1,720,986 research outputs found
Performance-Based Assessment Methodology for Retrofit of Buildings
No full textPostearthquake reconnaissance and recent research on seismic risk analysis have shown that nonductile concrete frame structures are much more susceptible to collapse than modern code-conforming frames. The performance-based assessment paradigm has been a persistent research theme over the last decade within the earthquake engineering community in order to estimate seismic fragilities and earthquake loss for these nonductile concrete frames. This paper proposes a nonlinear performance-based methodology to evaluate different retrofit methods considering hazard level, target performance levels, and life-cycle cost estimates. The structural performance is the main parameter considered for the optimization, although a life-cycle cost analysis is also presented. As a case study, the longitudinal frame of an existing building was modeled considering the effect of flexural-shear-axial load interaction in order to capture column shear and axial failures. The presented performance-based procedure identifies the most economic retrofit solution that satisfies structural response requirements for a given performance level
Seismic performance of masonry buildings during the 2007 Bala, Turkey earthquakes
No full textWOS: 000299957100012A field investigation was conducted near the town of Bala after two strong earthquakes struck the region on December 20 and 27, 2007. The main objectives of this study are to present the results of the field investigation and examine the characteristics of the recorded ground motions and the corresponding response spectra. The focus of the research was on the causes of damage and failures commonly observed in masonry structures. This study classifies single family masonry dwellings in rural areas and investigates the seismic damage in unreinforced masonry structures. Turkish Earthquake Code requirements for masonry buildings are summarized and compared with the field observations. Our field investigation showed that there has been lack of quality control and regulation for the masonry construction. Diagonal shear cracking and out-of-plane failure were the two major factors that contributed to widespread damage in masonry structures.BAP Unit of Karadeniz Technical University [2006.112.001.7]This study is supported by BAP Unit of Karadeniz Technical University (Project no. 2006.112.001.7)
Analytical fragility assessment using unscaled ground motion records
No full textIt is desirable that nonlinear dynamic analyses for structural fragility assessment are performed using unscaled ground motions. The widespread use of a simple dynamic analysis procedure known as Cloud Analysis, which uses unscaled records and linear regression, has been impeded by its alleged inaccuracies. This paper investigates fragility assessment based on Cloud Analysis by adopting, as the performance variable, a scalar demand to capacity ratio that is equal to unity at the onset of limit state. It is shown that the Cloud Analysis, performed based on a careful choice of records, leads to reasonable and efficient fragility estimates. There are 2 main rules to keep in mind for record selection: to make sure that a good portion of the records leads to a demand to capacity ratio greater than unity and that the dispersion in records' seismic intensity is considerable. An inevitable consequence of implementing these rules is that one often needs to deal with the so‐called collapse cases. To formally consider the collapse cases, a 5‐parameter fragility model is proposed that mixes the simple regression in the logarithmic scale with logistic regression. The joint distribution of fragility parameters can be obtained by adopting a Markov Chain Monte Carlo simulation scheme leading directly to the fragility and its confidence intervals. The resulting fragility curves compare reasonably with those obtained from the Incremental Dynamic Analysis and Multiple Stripe Analysis with (variable) conditional spectrum–compatible suites of records at different intensity levels for 3 older reinforced concrete frames with shear‐, shear‐flexure‐, and flexure‐dominant behavior
Progressive Collapse Analysis of an Existing Building
Get PDFThis research study investigates an actual structure’s potential to fail due to progressive collapse. Progressive collapse in a structure occurs when major structural load carrying members are removed suddenly, and the remaining structural elements cannot support the weight of the building and fail. This failure usually occurs in a domino effect and leads to a progressive collapse failure in the structure. The bombing of the Murray Federal Building in Oklahoma City is a typical example of progressive collapse failure. The initial bomb blast caused only 10% of the structure’s damage, and the resulting progressive collapse failure lead to 90% of the structure’s damage.
This experiment involved testing of a steel building scheduled for demolition in Northbrook, Illinois. The demolition team tore out four selected columns from the building to simulate the sudden column removal that leads to progressive collapse. The structure was instrumented with strain gauges that recorded the change in strain in various structural members while the columns were removed. The author instrumented the beams and columns in the building, managed the testing, and analyzed the recorded data.
The strain values recorded in the field were compared with the results from a computer model of the building. The model was created in a structural analysis program (SAP2000). The research is still underway, and the strain values recorded in the field and the computer model are being compared and analyzed. The percent error between the calculated and measured strains in a selected column was 21%.
