Cranes - Principles for seismically resistant design
1 Scope
This standard establishes general methods for seismically resistant design of crane, applicable to calculating seismic loads to be used as defined in the ISO 8686 (all parts) and to proof of competence as defined in ISO 20332, to the structure and mechanical components of cranes as defined in ISO 4306 (all parts).
This standard evaluates dynamic response behaviour of a crane subjected to seismic excitation as a function of the dynamic characteristics of the crane and of its supporting structure. The evaluation takes into account dynamic effects both of regional seismic conditions and of the local conditions on the surface of the ground at the crane location. The operational conditions of the crane and the risks resulting from seismic damage to the crane are also taken into account.
This standard is restricted to the serviceability limit state (SLS), maintaining stresses within the elastic range in accordance with ISO 20332.
The present edition does not extend to proofs of competence which include plastic deformations. When these are permitted by agreement between crane supplier and customer, other standards or relevant literature taking them into account can be used.
2 Normative references
The following documents contain requirements which, through reference in this text, constitute provisions of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 8686 (all parts) Cranes - Design principles for loads and load combinations
Note: GB/T 22437 (all parts) Cranes - Design principles for loads and load combinations [ISO 8686 (all parts)]
ISO 20332 Cranes - Proof of competence of steel structures
Note: GB/T 30024-2020 Cranes - Proof of competence of steel structures (ISO 20332:2016, IDT)
3 Terms, definitions and symbols
3.1 Terms and definitions
No terms and definitions are listed in this document.
3.2 Symbols
For the purposes of this document, the following symbols apply.
The main symbols used in this standard are given in Table 1.
Table 1 Main symbols
Symbol Meaning
Abg Normalized basic acceleration
Asg Normalized acceleration at ground surface
c Vertical influence factor
FH Horizontal seismic design force
FV Vertical seismic design force
FRH, FRV Seismic forces (horizontal and vertical) on suspended load
fcon Conversion factor
frec Recurrence factor
KH Horizontal seismic design coefficient
KV Vertical seismic design coefficient
β2 Subsoil amplification factor
β3 Acceleration response factor
β_3^* Basic acceleration response factor; β3 of the crane whose damping ratio is 0.025 and given by Figure 2
γn Risk factor
η Damping correction factor
δ Response amplification factor
ζ Damping ratio
4 Seismic design methods
There are three main methods of seismic response analysis used in seismic design:
——Modified Seismic Coefficient Method;
——Maximum Response Spectrum Method;
——Time History Response Method.
In the Modified Seismic Coefficient Method, the applied quasi-static seismic forces are calculated as a product of seismic coefficients and crane weights. The evaluation of seismic coefficients takes into account crane location, its seismic characteristics, basic dynamic characteristics of the crane, i.e. natural frequency or period and damping characteristics, in three principal orthogonal directions of the crane (one vertical and two horizontal).
The method is the basis of this standard on account of its simplicity (see Clause 5), and its procedure is executed as part of the design iterative process indicated in the flow chart in Annex A.
The Maximum Response Spectrum Method (see Clause 6 and Annex B) is an alternative method of seismic response analysis used where:
——more accurate seismic response of the crane is required than that produced by the Modified Seismic Coefficient Method;
——demand on significant computational resources is economically acceptable.
Its application is limited only to linear systems and to system where nonlinearities if present can be neglected.
In the Maximum Response Spectrum Method, natural frequencies or periods and associated mode shapes of the crane are calculated first. Seismic forces and the crane response are then calculated for the selected vibration modes of the crane structure, using the maximum response accelerations (selected from the maximum response spectra which again take into account seismic characteristics at crane location and the damping characteristics of crane structure) together with the calculated mode shapes, frequencies and mass distribution of the crane.
The Time History Response Method is the third method of seismic response analysis available. It is employed when:
Foreword i
1 Scope
2 Normative references
3 Terms, definitions and symbols
4 Seismic design methods
5 Seismic design by Modified Seismic Coefficient Method
5.1 General
5.2 Calculation of horizontal seismic design coefficient, KH
5.3 Calculation of vertical seismic design coefficient (KV)
5.4 Calculation of seismic design loads
6 Seismic design based on Maximum Response Spectrum Method
6.1 General
6.2 Calculation procedure for total seismic response (TSR)
7 Combinations of seismic and non-seismic effects
7.1 General
7.2 Proof of static strength: load combinations in accordance with ISO 8686-1
7.3 Proof of static strength: load combination according to SRSS Method
7.4 Proof of global stability
7.5 Proof of competence for crane structures
Annex A (Informative) Flow chart of seismic design
Annex B (informative) Information about maximum response method
Annex C (Informative) Time History Response Method and a comparison of different seismic methods available
Annex D (Informative) Relation between basic acceleration, Mercalli and Richter scales
Annex E (Informative) Vertical seismic intensity
Bibliography
