August 31 2021
Bridge Demolition For Our Clients, Every Step of the Way
Demolishing a structure is no easy task. It is complicated by continuously changing load paths, altered support conditions, compromised structural components, and increased sensitivity to environmental influences. The development of engineered demolition plans requires significant attention to detail and the careful consideration of the strength and stability of the remaining components through every step of the sequence.
Entuitive’s integrated Bridge and Construction Engineering teams approach bridge demolition with surgical precision, ensuring that contractors can realize their preferred plans and owners can protect their assets.
Our team is experienced with a wide range of bridge demolition techniques, from brute force methods like demolition using rig-mounted breakers under full closure, to carefully sequenced de-construction methods of saw cutting and lifting operations with live traffic on adjacent portions of the structure. Some projects require the design and construction of temporary components to facilitate the demolition, such as the Nipigon River Bridge, for which our team provided engineering support to introduce a temporary cable-stayed king post system to manage cantilevers in the existing girders up to 82 metres in length that arose during its de-launching.
Leveraging a 1+1=3 Approach to Bridge Demos
Contractors and owners benefit from our team’s unique blend of construction awareness and advanced bridge evaluation techniques to tackle complicated technical challenges, allowing them to remain on schedule and on budget, with alternatives built into their plans for good measure. Demolition sequences that are thoroughly vetted, remain compliant to the project specifications, and fully consider the demolition contractor’s equipment and preferred methods add value to the project by allowing the work to proceed in the most practical manner, minimizing both cost and risk.
No matter the bridge demolition needs, our team of experts can assist. Our three-pillared approach of being collaborative, creative, and technically advanced works together to support our clients.
Collaboration & Flexibility in Everything We Do: Bridge Demos Your Way
Our contractor clients, most with decades of experience, know how to sequence bridge demolitions. We collaborate with them as design partners, and as much as possible, engineer the demolition plan using equipment they already have available and following their preferred sequence.
We take a flexible approach for every project to support our clients in developing initial plans, which may change as the demolition progresses and field conditions necessitate a different solution. We often incorporate alternative removal methods into our demolition plans so that the crews completing the work can adapt quickly without losing precious time dealing with surprise conditions on site.
Nipigon River Bridge
Collaboration is key. This came to life on the Gardiner Expressway Rehabilitation project. Our team worked closely with the contractor to devise an accelerated construction sequence wherein demolition of the existing superstructure and reconstruction of the new superstructure were closely intertwined. Existing concrete deck and steel girder pairs of the existing superstructure were cut and lifted out and replaced in short order with new deck and girder modules for the new superstructure in a patchwork pattern along the bridge. As in that case, demolition plans that involve integrating the demolition of the existing structure with the construction of the new structure require a collaborative mindset throughout the full design team.
Creative Solutions That Are Cost-Effective & Sustainable: Making Sure You Stay on Budget
Ensuring that our clients stay on budget means developing cost-effective solutions that, as much as possible, make use of materials that are already on site to keep the bridge sufficiently restrained during demolition. Rather than introducing new and potentially costly temporary components for the project, we look for opportunities to provide creative solutions by using what is already there. Common examples include leaving narrow strips of deck slab in place to laterally brace girders while the remaining deck slab is removed and using temporary concrete barriers to ballast against uplift. In the case where a new bridge is being constructed beside an existing bridge to be demolished, we often rely on one structure to stabilize the other rather than introducing a temporary support structure.
The development of cost-effective solutions also means identifying construction efficiencies. It is generally least expensive to demolish a structure using rig-mounted breakers (e.g., hoe-rams or crushers). However, that approach is often minimized or precluded by project restrictions, leaving other demolition techniques, such as cutting, lifting, and hand-chipping, as the primary means of demolition. Other times, less common demolition techniques, such as de-launching or lifting out girders with the full deck slab attached, are more cost-effective.
Our clients realize value and efficiency on these projects through the development of creative solutions that maximize the use of less expensive demolition techniques.
Advanced Bridge Analysis & Evaluation: Equipping You with the Best Solutions
A cost-effective and efficient bridge demolition solution typically involves utilizing whatever strength and stability can be maintained in the existing structure without adding temporary components. Our integrated Bridge and Construction Engineering teams employ refined methods of structural analysis and evaluation to tease out the best solution for our clients.
Our experience with new bridge design helps us as demolition engineers to better understand how to fully utilize existing materials to their code-mandated limits and achieve more efficient outcomes. To do so, we use refined modelling techniques and staged construction analyses to capture the anticipated behaviour of a structure throughout every step of its demolition process. Our techniques go beyond the traditional simplified methods of analysis and include three-dimensional modelling to give us the full understanding of how the structure is responding and where efficiencies can potentially be gained throughout the process.
Frederick House River Bridge Truss with Barge Support at East Approach
When appropriate we also incorporate parametric modelling techniques into our work to enable the demolition analysis of large structures with complex geometry, such as the Gardiner Expressway. These methods of analysis give us the ability to adapt quickly if alternate demolition methods or sequences present themselves. To complement our advanced analysis methods, we use our consummate knowledge of the bridge code to take advantage of the full gamut of methods and techniques available for our evaluation of bridges and their demolition planning. Leveraging our memberships on bridge code technical sub-committees, we stay up to date on the full suite of technical tools that are available to us to help our clients achieve their preferred plans.
Our advanced approach to bridge engineering and analysis also allows us to handle the atypical heavy construction loading and the complicated traffic staging that commonly arises during bridge demolitions. It is common for demolition plans to include consideration for heavy excavator and telehandler loads, and it is important to find ways to minimize their travel restrictions on deck so that the sequence can move ahead as quickly as possible. Our analysis techniques have also allowed us to find ways to place heavy crane outrigger loads on existing structures so that sequences can be simplified with removal of larger components by crane. For many projects, we engineer the demolition to occur in stages alongside live traffic on the bridge.