The SAP2000 analysis conducted in this research was based on linear material properties. The numerical models and simulations will be expanded to include nonlinear effects and dynamic analysis. The ultimate goal of this ongoing progressive collapse research on real buildings is to develop better building evaluation and design guidelines for structural engineers to use to prevent progressive collapse in new and existing buildings. Future progressive collapse research recommendations are also presented. The instrumentation of strain gauges for optimum results is discussed, and column removal guidelines and linear displacement sensor instrumentation are also shown.No embarg
Repair and Strengthening of Reinforced Concrete Beams
Get PDFRepair and strengthening of damaged or vulnerable reinforced concrete structures is important in order to guarantee the safety of residents or users. Beams are important structural elements for withstanding loads, so finding the efficient repair and strengthening methods are necessary in terms of maintaining the safety of the structures.
This research study investigated various repair, retrofit, and strengthening techniques for reinforced concrete beams. The comparison and summary of each repair and strengthening method are provided in this thesis.
The thesis involves the literature review of current experimental test of repair and strengthening techniques for reinforced concrete beams. The experimental studies were summarized by describing the specimens and loading details, All the methods in the research were categorized into five chapters: section enlargement and concrete jacketing, external reinforcement, steel plates, unbonded-type strengthening, and concrete repairs. The installation procedures were summarized and the advantages, shortcomings, and considerations of each method were also discussed in the thesis.No embarg
Analytical Models for Reinforced Concrete Columns Retrofitted with Fiber-Reinforced Polymer Composites
Get PDFTraditional rebar reinforcement methods in concrete columns have been accepted for many years as the common practice among designers and contractors. There has been a tremendous amount of research completed and designers are capable of predicting the future performance of the columns. More recently, retrofit methods have been used on aging concrete columns. This includes adding an additional layer of concrete or composite material around the existing column to slow the deterioration and to increase the concrete confinement. Current models exist in the use of a combination of a rebar cage and concrete as the retrofit method.
Fiber-reinforced polymer (FRP) wraps are fast becoming a new form of technology to replace traditional rebar retrofit technology. The fiber-reinforced polymer wraps are a composite material that can be attached to the existing concrete column using an epoxy resin. The wrap increases the concrete confinement of the column and provides support for the concrete dilation in the column. However, FRP wraps are not heavily used in structural applications because there is not an accepted model that has been proven to accurately predict future strength characteristics of the confined concrete column.
The focus of this research project is to use the results of an already completed test of concrete columns confined by FRP wraps, and compare the resulting stress-strain curves to the commonly proposed modeling technology available. FRP modeling is still relatively new and there is not a widely accepted model.
The purpose of this research project is to determine how accurately the proposed FRP models predict the strength of the tested columns. There are many different models that have been proposed, but the key to the future of FRP retrofitting is to create a widely accepted, reliable model that engineers can use in design. It is important to normalize the design process of FRP retrofitted columns in order to better use the technology in the future.
Advisor: Halil SezenCollege of EngineeringDepartment of Civil & Environmental Engineering & Geodetic Scienc
PROGRESSIVE COLLAPSE: COMPUTER ANALYSIS OF BEAMS AND DETAILING
Get PDFThe term 'progressive collapse' can be simply defined as the ultimate failure or
proportionately large failure of a portion of a structure due to the spread of a local failure from
element to element throughout the structure. Progressive collapse can be triggered by manmade,
natural, intentional, or unintentional causes. Fires, explosions, earthquakes, or anything else
causing large amounts of stress and the failure of a structure's support elements can lead to a
progressive collapse failure. Progressive collapse is a complicated dynamic process where the
collapsing system redistributes the loads in order to prevent the loss of critical structural
members. For this reason beams, columns, and frame connections must be designed in a way to
handle the potential redistribution of large loads. Some of the more famous examples of
progressive collapse phenomena include the collapse of the World Trade Center towers due to
terrorist attack, the bombing of the Murrah Federal Building in Oklahoma City, and the collapse
of the Ronan Point building due to a gas explosion. Through research being done, such as that in
this study, progressive collapse can be better prepared for and possibly prevented in the future.
