Andrew Davol

STRUCTURAL CHARACTERIZATION OF FIBER-REINFORCED COMPOSITE SHORT- AND MEDIUM-SPAN BRIDGE SYSTEMS

The paper describes the development of a new structural system for short and medium span bridges wherein use is made of both advanced composites and conventional materials such as concrete. The concept uses prefabricated composite tubes as girders which are then filled with concrete, after which a conventional precast or cast-in-place, or advanced composite, deck system is integrated to form the bridge superstructure. The paper presents experimental results of large-scale tests aimed towards the structural characterization of the girders, anchorages, and girder-deck assemblies for both serviceability and ultimate limit states.

A Cartilage Growth Mixture Model With Collagen Remodeling: Validation Protocols

A cartilage growth mixture (CGM) model is proposed to address limitations of a model used in a previous study. New stress constitutive equations for the solid matrix are derived and collagen (COL) remodeling is incorporated into the CGM model by allowing the intrinsic COL material constants to evolve during growth. An analytical validation protocol based on experimental data from a recent in vitro growth study is developed. Available data included measurements of tissue volume, biochemical composition, and tensile modulus for bovine calf articular cartilage (AC) explants harvested at three depths and incubated for 13 days in 20% fetal borine serum (FBS) and 20% FBS+beta-aminopropionitrile. The proposed CGM model can match tissue biochemical content and volume exactly while predicting theoretical values of tensile moduli that do not significantly differ from experimental values. Also, theoretical values of a scalar COL remodeling factor are positively correlated with COL cross-link content, and mass growth functions are positively correlated with cell density. The results suggest that the CGM model may help us to guide in vitro growth protocols for AC tissue via the a priori prediction of geometric and biomechanical properties.

Flexural Behavior of Hybrid Fiber-Reinforced Polymer/Concrete Beam/Slab Bridge Component

An experimental and analytical investigation on the flexural behavior of a hybrid fiber-reinforced polymer (FRP)/concrete beam/slab bridge component is presented and discussed. The beam element consists of a carbon/epoxy cylindrical shell filled with concrete where the FRP shell serves the dual purpose of formwork and reinforcement. A conventional RC slab connects to the FRP/concrete girder through steel dowels anchored in the girder concrete core. The composite beam/slab system was experimentally studied through a full-scale 4-point bending flexural test. Section analysis procedures and approximate formulas for the flexural response of FRP/concrete beam/slab units were developed and correlated with experimental results. The shear connection efficiency was additionally evaluated through a push-out test and correlated with codified recommendations. The importance of stress concentrations on holes drilled for connection purposes on generally anisotropic shells was assessed. The investigation showed that the presented hybrid FRP/concrete concept is a viable option for beam-and-slab bridges.

Extended Two Compartmental Swelling Stress Model and Isotropic Cauchy Stress Equation for Articular Cartilage Proteoglycans

Proteoglycans (PGs), a constituent of cartilaginous tissues, have a negative fixed charge (FC) that causes an intratissue swelling stress [1]. This swelling stress is thought to balance tensile stress in the collagen network and contribute to the aggregate modulus of articular cartilage (AC) [1]. Stress constitutive equations that accurately characterize mechanical behavior of individual tissue constituents are crucial for the development of accurate total tissue models. The goal of this study is to extend the range of an existing two compartmental model for PG swelling stress by Basser et al. [1], and develop a continuum level equation for PG Cauchy stress. Specifically, the first aim is to increase the accuracy of the two compartmental model proposed in [1], to a lower range of FC density (FCD) typically found in bovine calf AC. The second aim is to use the extended model to develop a continuum level strain energy function and associated isotropic PG Cauchy stress constitutive equation.Copyright

A Bimodular Second-Order Orthotropic Stress Constitutive Equation for Cartilage

The design of tissue-engineered constructs grown in vitro is a promising treatment strategy for degenerated cartilaginous tissues. Cartilaginous tissues such as articular cartilage and the annulus fibrosus are collagen fiber-reinforced composites that exhibit orthotropic behavior and highly asymmetric tensile-compressive responses. They also experience finite deformations in vivo. Successful integration with surrounding tissue upon implantation likely will require cartilage constructs to have similar structural and functional properties as native tissue. Reliable stress constitutive equations that accurately characterize the tissue’s mechanical properties must be developed to achieve this aim. Recent studies have successfully implemented bimodular theories for infinitesimal strains (Soltz et al., 2000; Wang et al., 2003); those models were based on the theory of Curnier et al. (1995).Copyright

Investigation of Cartilage Biomechanical Properties: Dependence on Strain, Direction, and Biochemical Composition

Articular cartilage (AC) serves as the major load bearing material within synovial joints and provides a low friction and wear resistant interface. As an avascular tissue, AC lacks the ability to repair structural damage or degeneration. Thus, the need for replacement tissue was a motivating factor in the development of cartilage tissue engineering. Recently, a finite element model (FEM) of cartilage growth [1] has been developed to simulate various growth conditions such as in vitro (outside the body) tissue growth experiments. In order to validate growth laws used in the FEM, empirical measurements of AC properties (mechanical and biochemical) before and after in vitro growth are needed. The goal of this study is to design protocols to comprehensively quantify the biomechanical structure-function relations of AC.© 2007 ASME