MPC
Research Projects (2002-03)

Identifying Number

MPC-235

Project Title

Highly Flexible Crash Barriers

University

Colorado State University

Project Investigator

Paul Heyliger
Department of Civil Engineering
Colorado State University
(970)491-6685 or Fax (970)491-7727
prh@engr.colostate.edu

External Project Contact

N/A

Project Objective

The conceptual elements of highly flexible crash barriers will be investigated and conclusions drawn regarding the efficacy of such an approach using a combination of analytical modeling techniques and a small-scale experimental study. The first-year phase is an initial investigation of an overall effort to determine the load-displacement behavior of these structural components. Such an effort includes the following objectives:

• Develop a three-dimensional elastica element model of highly deformable wood elements.
• Determine the basic parametric effects of element and network properties on the load-deformation behavior of such components and their ability to absorb energy with non-permanent deformation.
• Construct a small-scale prototype and test the load-deformation behavior under static and dynamic forces with very large deformations.

Project Abstract

Most crash barrier systems are designed to provide certain margins of safety to life and property with inherent low cost. Most barriers require immediate replacement after impact, resulting in an increase in replacement cost, additional materials, and potential danger to work crews along with inconvenience to others as the work is completed. In addition, the damage to individual motorist's cars or trucks can be significant, as can the potential for injury and death.

In this study, we investigate a new paradigm of crash barriers that absorb energy of impact by undergoing very large deformations (thereby lessening the blow to drivers and occupants) that are completely elastic. Hence, rather than creating a rigid structure out of wood or metal that is designed to have strength sufficient to survive an impact by either yielding or fracturing, we propose a system or network of highly flexible wood elements that can deflect a large amount but when unloaded, will return to their original position.

There are two separate phases to this research: a numerical model that allows us to predict the response given a specific design, and a small experimental prototype that will allow us to compare theoretical results and determine practical limitations of such an approach. Our numerical model uses a three-dimensional elastica representation of long wood rods, which can undergo large bending deformation but the rods have a diameter that is very small relative to the length and hence can bend a large amount while remaining below the elastic modulus of rupture. Such an analysis is highly non-linear in the geometric sense, and developing this model will compose a large part of the research. Once completed, we will use this model to test various configurations of the wood elements in a network fashion, and also the various parameters such as cross-sectional properties, modulus, length, and orientation. Our testing specimen will be a small(less than 24 inches on a side) wood-rod network whose configuration will be determined after completion of the parametric studies using our numerical model.

Our entire hypothesis is based on the possibility of being able to design a cost-effective "soft" barrier that can successfully compete against modern crash barriers under certain situations where damage to vehicles or difficulty of replacement make such flexibility advantageous. Our initial work will test this hypothesis for basic design configurations with the eventual goal of developing conclusions as to the possibilities and limitations of such an approach.

Task Descriptions

• Task 1 – Complete formulation and development of three-dimensional structural elastic network algorithm. (February 2003)
• Task 2 – Testing of wood elements as an elastica: one-dimensional experiments. (May 2003)
• Task 3 – Completion of parametric studies for wood element properties using numerical model. (July 2003)
• Task 4 – Comparison of theoretical and experimental results for one-dimensional test specimens. (September 2003)
• Task 5 – Construction of prototype flexible wood element network and testing of low strain rate load-deformation behavior. (December 2003)
• Task 6 – Comparison of theoretical and experimental predictions of soft-barrier load-deflection behavior. (March 2004)
• Task 7 – Development of final guidelines and conclusions and complete discussion of design considerations and physical limitations for flexible crash barriers. (October 2004)

Milestones, Dates

• Starting Date: November 1, 2002
• Project Milestones:
  • Interim Report: December 2003
  • Final Report: December 2004
• Ending Date: October 31, 2004

Yearly and Total Budget

Year one budget is $37,539

Student Involvement

One graduate student and at least one undergraduate student will work on the project, with the graduate student completing most of the numerical studies and the undergraduate student involved in the construction and completion of the experiments.

Relationship to Other Research Projects

No other related MPC projects to date.

Technology Transfer Activities

This research will provide significant thrust to two key areas: (1) the use of wood, composite, or metal in a situation where very large deflections are not only acceptable, they are necessary, and (2) a completely different type of barrier that could be used not only for crashes, but many other applications. For example, the technology that will be developed as part of this research could be used as shock absorbers for air-dropped supplies. At a smaller level, there is no limitation on the size of the fiber elements we will be using, and hence our theoretical predictions could be used for materials such as fiberglass mechanics or even nanotube clusters.

Potential Benefits of the Project

If successful, this research could lead to a completely new class on crash barriers that possess the following traits:

• Less damage to vehicles.
• Low cost.
• Ability to survive multiple impacts without replacement.
• Less chance of injury or death to occupant of vehicle.
• Potential applications to other fields and areas.

Clearly, such a design could save thousands of dollars in material and medical costs if implemented on a grand scale. We are not predicting such benefits, but the possibilities and certainly tremendous. This study will provide much needed information to determine if such an approach is feasible and to what extent its implementation could be realized.

TRB Keywords

Inelastic design, crash barrier