This project involves use of two main computer programs to perform analysis on a
reinforced concrete structure. MATLAB and SAP2000 are used to determine the total amount of
steel rebar required to prevent progressive collapse at midspan of a continuous beam section
where a column loss has occurred. The research results provide insight into the minimum
amount of reinforcing steel actually needed to achieve a demand to capacity ratio of
approximately 1.0 and prevent collapse in the event of a single column loss. Several
relationships are developed between span lengths, distributed loading, column loading, and steel
required. The maximum allowable loads are calculated to show how to best prevent progressive
collapse. The results are obtained using different models where combinations of pinned end and
fixed end support configurations are used along with analysis of nominal moment strength of the
beam versus the plastic moment strength of the beam. Ultimately, tables and graphs are
developed that could eventually be used in design codes where there are currently very limited or
no specific rules or guidelines directed towards prevention of progressive collapse.No embarg
Earthquake Engineering
Get PDFRecent major earthquakes around the world have shown the vulnerability of infrastructure and the need for research to better understand the nature of seismic events and their effects on structures. As a result, earthquake engineering research has been expanding as more and more data become available from a large array of seismic instruments, large scale experiments and numerical simulations. The first part of this book presents results from some of the current seismic research work including three-dimensional wave propagation in different soil media, seismic loss assessment, probabilistic hazard analysis, geotechnical problems including soil-structure interaction. The second part of the book focuses on the seismic behavior of structures including historical and monumental structures, bridge embankments, and different types of bridges and bearings
Comparison of Prefabricated Cage System with Existing Reinforcement Methods in Concrete Columns
Get PDFA reinforced concrete column is composed of two main load bearing mechanisms; concrete and a steel reinforcing cage. The concrete is the primary vertical load bearing mechanism with the steel cage providing some vertical load carrying capacity while serving mainly to confine the core concrete. The steel cage consists of two types of bars; longitudinal, which carry any compressive or tensile loads, and transverse, which hold the longitudinal bars in place and also provide confinement of the core concrete under axial load. The transverse bars are bent and tied to the longitudinal bars.
A new type of steel cage has recently been proposed by Halil Sezen PhD and Mohammad Shamsai PhD, both of The Ohio State University. The new method is termed Prefabricated Cage System (PCS) reinforcement, and it consists of a cage constructed from a solid steel tube. A grid is cut into the tube through the use of a laser-cutter, resulting in a reinforcing cage that is very similar to a rebar cage. The main differences between the two are: 1) The PCS cage is a solid entity, while the rebar cage is held together through the use of ties. 2) The steel in the PCS cage is in rectangular form while the steel in the rebar cage typically consists of round bars. The machine fabrication of PCS provides a more accurately constructed column, compared to the manually constructed rebar cage, at the same or less cost than a rebar column due to the reduced on-site construction time required by PCS.
The research project will focus on the performance of PCS in circular columns. In all, six samples will be constructed and tested, consisting of two rebar reinforced columns and four PCS reinforced columns. Each test column will be 18 in. in height with a 6 in. diameter. There will be two test groups, each group containing one rebar column and two PCS columns. The strength of the steel, which is represented by the yield stress of the steel multiplied by the cross-sectional area of the steel, will be the same in each test group to allow for accurate comparisons.
The purpose of this research is to not only compare the performance of a PCS reinforced column to a rebar reinforced column, but also to compare PCS cages with differently sized grid openings. The objective is to investigate whether the PCS column has a higher maximum load and a larger displacement capacity, due to the increased confinement provided by the rectangular shape of the PCS cage over the round shape of the rebar cage.Ohio State University Undergraduate Student Government - Undergraduate Research GrantOhio State University College of Engineering - Undergraduate Research Scholarshi
A Review of Reinforced Concrete Building Progressive Collapse Studies
Get PDFIn an era marked by increasing exposure to extreme events, the robustness of building structures against unforeseen hazards has emerged as a critical concern and significant efforts have been made in identifying how to prevent local failures from propagating during the progressive collapse process. This study delves into the phenomenon of progressive collapse in reinforced concrete buildings, aiming to enhance understanding and mitigation strategies against extreme loading hazards. Through a systematic analysis of diverse sources, including case studies and experimental data, a novel database is formulated, comprising instances of partial or complete structural collapse due to progressive failure. The database encompasses contextual information, structural typology, geometry, failure characteristics, and consequences of collapse. To identify structural vulnerabilities, this database systematically presents information on hazards causing failure, failure locations, types of collapse, as well as structural information to facilitate a nuanced understanding of collapse triggers and propagation. By integrating analytical and experimental findings, this research aims to advance the knowledge on progressive collapse behavior and informs the development of robust mitigation strategies to enhance building robustness against extreme loads or unforeseen hazards.No embargoAcademic Major: Civil Engineerin
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