Browsing by Author "Widjaja, Matius Andy"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Influence of the new LRFD seismic guidelines on the design of bridges in Virginia
    Widjaja, Matius Andy; Roberts-Wollmann, Carin L. (Virginia Center for Transportation Innovation and Research, 2004-03-01)
    The Virginia Department of Transportation is currently using the AASHTO Standard Specifications for Highway Bridges, with some modifications, for its seismic highway bridge design. In April 2001, the Recommended LRFD Guidelines for the Seismic Design of Highway Bridges were published. The influence of the LRFD Guidelines on Virginia bridges was investigated by analyzing two existing bridges. The first bridge has prestressed concrete girders and is located in the Richmond area. The second bridge has steel girders and is located in the Bristol area. Both bridges were two-span overpass structures with integral abutments. The bridges were analyzed using the methods prescribed in the guidelines. Then, the combined effects of the dead, live, and earthquake loads were compared to the strengths of the columns and the pier caps. The details of the bridge designs were also checked against the corresponding seismic design requirement. Results indicate that typical column spiral reinforcement is not adequate to satisfy the requirements of the new seismic guidelines. For the bridge in the Richmond area, spiral reinforcement was increased from a No. 5 at a 5-in pitch to a No. 5 at a 4-in pitch. For the bridge in Bristol, the increase was greater, from a No. 3 at 10.5 in to a No. 5 at 4 in. In addition to the increase in spiral reinforcement, other details, such as beam-column joint reinforcing and splice locations, require modifications. The calculated cost increases for the two bridges were 0.1 and 0.3 percent. An associated parametric study explored the effects on substructure design of different column heights, superstructure lengths, and soil classifications in different parts of Virginia. The study indicated that for bridges located on good soil (Class B), typical column longitudinal reinforcing ratios (about 1.5%) provide adequate strength to resist seismic forces. For bridges on poor soils (Class D) in regions of low to moderate seismic activity, column longitudinal reinforcing may need to be increased, particularly in bridges with short columns, long spans, and sliding bearings at the abutments. For bridges on poor soils in regions of higher seismic risk (Southwestern Virginia), column sizes may need to be increased. For columns designed as spiral columns, the increases in transverse column reinforcement will not be great, but for columns designed as tied columns, the increases will be significant.
  • Thumbnail Image
    The Influence of the Recommended LRFD Guidelines for the Seismic Design of Highway Bridges on Virginia Bridges
    Widjaja, Matius Andy (Virginia Tech, 2003-02-04)
    The influence of the recommended LRFD Guidelines for the seismic design of highway bridges in Virginia was investigated by analyzing two existing bridges. The first bridge has prestressed concrete girders and is located in the Richmond area. The second bridge has steel girders and is located in the Bristol area. The analysis procedure for both bridges is similar. First the material and section properties were calculated. Then the bridge was modeled in RISA 3D. Live and dead load were imposed on the bridge to calculate the cracked section properties of the bridge. The period of vibration of the bridge was also calculated. After the soil class of the bridge was determined, the design response spectrum curve of the bridge was drawn. The spectral acceleration obtained from the design spectrum curve was used to calculate the equivalent earthquake loads, which were applied to the superstructure of the bridge to obtain the earthquake load effects. Live and dead loads were also applied to get the live and dead load effects. The combined effects of the dead, live and earthquake loads were compared to the interaction diagram of the columns and moment strength of the columns. The details of the bridge design were also checked with the corresponding seismic design requirement.A parametric study was performed to explore the effects of different column heights and superstructure heights in different parts of Virginia. The column longitudinal reinforcing was increased to satisfy the bridge axial loads and moments that are not within the column interaction diagram.