Xia, Nassif, Hwang, and Linzell 1 OPTIMIZATION OF DESIGN DETAILS IN ORTHOTROPIC STEEL DECKS SUBJECTED TO STATIC AND FATIGUE LOADS

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OPTIMIZATION OF DESIGN DETAILS IN ORTHOTROPIC STEEL DECKS SUBJECTED TO STATIC AND FATIGUE LOADS

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Ye Xia, Ph.D., Post-Doctoral Fellow Rutgers Infrastructure Monitoring and Evaluation (RIME) Laboratory Rutgers, The State University of New Jersey 96 Frelinghuysen Road, Piscataway, NJ 08854 Email: [email protected] Hani Nassif*, Ph.D., P.E., Professor Rutgers Infrastructure Monitoring and Evaluation (RIME) Laboratory Rutgers, The State University of New Jersey 96 Frelinghuysen Road, Piscataway, NJ 08854 & International Scholar, Dept. of Civil Eng., College of Eng., Kyung Hee University Phone: (732) 445-4414, Fax: (732) 445-4775 Email: [email protected] Eui-Seung Hwang, Ph.D., Professor Dept. of Civil Eng., College of Eng., Kyung Hee University Kihung-ku, Seochun-dong 1, Yongin-si, Gyeonggi-do, 446-701, S. Korea Email: [email protected] Daniel Linzell, Ph.D., PE, Shaw Professor of Civil Engineering Director, Protective Technology Center 231L Sackett Building, Dept. of Civil and Env. Eng. The Pennsylvania State University, University Park, PA 16802-1408 Email: [email protected]

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* Corresponding Author

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TRB 2013 Annual Meeting

Word count: Abstract: Figures & Tables: Total: Submission Date:

4942 242< 250 10x250 = 2500 7442 08/01/2012

Paper revised from original submittal.

Xia, Nassif, Hwang, and Linzell 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

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ABSTRACT In recent decades, orthotropic steel decks (OSDs) have been routinely incorporated in long span bridges. Employment of cutouts in diaphragms (or sub-floorbeams) that the OSDs frame into is the most widely used configuration to reduce stress concentration, improve fatigue performance, and control crack propagation. However, the capital cost of cutout fabrication in the United States is relatively high and may not be economically feasible. There is a need to study costeffective modified design details without cutouts and to compare their corresponding flexural and fatigue performance against current design details that utilize cutouts. In this paper, alternative design details (e.g., deck ribs welded directly to the transverse diaphragms using full-penetration welds) utilizing thicker deck plates, but without cutouts, was investigated for potential improvements with respect to fatigue resistance and capital cost. A parametric study was conducted using calibrated finite element models of a portion of the BronxWhitestone Bridge in New York City to study the effects of cutouts, deck plate thickness, and other important parameters on fatigue performance. Various traffic load combinations and truck types were considered using an elaborate Weight-In-Motion (WIM) database. Results detail equivalent stress ranges at critical locations in the OSDs that were calculated to quantitatively estimate fatigue lives for two orthotropic deck models: one containing cutouts and one with the cutouts removed. Based on these comparisons, recommendations related to overall structural performance are made to ensure a safe and rational design for various OSD options in long span bridges.

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Key Words:

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Orthotropic steel deck Diaphragm cutout Parametric study Deck thickness Fatigue life estimation

TRB 2013 Annual Meeting

Paper revised from original submittal.

Xia, Nassif, Hwang, and Linzell 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42

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INTRODUCTION Orthotropic steel decks (OSDs) have been routinely incorporated in long span bridges since they are lighter than traditional concrete decks. The primary advantage is to reduce the total dead load carried by the main superstructure elements and substructure, resulting in potentially longer span bridges (1). However, there are two major obstacles when choosing an OSD: fatigue performance and overall cost. OSDs have experienced fatigue problems due to high cyclic stresses and inadequate welding details. Fatigue cracking and propagation were detected on a number of long span bridges and are one of the greatest threats to the integrity of orthotropic steel bridge decks. In response, various designers have devised details that mitigate fatigue susceptibility but are considered difficult to manufacture and, as a result, are costly. In many instances, these OSD configurations require complicated welding details and costly fabrication work (e.g. complicated diaphragm cutouts) that necessitate rigorous quality control procedures. The OSD system was developed in Germany in the early 1950’s and utilizes close ribs and diaphragm cutouts to maintain rib continuity when they passed through the diaphragm webs (1). Previous research related to OSD performance has focused on OSDs with diaphragm cutouts mainly because of optimized stress distributions and the lack of stress concentrations that are perceived to result. These studies investigated various cutout geometry parameters and it was concluded that curved cutouts and increased cutout heights would significantly improve the fatigue resistance of the OSD system (2, 3). Other OSD system parameters, like the geometry and size of the diaphragm/floorbeam, rib, and bulkhead were also analyzed to optimize the designs (4). However, when compared against other countries, the capital cost of cutout fabrication in the United States is relatively high. Hence, alternative technologies are highly desired to technically prevent fatigue cracks and economically reduce the overall cost. OSDs having thicker deck plates are gradually being accepted due to better fatigue resistance despite the increase in weight. Mizuguchi et al. (2004) proposed a new rib-to-deck detail for OSDs having a deck plate that was 1.5 times thicker and closed ribs that were approximately 1.5 times larger when compared against details used for most OSDs (5). The new details were used in a number of new bridges in the New Tomei Expressway that connects Tokyo and Nagoya. Additionally, Xiao et al. (2008) showed that the use of a thick deck plate (5/8 in.) could improve the fatigue durability of rib-to-deck joints (6). However, both of these studies, as well as other available literature, are based on deck configurations containing cutouts. It can reasonably be expected that improved OSD fatigue performance can be realized by increasing the deck plate thickness when cutouts are not employed. To reduce labor and the overall cost of fabrication, an alternative design detail for OSD that utilized a thicker deck plate (3/4 in.), but without cutouts, was considered as one of the design options for the Wittpenn Bridge on Route 7 in New Jersey (7). This option might, or might not, be an overall improvement with respect to fatigue resistance and capital cost. To assist with assessing if this type design change would be beneficial, this paper analytically compared the fatigue resistance at critical locations of OSDs with and without cutouts by examining another long span structure for which OSDs with cutouts have been considered, the BronxWhitestone Bridge.

TRB 2013 Annual Meeting

Paper revised from original submittal.

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(a) Bronx-Whitestone Bridge with an OSD 37' 0'’

7’’

7’’

1' 5½’’ 1' 3’’

2' 2'’ × 13 = 28' 2'’ Lane 1

1’

Lane 2

Lane 3

0.86%

z

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x

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With cutout Diaphragm

Rib

Floorbeam

Girder Without cutout

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(b) OSD configurations with and without cutout (8)

With cutout

Floorbeam 63

Intermediate Diaphragm Floorbeam 64

Without cutout

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(c) OSD finite element model FIGURE 1 Bronx-Whitestone Bridge and OSD finite element model

TRB 2013 Annual Meeting

Paper revised from original submittal.

Xia, Nassif, Hwang, and Linzell

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FINITE ELEMENT MODEL

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The preliminary deck design that contained diaphragm cutouts for the Bronx–Whitestone Bridge, as shown in FIGURE 1a, is similar to orthotropic decks on most other bridges in the United States. Both the deck and diaphragm plates are 5⁄8 in. thick. The 5⁄16 in. thick ribs were spaced transversely at 26 in. on center and supported by floorbeams, which were spaced 19 ft. 9 in. on center (see FIGURE 1b). Fillet welds were used for the rib-to-diaphragm connections and complete-penetration groove welds were used for the deck plates. Bulkheads were located inside the ribs and were connected by complete-penetration welds. For this study, an alternate OSD design was introduced based on the Bronx–Whitestone Bridge that eliminated the cutouts. In order to facilitate comparison between models, the optional design, and subsequent model, maintains the global geometric configuration and material properties, eliminates the cutout on the diaphragms and increases the thickness of the deck plate. A detailed finite element (FE) model was developed using ABAQUS (9) to determine the stresses at various critical locations and to assess the fatigue life for various OSD configurations. FIGURE 1c shows two OSD details, with and without diaphragm cutouts. The structure was modeled using shell elements containing 5 integration points in the thickness direction. Instead of utilizing a FE model that was transversely symmetric to reduce computational time, the whole transverse deck system was modeled since the applied loads were anti-symmetric. An AASHTO HS20 fatigue truck with a 15% impact factor was used for the applied loads. Spacing between the fatigue truck’s middle and rear axis was conservatively chosen as 14 ft following AASHTO specifications. The tire pressure area was assumed to be rectangular and 20’’ in width and 10’’ in length following AASHTO specifications (10).

