The FIGG Bridge Engineers design of the rebar placement in node 11/12 resulted in less reinforcing steel being available and diminished resistance to the critical interface shear demand, which contributed to the collapse of the bridge.ġ4. The concrete distress initially observed in nodal region 11/12 is consistent with the underestimation of interface shear demand and the overestimation of identified capacity in the bridge design.ġ3. FIGG Bridge Engineers’ analytical modeling for the bridge design resulted in a significant underestimation of demand at critical and highly loaded nodal regions.ġ2. In several instances throughout the bridge design process, the FIGG Bridge Engineers models produced reasonable estimations for interface shear demand, but these values were not always used in the design of truss members to resist force demands.ġ1. Based on analytical modeling results, FIGG Bridge Engineers should have considered the loadings from all critical construction stages when designing the pedestrian bridge and determining the governing interface shear demands.ġ0. FIGG Bridge Engineers (1) made significant design errors in the determination of loads, leading to a severe underestimation of the demands placed on critical portions of the pedestrian bridge and (2) significantly overestimated the capacity of the member 1/2 and 11/12 nodal regions.ĩ. Because FIGG Bridge Engineers (1) did not use the lower bound load factor for determining the governing net compression, Pc, in the interface shear and (2) incorrectly increased and amplified the effects of the clamping force across the interface shear surface, its bridge design calculations resulted in a significant overestimation of capacity.Ĩ. ![]() The FIGG Bridge Engineers construction plans inconsistently identified when intentionally roughened surfaces were needed to fulfill the assumptions of the bridge design.ħ. Even if the cold joint surface of nodal region 11/12 had been roughened to a 0.25-inch amplitude, node 11/12 would not have had sufficient capacity to counteract the demand load for interface shear-and the bridge would still have been under-designed and could have failed.Ħ. (1) The FIGG Bridge Engineers (FIGG) bridge design was nonredundant because it provided only a singular load path, (2) FIGG used poor judgment when it determined the bridge was a redundant structure, and then, (3) FIGG erroneously used a redundancy factor of 1.0, which is commonly used for structures with redundant load paths.ĥ. ![]() The hydraulic jack used to post-tension the steel rods in member 11 was operating as expected at the time of the bridge collapse.Ĥ. ![]() The concrete and steel materials used during construction of the pedestrian bridge were not a factor in its collapse.ģ. The emergency response by local fire departments and law enforcement personnel was timely and adequate.Ģ. The attached information is subject to further review and editing to reflect changes adopted during the Board meeting.”ĭue to the list of findings' length, for our readers’ convenience-and to invite possible reader comment and discussion-ENR is publishing all of these findings here, in their entirety, without editing.ġ. The findings are included as part of the NTSB’s abstract report, the full version of which readers can find here.Īs the agency notes in its abstract, “The final report and pertinent safety recommendation letters will be distributed to recommendation recipients as soon as possible. 22 presentation into the bridge collapse’s probable cause, the NTSB listed 30 findings from its investigation.
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