<p> The structure-property relationships of Ultra-High Performance Concrete (UHPC) were quantified using imaging techniques to characterize the multiscale hierarchical heterogeneities and the mechanical properties. Through image analysis the average size, percent area, nearest neighbor distance, and relative number density of each inclusion type was determined and then used to create Representative Volume Element (RVE) cubes for use in Finite Element (FE) analysis. Three different size scale RVEs at the mesoscale were found to best represent the material: the largest length scale (35 mm side length) included steel fibers, the middle length scale (0.54 mm side length) included large voids and silica sand grains, and the smallest length scale (0.04 mm side length) included small voids and unhydrated cement grains. By using three length scales of mesoscale FE modeling, the bridge of information to the macroscale cementitious material model is more physically based.</p>

<p> The focus of this work is to advance the theoretical and modeling techniques for the fields of hybrid simulation and multi-slider friction pendulum systems (MSFPs). Hybrid Simulation is a simulation technique involving the integration of a physical system and a computational system with the use of actuators and sensors. This method has a strong foundation in the experimental mechanics community where it has been used for many years. The hybrid simulation experiments are performed with the assumption of an accurate result as long as the main causes of error are reduced. However, the theoretical background on hybrid testing needs to be developed in order validate these findings using this technique. To achieve this objective, a model for hybrid simulation is developed and applied to three test cases: an Euler-Bernoulli beam, a nonlinear damped, driven pendulum, and a boom crane structure. Due to the complex dynamics that these three test cases exhibit, <i>L</i>² norms, Lyapunov exponents, and Lyapunov dimensions, as well as correlation exponents were utilized to analyze the error in hybrid simulation tests. From these three test cases it was found that hybrid simulations are highly dependent on the natural frequencies of the dynamical system as well as how and where the hybrid split is located. Thus, proper care must be taken when conducting a hybrid experiment in order to guarantee reliable results. </p><p> Multi-stage friction pendulum systems (MSFPs), such as the triple friction pendulum (TFP), are currently being developed as seismic isolators. However, all current analytical models are inadequate in modeling many facets of these devices. Either the model can only handle uni-directional ground motions while incorporating the kinetics of the TFP system, or the model ignores the kinetics and can handle bi-directional motion. And in all cases, the model is linearized to simplify the equations. The second part of this dissertation presents an all-in-one model that incorporates the full nonlinear kinetics of the TFP system, while allowing for bi-directional ground motion. In this way, the model presented here is the most complete single model currently available. It was found that the non-linear model can more accurately predict the experimental results for large displacements due to the nonlinear kinematics used to describe the system. The model is also able to successfully predict the experimental results for bi-directional ground motions.</p><p>

Spherical indentation of thick and thin glass plates were investigated numerically and experimentally. The energy release rate at the tip of a cone crack was calculated by using finite element techniques and used to investigate the applicability in thick plates of Roesler's law relating the cone crack radius to the indentation load. Indentations of thin glass specimens resting on different substrates were also studied numerically and experimentally. The stresses in the thin specimens were calculated and correlated with the observed failures. On the basis of these results, a crack initiation mechanism map was developed for glass specimens on different substrates. Spherical indentation of two types of aluminas (AD90 and AD995) carried out by Widjaja et al. (1996) produced similar cracking patterns to those observed in glass specimens which consist of ring, cone and radial cracks. Using ABAQUS we calculated the stress distributions for 2 mm thick alumina specimens (AD90 and AD995) resting on a 3 mm thick steel substrate under spherical indentation of a 2 mm radius sphere. It was found that at a load of 1800 N and 2000 N for a specimen of AD90 and AD995 respectively, the maximum hoop stress $\sigma\sb{\theta}$ on the bottom surface of the alumina specimen reaches approximately the fracture strength $\sigma\sb{f} \approx 260$ MPa. This maximum hoop stress is believed to be responsible for the initiation of radial cracking in the alumina specimens as observed by Widjaja et al. (1996). Finite element analysis was also carried out on the spherical indentation of sandwich specimens. The stress distributions were obtained on the top surface and interface of the sandwich specimen. The energy release rates of a debonding crack on the interface of the sandwich specimen were calculated.

