Critical seismic issues for existing steet bridges

This report assesses the perfomance of existing steel bridges in the past earthquakes. There is an identification of the areas in existing steel bridge structures that are seismically vulnerable. Among the examined components there are: steel columns, steel tower bents, steel superstructures (particularly steel trusses), girder cross-frames, and steel connections. Vulnerable areas and details are identified, and recommendations for improved designs and retrofit techniques are made. Research needs are identified where existing knowledge is lacking. There is an examination of the three most common lateral force existing systems: MRF's: moment resisting frames; CBF's: concentrically braced frames and EBF's; eccentrically braced frames. It indicates that any of them can provide adequate seismic structural ductility. There is also an analysis of X-braces and X-braces and V-braced bridges piers as a way of getting potential structural ductility. It has a lis of illustrations, which include configurations, pier designs, axial loads and analytical models of connections, among others

Structural steel and steel / concrete interface details for bridges

This report assesses the seismic performance of details associated with steel bridge towers extending from a massive concrete substructure, as well as the seismic perfomance of other steel sub-and superstructure details for new construction. Issues addressed are: 1-Identifying the most ductile cross-sections 2-investigating the application of eccentrically braced frames. 3-Exploring details to replace buckled plates or sharpes following an earthquake. 4. Investigating anchor bolt performance under lateral and uplift loads. 5- developing economical moment connection details between steeel superstructures and concrete substructures. The most efficient member cross-sections were identified as tubular sections due to their self stiffening nature and optimal resistance both local and overall buckling. Other shapes can provide adequate perfomance, however and may be more economical due to savings in production and fabrication. Moment resisting frames (MRFs) concentrically braced frames (CBFs) and eccentrically braced frames (EBFs) can all supply adequate seismic resistance, providing that they are detailed correctly. Anchor bolts embedded in concrete can be designed with sufficient depth and edge distance or hairpin reinforcement such that failure does not occur in the concrete. Brittle fractures of anchor bolts in the northridge earthquake resulted in a recommmendation that upset threads shoulds be used. shear keys can be used when anchor bolts do not provide sufficient shear resistance, Anchor bolts can either be designed to remain elastic or to yield. (AU)