Our projects in this area illustrate our three-pillared approach to bridge demolition. Read our highlights below.
Frederick House River Bridge (Hwy 101 Near Timmins, Ontario)
Truss Jacked 4m with Temporary Barge Support in Place
In consultation with the contractor, it was determined that demolishing the existing Fredrick House River truss spans would be significantly simpler and faster if it could be done on shore rather than from barges in the river. Entuitive collaborated with the contractor to establish a work sequence that permitted removal of the existing 60-metre truss span from its piers onto the shore where final dismantling was significantly easier. The engineered sequence included jacking up the existing truss approximately 4 metres, setting a barge with a support frame under the truss’ west end, creating a rollway on the east approach spans, and then moving the truss onto the shore.
Barge Support at West End of Truss
As part of establishing the work sequence, Entuitive’s work programme included identifying all temporary support conditions through de-construction, evaluation of the truss for each of the conditions, and local strengthening of the truss as required to suit the altered support locations. A critical component of the work was the detailed evaluation of the weight of the existing structure to ensure that sufficient floatation was available in the barges and the capacity of all temporary support components were sufficient for the loads. Entuitive also provided the engineering design for the jacking frame to lift the existing truss 4 metres, the barge mounted temporary support frames, and the rollway on the approaches.
Fountain Street Bridge Over the Grand River (Cambridge, Ontario)
Fountain Street Bridge
The Fountain Street Bridge over the Grand River in Cambridge, Ontario, is a good example of how early consideration of the demolition plan can inform other facets of the project, including the new structure design and satisfaction of environmental requirements.
The existing structure was a four-span, continuous, haunched, concrete, four-cell voided slab bridge on wall piers. Its superstructure was ultimately replaced by a new slab-on-steel girder structure supported on the refurbished existing piers. Entuitive was retained by the Region of Waterloo early in the project to develop the conceptual and detailed schematic designs for demolition of the existing structure.
It is uncommon for owners to develop their own demolition plans because it is typically a third-party contractor who will undertake the demolition. While uncommon, this approach proved to be valuable, as our demolition design was used to inform the final design of the new superstructure. In particular, the new girder spacing was adjusted so that the existing structure could be kept stable during its demolition.
The demolition had to be devised to avoid adversely affecting the Grand River’s ecosystem. Our team developed a strategy that did not rely on access from the river, satisfying the environmental restrictions on in-water work. Our solution consisted of a sequence of structure removal and stabilization, including the use of balanced cantilever construction to remove the voided slab. The implementation of this approach proved crucial when a flash flood of the Grand River brought water to the underside of the existing bridge during the demolition work.
Lakeshore Bridge Over Sixteen Mile Creek (Oakville, Ontario)
Existing Box Girders After Deck Removal
The Lakeshore Road Bridge over Sixteen Mile Creek was replaced in 2017. The existing bridge, which was built in 1967, was a three-span steel girder bridge comprising a reinforced concrete deck slab supported by four variable-depth steel box girders. It carried four lanes of vehicular traffic and two sidewalks along Lakeshore Road, serving as a critical transportation link over Sixteen Mile Creek and connecting parts of downtown Oakville. Entuitive was retained by the contractor to provide construction engineering services for the demolition of the existing bridge.
The existing box girders were some of the oldest in the province and did not feature the bracing and stiffening that is typical of modern designs. Maintaining girder stability during deck slab removal was a significant challenge. Our team developed a careful sequence of deck slab removal that maintained the stability of the girders without hindering the contractor’s production. Discrete strips of composite deck slab were intentionally left in place at some locations to act as temporary bracing until the girders were lifted out.
The site is in a crowded downtown area next to a marina, which did not afford much space for setting up cranes to lift out the original girders. We devised the demolition plan so that two mobile cranes would lift out the main span girder segments instead of a single larger crane that would have conflicted with the marina property. The cranes were set up on either side of the creek and did not rely on access from the water, which aided in satisfying environmental restrictions for in-water work.
The end spans were lifted partially onto the bridge approaches in a tandem lift using a mobile crane and an excavator. The excavator was then used to drag the girders fully onto the approaches for demolition and disposal. Larger cranes would have been needed to lift the girders fully onto the approaches because of the additional reach. Since the use of excavators is less expensive than mobile cranes, we were able to reduce the demolition cost by keeping the crane size small and relying on the less expensive excavators.
QEW Over Bronte Creek (Oakville, Ontario)
Work Platform in Place for Removal of Bridge Deck
Entuitive was retained by the contractor to develop a demolition and reconstruction plan for the rehabilitation work on the westbound QEW bridge over Bronte Creek. The existing structure over Bronte Creek was composed of three primary concrete arch spans originally constructed in the 1930s. The rehabilitation works included full removal and replacement of the existing deck, floor beams, and spandrel columns.
Existing Spandrel Columns with Deck Removed
The demolition and reconstruction plans for the structure were developed by Entuitive using a surgical de-construction mindset. Full three-dimensional, staged construction, finite element models were utilized to track the force effects in the fragile existing arches through every phase of the anticipated work. The demolition plan included bracing of the existing arches and specific deck removal sequences to mitigate unbalanced loading on existing arches. Entuitive worked extensively with the demolition contractor to determine travel paths, track placements, and allowable payload weights so that the heavy excavators available could work on the spans.
Realizing Your Plans, Your Way
We exist to serve our clients and communities. Our Bridge Demolition service is focused on our clients, their needs, and their plans. Our creative, collaborative, and advanced approach enables them to achieve success.
To learn more about our Bridge and Construction Engineering services, dive into these articles: