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International Concrete Abstracts Portal

Showing 1-5 of 1022 Abstracts search results

Document: 

SP-342_10

Date: 

June 1, 2020

Author(s):

Anish Sharma and Serhan Guner

Publication:

Symposium Papers

Volume:

342

Abstract:

Due to the increase in traffic and transported freight in the past decades, a significant number of in-service bridges have been subjected to loads above their original design capacities. Bridge structures typically incorporate deep concrete elements, such as cap beams or bent caps, with higher shear strengths than slender elements. However, many in-service bridges did not account for the deep beam effects in their original design due to the lack of suitable analysis methods at that time. Nonlinear finite element analysis (NLFEA) can provide a better assessment of the load capacity of deep bridge bent beams while accounting for the deep beam action. However, there is little guidance on how to conduct a numerical strength evaluation using the NLFEA. This study presents a nonlinear modeling methodology for the strength evaluation of deep bridge bents while considering advanced concrete behavior such as tension stiffening, compression softening, and dowel action. Five existing bridge bent beams are examined using the proposed methodology. The effectiveness and advantages of the proposed methodology are discussed by comparing the numerical results, including the load-displacement responses, load capacities, cracking patterns and failure modes, with the strut-and-tie and sectional analysis methods. Important modeling considerations are also discussed to assist practitioners in accurately evaluating deep bridge bents.


Document: 

SP-342_09

Date: 

June 1, 2020

Author(s):

Denis Mitchell, Bruno Massicotte, William D. Cook, and Emre Yildiz

Publication:

Symposium Papers

Volume:

342

Abstract:

The existing Champlain Bridge is a major structure in Montreal. It contains 50 concrete spans. The 10 ft (3.1 m) deep I-girders span 172 ft (52.4 m) and are post-tensioned. Because the prestressing steel has suffered from corrosion, it was necessary to use advanced techniques to evaluate the performance of these I-girders. Detailed twodimensional non-linear finite element modelling was used to determine the responses at service load and at ultimate. Three-dimensional finite element modelling was carried out to determine the loading for the two-dimensional modelling. The serviceability checks examined if cracking would occur and the strength requirements were evaluated using predicted demand-to-capacity ratios (D/C). These analysis tools also enabled the influence of a number of strengthening techniques to be assessed. The influence of different strengthening techniques on the predicted responses of the diaphragms was also studied. The combinations of strengthening measures were found to be effective in achieving the desired serviceability and strength requirements. Keywords:


Document: 

SP-342_01

Date: 

June 1, 2020

Author(s):

Benjamin Z. Dymond, Catherine E. W. French, Carol K. Shield

Publication:

Symposium Papers

Volume:

342

Abstract:

An experimental investigation was conducted on a full-scale prestressed concrete girder laboratory bridge to determine whether linear elastic shear distribution principles are conservative for load rating at ultimate capacity. A secondary goal was to determine whether existing web-shear cracks would be visible in an unloaded state. Two tests were conducted to failure (one near the end with a partial-depth diaphragm and one near the end without) to determine if the most loaded interior girder shed shear force to adjacent girders as it transitioned from uncracked to cracked to failure. Failure during each test was characterized by web-shear crushing and bridge deck punching at the peak applied load. Differences in the behavior of the two ends (with and without partial depth end diaphragm) affected the diagonal crack pattern, shear distribution, and loads at cracking and failure. The effect on loading was less than 10%. Inelastic shear distribution results indicated the girder carrying the most load redistributed shear to the other girders as it lost stiffness due to cracking. Use of linear elastic load distribution factors was conservative considering shear distribution at ultimate capacity. The visibility of web-shear cracks in an unloaded state was found to be a function of stirrup spacing.


Document: 

SP-340-03

Date: 

April 1, 2020

Author(s):

Dan Su and Hani Nassif

Publication:

Symposium Papers

Volume:

340

Abstract:

Service I limit state in the AASHTO LRFD Bridge Design Specifications (BDS) is applied for the control of cracking in reinforced concrete elements in order to maintain its normal functionality and to achieve its design life. There are two methods specified in AASHTO LRFD BDS: 1) equivalent strip design method and 2) empirical method. For the empirical method, no exhaustive design calculation are needed and the reinforcement area is obtained as a percentage of the concrete section. However, usually, the reinforcement area designed using empirical method is less than that designed using the equivalent strip method, which could result in shortened service life and excessive crack width. Albeit arching action effects were considered in the empirical method which improves the flexural resistance of concrete deck after cracking, the effects of arching action on crack control of reinforced concrete deck were not studied. In addition, different exposure conditions and different design sections (positive moment vs. negative moment regions) were not considered in the empirical design method. Thus, it is extremely important to investigate and calibrate the Service I limit State for reinforced concrete decks designed using the AASHTO empirical method. In this study, the Service I limit state function is formulated and the load and resistance models are developed. The arching action effects are integrated into the resistance model. Detailed calibration is performed to ensure uniform target reliability will be achieved for different design parameters including exposure conditions, span lengths, deck thickness, and positive moment and negative moment regions.


Document: 

SP-340-06

Date: 

April 1, 2020

Author(s):

Maria Kaszynska and Adam Zielinski

Publication:

Symposium Papers

Volume:

340

Abstract:

The research paper presents an analysis of autogenous shrinkage development in self-consolidating concrete (SCC). The first stage of the study involved an evaluation of concrete susceptibility to cracking caused by shrinkage of SCC with natural and lightweight aggregate. The shrinkage was tested on concrete rings according to ASTM C 1581/C 1581M- 09a. The influence of aggregate composition, the water content in lightweight aggregate, and SRA admixture on the reduction of concrete susceptibility to cracking, due to the early-age shrinkage deformation was determined. In the second stage of the research, the innovative method measurement of autogenous shrinkage was developed and implemented. The tests were performed on concrete block samples, dimensions 35x150x1150 mm, that had the same concrete volume as ring specimen in the ASTM method. Linear deformation of the concrete samples was measured in constant periods of 500 s using dial gauges with digital data loggers. The investigation allowed evaluating of the influence of water/cement (w/c) ratio of 0.28, 0.34, 0.42, and of aggregate composition on the development of autogenous shrinkage in different stages of curing SCC. The results were compared to existing material models proposed by other researchers. The conducted study indicated a significant influence of the w/c ratio and composition of aggregate on the concrete susceptibility to crack caused by the autogenous shrinkage deformation.


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