Erem Melike Roman - Carol Roman ile Nazım Hikmet ve Türk edebiyatı üzerine

Taha Toros Arşivi, Dosya Adı: Nazım Hikmetİstanbul Kalkınma Ajansı (TR10/14/YEN/0033) İstanbul Development Agency (TR10/14/YEN/0033

REPAIR OF BRIDGE STEEL GIRDERS DAMAGED BY DISTORTION-INDUCED FATIGUE

This study investigates the repair of steel bridge girders damaged by distortion-induced fatigue. The study is presented in three parts. The first part describes finite element modeling techniques used to evaluate the potential for fatigue cracks in steel girders subjected to distortion-induced fatigue. The modeling techniques employed in this study were intended to identify areas near welded connections in bridge girders with the highest potential for developing fatigue cracks, and to evaluate the effectiveness of retrofit measures in reducing the potential for crack propagation near welded connections with existing fatigue cracks. Computer simulations correlated well with experimentally observed crack patterns and were useful in providing an indication of the effectiveness of various retrofit measures. The second part of the study investigates the use of composite materials to repair fatigue damage in steel girders. A total of 17 specimens with pre-existing fatigue cracks were tested under cyclic loading to evaluate the performance of composite overlays when used to repair fatigue damage in steel structures. Two control specimens were tested without overlays and the remaining 15 were repaired with Carbon Fiber Reinforced Polymer (CFRP) overlays of various thicknesses. Results indicate that this method was very effective, and that proper implementation of this type of repair can reduce the crack propagation rate to negligible values. The third part of the study consisted of physical and computer simulations of 914-mm (36-in.) deep girder-cross frame subassemblies subjected to cyclic loading. The simulations were carried out to investigate the stress demands caused by distortion-induced fatigue and to evaluate the effectiveness of various retrofit measures. Previously used repair methods for distortion-induced fatigue damage have attempted to reduce the stress demand in the web gap region by increasing the flexibility of cross-frame to girder connection or by restraining the lateral motion of the cross-frame by attaching the connection plate to the slab. A new retrofit approach was investigated in this study designed to reduce the stress demand in the web gap region by distributing the force at the girder-cross frame connection over a larger area. A new retrofit detail is proposed based on this approach, which consists of adding steel angles connecting the girder web and the connection plate, and a steel bar on the back side of the girder web to distribute the lateral force over a wider region of the web. Experimental and computer simulation results are presented showing that this repair method is very effective in preventing the growth of horseshoe-shaped cracks around the web-cross frame connection and of straight cracks near the junction between the flange and we

A Monte Carlo Study: The Impact of Missing Data in Cross-Classification Random Effects Models

Unlike multilevel data with a purely nested structure, data that are cross-classified not only may be clustered into hierarchically ordered units but also may belong to more than one unit at a given level of a hierarchy. In a cross-classified design, students at a given school might be from several different neighborhoods and one neighborhood might have students who attend a number of different schools. In this type of scenario, schools and neighborhoods are considered to be cross-classified factors, and cross-classified random effects modeling (CCREM) should be used to analyze these data appropriately. A common problem in any type of multilevel analysis is the presence of missing data at any given level. There has been little research conducted in the multilevel literature about the impact of missing data, and none in the area of cross-classified models. The purpose of this study was to examine the effect of data that are missing completely at random (MCAR), missing at random (MAR), and missing not at random (MNAR), on CCREM estimates while exploring multiple imputation to handle the missing data. In addition, this study examined the impact of including an auxiliary variable that is correlated with the variable with missingness (the level-1 predictor) in the imputation model for multiple imputation. This study expanded on the CCREM Monte Carlo simulation work of Meyers (2004) by the inclusion of studying the effect of missing data and method for handling these missing data with CCREM. The results demonstrated that in general, multiple imputation met Hoogland and Boomsma’s (1998) relative bias estimation criteria (less than 5% in magnitude) for parameter estimates under different types of missing data patterns. For the standard error estimates, substantial relative bias (defined by Hoogland and Boomsma as greater than 10%) was found in some conditions. When multiple imputation was used to handle the missing data then substantial bias was found in the standard errors in most cells where data were MNAR. This bias increased as a function of the percentage of missing data

