A numerical investigation of 3D structural behaviour for steel-composite structures under various travelling fire scenarios

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Experimental Assessment of the Current Load Rating Procedures for a Corroded Steel Ridge Girder in Massachusetts

The work conducted for this project involves an experimental assessment of the Massachusetts Department of Transportation’s (MassDOT) existing procedure for determining the resistance of a corroded steel girder end when load rating a bridge. Three steel girders with significant corrosion developed over a 79-year service life were obtained from a recently rehabilitated bridge and loaded to determine the girders corroded resistance. A testing rig was designed in the UMass Amherst Brack Structural Testing Laboratory to both apply a shear dominated load to the corroded girder and withstand the developed lateral loads throughout the analysis. Reaction force data obtained from the load testing was compared against the corroded web factored resistance determined from the MassDOT LRFD Bridge Design Manual. Resistances were under predicted by 75% for specimen 1, 37% for specimen 2 and the manual predicted no resistance for specimen 3. Lastly influences for the discrepancies between manual resistance and experimental resistance are determined

Deterministic, probabilistic and risk-based design for progressive collapse of RC structures based on a novel method

Progressive or disproportionate collapse is a structural failure mechanism accompanied with a significant disproportion between the initiating event and the ensuing failure consequence. Facing a possible huge economic loss and even large casualties, structures must be designed with sufficient robustness. Several structural design codes and standards have presented guidelines to increase the robustness of structures. However, these guidelines are largely of deterministic nature and may not be effective, because structures involve large variation in loading, material properties, etc. These variations can lead to significant uncertainty in the degree of robustness of structures and should be dealt with in a probabilistic framework. Based on a new direct design method developed by the authors recently, this study showed that how probabilistic and risk-based design for progressive collapse can be accomplished from a case study. The method can not only help engineers quickly conduct probabilistic performance-based design of structures against progressive collapse, but also communicate with stakeholders more efficiently if adopting risk-based design strategy.This research was partially supported by National Key Research Program of China (grant number 2016YFC0701400), National Natural Science Foundation of China (grant number 51338004), and the Discovery Grant program of the Natural Science and Engineering Research Council (NSERC) Canada. The study was conducted during the first authors visiting research at Ryerson University. The funding support from the China Scholarship Council (CSC) for the first author is also gratefully acknowledged

On the Analysis of the Disproportionate Structural Collapse in RC Buildings

Increasing structural robustness is the goal which is of interest for structural engineering community. The partial collapse of RC buildings is subject of this dissertation. Understanding the robustness of RC buildings will guide the development of safer structures against abnormal loading scenarios such as; explosions, earthquakes, fine, and/or long-term accumulation effects leading to deterioration or fatigue. Any of these may result in local immediate structural damage, that can propagate to the rest of the structure causing what is known by the disproportionate collapse. This work handels collapse propagation through various analytical approaches which simplifies the mechanical description of damaged reinfoced concrete structures due to extreme acidental event

Distributed Damage Effect on Progressive Collapse of Structures and Variability Response Functions in Stochastic 2D Elasticity Problems

