Seismic performance evaluations and analyses for composite moment frames with smart SMA PR-CFT connections

This thesis investigates the performance of composite frame structures with smart partially-restrained (PR) concrete filled tube (CFT) column connections through simplified 2D and advanced 3D computational simulations. It also provides a design methodology for new types of innovative connections based on achieving a beam hinging mechanism. These types of connections intend to utilize the recentering properties of super-elastic SMA tension bars, the energy dissipation capacity of low-carbon steel bars, and the robustness of CFT columns. In the first part of this study, three different PR-CFT connection prototypes were designed based on a hierarchy of strength models for each connection component. Numerical simulations with refined three dimensional (3D) solid elements were conducted on full scale PR-CFT connection models in order to verify the strength models and evaluate the system performance under static loading. Based on system information obtained from these analyses, simplified connection models were formulated by replacing the individual connection components with spring elements and condensing their contributions. Connection behavior under cyclic loads was extrapolated and then compared with the monotonic behavior. In the second part of this study, the application of these connections to low-rise composite frames was illustrated by designing both 2D and 3D, 4 and 6 story buildings for the Los Angeles region. A total of 36 frames were studied. Pushover curves plotted as the normalized shear force versus inter story drift ratio (ISDR) showed significant transition points: elastic range or proportional limit, full yielding of the cross-section, strength hardening, ultimate strength, and strength degradation or stability limit. Based on the transition points in the monotonic pushover curves, three performance levels were defined: Design Point, Yield Point, and Ultimate Point. All frames were stable up to the yield point level. For all fames, after reaching the ultimate point, plastic rotation increased significantly and concentrated on the lower levels. These observations were quantified through the use of elastic strength ratios and inelastic curvature ductility ratios. The composite frames showed superior performance over traditional welded ones in terms of ductility and stability, and validated the premises of this research.Ph.D.Committee Chair: Roberto T. Leon; Committee Member: Barry J. Goodno; Committee Member: Don White; Committee Member: Reginald DesRoches; Committee Member: W. Steven Johnso

Effects of Brace Configuration and Structure Height on Seismic Performance of BRBFs Based on the Collapse Fragility Analysis

The brace configuration and structure height are two factors that have a significant effect on the seismic behavior of braced frame buildings. In the present study, the buckling-restrained braced (BRB) frames were considered to estimate the effect of these two parameters using probabilistic seismic assessment methods. The uncertainty in the different parameters involved in the seismic design of the structural system was also considered. Four, six, and ten-story buildings with the Chevron and inverted Chevron bracing configurations were designed, and their responses due to various ground motions were estimated using incremental nonlinear dynamic analyses. Fragility curves, mean annual frequency of exceeding immediate occupancy (IO), and collapse prevention (CP) states were generated using probabilistic seismic analysis, fragility curves concept, and drift hazard curves. The results demonstrate that the inverted Chevron type BRBFs has better structural performance than Chevron bracing types. Furthermore, an increase of the height of structures, despite lower drift’s hazards, increases the fragility probability

Experimental Field Tests and Finite Element Analyses for Rock Cracking Using the Expansion of Vermiculite Materials

In the previous research, laboratory tests were performed in order to measure the expansion of vermiculite upon heating and to convert it into expansion pressure. Based on these test results, this study mainly focuses on experimental field tests conducted to verify that expansion pressure obtained by heating vermiculite materials is enough to break massive and hard granite rock with an intention to excavate the tunnel. Hexahedral granite specimens with a circular hole perforated in the center were constructed for the experimental tests. The circular holes were filled with vermiculite plus thermal conduction and then heated using the cartridge heater. As a result, all of hexahedral granite specimens had cracks in the surface after 700-second thermal heating and were finally spilt into two pieces completely. The specimen of larger size only requires more heating time and expansion pressure. The material properties of granite rocks, which were obtained from the experimental tests, were utilized to produce finite element models used for numerical analyses. The analysis results show good agreement with the experimental results in terms of initial cracking, propagation direction, and expansion pressure

An Extended Semantic Interoperability Model for Distributed Electronic Health Record Based on Fuzzy Ontology Semantics

Semantic interoperability of distributed electronic health record (EHR) systems is a crucial problem for querying EHR and machine learning projects. The main contribution of this paper is to propose and implement a fuzzy ontology-based semantic interoperability framework for distributed EHR systems. First, a separate standard ontology is created for each input source. Second, a unified ontology is created that merges the previously created ontologies. However, this crisp ontology is not able to answer vague or uncertain queries. We thirdly extend the integrated crisp ontology into a fuzzy ontology by using a standard methodology and fuzzy logic to handle this limitation. The used dataset includes identified data of 100 patients. The resulting fuzzy ontology includes 27 class, 58 properties, 43 fuzzy data types, 451 instances, 8376 axioms, 5232 logical axioms, 1216 declarative axioms, 113 annotation axioms, and 3204 data property assertions. The resulting ontology is tested using real data from the MIMIC-III intensive care unit dataset and real archetypes from openEHR. This fuzzy ontology-based system helps physicians accurately query any required data about patients from distributed locations using near-natural language queries. Domain specialists validated the accuracy and correctness of the obtained resultsThis work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIT) (NRF-2021R1A2B5B02002599)S

Gene expression programming application for prediction of ultimate axial strain of FRP-confined concrete

The last three decades have seen increasing applications of fiber-reinforced polymer materials in structural engineering because of their many advantages over traditional strengthening and reinforcing materials. On the other hand, soft computing approaches have recently been widely used to model human activity in many areas of civil engineering applications. This paper presents the use of genetic expression programming as a tool to predict the ultimate axial strain of fiber-reinforced polymer-confined concrete. A large experimental data set (219) of these tests is collected from published literature. The prediction of the proposed new genetic expression programming-based model was compared with the results obtained using the existing analytical equations proposed in the current literature. In this paper, attempts were made to present a complete review of genetic expression programming in structural engineering. Good agreement between the experimental data and predicted results is obtained

Comparison of thermal performance of steel moment and eccentrically braced frames

Eccentrically braced frames (EBFs) are typically employed in seismic design because they integrate the benefits of concentrically braced frames and moment-resisting frames, providing both high elastic stiffness and high ductility. However, the effect of fire on the structural stability of EBFs has not been well documented. Object-oriented techniques used in software program development have become popular in recent years, primarily because of their ability in addressing various complexity issues. Software developed based on an object-oriented approach is more robust than conventional software. Using the abovementioned approach, additional codes can be incorporated, thereby simplifying testing, refining, maintenance, and software extension. Furthermore, the object-oriented approach can be used for finite element analysis. This paper presents the further development of OpenSees software with the inclusion of other parameters:thermal parallel material, thermal spring element, thermal spring section, as well as beam with hinges and thermal elements subjected to fire loading. In contrast to the routine creation of fire-specific applications, these modifications improve the existing finite-element codes, thereby facilitating multi-hazard analysis (e.g., post-earthquake fire). OpenSees is considered in this study as it is an open-source application and suitable for object-oriented design. The abovementioned elements, particularly spring elements, are used extensively in structural simulations (e.g., the modeling of a link beam in an EBF); however, owing to the lack of thermal functions for these elements in OpenSees, the thermal performance of structures that involve these elements cannot be evaluated. Herein, the aforementioned new elements are introduced for the first time; furthermore, the behavior of an EBF system is investigated under thermal loads using open-source software. The thermal performance of EBFs subjected to realistic fire is evaluated in this study based on an analytical modeling of a three-story building. Finally, several compartment fire scenarios are simulated for both EBFs and gravity framing bays. Results show that the EBFs improve the fire performance of the system by extending the time to collaps