Arcon (United States)

Structural aspects of masonry facade repairs are not always obvious at the project's outset. Stone removal or in situ repairs may cause unintended overstress or instability. Through case studies, this technical note describes our work alongside preservationists, architects, and contractors to provide masonry repairs that address the hidden challenges of structural stability in both permanent and temporary conditions.

The goal of a pipeline condition assessment program is to identify individual distressed pipe pieces or distressed sections of the pipeline that have high risk of failure and to repair such pipes in order to maintain pipeline reliability at a desired level. Implementation of a pipeline condition assessment program requires prioritization of all pipelines in the system to determine which pipelines to focus on first, selection of appropriate inspection technologies, implementation of inspection technologies, and interpretation of the inspection results. The purpose of this paper is to present a desktop model for prioritizing pipelines for inspection based on their criticality, failure risk curves for evaluating sensitivity to wire breaks for PCCP for the purposes of selecting appropriate inspection technologies, and field inspections for validating and refining the desktop model.

Reinforced concrete (RC) structures constitute a significant portion of the building inventory. The quantitative performance assessment for such structures under extreme loading events is necessary to characterize the vulnerability of built communities to natural hazards. Three-dimensional finite element analysis of RC structures has been gaining popularity, due to its capability to capture the damage accumulation and the interaction of various mechanisms ultimately leading to structural collapse. This presentation is aimed to provide an insight on the use of three-dimensional, continuum-based models for the analysis of structural components under cyclic lateral loads, such as those experienced during an earthquake. A recently developed triaxial constitutive model for concrete is combined with a material model for reinforcing steel which can account for rupture due to low-cycle fatigue. The strain penetration effect is also explicitly accounted for in the models. The reinforcing steel bars are represented with nonlinear beam elements to explicitly account for buckling of the reinforcement. The modeling scheme is implemented in an explicit finite element program, which includes large-deformation formulations and element removal techniques to capture loss of concrete cover and rebar rupture. The analytical tools are validated with the results of experimental static and dynamic tests on RC columns and walls. The validation analyses are supplemented with a discussion elucidating modeling aspects, such as the well-established spurious mesh size effect for softening material response with the corresponding regularization procedures, and the significance of accurately modeling the bond-slip of the steel reinforcement.

The angle-only filtering problem in 3D using bearing and elevation measurements is an important problem in many passive tracking applications. Research in angle-only filtering in 3D began by extending the methods developed for the counterpart problem in 2D. This chapter defines the tracker and sensor coordinate frames and describes different coordinate systems for the target and ownship states. It presents the dynamic models of the target and ownship, whereas the measurement models for the Cartesian relative state and MSC. The chapter describes filter initialization, and presents algorithms based on the extended Kalman filter (EKF), unscented Kalman filter (UKF), and particle filter. It presents the continuous-time and discrete-time models for the time evolution of the target state in each coordinate system. The chapter considers a dynamic model obtained by transformation of the Cartesian discrete-time dynamic model. It summarizes the unscented transformation before showing how it is used as part of the UKF recursion for angle-only tracking.

This paper describes an evaluation of the lateral load-resisting system of an existing monolithic, cast-in-place, reinforced concrete (RC) stadium structure completed in the early 1930s. A major renovation/expansion of the stadium completed in the 1990s included modifications of some of the original exterior infill masonry wall, including removal of masonry and enlargement of existing openings. A preliminary study raised concerns about the impact of these modifications on the lateral load resistance of the stadium structure. A new study, which consisted of an evaluation of the structure’s performance using in situ lateral load testing of the structure, numerical analyses, and monitoring of the actual stadium-sway movements during football games, was undertaken in 2006 to determine the adequacy of the lateral load resisting system of the stadium. The results of this study, which are reported in this paper, demonstrate that the masonry modifications made during the renovations/expansion of the stadium did not impair the structure’s resistance to code-prescribed lateral loads and that no major structural repairs were required.

Chromosome design has been shown to be a crucial element in developing genetic algorithms which approach global solutions without premature convergence. The consecutive positioning of parameters with high-correlations and relevance enhances the creation of genetic building blocks which are likely to persist across recombination to provide genetic inheritance. Incorporating positional gene relevance is challenging, however, in multi-dimensional design problems. We present a hybrid chromosome designed for optimizing a fragmented patch antenna which combines linear and two-dimensional gene representations. We compare previous results obtained with a linear chromosome to solutions obtained with this new hybrid representation.

