1 / 23

RATIONAL K VALUES FOR BRIDGE PIER DESIGN

washington
Download Presentation

RATIONAL K VALUES FOR BRIDGE PIER DESIGN

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

    1. RATIONAL K VALUES FOR BRIDGE PIER DESIGN David Liu, Ph.D., P.E., S.E. Robert Magliola, P.E., S.E. PARSONS

    2. Part I – General Review What is the K value? effective length factor Its application Problems

    3. FIG. 1. Effective length factors, K for columns.

    4. FIG. 2. Alignment charts for effective length of columns in frames

    5.

    6. Mathematical formula Braced column Un-braced column

    7. AASHTO LRFD Un-braced Columns Ga 1.5 footing anchored on rock 3.0 footing not anchored on rock 5.0 footing on soil 1.0 footing on group piles

    8. Modified k Values Effective length factor for columns in braced or un-braced frames Journal of Structural Engineering, 1988,1989 Lian Duan and W.F. Chen

    9. AASHTO Guidelines Slenderness effects in compression members P-delta analysis Moment magnification method P-delta, 5 iterations, 5% difference of displacement at top of the column between previous and present iterationsP-delta, 5 iterations, 5% difference of displacement at top of the column between previous and present iterations

    10. Moment Magnification Method K=1 for braced column K>1 for unbraced column Neglect effects of slenderness K L/r < 34-(12 M1b/M2b) braced column K L/r < 22 un-braced column K L/r >100 use P-delta analysis

    11. Moment Magnification Method M2b is larger end moment due to dead load. M2s is larger end moment due to Dead load or lateral load M2b is larger end moment due to dead load. M2s is larger end moment due to Dead load or lateral load

    12. Moment Magnification Method Beta is ratio of maximum dead load moment to maximum total load moment. M1b is smaller end moment due to Dead load M2b is larger end moment due to dead load.Beta is ratio of maximum dead load moment to maximum total load moment. M1b is smaller end moment due to Dead load M2b is larger end moment due to dead load.

    13. Moment Magnification Method Pier cap design for un-braced column Total magnified moment at top of column

    14. FIG. 3. Structural Model for a Single Span Frame.

    15. FIG. 4. Bridge Elevation. 6 span bridge, 6 span bridge,

    16. FIG. 5. Typical Sections.

    17. FIG. 6. Pier Plan and Elevation

    18. Pier Top Connection

    19. FIG. 7. Pier Footings.

    20. FIG. 8. GT STRUDL Model.

    21. GT STRUDL INPUT Apply unit load at top of pier Perform buckling analysis List buckling shape Member releases are not allowed. To simulate pin condition, defined a very short member with very small ITo simulate pin condition, defined a very short member with very small I

    22. FIG. 9. Buckling Mode Shapes.

    23. Table 1: Buckling Loads and K Values    With the same pier section, the longer pier has higher buckling load because shorter piers provide more lateral stiffness.With the same pier section, the longer pier has higher buckling load because shorter piers provide more lateral stiffness.

    24. Findings The buckling load is sensitive to where the unit load is applied to. Applying the unit load to all the piers at the same time will give you too conservative results. Adding more members in the superstructure does not change the buckling loads. Adding more members in the substructure does not change the buckling loads. Typical K values used for pier design are very conservative.      

More Related