On November 21, a collapse occurred in the underground parking garage of a residential community in Chongqing? In the underground parking garage of the community, the ground suddenly caved in when a truck drove in, causing the ceiling of the underground garage to crack.

Let us first review the relevant codes for design loads:

Article 4.2.13 of the "General Code for Engineering Structures" requires that the characteristic value of construction live load on the basement roof shall not be less than 5.0 KN/m², and when there are temporary stockpiled loads or heavy vehicles passing through, the actual loads shall be checked in the construction organization design, and corresponding measures shall be taken.

For floors with relatively large construction loads, when designing the floor structure, the influence of construction-stage loads should preferably be considered. When construction loads exceed the design loads, verification should be carried out according to the actual situation, and corresponding measures such as installing temporary supports should be taken. It is inadvisable to completely replace the live loads of the service stage with the live loads of the construction stage for structural design, but the feasibility of construction should also be fully considered in the design.

Section 5.5 of the current load code sets out relevant requirements for construction live loads, but as for how to determine the construction live load on the basement roof, the code does not provide relevant requirements in its main text. In the explanation of the provisions of this article:

Other local standards and related technical measures also mention the determination of construction live loads on basement roofs. For example, Article 5.5.1 of the "Load Code for the Design of Building Structures of Guangdong Province" DBJ15-101-2014 requires that the indoor live load on the basement roof shall not be less than 5.0 KN/m², and the outdoor live load shall not be less than 10.0 KN/m².

Article 4.1.2 of the Guangdong high-rise code "Technical Specification for Concrete Structures of Tall Buildings (Guangdong Province)" DBJ/T 15-92-2021 mentions that the construction load on the first-floor slab should preferably not be less than 10.0 KN/m².

Specific requirements for construction loads on basement roofs can also be found in the technical measures of Huasen Architectural and Engineering Design Consultant Co., Ltd. and the structural technical measures of the Shenzhen General Institute.

Requirements for slab construction loads can also be found in the National Technical Measures for the Design of Civil Buildings, which require that temporary loads during construction be determined according to the expected maximum reasonable value, but do not give specific load values.

The load code requires that construction live loads generally be not less than 5.0 kN/m², but the self-weight of floor finishes and partition walls not yet constructed may be deducted depending on the situation, and corresponding detailed provisions should be given in the design documents. However, judging from the requirements of some local standards and technical measures, the live load values for basement roofs in actual design are generally greater than 5.0 kN/m², and many even require load values of 10.0 kN/m².

As structural designers, for floors with relatively large construction loads, when designing the floor structure, the influence of construction-stage loads should preferably be considered, and it is required to distinguish between the live loads of the structure in the actual service stage and the live loads in the construction stage. It is inadvisable to completely replace the live loads of the service stage with the live loads of the construction stage for structural design. In the design, the construction stage may be analyzed according to the equivalent live load on the roof, or when there are temporary stockpiled loads or heavy vehicles passing through, the actual loads shall be checked in the construction organization design, and corresponding measures shall be taken. The design should state that when construction loads exceed the design loads, verification shall be carried out according to the actual situation, and corresponding measures such as installing temporary supports shall be taken.

The situation of a concrete roof being crushed by a vehicle—this failure mode feels like it was never taught in textbooks. Let us first speculate under what circumstances such an accident would occur, and make the following guesses:

1. Material problems:The quality of concrete materials directly affects the strength and stability of the roof. If the concrete grade used is insufficient, or the specifications of the reinforcing steel do not meet the design requirements, the roof may be unable to withstand the weight of the vehicle and collapse. In addition, if there are impurities in the concrete, or if the concrete mix proportion is unreasonable, this may also affect the durability and load-bearing capacity of the roof.

2. Vehicle overloading:If the vehicle's load exceeds the load-bearing capacity of the roof, the roof may collapse. This is because vehicle overloading causes the stress on the roof to exceed its load-bearing capacity, leading to structural failure.

3. Design and construction problems:At the design stage, if the load-bearing capacity of the roof is not fully considered, or at the construction stage, if construction is not carried out strictly in accordance with the design requirements, the roof structure may be insufficient to withstand the weight of the vehicle and may collapse. In addition, if the foundation is unstable, or if the foundation treatment is improper, the roof may also collapse under the pressure of the vehicle.

As for what exactly caused the situation, no official statement has been seen so far. Let us wait quietly for the results to be announced~