Soft floor of the building
Soft flooring is a phenomenon caused by removing the blades and walls of a floor from a building, which does not have uniformity, order and repetition of the walls in front of the upper floors. This makes the floor less resistant to lateral loads as the weakest floor and poor performance.
In other words, a soft floor building refers to buildings whose lower floors are much less difficult than the upper floors. These buildings are very vulnerable to earthquakes due to the large number of openings in the lower floors. The reason for building a large number of openings in the lower floors is usually to create a suitable space for parking cars or to create commercial uses (something that was evident in the buildings of the Bam earthquake) or in some cases to create large windows downstairs. It happens.

Such buildings will be more vulnerable to external forces. When the lower floor is demolished, the upper floors are sandwiched on top of it, and the ceilings are stacked on top of each other, crushing the occupants under the roof. Soft floors must have at least 80% strength of their upper floors. Of course, this amount is equal to 60% of the required strength for new buildings.
Iran's 2800 Earthquake Standard places irregular lateral stiffness at an irregular height and describes it as such. According to this standard, the soft floor is said to be a floor that has less than 70% of the lateral hardness of the floor on that floor. It is also called soft flooring in floors where the lateral stiffness is less than 80% of the average stiffness of the three floors.

Many buildings collapsed during the earthquake
Examining the impact of the soft floor in a building, the collapse of many buildings during an earthquake can be attributed to a situation in which restraint members (such as shear walls, braces, etc.) have been removed in some floors. The reason for this elimination is mainly to meet the needs of architecture. Under these conditions, the floor is weakened against lateral forces and creates a kind of irregularity in the building, which is known as irregular lateral stiffness.
Reasons to create a soft floor
1. Soft floors usually occur on the ground floor of commercial buildings, which take into account the height of the columns more (the height of one floor is higher than other floors).
2. Excessive and large openings in the ground floor can cause a soft floor.
3. Sometimes in the middle floors, due to the reduction of the lateral stiffness of the load-bearing system, the soft floor does not occur on the ground floor (lack of resistance of the lateral load-bearing elements in the floors).

Is softening earthquake-resistant buildings the right solution?
.Survival and lateral hardship are key factors in building buildings against earthquakes. In buildings with soft floors, the lateral load members are either not designed and executed from the beginning or are not sufficient. The first step in making buildings with soft floors resistant is to analyze the structure to determine the best way to make it stronger. Structural engineers have to consider several factors to determine the best way to resist. Not only must they be sure that the structure has been properly rehabilitated, but it must have the least impact on the operation of the structure.
Strengthening buildings does not mean counteracting them, but only securing them. That is, after the earthquake, the structure will remain standing and the safety of the residents will be provided. The building may no longer be able to be used. However, a reinforced building will certainly not meet the standards of a building designed for earthquakes.

In addition, rehabilitation requires a lot of time and money, and in a country that is located on the earthquake belt and 80% of its buildings are not earthquake resistant, it cannot be implemented in the short term. On the other hand, we live in a country with an ancient historical background, and resistance requires the destruction of this historical and ancient fabric, and in fact there are many valuable buildings in it.
It is important to note that public earthquake education is effective when an earthquake occurs when people are awake so that they can use what they have learned. If earthquakes occur during sleep (such as the Bam earthquake), they will have no effect on human survival. Evidence from earthquakes shows that people buried under the rubble have died as a result of direct impact of the rubble or pressure under the rubble, and have witnessed this many times. We have a small table or a door frame or many of these things that have saved lives.