Francisco Gonzalez

Deformation Behavior of Welded Steel Sandwich Panels under Quasi-Static Loading

For the past two decades, the Federal Railroad Administration (FRA) Office of Research and Development has sponsored research conducted by the Volpe National Transportation Systems Center (Volpe Center) in safety matters related to the transportation of hazardous materials by railroad tank cars. Recent research conducted by the Volpe Center has included the application of semi-empirical and computational (i.e., finite element analysis) methods to estimate the puncture resistance of conventional railroad tank cars under generalized head and shell impact scenarios. Subsequent work identified sandwich structures as a potential technology to improve the puncture resistance of the commodity-carrying tank under impact loading conditions. This paper summarizes basic research (i.e., testing and analysis) conducted to examine the deformation behavior of flat-welded steel sandwich panels under two types of quasi-static loading: (1) uniaxial compression; and (2) bending through an indenter. The objectives of these tests were to: (1) confirm the analytical and computational (i.e., finite element) modeling of sandwich structures, (2) examine the fabrication issues associated with such structures (e.g., material selection and welding processes), and (3) observe the deformation behavior and local collapse mechanisms under the two different types of loading. In addition, the uniaxial compression tests were performed to rank or screen different core geometries. Five core geometries were examined in the compression tests: pipe or tubular cores with outer diameters equal to 2, 3, and 5 inches; a 2-inch square diamond core; and a double-corrugated core called an X-core with a 5-inch core height. The compression tests showed excellent repeatability of structural (i.e., force-crush) response for panels with similar cores and welding. The 3-inch pipe core and the diamond core were selected as candidate cores for the next test series because they possess attributes of moderate strength and moderate relative density. In addition, force-crush curves calculated from finite element analysis were in reasonable agreement with the measured curves for all cores. Bend tests using a 12-inch by 12-inch indenter with 1-inch radius rounded edges were also conducted. The panels were simply-supported over 4-inch diameter rollers spanning 24 inches between the centers of the rollers. The bend tests included three variables: (1) core type (diamond core and 3-inch pipe core); (2) core orientation relative to the supports (cores running either parallel or perpendicular to the rollers used to support the panels); and (3) face sheet type (solid plates on both sides, strips used as face sheets on both sides, and a combination of solid plates and strips. Finite element analysis of the bend tests produced nearly identical shapes to the measured force-displacement curves.Copyright

Fire Testing of Total Containment Pressure Vessels

In North America certain hazardous materials are transported in rail tank cars that must be able to survive an engulfing liquid hydrocarbon pool fire for 100 minutes without rupture. To meet this requirement these tanks are normally equipped with pressure relief valves (PRV) and some form of thermal insulation or thermal protection (TP). These tanks sometimes have non-accident releases (NAR) due to unwanted activation of, or leakage from the pressure relief valves (PRV). These NARs are a nuisance for Industry and for this reason, the industry now wants to remove the PRVs from certain tanks. This is known as total containment and is common practice in Europe. However, Europe does not have a 100 minute fire survival requirement. This paper is about a series of fire tests of 1/3 rd linear scale US DOT 111 Tanks cars. The 2.4 m3 vessels were subjected to fully engulfing fires generated by liquid propane fueled burners.

Full Scale Tank Car Rollover Test — Survivability of Top Fittings and Top Fittings Protective Structure

Full-scale rollover crash tests were performed on three non-pressure tank car bodies in order to determine the effectiveness of two different types of protective structures in protecting the top fittings and to validate previous analytical work. This included an unprotected base case car, a car with an added protective skid weldment, and a third car with an added protective bolt-on sleeve on the unloading nozzle with a reinforcing cone. Pivoting the carbodies in a fixture about a fixed axis controlled the test conditions. The fittings or protective structures impacted a concrete target pad. Dynamic Finite Element analysis work was done prior to each test to determine proper test conditions and parameters.Copyright

