Lauren Stewart

Effect Of Pre-cut Asphalt Fracture Planes On Highway Guardrail Performance

The preferred procedure for steel guardrails in the state of Georgia, USA for vehicle impact employs a post-installation machine to drive the posts through a layer of asphalt placed to retard vegetation growth around the system. However, in order to avoid undesirable restraint at the ground line, the AASHTO Roadside Design Guide recommends incorporating leave-outs. Using a leave-out in vegetation barriers is seen as less desirable because of issues including significantly higher expected costs, variability in the placement and spacing of posts, and the need for variable construction scheduling. In lieu of leaveouts, predetermined fracture planes, or “pre-cuts” were installed in the asphalt and evaluated in terms of ground restraint. An experimental program was carried out on an outdoor test site. Posts were installed in pre-cut asphalt and subjected to static loading to provide a better understanding of the behavior of a post restrained with an asphalt layer at the ground line. In parallel with the experimental program, a three dimensional finite element model was developed for a guardrail post installed through an asphalt layer. The model was refined using the experimental results from the test program as well as material testing. Results from the experimental program and finite element analyses indicate that certain precutting configurations lead to significantly less ground restraint as desired.

Development of High Performance Concrete Panels for Curtain Wall Systems

There has been an increasing interest in the use of advanced materials in the design of curtain wall systems to resist blast loading. This paper summarizes a series of tests on high performance concrete (HPC) and ultra high performance (UHPC) panels to characterize the panel strength in flexure and shear for several panel types under dynamic loading conditions. The tests were performing using three types of FORTOCRETE panels supplied by USG. One set of HPC panels was lightweight concrete fiber-reinforced FORTOCRETE structural panels developed by USG. Another set of UHPC panels consisted of FORTOCRETE Armor panels that use ultra high strength fiberreinforced concrete with and without E-glass face sheets. The testing was conducted at the University of California San Diego (UCSD) Blast Simulator Test Facility. A series of 20 panel tests were performed using the three panel types. Each panel was instrumented to provide experimental data to characterize the response of the panels that are suitable for developing and validating analytical models for the various configurations of FORTOCRETE panels. The instrumentation consisted of three types of measurements: 1) load measurements of the dynamic panel reactions, 2) strain measurements of the dynamic flexural strains in the panels, 3) velocity measurements of the overall panel deflection histories, and 4) dynamic reactions. Each panel type was tested at different levels of blast loading to achieve a range of panel damage responses ranging from light to failure. The experimental data was used to develop material property data, validate analytical response models and to generalize the panel results into PI response diagrams. Based on these results, several blast curtain wall concepts were developed for GSA Level C blast loads and above and were validated in full-scale wall experiments with the UCSD Blast Simulator. 333 Structures Congress 2012

High-g Shock Acceleration Measurement Using Martlet Wireless Sensing System

This paper reports the latest development of a wireless sensing system, named Martlet, on high-g shock acceleration measurement. The Martlet sensing node design is based on a Texas Instruments Piccolo microcontroller, with clock frequency programmable up to 90 MHz. The high clock frequency of the microcontroller enables Martlet to support high-frequency data acquisition and high-speed onboard computation. In addition, the extensible design of the Martlet node conveniently allows incorporation of multiple sensor boards. In this study, a high-g accelerometer interface board is developed to allow Martlet to work with the selected microelectromechanical system (MEMS) high-g accelerometers. Besides low-pass and high-pass filters, amplification gains are also implemented on the high-g accelerometer interface board. Laboratory impact experiments are conducted to validate the performance of the Martlet wireless sensing system with the high-g accelerometer board. The results of this study show that the performance of the wireless sensing system is comparable to the cabled system.

Influence of geometric parameters on the restraint of guardrail posts by asphalt mow strips

Abstract Asphalt pavement mow strips, used as a vegetation barrier in guardrail systems, have typically been regarded as a rigid layer in roadside design. However, geometric parameters of the mow strip such as thickness and rear distance behind the post have a significant impact on the amount of restraint the asphalt layer provides to resist translation and rotation by the posts. In this paper, a standard steel guardrail post designed with a range of asphalt mow strip dimensions is evaluated. A survey of the use of asphalt pavement mow strips in the United States was undertaken to determine an initial set of mow strip designs for investigation. Static tests were performed based on these designs, and finite element models were calibrated using the test data and parallel material characterization experiments. Utilizing the calibrated finite element model, simulations were performed on a wide variety of asphalt mow strip designs. Simulation and experimental results were correlated to develop a set of quantitative performance criteria. These criteria were used to assess the amount of ground-level restraint on a guardrail post caused by a given asphalt mow strip design in comparison with the existing design recommended by American Association of State Highway and Transportation Officials.

Implementation of Bond-Slip Performance Models in the Analyses of Non-Ductile Reinforced Concrete Frames Under Dynamic Loads

ABSTRACT Non-ductile reinforced concrete frames have seismic vulnerabilities due to inadequate reinforcing details. Adequately characterizing the performance of these details is critical to the development of analytical models. This study presents a methodology to simulate the response of such frames with and without fiber-reinforced polymer column jackets. The bond-slip effects between reinforcing bars and surrounding concrete, observed in column lap-splice and beam–column joints, are modeled with one-dimensional slide line models in LS-DYNA. The model is defined from failure modes and bonding conditions observed in full-scale dynamic tests and can predict story displacements, inter-story drifts, and damage mechanisms.

ANALYSIS METHODS FOR CFRP BLAST RETROFITTED REINFORCED CONCRETE WALL SYSTEMS

A blast retrofit technique for concrete structures using carbon fiber-reinforced polymer (CFRP) layers was investigated for use in large infrastructure systems with the overarching goal of preventing against major loss of life and considerable damage that would require extensive repair. Large-scale experiments were conducted and the retrofit behavior was investigated for application on relatively large reinforced concrete walls subjected to blast-like loadings. The experimental program utilized the University of California San Diego (UCSD) Blast Simulator. The Blast Simulator is able to induce various blast-like shock waves to the test specimen in a controlled laboratory environment. The performance of this blast retrofit was tested and then analyzed using SDOF and finite element modeling methods. A finite element model was created using LS-DYNA and utilized contact algorithms for the CFRP-concrete interface. Results and comparisons between the two analysis methods are given.

Experimental and Analysis Methods for Blast Mitigating Designs in Civil Infrastructure

The incorporation of blast and shock loading into a multi-hazard framework for civil infrastructure requires consideration of the mechanical and structural behavior of the component or system outside of the traditional quasi-static and dynamic regimes and into the impulsive loading regime. In dealing with high-rate loading of this nature, material and structural response must often be evaluated experimentally in order to produce basic mechanical properties, initial design validation, and final acceptance for implementation into existing and new infrastructure. The following provides a brief summary of the fundamentals of blast loading and the extension of these types of loads into various analysis methods. Further, the chapter includes a discussion of experimental techniques used to obtain information on behaviors important to analysis. Among these is a relatively new method for experimentation using hydraulic actuators known as blast generators. Using a case study of a curtain wall system for blast response, various analysis and experimental procedures are used to highlight the process of designing and validating systems for blast mitigation.