Source: Popular Science China
Recently, many places have experienced rare torrential rains and floods. After the flood, seeing that many buildings were soaked in floodwater, and sewage flooded the underground garage, many people began to worry: how to avoid risks in high-rise buildings? Will there be a problem if my house is flooded? Will the house still be inhabitable after the floodwaters recede? How to check if the house is damaged?
When the flood comes, how to avoid danger indoors?
When flooding comes, you should first try to stay away from the balcony. If you are on the first floor, you should try to move to the height of the floor. At the same time, attention should be paid to assessing whether the house is likely to collapse after flooding, and special attention should be paid to the old houses and village buildings in towns, and regularly observe whether there are settlements, tilts and cracks in the walls, floors, ceilings and other positions in the houses. If the house has cracks or has tilted, it should be moved to safety immediately.
If possible, people living on the lower floors can prepare sacks, woven bags or rice bags in advance, load sand, soil, etc. to make sandbags, build a waterproof wall outside the threshold and window sill, and plug the gaps between doors and windows with blankets, cotton wool and other fillers to prevent water seepage, and at the same time properly reinforce the doors and windows. You can also use the wide sealing tape always available at home to paste the glass window with a beige shape to enhance the bearing capacity of the window glass.
Different structures of buildings have different flood resistance, brick-concrete structures have poor flood resistance, and special attention should be paid to:
So how do you assess your home's flood resistance? There are actually two questions involved here, one is whether the flood will be directly washed away; The second is whether long-term flooding will corrode the building, making it at risk of collapse. This requires specific analysis of buildings with different structural types.
Building structure refers to the system composed of load-bearing components (columns, beams, walls, floors, foundations, etc.) in the building, according to the common types of buildings, buildings can generally be divided into 4 categories:
Damage to buildings by flooding can generally be divided into the following three forms:
1. Impact damage. Flood under the influence of water level difference, the formation of water pressure directly impact buildings and structures (such as roads, dams, etc.), the damage is great, generally speaking, the closer to the breach, the greater the flow rate of the flood, the greater the harm to the building.
2. Soaking destruction. After flooding, it remains at a certain level and only fades over time. Flood immersion will weaken the mechanical properties of the main building materials of the house, and the disturbance and uneven settlement of the bearing capacity of the foundation will cause immersion failure.
3. Wave destruction. In areas with harsh climates, buildings in flooding are subjected to flood wave loads in windy weather. Structures such as inter-window walls or under-window walls in buildings that are not designed to withstand floods may be damaged.
Many buildings in the floodplain, such as old urban houses, have poor structural performance, and the walls of the houses will be damaged due to the impact of the flood, or even the walls will collapse. For such buildings with poor quality or low strength grade of masonry mortar, the mortar strength will be reduced under flooding, which will affect the safety of the structure, mainly old urban houses and village buildings. In addition, long-term flooding will soften and peel off the mortar of the wall stucco, causing structural damage to the building.
On the whole, masonry structures (structural types built of brick, stone or block, mainly load-bearing by brick or block walls) have poor integrity and poor ability to resist floods; Steel structure and concrete structure are ideal. However, long-term flooding will also cause the concrete protective layer to fall off, the steel bar to rust, and the structural bearing capacity to weaken, resulting in the structure exceeding the limit bearing capacity it can bear, and the local structure or the overall structure will collapse in severe cases.
The use of building materials with good waterproof performance in building design is beneficial to flood resistance. For brick masonry commonly used in villages and towns, veneer materials can be used to protect the wall surface and reduce the erosion and erosion of floods. In urban buildings, concrete structures have good waterproof performance and are the preferred structural materials for flood and waterlogging buildings.
Prolonged flooding of the garage can indeed affect foundation stability
In fact, buildings are designed with measures to prevent rainwater inflow. According to the national standard "Unified Standard for Civil Building Design" (GB50352-2019), in areas threatened by flooding, tidal flooding and waterlogging, the site design elevation should not be lower than the design flood level/waterlogging level of 0.5 m. Generally, when designing buildings, the indoor height of the ground floor will be 3~5 steps higher than the outdoor level, about 300~500 mm in height, which plays a role in water barrier. As for the underground garage that many people worry about, it is also designed with gutters, and rainwater entering the underground garage will be diverted through the gutter.
The main reason why the underground garage of the community cannot be drained after heavy rainfall is that the water volume far exceeds the maximum capacity of basement drainage in the short term. Many people are worried that the flooding of the underground garage will lead to unstable foundation, in fact, the short-term flooding of the underground garage has a relatively small impact on the structure, if it is flooded for a long time, it may indeed cause the deformation and cracking of the garage floor, resulting in the failure of waterproof measures and the soft soil layer of the surrounding foundation, which directly affects the stability of the foundation and causes uneven settlement and other safety hazards. In addition, weak developers (construction contractors) cannot guarantee the quality of the project, and the risk will be greater.
In short, if the underground garage is flooded, a pumping pump should be added as soon as possible to speed up the drainage and reduce the flooding time. The assessment of the risk of the building after the completion of drainage is mentioned below.
After the floodwaters have receded, it is recommended to ask a professional to check the safety of the house before moving in
Soaked buildings can be potentially risky after the floodwaters recede, so how can the general public check and spot problems to avoid the risks?
First of all, for wood structure buildings, we should focus on checking the defects of wood immersion and decay, the deformation and instability of structural components, the condition of shear cracks at the end nodes of wooden roof trusses, and the displacement and stability of roof structure. For masonry structures, the structural connection parts of masonry, the junction of longitudinal and horizontal walls, and the cracks of the load-bearing walls of masonry should be checked; Concrete structures should be inspected for column, beam, slab cracks and steel bar rust; The steel structure should check the connection nodes, the connection form of the steel column and the beam, the supporting members, the connection damage between the column foot and the foundation, etc.
In addition to the above-mentioned changes in the above-ground building structure itself, after the house is soaked in water for a long time, the foundation will be soft and expanding, the bearing capacity will become weak, and the structural safety may be affected, and after the water subsides, the previously expanded foundation will shrink and deform, and the bearing stability of the foundation will be affected. Uneven soil distribution on the building site will lead to uneven settlement of the foundation.
After the flood water recedes, it is recommended to ask the housing safety appraisal agency to test the structure and adopt corresponding reinforcement measures for the situation. Houses made of reinforced concrete generally do not need to be particularly worried, and you can regularly observe whether there are cracks in the wall or floor; Brick-concrete old houses should pay special attention to the fact that after such houses are soaked in rainwater for a long time, the strength of the masonry structure will decrease significantly, and before re-moving in, it is necessary to ask the housing safety appraisal agency to conduct structural safety appraisal to ensure structural safety.