Martin Marietta Materials, Inc. is an American-based company and a member of the S&P 500 Index. The company is a supplier of aggregates and heavy building materials, with operations spanning 26 states, Canada and the Caribbean. In particular, Martin Marietta Materials supplies resources for the construction of roads, sidewalks and foundations.Martin Marietta's Magnesia Specialties business provides a full range of magnesium oxide, magnesium hydroxide and dolomitic lime products.The present-day materials business is distantly descended from Superior Stone, an aggregates company founded in 1939 in Raleigh, North Carolina. In 1959 the company was purchased by the American-Marietta Corporation, which merged with the Glenn L. Martin Company a year later to form Martin Marietta Corporation. Martin Marietta in turn merged with Lockheed Corporation in 1995, and a year later the "new" Martin Marietta was spun off as independent company, with Lockheed Martin retaining various aerospace, defense, and other manufacturing lines of business..
One challenge with structural health monitoring (SHM) for highway bridges is managing large amounts of response data. This paper discusses a proposed SHM system that was developed to collect, store, and prioritize excitation data caused by traffic loads, especially overweight trucks. In the proposed system, a microcontroller is used to trigger the release of data. A radio-frequency identification (RFID) reader and antenna combinations are installed on the truck and at the bridge of interest. The truck information, including axle weights and configuration, is assigned to the RFID tag and placed on the windshield. The transponder at the bridge detects the approaching RFID tag and triggers the data acquisition system to release the response (strain) data from a sensor interrogator through a microcontroller to a network portal (such as a cellular modem or Ethernet radio) while the truck passes over the bridge. Field tests were conducted to validate the proposed system. The optimal position of the vehicle relative to the transponder, the height and horizontal position of the transponder, and the location of the RFID tag were investigated for a vehicle travelling at 105 kph (65 mph). The tests results indicated that the triggering system was successful, but it was sensitive to the position of the tag relative to the transponder.
The acceptability of unbonded neoprene caps has been established for over 20 years, and both bonded (ASTM C617) and unbonded (ASTM C1231) caps are currently used in commercial testing and in research. In this study, compressive strength results from one hundred 6 x 12 in. (152 x 304 mm) cylinders cast from a single batch of ready mixed concrete, tested with both types of caps, indicated that while either cap type produced approximately equivalent strength, there was a significant difference in the standard deviations of the two populations. Further, strength obtained with unbonded caps was less sensitive to variations in cylinder eccentricity during testing. Response to eccentricity was most pronounced at 1/4 in. (6 mm), with neoprene-capped specimens showing increased strength and sulfur-capped specimens showing decreased strength. Predominant failure modes differed with both cap type and eccentricity. Observed differences in variability would impact the probability of meeting building code requirements for acceptance based on compressive strength.
Part I of this paper analyzed compressive strength results from one hundred 6 x 12 in. (152 x 304 mm) cylinders cast from a single batch of ready mixed concrete, tested with both bonded and unbonded cylinder caps, concluding that while either cap type produced approximately equivalent strength, there was a significant difference in the standard deviations of the two populations. Further, strength obtained with unbonded caps was less sensitive to variations in cylinder eccentricity during testing. Part II continues with the observations that predominant failure modes differed with cap type and eccentricity. There is some evidence of connection between the end condition or flatness of the cylinders and failure mode.
The Advanced Composites Consortium is a US Government/Industry partnership supporting technologies to enable timeline and cost reduction in the development of certified composite aerospace structures. A key component of the consortium's approach is the development and validation of improved progressive damage and failure analysis methods for composite structures. These methods will enable increased use of simulations in design trade studies and detailed design development, and thereby enable more targeted physical test programs to validate designs. To accomplish this goal with confidence, a rigorous verification and validation process was developed. The process was used to evaluate analysis methods and associated implementation requirements to ensure calculation accuracy and to gage predictability for composite failure modes of interest. This paper introduces the verification and validation process developed by the consortium during the Phase I effort of the Advanced Composites Project. Specific structural failure modes of interest are first identified, and a subset of standard composite test articles are proposed to interrogate a progressive damage analysis method's ability to predict each failure mode of interest. Test articles are designed to capture the underlying composite material constitutive response as well as the interaction of failure modes representing typical failure patterns observed in aerospace structures.
A braced-frame, lateral-load-resisting system was developed in which inelastic deformations due to seismic loading were intended to be isolated to easily replaceable buckling restrained braces (BRB). Bolted brace-to-gusset and gusset-to—beam and column connections were utilized to facilitate simple brace and gusset plate installation and replacement. Full-scale testing using two BRBs was executed to assess performance. Analytical frame models were developed using the nonlinear load-deformation characteristics of the braces. The experimental and analytical results were compared to validate reasonable nonlinear parameters for industry use. All-bolted brace connections designed per AISC requirements provided adequate capacity to develop the BRBs. With proper detailing, inelastic deformations can be isolated substantially to the BRBs such that a repairable system is achieved. Load-deformation data for individual braces as provided by the supplier can be used to create reasonable analytical models for frames designed with all-bolted connections.
