Bridge Demolition in Ontario: Structural Engineering, MTO Permits & OHSA Safety

OHSA Requirements for Bridge Demolition

Bridge demolition is governed by OHSA Construction Regulation O.Reg 213/91 Parts IX (Demolition) and X (Structural Alterations). Key requirements:

• Section 202 (Demolition plan): Before demolition begins, a demolition plan must be prepared by a P.Eng. The plan must address the structural condition of the bridge (assessed through inspection), the proposed demolition sequence, and how each stage of partial demolition will be structurally stable.
• Section 200 (Inspection before demolition): The constructor must have the structure inspected by a P.Eng before demolition begins. Deteriorated or structurally weakened bridges — the typical candidates for demolition — may be in worse structural condition than their original design assumed, requiring careful assessment of how elements will behave when disturbed.
• Section 201 (Adjacent structures): Measures must be taken to ensure that demolition does not damage, destabilize, or endanger adjacent structures, highways, utilities, or railway corridors.
• Section 194 (Utility locates): All utilities (hydro, gas, telecom, water, sanitary, storm sewer) must be located and marked before any excavation or major mechanical demolition begins. Ontario One Call (1-800-ONTARIO) notification is required.

What a Bridge Demolition Plan Includes

A P.Eng bridge demolition plan for an Ontario bridge project includes:

• Condition assessment: Current structural condition of the bridge — deterioration levels in concrete, steel corrosion, foundation condition, and any pre-existing structural deficiencies that affect stability during demolition
• Demolition sequence: The ordered removal of structural elements — which elements come down first, what temporary supports are needed while elements remain partially supported, and the critical constraint at each stage (traffic loading, wind load on completed partial structure)
• Temporary shoring / falsework: Where elements must be supported during staged removal (common for bridges being replaced in stages with traffic maintained nearby), temporary shoring designed to carry the partial structure loads
• Crane and equipment plan: Crane positions, pick weights, boom radii, and ground loading analysis to confirm crane outrigger loads do not damage bridge abutments, embankments, buried utilities, or adjacent structures
• Traffic management: Staged traffic plan — road closures, detours, temporary traffic signals, MTO or municipal approval — for each demolition phase
• Waterway protection: Silt curtains, debris barriers, concrete cutting isolation measures, and timing restrictions for in-water work (fish window compliance with DFO permits)
• Material disposal: Concrete rubble, steel scrap, and deck material disposal — quantities and designated disposal or recycling sites

MTO Authorization for Highway Bridges

For bridges on Ontario's provincial highway network, the Ministry of Transportation Ontario (MTO) has authority over any work affecting the bridge structure, highway right-of-way, or highway traffic. Demolition of a provincial highway bridge typically proceeds under an MTO contract or an encroachment permit, with conditions including:

• Submission of the P.Eng demolition plan for MTO review and acceptance before any work begins
• Stage traffic management plan approved by the MTO District Office
• Night work windows or highway closures coordinated with MTO Traffic Management
• Insurance and bonding requirements for MTO right-of-way work
• MTO-specified environmental protection measures for in-water work in MTO rights-of-way

Municipal bridges (city and regional road crossings) require authorization from the applicable municipality's transportation and infrastructure department. Processes vary by municipality; larger municipalities (Toronto, Ottawa, Hamilton) have formal permitting processes similar to MTO.

Bridge Demolition Methods

The demolition method is selected based on the bridge type, site constraints, proximity to traffic and watercourses, and the replacement construction program:

• Piece-by-piece mechanical demolition: Excavators and breakers dismantle the bridge in manageable pieces — the most common method for concrete bridges. Traffic is maintained on adjacent lanes or detoured during each demolition stage.
• Controlled demolition (drop-in-place): Superstructure is cut into sections and dropped into a controlled catch zone below — used where traffic can be fully detoured and the dropping zone is isolated. Requires precise explosive or mechanical cutting at all support points simultaneously.
• Slide-out or slide-in replacement: New bridge is constructed adjacent to the existing bridge; the existing bridge is slid out and the new bridge slid in over a traffic closure weekend — demolition occurs after the new bridge is in place and traffic is already on the new structure. Popular for MTO bridge replacements minimizing traffic disruption.
• Strand-by-strand replacement (post-tensioned bridges): For deteriorated post-tensioned bridges, partial demolition may involve strand-by-strand de-tensioning under P.Eng supervision before concrete removal — uncontrolled de-tensioning of post-tensioned bridges can result in explosive failure.

Traffic Management During Demolition

Traffic management during bridge demolition must be designed by a certified traffic control planning professional and approved by MTO or the municipal authority. Key considerations:

• Stage traffic plans that maintain service levels on the affected highway during non-closure demolition stages
• Full closure windows (typically weekend or overnight) for critical demolition lifts where traffic cannot safely co-exist with crane operations or falling debris risk
• Detour signage meeting OTM (Ontario Traffic Manual) Book 7 (Temporary Conditions) standards
• Advance public communication for significant closures
• Emergency vehicle access maintained throughout all demolition stages

Environmental Permits for In-Water Bridge Demolition

Most Ontario bridge demolitions over watercourses trigger environmental permitting requirements. The typical permit stack includes:

• MNRF (Lakes and Rivers Improvement Act): Required for work affecting the bed or banks of any Ontario lake, river, or stream — including concrete demolition debris falling on the riverbed, cofferdam installation, abutment removal, or pier demolition in the water
• DFO (Fisheries Act): Authorization required where serious harm to fish or fish habitat is possible. DFO specifies work windows (fish passage timing restrictions — typically no in-water work during spring and fall fish migration seasons), and may require habitat offsetting
• Conservation Authority: Permits for work in regulated watercourses under the Conservation Authorities Act
• Spill Prevention Plans: Required for equipment operating over or adjacent to water — hydraulic oil, fuel, and concrete curing compound are all potential environmental contaminants

Vibration & Settlement Monitoring

Bridge demolition creates ground vibrations from excavator-mounted breakers and blasting (where used). Ontario guidelines for vibration near sensitive structures are based on Peak Particle Velocity (PPV) measurements:

• Residential structures: typically 50 mm/s PPV maximum (Transport Canada/MTO guidelines)
• Historic or architecturally sensitive structures: 25 mm/s PPV maximum
• Utilities and buried infrastructure: confirmed with the utility owner

Pre-demolition vibration monitoring baseline readings and continuous monitoring during demolition operations near sensitive structures are standard practice. Settlement monitoring (survey prisms, tiltmeters) on adjacent structures should also be maintained throughout demolition when the bridge is in proximity to buildings or critical infrastructure.