New paradigms for the seismic design and retrofit of bridge piers.

摘要

This dissertation is concerned with developing new paradigms for the seismic design and retrofit of bridge structures. The intent of these methodologies is to not only maintain life safety of bridge structures in a strong earthquake, but also to control or avoid damage while accommodating large seismically-induced deformations in order to maintain post-earthquake serviceability.;The first new seismic design paradigm is referred to as Control and Repairability of Damage (CARD). Sacrificial hinge zones, through the use of special (fuse-bar) detailing, permit the repair of damage inflicted on those zones after an earthquake. All regions outside the hinge zones remain elastic at all times. A fatigue theory for structural concrete columns is proposed. Using this theory, the fuse-bars in the potential plastic hinge zones are designed such that their fatigue capacity exceed the fatigue demand. Experiments are conducted and results presented to verify the CARD philosophy. This type of construction enables faster restoration to full service than conventional construction.;The second design paradigm is called Damage Avoidance Design (DAD). In this approach, piers are designed such that they are free to rock on specially detailed foundation beams to accommodate large deformations without inducing damage. Premature uplifting leading to rocking can be restrained by using supplementary unbonded prestressing in the columns. A generalized energy-based seismic design procedure is proposed for bridge structures with rocking piers based on pushover analysis. Results of an experimental study show that it is possible to sustain very large lateral deformations without inducing any form of damage.;The proposed new design concepts can also be applied in retrofitting existing bridge columns. Results of an experimental study show that earthquake imposed damage to lapped splice columns can be repaired (and then reused) in accordance with a Retrofit, Control and Repairability of Damage(ReCARD) philosophy. Further experiments show that it is possible to deploy a Retrofit Design to Avoid Damage(ReDAD) philosophy whereby the longitudinal column reinforcement is cut and a rocking base formed. Experimental results show that a steel-steel rocking interface performs best; in that neither damage, strength and stiffness degradation nor residual drift are expected.