Fabrication error Indexed eXamples and Solutions: FIXS

The major goal of the Regional/National Bridge Fabrication Error Expert System research project is to develop a sharable and well reasoned bridge fabrication error repair database which can be used by several state: DOTs within a geographical,. region. This report focuses on the enhancement of the knowledge base and improvement of the system performance based on the initial work of Fabrication error Indexed examples and Solutions (FIXS). FIXS is a knowledge-based system in the domain of steel bridge fabrication errors using both rule-based reasoning and casebased reasoning. To expand the knowledge base to cover errors experienced by multiple DOTs and to improve the system effectiveness, 38 new cases were solicited from the North Central States Consortium and the Repair Database Task Group of the AASHTONSBA Steel Bridge Collaboration. The new cases, along with the existing 120 rule solutions and 112 case solutions in the knowledge base, were reviewed by the Task Group members. The sketches and instructions summarized from actual cases and the comments obtained from the Task Group members were implemented in the ,, software to provide graphical and instructive information for case solutions. In addition, generic problems and corrections were also collected and implemented in the software as a tutorial tool for common fabrication errors. To improve the accuracy of similar case retrieval, the case-based reasoning shell SCBR was revised by introducing continuous feature evaluation for numeric features, replacing the simple match approach in the first version of FIXS. The explanation facility was also improved

Comparison of QPE and QSIM as Qualitative Reasoning Techniques

Qualitative reasoning predicts and explains the behavior of physical systems using the system's structure through modeling and simulation. There are several approaches to qualitative reasoning. Two of the most prominent software implementations are QPE (Qualitative Process Engine) by Forbus and QSIM (Qualitative Simulation) by Kuipers. A comparison of the two systems is done on the basis of representation and reasoning ability of physical systems. The standard examples in qualitative reasoning and examples in fatigue and fracture in metals are used in the comparison. The fatigue and fracture domain of study can serve as a prototype for other related models of material behavior. A thorough comparison of QSIM and QPE identifies future directions of qualitative reasoning development

Torsion of Exterior Girders of a Steel Girder Bridge During Concrete Deck Placement Loads: Field Test Report

This report is the second part of a two part report. The first part is written and developed as a design aid to determine the torsion acting on outside steel bridge girders during concrete deck placement. This second part reports results of measurements taken from two bridges. The first bridge is located at K-10 highway over I-70 between Lawrence and Topeka, Kansas. The second bridge is located on southbound I-635 highway over Swartz Road in Kansas City, Kansas. During bridge construction, deck overhang loads occur on steel plate or rolled beam girders and are supported by cantilever brackets. In addition to supporting the weight of the placement screed, these brackets must also support the weight of the additional construction loads. The vertical loads applied on the deck are eccentric and generate large torsional moments at the intervals between cross bracing. The result of this loading effect is torsional moments that generate a combination of longitudinal stresses and loads from the cantilever brackets. Strain gages were installed on the Swartz Road bridge to measure these overhang loads. A "Multiframe 4D" computer model was made to compare the results measured in the field, with AISC recommendations, and with TAEG ( Torsional Analysis of Exterior Girders) results. The screed loads measured from the static load runs and analytical model were based on the locations of bogey and gang vibrators. In the analytical model, the loads were moved across the beam at quarter points beginning at midspan, then tabulated and plotted alongside the field results. After all of the moments representing the various load cases were compiled, an influence diagram was constructed from the loads measured in the field and the analytical model. Loads were analyzed for two cases using the AISC method outlined in the "Design for Concrete Overhang Loads". The first load case represented the static field test while the second represented the results measured the day of concrete placement. The same wheel loading for the analytical model was used for the AISC calculations. In some instances, the strains measured on the Swartz Road bridge were small. In these situations it can be difficult to guarantee the sensitivity and output of gage readings, however, the major axis moments measured on the Swartz Road bridge during static load testing were almost identical to the moments calculated with the Multiframe analysis. This shows that the loads that were used and how they were distributed in the Multiframe analysis were close to actual field conditions. This also shows consistent. and accurate behavior of the strain gages. No significant differences were found with the moments measured from the static load runs where blocking had been removed. More blocking had been provided than what was needed on the Swartz Road bridge, however, when concrete and live loads are added, the change in load response should be greater. Surveying prisms were used to measure deflections during the load tests. The recorded and predicted maximum vertical deflections on the Swartz Road bridge were consistently ~lose for all load runs. Horizontal deflections were not observed at any location. The Multiframe model used to calculate torsional bending did match closely with the moments measured in the field at midpoint between stiffeners but varied greatly between measured and analytical results for endpoint locations. The computer model used to calculate torsional bending did not match as closely with the moments measured in the field. The difference between measured and analytical results varied for maximum values but was in relative agreement for the trends of the moments. Most of the differences can be attributed to the lateral stiffness provided by a combination of deck formwork and a portion of concrete deck in place in the Northbound lanes. Unfortunately, the loose play of the form work connections to the girder makes the lateral stiffness difficult to measure. Some of the differences in the torsional moments that were calculated using the Multiframe model and the TAEG program can be attributed to some basic model assumptions. The Multiframe analysis was based on a non-prismatic girder section that was continuous over diaphragm locations. The T AEG program assumes a three span, prismatic member. A comparison of torsional moments calculated by T AEG show a large difference in results from field measurements, the torsional model, and AISC calculations. In some cases the differences are small and in others they are significant. For the static field tests and the Multiframe torsion models, the trends show close similarity, however the maximum loads for all locations do vary. The TAEG program was always conservative in comparison to the field results and the multiframe model. Since the T AEG program is intended to be used as an in-house design aid, this conservative approach is regarded as positive

