No description available.

No description available.

No description available.

This research investigated the behavior of nonseismically detailed reinforced concrete exterior beam-column joints subjected to bidirectional lateral cyclic loading using nonlinear finite element analysis (NLFEA). Beam-column joints constitute a critical component in the load path of reinforced concrete buildings due to their fundamental role in integrating the overall structural system. Earthquake reconnaissance reports reveal that failure of joints has contributed to partial or complete collapse of reinforced concrete buildings designed without consideration for large lateral loads, resulting in significant economic impact and loss of life. Such infrastructure exists throughout seismically active regions worldwide, and the large-scale risk associated with such deficiencies is not fully known. Computational strategies provide a useful complement to the existing experimental literature on joint behavior and are needed to more fully characterize the failure processes in seismically deficient beam-column joints subjected to realistic failure conditions. Prior to this study, vulnerable reinforced concrete corner beam-column joints including the slab had not been analyzed using nonlinear finite element analysis and compared with experimental results. The first part of this research focused on identification and validation of a constitutive modeling strategy capable of simulating the behaviors known to dominate failure of beam-column joints under cyclic lateral load using NLFEA. This prototype model was formulated by combining a rotating smeared crack concrete constitutive model with a reinforcing bar plasticity model and nonlinear bond-slip formulation. This model was systematically validated against experimental data, and parametric studies were conducted to determine the sensitivity of the response to various material properties. The prototype model was then used to simulate the cyclic response of four seismically deficient beam-column joints which had been previously evaluated experimentally. The simulated joints included: a one-way exterior joint, a two-way beam-column exterior corner joint, and a series of two-way beam-column-slab exterior corner joints with varying degrees of seismic vulnerability. The two-way corner joint specimens were evaluated under simultaneous cyclic bidirectional lateral and cyclic column axial loading. For each specimen, the ability of the prototype model to capture the strength, stiffness degradation, energy dissipation, joint shear strength, and progressive failure mechanisms (e.g. cracking) was demonstrated.

This study examines the use of performance-based engineering in earthquake liquefaction hazard analysis with Cone Penetration Test data (CPT). This work builds upon previous research involving performance-based liquefaction analysis with the Standard Penetration Test (SPT). Two new performance-based liquefaction triggering models are presented herein. The two models used in this liquefaction analysis are modified from the case-history based probabilistic models proposed by Ku et al. (2012) and Boulanger and Idriss (2014). Using these models, a comparison is made between the performance-based method and the conventional pseudo-probabilistic method. This comparison uses the 2014 USGS probabilistic seismic hazard models for both methods. The comparison reveals that, although in most cases both methods predict similar liquefaction hazard using a factor of safety against liquefaction, by comparing the probability of liquefaction, the performance-based method on average will predict a smaller liquefaction hazard.

This dissertation develops a new concept for performance-based monitoring (PBM) of instrumented buildings subjected to earthquakes. This concept is achieved by simultaneously combining and advancing existing knowledge from structural mechanics, signal processing, and performance-based earthquake engineering paradigms. The PBM concept consists of 1) optimal sensor placement, 2) dynamic response reconstruction, 3) damage estimation, and 4) loss analysis. Within the proposed concept, the main theoretical contribution is the derivation of a nonlinear model-based observer (NMBO) for state estimation in nonlinear structural systems. The NMBO employs an efficient iterative algorithm to combine a nonlinear model and limited noise-contaminated response measurements to estimate the complete nonlinear dynamic response of the structural system of interest, in the particular case of this research, a building subject to an earthquake. The main advantage of the proposed observer over existing nonlinear recursive state estimators is that it is specifically designed to be physically realizable as a nonlinear structural model. This results in many desirable properties, such as improved stability and efficiency. Additionally, a practical methodology is presented to implement the proposed PBM concept in the case of instrumented steel, wood-frame, and reinforced concrete buildings as the three main types of structural systems used for construction in the United States. The proposed methodology is validated using three case studies of experimental and real-world large-scale instrumented buildings. The first case study is an extensively instrumented six-story wood frame building tested in a series of full-scale seismic tests in the final phase of the NEESWood project at the E-Defense facility in Japan. The second case study is a 6-story steel moment resisting frame building located in Burbank, CA, and uses the recorded acceleration data from the 1991 Sierra Madre and 1994 Northridge earthquakes. The third case is a seven-story reinforced concrete structure in Van Nuys, CA, which was severely damaged during the 1994 Northridge earthquake. The results presented in this dissertation constitute the most accurate and the highest resolution seismic response and damage measure estimates obtained for instrumented buildings. The proposed PBM concept will help structural engineers make more informed and swift decisions regarding post-earthquake assessment of critical instrumented building structures, thus improving earthquake resiliency of seismic-prone communities.

