T. Russell Gentry

Accelerated Test Methods to Determine the Long-Term Behavior of FRP Composite Structures: Environmental Effects

Technical literature on the subject of environmental exposure effects related to determining accelerated test methods for the prediction of long-term performance of FRP composite materials for highway structural applications is reviewed in this paper. Effects of environmental exposure of a chemical and a thermal nature on fiberreinforced polymer (FRP) composites are considered. Such exposures include temperature, moisture and chemicals in liquid solutions or in gaseous mixtures. The effects include the changes in the physical and mechanical properties of the composite materials. Such changes are typically related to the degradation or deterioration of the composite material. Synergistic effects of mechanical load and exposure are also reviewed. The review is divided in topics entitled Materials, Exposure Conditions, Experimental Techniques, Failure Mechanisms and Theoretical Modeling.

A model specification for FRP composites for civil engineering structures

Abstract A proposed model specification for FRP composite materials for use in civil engineering structural systems is described in this article. The model specification provides a classification systems for FRP materials, describes admissible constituent materials and limits on selected constituent volumes, describes tests for specified mechanical and physical properties, specifies limiting values of selected properties in the as-received condition and in a saturated state, and provides a protocol for predicting long-term property values subjected to accelerated aging based on the Arrhenius model. The model specification is included as an appendix to the article.

PROGRESSIVE TEARING FAILURE OF PULTRUDED COMPOSITE BOX BEAMS: EXPERIMENT AND SIMULATION

The phenomenon of progressive tearing failure in thin-walled, rectangular-cross-section pultruded composite beams has been observed in beams loaded in flexure. In this failure mode, unique to composite materials, tearing refers to the separation of the vertical and horizontal members at the corners of the cross-section. In the experimental part of this investigation, pultruded composite box beams were loaded in three-point bending and subjected to a midspan deflection large enough to cause failure. This test measured the force vs displacement behavior of the beam. Tearing typically begins directly under the loading head and progresses toward the ends of the beam as vertical deflection increases. A methodology to simulate the three-point bending test numerically is being developed. The tearing action was modeled by using the LS-DYNA3D explicit finite-element software package. Comparison of numerically obtained force vs displacement results and experimental data showed that the finite-element model captures the overall behavior of the beam with sufficient accuracy to demonstrate its feasibility.

Performance of Glued-Laminated Timbers with FRP Shear and Flexural Reinforcement

Glued-laminated wood beams (glulams) have low allowable shear stresses relative to competitive engineering wood products such as parallel strand lumber and laminated veneer lumber. For heavily loaded applications such as garage door headers, the lower shear allowable stresses typically necessitate the use of larger glulam members relative to other engineered lumber. This paper reports on experimental research aimed at increasing the shear capacity of glulams. To increase the shear strength, a series of fiber-reinforced polymeric (FRP) pins are inserted into holes drilled transversely across the plies of the glulam. These pins are epoxy-bonded into place after the glulam has been produced. The test results show that the shear strength scatter in the pinned set of glulams is significantly reduced as compared to the unpinned specimens. Two- and three-parameter Weibull estimates of the service-level allowables increases between 40% and 100% for specimen sets reinforced by the FRP pins. The transverse reinforc...

Transformative Solar Panels: A Multidisciplinary Approach

This paper focuses on the applications of geometrically transformable and expandable structures with deployed “energy production” mode and retracted “wind shedding” mode to replace the fixed photovoltaic (PV) panels and racking systems currently used in buildings rooftop installations. The significance of this expandable geometric system relies on its embedded motion grammar, i.e. rotation and translation transformations, in the system. The research draws inspiration from reconfiguration of compound tree leaves in nature, and addresses issues of redesign and modeling challenges that led to digital fabrication of the prototype. Finally, the research studies the development of a multidisciplinary research from the distributed cognition point of view, and emphasizes on the role of an iterative creation, sharing and reflection method for the development of a common ground for a successful collaboration.

In Situ Materials and Structural Assessment of Stress-Laminated Deck Bridge Treated with Chromate Copper Arsenate

A bridge consisting of three 6.7-m spans with a stress-laminated deck was constructed in 1991 in the Spirit Creek State Forest near Augusta, Georgia. The bridge was constructed by the Georgia Forestry Commission, with guidance from the U.S. Department of Agriculture, Forest Service, Forest Products Laboratory (FPL). Water-borne chromated copper arsenate lumber was used for the deck, instead of the oil-borne preservatives recommended by AASHTO. The bridge was initially monitored by FPL and remained in service from 1994 to 2001 with no maintenance, at which time the bridge was inspected and load tested and the posttensioning bars were restressed. In 2005 the bridge was again inspected and load tested, and the bars were retensioned. The results of the inspection and load tests are presented. The overall condition of the bridge is reported, along with details on the moisture condition, overall deck deflection, and timber strains under load. Details on the loss of posttensioning forces in the bars, and an investigation of the causes of this loss, are presented.