Steel Bridge Fabrication Errors Indexed Examples and Solutions: Combining Rules and Cases

This research focuses on the development of a knowledge-based system in the domain of steel bridge fabrication errors using both rule-based reasoning (RBR) and case-based reasoning (CBR). Fabrication error Indexed and Solutions (FIXS) was developed to combine the benefits of two previous research projects: 1) the rule-based Bridge Fabrication error solution eXpert system (BFX), and 2) its case-based counterpart (CB-BFX). Errors that occur during the fabrication of steel bridg~ members can have a costly effect on the performance of a bridge if not repaired properly. FIXS is an effort to provide guidance to the bridge engineer responsible for cost effective solutions in a time sensitive manner. FIXS is implemented in the programming language PROLOG and runs in the Windows environment as a stand-alone application. RBR facilities are provided by the expert system shell MESS (Modest Expert System Shell). Similarly, CBR functions are provided by the simple case-based reasoner shell SCBR (Simple Case Based Reasoning). The application has been designed for addition of new domain knowledge. The addition of new and updated knowledge allows the application to keep pace with changes in the steel bridge design industry and the methods of repairing errors

Heuristic, qualitative, and quantitative reasoning about steel bridge fatigue and fracture

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Civil Engineering, 1989.Includes bibliographical references.by W.M. Kim Roddis.Ph.D

Torsional Analysis for Exterior Girders

Concrete deck placement imposes eccentric loading on exterior steel bridge girders. This report describes a design tool that aids bridge engineers in evaluating the response of the exterior girder due to this eccentric loading. Computer analyses are conducted in order to gain a detailed understanding of the factors influencing the response of the girder. It is shown that the “flexure analogy” is correct and can be used in the design tool. The “flexure analogy” is the assumption that torsional loads on the girder are mainly carried by the flanges in minor axis bending. Top and bottom flanges need to be analyzed independently since the boundary conditions for them vary significantly. Furthermore, analyses indicate that a substantial improvement in accuracy can be achieved if the boundary conditions on the local system used to analyze the behavior of the girder are changed. The influence of dynamic loads, such as the movement of the finisher and the impact of concrete during the placement process, is investigated and found to be negligible. Based on these findings, a design tool in the form of a Visual Basic © application, TAEG (Torsional Analysis of Exterior Girders), for Windows 95/NT © has been created. It uses the stiffness method to calculate the stresses and deflections of the flanges due to torsional loads. Results for bracket forces and diaphragms are also calculated. TAEG can be used to evaluate the effect of temporary support in the form of tie rods and blocking. Three examples are provided to justify the results and are compared with existing methods or field data. TAEG uses a 3-span fixed end continuous beam analysis model for finding torsional stresses while the AISC Design Guide method uses a less accurate single span fixed end model. Therefore, in comparison to the AISC Design Guide method stress results calculated with ATEG are approximately 20% higher for the positive moment region and approximately 20% lower for the negative moment region. Generally, stresses at the negative moment region govern

Reduced Brace Section (RXS) Proof of Concept: Phase 1B

This report presents the results from the second phase of a proof-of-concept series of tests of the reduced braced section (RXS) system. This system is intended to provide a cost-effective alternative for the design of Concentrically Braced Frames (CBFs) under earthquake loads. The second test investigated the behavior of the RXS system under cyclic loading. The hysteretic behavior of the specimen indicated that the behavior of the RXS system was sensitive to the eccentricity of the load imposed on the brace. Eccentric loading caused premature local bucking of the reduced section, which reduced the ability of the system to dissipate energy under repeated load reversals into the nonlinear range of response. The behavior observed during the test shows that local buckling is a mode of failure that must be prevented in this type of system because of its adverse effect on the ability of the system to dissipate energy. Also, the design of the system must take into account a minimum eccentricity of the load transmitted to the brace at the brace-frame connection. An alternative to improve the behavior of the system under repeated load reversals is to reinforce the reduced section in order to increase the local bucking load. This report includes the applicable information specified in TEST REPORTING REQUIREMENTS [AISC, 2002, S9].This research was sponsored in part by Butler Heavy Structures

