Zhongxian Cement Prefabricated House

A prefabricated cement house in Zhongxian once experienced a prefabricated slab fracture incident, posing certain safety hazards and gradually being replaced by safer construction techniques.

Incident Case and Causes

At around 12:00 PM on April 11, 2024, a three-story prefabricated cement slab building in Fengshou Community, Guanba Town, Zhongxian County, suffered a prefabricated slab fracture, resulting in 2 deaths and 3 injuries. The direct cause of the incident was excessive temporary load accumulation on the second-floor slab, exceeding the load-bearing capacity of the prefabricated slab, leading to brittle fracture and collapse of the slab. The ground floor of the building housed a mahjong parlor, while the second floor was used as a warehouse. At the time of the incident, about five or six people were having a meal inside, and uneven load distribution exacerbated the structural risk.

Characteristics and Defects of Prefabricated Slab Houses

Prefabricated slabs are concrete prefabricated components produced and processed using materials such as cement and steel bars, and are directly transported to the construction site for installation. Their advantages lie in standardized production and convenient construction, which can shorten the construction period and reduce labor costs. However, their defects are more prominent:

1. Weak Earthquake Resistance: Prefabricated slabs are installed by splicing, with node connection strength lower than that of monolithic cast structures, making them prone to dislocation or detachment during earthquakes.
2. Inconsistent Quality: Insufficient steel bar configuration, substandard concrete strength, or improper curing during production can lead to a decrease in the load-bearing capacity of prefabricated slabs.
3. Prone to Leakage and Cracking: Splicing gaps and material aging may cause leakage problems, affecting the durability of the house.
4. Limited Service Life: The theoretical lifespan is about 40 years, but in actual use, it may be damaged prematurely due to improper maintenance or overloading.

Safety Hazards and Replacement Trends

Currently, prefabricated slab houses are gradually being replaced by reinforced concrete on-site casting techniques. The latter forms a continuous structure through monolithic casting, significantly improving earthquake resistance and load-bearing capacity, and allowing for flexible design according to needs. However, due to the large number of existing prefabricated slab houses, some still have problems such as design defects, overextended use, or unauthorized modifications, posing safety hazards that cannot be ignored. For example, the Zhongxian incident house had its second floor converted into a warehouse, with heavy items stored for a long time, further weakening the structural safety.

Safety Recommendations

For existing prefabricated slab houses, it is recommended to conduct regular structural safety inspections, focusing on the connection nodes of prefabricated slabs, crack conditions, and load distribution. Avoid unauthorized changes in house usage or overloading, and if necessary, enhance safety through reinforcement measures (such as adding supports or attaching carbon fiber sheets). For new construction, priority should be given to on-site casting techniques to ensure structural safety and durability.