Seismic rehabilitation of structural systems is an effective approach for reducing potential seismic losses such as social and economic losses. However, little or no effort has been made to develop a framework for making decisions on seismic rehabilitation of structural systems that systematically incorporates conflicting multiple criteria and uncertainties inherent in the seismic hazard and in the systems themselves. This study develops a decision support framework for seismic rehabilitation of structural systems incorporating uncertainties inherent in both the system and the seismic hazard, and demonstrates its application with detailed examples. The decision support framework developed utilizes the HAZUS method for a quick and extensive estimation of seismic losses associated with structural systems. The decision support framework allows consideration of multiple decision attributes associated with seismic losses, and multiple alternative seismic rehabilitation schemes represented by the objective performance level. Three multi-criteria decision models (MCDM) that are known to be effective for decision problems under uncertainty are employed and their applicability for decision analyses in seismic rehabilitation is investigated. These models are Equivalent Cost Analysis (ECA), Multi-Attribute Utility Theory (MAUT), and Joint Probability Decision Making (JPDM). Guidelines for selection of a MCDM that is appropriate for a given decision problem are provided to establish a flexible decision support system. The resulting decision support framework is applied to a test bed system that consists of six hospitals located in the Memphis, Tennessee, area to demonstrate its capabilities.

Shape memory alloys are a class of alloys that display the unique ability to undergo large plastic deformations and return to their original shape either through the application of heat (shape memory effect) or by relieving the stress causing the deformation (superelastic effect). This research takes advantage of the unique characteristics of shape memory alloys in order to provide a moment resisting connection with recentering capabilities. In this study, superelastic Nitinol, a nickel-titanium form of shape memory alloy that exhibits a flag-shaped stress versus strain curve, is used as the moment transfer elements within a partially restrained steel beam-column connection. Experimental testing consists of a one-half scale interior connection where the loading is applied at the column tip. A pseudo-static cyclic loading history is used which is intended to simulate earthquake loadings. The energy dissipation characteristics, moment-rotation characteristics, and deformation capacity of the connection are quantified. Results are then compared to tests where A36 steel tendons are used as the moment transfer elements. The superelastic Nitinol tendon connection showed superior performance to the A36 steel tendon connection, including the ability to recenter without residual deformation.

The goal of this study is to design and evaluate economic and rapid seismic retrofit strategies for relatively small rehabilitation projects for steel structures consistent with the tenets of sustainable design. The need to retrofit existing structures in earthquake prone regions may arise directly from the problem of aging and deteriorating conditions, recognition of the vulnerability of existing infrastructure, from updates in seismic code requirements, or changes in building performance objectives. Traditional approaches to seismic hazard mitigation have focused reducing the failure probabilities, consequences from failures, and time to recovery. Such paradigms had been established with little regard to the impact of their rehabilitation measures on the environment and disruptions to occupants. The rapid rehabilitation strategies proposed here have sustainability benefits in terms of providing a more resilient building stock for our communities as well as minimizing environmental and economical impacts and social consequences during the rehabilitation project. To achieve these goals, a unique approach to design supplemental systems using tension-only elements is proposed. In this design approach undesirable global and local buckling are eliminated. Two rapid rehabilitation strategies are presented. The first is a bracing system consisting of cables and a central energy dissipating device (CORE Damper). The second is a shear wall system with the combined use of thin steel plate and tension-only bracing. Analytical studies using both advanced and simplified models and proof-of-concept testing were carried out for the two devices. The results demonstrated stable, highly efficient performance of the devices under seismic load. Preliminary applications of the CORE damper to the retrofitting of a braced steel frame showed the ability of the system to minimize soft story failures. Both techniques can be implemented within a sustainability framework, as these interventions reduce the seismic vulnerability of infrastructure, are low cost, utilize materials and fabrication processes widely available throughout the world, can be handled by unskilled labor and carried out with minimal disruptions to the environment. The approach taken in this study can provide a road map for future development of sustainability-based rehabilitation strategies.

