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Author: Hani Melhem Publisher: ISBN: Category : Bridges, Iron and steel Languages : en Pages : 92
Book Description
The changes in the properties of a multi-span continuous steel girder composite bridge during construction can cause final dead load deflections that are quite different from the calculated theoretical values. The casting rate and the sequence of span casting affect the development of concrete stiffness which can significantly affect the final dead load deflections. The study involved two activities: collecting data from the testing of concrete cylinders and laboratory-size beams representative of composite bridge girders and developing a computer program that calculates dead load deflections during construction based on the data from the laboratory testing. The 300 concrete cylinders were tested at ages varying from 2 to 36 hours after pouring to establish stress-strain relations in axial compression. The four composite beams (20 ft (6.1 m) long) with 16 strain gages and 4 deflection gages were tested by applying small incremental loads starting soon after the concrete was poured. Based on these measurements, the change in stiffness of the composite beam was computed and the concrete properties evaluated. The test results helped obtain a relationship that describes the variation of the concrete Young's Modulus with time varying from 2 to 36 hours. Best results were obtained between 4 and 19 hours. The relationship established seems logical and appeared to be consistent in all tests. It was implemented in the computer program and is most valid for ages up to 10 hours. The additional concrete stiffness gained after 10 hours is based on the slope of the curve at 10 hours and a limitation factor that determines the characteristic length of the transition polynomial and which specifies how soon the curve should be asymptotic to the standard value of the 28-days modulus of elasticity. The computer program was verified, however, additional research is needed to test the program more rigorously, to study the effect of concrete confinement and the use of plasticizers, and to compare the results of additional test data with actual field measurements. The effect of the weight of construction equipment should also be studied. Excessive bridge deflection could be avoided with a better understanding of the factors and parameters that affect the deflection.
Author: Hani Melhem Publisher: ISBN: Category : Bridges, Iron and steel Languages : en Pages : 92
Book Description
The changes in the properties of a multi-span continuous steel girder composite bridge during construction can cause final dead load deflections that are quite different from the calculated theoretical values. The casting rate and the sequence of span casting affect the development of concrete stiffness which can significantly affect the final dead load deflections. The study involved two activities: collecting data from the testing of concrete cylinders and laboratory-size beams representative of composite bridge girders and developing a computer program that calculates dead load deflections during construction based on the data from the laboratory testing. The 300 concrete cylinders were tested at ages varying from 2 to 36 hours after pouring to establish stress-strain relations in axial compression. The four composite beams (20 ft (6.1 m) long) with 16 strain gages and 4 deflection gages were tested by applying small incremental loads starting soon after the concrete was poured. Based on these measurements, the change in stiffness of the composite beam was computed and the concrete properties evaluated. The test results helped obtain a relationship that describes the variation of the concrete Young's Modulus with time varying from 2 to 36 hours. Best results were obtained between 4 and 19 hours. The relationship established seems logical and appeared to be consistent in all tests. It was implemented in the computer program and is most valid for ages up to 10 hours. The additional concrete stiffness gained after 10 hours is based on the slope of the curve at 10 hours and a limitation factor that determines the characteristic length of the transition polynomial and which specifies how soon the curve should be asymptotic to the standard value of the 28-days modulus of elasticity. The computer program was verified, however, additional research is needed to test the program more rigorously, to study the effect of concrete confinement and the use of plasticizers, and to compare the results of additional test data with actual field measurements. The effect of the weight of construction equipment should also be studied. Excessive bridge deflection could be avoided with a better understanding of the factors and parameters that affect the deflection.
Author: Publisher: ISBN: Category : Dead loads (Mechanics) Languages : en Pages : 374
Book Description
Many of today's steel bridges are being constructed with longer spans and higher skew. The bridges are often erected in stages to limit traffic interruptions or to minimize environmental impacts. The North Carolina Department of Transportation (NCDOT) has experienced numerous problems matching the final deck elevations between adjacent construction stages due to inaccuracies in predicting the dead load deflections of steel plate girder bridges. In response to these problems, the NCDOT has funded this research project (Project No. 2004-14 - Developing a Simplified Method for Predicting Deflection in Steel Plate Girders Under Non-composite Dead Load for Stage-constructed Bridges). The primary objective of this research was to develop a simplified procedure to predict the dead load deflection of skewed and non-skewed steel plate girder bridges. In developing the simplified procedure, ten steel plate girder bridges were monitored during placement of the concrete deck to observe the deflection of the girders. Detailed three-dimensional finite element models of the bridge structures were generated in the commercially available finite element analysis program ANSYS. The finite element modeling results were validated through correlation with the field measured deflection results. With confidence in the ability of the developed finite element models to capture bridge deflection behavior, a preprocessor program was written to automate the finite element model generation. Subsequently, a parametric study was conducted to investigate the effect of skew angle, girder spacing, span length, cross frame stiffness, number of girders within the span, and exterior to interior girder load ratio on the girder deflection behavior. The results from the parametric were used to develop an empirical simplified procedure, which modifies traditional SGL predictions to account for skew angle, girder spacing, span length, and exterior to interior girder load ratio. Predictions of the deflections from the simplified procedure and from SGL analyses were compared to the deflections predicted from finite element models (ANSYS) and the field measured deflections to validate the procedure. It was concluded that the simplified procedure may be utilized to more accurately predict dead load deflection of simple span, steel plate girder bridges. Additionally, an alternative prediction method has been proposed to predict deflections in continuous span, steel plate girder bridges with equal exterior girder loads, and supplementary comparisons were made to validate this method.
