Guardrail Terminal End Energy Absorption via Sequential Bolt Shear
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Solution Overview
Problem
Current guardrails are limited in energy absorption at the terminal end due to unreliable sequential failure of shear bolts, leading to premature halting of telescoping and reduced energy absorption in head-on impacts.
Innovation Solution
A guardrail design with a first set of frangible bolts connecting rails 2 and 3, a second set connecting rails 3 and 4, and additional standard post bolts to control the sequential failure of bolts, ensuring upstream bolts shear before downstream ones during impacts, allowing more rails to telescope and absorb energy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a second set of shear bolts is used to join the third and fourth rails, then more rails can telescope to absorb more energy, but the downstream bolts may shear before the upstream bolts, prematurely halting telescoping
Solution Approach 1:
The patent applies different bolt configurations at different locations along the rail assembly. Upstream joints (between rails 1-2 and 2-3) use only frangible shear bolts, while downstream joints (between rails 3-4 and 4-5) use both frangible shear bolts and standard post bolts. This local differentiation in connection strength ensures that upstream joints fail first during impact, allowing controlled sequential telescoping while preventing premature failure of downstream joints.
Solution Approach 2:
The rail connection system is segmented into multiple joint types with different failure characteristics. The frangible shear bolts are designed to fail at lower loads, while standard post bolts maintain structural integrity at higher loads. This segmentation allows the system to progress through controlled failure stages, with each segment (joint) failing in a predetermined sequence to maximize energy absorption.
2Reliability
If only one set of shear bolts is used to join rails, then sequential failure can be controlled, but fewer rails telescope and energy absorption is limited
Solution Approach 1:
The patent changes the structural parameters of the joint connections by introducing standard post bolts in addition to frangible shear bolts at downstream locations. This parameter change increases the load-carrying capacity and reliability of downstream joints, preventing premature failure while maintaining the controlled sequential failure mechanism. The result is that more rails (up to 5 rails) can telescope in sequence, significantly increasing energy absorption capacity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design ensures controlled telescoping and increased energy absorption by ensuring upstream frangible bolts fail before downstream ones, allowing more rails to engage sequentially and absorb impact energy effectively.
Implementation Method 1
a first set of frangible bolts which are the sole bolts connecting rail 2 and adjacent rail 3 together; and a second set of frangible bolts which connect rail 3 and adjacent 4 together
Implementation Method 2
an impact slider assembly joined to a downstream portion of terminal rail 1, surrounding a downstream portion of terminal rail 1 and an upstream portion of an adjacent and rail 2
Data Source
AI summary
A guardrail or other energy absorbing apparatus includes a plurality of terminal end rails extending longitudinally extend between a plurality of support posts, wherein a first four of said plurality of rails (labelled 1-4 below) situated at a terminal end of a guardrail, or impact end of an energy absorbing apparatus; are connected to one another at respective downstream and upstream ends via: an impact slider assembly joined to a downstream portion of terminal rail 1, and surrounding a downstream portion of terminal rail 1 and an upstream portion of an adjacent rail 2; a first set of frangible bolts which are the sole bolts connecting rail 2 and adjacent rail 3 together; and a second set of frangible bolts which connect rail 3 and adjacent rail 4 together, wherein at least one standard post bolt connects the rails 3 and 4 to a post at this joint.