Στην παρούσα διατριβή παρουσιάζεται μια μέθοδος αντισεισμικού σχεδιασμού μεταλλικών κατασκευών με βάση τη χρήση λόγων ιδιομορφικής ιξώδους απόσβεσης. Η μέθοδος αυτή βρίσκει τη μέγιστη σεισμική απόκριση μιας κατασκευής με φασματική ανάλυση και χρήση των λόγων ιδιομορφικής ιξώδους απόσβεσης αντί του χονδροειδούς συντελεστή συμπεριφοράς. Η βασική ιδέα της μεθόδου είναι η κατασκευή μιας ισοδύναμης γραμμικής πολυβάθμιας κατασκευής η οποία να μπορεί να αναπαράξει τη σεισμική απόκριση μιας πραγματικής μη γραμμικής. Συγκεκριμένα, αυτή η ισοδύναμη γραμμική κατασκευή έχει την ίδια μάζα και αρχική δυσκαμψία με την πραγματική μη γραμμική κατασκευή και λόγους ιδιομορφικής ιξώδους απόσβεσης οι οποίοι ποσοτικοποιούν το έργο όλων των μη γραμμικών παραμορφώσεων. Αυτοί οι λόγοι ισοδύναμης ιξώδους απόσβεσης για τις πρώτες σημαντικές ιδιομορφές υπολογίζονται συναρτήσει της παραμόρφωσης και της βλάβης της κατασκευής αρχικά σχηματίζοντας επαναληπτικά μια συνάρτηση μεταφοράς στο πεδίο των συχνοτήτων, μέχρις ότου αυτή να ικανοποιήσει συγκεκριμένα κριτήρια ομαλότητας, και μετά επιλύοντας ένα σύστημα μη γραμμικών αλγεβρικών εξισώσεων. Αφού κατασκευαστούν εξισώσεις σχεδιασμού που παρέχουν τους λόγους ιδιομορφικής ιξώδους απόσβεσης, γίνεται χρήση φασμάτων σχεδιασμού τροποποιημένων για μεγάλη απόσβεση και ιδιομορφικής σύνθεσης για τον υπολογισμό των σεισμικών δυνάμεων σχεδιασμού. Μέσω των ελαστικών φασμάτων για διάφορες τιμές απόσβεσης υπολογίζεται ο ιδιομορφικός συντελεστής συμπεριφοράς ο οποίος επίσης δίνεται για τις πρώτες σημαντικές ιδιομορφές συναρτήσει της παραμόρφωσης και της βλάβης της κατασκευής. Τέλος, πραγματοποιείται ο αντισεισμικός σχεδιασμός μιας μεταλλικής πλαισιωτής κατασκευής με ελαστική φασματική ανάλυση τόσο με βάση τους λόγους της ισοδύναμης ιξώδους ιδιομορφικής απόσβεσης όσο και με βάση τους ιδιομορφικούς συντελεστές συμπεριφοράς. Και οι δυο τρόποι σχεδιασμού ελέγχονται χρησιμοποιώντας μη γραμμικές ανελαστικές δυναμικές αναλύσεις και συγκρίνονται με την συνηθισμένη μέθοδο των αντισεισμικών κανονισμών η οποία χρησιμοποιεί μια κοινή τιμή του συντελεστή συμπεριφοράς για όλες τις ιδιομορφές. Συμπεραίνεται ότι η προτεινόμενη μέθοδος αντισεισμικού σχεδιασμού οδηγεί σε ορθολογικότερα και ακριβέστερα αποτελέσματα σε σχέση με τη συνηθισμένη μέθοδο. / A rational method for seismic design of plane building frames based on the use of equivalent modal damping ratios is developed. The method determines the maximum seismic structural response through spectrum analysis using rationally obtained equivalent modal damping ratios instead of the crude strength reduction (behavior) factor. This is materialized in the second part of this work. In this first part, all theoretical aspects regarding equivalent modal damping ratios are developed and described in detail. The basic idea is the establishment of an equivalent linear multi-degree-of-freedom (MDOF) structure which can reproduce the seismic response of a MDOF geometrically and materially non – linear structure. More specifically, this equivalent linear structure retains the mass and stiffness of the original non – linear structure and takes into account geometrical non – linearity and inelasticity in the form of equivalent, time – invariant, modal damping ratios. The equivalent damping ratios for the first few significant modes are numerically computed by first iteratively forming a frequency response transfer function until it satisfies some specific smoothness criteria and then by solving a set of non – linear algebraic equations. Moreover, it is shown that these equivalent modal damping ratios can be computed in such a way so as to be deformation and damage dependent, which can lead to a better design in a direct manner. The concept of equivalent modal damping ratios developed is then employed for the seismic design of plane steel moment resisting frames. The goal is the determination of the maximum seismic structural response through spectrum analysis using rationally obtained equivalent modal damping ratios instead of the crude strength reduction factor. Therefore, design equations providing equivalent damping ratios as functions of period and allowable deformation and damage for the first few significant modes are constructed using extensive numerical data coming from a representative number of plane steel moment resisting frames excited by various seismic motions. These equations can be used in conjunction with a design spectrum, appropriately modified for high damping values, and modal synthesis tools to calculate the seismic design forces of the structure. The proposed method is illustrated by performing the seismic design of a steel moment resisting framed structure. It is concluded that unlike the usual code – based approach, which employs a single and crude strength reduction factor value for all modes, the proposed approach works with deformation and damage dependent equivalent modal damping ratios and thus leads to more accurate and deformation and damage controlled results in a direct and more rational way. Moreover, it is shown that by using equivalent modal dampiing one may define modal strength reduction factors. Thus, alternatively, maximum seismic response may be obtained by spectrum analysis and modal strength reduction factors.