CONCEPTUAL DESIGN AND CONTROL OF BRIDGE STRUCTURES IN SEISMIC AREAS

1. CONCEPTUAL DESIGN AND CONTROL OF BRIDGE STRUCTURES IN SEISMIC AREAS Dr Radomir FOLIC, Professor Institute for Civil Engineering Faculty of Technical Sciences University of Novi Sad E-mail: folic@uns.ns.ac.yu

2. INTRODUCTION • The extensive damage of the recent earthquake have led to a significant damage of B S`s. • The cause is often the error of conceptual design, i. e. the choice of the structural and foundation system, spacing of piers and connections between them, deck and abutments, the spacing of joints, etc. • This presentation reviews philosophies of seismic design and protection which can be used in the conceptual phase of bridge design (Eurocode 8-part 2 provisions and recommendations used in U.S.A. and Japan).

3. Taiwan, September 21,1999 Traditional design procedureEarthquake—Structure—Response

7. Buckling long. bars caused by bed confinement

8. INTRODUCTION • Beam system is used for small and medium spans, arch and suspension system for large spans. • Importance of structure, site conditions and regularity of structure influence on methods of analysis. Based on regularity in plane and elevation structures are classified as regular or non-regular. • Based of the need for the B, to maintain emergency communications after the design seismic event, classified: greater than average (I=1.3); average (I=1.0); less than average (I=0.7)- (EC 8-2).

9. INTRODUCTION • In the most current seismic code aim is to prevent collapse of the structure under the design earthquake. The importance of conceptual analysis in B designing problems cannot be stressed enough. • Choice of appropriate earthquake resisting structural system (ERS) must provide in early phase of design.

10. DESIGN Three steps in design of bridge structures (BS) are: • Conceptual design, • Analysis, & • Detailing. Three approaches in design of BS are: • Force - Based Seismic Design FB SD, • Displacement - Based Seismic Design DBD –(N. Priestley), and • Performance - Based Seismic Design PB SD.

11. DESIGN Performance requirements depend on the importance and configuration-regularity of bridges (B′s). We can divided (B′s) on: normal (B′s) & special bridges: arch bridges, cable-stayed B′s, B′s with extreme geometry, and B′s with distinctly different yielding strengths of piers. Special B′s designed to behave elastically under the design earthquake or use seismic isolation to achieved elastic response.

12. Elastic and inelastic response (R=q) Design Force-reduce

13. BEHAVIOUR OF B`s IN EARTHQUAKE and BASIC DEISGN PHILOSOPHIES (BDPh) • The BDPh is to prevent B from collapse during severe earthquake with small probability of occurring during service life of the B. • The ductility behaviour using elastic calcul. with reduced seismic forces (with behaviour factor q=R) lead to economic solutions. • The alternative is use of elastic systems on the isolated base or used devices for dissipation of input seismic energy. • In concrete Binelastic damage located in the pier and abutments, and plastic hinges develop simultaneously in as many piers as possible greater energy is dissipated.

14. Demand for seismic performance of infrastructures-Japan

15. According EC 8: in regions of low and moderate seismicity frequently chosen limited ductile behaviour It is needed access for inspection and repair of the pot. plastic hinges and the bearings. In regions of moderate and high seismicity the ductile behaviour is required. BEHAVIOUR OF BRIDGES IN EARTHQUAKE AND BASIC DEISGN PHILOSOPHIES

16. BEHAVIOUR OF BRIDGES IN EARTHQUAKE AND BASIC DEISGN PHILOSOPHIES The performance-based crit. to provide ductile failure  usually require two level design: • to ensure service performance of B for earthquake with small magnitude that can occur several times during service life; • is to prevent collapse under severe earthquake with small probability of occ. during service life of bridge.

17. Development of performance-based criteria is obtained through following steps: • Establish post-earthquake performance requirements. • Determine B specific loads and various combinations. • Determine materials and their properties. • Determine analysis method for evaluation of demands. • Determine detailed procedures for evaluation of capacity. • Establish detailed performance acceptance criteria.

