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)

Methodologies for evaluating the importance of highway bridges

The location of a structure with respect to seismic hazards, its seismic vulnerability and its importance are factors which are used in determining what seismic design or seismic retrofit level a structure belongs in. This reseach evaluated methods for determining the importance of a structure and how to use this importance in seismic design and retrofitting specifications. This report develops a method for determining the importance of a bridge. this importance ranking of a bridge is then used in proposed revision to seismic bridge design and retrofitting specifications. Depending on the relative importance bridge ranking, design or retrofitting requirements will be increased or decreased. This report also provides for existing importance methods to be used with the seismic design and retrofitting specifications (AU)

Structural details to accommodate seismic movements of highway bridges and retaining walls

This report describes datailing for structural movements for bridges and retaining walls for new construction in the western and eastern U.S. Bridge retaining devices such as longitudinal joint restrainers, vertical motion restrainers, shear keys, and integral superstructure ti substructure connections are described. Many of these details are traditional methods that have been used in new bridge construction to limit displacements for seismic events. Sacrificial elements, which include abutments and joints, are also described. These types of details have been used in new seismic designs within the last two decades. An introduction to passive energy dissipating devices and isolation bearing systems is provided as well as recommendations for detailing. Both devices are relatively new as a method to limit displacements in bridges within the U.S. In fact, isolation bearing systems have just emerged for new bridge construction within the last few years. The minimun support length requirements are reviewed. The current practice for designing earth retaining systems for seismic displacements is reviewed and some recommendations for detailing are provided. The effects of substructure flexibility on the isolation system is documented. An example study and comparison is given to illustrate the impact of substructure flexibility.(AU)

Establish representative pier types for comprehensive study : Eastern United States

This report describes bridge types and seismic design and detailing procedures typical of the eastern part of the United States. The report contains examples taken from state bridge plans and actual bridge designs. Some of the examples comply with current seismic provisions, while others represented older designs made before these requirements were introduced. Advantages and disadvantages of various bridge configurations and details with respect to seismic behavior are discussed. Historical accounts of changes in bridge design and detailing practices are also included (AU)