Enhancing the Seismic Performance of Steel Structures Utilizing Superelastic Shape Memory Alloys

Although conventional earthquake-resisting structural systems provide the life safety level during earthquakes, they experience significant structural damage when exposed to strong ground shaking that render structural retrofitting as uneconomical. Superelastic shape memory alloys (SMAs) can be used in steel structures to reduce the residual deformations due to their recentering capability, which can facilitate post-seismic retrofitting. The primary aim of this thesis is to enhance the seismic performance of both regular and modular steel structures using an optimum amount of superelastic SMAs material in terms of maximum inter-storey drift, residual drift, and damage scheme. First, a simplified method based on pushover analysis is proposed to identify the severely damaged floor of a typical SMRF. It was validated with the studies by other researchers. Three and ten-storey SMRFs are considered to further validate the method. The predicted location of damage for the SMRFs using this method is compared to the results of static pushover and nonlinear dynamic analyses. The method accurately identified the severely damaged floors of SMRFs. The proposed simplified method as well as incremental dynamic analysis is then utilized to determine the best locations of SMA connections to improve the seismic performance of SMRFs. Six different SMA frames are examined using nonlinear dynamic analyses. Among all SMA frames, the frame using SMA connections at the critical first and fourth floors showed very good seismic performance compared with the steel frame. The seismic performance of modular steel braced frames (MSBFs) is significantly different from regular steel braced frames because of their unique detailing and construction procedure. An analytical model that can accurately predict the seismic behaviour of MSBFs equipped with buckling restrained SMA braces is first developed. This model is then implemented to identify the locations of SMA braces to improve the seismic performance of MSBFs. The study highlighted the need to use SMA braces at all floors. The study also examines the seismic performance of MSBFs utilizing superelastic SMA bolts at the vertical connections between the modules. It was observed that the seismic performance of a MSBF can be improved by using SMA connections at the right locations

Prediction of local seismic damage in steel moment resisting frames

Steel moment resisting frames (SMRFs) are widely utilized as a lateral load resisting system. Their seismic performance is usually assessed by examining the maximum value of inter-storey drift (MID) of all floors. The accuracy of such assessment is debatable given the wide spread of values of MID at collapse that exist in the literature. In this study, a simplified method to define the failure inter-storey drift for each floor of a SMRF is proposed. The method was validated with the experimental and analytical studies by other researchers. Three- and ten-storey SMRFs were considered to further validate the proposed method. The effects of the vertical and/or horizontal seismic components of five different ground motions on the SMRFs were evaluated using incremental dynamic analysis. The proposed method accurately identified the severely damaged floors of SMRFs

Seismic performance of modular steel frames equipped with shape memory alloy braces

The demand for modular steel buildings (MSBs) has increased because of the improved quality, fast on-site installation, and lower cost of construction. Steel braced frames are usually utilized to form the lateral load resisting system of MSBs. During earthquakes, the seismic energy is dissipated through yielding of the components of the braced frames, which results in residual drifts. Excessive residual drifts complicate the repair of damaged structures or render them irreparable. Researchers have investigated the use of superelastic shape memory alloys (SMAs) in steel structures to reduce the seismic residual deformations. This study explores the potential of using SMA braces to improve the seismic performance of typical modular steel braced frames. The study utilizes incremental dynamic analysis to judge on the benefits of using such a system. It is observed that utilizing superelastic SMA braces at strategic locations can significantly reduce the inter-storey residual drifts

Seismic Performance of Modular Steel-Braced Frames Utilizing Superelastic Shape Memory Alloy Bolts in the Vertical Module Connections

In modular construction, individual modules are constructed at a controlled industrial environment before being transported to site. They are then connected horizontally and vertically to form a structure. The vertical connections can be achieved by welding or bolting the columns of stacked modules. This study investigates the seismic performance of modular steel-braced frames (MSBFs) connected vertically using superelastic shape memory alloy (SMA) bolts. The study also identifies the required locations of SMA connections, in a typical MSBF, to optimize its seismic performance in terms of maximum inter-story drift (MID), maximum residual inter-story residual drift (MRID), and damage scheme

Predictions of Flexural Behaviour of Built-Up Cold-Formed Steel Sections

In recent years, light gauge cold-formed steel members have been used extensively in low and mid- rise residential building construction. In cold-formed steel design there are several applications where built-up box girders are used to resist load induced in a structure when a single section is not sufficient to carry the design load. The cold-formed steel box girders may be subjected to eccentric loading when the web of one of the sections receives the load and transfers it through the connection to another section. There may be an unequal distribution of load in built-up girder assemblies loaded from one side. In the current North American Specification for the Design of Cold-Formed Steel Structural Members (CSA-S136-01, 2001), there is no guideline or design equation to calculate the flexural capacity of this type of section. AISI cold-formed steel framing design guide (2002) has recommended that the moment of resistance and inertia of the built-up section are the simple addition of the component parts, based on deflection compatibility of the two sections. However, this design approximation has not been justified by any experimental or numerical study. Very little information was found in literature about this topic. The objective of this study is the investigation of the flexural behaviour of built-up box girders assembled from cold-formed stud and track sections when subjected to eccentric loading. Finite element analysis is conducted for this purpose, being much more economical than expensive experimental testing. Detailed parametric studies are carried out to identify the factors affecting the flexural capacity of built-up cold-formed steel sections. The parametric results are used to develop a design equation for calculating the flexural capacity of built-up cold-formed steel sections

Study of thermal performances of falling film absorbers with and without film-inversion

