GB/T 39830-2021Code for seismic design of steel static storage systems (English PDF)

4.1 Basic parameters of seismic fortification

4.1.1 The site is divided into five categories. I0, I1, II, III, and IV, which shall be determined through site survey.

4.1.4 According to the amax calculated by 4.1.2, look up Table 3 to determine the maximum value of the horizontal seismic influence coefficient alphamax.

4.1.5 The damping ratio eta of steel rack structures should refer to the damping ratio of steel structures in 8.2.2 of GB 50011-2010. When the height is not more than 50 m, it can be taken as 0.04; when the height is greater than 50 m, it can be taken as 0.03.

4.1.6 The natural vibration period T of steel racks can be calculated according to theory or determined according to empirical formula (2).

4.1.7 For the calculation of the seismic influence coefficient alpha, it shall be determined according to 5.1.5 in GB 50011-2010.

4.3 Structural seismic calculation

The structural seismic calculation shall be carried out according to the analysis model of 4.2 and the seismic analysis method specified in 6.1. The horizontal seismic action shall be determined by 5.2. For the structure shown in Figure 1, the vertical seismic action shall be calculated.

4.4 Determination of load and load combination

The various permanent loads and variable loads for seismic design shall be determined according to 5.5. The load combination shall be determined according to 5.6.1. Data such as the internal force of members, the reaction force of upright foot and the node displacement shall be calculated according to the load combination.

5.1 Description of seismic action

The seismic action is generally described by response spectrum, which shall follow the design response spectrum of GB 50011-2010, and be represented in the form of seismic influence coefficient curve alpha, see 5.1.5 in GB 50011-2010.

5.5 Loads considered simultaneously with seismic action

5.5.1 Permanent load PDL

Permanent loads of steel racks include.

5.5.3 Wind load PWL

For static storage system such as rack-clad building, the wind load shall be considered, and the combined action shall be considered according to the relevant provisions of GB 50011-2010.

5.6 Design and check of bearing capacity limit state

5.6.1 Load combination

When calculating the horizontal seismic action, take the most unfavorable load combination, and determine the design value Pmax in the following two cases.

5.6.2 Gravity second order analysis

The seismic analysis shall consider the influence of the gravity second order, and refer to the relevant requirements in 5.1.6 of GB 50017-2017.

5.6.3 Sectional seismic check

Under the load combination specified in 5.6.1, the design value of internal force combination of structural member Pmax shall meet the following requirements.

5.6.4 Steel rack spacing

The steel racks shall have enough spacing to prevent collisions in earthquakes. The spacing shall not be less than 3 times the maximum deformation of the racks under the action of frequent earthquakes, including the following two typical cases.

5.6.5 Seismic deformation check

The seismic analysis results of steel racks shall meet the requirements of inter-level displacement. The inter-level displacement can be calculated according to formula (8).

6.1 Selection of seismic analysis methods

6.1.1 Bottom shear method

The bottom shear method is generally used for steel racks with a height of no more than 40 m, of which the structural rule is mainly shear deformation, and the distribution of mass and stiffness along the height is relatively uniform.

6.2 Structural modeling

6.2.1 Load distribution

The seismic analysis shall consider the most unfavorable load distribution. At least the following load distribution forms shall be considered.

6.2.2 Position of the center of gravity of unit cargo

6.2.2.1 The unit cargo can be regarded as a substructure of the steel rack structure. If the unit cargo is larger in size, it shall consider the influence of the position of its center of gravity on the steel rack structure.

6.2.2.2 In the Z direction, it shall consider the height of center of gravity of the load unit relative to the beam (may be called vertical eccentricity).

6.2.2.3 The vertical eccentricity of unit cargo in the X direction may not be considered, except for the case where the rack has only one row.

6.2.3 Specific modeling requirements

6.2.3.1 In the X direction, the restraint form of beam-upright joints and upright foot joints shall be handled according to 5.2.5 in GB/T 28576-2012, and the stiffness value of beam-upright joints and upright foot should be obtained through the test according to 7.5 and 7.6 of GB/T 39681-2020.

6.2.3.3 When the steel rack adopts flexible cross bracing, the cross bracing shall be set as a tension-only member in the analysis model.

6.2.3.4 It shall add plane connectors between the back bracing and the rack to improve the lateral resistance of the structure, see Figure 8 Structure 1.

7.1 Horizontal lateral force resistance structure

7.1.1 In the Z direction, the main lateral force resistance structure is the upright frame.

The upright frame structure should use the K-shaped, D-shaped, Z-shaped support and X-shaped support without cross bar, as shown in Figure 6.

7.1.2 In the X direction, there are three types of lateral force resistance structures.

7.2 Other constructions

7.2.1 The upright is generally fixed on the ground through the upright foot connector.

The upright and the upright foot connector can be fixed by welding or by bolts. When using bolts to fix, if it is fixed through long holes (the direction of the force is the direction of the long holes) or oversized holes, it shall have anti-slip design, such as high-strength friction bolt connection, to avoid displacement of the upright foot.

7.2.2 When members such as flat steel, round steel and cable are used as bracings, it shall be ensured that these bracings are always in a tensioned state under gravity.