1. Design of Steel and Composite-Structures for Seismic Loading – Safety Requirements, Concepts and Methods –
Prof. Dr.-Ing. Ekkehard Fehling, University Kassel
Dr.-Ing. Benno Hoffmeister, University / RWTH Aachen

2. Design of Buildings for Seismic Action reduced regularity
different structural systems for lateral bracing
discontinuous bracing systems
Diagonal
bracing
frame
structure
Ungleichmäßige Beanspruchung wegen verschiedener Massen, Steifigkeitssprünge etc. Nicht berücksichtigte Torsionseffekte bei L-förmigen Bauwerken
Diagonal
bracing

3. Design of Steel Structures for Seismic Action Ductility
Sudden or brittle failure shall not occur
Examples:
Buckling
Connection failure
Load
Deformation
Ductility bedeutet de Deformationsfähigkeit eines Tragwerks, bei der kein plötzliches Versagen von vitalen Membersn auftritt

4. Design of Steel Structures for Seismic Action Ductility
Examples:
Typische Examples, die sich immer wiederholen, sind hier zu sehen

5. Design of Steel Structures for Seismic Action Ductility
Specially endangered: Corner Columns
Typische Examples, die sich immer wiederholen, sind hier zu sehen
most
endangered column

6. Design of Steel Structures for Seismic Action Ductility
Examples:
Typische Examples, die sich immer wiederholen, sind hier zu sehen

7. Design of Steel Structures for Seismic Action Dissipative Behaviour
Cyclic defomability with dissipation of energy
Exploitation of plastic material behaviour
Principle:
Elastic
behaviour
Load
Deformation
Dissipative Behaviour ist neben der Ductility die Kerneigenschaft von erdbebenresistenten Bauwerken. Die Dissipation geht von plastisch verformbaren Elementen aus, wie hier am Example eines Kragarms dargestellt.

8. Design of Steel Structures for Seismic Action Dissipative Behaviour
Cyclic defomability with dissipation of energy
Exploitation of plastic material behaviour
Principle:
Load
Deformation
Plastification
Plastification

9. Design of Steel Structures for Seismic Action Dissipative Behaviour
Cyclic defomability with dissipation of energy
Exploitation of plastic material behaviour
Principle:
Load
Deformation
Plastification
dissipated
energy
Plastification

10. Design of Steel Structures for Seismic Action Dissipative Mechanisms
Bending (Frame)
Normal Force (Bracings)
Shear (ecc. Bracings)
Die Dissipationsfähigkeit einzelner Elemente ergibt das Dissipative Behaviour eines Bauwerks.

11. Design of Steel Structures for Seismic Action Dissipative Mechanisms
Bending (Frame)
Normal Force (Bracings)
Shear (ecc. Bracings)
Die Dissipationsfähigkeit einzelner Elemente ergibt das Dissipative Behaviour eines Bauwerks.

16. Design of Steel Structures for Seismic Action Dissipative Behaviour – Global System
Successive Formation of Plastic HInges
Load
Die Dissipationsfähigkeit einzelner Elemente ergibt das Dissipative Behaviour eines Bauwerks.
Deformation

17. Design of Steel Structures for Seismic Action Dissipative Behaviour – Global System
Succesive Formation of Plastic Hinges
Load
Die Dissipationsfähigkeit einzelner Elemente ergibt das Dissipative Behaviour eines Bauwerks.
Deformation

18. Design of Steel Structures for Seismic Action Dissipative Behaviour – Global System
Succesive Formation of Plastic Hinges
Load
Die Dissipationsfähigkeit einzelner Elemente ergibt das Dissipative Behaviour eines Bauwerks.
Deformation

19. Design of Steel Structures for Seismic Action Dissipative Behaviour – Global System
Succesive Formation of Plastic Hinges
Load
Die Dissipationsfähigkeit einzelner Elemente ergibt das Dissipative Behaviour eines Bauwerks.
Deformation

20. Design of Steel Structures for Seismic Action Dissipative Behaviour – cyclic
Experimental Investigations on Frame Structures
Die Dissipationsfähigkeit einzelner Elemente ergibt das Dissipative Behaviour eines Bauwerks.

23. Design of Steel Structures for Seismic Action Functioning dissipative Mechanisms
Die Dissipationsfähigkeit einzelner Elemente ergibt das Dissipative Behaviour eines Bauwerks.

24. Design of Steel Structures for Seismic Action Inadequate Dissipation Capacity
Die Dissipationsfähigkeit einzelner Elemente ergibt das Dissipative Behaviour eines Bauwerks.

25. Design of dissipative Members „Overstrength“ of Material
Example S 235, nominal Yield Strength fy,k = 235 N/mm²
Consequences:
in the dissipative member the forces will become bigger than intended
Failure of connections (e.g. bolts)
Stability failure (e.g. columns)
Stress
235
Overstrength
Die Dissipationsfähigkeit einzelner Elemente ergibt das Dissipative Behaviour eines Bauwerks.
Strain

26. Design of dissipative Members „Overstrength“ of Material
how to ensure dissipative behaviour
Measures:
Capacity Design (design of critical members and connections with „overstrength“)
Limitation of maximum yield strength in dissipative Members
Control of execution (strength as ordered = delivered strength?)
Stress
235
Overstrength
Die Dissipationsfähigkeit einzelner Elemente ergibt das Dissipative Behaviour eines Bauwerks.
Strain

27. Design of dissipative Members Plastic Fatigue of Materials
Elastic Fatigue Strength
Plastic Fatigue (Low Cycle Fatigue)
Die Dissipationsfähigkeit einzelner Elemente ergibt das Dissipative Behaviour eines Bauwerks.