This dissertation investigates the distributed damage effect on Progressive Collapse of structures highlighted by applications on the nonlinear static and dynamic behavior of buildings, and contributes to the theoretical development of the Variability Response Function concept and its applicability extension in two-dimensional elasticity stochastic problems. Part I of this dissertation focuses on the recently emerging research field of Progressive Collapse of structures. The alternate load path method has so far dominated the field of progressive collapse of structures; in order to assess the resilience of structural systems, the concept of the removal of a key element is utilized as a means of damage introduction to the system. Recent studies have indicated that the complete column loss notion is unrealistic and unable to describe a real extreme loading event, e.g. a blast, that will introduce damage to more than one elements in its vicinity. This dissertation presents a new partial distributed damage method (PDDM) for steel moment frames, by utilizing powerful finite element computational tools that are able to capture loss of stability phenomena. Through the application of a damage index δj and the investigation of damage propagation, it is shown that the introduction of partial damage in the system can significantly modify the collapse mechanisms and overall affect the response of the structure. Subsequently, Part I elaborates on the distributed column damage effect on Progressive Collapse vulnerability in steel buildings exposed to an external blast event. Recent terrorist attacks on civil engineering infrastructure around the world have initiated extensive research on progressive collapse analysis of multi-story buildings subjected to blast loading. The widely accepted alternate load path method is a threat-independent method that is able to assess the response of a structure in case of extreme hazard loads, without the consideration of the actual loads occurring. Such simplification offers great advantages but at the same time fails to incorporate the role of a wider damaged area into the collapse modes of structures. To this end, the investigation of damage distribution on adjacent structural members induced by blast loads is considered critical for the evaluation of structural robustness against abnormal loads that may initiate progressive collapse. This dissertation presents detailed 3D nonlinear finite element dynamic analyses of steel frame buildings in order to examine the spatially distributed response and damage to frame members along the building exterior facing an external blast. A methodology to assess the progressive collapse vulnerability is also proposed, which includes four consecutive steps to simulate the loading event sequence. Three case studies of steel buildings with different structural systems serve as examples for the application of the proposed methodology. A high-rise (20-story) building is firstly subjected to a blast load scenario, while the complex 3D system results in the heavily impacted region are compared with individual column responses (SDOF) obtained from a simplified analytical approach consistent with current design recommendations. Parameters affecting the spatially distributed pressure and response quantities are identified, and the sensitivity of the damage results to the spatial variation of these parameters is established for the case of the 20-story building. Subsequently, two typical mid-rise (10-story) office steel buildings with identical floor plan layout but different lateral load resisting systems are examined; one including perimeter moment resisting frames (MRFs) and one including interior reinforced concrete (RC) rigid core. It is shown that MRFs offer a substantial increase in robustness against blast events, and the role of interior gravity columns identified as the `weakest links'\ of the structural framing is discussed. Part II of this dissertation focuses on the development of Variability Response Functions for apparent material properties in 2D elasticity stochastic problems. The material properties of a wide range of structural mechanics problems are often characterized by random spatial fluctuations. Calculation of apparent properties of such randomly heterogeneous materials is an important procedure, yet no general method besides Monte Carlo simulation exists for evaluating the stochastic variability of these apparent properties for structures smaller than the representative volume element (RVE). In this direction, the concept of Variability Response Function (VRF) has been proposed as a means to capture the effect of stochastic spectral characteristics of uncertain system parameters modeled by homogeneous stochastic fields on the uncertain response of structural systems, without the need for computationally expensive Monte Carlo simulations. Recent studies have formally proved the existence of VRF for apparent properties for statically determinate linear beams through elastic strain energy equivalence of the heterogeneous and equivalent homogeneous bodies, while a Monte-Carlo based methodology for the generalization of the VRF concept to statically indeterminate beams has been recently developed. In this dissertation, the VRF methodology of apparent properties is extended to two-dimensional elasticity stochastic problems discretized on a finite element domain, in order to analytically formulate a VRF that is independent of the marginal distribution and spectral density function of the underlying random heterogeneous material property field (it depends only on the boundary conditions and deterministic structural configuration). Representative examples that illustrate the approach include two-dimensional plane stress problems and underline the dependence of the VRFs on scale, shape and aspect ratio of the finite elements

