In this individual project, Gaurav used CSiBridge to model a roadway bridge on MD 140 over MD 27 currently managed by MSHA. Only 8 out of 15 girders were modeled due to symmetry. The bridge is a non-prismatic section with various types of sections and was modeled as such. The deck was 4 ksi concrete and the steel girders were plate girders and steel diaphragms were angle section of V Brace type. Gaurav chose moving load analysis for the live load cases. Moving load analysis uses influence load diagrams and gives maximum moments cases and thus used for accurate answers. Gaurav compared results with a similar existing analysis conducted in Merlin DASH software for the same bridge. The comparison was done for strength and serviceability load cases given in AASHTO. Gaurav analyzed the latest inspection report from September 2018 and provided Engineer comments. Gaurav found that currently, the deck is in good condition. the superstructure and substructure are in very good condition. Thus no immediate repair was recommended and the bridge was kept at the same 2-year inspection frequency. After Analysis in CSiBridge, Gaurav found the following results and all units are in kip-ft or inches or kips appropriately-
Bridge Model in CSiBridge after all inputs
Typical girder section according to plans.
Gaurav found the above results and compared them with DASH results in last column to find mostly all values are in the 10% range. DL deflection varies much as a parapet, sidewalk and median were ignored in CSi bridge along with mesh size were 4 ft. Finer mesh size like 0.5 ft gave more accurate results.
Dead load moments for interior girder 2
Live load values for analysis done for all 4 lanes with a multilane distribution factor applied.
Strength 1 load combinations moments found in CSiBridge
Strength 1 load combinations shear and also can be used to find reactions
Service 2 load combination Dead load deflection
Service 2 LL+I deflections
Gaurav concluded with the existing fact that continuous bridge do have a maximum negative moment at interior support and positive moment at 0.4L. Gaurav also used modular ratio and composite dead loads in the analysis and thus concluded that these can be used for accurate results. For non-linear analysis or cracked section analysis, LS-DYNA should be used.
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