Rail Tank Car Total Containment Fire Testing: Results and Observations

The frequent incidences of Non-Accident Releases (NARs) of lading from tank cars have resulted in an increasing interest in transporting hazardous materials in total containment conditions (i.e., no pressure relief devices). However, the ability of tank cars to meet thermal protection requirements provided in the Code of Federal Regulations under conditions of total containment has not been established. The intent of this effort was to evaluate through a series of third-scale fire tests, the ability of tank cars to meet the thermal protection requirements under total containment conditions, with a particular focus on caustic ladings. A previous paper on this effort described the test design and planning effort associated with this research effort.A series of seven fire tests were conducted using third scale tanks. The test fires simulated fully engulfing, hydrocarbon fueled, pool fire conditions. The initial tests were conducted with water as a lading under jacketed and non-jacketed conditions and also with different fill levels (98% full or 50% full). Additionally, two tests were conducted with the caustic, Sodium Hydroxide as the lading, each test with a different fill level. In general, the tanks with water were allowed to fail or reach near-failure conditions, whereas, the tests with the caustic lading were not allowed to proceed near failure for safety reasons. This paper describes the results and observations from the fire tests, and discusses the various factors that affected the fire test performance of the test tanks.Review of results from the one-third scale tests, and subsequent scaling to full-scale suggest that a full-scale tank car filled with 50% NaOH solution is unlikely to meet the 100-minute survival requirement under conditions of total containment.Copyright

Evaluation of Risk Reduction From Tank Car Design and Operations Improvements: An Extended Study

Critical derailment incidents associated with crude oil and ethanol transport have led to a renewed focus on improving the performance of tank cars against the potential for puncture under derailment conditions. Proposed strategies for improving puncture performance have included design changes to tank cars as well as operational considerations, such as reduced speeds and upgraded brake systems. In a prior paper on this topic, the authors conceptualized a novel and objective methodology for quantifying and characterizing the reductions in risk that result from changes to tank car design or to the tank car operating environment.This paper describes an extension of that effort to include additional derailment cases, additional operating speeds, considerations for alternate train configurations, such as Distributed Power (DP) and Electrically Controlled Pneumatic (ECP) brakes, as well as options for component level studies. In essence, the developed methodology considers key elements that are relevant to tank car derailment performance and combines these elements into a consistent probabilistic framework to estimate the relative merit of proposed mitigation strategies. The relevant elements considered include variations in the derailment scenarios, chaotic derailment dynamics, the distribution of impact loads and impactor sizes, various operating speeds, brake system differences, and variations in tank car design. The paper also provides an overview of the validation efforts which suggest that the gross dynamics of a tank car train derailment, and the resulting puncture performance of the tank cars, are captured well by this methodology.Copyright

Mitigating Strategies for Hazardous Material Trains: Evaluating the Risk Reduction

There is a significant increase in the transportation by rail of hazardous materials such as crude oil and ethanol in the North American market. Several derailment incidents associated with such transport have led to a renewed focus on improving the performance of tank cars against the potential for puncture under derailment conditions. Proposed strategies for improving puncture resistance have included design changes to tank cars, as well as, operational considerations such as reduced speeds. Given the chaotic nature of derailment events, it has been difficult to quantify globally, the overall ‘real-world’ safety improvement resulting from any given proposed change. A novel and objective methodology for quantifying and characterizing reductions in risk that result from changes to tank car designs or the tank car operating environment is outlined in this paper. The proposed methodology captures several parameters that are relevant to tank car derailment performance, including multiple derailment scenarios, derailment dynamics, impact load distributions, impactor sizes, operating conditions, tank car designs, etc., and combines them into a consistent probabilistic framework to estimate the relative merit of proposed mitigation strategies. INTRODUCTION Given that tank cars are exposed to a wide range of hazards during derailments (different impactor sizes, shapes, speeds, etc.) It is a challenge to quantify the overall safety improvement from any proposed mitigating strategy. To compare the overall effectiveness of a proposed strategy, whether it is a shell thickness increase or an operational change (such as a speed restriction), one needs an engineering and risk-based measure of how the solution is expected to perform in real life, against a variety of potential hazards. This paper describes a methodology that addressees this need by tying together the load environment under impact conditions with objective measures of tank car puncture resistance, further adapted for expected operating conditions, to calculate resultant puncture probabilities and risk reduction. While not intended to predict the precise results of a given accident, this methodology provides a basis for comparing the relative benefits or risk reduction resulting from various mitigation strategies. TECHNICAL OVERVIEW The likelihood of a given tank car being punctured during a derailment is affected by several variables and circumstances, among which are the: Derailment scenario, including the speed of derailment initiation, the surrounding terrain, etc. Impact load spectrum experienced by the tank Distribution of impactor sizes Puncture resistance of the tank shell, etc. The approach described here ties together the above variables and circumstances to evaluate the likelihood that a certain number of tanks of a given design might experience puncture during a particular derailment event. Rather than focusing on specific values of the above parameters, the approach considers the nominal distribution of values for each given parameter to ensure that the method is not specific to, or biased towards, any particular event or circumstance. An overview of this approach is presented in Figure 1. Comparison of the model against known historical derailment data for the purposes of validation is a critical element of the overall methodology. 1 Copyright