Risk-based design of structures for fire

Techniques of performance-based design in fire safety have developed notably in the past two decades. One of the reasons for departing from the prescriptive methods is the ability of performance-based methods to form a scientific basis for the cost-risk-benefit analysis of different fire safety alternatives. Apart from few exceptions, observation of past fires has shown that the structure’s contribution to the overall fire resistance was considerably underestimated. The purpose of this research is to outline a risk-based design approach for structures in fire. Probabilistic methods are employed to ascertain uniform reliability indices in line with the classical trend in code development. Modern design codes for complex phenomena such as fire have been structured to facilitate design computations. Prescriptive design methods specify fire protection methods for structural systems based on laboratory controlled and highly restrictive testing regimes. Those methods inherently assume that the tested elements behave similarly in real structures irrespective of their loading, location or boundary conditions. This approach is contested by many researchers, and analyses following fire incidents indicated alarming discrepancy between anticipated and actual structural behaviour during real fires. In formulating design and construction codes, code writers deal with the inherent uncertainties by setting a ceiling to the potential risk of failure. The latter process is implemented by specifying safety parameters, that are derived via probabilistic techniques aimed at harmonising the risks ensuing different load scenarios. The code structure addresses the probability of failure with adequate detail and accuracy. The other component of the risk metric, namely the consequence of failure, is a subjective field that assumes a multitude of variables depending on the context of the problem. In codified structural design, the severity of failure is implicitly embodied in the different magnitudes of safety indices applied to different modes of structural response. This project introduces a risk-based method for the design of structures in fire. It provides a coherent approach to a quantified treatment of risk elements that meets the demands of performance-based fire safety methods. A number of proposals are made for rational acceptable risk and reliability parameters in addition to a damage index with applications in structural fire safety design. Although the example application of the proposed damage index is a structure subjected to fire effects, the same rationale can be easily applied to the assessment of structural damage due to other effects

3D Printed Architected Materials for Improving Biofilm Carriers for Wastewater Treatment Applications

Wastewater infrastructure in the United States has been in dire need of improvement for quite a while. It was estimated that wastewater treatment systems would need about $57.2 billion to maintain acceptable levels of treatment in the coming years (Christen, 2003). This is just for maintaining the treatment systems in place, without any room for improvement, and it only accounts for about 31.6$84 billion (67% of total need) by 2020, and $144 billion (73% of total need) by 2040 (ASCE, 2013). Because of this funding gap, wastewater treatment plants have to be able to address many of the shortcomings themselves. Therefore, wastewater treatment plants have to be able to perform more efficient treatment with less investment

NONLINEAR ANALYSIS OF STEEL BUILDINGS WITH RC SHEAR WALLS USING IMPROVED APPLIED ELEMENT METHOD

Ph.DDOCTOR OF PHILOSOPH

Utilizing Unmanned Aerial Vehicles (UAVs) for the Estimation of Beam Corrosion of Steel Bridge Girders

The transportation infrastructure in the United States is a complex system that is vital to the everyday operations of the country. Bridges are a significant asset of this network, with many of them approaching the end of their service life. Corrosion is a common cause of deterioration which ultimately results to structural deficiency for the aging bridges. The deterioration rate is a multi-aspect factor that makes bridge inspections crucial. However, the current bridge inspections are very costly and potentially unsafe for the involved personnel. To lower costs and increase safety, many state DOT’s and universities have decided to perform research on Unmanned Aerial Vehicles (UAVs), or drones. This thesis explores the implementation of drone technology in bridge inspections and investigates their limits for corrosion detection and estimation. The first part of this thesis summarizes the responses obtained from a questionnaire sent to the personnel from the Massachusetts Department of Transportation (MassDOT). The second and third parts of this thesis summarizes how states have utilized UAVs for bridge inspections, including the selected drones and the attached equipment. The last part presents technologies that can be used to detect and measure corrosion, and how they can be used in conjunction with drones to quantify section loss of steel beams

Harmony Search Optimization and Damage Tolerance of Structural Systems

In this thesis, multiple structural systems are investigated by utilizing the Harmony Search optimization algorithm for least weight optimization. An analytical overview of structural optimization, matrix analysis, damage tolerance, steel connections and structural reliability analysis and methodology are presented. To support the methodology, three example problems have been provided. The first example demonstrates damage tolerant optimization of a simple truss structure. The second example focuses on the harmony search optimization of a more complex steel frame along with damage tolerant optimization. The third example provides a brief connection between damage tolerance and structural reliability. The findings show that the harmony search algorithm can be a powerful tool when optimizing structural systems. They also show the power of linking optimization, damage tolerance and structural reliability when considering the design of a structure