Laefer, Debra F.
Laefer, Debra F.
Laefer, Debra F.
Now showing 1 - 10 of 124
- PublicationUnderstanding microcrystalline waxes for the seismic protection of art objectsUse of microcrystalline waxes for the protection of ceramic art objects from seismic events is an inexpensive and relatively popular technique. This paper presents performance results for three commercial, microcrystalline waxes based on anchoring requirements of resisting seismic-induced tensile and shear forces, while exhibiting a ductile failure mode to prevent objects from suddenly detaching themselves from their display units and becoming sufficiently mobile to fall off stands or collide with other art objects. As many of the testing techniques described in this paper are not easily accessible to the average museum conservator, and some of the products may not be readily available, emphasis is placed on establishing an expected range of strengths, and correlations are suggested for predicting the general performance of any microcrystalline wax in a specific application arrangement, based on easily performed, simplified tests that were found to be able to predict tensile capacity within 10%. Distinctive performance trends were found amongst various products with capacity being as much as 183 kPa in tension and 42kPas in shear. The pre-application of a methylacrylate copolymer to the bonding surface consistently improved performance, while increasing wax thickness did not.
- PublicationCharacteristic damage concentration: a new damage index for historic interiorsA crack-by-crack documentation and characterization of damage for historic interiors is often an extremely resource-intensive process resulting in either the investment of an enormous amount of resources or a low-quality record. Neither situation readily lends itself to longitudinal studies. To overcome this situation, a new damage documentation system is devised for the recording and categorization of damage for the interior spaces of historic structures. In this paper, the system is presented in the context of an early 20th century American church that was experiencing on-going damage. The structure was evaluated three times over a six-year period. The graphical results enable visualization of the progression of damage over time and an acute understanding as to its spatial distribution.
- PublicationDynamic analysis of a plate resting on elastic half-space with distributive propertiesThis work gives a semi-analytical approach for the dynamic analysis of a plate resting on an elastic, half-space with distributive properties. Such calculations have been associated with significant mathematical challenges, often leading to unrealizable computing processes. Therefore, the dynamic analysis of beams and plates interacting with the surfaces of elastic foundations has to date not been completely solved. To advance this work, the deflections of the plate are determined by the Ritz method, and the displacements of the surface of elastic foundation are determined by studying Green's function. The coupling of these two studies is achieved by a mixed method, known in the theory of elasticity as Zhemochkin’s method, which allows determination of reactive forces in the contact zone and, hence, the determination of other physical magnitudes. The obtained solutions can be applied to study the dynamic interaction between soils and structures and to assess numerical computations through various numerical methods programs. Natural frequencies, natural shapes, and the dynamic response of a plate due to external harmonic excitation are determined. Validation with a Winkler problem illustrates the distributive property effects on the results of the dynamic analysis.
- PublicationHomogenization of a Composite, Multi-Girder Bridge Deck as an Equivalent Orthotropic PlateMost bridge decks are orthotropic, because of the orthotropic nature of their component parts (e.g. isotropic slabs, grillages, T-beam bridge decks, multi-beam bridge decks, multi-cell boxbeam bridge, and slabs stiffened with ribs of box section). Thus, the orthotropic plate theory plays an important role in the static and dynamic analysis of bridges. For example, a multicellular Fiber Reinforced Polymer (FRP) composite bridge deck can be modeled as an orthotropic plate with equivalent stiffnesses that account for the size, shape, and constituent materials of the cellular deck. Thus, the complexity of material anisotropy of the panels and orthotropic structure of the deck system can be reduced to an equivalent orthotropic plate with global elastic properties in two orthogonal directions – parallel and transverse to the longitudinal axis of the deck cell. This paper investigates a homogenization of composite, orthotropic, three-span, multi-girder bridge to explore the concept of the volumetric and mass fractions of a reinforced composite material. This homogenization takes into account all properties of this composite structure (deck slab, girders and diaphragms). From those, all the equivalent orthotropic plate properties were obtained. The work is highly relevant with respect to evaluating the dynamic interaction between bridges and vehicles.