USE OF COMPOSITE MATERIALS TO REPAIR STEEL STRUCTURES VULNERABLE TO FATIGUE DAMAGE

This study investigates mainly two different topics related to the use of CFRP's for strengthening and repair of steel bridges: the use of CFRP's to prevent damage in fatigue vulnerable welded connections prior to fatigue-crack initiation, and the use of CFRP's to stall the propagation of fatigue cracks in welded connections and in steel plates subjected to tension. The findings are discussed in three different papers presented in the following chapter

Meclis'te Akif

Taha Toros Arşivi, Dosya No: 134-Mehmet Akif Ersoy. Not: Ekteki belge Mehmet Ekif Ersoy'un doğumunun 110'uncu ve İstiklal Marşı'nın kabulünün 62'inci yıldönümünde Türk Edebiyatı dergisi tarafından çıkarılan Mehmet Akif Ersoy özel sayısıdır

MATLAB for All Steps of Dynamic Vibration Test of Structures

With the recent advances in computer technology and digital simulation software, it is now possible to rapidly and accurately build computer models for complex linear and nonlinear dynamic systems. MATLAB is a unique system that can be used for structural and earthquake engineering problems. This study presents MATLAB tools developed for numerical process of all steps of dynamic vibration test of structures. The functions of the tools are processing the signals obtained from forced and ambient vibration tests of structures, determining the dynamic characteristics of structural systems, and automatically updating the analytical finite element (FE) models. The software group is composed of three programs named as SignalCAD, ModalCAD, and FemUP. The SignalCAD program is developed for processing raw measured data obtained from forced and ambient vibration tests of engineering structures. The ModalCAD program is developed for dynamic characteristic identification and validation procedure. The peak picking method, complex exponential method, and polyreference time domain method are used for modal identification process. The FemUP program is developed for automatically updating the numerical models of structures compared to modal testing results. Each program has a unique graphical user interface and is designed as user friendly. The possibilities of the programs are demonstrated with the model vibration test of a steel cantilever beam. The obtained results are compared to the analytical model, and the FE model is automatically updated, whereas the experimental model is considered as the reference model. Finally, it is seen that MATLAB can be used as a scientific programming platform in all vibration test and modal analysis applications

Identification of the unknown diffusion coefficient in a linear parabolic equation by the semigroup approach

AbstractIn this article, we study the semigroup approach for the mathematical analysis of the inverse coefficient problems of identifying the unknown coefficient k(x) in the linear parabolic equation ut(x,t)=(k(x)ux(x,t))x, with Dirichlet boundary conditions u(0,t)=ψ0, u(1,t)=ψ1. Main goal of this study is to investigate the distinguishability of the input–output mappings Φ[⋅]:K→C1[0,T], Ψ[⋅]:K→C1[0,T] via semigroup theory. In this paper, we show that if the null space of the semigroup T(t) consists of only zero function, then the input–output mappings Φ[⋅] and Ψ[⋅] have the distinguishability property. Moreover, the values k(0) and k(1) of the unknown diffusion coefficient k(x) at x=0 and x=1, respectively, can be determined explicitly by making use of measured output data (boundary observations) f(t):=k(0)ux(0,t) or/and h(t):=k(1)ux(1,t). In addition to these, the values k′(0) and k′(1) of the unknown coefficient k(x) at x=0 and x=1, respectively, are also determined via the input data. Furthermore, it is shown that measured output data f(t) and h(t) can be determined analytically, by an integral representation. Hence the input–output mappings Φ[⋅]:K→C1[0,T], Ψ[⋅]:K→C1[0,T] are given explicitly in terms of the semigroup. Finally by using all these results, we construct the local representations of the unknown coefficient k(x) at the end points x=0 and x=1