Bridge Engineering for Maritime Conditions

Understanding Maritime Bridge Engineering Challenges

Bridge engineering in Atlantic Canada presents a unique set of challenges that demand specialized knowledge, innovative design approaches, and a deep understanding of the harsh maritime environment. From the tidal extremes of the Bay of Fundy to the ice-laden waters of the Northumberland Strait, engineers working in this region must account for environmental forces that can be significantly more severe than those encountered in other parts of Canada.

The combination of salt spray corrosion, freeze-thaw cycles, ice loading, and powerful storm surges creates an engineering environment where conventional design approaches often fall short. Bridges serving Nova Scotia's coastal communities must be designed to withstand not only typical traffic loads but also the relentless assault of maritime conditions that can accelerate deterioration and compromise structural integrity within decades rather than centuries.

For communities throughout the Maritimes, bridges represent critical infrastructure connections. Whether linking island communities to the mainland, spanning tidal rivers, or providing essential transportation corridors for resource industries, these structures must deliver reliable service throughout their design life while remaining economically viable to construct and maintain.

Environmental Loading Considerations in Maritime Regions

Designing bridges for maritime conditions requires careful analysis of multiple environmental loading scenarios that may occur simultaneously or in rapid succession. Understanding these forces and their interactions is fundamental to creating structures that will perform reliably throughout their intended service life.

Ice Loading and Impact Forces

Ice represents one of the most significant design considerations for bridges in Atlantic Canada. The Canadian Highway Bridge Design Code (CHBDC) provides specific guidance for ice loads, but engineers must carefully evaluate local conditions to determine appropriate design parameters. In Nova Scotia's coastal waters, ice thickness can regularly reach 300 to 600 millimetres during severe winters, with pressure ridges potentially doubling these values.

Ice forces on bridge piers can be categorized into several types:

• Static ice pressure: Resulting from thermal expansion of ice sheets, which can generate forces exceeding 1,500 kilopascals against pier faces

• Dynamic ice impact: Caused by moving ice floes striking piers during spring breakup or tidal fluctuations

• Ice jacking: Vertical forces from ice adhered to piers that rises and falls with changing water levels

• Ice accumulation loads: Additional dead load from ice buildup on structural members

Pier design in ice-prone waters typically incorporates sloped ice-breaker noses that force ice sheets to fail in bending rather than crushing, significantly reducing the forces transmitted to the structure. The angle of these ice-breakers, typically between 30 and 45 degrees from horizontal, must be optimized based on expected ice thickness and water level fluctuations.

Wave Action and Storm Surge

Atlantic Canada's exposure to powerful ocean storms, including post-tropical cyclones, means bridges must be designed for significant wave heights and storm surge elevations. The Bay of Fundy region experiences some of the world's highest tides, with typical ranges of 12 to 16 metres in the upper bay, creating complex hydrodynamic conditions that must be carefully analysed.

Storm surge events can add 2 to 3 metres of additional water elevation above predicted astronomical tides, potentially exposing bridge decks to wave impact forces they would not normally experience. Climate change projections suggest these extreme events will become more frequent, prompting engineers to incorporate additional freeboard into modern designs.

Corrosion from Salt Spray and Deicing Chemicals

The corrosive maritime environment accelerates deterioration of both concrete and steel bridge components. Chloride ion penetration into concrete can initiate reinforcing steel corrosion at chloride concentrations as low as 0.4 percent by weight of cement. In marine exposure zones, these threshold concentrations can be reached within 10 to 15 years without adequate protection measures.

Effective corrosion mitigation strategies for maritime bridges include:

• Specifying high-performance concrete with water-cement ratios below 0.40 and minimum compressive strengths of 45 megapascals

• Incorporating supplementary cemite materials such as silica fume, fly ash, or slag to reduce permeability

• Using epoxy-coated, galvanised, or stainless steel reinforcement in splash zones

• Applying penetrating sealers and surface coatings to exposed concrete

• Implementing cathodic protection systems for steel components

Foundation Design for Coastal Conditions

Foundation engineering for maritime bridges must address challenging soil conditions, scour potential, and the long-term effects of cyclic loading from waves and ice. Atlantic Canada's coastal geology, shaped by glacial processes, often presents variable subsurface conditions that require thorough geotechnical investigation.

Scour Analysis and Protection

Scour around bridge piers and abutments represents the leading cause of bridge failures in North America. In tidal environments, the reversing flow directions create complex scour patterns that can excavate significant volumes of material from around foundations. The combination of live-bed scour, contraction scour, and local pier scour can result in total scour depths exceeding 5 to 8 metres in some locations.

Design approaches to manage scour risk include:

• Extending foundations below predicted scour depths with appropriate safety factors

• Installing riprap armour protection with appropriately sized stone for design velocities

• Constructing sheet pile or concrete scour collars around piers

• Implementing real-time scour monitoring systems with alert thresholds

Deep Foundation Systems

Many coastal sites in Nova Scotia feature soft marine clays, loose granular deposits, or highly variable glacial till that necessitate deep foundation systems. Driven steel piles, drilled shafts, and micropiles are commonly employed depending on site conditions and loading requirements.

Steel H-piles in marine environments require careful consideration of corrosion allowances. Typical practice adds 1.5 to 3.0 millimetres to the structural steel thickness to account for corrosion over a 75-year design life in aggressive marine conditions. Alternatively, protective coatings or cathodic protection systems may be specified to extend pile service life.

Material Selection for Durability

The selection of appropriate materials is critical to achieving the desired service life for maritime bridges. While initial construction costs are important, life-cycle cost analysis often favours materials with higher upfront costs but superior durability performance.