<p> A smart building is an intelligent living space that elevates energy efficiency, comfort and safety. The word &ldquo;smart&rdquo; implies that the building would have a decision making system that can sense its conditions and reacts to them in an automatic and effective manner. Modem buildings contain many subsystems and, thus, to achieve automation, sophisticated sensing networks and robust control systems must be installed. The proposed research focuses on integrating several building systems&mdash;structural health monitoring (SHM), and structural and environmental controls&mdash;and explores synergy among them to improve efficiency and sustainability of buildings. </p><p> More specifically, an integrative, smart building system is developed by combining double skin fa&ccedil;ades and mass dampers in buildings to improve both safety and energy efficiency. Double skin fa&ccedil;ade systems protect and insulate buildings with two heavy glass layers between which air is allowed to flow for ventilation. By enabling movements in the outer fa&ccedil;ade skin, the fa&ccedil;ade can be used as a mass damper that reduces structural vibration and damage during earthquakes and wind storms. The added mobility also leads to innovative ways to control ventilation rate and improve energy efficiency by adjusting the gap size between the outer and inner skins. </p><p> In this dissertation research, the energy impact of the integrated system was first investigated. Then both passive and active structural control strategies were experimented and analyzed on a six-story shear building model. Results indicated the proposed system can significantly reduce structural response under the earthquakes excitations. In addition, the sensor networks and actuators introduced by the active structural control system were utilized for structural health monitoring purposes. The actuators provided harmonic excitations while the acceleration data were collected by the sensor networks to perform damage diagnosis. </p><p> Finally, since typical SHM systems require large networks of sensors that are costly to install, this dissertation research also examined using smartphones as alternative sensors. Using the aforementioned six-story experimental structure, a sensing system consisted of six smartphones was tested and proven effective in detecting structural damage. The experimental result demonstrates that further developments of smartphone SHM can lead to cost-effective and quick sensor deployments.</p><p>

<p> Due to the continuous operation of HVAC systems and stringent requirements of indoor environmental conditions, the total energy use per floor area in healthcare facilities is second only to that in food service buildings, and significantly higher than that in any other commercial building types. In order to evaluate potential opportunities for saving energy in healthcare facilities, a model of a hospital located in south Louisiana was developed in EnergyPlus simulation software. Building information required for the model development was taken from the hospital architectural and mechanical plans. Two field surveys were also conducted to identify the operating characteristics of electrical equipment and gas equipment. The annual electricity and natural gas consumption estimated by the developed model was compared with utility data for model validation. Five energy efficient measures were evaluated using the developed models, namely reducing LPD, installing high efficiency windows, the combination method of reducing LPD and window changing approaches, installing a separate chiller for OR, and another combination of LPD reduction and chiller separation. Simulation results showed 12% annual energy savings by reducing LPD from 2.5 to 0.86 W/ft² while only 1% savings resulted from using high-efficiency windows. The combination of LPD reduction and window changing could reduce the annual energy consumption by 13%. Building energy usage has been decreased by 8% after separating the OR chiller and 18% by the combination method of reducing LPD and separating chillers.</p><p>

The purpose of this research was to study the static and dynamic behavior of tall guyed radio navigation towers in order to evaluate the feasibility of using vibration analysis as a means to determine the tensions in the guy wires and to identify the presence of structural defects in the tower. The static response of guy wires was studied as a precursor to the dynamic response. Results of a detailed experiment on a scale model guy wire corresponded with predictions from the equations of the elastic catenary within $\pm$6%. The dynamic response of guy wires was studied and the results of a detailed experiment on a scale model guy wire compared with theoretical predictions for natural frequencies with an average difference of 0.7%. The experimental results showed hybrid mode shapes and gave clear evidence of avoided crossings in the natural frequencies. The theoretical results indicated that the accuracy of the curvature term has a profound impact on the accuracy of the solutions. The tension at the base of the scale model guy wire was determined within 2.5% by correlating experimentally measured natural frequencies with theoretical predictions. It was determined that a useful tool could be made which would allow for determination of the tension at the base of a full size guy wire by measuring the guy wire vibrations. The dynamic response of a model guyed tower was studied. It was determined that the proposed method of vibration analysis would not provide a useful means of identifying small structural defects in tall guyed radio navigation towers.

This dissertation presents the analytical and numerical investigation of the response of a slab-supported liquid storage tank taking into account soil-structure interaction and nonlinear uplift effect. The dissertation consists of two parts. In the first part, a generalized approach based on the variational principle is developed to analyze the dynamic response of liquid storage tanks taking into account soil-structure interaction. Two types of tank movements are studied: (i) a liquid storage tank on a deformable soil undergoing lateral and rocking motion; (ii) a liquid storage tank on a deformable soil subjected to a vertical excitation. Also in this part of the analysis, governing equations for the liquid sloshing motion in a flexible tank are derived in a concise form. Examples with various properties are presented for the two types of tank movements to illustrate the significant effects of soil-structure interaction. Comprehensive numerical data are also presented which may be used readily in design applications. The second part studies the nonlinear uplift behavior of a liquid storage tank from its rigid supporting slab under static loadings. In this part of the study, the nonlinear large deflexion plate theory is used to model the tank bottom plate while, for simplicity, the linear shell theory is used for describing the tank shell. To describe the uplift behavior of the bottom plate, a set of nonlinear differential equations and the corresponding boundary conditions for the plate are derived using the variational principle. According to the interface conditions between the tank shell and the bottom plate, a complete nonlinear boundary value problem is defined for the uplifting tank system. An approximate solution procedure based on the Ritz method is developed for such an uplifting tank system. An example is also provided to show the tank performance during its uplifting.