Abstract Traditional steep-slope roof systems for the residential buildings (single-family homes and multi-building apartment or condominium buildings) consist of asphalt glass-fiber shingles applied over vented or unvented attics. The long-term performance of these roofs is primarily dependent on geographic location, proper roof ventilation, roof slope, material component selection and color, as well as proper detailing and construction. There is a trend towards maximizing interior space in residential dwellings by constructing compact steep-slope roof systems with cathedral or vaulted ceilings without proper venting of the asphalt shingle roof system, which, in turn, may reduce the life of the shingles. The primary reason for venting is to convey water vapor. Build up in the roof, to outside the building. Although few building code jurisdictions are relaxing the requirement for roof ventilation in compact steep slope roof systems, ventilation is still typically required by most building codes. Where allowed by the code, designers and contractors tend to omit the vented air space and favor the use of closed cell spray-applied foam insulations (polyurethane) or permeable insulation combined with vapor retarders to help control the build up of destructive moisture levels within the roof. This article presents the results of numerical case studies created in WUFI® that demonstrate the need for venting in unvented asphalt shingle roof systems with a variety of insulation and vapor retarder materials in a hot (Miami, FL) and cold (Boston, MA) climates. The models utilize historical hourly weather data to simulate the time-varying exterior conditions and examine the effect of natural ventilation and incidental roof leakage on hygrothermal performance of unvented and vented steep-slope roof assemblies. The interior conditions for residential buildings in the models are set at 21.1°C±1.1°C (70°F±2°F) and 35 %±15 % relative humidity. We selected the drying potential and the robustness of the moisture-sensitive roof system materials in response to incidental roof leakage to measure the performance of the roof assembly. Our study showed better durability of vented roof assemblies with permeable insulation in cold climates due to redundancies that can tolerate incidental moisture and provide visual indicators of roof leakage; roof sheathing typically dries in 1-1/2 to 2 months. All of the unvented roof assemblies are intolerant of incidental water leakage and the moisture-sensitive layers (i.e., sheathing and gypsum wallboard (for open-cell polyurethane insulation)) exceed the threshold for decay. In hot, humid climates, the most durable roof assemblies are the vented, open-cell polyurethane systems with shorter drying time of the interior gypsum wallboard when compared to the unvented roof assembly; both the sheathing and gypsum wallboard dry out within 2-1/2 months. In an unvented assembly, the drying time for sheathing is similar but the drying time for gypsum wallboard increases to 6.5 months on average. Alternatively, unvented permeable shingled roofs are a viable option in hot, humid climates, although they are slightly less durable. The least tolerant roof assemblies in either climate are the unvented closed-cell polyurethane roof assembly due to trapped moisture and slow drying of the roof sheathing (up to 12 months in Miami, FL and 27 months in Boston, MA).

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> A scheme is proposed to detect, identify, and estimate failures, including abrupt total, partial, and multiple failures, in a dynamic system. The new approach, named IM<formula formulatype="inline"><tex>$^{3}$</tex></formula>L, is developed based on variable-structure multiple-model estimation, which allows to improve performance by online adaptation. It uses an interacting multiple model estimator for fault detection and identification but the maximum likelihood estimator for estimating the extent of failure. It provides an effective and integrated framework for fault detection, identification, and state estimation. For two aircraft examples, the proposed approach is evaluated and compared with hierarchical multiple-model approaches and a widely used single-model residual-based generalized likelihood ratio approach in terms of detection and estimation performance. The results show that the IM<formula formulatype="inline"><tex>$^{3}$</tex></formula>L provides not only fast detection and proper identification, but also good estimation of the failure extent as well as robust state estimation. </para>

This paper presents an observer designed under the assumption that differences between predicted and measured outputs arise from discrepancies between the real structural system and the nominal model used to represent it. The observer gain is independent of the assumed model error parametrization and proves to be the transpose of the state to output matrix of a state space formulation. The estimated state with the proposed observer is shown to be identical to that obtained by exciting the nominal model with the known input while adjusting the measured portion of the state to match the measurements at the start of every step. Numerical experiments suggest that the proposed observer can provide state estimates that are substantially more accurate than results predicted by projecting the measurements in a truncated modal space.