Bottom Flange: Width 300-1200 mm, Thickness 20-100 mm

Component Specifications

Definition

The bottom flange is a critical structural component in bridge girders, typically an I-beam or box girder configuration, designed to withstand compressive stresses from bending moments. It works in conjunction with the top flange and web to distribute loads efficiently across the span, ensuring structural integrity and load-bearing capacity. In most bridge designs, the bottom flange experiences compression when the girder is subjected to positive bending moments (sagging).

Working Principle

The bottom flange functions as part of the girder's flexural system, resisting compressive forces through its cross-sectional area and material strength. When the girder bends under load, the bottom flange compresses while the top flange experiences tension, creating a force couple that maintains structural equilibrium. The flange's width and thickness are engineered to prevent buckling and ensure stable load transfer to supports.

Materials

Typically ASTM A572 Grade 50 or A709 Grade 50 steel for highway bridges, or higher grades for heavy-load applications. European equivalents include S355J2 or S460ML. Material must meet specific yield strength (min 345 MPa), tensile strength, and toughness requirements for bridge applications.

Technical Parameters

Parameter	Typical range	Notes & selection driver
Width	300-1200 mm
Thickness	20-100 mm
Surface Finish	SA 2.5 blasted, primed
Yield Strength	≥345 MPa
Corrosion Protection	Hot-dip galvanized or painted per ASTM A123

Ranges are indicative industry figures for RFQ preparation, not a supplier commitment. Confirm every value and standard with the legal manufacturer before ordering.

Standards

ISO 10721, DIN 18800, AASHTO LRFD, EN 1993-1-1

Parent Products

This component is used in the following industrial products

Bridge Girder

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Holder/Flange Assembly

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Engineering Analysis

Risks & Mitigation

Buckling under compression
Fatigue cracking at connections
Corrosion in harsh environments
Weld defects leading to structural failure

FMEA Triads

Trigger: Inadequate thickness for design loads
Failure: Local buckling or yielding
Mitigation: Follow AASHTO LRFD design specifications with appropriate safety factors, conduct finite element analysis

Trigger: Poor weld quality at flange-web connection
Failure: Crack propagation leading to structural collapse
Mitigation: Implement AWS D1.5 welding procedures, perform non-destructive testing, certify welders

Trigger: Insufficient corrosion protection
Failure: Section loss reducing load capacity
Mitigation: Apply appropriate coating systems, implement regular inspection schedules, use weathering steel where applicable

Industrial Ecosystem

Compatible With

Typical Suppliers & Equivalents

Compliance & Inspection

Tolerance

±2 mm for thickness, ±3 mm for width, ±1.5 mm for flatness over 3m length

Test Method

Ultrasonic testing per ASTM A435, tensile testing per ASTM A370, Charpy V-notch impact testing per ASTM A673

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Technical documentation

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Manufacturers of Bottom Flange

Manufacturer profiles associated with Bottom Flange.

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Frequently Asked Questions

What is the primary function of a bottom flange in bridge construction?

The bottom flange primarily resists compressive forces during positive bending moments, working with the web and top flange to maintain structural stability and distribute loads across the bridge span.

How are bottom flanges connected to other girder components?

Bottom flanges are typically welded to the web using full-penetration groove welds or connected with high-strength bolts in splice connections, following AWS D1.5 or EN ISO 5817 standards for bridge welding.

What inspection is required for bottom flanges during installation?

Visual inspection for defects, ultrasonic testing for weld quality, dimensional verification per design drawings, and coating thickness measurement for corrosion protection systems.

Data Basis

Editorial classification, named public sources where available, and source-reviewed manufacturer records. See the editorial policy.

Preliminary Technical Classification

This page supports structured research, RFQ preparation, and supplier evaluation. It does not replace buyer-led supplier qualification, standards review, or technical approval.

Bottom Flange