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1. Workshop Example Bridge

This section provides the basic instructions on how to model, analyze and design the Steel I Girder Bridge using OpenBrIM.App. The Excel file provides the complete set of bridge inputs ready to copy and paste into the OpenBrIM.App DATA spreadsheet.

1.1.1 OVERVIEW OF BRIDGE MODEL

The bridge model adapted from Federal Highway Administration Design Example 3: Three-Span Continuous Horizontally Curved Composite Steel I-Girder Bridge, Publication No. FHWA-HIF-16-002 - Vol. 23.

1.1.1.1 DESIGN PARAMETERS

• Structural Steel: AASHTO M270, Grade 50 (ASTM A709, Grade 50) steel with Fy = 50 ksi, Fu = 65 ksi

• Concrete: fc′ = 4.0 ksi,  = 150 pcf

• Slab Reinforcing Steel: AASHTO M31, Grade 60 (ASTM A615, Grade 60) with Fy = 60 ksi

The bridge has spans of 160.0 feet – 210.0 feet – 160.0 feet measured along the centerline of the bridge. Span lengths are arranged to give similar positive dead load moments in the end and center spans. The radius of the bridge is 700 feet at the centerline of the bridge. The out-to-out deck width is 40.5 feet, and there are three 12-foot traffic lanes. All supports are radial with respect to the bridge centerline. There are four I-girders in the cross-section. The total deck thickness is 9.5 inches, with an assumed 0.5- inch integral wearing surface. Therefore, the concrete deck’s structural thickness is 9.0 inches. The deck haunch thickness is taken as 4.0 inches and is measured from the top of the web to the bottom of the deck. That is, the top flange thickness is included in the haunch. The roadway is superelevated 5 percent. The girders in this example are composite throughout the entire span, including regions of negative flexure since shear connectors are provided along the whole length of each girder. The bridge cross-section in this design example consists of four I-girders that are spaced at 11 feet in the center with 3.75-foot deck overhangs.

1.1.1.2 DESIGN LOADS

Permanent steel stay-in-place deck forms are used between the girders; the forms are assumed to weigh 15.0 psf since it is assumed concrete will be in the flutes of the deck forms. An allowance for a future wearing surface of 30.0 psf is incorporated in this design example. The bridge is designed for HL93 live load per Article 3.6.1.2. Live load for fatigue is taken as defined in Article 3.6.1.4. The bridge is designed for 75-year fatigue life, and single-lane average daily truck traffic (ADTTSL) in one direction is assumed to be 1,000 trucks per day. The bridge site is assumed to be in Seismic Zone 1, so seismic effects are not considered in this design example. Steel erection is not explicitly examined in this example, but the sequential placement of the concrete deck is considered. The concrete is the first cast from the left abutment to the dead load inflection point in Span 1, the concrete between dead load inflection points in Span 2, and the concrete beyond the dead load inflection point to the abutment in Span 3. Finally, the concrete between the points of dead load contra flexure over the two piers is cast.

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