Overturning Failures of Building Foundations
Dr.Subramanian, Ph.D., FNAE, F.ASCE, M.ACI Narayanan
INTRODUCTION
Civil engineering is one of the most important professions in today’s society. But, when civil engineers make mistakes, the consequences can be catastrophic and result in loss of property and human life and may even affect the economy of the state. Thus, engineering is a career that does not afford mistakes. A major concern in everything engineers do is safety. In addition, structural engineers must consider the environmental and economic outcomes of their work. The safety of structures is achieved by analyzing the building using appropriate software to resist various possible loads and their combinations as specified in the codes specified by the Bureau of Indian Standards (e.g., various parts of IS 875 and IS 1893). Then they have to be designed and detailed properly using IS 456:2000. Finally, they have to be executed at the site using quality materials under strict supervision.
RC FOUNDATIONS
?RC foundations are the most important elements in any type of structure, as they transfer all the loads that come on the superstructure to the ground below. There should not be any compromise in their analysis, design, and execution, as any error in them may lead to the failure of the whole structure.
?RC foundations are to be designed keeping in mind the following (Varghese, 2005):
1.?????All the applied vertical and horizontal loads and moments have to be resisted by the soil pressure, which should not exceed the safe bearing capacity of the soil at the site.
2.?????The foundation should have adequate safety against sliding, overturning, or pull-out (in case of tensile loads due to wind or earthquake).
3.?????In addition, the total settlement and the differential settlements of the structure should be within the allowable limits (These limits are prescribed in IS 1904).
It has to be remembered that a non-uniform pressure under the foundation in compressible (clay) soils can lead to the long-term effect of tilting the foundation. It is also important to conduct enough soil investigations at the site using geotechnical engineers, and determine soil properties at the foundation level, the type of soil below the foundation up to the required level of dispersion of load, and to determine the type of foundation for the structure at hand.
Usually, the factor of safety adopted for the soil is in the range of 2.0 to 4.0, depending on the type of structure as compared with the factor of safety of 1.5 for concrete or steel structures (Varghese, 2005). In general, foundations in clays should be given a larger factor of safety against shear failure than foundations in sands (Varghese, 2005). A higher factor of safety for soils is used because the properties of soil can vary greatly depending on the location, the type of soil, and the depth of the soil. This variability makes it difficult to accurately predict the behavior of soil under load.?
OVERTURNING FAILURE
Overturning failure is a type of structural failure that occurs when a load causes a structure to rotate about its base. This type of failure is most commonly seen in retaining walls, but it can also occur in other structures, such as buildings and bridges.
Overturning failure can be caused by several factors, including:
?1. The height of the structure:?The taller the structure, the more likely it is to overturn.
2.?The weight of the load:?The heavier the load, the more likely the structure is to overturn, if the load has more eccentricity.
3. ?The properties of the soil:?The soil that the structure is built on must be able to support the weight of the structure without allowing it to overturn.
4. The design of the structure:?The structure must be designed to resist overturning forces.
Overturning failure can be prevented by:
1.??Using lightweight materials:?Using lightweight materials will reduce the weight of the structure, making it less likely to overturn.
2.?Lowering the structure's height: Lowering the structure's height will reduce the overturning moment, making it less likely to overturn.
3. ?Using a solid foundation:?The foundation must be strong enough to support the weight of the structure and resist overturning forces.
4. Properly designing the structure:?The structure must be designed to resist overturning forces.
If a structure is experiencing overturning forces, it is important to take steps to mitigate the risk of failure. This may involve reinforcing the foundation, lowering the structure's height, or using lighter materials. In some cases, it may be necessary to demolish the structure.
References
Studium: Leibniz University Hannover
10 个月Thanks a lot for the post, it really add more to our knowledge, I think you are with many here are giving great efforts, so great thanks.
--
1 年I am a student at the Peruvian Union University. Lima, Peru Headquarters of the Professional School of Civil Engineering. I have read your post and it seems interesting to me, so I would like to know more about it. Specifically the subject of the stabilization of clayey soil using some stabilizing agent, without considering conventional agents such as cement, lime, etc. Lately, stabilizers such as Bioenzymes, or chemical additives have been used, many of which have shown a favorable economic impact. I would like to exchange opinions with you, and to know what types of agents are being studied recently, since you have more knowledge in the field. I look forward to your kind reply.
Continuous Improvement Manager
1 年https://doshinrubber.com/
Executive
1 年If I am not wrong, this article was published a few days back and I had mentioned that how if the load is heavier , over turning may occur. But in that article probab;ly the line " if the load has more eccentricity." was missing. With this line, the statement is correct. The weight of the load:?The heavier the load, the more likely the structure is to overturn, if the load has more eccentricity. Its a good article, may not be new but informatory.