10/11/2017. Objectives. Overview

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1 KDOT Concrete Ratings Project: Analysis and Live Load Ratings of Illinois Bulletin Slab (IBS) Bridges 24 th Annual Bridge Design Workshop Kansas State University Mike Briggs, PE, SE HNTB Corporation - Kansas City, MO Objectives To gain familiarity with: IBS Bridges and Their Use in Kansas Refined Analysis of IBS Bridges Structural modeling Implementation in Bentley STAAD.Pro Rating of IBS Bridges Simplified analysis Implementation in AASHTOWare BrR Overview IBS Bridges Description, development and history 1990s Field Investigations Refined analysis Simplified rating method Example IBS Results and Conclusions 1

2 Illinois Bulletin Slab (IBS) Bridges Description: Reinforced Concrete Slab Short Span Length Integral Edge Curbs Stiffen the slab Reduce deck thickness Economize reinforcement Limited Width (Two Lanes) Example Edge Curbs Illinois Bulletin Slab (IBS) Bridges Development: University of Illinois Engineering Experiment Station Bulletin No. 315 (1939) Bulletin No. 346 (1943) Semi-Empirical Design Method Simple-Span Only Bulletin 346 Cover Illinois Bulletin Slab (IBS) Bridges Use In Kansas: State Highway Commission Adapted to Make Continuous Go-To Type in 1940s-1950s 73 Bridges (43 Counties) Continuous up to 8 spans Only two are simple-span Example IBS 2

3 Illinois Bulletin Slab (IBS) Bridges Use In Kansas: Span Length = feet Widths = feet 1960s widening up to 46 feet Example IBS - Elevation Example IBS Widening - Section Example IBS Widening T-Beam 1990s Field Investigations Scope: Develop IBS Ratings 113 in service 6 Bridges Studied Inspect, instrument, and load test (H/HS) Load Test Vehicles Field Inspection 1990s Field Investigations Scope: 6 Bridges Studied Refined structural analysis Integrated shells, beams, support springs Stiffness calibrated with measured results Example Calibration Data Example Refined Analysis Model 3

4 1990s Field Investigations Simplified Rating Method: Line Analysis Edge L beams Center slab Load Distribution from Refined Analyses Spreadsheet Rating Tool 1998 Review at KSU Edge L-Beam - Section Load Distribution Plots Rationale: Specialized Hauling Vehicle (SHV) Ratings per FHWA Not supported, but Model in AASHTOWare BrR Add into statewide database Integrate K-TRIPS permitting Easily consider future vehicles Example SHV Scope: Develop Methodology Analyze/Load Rate Deliver BrR Models 73 IBS Bridges 29 Others SHV Axle Configurations 4

5 Refined Analysis Rationale: 1990s Study Limitations SHVs not considered Limited scope (6 bridges) Calibrated results only Site-specific: soil, site, and structural condition Vehicle-specific: H and HS Increase Confidence, Understanding, and Extend Applicability Refined Analysis Scope: K42; Kingman Co New-Build Assumptions Uncalibrated plan dimensions Half Section Plan Refined Analysis Model Construction: Mixed-Modeling: Frames and Thick Shells Replicate 1990s methodology Section properties based on plans Discretization Coarser mesh than 1990s model Discretize L-beam/center slab boundary Node Map - Plan 5

6 Refined Analysis Model Construction: Boundary Conditions Fixed supports at column bases Abutment restraint per 1990s study Loads Self-weight dead load Five lane positions H20, HS20, T170, SU4, SU7 Node Map - Section Refined Analysis Model Construction: STAAD Live Load Positioning BEAVA influence surface not used Shell element loading not used Load Generation frame elements only Dummy Frame Elements Placed along each line of nodes Very low stiffness Live load applied to frames Transfers into shared joints Example Influence Surface Node Map - Section Refined Analysis Model Construction: Load Generation One command per lane 4-foot increments (0.1*L) Vehicles completely enter and exit bridge Each load case is one vehicle position Coincident forces for discrete members SU7 Lane 1 6

7 Refined Analysis Output: Model Live Load Dead Load Refined Analysis Output: Critical Sections (-) at face of integral pier capbeams (+) at 0.4L (end spans) and 0.5L (all spans) (-) (-) (-) (-) Symmetric (+) (+) (+) (+) Elevation Refined Analysis Output: Store Forces at Critical Sections Frame ends and shell corners Load case = coincident forces Integrate Elements Forces L-beams and Center Slab Translate to member centroid Combine moments and eccentric axial Force Integration H20 7

8 Refined Analysis Results: VBA Macro Automation Update inputs Recalculate Stored outputs in summary Distribution Factors (DF) Member/total at critical section Valid at peak member moment Partial Results Summary H20 Refined Analysis Results: Distribution Factors (DFs) Generally confirmed 1990s results Insensitive to vehicle configuration New build modeling estimates higher center slab moments LLDF Vehicle Configuration DEAD 1990s 1990s STAAD LOAD General L-Beam L-Beam Ct Slab Ct Slab DLDF Calibration vs. New Build Simplified Rating Method Model Construction: ASHTOWare BrR Line girder superstructure T-Beam Member Type Inverted L-Beam Wide web is unconservative for shear, but does not control T-Beam Input 8

9 Simplified Rating Method Model Construction: Re-Define Self-Weight Member alternative definition Remove tributary self-weight Apply as line load Self-Weight Input Simplified Rating Method Model Construction: Substructure Restraint Add springs Support Springs Control Options Omit support point POIs Control Options Results and Conclusions Refined Analysis Confirmed 1990s results Expanded applicability of DFs Bentley STAAD.Pro appropriate for advanced modeling Simplified Rating Method Significant time-savings DFs applicable within scope of refined analyses Successful T-beam implementation in AASHTOWare BrR 9

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