Concrete Utility Lid with Plastic Frame and Trusses
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Solution Overview
Problem
Existing concrete lids for underground utility boxes are prone to damage, costly to produce, and labor-intensive to manufacture, with issues such as chipping, cracking, and difficulty in removal due to freezing conditions, while alternative materials like composite resin are expensive and susceptible to discoloration.
Innovation Solution
A lid design featuring a concrete core surrounded by an injection-molded polypropylene plastic frame with reinforcing trusses, which provides structural reinforcement and reduces the need for additional reinforcement materials, and a method of fabrication that includes attaching trusses to the frame, filling with concrete, curing, and removing the mold.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If concrete lids are used for utility boxes, then strength and durability are improved, but weight increases and susceptibility to damage from handling and freezing conditions worsens
Solution Approach 1:
The lid is constructed as a composite structure combining concrete core with polypropylene plastic frame and reinforcing trusses. The concrete provides compressive strength while the plastic components provide tensile strength, impact resistance, and freeze-thaw durability. This composite approach maintains strength while reducing weight compared to solid concrete construction.
Solution Approach 2:
The lid is divided into distinct functional segments: a concrete core for compressive load bearing, polypropylene frame members for structural containment, and reinforcing trusses for tensile strength. This segmentation allows each component to be optimized for its specific function while working together to provide overall durability with reduced weight.
2Strength
If concrete lids are used for utility boxes, then structural strength is improved, but manufacturing cost and labor intensity increase
Solution Approach 1:
The lid is manufactured as separate components (concrete core, plastic frame, trusses) that can be produced independently using optimized processes for each material, then assembled together. This segmentation enables specialized manufacturing techniques for each component and simplifies quality control while reducing overall production cost and labor requirements.
Solution Approach 2:
The composite construction allows use of cost-effective materials and manufacturing methods for each component. The polypropylene elements can be injection-molded efficiently, while the concrete core uses standard casting processes. This approach is more economical than manufacturing a solid concrete lid with embedded reinforcement, reducing both material and labor costs.
3Reliability
If concrete lids are used for utility boxes, then durability is improved, but susceptibility to chipping and cracking from handling worsens
Solution Approach 1:
The polypropylene plastic frame and trusses provide impact resistance and crack prevention while the concrete core maintains structural integrity. The plastic components absorb impact energies that would otherwise cause concrete chipping or cracking, significantly improving durability during handling and installation.
Solution Approach 2:
The plastic frame and trusses act as protective cushioning layers that prevent direct impact between the lid and ground or other surfaces during handling. This beforehand protection prevents chipping and cracking before they can occur, enhancing the lid's resistance to handling damage.
4Strength
If concrete lids are used for utility boxes, then strength is improved, but difficulty in removal due to freezing conditions worsens
Solution Approach 1:
The material composition parameters are changed from solid concrete to a composite structure with polypropylene components. The plastic materials have different thermal expansion and freezing characteristics than concrete, reducing the development of freezing bonds between lid and box. This parameter change maintains strength while significantly improving ease of removal in freezing conditions.
Data Source
AI summary
A concrete lid for an in-ground utilities box includes a reinforcement structure filled with concrete. The reinforcement structure includes a plastic frame and one or more reinforcing trusses that extend between opposing sidewalls of the plastic frame. The reinforcing trusses also extend substantially between the upper and lower edges of the opposing sidewalls. For example, a reinforcing truss may include a flat truss member that is substantially coplanar with the lower edges of the sidewalls, and an arched truss member that extends towards (but does not reach) a plane defined by the upper edges of the sidewalls. The reinforcing trusses include openings that allow wet concrete to pass through. The sidewalls of the plastic frame protect the edges of the lid from damage. The reinforcing trusses reinforce the concrete lid, eliminating the need for separate reinforcement material.