18. BEHAVIOUR OF BRIDGES IN EARTHQUAKE AND BASIC DEISGN PHILOSOPHIES • EC 8 seismic resistance (SR) requir. That emergency communications shall be maintained, after the design seismic event (SDE). • Non-collapse req. (ultimate limit state): after SDE the bridge shall retain its structural integrity, at some parts considerable damage may occur. • Deck shall be protected from plastic hinges and unseating under extreme displacements only minor damage without reduction of the traffic or the need of immediate repair. Capacity design shall be used to provide the hierarchy configuration of plastic hinges in piers.

19. CONCEPTUAL DESIGN • Majority of Codes relates to modeling and analysis elements and structures (E/S). Only rarely they deal with conceptual design (Russian and Swiss). • Russian Code beam system are recommended. The arch bridges can be applied only in rock terrains. In the IXth zone MCS scale precast concrete, composite-monolithic and concrete structure bearings is recom. • Swiss Code local damage - destruction of bearings or expansion joints tolerated provided that the superstructure is prevented from falling

20. CONCEPTUAL DESIGN • Bridges should be as straight as possible. Skew angle should be as small as possible.Curved bridges complicate seismic responses. • Vibrations along the axis of a skew bridge cause torsional response - large rotation demands on piers heads. In single pier bridges, an eccentricity between the deck and pier axis would also lead to torsional response. • Behaviour of continuous B`s is better than other types. Necessary restrainers and sufficient seat width should be provided between adjacent bents at all expansion joints.

21. Balance mass and stiffness distribution FRAME STIFFNES

22. CONCEPTUAL DESIGN • B`s are long period structures - effected by higher modes. • Adjacent bents or piers should be design to minimize the differences in fundamental periods, and to avoid drastic changes in stiffness and strength in both longitudinal and transverse directions. • Stiffer frame receives greater part of load. • The pier causing the most irregular effect due to its stiffness and damaged first (unequal pier heights) in special situation of full isolation applied.

23. CONCEPTUAL DESIGN It is recommended that: • Effective stiffness between any two columns within a bent, does not vary by a factor of more than 2. • Ratio of the shorter fundamental period to the longer ones for adjacent frames in the longitudinal and transverse directions should be larger than 0.7. • Balanced mass and stiffness distribution in a frame results in a good response. Irregularities in geometry increase complex nonlinear response.

24. Unfavorable distribution of transverse seismic action

25. Permissible Earthquake Resistance systems -ATC

26. Permissible Earthquake -resisting elements- ATC

27. require owner's approval - ATC

28. require owner`s approval - ATC

29. Earthquake-resisting elements that are not recommended for new bridges- ATC

30. Methods of minimizing damage to abutment foundation ATC

31. Location of primary plastic hinge, a) conventional design, b) menshin-seismic isolation design, c) bridge on a wall type pier (Japan Code 1996)

32. MODELING AND ANALISYS

33. MODELING AND ANALISYS-without base isolation

34. MODELING AND ANALISYS-WITH BASE ISOLATION

35. PROTECTION OF BRIDGE STRUCTURES • Concrete B design to direct inelastic damage into columns, pier walls, and abutments. • The superstructure should sufficient over-strength to remain essentially elastic if piers reach plastic M capacity • Seismic protection devices-energy dissipation and isolation at approp. location provide good behaviour.

36. PROTECTION-CONROL OF BRIDGE STRUCTURES Spri-ng Spring

37. Bridge control system – devices, advantages and disadvantages

38. BASE ISOLATION

39. FRICTION DAMPER

40. Deformation response spectra/with variation damping ratio  for SDOF system

41. Pseudo-acceleration spectrapeak value of A(t)

42. CONTROL OF STRUCTURES

44. Three-span C. Frame B.S. of MDOF ex. b) Long. Degree of freedom, c) Tran. DOF,d) rotational DOF, e) mode shape I, f) mode shape 2, g) mode shape 3. WITHOUT PROTECTION

45. Three span bridge with active control system (a); b) B model for analysis; c) SDOF system controlled by actuator

46. Controllable sliding bearing

47. Base isolation + Active control

48. Simple-span bridge with hybrid control system & b) lumped mass system model; c) four-degree- of-freedom system

49. Multi column structures offer the option of fixed or pinned base solutions. Displacements at the deck level are reduced, especially in the transverse direction. Options for lateral force resisting systems

50. Monolithic connections between deck and abutment are more commonly used for small bridges, solution b) is more reliable Than of a). Bearing supports have many configurations c) and d). For both configurations the bearings may be substituted by isolators. Options for abutment- deck connection