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D5484-99 – Standard Test Method Technical Guide
ASTM D5484-99, under the jurisdiction of Committee D-04 on Road and Paving Materials, specifies the requirements for steel grid bridge flooring systems. This specification covers the design, materials, fabrication, coatings, and installation practices for three distinct types of grid flooring systems.
📐 Specification Scope and Classification
The standard classifies steel grid bridge flooring into three main types:
- Type I – Open Steel Grid System: Designed for vehicular traffic, it requires a maintainable skid-resistant surface, often achieved through a serrated surface or other methods. Fatigue life must be specifically addressed in the design.
- Type II – Concrete Filled System: A steel grid filled with concrete. Two grades are defined:
- Grade 1: Concrete is filled to the full depth of the grid and finished flush, or topped with an additional wearing surface.
- Grade 2: The grid is partially filled with concrete using a pan form, not exceeding the midpoint from the bottom. The grid is filled full depth over supporting floor system flanges.
- Type III – Unfilled Composite Grid (Exodermic): An unfilled composite grid system designed to act compositely with a concrete overlay.
| 🟦 Type | 📐 Description | ⚡ Grade | 🎯 Key Requirement |
|---|---|---|---|
| Type I | Open Steel Grid | N/A | Skid resistance & fatigue life |
| Type II | Concrete Filled | Grade 1 (Full Depth) | Flush finish or overlay |
| Type II | Concrete Filled | Grade 2 (Partial Fill) | Pan forms, max midpoint depth |
| Type III | Composite (Exodermic) | N/A | Composite action with overlay |
⚠️ Minimum Overlay Requirement: A minimum 1¾-inch overlay is required on all Type II flooring systems. If an additional surface course is placed, dependable bonding at the top of the filled grid must be ensured.
⚙️ Material Specifications and Referenced Standards
The specification relies heavily on various ASTM standards to define material properties for the steel grid, concrete fill, and protective coatings. Key referenced documents include standards for steel sheet (A 366/A 366M, A 569/A 569M), structural steel (A 709/A 709M), concrete reinforcement (A 615/A 615M, D 3963/D 3963M), and zinc coatings (A 123/A 123M). The Bridge Welding Code (AWS D1.5) and AASHTO Standard Specifications for Highway Bridges are also integral to this standard.
| 📏 Standard | 🔩 Title / Application |
|---|---|
| A 123/A 123M | Zinc (Hot-Dip Galvanized) Coatings on Iron and Steel |
| A 709/A 709M | Structural Steel for Bridges |
| C 94/C 94M | Ready-Mixed Concrete |
| D 6275 | Laboratory Testing of Bridge Decks |
💡 Design Consideration (Type II, Grade 2): When dead load is a primary concern for the bridge structure, the Grade 2 (partial fill) concrete filled system may be more beneficial than the Grade 1 (full depth) system, as noted in the standard.
📋 Installation Practices and Skid Resistance
Proper fabrication and installation are critical to the performance and longevity of steel grid bridge flooring. Coatings must be applied and maintained according to specifications such as A 780 for repair of damaged galvanized coatings. For Type I systems, it is imperative that the skid-resistant surface is maintainable throughout the service life of the deck. The standard also mandates investigating design options to achieve an acceptable fatigue life for open grid decks.
❓ Frequently Asked Questions
🔍 What is the primary scope of ASTM D5484-99?
The specification covers the requirements for steel grid bridge flooring systems, including design, materials, coatings, fabrication, and installation for Type I (Open), Type II (Concrete Filled), and Type III (Composite/Exodermic) grids.
💡 What is the difference between Grade 1 and Grade 2 of Type II systems?
Grade 1 involves filling the steel grid to its full depth with concrete. Grade 2 employs a pan form in the fabrication plant to partially fill the grid, never exceeding the midpoint from the bottom, though it is filled full depth over supporting flanges.
⚡ What is the specific minimum overlay requirement for Type II bridge flooring?
A minimum 1¾-inch overlay is required on all Type II flooring systems, according to Note 3 of the standard.
📌 Which organizations provide design data referenced by this standard?
The standard references the Bridge Grid Flooring Manufacturers Association (BGFMA) and Exodermic Bridge Deck Inc. for their respective design and specification data.