Regarding the thickness of the concrete cover for equipment foundations
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I’m a beginner in process design and don’t know much about civil engineering. When I first arrived, my supervisor assigned me a task: to prepare basic construction drawings for the plasticizing extruders in the rubber factory. There is already a layout diagram for the holes of the steel expansion bolts in the equipment. I would like to ask everyone the following question: For the cushion layer under the equipment foundation, I plan to use C15 with a thickness of 100 mm, while for the concrete cover layer, I will use C20 or C35. May I ask how the thickness of the protective layer is generally calculated? My equipment weighs 20,000 kg in total. Is it calculated based on the average weight of the equipment? What is the commonly used thickness? 2. First, dig a large hole for the equipment foundation – what is the typical depth? What is the general scale for basic construction drawings? All I have are the regulations for chemical process design, which are all about the scale of piping diagrams. No reference found. It would be better if there were sources or designated names for the above issues. Thank you very much to everyone for your help.
The main problem encountered by the poster is related to the design of the foundation for the equipment. I will provide the poster with some basic concepts in this area for reference: The foundation is the base of a building; it belongs to the category of underground concealed works. The quality of its investigation, design, and construction has a direct impact on the safety of the building. A foundation is a structure that bears the loads of the superstructure and transfers those loads to the underlying soil layer. After the loads on the superstructure are transmitted to the soil through the foundation, they continue to spread deeper into the soil. Since the soil is a semi-infinite volume, the stress in the soil decreases rapidly as depth of diffusion increases. Beyond a certain depth, the increase in soil stress due to the upper loads is so small that it has no practical significance for engineering purposes. Therefore, the soil within this depth range at which the foundation base is located is generally referred to as the foundation of the building (structure). Foundation engineering design consists of two main parts: foundation design and soil foundation design. The contents of the foundation design include the selection of foundation type, the burial depth of the foundation and the size of the base area, as well as the calculation of foundation internal forces and cross-sections. Foundation design includes determining the bearing capacity of the foundation soil, calculating foundation deformation, and assessing the foundation’s resistance to overturning and sliding. The main considerations in the design of foundation engineering are, on the one hand, the loads on the superstructure and their distribution, and on the other hand, the mechanical properties of the soil foundation, the distribution of soil layers, the groundwater level and its variations. Therefore, foundation engineering is also known as subgrade foundation design. When the strength of the foundation is insufficient or its compressibility is too high to meet the design requirements, foundation treatment is necessary; the foundation after such treatment is called an artificial foundation. The above is a basic overview of foundation design. The structure referred to by the original poster is the superstructure, and its weight constitutes the load. What needs to be done is to design the foundation for this structure; the foundation construction drawings are merely part of the results of such design. There are still many factors to consider in foundation design. It’s possible that the load generated by the equipment to be installed by the owner is quite low, and the mechanical properties of the soil beneath the factory building where the equipment will be located are also good; nevertheless, the design of the foundation still needs to be handled with care. It is recommended that the original poster ask the structural design engineers in your company’s civil engineering department; this will be very helpful for the poster’s work.
The original poster’s question – regarding the issue of no protective layer in the absence of reinforced concrete. If there is a equipment foundation with rebar, the reinforcement cover thickness for the foundation can be used as reference.
The OP’s question--what was said above is correct. If there is an equipment foundation with rebar, the rebar cover thickness of the foundation can be used; in the presence of corrosive agents, the cover thickness should be increased.
It is recommended that the poster read more about the relevant specifications for equipment foundations
The thickness of the base protective layer is generally 30-50 MM, depending on the circumstances Such as whether there is groundwater, and whether considerations have been given to corrosion prevention, fire protection, and heat dissipation!
Reply to 6# julian609: The note in Article 9.2.1 of the «Code for Design of Concrete Structures» states that: \"The thickness of the concrete cover around the longitudinal load-bearing rebars in the foundation should not be less than 40 mm; when there is no cushion layer, it should not be less than 70 mm.\" “ I’m not sure where the 30–50mm figure you mentioned comes from
Reply to 7# moqichangqing: I’m referring to the case where there is a 100mm cushion layer. 30 mm is the minimum thickness of the protective layer based on the existing design drawings I referred to, while 50 mm is taken from clause 3.0.6 of HG/T20643/98 \"Specifications for the Design of Foundations for Chemical Equipment\". Specifically, it falls within this range based on the basic soil conditions and requirements for corrosion prevention.
Reply to 8# julian609: The value of 30mm is based on the drawings, not on the specifications; that seems a bit arbitrary! When there is a cushion layer, it is still necessary to ensure a protective layer of at least 40 mm; as for industry standards, which require a higher thickness of 50 mm, that should be followed.