Concrete Technology

Modern high-performance concrete formulations offer significantly improved durability compared to conventional mixtures. For maritime bridge applications, engineers typically specify:

• Low permeability: Rapid chloride permeability test results below 1,000 coulombs

• Air entrainment: 5 to 8 percent entrained air for freeze-thaw resistance

• Adequate cover: Minimum 75 millimetres clear cover to reinforcement in marine splash zones

• Crack control: Maximum crack widths of 0.25 millimetres for severe exposure conditions

Ultra-high performance concrete (UHPC), with compressive strengths exceeding 120 megapascals and virtually zero permeability, is increasingly being used for critical elements such as bridge deck overlays and closure pours in precast construction.

Structural Steel and Corrosion Protection

Weathering steel, which forms a protective oxide patina, has historically been used for bridges in many regions. However, its performance in marine environments where salt spray is prevalent is generally unsatisfactory, as the protective patina cannot form properly under constant chloride exposure.

For steel bridges in maritime settings, robust paint systems or hot-dip galvanising are typically required. Modern three-coat paint systems with zinc-rich primers can provide 20 to 30 years of service between major maintenance interventions when properly applied and inspected.

Design Code Requirements and Regional Considerations

Bridge design in Canada is governed by the Canadian Highway Bridge Design Code (CSA S6), which provides comprehensive requirements for structural design, loading combinations, and serviceability criteria. However, provincial transportation authorities often impose additional requirements that reflect regional conditions and priorities.

Load Combinations for Maritime Conditions

The CHBDC specifies load combinations that must be evaluated for all bridges, including combinations involving ice loads, stream pressure, and wave forces. For maritime bridges, the critical combinations often involve:

• Ice pressure combined with reduced live load

• Wave forces combined with storm surge and wind

• Ship impact loads for navigable waterways

• Thermal effects combined with shrinkage and creep

Engineers must carefully evaluate which combinations govern the design of various structural elements, as the critical case may differ significantly between substructure and superstructure components.

Climate Change Adaptation

Recognising the potential for significant changes in environmental conditions over the 75 to 100-year design life of bridges, many Canadian jurisdictions now require explicit consideration of climate change impacts. For Atlantic Canada, key considerations include:

• Sea level rise projections of 0.5 to 1.0 metres by 2100

• Increased intensity of extreme precipitation events

• Changes in ice formation patterns and thickness

• More frequent and intense coastal storms

Adaptive design approaches may include increased freeboard, enhanced scour protection, or foundations designed to accommodate future raising of the bridge deck.

Inspection and Maintenance Strategies

Even the best-designed bridge requires ongoing inspection and maintenance to achieve its intended service life. Maritime conditions accelerate many deterioration mechanisms, making proactive maintenance programmes particularly important for coastal structures.

Inspection Protocols

Regular inspections should follow Transport Canada guidelines and provincial requirements, typically including:

• Routine inspections: Visual assessments every 1 to 2 years to identify obvious deficiencies

• Detailed inspections: Comprehensive hands-on inspections every 3 to 5 years with element-level condition rating

• Special inspections: Following significant events such as major storms, ice impacts, or vessel strikes

• Underwater inspections: Diving or remotely operated vehicle inspections of submerged elements every 5 years

Preventive Maintenance Measures

Effective maintenance programmes for maritime bridges emphasise preventing deterioration before it begins rather than responding to damage after it occurs. Key preventive measures include:

• Maintaining functional expansion joints and drainage systems to prevent ponding

• Applying penetrating sealers to concrete surfaces on a 5 to 7-year cycle

• Touch-up painting of steel components before corrosion advances

• Maintaining scour countermeasures and monitoring scour-critical foundations

• Removing debris accumulation that can trap moisture against structural elements

Innovative Solutions for Maritime Bridge Challenges

Advances in materials, construction methods, and monitoring technologies are providing engineers with new tools to address the challenges of maritime bridge construction. These innovations can improve durability, reduce construction time, and provide better information for asset management decisions.

Accelerated Bridge Construction

Prefabrication and accelerated bridge construction (ABC) techniques offer particular advantages in maritime environments where weather windows for construction may be limited. Precast concrete elements can be fabricated under controlled conditions, ensuring consistent quality, before being rapidly assembled on site during favourable weather.

Structural Health Monitoring

Embedded sensors and automated monitoring systems can provide continuous data on structural performance, environmental conditions, and potential deterioration. For maritime bridges, monitoring systems may track:

• Chloride penetration depth in concrete elements

• Corrosion current in reinforcing steel

• Scour depth at critical foundations

• Structural deflections and vibrations

• Ice and wave impact forces

This data enables condition-based maintenance strategies that optimise intervention timing and extend structure service life.

Partner with Experienced Maritime Bridge Engineers

Successful bridge engineering for maritime conditions requires specialised expertise that combines structural engineering fundamentals with deep knowledge of the unique challenges presented by the Atlantic Canadian environment. From initial feasibility studies through detailed design, construction support, and ongoing inspection services, experienced guidance is essential to achieving durable, cost-effective infrastructure.

Sangster Engineering Ltd. has served communities throughout Nova Scotia and Atlantic Canada for decades, providing professional engineering services that reflect our understanding of local conditions and requirements. Our team combines technical excellence with practical experience to deliver bridge solutions that perform reliably in the demanding maritime environment.

Whether you are planning a new bridge construction, evaluating rehabilitation options for an existing structure, or developing a long-term infrastructure management strategy, we invite you to contact our Amherst office to discuss how our expertise can support your project goals. Let us help you build connections that will serve your community for generations to come.

Partner with Sangster Engineering

At Sangster Engineering Ltd. in Amherst, Nova Scotia, we bring decades of engineering experience to every project. Serving clients across Atlantic Canada and beyond.

Contact us today to discuss your engineering needs.