Author: Publisher: ISBN: Category : Bridges Languages : en Pages : 182
Book Description
The need to upgrade a large number of understrength and obsolete bridges in the U.S. has been well documented in the literature. Through several Iowa DOT projects, the concept of strengthening simple-span bridges by post-tensioning has been developed. The purpose of the project described in this report was to investigate the use of post-tensioning for strengthening continuous composite bridges. In a previous, successfully completed investigation, the feasibility of strengthening continuous, composite bridges by post-tensioning was demonstrated on a laboratory 1/3-scale-model bridge (3 spans: 41 ft 11 in. x 8 ft 8 in.). This project can thus be considered the implementation phase. The bridge selected for strengthening was in Pocahontas County near Fonda, Iowa, on County Road N28. With finite element analysis, a post-tensioning system was developed that required post-tensioning of the positive moment regions of both the interior and exterior beams. During the summer of 1988, the strengthening system was installed along with instrumentation to determine the bridge's response and behavior. Before and after post-tensioning, the bridge was subjected to truck loading (1 or 2 trucks at various predetermined critical locations) to determine the effectiveness of the strengthening system. The bridge, with the strengthening system in place, was inspected approximately every three months to determine any changes in its appearance or behavior. In 1989, approximately one year after the initial strengthening, the bridge was retested to identify any changes in its behavior. Post-tensioning forces were removed to reveal any losses over the one-year period. Post-tensioning was reapplied to the bridge, and the bridge was tested using the same loading program used in 1988. Except for at a few locations, stresses were reduced in the bridge the desired amount. At a few locations flexural stresses in the steel beams are still above 18 ksi, the allowable inventory stress for A7 steel. Although maximum stresses are above the inventory stress by about 2 ksi, they are about 5 ksi below the allowable operating stress; therefore, the bridge no longer needs to be load-posted.
Author: Marvin Henry Hilton Publisher: ISBN: Category : Bridges Languages : en Pages : 88
Book Description
Problems involved in obtaining the desired thickness of bridge decks were investigated. The study, which was limited to decks which were longitudinally screeded during construction, included (1) field measurements of the girder deflections during construction, and (2) a theoretical frame analysis of the girder deflections under the field loading conditions. Each of the two spans investigated were simply supported steel plate girder designs. When full span length longitudinal screeding is used, the finished grade elevations are set on the screeding edge of the machine, and remain independent of the bridge girder deflections during deck placement. Consequently, any factor affecting the girder deflections, and thus the forming elevations, will, in turn have bearing on the final thickness of a bridge deck. In addition, all factors which, in effect, cause the deck forming to be too high at the time the concrete is screeded to grade have the potential of causing a shy deck thickness. The most significant factors were found to be: (1) Plan dead load deflection values which are in error, (2) the differential temperatures existing between the top and bottom flanges of the girders during concrete placement as opposed to those that may have existed when the forming elevations were established, and (3) the transverse position of the concrete dead loading at the time a final screeding pass is made over a given point on a span. Based on the results of the study, certain recommendations are offered regarding the computation of dead load deflections and precautions to be observed during construction when longitudinal screeding of the concrete deck is used.
Author: Publisher: Transportation Research Board ISBN: 0309258391 Category : Curves in engineering Languages : en Pages : 199
Book Description
"TRB's National Cooperative Highway Research Program (NCHRP) Report 725: Guidelines for Analysis Methods and Construction Engineering of Curved and Skewed Steel Girder Bridges offers guidance on the appropriate level of analysis needed to determine the constructability and constructed geometry of curved and skewed steel girder bridges. When appropriate in lieu of a 3D analysis, the guidelines also introduce improvements to 1D and 2D analyses that require little additional computational costs."--Publication information.
Author: William Leo Gamble Publisher: ISBN: Category : Concrete bridges Languages : en Pages : 280
Book Description
Tests of two prestressed concrete composite bridge girders which were continuous over two spans are reported. Both were I-section girders with cast-in-place decks, and had spans of about 37 ft (11 m), and were approximately 1/3 scale models of structures spanning 125 ft (38 m). Each girder was constructed from three segments which were joined end-to-end by cast-in-place concrete splices. Modell was post-tensioned after erection of the girders and casting of the deck and splice concrete. The two end segments, each supported on the final abutments and on temporary supports located about 1/3 of the span from the central pier, were pretensioned for their dead loads plus the deck concrete. The central segment, which was supported on the central pier of the structure plus the two temporary supports was precast reinforced concrete, plus a small amount of pre= tensioned reinforcement. Model 2 was externally similar, but was not post-tensioned. The segments were pretensioned for the final moments, and were joined by splicing reinforcing bars which extended into the splice region. Both structures were subjected to a series of loadings to the service load, design ultimate, and high over-load levels. Both had capacities which were significantly higher than the design ultimate values. The capacities were generally predictable on the basis of flexural strength calculations, and shear did not cause major problems. Joint details in Modell lead to difficulties in two tests, and this aspect of the design is discussed in detail.
Author: Hani Melhem
Author: Hani Melhem
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Author: Atorod Azizinamini
Author: Ivan Miroslav Viest
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Author: Andrzej S. Nowak
Author: Marvin Henry Hilton
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Author: William Leo Gamble
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