- PublicationForensic investigation methodology for structures experiencing settlementThe progressive settlement of a plantation in North Carolina is explored through a post-damage inspection. If a building is experiencing settlement or other deleterious movement, the underlying causes must be established to prevent further damage and ensure effective repair. This article outlines a methodology for the forensic investigation of historic structures experiencing what may appear to be structural distress and provides a case history exemplifying the effectiveness of the proposed method for establishing settlement-related movements. Through simple and straightforward engineering principles, a logical and methodical approach can be applied to determine contributing factors to historic-building distress. Key elements of this method include documentation of the history of architectural damage and apparent distress, consideration of initial and existing structural loading capacity (including both the structural system and specific materials), exploration of soil conditions, and investigation of groundwater factors.
- PublicationGeneration of a Building Typology for Risk Assessment due to Urban TunnellingMajor underground infrastructure projects are often located beneath dense urban environments in an effort to relieve congested areas. The effects of urban tunnelling works can impinge on hundreds, if not thousands of structures, many of which a re historically significant. Tunnel-induced ground movements can result in significant building damage and, therefore, require an accurate risk assessment of the existing built heritage and the selection of appropriate preventative measures. Damage prediction techniques extend from traditional empirical and analytical methods to modern computational modelling techniques. A common requirement for many damage assessment methodologies is the development of a building typology. Such typologies can provide critical information where measured drawings, particularly of structural elements (e.g. floor and wall thickness), are not otherwise available. This study begins to establish a building typology for a historic area of Dublin's city centre for which an underground railway system has been planned.
- PublicationPhysical and chemical properties of pre-regulated American cementsThe characteristics of pre-regulated American cements differ fundamentally from those manufactured afterwards, both in terms of physical and chemical properties and with regard to cement consistency. This paper presents an overview of cementitious products available in America from 1875 to 1909. Historical testing data is compared to that expected of modern materials. The data presented show that a lack of consistency and a less rigorous manufacturing processes resulted in an original product much inferior to modern expectations regarding the compressive capacity of concrete and that this was true for both natural and Portland cements.
- PublicationFactors affecting traffic-generated vibrations on structures and the masonry minaret of Little Hagia SophiaIncreasingly buildings and their occupants are negatively impacted by traffic–induced vibrations. The continuous application of vibrations is particularly detrimental for historic masonry buildings and for very modern structures constructed of strong and light materials. Population and land development trends indicate greater proximity of traffic flow near buildings in coming years. This paper outlines the factors influencing the frequency content and the magnitude of vibrations on nearby structures in an attempt to enable local communities and their designers to be more proactive in vibration mitigation. Using these described factors, the paper assesses the effects of traffic-induced vibrations on a portion of a monumental masonry building: the minaret of Little Hagia Sophia Mosque (former Byzantine Church of the Saints Sergius and Bacchus) based on adjacent railway field measurements.
- PublicationThree-dimensional spatial information systems : state of the art reviewA spatial information system (SIS) is critical to the hosting, querying, and analyzing of spatial data sets. The increasing availability of three-dimensional (3D) data (e.g. from aerial and terrestrial laser scanning) and the desire to use such data in large geo-spatial platforms have been dual drivers in the evolution of integrated SISs. Within this context, recent patents demonstrate efforts to handle large data sets, especially complex point clouds. While the development of feature-rich geo-systems has been well documented, the implementation of support for 3D capabilities is only now being addressed. This paper documents the underlying technologies implemented for the support for 3D features in SISs. Examples include ESRI’s ArcGIS geo-database with its support for two-and-a-half dimensions (2.5D) in its Digital Elevation Model (DEM) and Triangular Irregular Network (TIN), the more recent development of the Terrain feature class, and support for 3D objects and buildings with its multi-patch feature class. Recent patents and research advances aim to extract DEMs and TINs automatically from point cloud data. In this context, various data structuring innovations are presented including both commercial and open source alternatives.
- PublicationSteps toward a probabilistic framework for tunnelling damageGlobally, the high rates of urbanization over the past century have spurred unprecedented levels of tunnel construction. With each tunnel installation, there is a large affiliated risk for damage to aboveground structures, especially those of unreinforced masonry. Such damage (and the subsequent costs and litigation) occur, despite huge sums committed to construction monitoring and pre-tunnel mitigation. Arguably, damage still happens because the wide range of parameters and the extent of their variability are not sufficiently considered in the risk assessment process. To address these uncertainties, a probabilistic framework for the large-scale risk assessment of existing, unreinforced masonry buildings subjected to bored tunnelling is proposed by the Urban Modelling Group (UMG) at the University College Dublin (UCD). This paper summarizes the initial steps needed to achieve such a framework.