Dubina Dan, Prof. PhD, Director of CMMC Department The “Politehnica” University of Timisoara Corresponding Member of the Romanian Academy Timisoara, Romania.

Actual seismic design is based on the reduction of the seismic forces obtained from linear analysis, in order to take into account the non-linear response of the structure. The reduction is obtained by multiplying the base shear force with the behavior factor q.

Conventional definition of q factor has no direct relation with the internal forces in the structure. q factor is sometimes too conservative, other times too optimistic. European seismic code EN 1998-1 gives just a generic estimation of the q factor, generally related to the typology of the structure and minimum ductility requirements for members and connections. There is always available the dynamic nonlinear analysis, but it operates with sophisticated models that need for calibration. If the problem is new and no benchmark models are available, the reference tests are the only solution.

In order to calibrate the q factor, a testbased methodology is proposed. In the first step, the dissipation capacity of the structure is investigated experimentally, and q factor is evaluated at the level of a relevant subassembly. The modeling parameters and acceptance criteria are then defined and calibrated, based on the results of the experimental tests. In the third step, real structural configurations are proposed and tested numerically to confirm the q factor.

To design dissipative structure, according to capacity design approach, reduction factors are widely used in design codes to reduce the elastic earthquake spectrum. Structural design stresses
considering the earthquake induced forces are lower than those corresponding to the elastic response and are derived from the observation that, most structures are able to survive a major earthquake due to dissipation of energy by plastic excursions and overstrength. Currently, for a given structure, a single reduction factor is used. However, distinction and quantification of different components of the force reduction factor are useful for a better understanding of the seismic response of structures.

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