<p> This research shows that worst-case methane-air detonation loading on coal mine seals could be more severe than the design loads required by federal regulations, and therefore mine seals should be designed with sufficient ductility beyond the elastic regime. For this study, reinforced concrete mine seals were designed according to traditional protective structural design methods to meet the federal regulation requirements, and then the response to worst-case loads was analyzed in a single-degree- of-freedom model. Coal mine seals designed to resist the regulation loads elastically experienced support rotations up to 4.27 deg when analyzed with the worst-case loads. The analysis showed that coal mine seals designed to satisfy the federal regulations can survive worst-case methane-air detonations if they have sufficient ductility, but will undergo permanent, inelastic deformation.</p>

<p> Thermal bridging through structural steel members in building envelopes poses issues with heat loss and condensation in cold regions. Structural steel thermal breaks, taking the form of low-thermal conductivity, high-strength and stiffness materials placed between the faying surfaces of a steel connection, serve to reduce heat flow through the steel element and have seen extensive use in the construction industry. However, current steel construction code provisions in the US prohibit the use of compressible materials in a steel connection. While the practical benefits of thermal breaks in structural steel beams and columns have been well demonstrated, there is a lack of guidance on the structural design of these thermal breaks, as well as a yet undetermined thermal efficacy of thermal break design parameters.</p><p> The objective of this thesis was to determine the thermal and mechanical behavior of structural steel beam thermally broken connections and continuous beam thermal bridges. Heat flow through a thermally broken steel end-plate connection was determined experimentally using a calibrated hot box. Results were used to validate a finite element heat transfer model, which was used to perform a parametric analysis on the thermal break using different break and bolt materials. From the analyses, it was determined that the thickness of the break is effective in reducing heat flow and condensation potential. The use of stainless steel or fiber-reinforced bolts provides a significant reduction in heat flow and condensation potential. The mechanical behavior of the thermally-broken connection was analyzed using cantilever bending tests and shear tests on an identical set of connections using three different thicknesses of neoprene pad. Results showed that the rotational stiffness of the connection was reduced approximately linearly with increasing neoprene pad thickness. Shear deflection stiffness was reduced exponentially with increased pad thickness. Structural experimental results were validated against a finite element model which was used to investigate stresses in the end-plate and the bolt. Bolt rupture was found to occur at a reduced applied bending moment due to the increased rotation of the end-plate due to the soft intermediate layer of neoprene between the end-plate and the connection member.</p>

<p> Multiscale simulation is a long standing dream in computational physics and materials. The motivation is natural: each single-scale model has its deficiencies. For example, microscale models such as Molecular Dynamics are limited to size in space and time; macroscale models such as Finite Element Method find difficulty recovering some fundamental physical phenomena such as materials defects. Simulations across scales are challenging because quantities in different scales have distinct properties. Mechanism needs to be harnessed to translate the information. Cross-scale communication is a typical two-way message passing: bottom-up and top down. Bottom-up approach is relatively straightforward, where statistical theory or homogenization is used to collect lower-scale information and interpret it in higher levels. On the other hand, top-down approach requires physical insights. Specifically, in a mechanical system, top-down message passing can be the response of the molecular system when macroscale boundary conditions such as distributed load are enforced. </p><p> In this work, we reveal an intrinsic multiscale structure in solid materials. A &ldquo;supercell&rdquo; is introduced as a cluster of particles. Compare with &ldquo;material point&rdquo; in continuum mechanics, the &ldquo;supercell&rdquo; has internal degrees of freedom, which makes it equivalent to molecular systems. By introducing different force fields, we derive the dynamical equations for the different scales in the structure. The systematic multiscale framework solves the issue of top-down message passing by including quantities from different scales and connecting them in a uniform dynamical framework. We discuss the technical aspects in implementing the theory, i.e. constraints of the variables, integrators and temperature control. Numerical example of phase transition are presented to validate the theory, including bulk Nickel lattice under displacement and traction boundary conditions and Nickel nanowire with traction. Furthermore, based on the developed multiscale theory, we establish a computational model to achieve efficiency in realistic multiscale simulations. The model includes three parts: atomistic region, macro region and transition zone. Atomistic region is where physical details are desired and is simulated by Molecular Dynamics. Macro region only concerns macroscale deformable behaviors of solid materials, which can be calculated by various models depending on the problem of interests. We choose state-based peridynamics in this work as a demonstration. The essential part is the transition zone which is responsible for translating messages across different domains. The &ldquo;supercell&rdquo; developed in the previous theory is employed as a transition element to carry those different messages. With solid theoretic foundation, the cross-scale message translation is clearly characterized. We also construct a filter to solve the issue of high-frequency wave reflection. Examples of 1-D and 2-D wave propagations are presented to demonstrate the procedure of cross-scale transition and the effect of the filter.</p>