Qk

Multiple simply supported spans with adequate seat widths. Plastic hinges in inspectable locations or elastic design of columns

FIGURE 20.7 Permissible earthquake resisting systems [37].

performance. Higher level of performance maybe required depending upon the bridge's importance and owner's requirements.

The seismic performance criteria shown in Table 20.1 shall be achieved by the following design objectives:

• Columns as primary energy dissipation mechanism. The main objective is to force the inelastic deformations to occur primarily in the columns in order that the earthquake damage can be easily inspected and readily repaired after an earthquake. The amount of longitudinal steel in the reinforced columns should be minimized to reduce foundation and connection costs.

• Abutments as an additional energy dissipation mechanism. The objective is to expect the inelastic deformations to occur in the columns as well as the abutments in order to either minimize column size and reduce ductility demand on the column.

• Isolation bearings as main energy dissipation mechanism. The objective is to lengthen the period of a relatively stiff bridge and which results in a lower design seismic force. Energy dissipation will occur in the isolation bearings and columns are usually then expected to perform elastically.

• Structural components between deck and columns/abutments as energy dissipation mechanism. The objective is to design ductile components that do not result in reduced design force but will reduce the ductility demands on the columns in order to minimize the energy that is dissipated in the plastic hinge zone of columns.

Above ground plastic hinges

Piles with "pinned-head" conditions

Plastic hinges below cap beams including pile bents

Seismic isolation bearings (or bearings designed to accommodate expected seismic displacements with no damage)

Piles with "pinned-head" conditions

Capacity-protected

Above ground plastic hinges

Seismic isolation bearings (or bearings designed to accommodate expected seismic displacements with no damage)

Tensile yielding and inelastic compression buckling of ductile concentrically braced frames

Columns with moment reducing hinge details

Wall piers designed to resist 3% in 75-year induced elastic forces in transverse direction

Passive abutment resistance required as part of ERS Passive strength = 0.70 X Presumptive value given in Article 7.5.2 in Guidelines

Tensile yielding and inelastic compression buckling of ductile concentrically braced frames

Capacity-protected

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