28. Design of dissipative Members Plastische Ermüdung des Werkstoffs
Elastic Fatigue Strength
Plastic Fatigue (Low Cycle Fatigue) Δσ
104
5·106
>108 N 1
100 N
ΔRpl
Die Dissipationsfähigkeit einzelner Elemente ergibt das Dissipative Behaviour eines Bauwerks.

29. Design of dissipative Members Toughness of Material
Toughness of material – basic requirement for dissipation
Die Dissipationsfähigkeit einzelner Elemente ergibt das Dissipative Behaviour eines Bauwerks.

30. Design of dissipative Members Zähigkeit des Werkstoffs
Toughness of material – basic requirement for dissipation
Mesures:
Selection of material quality / grade (sufficient toughness even for low temperatures)
Dissipative zones outside the heat influence zones due to welding
Die Dissipationsfähigkeit einzelner Elemente ergibt das Dissipative Behaviour eines Bauwerks.

31. Design of dissipative Members Stability of cross sections
Slender cross section show premature local buckling:
dissipation will be less
premature damage
Die Dissipationsfähigkeit einzelner Elemente ergibt das Dissipative Behaviour eines Bauwerks.

32. Design of dissipative Members Stability of cross sections
Slender cross section show premature local buckling:
dissipation will be less
premature damage
Measures:
Compact Cross Sections (Cross sectional class 1)
For thin walled Structures design for elastic behaviour consider stability aspects (e.g. fluid tanks)
Die Dissipationsfähigkeit einzelner Elemente ergibt das Dissipative Behaviour eines Bauwerks.

33. Design für Dissipative Behaviour Global capacity design
g+q
Die Dissipationsfähigkeit einzelner Elemente ergibt das Dissipative Behaviour eines Bauwerks.
Vanchor
Vanchor
Nanchor
Ncolumn

38. Design für Dissipative Behaviour local capacity design
Measures:
avoid premature brittle failure of non dissipative connections for bolted / or welded connections: design with overstrength for bolted connections: bearing stresses should be more critical than shear in bolt
weld
net-section
Die Dissipationsfähigkeit einzelner Elemente ergibt das Dissipative Behaviour eines Bauwerks.
Bearing resistance
Bolts

39. Seismic Design of Steel Structures
Codes:
EN 1998 (or: DIN 4149 = EN 1998 simplified)
codes for steel structures and materials
Seismic Design:
Make use of dissipation, assuming behaviour factor q (Reduction of „elastic“ action)
Application of capacity design e.g. for bolted connections: Rbolt > Rbearing > Rcross-section,pl > Eseismic/q for comparison: static design verification: (Rbolt , Rbearing , Rcross-section) > Ed
Die Dissipationsfähigkeit einzelner Elemente ergibt das Dissipative Behaviour eines Bauwerks.

41. Flow chart for design (1)
Preliminary design of building (e.g. for wind loads)
Result: dimensions, topology, permanent and variable loads
Decision about conceivable dissipation mechanisms
Combination of actions for earthquake
Calculation using response spectrum
Comparison of actions due to wind and earthquake
yes
No further
checks
Wind > Earthquake
Possible
behaviour factors
(system topology,
regularity) no
yes
ductility
class L
Exploitation < 150 % no
Natural Ductility
q = 1,5
Ductility class M or H (q >1,5)
Selection of behaviour factor
q = max. exploitation [%] / 100

42. Flow chart for design (2)
Selection of behaviour factor
q = max. exploitation [%] / 100
Calculation using design spectrum
Ed = Eelast / q
member forces
Check of degree of exploitation (dissipative members)
usually max. exploitation ≈ 100 %
min. exploitation ≈ 80 %
Inverse degree of exploitation Ω = 1 / 0,80 = 1,25
global capacity design with
g + q and 1,2 Ω Ed
local capacity design (connection of dissipative elements)

43. Application Example:
Reactor- and Heater Towers for a steel producing direct reduction plant in Indonesia

48. Assuming an Elastic system
atop
atop = 0,5 … 1,0 g
ag = 0,2 … 0,4 g
Ground and Response Acceleration

49. Assuming an Elastic system
1 g horizontal =

50. Ductility: where to get it from?
not o.k. !
not o.k. !
buckling = failure

51. Ductility: where to get it from?
Buckling o.k.
o.k. !
o.k. !

52. First possible solution

53. Example: Shear –Link in Eccentrically Braced Frame (EBF)
Dissipative Elements
Vpl V
Example: Shear –Link in
Eccentrically Braced Frame (EBF)

55. Second possible solution
Vertical Shear links

56. Biggest possible ductility in shear Avoid flexural failure mode
Design of Shear Links
Biggest possible ductility in shear
Avoid flexural failure mode
Web buckling should occur at large deformations only
Ensure lateral stability of flanges

58. Calculate system again and diagonals for this load
Capacity Design: 2nd loop of calculation
from shear link: Vpl
Vpl * γRd
Calculate system again
with
Vpl * γRd !
Design columns, beams
and diagonals for this load

59. Spacing of stiffener plates, type of link
Plastic deformability θ= rad

61. Conclusions
Design for Earthquake requires different way of thinking: verification of behaviour rather than verification of strength
The behaviour of a structure under seismic loading is mainly determined by:
Regularity – avoid extreme straining/ loading of certain members
Redundancy – enable reserves of saftey
Ductility – plastic deformations without premature failure
Dissipation – from formation of cyclic plastic hystereses
Quality and Control of Execution – too much of strength may be dangerous
Die Dissipationsfähigkeit einzelner Elemente ergibt das Dissipative Behaviour eines Bauwerks.