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FE Model Validation

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To validate the FE model select results from field tests of Bronx-Whitestone Bridge were examined (8). One quasi-static, crawl test (20

with cutout, location II Frequency Cycles (γi ) (N) 593993 19.60% 626731 20.68% 567263 18.71% 418062 13.79% 262272 8.65% 197613 6.52% 163617 5.40% 126252 4.16% 55186 1.82% 14405 0.48% 3528 0.12% 1370 0.05% 476 0.02% 182 0.01% 122 0.00% 194 0.01% 32 0.00% Effective stress range

Sre = (∑γ i Sri 3 )1/3

Fatigue category Fatigue life in cycles, N

γ i S ri 3 1.57 5.58 11.98 17.24 18.69 22.36 27.64 30.36 18.21 6.33 2.01 0.99 0.43 0.20 0.16 0.51 0.16 5.46 ksi C 2.70E+07

S ri

with cutout, location III Frequency Cycles (γi ) (N)

(ksi) 2 256086 8.11% 3 398985 12.63% 4 363354 11.50% 5 332756 10.53% 6 312172 9.88% 7 307830 9.74% 8 269036 8.52% 9 194856 6.17% 10 156170 4.94% 11 128781 4.08% 12 112401 3.56% 13 79945.6 2.53% 14 92046 2.91% 15 72614 2.30% 16 44181 1.40% 20 35215 1.11% >20 2424 0.08% Effective stress range

Sre = (∑γ i Sri 3 )1/3

Fatigue category Fatigue life in cycles, N

γ i S ri 3 0.65 3.41 7.36 13.17 21.35 33.43 43.61 44.97 49.44 54.26 61.49 55.60 79.96 77.58 57.29 89.18 20.72 8.93 ksi A 3.51E+07

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TRB 2013 Annual Meeting

Paper revised from original submittal.

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TABLE 2 Fatigue life comparison using 12-months of WIM data Deck Critical Fatigue Equivalent Fatigue life Fatigue life thickness location category stress range in cycles in years (in) (ksi) 5/8 II C 5.46 2.70E+07 54 5/8 III A 8.93 3.51E+07 70 with cutout 3/4 II C 5.02 3.47E+07 69 3/4 III A 8.71 3.78E+07 76 5/8 I C 5.76 2.31E+07 46 without cutout 3/4 II C 4.98 3.56E+07 71 Figure 8 shows a comparison of fatigue life for the OSD designs with and without cutouts as a function of deck plate thickness. This result is consistent with the stress distribution in FIGURE 5a, with the OSD detail design having a thicker deck plate (3/4 in.) and no cutout producing slight improvement in fatigue life. Increasing the deck plate thickness would help to extend the fatigue life by reducing the vehicular bending moment for both design options. When compared to the OSD designs with the cutout, those without the cutout benefited less from an increase of deck thickness above 7/8 in. This was mainly because no cutout geometry was more integrated and stiffer than this design. Hence, it suffered more from local stress concentrations caused by out-of-plane motions and distortion inducing secondary stresses. Parameters

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FIGURE 8 Fatigue life comparison for OSD with and without cutout

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CONCLUSIONS AND SUGGESTIONS

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A parametric study was performed that examined the influence of various parameters, including deck plate thickness, on stress ranges generated at critical locations under applied traffic load for two OSD design options on the Bronx-Whitestone Bridge, one containing cutouts in the transverse diaphragms that accommodated the deck ribs and one that did not use cutouts and directly welded the ribs to the diaphragms webs. A general solution for simplifying vehicular loads on a bridge was also introduced to facilitate fatigue life analyses by estimating accumulated damage under applied live loads. Overall fatigue performance was compared for the

TRB 2013 Annual Meeting

Paper revised from original submittal.

