Composite Mull Post with Steel and Wood Reinforcement
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Solution Overview
Problem
Traditional wood and extruded polymer mull posts fail to withstand high winds and impacts from flying debris in coastal regions, leading to structural integrity issues and non-compliance with stringent building codes, as they are prone to breaking, splitting, and deflection.
Innovation Solution
A reinforced mull post design featuring an elongated support portion with a hollow central chamber containing first and second reinforcing members made of different materials, such as engineered wood and steel, enhancing structural strength and rigidity, while maintaining a decorative appearance similar to traditional wood mullions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If traditional finger jointed wood mull posts are used, then the mull posts can be manufactured easily and inexpensively, but they break apart at finger joints and split along the grain under high wind pressure
Solution Approach 1:
The mull post is divided into multiple components: an outer polymer profile, internal reinforcing members (such as wood I-joists or metal channels), and foam core material. This segmentation allows each component to contribute specific properties - the polymer provides weather resistance and aesthetics, the foam provides insulation and structural support, and the internal reinforcing members provide resistance to bending and impact forces.
Solution Approach 2:
The mull post employs composite construction by combining dissimilar materials - extruded polymer (PVC or similar), foam core, and internal reinforcing elements (wood or metal). This composite approach creates a structure that leverages the advantages of each material while compensating for their individual weaknesses, resulting in a mull post that resists breaking, splitting, and deflection under extreme coastal conditions.
2Strength
If solid wood mull posts are used to eliminate finger joint failures, then strength at joint locations is improved, but the wood still splits along the grain at hardware locations under high pressure
Solution Approach 1:
The polymer composite construction eliminates the grain structure inherent in solid wood that causes splitting. The homogeneous polymer material distributes stress evenly throughout the structure, preventing the concentrated stress at hardware locations that causes wood to split along the grain.
Solution Approach 2:
The invention changes the fundamental material parameter from natural wood with directional grain to engineered polymer composite with isotropic properties. This parameter change allows the mull post to withstand high wind pressures and impact forces without the splitting failures characteristic of solid wood construction.
3Reliability
If extruded polymer mull posts are used, then resistance to breaking and splitting is improved, but the mull posts deflect or bend under high pressure
Solution Approach 1:
The multi-material composite construction combines the advantages of polymer (weather resistance, no splitting) with the rigidity of internal reinforcing members. The foam core and internal I-joists or metal channels provide the structural stiffness needed to resist deflection and bending under high wind pressure while the outer polymer shell maintains reliability by preventing breaking and splitting.
Solution Approach 2:
The segmented construction with discrete internal reinforcing members distributed throughout the polymer profile creates a structure that resists bending through multiple load paths. The reinforcing members act as internal ribs that prevent the polymer from deflecting under pressure while maintaining the overall integrity of the structure.
4Ease of manufacture
If traditional wood or polymer mull posts are used, then manufacturing is simple, but they fail to withstand direct impact from airborne debris such as tree limbs
Solution Approach 1:
The composite construction with foam core and internal reinforcing members creates a structure that absorbs and distributes impact energy from airborne debris. The foam core acts as a energy-absorbing buffer, while the distributed reinforcing members prevent localized failure from impact forces, maintaining structural integrity after debris impact.
Solution Approach 2:
The foam core material serves as pre-installed cushioning that absorbs impact energy from flying debris before it can cause structural damage. This beforehand cushioning protects the reinforcing members and the overall structure from the full force of impacts during hurricane conditions.
Data Source
AI summary
A composite reinforced mull post is disclosed or use in an exterior building entryway assembly, engaging a door on one side and a side light window on the other side. The mull post may comprise a polymer profile portion and first and second reinforcing members. The profile portion comprises a layer of polyvinyl chloride with a hollow center. The first reinforcing member comprises an engineered material such as a wood laminate, and the second reinforcing member comprises a U-shaped steel channel that fits around one end of the first reinforcing member. The reinforcing members are received within the hollow center of the polymer profile portion and run the entire length of the mull post to provide substantial rigidity to the assembly. A polymer cap layer may be co-extruded on the outer surface of the polymer profile portion to provide the mull post with a desired finished surface appearance and/or color.