PSI - Issue 5

M.H. Hebdon et al. / Procedia Structural Integrity 5 (2017) 1027–1034 Liu et al. / Structural Integrity Procedia 00 (2017) 000 – 000

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1. Introduction

Fatigue of steel bridges is a critical and troublesome damage under repeated daily traffic (Guo et al., 2012). The fatigue damage can occur at low stress levels under alternating stresses, which results in considerable repair costs and influence on bridge performance (De Jesus et al., 2010, 2011, 2015, 2015; Guo et al., 2010). However, a number of existing bridges are still in operation and many are expected to remain in service for the foreseeable future (Hebdon et al., 2017; Mayorga et al., 2016, 2017; Lesiuk et al. 2015), although many of those bridges are reaching the end of the original design life. The Hercílio Luz Bridge (i.e. HLB), which was built in 1926, was closed to traffic in 1991 due to high corrosion levels and deterioration of critical structural elements. A complete rehabilitation project was developed and currently underway for the bridge which includes the replacement of the compromised members and strengthening of the foundations (Carvalho et al., 2017). The original design and construction were completed under the AASHTO, while the rehabilitation project was conducted under the Brazilian codes and Eurocode. Intensive research on the fatigue performance assessment has been carried out based on calculated/measured stress ranges and fatigue provisions for existing bridges (Guo et al., 2011; De Jesus et al., 2010, 2011, 2014, 2015). Field measure data or different local field comprehensive truck models have been applied and demonstrated with high accuracy, the localization of field data and field truck models limited its board application. Hence, fatigue life evaluation based on the concise fatigue truck model prescribed in commonly available design codes is still significant, especially for structural designers. In this paper, a fatigue life evaluation has been carried out using the fatigue load models 3 (FLM-3) indicated by Eurocode EN 1991-2 (CEN, 2003) to obtain the calculated stress ranges for the critical members of the HLB, as well as the simplified equivalent stress range and fatigue damage accumulation method for the fatigue safety verification defined by Eurocode EN 1993-2 (CEN, 2005) and Eurocode EN 1993-1-9 (CEN, 2008). Fatigue provisions specified in Eurocode are reviewed and fatigue life assessment analyses are conducted on critical connections of the HLB.

2. Hercílio Luz Bridge

2.1. Bridge description

The HLB is an eyebar suspension bridge which consists of a central span suspended by two eyebar chains and 27 secondary spans of the access viaducts supported by 12 secondary towers (Carvalho et al., 2017), as illustrated in Fig. 1. The central span is primarily composed of beams and modified Warren trusses. Fig. 2 presents the cross-section near the mid-span and near the end of the central span, where the configuration of some members are listed. The cross section of the central span is 13.5 m (44.42 ′ ) wide, which includes two traffic lanes. Generally, deck trusses, trusses and beams are riveted built-up members, which have lattices and lacings.

Fig. 1. Profile of Hercílio Luz Bridge.

The trusses are formed by upper chords, lower chords, uprights and diagonals, as shown in Fig. 3, which are connected by cross-beams, X-shaped bracings and traverses. At the 1/4 span and 3/4 span point shown in Fig. 3(a), the eyebar suspension chains are incorporated into the trusses, serving as the upper chords of the truss for the middle 1/2 of the main span. The remainder of the central span (first and last 1/4 span) is connected to the eyebar chain through vertical suspenders. The connections between the floor beams and stringers are shown in Figs. 3(b) and (c). The components of the stringer were welded to the web of the floor-beam by a pair of fillet welds with a throat thickness=5