Ductile Masonry Wall Tie for Lateral Load Resistance
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Solution Overview
Problem
Unreinforced masonry cavity walls, particularly those made of clay brick or soft stone, face structural instability and safety issues due to inadequate tie systems, which fail under lateral loads like earthquakes and winds, and lack sufficient shear and tension connections between wall layers and floor/roof diaphragms.
Innovation Solution
A masonry cavity wall tie with a ductile shank design featuring a combination of threaded and unthreaded portions, providing a high bending angle without rupture, and a tapered helical screw structure for enhanced interleaf shear transfer, suitable for use with clay brick or soft stone masonry, allowing for composite out-of-plane behavior under lateral loading.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If traditional tie systems are used in unreinforced masonry cavity walls, then the wall construction is simpler and easier to install, but the lateral strength and structural stability are significantly reduced
Solution Approach 1:
The tie system is segmented into multiple functional components: a shank with threaded portions at both ends and an unthreaded central portion, a head portion for engagement, and specific geometric features like flutes and ridges. This segmentation allows each part to perform its specific function optimally while maintaining overall system effectiveness.
Solution Approach 2:
The wall tie combines different material properties and structural features within a single component - threaded sections for anchorage, unthreaded section for flexibility, and specific geometric features for shear transfer. This composite approach enables the tie to simultaneously provide tension resistance, shear transfer, and ductility.
2Duration of action of moving object
If traditional tie systems are used in unreinforced masonry cavity walls, then the installation process is faster and less disruptive, but the displacement capacity under lateral loading is significantly reduced
Solution Approach 1:
The tie system incorporates specific parameter optimizations including shank diameter (5.5-10 mm), unthreaded portion length (25-30% of total length), and thread specifications that provide optimal balance between installation ease and displacement capacity. These parameter changes enable the tie to achieve high bending angles (12.5°-26°) without rupture.
Solution Approach 2:
The unthreaded central portion of the shank provides ductility and flexibility, allowing the tie to undergo significant bending and deformation under lateral loads without rupture. This dynamic capability enables the wall to dissipate energy through controlled deformation while maintaining structural integrity.
3Reliability
If corrosion-resistant materials are used for wall ties, then the connection durability between masonry layers is improved, but the cost and complexity of the tie system increases
Solution Approach 1:
The tie system applies different properties to different portions of the shank - threaded portions for anchorage, unthreaded portion for flexibility and corrosion resistance, and specific surface features for shear transfer. This local differentiation optimizes each section's performance while managing overall complexity.
4Stability of the object's composition
If adequate shear and tension connections are provided between masonry walls and diaphragms, then the structural stability under earthquake and wind loads is improved, but the device complexity and installation requirements increase
Solution Approach 1:
The tie system is designed to be installed during the initial construction phase, with threaded portions embedded in masonry units and the head portion engaging with diaphragms or wall ties. This preliminary installation ensures that shear and tension connections are established before lateral loads are applied, simplifying the overall construction process.
Data Source
AI summary
A masonry cavity wall tie comprises a shank having a tip at one end, a head at a second distal end, ductility measured as a bending angle under complete three repeated cycles without rupture of between about 12.5° and 26°, a shank diameter between about 5.5 mm and about 10 mm, and first, second, and third shank portions extending at least partially towards the head. The first shank portion commences at the tip and has a helical thread of a diameter along a predetermined longitudinal length of the first shank portion. The second shank portion commences at an end of the first shank portion, is unthreaded, and is between about 25% and about 30% of the wall tie length. The third shank portion commences at an end of the second shank portion and has a helical thread of the diameter along a predetermined longitudinal length of the second shank portion.