Floating Mortise and Tenon Joint for Seismic Stress Absorption
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Solution Overview
Problem
Current construction joint technologies, particularly mortise and tenon joints in timber framed buildings, are vulnerable to failure during seismic events due to their rigidity, which cannot effectively absorb horizontal and vertical stresses caused by earthquakes, leading to potential building collapse.
Innovation Solution
A construction joint system featuring a floating tenon within a variable mortise joint, allowing vertical and horizontal motion, supported by pins that engage with apertures and stabilisation pins to absorb seismic stresses without causing permanent joint failure, and allowing the joint to revert to its original position post-event.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If standard mortise and tenon joints are made rigid and inflexible, then joint strength and stability are improved, but the joint becomes vulnerable to failure during seismic events
Solution Approach 1:
The tenon is transformed from a fixed rigid component to a dynamic floating element that can move vertically and horizontally within the mortise. The tenon includes an aperture that receives a pin, allowing the tenon to shift position during seismic events while maintaining connection. This dynamic capability enables the joint to absorb earthquake stresses through controlled movement rather than rigid resistance, preventing joint failure during seismic activity.
Solution Approach 2:
The joint's mechanical parameters are changed by introducing a pin-aperture mechanism that allows controlled displacement. The tenon's position parameters (vertical and horizontal location within the mortise) become variable rather than fixed. This parameter change enables the joint to transition from a rigid static connection to a flexible dynamic connection that can adapt to seismic movements while maintaining structural integrity.
2Stability of the object's composition
If the beam is made too rigid, then structural stability is improved, but the beam or joints may fail during earthquakes when movements exceed flexibility
Solution Approach 1:
The beam's connection to the pillar is made dynamic through the floating tenon mechanism. During seismic events, the tenon can move within the mortise, allowing the beam to accommodate vertical and horizontal movements without transmitting excessive stresses to the joint. This dynamic connection preserves structural stability while preventing beam or joint failure during earthquake-induced movements.
Solution Approach 2:
The rigid beam-pillar connection is segmented into movable components: the tenon with aperture and pin, and the mortise with stabilization features. This segmentation allows the connection to be divided into fixed elements (mortise, pin) and movable elements (tenon), enabling the beam to maintain stability while accommodating seismic movements through controlled displacement of the tenon within the mortise.
3Strength
If earthquake stresses are absorbed by rigid joints, then joint strength is maintained, but the joints and connected beams are vulnerable to permanent fracture and collapse
Solution Approach 1:
The harmful seismic stresses that would normally cause joint failure are converted into beneficial controlled movements of the floating tenon. The tenon's ability to move vertically and horizontally within the mortise transforms the harmful vibrational and compressive forces into useful displacement that dissipates energy without causing permanent damage. The joint absorbs earthquake energy through controlled motion rather than rigid resistance, preventing permanent fracture.
Solution Approach 2:
The joint is designed with beforehand cushioning features including the aperture-pin mechanism and stabilization pins that prevent excessive movement. These features are built into the joint structure in advance to cushion against seismic stresses. The aperture provides vertical movement capacity, while stabilization pins limit horizontal displacement, creating a pre-configured cushioning system that protects the joint from earthquake-induced permanent damage.
4Reliability
If flexible joint mechanisms are added to absorb seismic stresses, then seismic resistance is improved, but device complexity increases
Solution Approach 1:
The tenon serves multiple functions: it provides the primary structural connection between beam and pillar, enables vertical and horizontal movement during seismic events, and incorporates the aperture-pin mechanism for controlled displacement. The mortise similarly serves multiple functions: receiving the tenon, providing stabilization, and limiting excessive movement. This multi-functionality reduces the need for separate dedicated seismic protection devices, maintaining relatively simple joint structure while achieving improved seismic resistance.
Solution Approach 2:
The flexible mechanism is nested within the traditional mortise and tenon joint structure. The aperture is nested within the tenon, the pin is nested within the aperture, and stabilization pins are nested within the mortise. This nesting approach integrates the seismic protection mechanism into the existing joint geometry without requiring separate external devices, thereby minimizing added complexity while providing flexible stress absorption capability.
Data Source
AI summary
A joint comprising: a tenon, a mortise for receiving the tenon, an aperture formed in one of the tenon and an interior wall of the mortise and a pin which extends from the other of the tenon and the interior wall of the mortise; wherein the aperture is a hole which is engaged by the pin in use such that the tenon is supported within the aperture, and the tenon is capable of vertical and horizontal motion within the mortise in a plane substantially orthogonal to a longitudinal axis of the pin, the motion being limited by the edges of the aperture.