Choosing the right bridge design is one of the most critical decisions in any infrastructure project. 

From span length to load capacity, site constraints to cost considerations, the structural form you select will directly impact construction timelines, maintenance needs, and lifecycle performance.

In this detailed comparison, we’ll explore three common steel bridge types — box girder, truss, and I-beam — and help you determine which is best suited for your application.

Overview of Each Bridge Type

1. Steel Box Girder Bridges

A box girder bridge uses hollow steel girders, often rectangular or trapezoidal in shape, formed by welding together steel plates. 

The result is a high-torsion-resistance section ideal for curved, skewed, or high-load bridge designs.

Typical Use Cases:

Urban flyovers

Coastal highway bridges

Industrial zone crossings

2. Steel Truss Bridges

Truss bridges use a triangulated framework made of connected steel elements (compression and tension members) to distribute loads. 

They’re visually open, strong, and efficient over long spans.

Typical Use Cases:

Railway bridges

Long-span highway crossings

River and canyon crossings

3. Steel I-Beam (Girder) Bridges

These are constructed using simple I-shaped girders placed in parallel. 

The deck rests on top or is integrated into the I-beams. 

They’re straightforward, cost-effective, and widely used.

Typical Use Cases:

Local road overpasses

Short-span urban bridges

Pedestrian or bike bridges

Key Comparison Factors

1. Torsional Rigidity

Box Girder: Excellent. Ideal for curved alignments and asymmetric loading.

Truss: Good. Loads are triangulated but can require bracing.

I-Beam: Poor. Not suitable for curved spans; prone to twisting.

2. Structural Depth & Clearance

Box Girder: Shallow depth, suitable for low-clearance needs.

Truss: Deep trusses can obstruct sightlines and aesthetics.

I-Beam: Medium depth. Simple appearance but limited span efficiency.

3. Aesthetics

Box Girder: Clean, modern, and minimal profile.

Truss: Traditional or industrial appearance; sometimes visually bulky.

I-Beam: Neutral appearance; minimal architectural impact.

4. Span Length Capacity

Box Girder: Up to 150m without intermediate piers.

Truss: Can exceed 300m with optimized design.

I-Beam: Limited to 40–50m economically.

5. Fabrication & Construction Speed

Box Girder: High — factory prefabrication and modular assembly.

Truss: Moderate — on-site assembly of many members.

I-Beam: Very high — standard profiles and minimal welding.

6. Maintenance Requirements

Box Girder: Low. Fewer exposed joints and less corrosion risk.

Truss: High. Numerous nodes and connections to inspect.

I-Beam: Moderate. Depends on coating and drainage design.

7. Cost Considerations

Box Girder: Higher initial cost, lower lifecycle cost.

Truss: Medium to high cost depending on span and complexity.

I-Beam: Low upfront cost but may need more frequent replacement.

Project Suitability Chart

Case Study: Hybrid Design in a Coastal Highway Project

In 2023, WZH Build was tasked with designing a 120m highway bridge with a curved alignment along a coastal region in Chile. 

Engineers initially considered a truss design but opted for a modular steel box girder structure due to its torsional stability, clean profile, and reduced maintenance in the saline environment. 

The bridge was erected in 21 days using four prefabricated sections.

Summary: Which Bridge Type Should You Choose?

Each project has unique parameters. In general:

Choose box girder for high torsion needs, fast builds, or curved designs.

Choose truss for ultra-long spans or rail traffic.

Choose I-beam for local, short-span, budget-limited projects.