Bending behavior of concrete-encased composite I-girder with corrugated steel web
Introduction
Prestressed concrete girders with corrugated steel webs are one of the promising concrete–steel hybrid structures applied to highway bridges, which include prestressed slabs, corrugated steel webs and internal or external tendons. The way to substitute corrugated steel webs for concrete webs of a box girder bridge will result in no restraint among the upper or lower deck slab and webs of the bridge, which will alleviate influences on the structure due to concrete creep, drying shrinkage and temperature differences. Prestressing can be efficiently introduced into the top and bottom concrete flanges due to the so-called “accordion effect” of corrugated webs. The strength, stability of structures and material efficiency can be improved by concrete slab combined with corrugated steel webs [1], [2], [3].
Flexural strength of steel girder with corrugated steel web is provided by the flanges with almost no contribution from the web. Furthermore, there is no interaction between flexure and shear behavior. Thus, the ultimate flexural strength of steel girder with corrugated steel web can be based on the flange yield strength [4], [5], [6], [7], [8]. The flexural capacity of composite girders with corrugated steel webs was also investigated and the same aspects defined for steel girders were found to be applicable to composite girders [9]. Lindner [10], Aschinger and Lindner [11] studied the elastic flexural behavior of corrugated web I-girders under in-plane loads. In their analyses, they assumed that the flanges carry only the moment and the web carries only the shear. Elgaaly et al. [6] did experimental and analytical studies on bending strength of steel beams with corrugated webs. Parametric analytical studies were also conducted to examine the effect of the ratio between the flange and web thicknesses, the yield stresses, the corrugation configuration, the panel aspect ratio, and the stress-strain relationship to the ultimate bending moment capacity of steel beams with corrugated webs. Chan et al. [12] and Khalid et al. [13] studied the effect of web corrugation on the bending capacity of the beam using finite element method. Beams with flat web, horizontally and vertically corrugated web respectively were studied. Mo et al. [14] presented the experimental and analytical results of four scaled prestressed concrete box-girder bridges with corrugated steel webs. It was found that both the thickness of end diaphragms and the location of prestressing strands at both ends of the specimens were insignificant when the specimens failed in the mid-span due to concrete crushing. Huang et al. [15] performed finite spring element analysis on the accordion effect of steel beams with corrugated web. The accordion effect is a phenomenon that, when prestressing is introduced to a member with corrugated web, the web behaves like an accordion and folds easily to the longitudinal direction. Song et al. [16] investigated and analyzed the mechanical behavior of externally prestressed composite beams with corrugated steel webs by using a nonlinear program and model tests. Watanabe and Kubo [17] presented experimental and numerical analysis results of corrugated web girders with four different trapezoidal corrugation configurations, including a flat web under pure bending. A predicting method of the ultimate strength considering local flange buckling was also proposed based on the parametric analysis of corrugated web girders. He et al. [18] analyzed the mechanical behaviors of corrugated steel web box girders with different internal and external tendon parameters under flexural load, including the arrangement of the internal and external tendon, the tensile force, the position of the anchorage point and the distance of the diversion point.
In Japan, continuous and rigid frame bridges with the main span length from 50 m to 150 m account for about 80% of the total number for composite bridges with corrugated steel webs. However, at the intermediate supports of continuous or rigid frame bridges, large bending moments and shear forces exist; the concrete slab is in tension due to hogging bending moment and does not contribute to the bending strength. The lower flanges and lower parts of webs are in compression and are vulnerable to lateral-torsional buckling. Thus, there are weak points with regard to durability and strength. Partially encased composite I-girder with corrugated web has been proposed to improve the structural performance of continuous composite girder under hogging moment. Concrete is poured in the area surrounded by the upper flange, lower flange and web around the intermediate supports especially the section of large height. The encased concrete is expected to prevent buckling of the web in compression and the concrete itself also contributes to the bending and shear strength, as shown in Fig. 1.
At present, there are few reports about design codes and methods for concrete-encased composite I-girder with corrugated steel web. The authors [19] tested seven steel and composite I-girders with flat or corrugated web to investigate the shear performance, the varying parameters such as the thickness of steel web and shear connection degree between steel web and encased concrete were considered in the test. On the basis of experimental results, analytical and numerical models were established and verified to predict the shear strength of encased composite girder with corrugated web [20].
This paper focuses on the experimental and analytical studies on bending behavior of steel and composite girder with corrugated web. Four steel and composite I-girders with corrugated or flat web were tested under bending moment to investigate the flexural strength and failure mechanism, such as load-displacement relation, failure mode and strain distribution. On the basis of experimental failure modes and strain distribution, analytical methods to estimate bending strength were proposed, and the analytical equations were validated through comparisons with experimental results. The overall investigation can serve as a basis for bending strength calculation and design of partially encased composite I-girder with corrugated web.
Section snippets
Test specimens
Four steel or composite I-girders with the height of 0.44 m and length of 3.94 m were fabricated and tested to investigate the bending performance. The web was 400 mm high and 10 mm thick, and the flange was 300 mm wide and 20 mm thick.
Two series of specimens were classified: one was the steel I-girders (Series BS), the other was the concrete-encased composite I- girders (Series BC). In comparison to the I-girders with corrugated web, specimens with flat web (BS-0, BC-0) were provided in each series.
Load–displacement relationship
The relationships between load and vertical displacement at mid-span of each specimen until the ultimate state are shown in Fig. 5. The load was the concentrated load applied on the distributive girder by servo loading system. And out-of-plane deformation for web was measured by lateral displacement gauge on the middle section, the load-deformation relationship curves are described in Fig. 6.
As for steel I-girders with corrugated or flat web (BS-0,-1), the vertical displacement increased almost
Bending strength of steel girders with flat web
The load-carrying capacity of plate girders under pure bending mainly depends on the ultimate strength of compression flanges and in particular on their resistance to torsional buckling, local buckling of plates with three edges supported and one edge free, lateral buckling, and also vertical buckling in the plane of the web plate. The torsional and vertical buckling of compression flanges can be avoided by limiting the width-to-thickness ratios of outstanding flange and web plates
Conclusion
Partially encased composite I-girder with flat or corrugated web has been proposed to improve the structural performance of continuous girder under hogging moment. The bending behavior of such structure under two points symmetric loading has been experimentally and analytically investigated. The following conclusions may be drawn from the present study:
- (1)
Flexural experiments show that the partially encased composite girder has higher bending strength in comparison to steel girder, since local
Acknowledgments
This research is sponsored by the National Nature Science Foundation of China under Grant no. 51308070, and the Liaoning Province Transportation Construction Technology Program. These supports are gratefully acknowledged. This paper was written when the first author visited the Department of Civil and Environmental Engineering of Waseda University in Japan. The assistance is also gratefully appreciated.
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