Xia, Nassif, Hwang, and Linzell

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original OSD design, that which used the cutouts, and the alternative design that did not utilize cutouts. The main conclusions from the study are summarized as follows: • Increasing the deck plate thickness and the diaphragm web thickness were found to significantly improve the fatigue resistance of both OSD systems while simultaneously keeping weight under control. However, increases in the diaphragm web thickness were found to have limited effect on the fatigue resistance. • As for the OSD design with cutouts, the component most sensitive to fatigue damage was the toe of the weld connecting the diaphragm web to the longitudinal ribs (II in FIGURE 4a). It was also observed that, for this design, an increase of deck plate thickness improved the fatigue performance by decreasing the detrimental in-plane moments in the deck components. • For the OSD system without cutouts, the critical location was identified to be at the ribdeck-diaphragm zone (I) for a deck plate thickness of 5/8 in. but the critical location shifted to rib-diaphragm zone (II) when the deck plate thickness increased to 3/4 in. Therefore, an increase in deck thickness did not only relieve the bending moment due to traffic loads but also enhanced the fatigue resistance, especially at the rib-deckdiaphragm connections. • For the designs and parameters that were examined, the OSD design that had a thicker deck plate without cutouts had optimal overall fatigue performance.

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ACKNOWLEDGEMENTS

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Advice and suggestions from Prof. Ben T. Yen in Lehigh University to the first author are acknowledged. The help of Dr. Yingjie Wang and graduate student Dan Su is also acknowledged.

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REFERENCES

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1. Chen, W. F., and L. Duan. Bridge engineering handbook. CRC Press, 2000. 2. Connor, R. J. Influence of cutout geometry on stresses at welded rib-to-diaphragm connections in steel orthotropic bridge decks. In Transportation Research Record: Journal of the Transportation Research Board, No. 1892, Transportation Research Board of the National Academies, Washington, D.C., 2004, pp. 78-87. 3. Abdou, S., W. Zhang, and J. W. Fisher. Orthotropic deck fatigue investigation at Triborough Bridge, New York. In Transportation Research Record: Journal of the Transportation Research Board, No. 1845, Transportation Research Board of the National Academies, Washington, D.C., 2003, pp. 153-162. 4. Oh, C. K., K. J. Hong, D. Bae, H. Do, and T. Han. Analytical and experimental studies on optimal details of orthotropic steel decks for long span bridges. International Journal of Steel Structures, Vol. 11, No. 2, 2011, pp. 227-234. 5. Mizuguchi, K., K. Yamada, M. Iwasaki, and S. Inokuchi. Rationalized steel deck structure and large model test for developing new type of structure. In Proc., Int. Orthotropic Bridge Conf., ASCE, CD-ROM, Reston, VA, 2004, pp. 675-688. 6. Xiao, Z. G., K. Yamada, S. Ya, and X. L. Zhao. Stress analyses and fatigue evaluation of rib-to-deck joints in steel orthotropic decks. International Journal of Fatigue, Vol. 30, No. 8, 2008, pp. 1387-1397.

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Paper revised from original submittal.

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7. New Jersey Dept. of Transportation. Design and Fabrication of Orthotropic Deck Details. Request For Proposals (and addendum), Project No. 2011-14, Bureau of Research, New Jersey, 2011. 8. Connor, R. J., and J. W. Fisher. Results of Field Measurements Made on the Prototype Orthotropic Deck on the Bronx-Whitestone Bridge New York City, NY. ATLSS Report 04-03, 2004. 9. ABAQUS Standard User’s Manual Version 6.12. Hibbit, Karlsson and Sorensen Inc., Pawtucket, RI, 2012. 10. AASHTO. Load Resistance and Factor Design, Bridge Design Specifications, 5th Edition. America Association of State Highway and Transportation Official, Washington, D.C., 2010. 11. Miner, M. A. Cumulative Damage in Fatigue. Journal of Applied Mechanics, Vol. 12, 1945, pp. A159-A164. 12. Schilling, C. S., K. H. Klippstein, J. M. Barsom, and G. T. Blake. Fatigue of welded steel bridge members under variable amplitude loading. NCHRP Report 188, Transportation Research Board, Washington, D.C., 1978.

TRB 2013 Annual Meeting

Paper revised from original submittal.

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