Modeling of Moisture Loss in Cementitiously Stabilized Pavement Materials

The paper presents a theoretical and experimental approach for the modeling of moisture loss during the drying of cementitiously stabilized pavement materials containing varying contents of fine-grained soil. The process of moisture loss was characterized by the isotropic nonlinear diffusion theory. Laboratory tests were undertaken using general purpose Portland cement and two binders comprising industrial waste products. Measurement of material characteristics included the coefficient of moisture diffusivity and the humidity isotherm. Locally available basaltic crushed rocks and clay were respectively used as the host pavement material and fine-grained soil. Independent laboratory tests were undertaken to validate the adopted theoretical approach, which showed close agreement between the experimental and predicted results. The laboratory results indicated that moisture loss decreased with the inclusion of clay soil within the mix. As the drying progressed, the rate of moisture loss became slower, which can be explained by the reduction in the coefficient of moisture diffusivity with the decrease of moisture content.     

Test Method to Measure the Relative Capacity of Wall Panels to Evacuate Moisture from Their Stud Cavity

Rainwater penetration is the source of moisture that causes the greatest damage to building envelope assemblies. The building envelope should be designed to reduce the amount of rainwater penetration by deflection and drainage. Since it is not realistic to assume a perfect wall without any leakage, the envelope should have the drying capacity to tolerate defects that may arise from the design, construction, and aging of the exterior wall system. Systems with a greater capacity to evacuate moisture from the stud cavity are less likely to undergo moisture damage. A new testing method is developed and deployed to evaluate the relative drying capacity of six wood-framed wall panels of different configurations built into a test hut and tested within a large scale environmental chamber. The wall panels used plywood, oriented strand board (OSB), or fiberboard as sheathing, but did not include cladding. A uniform moisture source was introduced in a water tray set on a load cell at the bottom of each stud cavity. The protocol is based on the hypothesis that the potential for moving a water molecule from the bottom plate to the exterior of the stud cavity is independent of the previous journey of that molecule, i.e., whether it has traveled from the interior of the bottom plate to the surface of the plate or whether it comes from free water in a tray at the level of the bottom plate. For a given set of boundary conditions, this potential is a function of the characteristics of the wall panel, and is identified as the drying capacity of the panel or its drying by evaporation index (DEI). The value of DEI corresponds to the evaporation rate. The moisture response of wall materials enclosing the stud cavity and the evaporation rate of the moisture source were monitored. The results show that this index can be used as an indicator of the relative drying capacity of different wall systems.     

Modeling of Moisture Behavior of Wood Planks in Nonvented Flat Roofs

A computer model was extended and adapted to simulate the hygrothermal behavior of building envelope-wood components. The model was used to predict moisture movement in wood planks forming the decks of nonvented flat roofs insulated with cellulose. The gradient of water potential was considered as the driving force for moisture movement in wood. The model required the determination of convective heat- and mass-transfer coefficients, the sorption curves, the effective water conductivity for different wood species, and the hygrothermal conditions within the assembly to characterize the mass-conservation equation. Once these parameters were integrated in the computer model, this approach was then validated by carrying a simulation of the drying process of wood planks using experimental data from a large-scale test.     

Analytical Modeling of Three-Layered HMA Mixtures

This paper presents the analytical modeling of three-layered hot mix asphalt (HMA) mixtures. Conventional HMA mixtures can be regarded as a two-layered composite with asphalt-coated aggregate particles dispersed in an equivalent medium. The three-layered HMA mixtures can be constructed by introducing an intermediate layer of stiff binder coated over coarse aggregates prior to mixing them with hot asphalt cement. Based on the equivalent medium theorem reported by Eshelby in 1957 in “The Determination of the Elastic Field of an Ellipsoidal Inclusion, and Related Problems,” HMA mixtures were treated as particulate-filled composite materials. Theoretical formulations of the composite modulus were developed and finite element analysis of stress concentration in the asphalt binder was conducted. To validate the analytical results, a three-layered HMA utilizing natural asphalt (gilsonite) as the intermediate layer was prepared and dynamic modulus and indirect tensile strength tests were conducted. The lab-scale tests agreed with the theoretical results and further ascertained the benefits of utilizing the three-layered structure in HMA mixtures.     

