Seven days earlier, part of Building No. 29 in Jujing Community, Jinping Subdistrict, Fenghua City, Zhejiang Province, suddenly collapsed, causing 1 death and 6 injuries. Although the cause of the accident is still under investigation, the Ministry of Housing and Urban-Rural Development immediately launched a nationwide inspection, indicating that the risks exposed by the Fenghua accident are widespread.

In fact, the Anhui Provincial Department of Housing and Urban-Rural Development acted before the national campaign by the Ministry, issuing an emergency notice on April 8, requiring the province to focus on inspecting six types of dangerous buildings, including: old and dangerous directly managed public housing, brick-concrete (brick-wood) structures over 20 years old, dangerous buildings not yet remediated, buildings with tilted or cracked walls, sudden large-scale falling of plaster, or recently appearing doors and windows that cannot open or close freely.

Among them, the second type of dangerous buildings seems to be defined according to the characteristics of the residential building that failed in Fenghua. Where exactly do the safety risks of old residential buildings come from?

Many hidden dangers in old buildings

Building No. 29 in Jujing Community has five floors and three units, running east-west. At about 9 a.m. on April 4, a half-unit of 15 households on the west side suddenly collapsed. This brick-concrete building, completed in July 1994, was just about to reach 20 years when it met its end.

According to Xinhua Net, this dangerous building had been assessed as a Class C dangerous building in 2013. It was developed by Fenghua Real Estate Company, built by Xiangshan No.1 Construction, and designed by Fenghua Design Institute.

According to the "Standard for Dangerous Building Appraisal" issued and implemented in 2000, building danger is divided into four levels. Among them, Class C dangerous buildings refer to those where the load-bearing capacity of some load-bearing structures cannot meet normal use requirements, with local dangerous conditions, constituting a partially dangerous building; Class D dangerous buildings refer to those where the load-bearing capacity of load-bearing structures can no longer meet normal use requirements, with dangerous conditions throughout the building, constituting a wholly dangerous building. Class C dangerous buildings only need reinforcement, while Class D dangerous buildings require evacuation.

Before the 1980s, under severe conditions of insufficient quotas, funds, and materials, China's architectural policy was "applicable and economical." As early as 2000 years ago, the ancient Roman architect Vitruvius proposed three basic principles of architecture: "firmitas, utilitas, venustas" (durability, utility, beauty). The absence of the "durability" principle is also related to the current safety problems of old buildings.

A survey conducted by the former Ministry of Construction in the 1980s showed that most domestic industrial buildings require major repairs after 25-30 years of use, and buildings in harsh environments have a service life of only 15-20 years.

In 1980, after the State Council officially allowed commercial housing, urban housing grew rapidly. According to statistics from the former Ministry of Construction, from 1979 to 1990, cumulative investment in urban housing construction nationwide was more than 6 times that of the previous 30 years, and newly built housing area was nearly 3 times that of the previous 30 years.

However, housing construction standards during this period were low, and many projects even failed to comply with building standards. At that time, the entire system of approval, engineering supervision, acceptance, and quality control was incomplete. For example, the "Construction Law" only came into effect in 1998, and the "Regulations on Quality Management of Construction Projects" was adopted and implemented by the State Council in January 2000. It was not until 2001 that China first determined the design service life of ordinary houses and buildings to be 50 years.

Li Qiming, director of the Institute of Construction and Real Estate at Southeast University, told reporters that most of the current dangerous old buildings are brick-concrete structures. This is because in the 1970s and 1980s, residential buildings below six stories built in China almost uniformly adopted brick-concrete structures.

Building structure is like a person's skeleton, supporting the entire building. Unlike today's reinforced concrete frame structures, brick-concrete structures use mostly brick walls and a small portion of reinforced concrete for load-bearing, suitable for low-rise or multi-story buildings. Regarding which is better, brick-concrete or frame structure, Ma Guoxin, academician of the Chinese Academy of Engineering and chief architect consultant of Beijing Institute of Architectural Design Co., Ltd., said, "It cannot be generalized; the key lies in design skills."

The biggest characteristic of brick-concrete structures is that once their load-bearing walls are damaged, structural safety is endangered. Shen Jinzhen, senior engineer of the Beijing Municipal Planning Commission, told reporters that the owner turnover cycle of old buildings is now greatly shortened, and frequent renovations can cause damage to building structures.

In this nationwide inspection by the Ministry of Housing and Urban-Rural Development, buildings involving decoration that removes or alters main structures or significantly increases loads are also one of the key targets. At the end of 2012, a residential building collapse in Xurong Third Village, Ningbo, caused one death. The investigation report released by the Ningbo municipal government showed that almost every floor of the collapsed building had phenomena such as removal or alteration of load-bearing walls, illegal construction, and changes in building use.

In addition, there are problems with the engineering quality of the buildings, such as insufficient strength of some structural materials, non-standard construction of moisture-proof layers, and multiple indicators such as the compressive strength of wall masonry mortar not meeting standards. It can truly be said to be congenitally deficient and acquired with many illnesses.