Composite Joist Floor Stand-off Fastener Hardness Profile
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Solution Overview
Problem
Existing composite floor systems are time-consuming and prone to installation errors, requiring significant labor and materials to achieve the same load-bearing capacity, while also being costly and difficult to install safely.
Innovation Solution
The introduction of stand-off fasteners with specific hardness profiles and thread-forming capabilities, allowing for rapid installation with lower torque requirements and improved load-carrying capacity, combined with a composite joist floor system design that includes corrugated steel decking and cementitious slabs, facilitates faster and more error-free assembly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If traditional composite floor systems are used with welded shear studs or partial extension of joist upper chord, then load-bearing capacity is achieved, but installation time is excessive and installation complexity is high
Solution Approach 1:
The fastener is divided into distinct functional segments: a fluted lead portion for hole formation, a thread-forming portion for thread creation, and a threaded portion for clamping. This segmentation allows each portion to perform its specific function efficiently, reducing overall installation time and complexity while maintaining load-bearing capacity.
Solution Approach 2:
The fluted lead portion performs preliminary action by forming the fastener opening in the joist upper chord before the thread-forming portion creates threads. This preliminary hole formation reduces resistance during thread formation, enabling faster installation with lower torque requirements and reducing installation errors.
2Ease of manufacture
If traditional fastening methods are used, then structural integrity is maintained, but labor costs and material costs are high
Solution Approach 1:
The fastener utilizes controlled hardness variations at different portions: the fluted lead portion and thread-forming portion have higher hardness (HRC 50-65) for cutting and forming operations, while the threaded portion has lower hardness (HRB 70-HRC 40) for ductility and clamping. This parameter change enables easier installation with standard tools and reduces material waste from installation errors.
Solution Approach 2:
The thread-forming portion automatically creates threads in the joist upper chord as the fastener is driven in, eliminating the need for pre-drilled holes or separate threading operations. The fluted lead portion self-forms the initial opening, making the installation process self-sufficient and reducing labor requirements.
3Manufacturing precision
If higher torque is applied during fastener installation, then thread-forming capability is improved, but drive torque requirement increases installation difficulty
Solution Approach 1:
The fastener applies local quality through differentiated hardness at specific portions. The thread-forming portion has high hardness (HRC 50-65) concentrated exactly where thread formation occurs, providing precise thread cutting capability. The fluted lead portion also has high hardness for clean hole formation. This localized hardness distribution achieves precise thread-forming without requiring excessive overall torque.
Solution Approach 2:
The mechanical cutting action of the fluted lead portion replaces the need for conventional drilling operations, and the thread-forming portion replaces separate threading operations. This substitution of mechanical actions reduces the cumulative torque requirements and simplifies the installation process while maintaining manufacturing precision.
Data Source
AI summary
The composite joist floor system includes joists supporting metal decking and a stand-off fasteners are spaced along the length of the joist Each fastener has an upper portion with a through hardness between HRB 70 and HRC 40 and a lower portion having a threaded portion with a through hardness of between HRB 70 and HRC 40 and a thread-forming portion adjacent the threaded portion with at least a HRC 50 hardness and failure torque to thread-forming torque of at least 3.0 and a drive torque at least 20% less than a thread-forming torque, and a fluted lead portion adjacent the thread-forming portion with a nominal diameter between 70 and 95% of major diameter of the threaded portion adapted to form a fastener opening. These stand-off fasteners extend into and are encapsulated by a cementitious slab supported by the metal decking to form a composite floor system.