Guardrail Deflection Analysis – Phase I (405160-24)

Problem Statement

Designers are often faced with having to design beam guardrail systems to accommodate a variety of allowable maximum deflections to fit specific site conditions. Tools for determining those deflections are limited, and it is time consuming to research crash test data to review work that is already conducted. With the wealth of information available through crash test reports and FHWA acceptance letters, information can be categorized and tabulated into a table for use by designers for selecting appropriate beam guardrail for the desired maximum deflection.

Background

The AASHTO Roadside Design Guide contains a table (5.4) in Chapter 5 that lists deflections for various beam guardrail configurations. The majority of values listed in the table are based on simulations and few have field tests to support deflection values using a 2000 kg (4400 lb) sedan only.

Objective

The objective of this study is to review available crash test data on beam guardrail systems to provide current information on dynamic deflections of a variety of beam guardrail systems. The beam guardrails to be included in this study are W-Beam and Thrie-Beam rail elements including 12 gauge and 10 gauge thickness.

A subsequent phase (Phase II) to be proposed the next cycle shall have the objective of simulating additional systems to broaden the range of system configurations available in such synthesis.

Benefits

The information compiled from this research will aid designers in developing site specific solutions for beam guardrail systems by providing them with an informational summary presenting deflection characteristics. This will reduce time spent searching for information on deflection data, and will result in greater consistency in application.

Products

TTI will provide a tabular listing of system configurations as variables along with their measured crash test dynamic deflections. The table will be presented in a summary report that outlines the processes used to compile the data in the table.

Implementation

As stated above, the information compiled from this research will aid designers in developing site specific solutions by choosing an appropriate guardrail system from the tabulated deflection data. The results of this research are expected to be implemented without impeding issues since neither new standards nor policy are derived from this synthesis study.

Work Plan

The researchers will review available literature of crash tests conducted using beam guardrails with a focus on NCHRP Report 350 and MASH test level 3-11 (2000P pick-up truck impact on length of need of the beam guardrail). The researcher will synthesize present systems deflection information:

1. 6 ft-3 inch span system
2. 3 ft-1.5 inch span system
3. 6 ft-3 inch with one post omitted (12 ft-6 inch span) system.

Variables within each system that will be included in this study are:

1. Single rail
2. Nested rail
3. 12 gauge rail
4. 10 gauge rail
5. Thrie beam rail
6. W-Beam rail
7. 27-inch (true or metric) rail height
8. 31-inch rail height.

The researchers will not investigate guardrail terminals or transitions. Phase I will also identify configurations that were not crash tested in accordance with NCHRP Report 350 or MASH criteria and develop a cost estimate for simulation of these configurations.

Phase II will simulate MASH crash tests for the untested configurations identified in Phase I. Phase II work may not necessarily include all the simulation work identified through Phase I and it will have its own budget in a subsequent proposal subject to the pool fund approval. The researchers will tabulate these deflection data into a format suitable for utilization by design engineers.

FINAL REPORT ON PHASE I:

   Guardrail Deflection Analysis:  Phase I

   Guardrail Deflection Analysis Spreadsheet referenced in the above report.