Ph.DDOCTOR OF PHILOSOPH

STR-834: SEISMIC PERFORMANCE OF MODULAR STEEL FRAMES EQUIPPED WITH SHAPE MEMORY ALLOY BRACES

Modular steel buildings (MSBs) are widely used for one to six storey schools, apartments, and similar buildings, where repetitive units are required. Modular units are first built and finished under a controlled manufacturing environment. They are then transported to the building site, where they are connected horizontally and vertically. The lateral load resisting system for MSBs usually relies on steel braced frames, which dissipate the seismic energy through steel yielding. This behaviour leads to residual drifts complicating the repair of seismically damaged buildings or rendering them as irreparable. Systems that can minimize the seismic residual drifts are thus needed. Superelastic Shape Memory Alloys (SMAs) have the ability to undergo large plastic deformations and recover them upon unloading. Their utilization in steel structures can significantly reduce seismic residual deformations, which will facilitate post-seismic retrofitting. The purpose of this study is to examine the seismic performance of modular steel braced frame (MSBF) that utilizes SMA braces. A six-storey buckling restrained MSBF was considered as a case study. Nonlinear dynamic analysis was conducted to compare the seismic performance of this MSBF when it is fitted with steel and SMA braces. The use of SMA braces was found to improve the seismic performance of MSBs in terms of maximum residual inter storey drift (MRID) and damage scheme

Seismic performance of steel moment resisting frames utilizing superelastic shape memory alloys

Steel structures dissipate the seismic energy through steel yielding, which results in residual deformations. Although conventional earthquake-resisting structural systems provide adequate seismic safety, they experience significant structural damage when exposed to strong ground shaking. Seismic residual drifts complicate the repair of damaged structures or render the structure as irreparable. Therefore, systems that can minimize the seismic residual deformations are needed. Superelastic shape memory alloys (SMAs) have the ability to undergo large deformations and recover all plastic deformations upon unloading. Their utilization in steel structures can significantly reduce seismic residual deformations, which will facilitate post-seismic retrofitting. Although the literature provides few research data on using SMA in steel beam-column connections, previous research did not address their optimum use. This paper identifies the required locations of SMA connections in a typical steel moment resisting frame to enhance its seismic performance in terms of maximum inter-storey drift, residual deformations, and damage scheme

Assessment of glycemic status and BMI of resident and non - resident female students of Jessore University of science and technology, Bangladesh

Background: Glycemic status means blood glucose level in an individual is measure by using the term hyperglycemia and hypoglycemia. Hyperglycemia is a condition in which an excessive amount of glucose circulates in the blood plasma whereas hypoglycemia is below normal level of glucose in blood.  Abnormal Glycemic status develops various short as well as long term health complications. Constant monitoring of health status of an individual’s is important in maintaining good glycemic status in preventing development of hyperglycemia and hypoglycemia related complication.Methods: Female students ages 20 – 23 of hall resident and non resident of Jessore University of Science and Technology were randomly selected. Fasting blood glucose data and Body Mass Index (BMI) were collected on the basis of family status, income and eating pattern, family environments using standard laboratory procedures.Results: The study found that 68% resident students were in hypoglycemic whereas 60% nonresident female students were in hypoglycemic but hyperglycemic and acute hyperglycemic effect was totally absent in both group of students. Differences of BMI irregularities of both groups of students were not observed. Most of residential students (88%) were only depends on the provided food in the dining hall. Whereas nonresident students majority of them are belonged to upper middle class, living in their own house and their eating patterns were better than residential female students. Therefore, most of the nonresident female students are able to intake nutritious foods. As a result the hypoglycemic students were found less abundant in nonresidential student compared to the resident group. Therefore dieting habit is one of the most important reasons to develop irregular glycemic status.Conclusions: The need of awareness of good health care practice, intake good quality nutritious diet, avoid of abnormal dieting practice is prerequisite to maintain static glycemic status which directly linked to good health

Stigma and its associated factors among patients with COVID-19 in Dhaka City: evidence from a cross-sectional investigation

Background: Coronavirus disease 2019 (COVID-19) has become a significant disease pandemic. Dhaka City alone has contributed about one-third to the total COVID-19 cases in Bangladesh. Globally, patients with infectious diseases, including COVID-19, experience stigma. There was no quantitative estimate of stigma experienced by patients with COVID-19 in the country. Therefore, this study aimed to assess the prevalence of stigma and its associated factors among patients with COVID-19 in Dhaka. Methods: A cross-sectional study was conducted among 384 respondents aged 18 years or older who had been hospitalized or had stayed at home and were tested negative 15 days to 6 months before the day of data collection. Data collection was done through in-person and telephone interviews using a semi-structured survey questionnaire. A 15-item COVID-19-related stigma scale questionnaire was used to assess stigma. Binary logistic regression analysis was performed to identify the predictors of stigma. Results: More than half (53.1%) of the respondents experienced stigma when they were COVID-19 positive. Females were at a 3.24 times higher risk of experiencing stigma than their male counterparts. Respondents from the 60+ age group and 40–59 age group were 63.0% and 48.0% less likely to experience stigma than those from the 18–39 age group. Non-hospitalised patients had 1.67 times higher odds of facing stigma than those hospitalised. Conclusions: This study reported a high prevalence of stigma among the patients with COVID-19 in Dhaka City. The current evidence base of stigma experience among patients with COVID-19 offers a solid foundation for creating effective strategies and policies and designing appropriate interventions to counter stigma, which will improve the psychological well-being of patients with COVID-19 in Bangladesh