Concept for Type-Local Instance–Global Instance Object Modeling and Application to Structural Design of Buildings

Rational data modeling is prerequisite to the computerization of design, and the use of design information in the subsequent work, in areas such as cost estimation and construction. In particular, the structural design of buildings consists of a long series of unit steps and is nonprocedural and data intensive compared with structural analysis problems that are procedural and computation intensive. Hence, there is a need to investigate the characteristics of the problem and to structure design information properly to effectively manage it in the structural design process. This paper discusses modeling concepts for managing design information efficiently and supporting the design process effectively. Type-local instance–global instance object modeling is the conceptual backbone of the model in this study and provides consistent modeling of structural components including not only primitive members such as beams and columns, but also composite elements such as floors, frames, and even whole buildings. This paper also provides core and extended object concepts for classifying structural design information into an overall design and for processing dependent temporary stages in the design. Foundational and application object concepts are introduced for extending the model to various types of structures. An integrated structural design system for buildings is developed based on these modeling concepts, and finally a brief discussion of the application of the object model throughout the entire structural design process in the integrated structural design system is given. It is expected that the modeling concepts proposed in this research can be applied to a range of other engineering applications.     

Modeling Response of Flexible High-Aspect-Ratio Wings to Wind Turbulence

Analytical modeling of the effect of wind turbulence on flexible high-aspect-ratio aircraft wings typical of unmanned air vehicles (UAVs). The wind model is derived from the Kolmogorov power-law spectrum random field turbulence model invoking the Taylor “frozen-field” hypothesis. The aerodynamic model is based on the typical-section compressible attached-flow with Kutta–Joukowski boundary conditions. The gust loading—both lift and moment—is calculated explicitly for M = 0 and M = 1 as typical of subsonic and transonic flow. The gust loading intensity is shown to decrease as the speed increases, so that the turbulence effects are not significant at transonic speeds. To calculate the wing response we use the continuum two degree-of-freedom cantilever beam model of Goland and derive explicit expressions of the spectral density of both the plunge (bending) and pitch (torsion) response for M = 0. Numerical results are presented for two illustrative wings. Most of the turbulence energy is in the 0–10H range. Since flexibility and high aspect ratio push flutter modes and speeds down, turbulence can be a significant safety issue for UAVs in particular.     

Analyses of Heated Concrete Spalling due to Restrained Thermal Dilation: Application to the “Chunnel” Fire

Two spalling mechanisms are generally quoted in the literature. The first one is due to pore pressure buildup. The second one, which is analyzed in this paper, is generated by restrained thermal dilation. We seek to model the channel tunnel fire by a thermochemoplastic constitutive model. A simplified analytical approach allows us to express mechanical variables as stresses and strains near the heated surface (the concrete wall). This study leads to introducing a “plastification” temperature and to deduce a plastification depth that can be useful for determining the spalling localization. A comparison between different cases (with and without chemical softening or decohesion) shows that thermal spalling is due to chemical decohesion (strength degradation) and not to chemical softening (rigidity reduction).     

An Application of Item Response Theory Analysis to Alcohol, Cannabis, and Cocaine Criteria in DSM-IV.

Item response theory (IRT) is supplanting classical test theory as the basis for measures development. This study demonstrated the utility of IRT for evaluating DSM-IV diagnostic criteria. Data on alcohol, cannabis, and cocaine symptoms from 372 adult clinical participants interviewed with the Composite International Diagnostic Interview--Expanded Substance Abuse Module (CIDI-SAM) were analyzed with Mplus (B. Muthen & L. Muthen, 1998) and MULTILOG (D. Thissen, 1991) software. Tolerance and legal problems criteria were dropped because of poor fit with a unidimensional model. Item response curves, test information curves, and testing of variously constrained models suggested that DSM-IV criteria in the CIDI-SAM discriminate between only impaired and less impaired cases and may not be useful to scale case severity. IRT can be used to study the construct validity of DSM-IV diagnoses and to identify diagnostic criteria with poor performance. (PsycINFO Database Record (c) 2010 APA, all rights reserved)