SEISMIC SPILLWAY PIER MODIFICATION DESIGNS AT FOLSOM DAM

摘要

The piers for the existing spillway at Folsom Dam have been modeled in detail and will be subject to high moment and shear forces as a result of seismic loadings. This is observed as a result of both upstream-downstream and cross-canyon motions, and is most evident near the pier-to-monolith contact. The upstream-downstream motions increase the loads on the gate and as a result produces high loadings at the trunnion pin. These trunnion pin loads are oriented in such a way that there is thepotential for a large earthquake to create enough shearing force in the concrete under the pin to shear through the pier and cause the trunnion pin to lose support, similar to a shearing failure in a corbel. Cross-canyon motions induce high moment and tensile stresses in the pier, as well as horizontal shearing forces. Large earthquake events have the potential to fail the concrete at the bases of the piers and cause them to "kick out" and topple. A system of components has been designed to stabilize the piers under seismic loading and prevent catastrophic failure. The system includes large steel wraps below the trunnion pins on each pier to contain the failure wedge that forms from high shearing forces, vertical high-strength-steel passive anchors to carry tensile and shear forces at the base of the pier, and a horizontal bracing systems within each spillway bay to decrease cross-canyon pier sway and resulting moment loading.