Are you currently involved in a complex infrastructure project and seeking clarity on the precast design process? Understanding the processes involved in your project is crucial, as it directly impacts procurement lead times and installation schedules. Continue reading to gain insights into common processes that can help minimize costs and mitigate program risks.
To understand design responsibilities, it's essential to consider the construction methodology chosen by the asset owner. Common processes include:
- Construct Only: The asset owner hires an architect or designer to create a detailed project design. Different specialist engineers are involved in designing critical parts like bridge and culvert structures. While contractors may propose alternative approaches, they typically follow the original design during construction.
- Design & Construct: Here, the asset owner provides a high-level brief with design intentions. Head contractors submit concept designs and methodologies during the tender process, allowing experienced contractors to offer effective solutions based on their expertise.
- Early Contractor Involvement (ECI): This process involves engaging a construction contractor early in the design phase, bypassing the typical tender process. This approach can lead to cost savings and faster project completion by allowing contractors to suggest enhanced methodologies.
To learn more about the benefits of ECI, refer to our guide.
In each of these construction processes, the design of precast elements follows a specific set of steps:
- Project Design: A civil engineer typically develops the overall design for a simple culvert structure, considering factors like location, geography, geotechnical conditions, and hydraulic flow requirements. The design may also encompass details such as pavement and guardrails. When proprietary precast elements are part of the design, like culverts, the designer specifies size, loading, and exposure requirements.
- Precast Design: The design of precast elements is usually done by the precast manufacturer. They engage external or internal structural engineers to design the precast elements according to the specifications in the overall design, including reinforcing, concrete strengths, and element sizes.
- Highly Integrated Structures: For structures with intricate integrations between elements, such as prestressed bridges, the design engineer oversees the complete design process, including the precast elements. In such cases, the precast manufacturer only produces shop drawings and does not handle any structural design work.
For large culvert structures on private property, it may seem appealing for an asset owner to simply purchase standard precast units and assemble them on-site. While this approach may offer cost savings, there is a higher risk of failure due to factors such as geotechnical and hydraulic considerations not being accounted for. It is highly recommended to consult with a civil engineer for guidance on culvert structures located on private property.
Understanding the specifications for subbase and fill can sometimes be complex. Typically, the design engineer will provide detailed requirements for subbase preparation, backfill, and overfill, taking into consideration the specific geotechnical conditions and relevant standards of the site.
In cases where these details are unavailable, the precast structural engineer may need to make educated assumptions and propose a subbase specification accordingly. However, this approach may not be fully optimized for the site conditions, potentially leading to a less cost-effective solution.
It is common for civil structures to incorporate a mix of precast and cast-in-place elements. For instance, a culvert structure may necessitate precast crown units alongside a cast-in-place base slab and wing walls. Clear drawings should indicate this differentiation, and it is crucial for contractors to grasp which elements will be constructed on-site.
While precast manufacturers may offer precast alternatives instead of cast-in-place, careful consideration must be given to align with the overall design intent and obtain approval from the original designer. Refer to this helpful guide on the advantages of precast solutions.
Each project will have unique design approval requirements, which may involve reviews by contractors, the original designer, and the asset owner. Additionally, some project specifications may necessitate 'proof engineering', where a third-party engineer conducts a thorough review of the design to ensure compliance with relevant standards and loadings. Proof engineers maybe engaged by either the contractor or precast manufacturer.
At any phase of your design or construction process, our knowledgeable team is here to help you understand your design process, provide reviews, and optimize for improved project outcomes.