An overlooked design detail in footing loading upon the substructure noted "competent rock" at the FCO Headworks and Spillway Bridge "Lift" column reveals a "Diagonal Cracking" or "Shear Cracking" Flaw mechanism. This "Flaw" risks a "Failing" of Gates 1 and 8 Pier supports via a potential shifting of the Trunnion pin axis alignment to the Radial Gate Skin Plate radius. A "shift" in the axis alignment is amplified by the radial gate radius length. Thus a small "shift" could "bind" the gate. Anchor tendons, below within the pier columns, traverse across this shear cracking "plane" centered at the corner of the spillway bridge support notch. Thus, the anchor tendons will absorb "Shear Cracking" forces transferred from crack expansion. This would create an additional load to the Anchor Tendons beyond the original design loads of Radial Trunnion Gate Hydrostatic pressures in flood release operation.
The overlooked design detail was the "footing" settling forces upon the "competent rock". The FCO Gate Structures (Piers, Headworks, Footing) are all secured with reinforcement (rebar). Two FCO Gate Structures were built with a contraction seam where these meet. Gates 1-4 form one FCO reinforced Monolith structure, and Gates 5-8 form the second reinforced Monolith structure. Both have their own individual large reinforced footings constructed of thick concrete as further anchorage. However, the spillway bridge "lift" columns (5ft+ thick) have their own footings separate from the FCO reinforced Monolith structures. Blueprints do not show any design of footings wider than the original width of the Bridge Abutment (5ft thick, thus 5ft wide in drawings). Differences in settlement of the Bridge Abutment "lift" column vs the FCO Gate structure from - Phreatic pressure, "rock competency", and heavy bridge crossing loadings, all could influence the forces concentrated into the corner of the notch in the Pier. The evidence of the large diagonal cracks originating at this corner in the notch confirms the presence of a "shear force". This is the exact location that this design flaw would manifest if the Bridge Abutment were to "settle" deeper than the FCO structure.
DSOD Inspection reports confirm that both end piers have the same "Shear Cracking" problem at the same corner location(s). DSOD 1998 Inspection report also notes that this dual "shear cracking" condition has been noted in prior inspections. Thus, this "flaw" cracking result has been developing for many years (& prior to 1998). This means that for 19 years this issue either was not considered a "structural risk" to the Headworks by DWR, or that the issue may not have been understood, or ?.
The immediate "arresting" of this Shear Cracking would require the shutting down of the spillway bridge and removing the corner load forces on the end pier corner notches. With all of the extreme tonnage of emergency repair work loads across the spillway bridge, this likely has risked further aggravation of the shear cracking flexing on these existing cracks. With nothing but red paint as a mechanism in addressing these "cracks", and all of this heavy stress loading placed upon this "flaw", is there proper engineering judgement being applied? DWR has placed metal plates across these end junctions, but should they even be operating this bridge knowing that they are risking further structural damage potential? (including stress loading the end pier Anchor tendons).
"Flaw" in headworks design. Different settlements of the Bridge Abutment concrete support column between the FCO Structure will create a focus force in the corner notch in the 5ft thick Gate end Piers 1 & 10. This is where DSOD inspectors are watching "Shear Cracks" grow."
DSOD Inspectors documenting the "Shear Cracking" at the corner notch of both end piers. Cracks have been present and growing for 19+ years. Why hasn't this "flaw" been figured out and addressed? (instead of using red paint).
