USING NSBA’S “LRFD SIMON” SOFTWARE FOR

PRELIMINARY DESIGN OF A CURVED HAUNCHED STEEL

PLATE GIRDER BRIDGEThomas Densford Eric Pheifer

PDH Code: 11978

Purpose

• Describe using LRFD SIMON for preliminary design of a two-span, horizontally curved, parabolicallyhaunched steel plate girder bridge

• With some basic adjustments to a straight girder analysis, a curved girder analysis can be made with LRFD SIMON

• Using LRFD SIMON in preliminary design gives a good check on more sophisticated 3-D finite element bridge design packages

Design Build Project, Turner-Greene ME

• Design Build Project to replace two-single span trusses of about 200’ span each, straight

• Contractor originally intended to build on the existing straight alignment

• Bryon Tait/Casco Bay Steel in So.Portland ME gave us a copy of NSBA LRFD SIMON software

LRFD SIMON Features and Limitations

• LRFD SIMON is a free highway bridge line-girder analysis program offered by NSBA

• Girder types are I-girder and Box-girder• A single, straight line, continuous, composite, girder is

analyzed• SIMON computes girder section properties, and

allows variable web depths• SIMON computes live load and dead load member

forces and section stresses• SIMON provides strength, service and fatigue

AASHTO LRFD code checks• SIMON provides output in XML format for post-

processing

Design Build = Changes

• Haunched 2-span girder, fit profile constraints• 1st Try: Straight, 4 girders at 9’-9” spacing• Check LRFD SIMON, optimize girder flanges• Girders too heavy for 75 Ton barge crane• 2nd Try: Straight, 5 girders at 7’-4”, OK for crane• Traffic Staging: Shift trusses onto temp supports

Design Build = Changes

• About a month before the bid, the Contractor realized that shifting the trusses to accommodate traffic while building new bridge on straight existing alignment, was undesirable

• FST was asked to provide a curved girder design on an offset alignment, to keep traffic on existing bridge

• With the SIMON post-processing spreadsheets already made, we modified them to analyze a curved girder, still using LRFD SIMON for design iterations, in about two weeks

Turner-Greene Bridge Data• 2 spans at 240 ft.• 35.33 ft. deck width• 5 girders at 7.33 ft. spacing• Web depth varied from 4.5 ft. to 9.83 ft.• 1240 ft. radius horizontal curve centerline

Curved Flange Forces

OUT OF PLANE FLANGE LOAD--FLANGE FORCES ARE NOT COLLINEAR, WHICH GENERATES LATERAL FORCES--MAGNITUDE FOLLOWS MOMENT

Curved Flange Lateral Forces Along Girder

PIERGIRDER FLANGE

RADIUS,

LATERAL FLANGE FORCE, ,FOLLOWS PRIMARY MOMENT DIAGRAM

PLAN OF LATERAL FORCES ON GIRDER FLANGE

V-Loads on Curved Girders

G1 G2 G3 G4 G5

V-LOAD AT EACH CROSSFRAME LOCATION

OUT OF PLANE FLANGE DISTRIBUTED LOAD COLLECTS AT EACH CROSSFRAME, WHICH REACTS AS A RIGID BODY TO RESIST FLANGE LATERAL LOAD

FORCES AT CROSSFRAME

V-Loads on Curved Girders

G1 G2 G3 G4 G5

in which:number of girderstransverse girder spacinglongitudinal crossframe spacing along the arc length of the girder

where:

V-Loads on Curved Girders

in which:

number of girderstransverse girder spacinglongitudinal crossframe spacing along the arc length of the girder

where:

Sum of Stresses

Design Flanges for:• Stresses due to Primary Moment• Stresses due to V-loads• Stresses due to out-of-plane flange forces

CUGAR Load Amplification Charts

LRFD SIMON Load Adjustments

Dead Loads: • Girder G1, 25% increase• Girder G2, 12.5% increase

Live Load:• Girder G1, 20% Increase in LL distribution factor• Girder G2, 10% Increase in LL distribution factor

Post-Processing SIMON Output

Check:• Wind • Temporary Overhang

Construction Loads on Flanges

• Optimize Flanges

Flange Plate Layout

Optimize girder flange plates by:

1. In each girder field section, provide constant width flanges. Step flange thicknesses to follow the stress demand.

2. Keep plate thicknesses similar between girders, so that wide slabs of plate may be ordered and cut to width for multiple flanges.

3. Do not introduce a plate butt splice to reduce flange area unless about 1,000 lbs. of steel may be saved.

Flange Plate Layout4. Consider using 80 to 85 feet as the maximum plate

length for thicker flange plate to determine plate splice locations.

5. Plate availability industry-wide is further discussed in Christopher Garrell’s article in Modern Steel Construction (Sept. 2011).

Flange Plate Optimization

Graphical methods can be used to visualize optimization process:

Flange Plate Optimization

Graphical methods can be used to visualize optimization process:

Flange Plate Optimization

Optimize flanges to reduce “wasted” area of steel:

Flange Plate Optimization

Optimize flanges to reduce “wasted” area of steel:

Flange Plate Optimization

Questions?

PDH Code: 11978