To prevent the sinking of the foundation of the steel structure workshop building, it is necessary to start with the foundation cap. When the weight per square meter of the steel structure workshop building reaches more than 25KG, the foundation cap needs to be in size of 1 meter high, 1 meter wide and 1 meter deep, and if the weight per square meter is above 35KG, then the steel workshop needs to be made of ring beams and 1.2 meters of foundation, and it also depends on the ground itself.
When the construction of the steel structure workshop building has been completed while the initial precautionary measure has not been made, how can we prevent the foundation of the steel structure workshop building from sinking? To put it simply, it is reinforcement. All the steel structure columns are circled with I-beam or channel steel to form a mesh. This method can prevent the sinking of the foundation of the steel structure factory building.
The force characteristics of the foundation of steel structure workshop
The foundation of the steel structure workshop building usually adopts a separate foundation, which is designed according to eccentric compression.
For low-height portal rigid-frame steel structure workshops without cranes, the connection between the column feet and the foundation is usually designed as hinged joints. The top surface of the foundation is only subject to the vertical pressure generated by the superstructure and the horizontal force generated by the wind load. The additional eccentric bending moment on the bottom of the foundation caused by the horizontal wind load is small, and the foundation design is relatively simple.
For high-height portal rigid frame steel structure workshops with bridge cranes, especially when the crane tonnage is large (two 20t cranes or more in a single span), in order to effectively improve the structure's anti-side movement rigidity and control lateral displacement, the column feet are usually designed for horizontal rigid connection and longitudinal hinged connection. The longitudinal horizontal load on the workshop building is transmitted to the top surface of the foundation through the support between the columns. In the lateral direction, because of the light weight and long natural vibration period of the steel structure, the horizontal seismic effect is relatively small, the horizontal load that plays a controlling role is usually the horizontal braking load of the crane plus the wind formula, and the axial forces of the two rods may not be equal.
Basic requirements of foundation design
The reaction force on the bottom surface of the foundation is unevenly distributed due to the relatively large eccentric load, which may cause the foundation to tilt greatly, and even affect the normal use of the plant, especially the plant with a crane. Therefore, the pressure on the foundation soil on the bottom of the industrial plant foundation must also meet the following requirements:
1.When wind load is taken into account for the column foundation without crane load, zero stress area is allowed in the foundation soil at the bottom of the foundation, but the ratio of the length of the non-zero stress area to the length of the foundation must be satisfied L'/ L≥0175, and at the same time it is also necessary to check the bending strength of the tensile side of the foundation slab under the action of the foundation's own weight and the upper soil weight.
2.For column foundations subjected to general crane loads, it is not allowed to have a zero-stress zone in the foundation soil on the bottom of the foundation, that is, pmin≥0. The eccentricity of the base must be required to e≤b/6 to meet this condition.
The general method of foundation design
According to the above-forced characteristics and design requirements of the foundation, for the side columns of a single-story steel structure factory building with a crane that is rigid connected to the column foot, when the crane tonnage is large, if the conventional separate foundation design is used, then eccentricity is often a controlling condition for the size of the base surface. The bearing capacity of the foundation does not have a controlling effect, and a larger eccentricity will cause the size of the foundation bottom to be too large (sometimes the side length reaches more than 6m), which is very uneconomical and unacceptable in the project. After analyzing and comparing some specific projects, it is believed that such problems can be solved by the following methods in the design process:
1.Adopt an eccentric foundation
This method is more effective when the eccentricity of the bottom surface of the foundation is small (e≤015m in general). The principle is equivalent to pre-adding a reverse bending moment in the direction of the larger bending moment to reduce the eccentricity. However, since the horizontal wind load and crane load on the plant are both acting in two directions, the unfavorable combination of the positive and negative directions should be selected for verification and control during the design.
2.Increase the additional weight of the foundation
This method is more effective when the eccentricity of the foundation bottom surface is more than 015m and less than 112m (015m <e≤112m). Increasing the additional weight of the foundation can be achieved in two ways: increasing the buried depth of the foundation, and adopting a weighted wall at the lower part of the outer maintenance system of the factory building. In engineering design, the combination of the above two methods has a better effect.
3.Adopt pile foundation
When the eccentricity of the foundation bottom surface is large (e>112m) and the supporting layer is buried deep, which cannot be solved by the above method; or the tonnage of the plant crane is large, the long-term large-scale stacking on the ground exceeds 60kN/m2, the base soil is medium or high compressible soils, pile foundations should be adopted. The type of pile foundation can be determined comprehensively according to the soil condition of the foundation and local construction conditions.
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