Issue 9

Z.H. Qian et alii, Frattura ed Integrità Strutturale, 9 (2009) 105 - 112; DOI: 10.3221/IGF-ESIS.09.11 108 design when choosing the detail geometry, the structural material and the welding technique and requirements . Fig. 5 shows a submodel of rib-to-deck plate connection with a crack [11]. Figure 4 : Stresses at the center deck plate of the middle span (Abruzzese et al., 2008) R IB - TO - DIAPHRAGM CONNECTION ib-to-diaphragm connection is one of the most complex joint in the orthotropic deck. Cutout has a significant influence to the stress performance at the diaphragm, especially the area near the cutout. The previous investigations have demonstrated that peak stresses occur at the rib-to-diaphragm connections easily due to concentrated influence. Numerical as well as experimental work at ECSC research showed a reduction of the stress concentration at the edges of cutout by increasing the notch radius of cutout [12]. After investigating different continuous types of rib-to-diaphragm connection of railway bridges in the laboratory, Haibach et al. proposed a new shape of cutout for rib passing through diaphragm [13], and it is applied in Eurocode3 (2004). Fatigue tests were carried out at Delft University of Technology by Kolstein et al [14]. The results demonstrated that fatigue life of the continuous rib-to-diaphragm connection without cutout resulted in a longer fatigue life than the connection with cutout. Furthermore, the fatigue life of the rib-to-diaphragm connection with additional cutouts is strongly affected by high shear stresses in the diaphragm. It was presented as well that besides quality aspects the durability of the rib-to-diaphragm connection is mainly restricted, due to shortcomings in design with respect to the underestimation of high shear forces (out-of-plane stress). ATLSS research center of Lehigh University has investigated the fatigue performance at cutout more than 10 years, particularly at rib-to-diaphragm connection [15, 16] . Both field measurements and laboratory tests were carried out to Williamsburg Bridge and Bronx-Whitestone Bridge in New York City under supervision of Fisher. From the long term remote monitoring of the Williamsburg Bridge orthotropic deck diaphragm, it is found that a number of stress cycles exceed the constant-amplitude fatigue limit for Category C, which was found to be applicable to the rib-to-diaphragm welded joint at the cutouts. Meanwhile, both in-plane and out-of-plane stresses were studied in ATLSS researches. It is in- plane stress, not out-of-plane stress, dominant the stress range at diaphragm. However, out-of-plane bending can influence the fatigue behavior of rib-to-diaphragm connection significantly. FE method was used to analyze the influence of cutout geometry (with bulkhead) to welded rib-to-diaphragm connections by Connor [17]. Parameters considered included overall cutout shape, cutout depth, diaphragm plate thickness, and deck plate thickness. Results of this study indicate that larger cutout geometries offer less resistance to out-of-plane displacements induced by longitudinal ribs rotations. However, cutouts that are excessively deep will increase in-plane stresses at the welded rib-to-diaphragm R