Side Impact Testing and Analyses of Unpressurized Tank Cars

There has been significant research in recent years to analyze and improve the impact behavior and puncture resistance of railroad tank cars. Ultimately, the results of this work will be used by the Government regulatory agencies in the United States and Canada to establish performance-based testing requirements and to develop methods to evaluate the crashworthiness and structural integrity of different tank car designs.This paper describes results of recent side impact testing and corresponding analyses using detailed finite element analyses (FEA). The test and analyses were performed to evaluate the side impact puncture performance of DOT-111 tank cars. The tank car was filled with water to approximately 97 percent of the volume. The tank was then sealed but not pressurized. The tank car was impacted at the Transportation Technology Center, Inc. by a 297,125-pound ram car with 12-by 12-inch ram head fitted to the ram car impacted the tank center.The analyses were on overall good agreement with the measured impact response. The lading was found to play a more significant role in the impact response than in previous testing and analyses of pressure tank cars. This is not surprising considering the reduced structural stiffness of the tanks compared to thicker pressure tank cars and the reduced effective stiffness from the initially unpressurized tank at impact. The smaller outage volume also contributes to a dramatic increase in the tank pressure as the dent formation reduces the tank volume and compresses the contents of the tank.Copyright

Rail Tank Car Total Containment Fire Testing: Planning and Test Development

Given the frequent incidences of Non-Accident Releases (NARs) of hazardous materials from tank cars, there in an increasing interest in transporting hazardous materials in total containment conditions (i.e., no pressure relief devices). However, the ability of tank cars to meet thermal protection requirements provided in the Code of Federal Regulations under conditions of total containment has not been established. Also, the modeling tool commonly used by industry to evaluate thermal protection, AFFTAC, has not been validated under these conditions. The intent of this effort was to evaluate through a series of third-scale fire tests, the ability of tank cars to meet the thermal protection requirements under total containment conditions, and also, to validate AFFTAC for such conditions.This paper describes the test design and planning effort associated with this research, including the design and evaluation of a fire test setup to simulate a credible, fully engulfing, pool fire that is consistent and repeatable, and the design and hydro-static testing of a third-scale tank specimen. The fire design includes controls on the spatial distribution and temperature variation of the flame temperature, the heat flux, and the radiative balance, to best reflect large liquid hydrocarbon pool fire conditions that may be experienced during derailment scenarios.Copyright

Analysis and Development of Performance-Based Requirements for Railroad Tank Cars

There has been significant research in recent years to analyze and improve the impact behavior and puncture resistance of railroad tank cars. Ultimately, the results of this work will be used by the Government regulatory agencies in the United States and Canada to establish performance-based testing requirements and to develop methods to evaluate the crashworthiness and structural integrity of different tank car designs.This paper describes analyses of current impact testing requirements and impact test methodologies using detailed finite element analyses (FEA). The results of these analyses are used to identify characteristics of the test methodologies that are desirable or undesirable for the test requirements in future tank car safety regulations.Copyright

Protecting Fittings on Tank Cars: Preliminary Evaluation of Pressure Tank Cars

Railroad tank car top fittings are susceptible to damage and failure in rollover derailments, which might result in release of hazardous material lading. Prior research has focused on the susceptibility of fittings on non-pressure tank cars and potential mitigation strategies. This paper presents current work that extends the analysis/test methods and lessons learned to fittings on pressure tank cars. Pressure tank cars carry significantly more hazardous materials such as Chlorine and Anhydrous Ammonia, which are classified as Toxic Inhalation Hazards (TIH). In particular, this paper presents the results of analytical modeling and validation testing of top fittings on a base design Chlorine car.In addition, the paper compares and contrasts the test methodology employed in prior full scale tests of tank car fittings against the 9 mph evaluation scenario outlined in current Federal regulations governing the design of fittings on TIH tank cars, and further explores how full scale test results may be interpreted.© 2014 ASME