bearing capacity, they will break instantly without any warning. Stacking heavy objects, knocking on the ground during renovation, or aging over time can all cause them to collapse suddenly.

Existence of Safety Hazards

Among the prefabricated panel houses built before 2000, one-third have safety hazards. However, if the design level is reasonable, including having appropriate structural design, component dimensions, and effective anti-leakage measures; if the construction quality is good, such as high-quality production of prefabricated components, proper handling of connection details, and good on-site assembly techniques; and if the later management is proper, the average service life of prefabricated panel buildings built in the 1990s can even exceed 50 years, and some well-maintained buildings can have a service life of up to 60 - 70 years.