Field Instrumentation and Analysis of the Tuttle Creek Bridge

Fatigue cracking has been an extensive problem for many steel bridges designed prior to the identification of fatigue-prone details. Distortion in bridges coupled with stress concentrations within bridge components can eventually lead to crack initiation. The Tuttle Creek Bridge, built in 1962, has developed fatigue cracks like many older steel bridges. The structure is a 5,350 ft. long, plate-girder bridge with two girders supporting a non-composite concrete deck. The majority of the cracks on the bridge are found in the upper web-gap region, which lies between the vertical connection stiffener and the upper flange. Cracks also have occurred in the transverse welds attaching the lateral gusset plates to the lower flange. Both these crack types are believed to be caused by differential deflection of the two girders. In 1986, the bridge was retrofitted to prevent further cracking. Cracking, however, continued after the 1986 retrofit. In 2000, the Kansas Department of Transportation retained the services of the University of Kansas to investigate the fatigue cracking. Finite element models were created to estimate the stresses in the upper web-gap regions in order to determine a proper repair plan. The recommended repair scheme was to positively attach the connection stiffener to the upper flange, which was also successfully performed in similar web-gap repairs. The University of Kansas also was retained to perform two load tests on the bridge to investigate the effectiveness of the repair. The first load test, which this report entails, examined the stresses within the fatigued regions prior to retrofit. A second test will be conducted after the repairs have been performed. Measurements taken during both tests will be compared to determine the fatigue improvement within the structure. Also, information gathered during the first test will also provide insight to improving the finite element models. This report includes information about the Tuttle Creek Bridge and a summary of its structural deficiencies. Details of the gage installation and load testing are provided. Stresses induced by the truck loadings are presented in addition to the inferences from the measurements taken

Multiorgan MRI findings after hospitalisation with COVID-19 in the UK (C-MORE): a prospective, multicentre, observational cohort study

Introduction: The multiorgan impact of moderate to severe coronavirus infections in the post-acute phase is still poorly understood. We aimed to evaluate the excess burden of multiorgan abnormalities after hospitalisation with COVID-19, evaluate their determinants, and explore associations with patient-related outcome measures. Methods: In a prospective, UK-wide, multicentre MRI follow-up study (C-MORE), adults (aged ≥18 years) discharged from hospital following COVID-19 who were included in Tier 2 of the Post-hospitalisation COVID-19 study (PHOSP-COVID) and contemporary controls with no evidence of previous COVID-19 (SARS-CoV-2 nucleocapsid antibody negative) underwent multiorgan MRI (lungs, heart, brain, liver, and kidneys) with quantitative and qualitative assessment of images and clinical adjudication when relevant. Individuals with end-stage renal failure or contraindications to MRI were excluded. Participants also underwent detailed recording of symptoms, and physiological and biochemical tests. The primary outcome was the excess burden of multiorgan abnormalities (two or more organs) relative to controls, with further adjustments for potential confounders. The C-MORE study is ongoing and is registered with ClinicalTrials.gov, NCT04510025. Findings: Of 2710 participants in Tier 2 of PHOSP-COVID, 531 were recruited across 13 UK-wide C-MORE sites. After exclusions, 259 C-MORE patients (mean age 57 years [SD 12]; 158 [61%] male and 101 [39%] female) who were discharged from hospital with PCR-confirmed or clinically diagnosed COVID-19 between March 1, 2020, and Nov 1, 2021, and 52 non-COVID-19 controls from the community (mean age 49 years [SD 14]; 30 [58%] male and 22 [42%] female) were included in the analysis. Patients were assessed at a median of 5·0 months (IQR 4·2–6·3) after hospital discharge. Compared with non-COVID-19 controls, patients were older, living with more obesity, and had more comorbidities. Multiorgan abnormalities on MRI were more frequent in patients than in controls (157 [61%] of 259 vs 14 [27%] of 52; p<0·0001) and independently associated with COVID-19 status (odds ratio [OR] 2·9 [95% CI 1·5–5·8]; padjusted=0·0023) after adjusting for relevant confounders. Compared with controls, patients were more likely to have MRI evidence of lung abnormalities (p=0·0001; parenchymal abnormalities), brain abnormalities (p<0·0001; more white matter hyperintensities and regional brain volume reduction), and kidney abnormalities (p=0·014; lower medullary T1 and loss of corticomedullary differentiation), whereas cardiac and liver MRI abnormalities were similar between patients and controls. Patients with multiorgan abnormalities were older (difference in mean age 7 years [95% CI 4–10]; mean age of 59·8 years [SD 11·7] with multiorgan abnormalities vs mean age of 52·8 years [11·9] without multiorgan abnormalities; p<0·0001), more likely to have three or more comorbidities (OR 2·47 [1·32–4·82]; padjusted=0·0059), and more likely to have a more severe acute infection (acute CRP >5mg/L, OR 3·55 [1·23–11·88]; padjusted=0·025) than those without multiorgan abnormalities. Presence of lung MRI abnormalities was associated with a two-fold higher risk of chest tightness, and multiorgan MRI abnormalities were associated with severe and very severe persistent physical and mental health impairment (PHOSP-COVID symptom clusters) after hospitalisation. Interpretation: After hospitalisation for COVID-19, people are at risk of multiorgan abnormalities in the medium term. Our findings emphasise the need for proactive multidisciplinary care pathways, with the potential for imaging to guide surveillance frequency and therapeutic stratification

Concrete bridge deck assessment using thermography and radar

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Civil Engineering, 1987.MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING.Bibliography: leaves 263-272.by W. M. Kim Roddis.M.S