Fatigue behavior of orthotropic composite deck integrating steel and engineered cementitious composite

Highlights

• An innovative orthotropic composite deck is proposed to achieve desired fatigue behaviors.

• Engineered cementitious composite (ECC) is employed as a high-performance overlay.

• The innovative orthotropic composite deck integrates conventional steel deck and ECC.

• Full-scale orthotropic composite decks are experimentally tested under fatigue loading.

• The innovative orthotropic composite deck exhibits desired fatigue resistance and robustness.

Abstract

Orthotropic steel decks offer many advantages in bridges, but they are prone to fatigue damage. One of the effective approaches to increase the fatigue resistance is to enhance the stiffness through applying a concrete layer, forming a composite section with the steel deck. However, once the concrete is cracked, the composite action is compromised. To improve the fatigue resistance, this study proposes a composite deck using engineered cementitious composite (ECC) and large U-ribs through experimentation and simulations. Two full-scale composite decks were tested to investigate the fatigue resistance and failure process, and validate a finite element model that was used to elucidate the effect of ECC on the fatigue performance. The test results showed that the composite deck had sufficient fatigue resistance, and the analysis results showed that the ECC overlay reduced the stress range by 90% at the rib-to-deck and diaphragm welded joints and 54% at the rib-to-diaphragm welded joints. One interesting finding is that the proposed deck has a robust fatigue resistance even after damages were caused in the deck system. This study is expected to advance the knowledge of the effect of ECC on the fatigue resistance, understand the underlying mechanisms, and promote further research and potential applications of the proposed composite deck.

Introduction

Orthotropic steel decks (OSDs) are widely used in long-span bridges because they have low self-weight and high load-bearing capacity [1], [2], [3]. Typically, an OSD consists of a grillage of longitudinal U-ribs (along bridge length), transverse diaphragms (perpendicular to bridge length), and a thin deck plate, as shown in Fig. 1(a). The intersection of these components results in a number of complex welded joints, which are subjected to high local stresses induced by vehicle loads. Typically, fatigue cracks initiate from multiple fatigue-prone details where high stresses are generated [3], [4], [5]. Under vehicle loading, fatigue cracking is one of the primary issues that affect the safety and reliability of OSDs [4], [5], [6]. In addition to vehicle loading, there are other reasons for fatigue cracking in OSDs [7], [8], [9], [10], [11], [12], such as: (1) fabrication defects and residual stress, (2) insufficient local stiffness, and (3) severe stress concentration due to the geometry.

Many efforts have been made to increase the fatigue resistance of OSD, which can be classified into two major categories: (1) improve the fatigue strength of a single fatigue-prone detail by introducing new welding and manufacturing techniques, such as the uses of U-ribs with thickened edges and double-sided welded joints [13], [14]; (2) enhance the stiffness of OSDs through employing a reinforced concrete layer, which forms a composite section with the steel deck [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], as shown in Fig. 1(b). The composite section reduces the stress ranges at various welded joints of OSDs, thereby effectively increasing the fatigue life [26], [27], [28], [29]. Currently, the U-ribs in most composite decks have the same dimensions as those of conventional OSDs [2], [3]. Typically, the U-ribs measure 300 mm × 300 mm (width × height) and have a consistent wall thickness (8 mm). However, with the increased stiffness due to the composite action, it is possible to use U-ribs that have a wider opening and spacing between their webs (Fig. 2). The large U-ribs reduce the number of welded joints and improve the reliability of the composite bridge deck [23], [27], [28], [30].

Although composite decks demonstrated improved fatigue resistance over conventional OSDs, the existing composite decks have limitations. First, the concrete layer is weak in tension. In real applications, cracks have been observed in concrete, and cracks may compromise the composite action, thus reducing the fatigue resistance of the composite deck [18]. There are many causes for the formation of concrete cracks, such as temperature effect, shrinkage, vehicle loading, etc. To improve the crack resistance, steel bars have been embedded in the concrete layer. However, cracks continue occurring. The cracks may accelerate the corrosion of steel bars, further promoting concrete cracking because the corrosion products are expansive [31], [32]. Ultra-high-performance concrete (UHPC) and engineered cementitious composites (ECC) have been proposed to replace the conventional concrete, in order to achieve better crack resistance and long-term durability [25], [26], [27], [28], [29], [33], [34], [35]. UHPC and ECC are two representative families of high-performance fiber-reinforced cementitious composites, and designed following different philosophies. UHPC is designed to achieve a high packing density, featuring high mechanical strengths and durability [36], [37]. ECC is designed to achieve high tensile ductility (about 4%), featuring multiple-cracking, tensile strain-hardening behavior, tight crack width, and self-healing properties [38], [39], [40], [41], [42], [43]. Recently, both UHPC and ECC have been applied for structural rehabilitation or retrofit, and demonstrated great promise in improving the structural performance [44], [45], [46], [47], [48], [49], [50], [51], [52], [53].

Both UHPC and ECC are expected to improve the fatigue resistance of the composite deck. To date, there have been limited studies on using ECC in composite bridge decks. Walter et al. [21] conducted numerical simulations to study the effects of traffic and environmental loads on the cracking of the steel-ECC composite deck. Ma et al. [29] and Liu et al. [54] conducted push-out tests to evaluate the shear strength and load-slip behaviors of headed studs embedded in the ECC layer. Kakuma et al. [55] conducted numerical simulations and concluded that using ECC would likely improve the fatigue resistance of the composite deck.

Currently, there is no experimental testing of the fatigue resistance of the steel-ECC composite deck. The post-cracking behaviors of the steel-ECC composite deck under fatigue loads are unknown. It is unclear how the cracks in ECC are developed with the increase of loading cycles and how the cracks affect the fatigue performance. There is speculation that using large U-ribs in the composite deck will achieve desired fatigue performance [18], [27], [28]. These unknown questions motivate the objective of this study.

This study proposes a steel-ECC composite deck to combine ECC and large U-ribs, and investigates the fatigue behavior of the steel-ECC composite deck, as depicted in Fig. 3. The fatigue behaviors of two full-scale steel-ECC composite decks were tested, and finite element analysis were performed to understand the mechanisms of the effect of ECC on the fatigue behavior of the composite decks. This study is expected to advance the knowledge of the effect of ECC on the fatigue resistance of composite bridge decks, understand the underlying mechanisms, and promote further research and potential applications of the proposed composite deck.

The rest of the paper is organized as follows: Section 2 describes the experimental program. Section 3 presents the experimental results. Section 4 discusses the experimental results using finite element analysis. Section 5 summarizes the conclusions of the study. This study is expected to advance the understanding of the role of ECC overlay in the composite bridge deck and further the knowledge of the fatigue performance of the proposed bridge deck.