# Experimental and Numerical Study on UHPC-RC Decks within Hogging Moment Region
## 1 Introduction  
Steel-concrete composite bridges can make use of the advantages of steel and concrete materials, and can also reduce the time of interruption for normal traffic during bridge construction (e.g., steel girders provide form support for concrete deck placement construction). Thus, they are widely used in bridge structures with small and medium spans. Since most steel-concrete composite bridges are continuous girder bridges, the concrete deck is in tension within the hogging moment region (i.e., at the top of the interior pier). Cracking of the concrete deck often occurs within the hogging moment region, which reduces the overall stiffness of the composite section and causes corrosion of the reinforcements and shear connectors in the concrete deck. Thus, the durability of the overall structure is reduced. Therefore, the most critical issue in the design of steel-concrete composite continuous bridges is to effectively inhibit the occurrence and development of cracking of the concrete deck within the hogging moment region. Many researchers have studied different ways to improve the anti-cracking capacity of the concrete deck, including pre-tension of the concrete deck and pre-jacking of the interior supports to induce shanginitial compressive stress in the concrete deck [1; 2; 3; 4; 5; 6]. However, for these methods, due to the creep and shrinkage of concrete, the initial compressive stress in the concrete deck transfers to the steel girders, and concrete cracking problems occur. Research by [PERSON] et al. [4] showed that double compositeaction can make concrete crack development slower and can increase the sectional stiffness but cannot avoid deck cracking. The study of crack propagation is also of importance in other engineering applications [7; 8; 9]. Crack propagation tests were conducted to investigate the effect using high-density polyethylene [8], and fatigue crack retardation can be obtained [9]. For steel-concrete composite bridge structures, one possible solution to this problem is to replace conventional concrete with ultrahigh-performance concrete (UHPC) for a deck that has much better tensile strength. UHPC is an advanced cement composite material with high tensile strength, which was first used in bridge engineering in 1997 and started to be applied to bridge structures in China in the 21 st century [10; 11]. Several researchers have investigated the behavior of steel-UHPC composite girders or decks. [PERSON] et al. [12] investigated the cracking resistance, flexural performance, and deformation characteristics of steel-UHPC composite beams under the hogging moment with experiments and theoretical analyses. They found that the crack resistance and flexural capacity of steel-UHPC composite beams under the hogging moment were significantly higher than those of steel-NSC composite beams, and that the development and propagation of cracks was much slower. [PERSON] et al. [13] conducted full-scale experiments of three steel-UHPC composite slabs and one steel-concrete composite slab to investigate the effect of the number and type of shear connectors. [PERSON] et al. [14] studied the flexural behavior of a composite bridge deck composed of a corrugated steel deck and a UHPC slab connected using MCL-shaped dowels. [PERSON] et al. [15] analyzed the mechanical behavior of steel-UHPC composite slabs before ultimate loading and obtained the mechanical indexes, including the cracking and ultimate loads, using a pure bending test model. [PERSON] et al. [16] investigated the flexural performance of steel-UHPC composite beams composed of a pre-cast UHPC slab through a large-scale and four-point bending test. [PERSON] et al. [17] proposed three new types of steel-UHPC lightweight composite bridge girders and analyzed crack resistance and fatigue performance. [PERSON] et al. [18] investigated the static bending performance of HSS-UHPC composite beams through experiments and finite element analysis. [PERSON] et al.