Prevention of foundation settlement of steel structure building

How to prevent the settlement of the foundation of the steel structure house, we must first start from the basic platform, when the steel structure house reaches 25 KG per square meter, the basic platform to reach 1KG high, 1 meter wide, 1 meter deep, the steel structure house per square meter foundation settlement of more than 355KG, need to do ring beams and 1.2 meters foundation, actually according to the situation of the site itself.

After the construction of the steel structure house is completed, there is no good early investment, how to avoid the sinking of the steel structure house foundation, simply put, is the reinforcement, all the steel structure and industrial steel or channel steel ring, resulting in a network. The invention can prevent the settlement of steel structure building foundation.

In recent years, steel structure houses have been widely used in coal engineering because of their light weight, good seismic performance, flexible structure layout and fast processing and installation speed. In this paper, we only discuss one layer plant, namely door rigid frame light steel structure and steel row structure, in which door rigid frame light steel structure is a common structural form. The foundation of the steel structure house with large weight is light, the axial force of the column bottom is small, the bending distance is large, and the eccentric distance is too large, which brings some difficulties to the foundation design.

1. Foundation bearing characteristics of steel structure plant.

Steel foundation generally adopts single-sided foundation, biased design.

Door rigid frame steel structure house height is not high, no crane, column foot and foundation connection generally adopt hinged design. The top surface of the foundation is only affected by the horizontal force of the horizontal force load from the vertical pressure of the superstructure. Under the wind load of foundation, the eccentric bending distance is small, and the foundation design is relatively simple.

Gantry rigid frame, steel bent frame, especially crane (20)t crane or double machine 20t for steel structure houses above the crane, in order to effectively improve the anti-lateral stiffness of the structure and control horizontal migration, horizontal rigid connection and vertical fixed connection are generally used. The factory is a treat.

The horizontal load is transferred to the top surface of the foundation according to the intercolumn support. However, due to the light weight of the steel structure, long natural vibration period, and relatively small horizontal seismic effect, the horizontal load control is generally the air increase method of the horizontal brake load of the crane, so the axial force of the two rods is not equal. The formula is based on elastic stability theory,

It is suitable for two diagonal rods of the same length and the same length.

(1) The other pole of the cross is pressed, the two poles are the same boat, and the intersection is not interrupted:

In the formula.

Second, the other rod of the cross-joint is under pressure, and the rod is interrupted at the cross-joint, but is overlapped by the node plate.

Third, the other pole of the cross is pulled, and the two poles are in the same boat, without interruption at the intersection:

4) The other bar of the cross-tension, broken at the intersection, but when bonded on the node plate:

The second is the basic design regulations.

Due to the relatively large eccentric load, the reaction force of the substrate is not uniform, which will lead to a large tilt of the substrate, and even affect the normal use of the factory, especially the crane factory. Therefore, the pressure of the foundation soil at the bottom of the large foundation should also meet the following requirements:

1) For pile foundation without crane load, when considering wind load, it is allowed to have a zero stress region in the foundation soil at the bottom edge of the foundation, provided that the length of the non-zero stress region and the foundation length ratio L/L≥0175, and the bending capacity of the tension side of the foundation floor and the soil quality of the upper end of the soil.

2) On the column base bearing the load of the general crane, there can be no zero stress area of the soil at the bottom of the foundation, that is, pmin≥0, if this standard is met, there must be a basic eccentric distance e≤b/6.

3. Basic design method.

For the stress characteristics and design requirements of the above foundation, when the crane tonnage is large, if in accordance with the traditional independent foundation design, the eccentric distance often becomes the control condition of the base size, the base bearing capacity is not controlled, the larger eccentric distance will lead to the base specification is too large (sometimes the circumference can reach 6m or more), very uneconomic, in engineering is unacceptable. After the analysis of some practical engineering cases, the author believes that such problems in the design process can be solved in the following ways:

3.1 Applying Eccentric Bases.

If the base eccentricity is small (generally e≤015m), this method is more effective. The principle of this method is to place a reverse bending distance in the direction of a larger bending distance effect to reduce the eccentricity effect. However, since the factory is doubly affected by horizontal wind load and crane load, the negative adverse combination should be checked and controlled separately in the design. The current steel structure design "STS" program can not meet the needs of checking, designers can "correct" other assistance programs to "STS" plan checking.

The basis of eccentricity can generally be reduced, but for large tonnage and working level A6~A8 cranes, this method should be used with caution.

3. Add additional weight to the base.

The eccentricity (015)m1) with the foundation used to be large, and the buried depth was large: the buried depth of the foundation was large, the foundation was heavy, and the eccentric distance of the foundation was reduced; At this time, the foundation can be designed as an independent short column foundation of concrete structure. The connection specifications of short columns are generally determined by the specifications of steel beam foot plates, and the connection strength is subject to the value. However, when the depth of the foundation is larger, the extra bending distance of the bottom edge of the foundation will be larger and the eccentric distance of the bottom edge of the foundation will be larger due to the horizontal shear force of the column foot. Therefore, the above two factors should be fully considered in the design, and through the test calculation, choose a reasonable foundation burial depth.

Second, the reinforced wall for the plant protection structure: the reinforced wall can be made of non-clay sintered bricks, and the net weight can be transferred to the foundation through the ground beam under the wall. The wall thickness can be 370mm from the top of the floor beam to the height of the window. In order to improve the height of the wall, the height of the bottom balcony can be appropriately raised according to the situation. The ground beam can be poured at the same time with the short column of the foundation, and the ground beam is suitable for adjusting the uneven isomorphism of the adjacent foundation.

The combined application of the above two methods in engineering design is good.

3. Pile foundation.

The eccentricity of the bottom edge of the foundation is large (e>112m), and the buried depth of the bearing layer is deep, which can not be solved by the above method, or the crane tonnage of the plant is large, and the road surface is piled up 60kN/m2 for a long time. The above substrate soil is medium and high expansive soil, and additional uses of pile foundation should be considered. The type of pile foundation soil can be determined according to the soil quality and local construction conditions.