1- Introduction

2- Measurements of incident turbulence and fluctuating pressure

3- Three-dimensional aerodynamic admittance function (3D-AAF) of the bridge decks

4- Conclusions

References

Abstract

Via wind tunnel tests, the fluctuating pressures on the surfaces of three streamlined box bridge models are measured in two turbulent flow-fields with different turbulence characteristic parameters. The distributions of the fluctuating pressures on the models are presented and discussed in detail. The correlations between the fluctuating pressures on a crosswise section and the coherences of the buffeting force along the spanwise direction of the models are investigated. Furthermore, the 3D aerodynamic admittances of the models are identified and analyzed. An empirical formula for determining the 3D aerodynamic admittance of a streamlined bridge deck is proposed based on the extensive results of the experimental data and analysis. Clarifications are made regarding the differences between the real 3D aerodynamic admittances and the existing formulas. It is then further revealed that the real value of a 3D aerodynamic admittance is not between 1 and the number determined by the Sears function. This is followed by a rational explanation for the observations based on the experimental results.

Conclusions

Extensive wind tunnel tests were conducted to measure the fluctuating pressures on the surfaces of three streamlined box bridge models in two turbulent flow-fields with different free-stream turbulence characteristic parameters. The distributions of fluctuating pressures on the models, the correlations of fluctuating pressures on crosswise sections and the coherences of the buffeting force along the spanwise direction of the models were presented and discussed. An empirical formula for determining the 3D aerodynamic admittances of streamlined bridge decks was proposed based on the results of the experimental data and analysis, which was verified to be an accurate aerodynamic admittance model for the simulation of the buffeting loads acting on bridges. Based on a detailed analysis of the measured data and comparative studies, conclusions are summarized as follows: • The aerodynamic forces acting on bridges have strong 3D features; the existing aerodynamic admittance models based on the strip assumption may not be able to accurately simulate the buffeting forces on bridge decks. • The aerodynamic admittance of a bridge deck is affected by the coherence of the fluctuating pressures on a crosswise section and the buffeting forces along the spanwise direction. Therefore, a reasonable 3D-AAF should be a function of reduced frequency Lw and structural characteristic width B.

1- Introduction

2- Experimental program

3- Conclusions

References

Abstract

Because of the current geopolitical situation, research on improving the resistance of the civil and transport infrastructure to blast or impact loads has gained considerable attention. This paper presents the results of full-scale blast experiments designed to characterize the resistance of concrete-based composite bridge decks subjected to close-in blast loading. Three composite decks with different degrees of heterogeneity were proposed and tested: a slab with basalt fiber meshes in multiple layers along the depth of the specimen, a slab with recycled textile sheets 100 mm in total thickness, and a typical hollow-core prestressed slab. The dependence of the extent of the blast damage on the material characteristics of the composite material was studied. A detailed study of the damage to the specimen caused by the close-in explosion found apparent delamination of all tested composite specimens. The heterogeneity of the layered composite material converts the blast damage due to internal rebounds into layer delamination.

Introduction

Due to the current geopolitical situation, there has been a considerable increase in the number of terrorist acts in recent years. The need to improve the resistance to blast or to impact of the civil and transport infrastructure has led to increased interest in research and development on various materials, and on their resistance to high strain-rate loading. This paper presents the results of a full-scale experimental program focused on the blast resistance of hybrid concrete specimens subjected to close-in blast loading, and the dependence of the resistance on the composition and the material properties of the specimen. This research program built on previous research conducted by the authors. Since 2010, the authors have been conducting experiments with an unchanged arrangement, using various types and compositions of concrete, ranging from normal-strength concrete without distributed reinforcement (NSC) to ultrahigh-performance fiber-reinforced concrete (UHPFRC). The results of earlier experiments are presented in [1–3]. To explore ways of further enhancing the blast resistance of concrete, the experiments presented in this paper introduced three specimens with an atypical internal structure made of newly-developed concrete-based composite materials utilizing basalt fiber meshes and recycled textile sheets. One conventional specimen with a hollow core was also used for comparison. 1.1. State-of-the-art on blast performance of composites Shock wave propagation through a heterogeneous environment is a very complex issue, because the shock wave is partially reflected from and partially passes through any interface of environments with different densities. This partial reflection can effectively mitigate the effects of a blast wave. This paper builds on the research on air shock wave propagation and interactions in heterogeneous environments previously conducted by the authors, see [4,5]. The use of heterogeneous materials in blastresistant devices and structures can significantly increase their effectiveness. Composite building materials are generally well suited to achieve the required material heterogeneity.

After casting concrete it is typically necessary to maintain suffi- cient moisture content on the surface to sustain hydration [1]. This process is called curing [2]. Maintaining the moisture in concrete promotes reaction of the binder to develop a torturous and strong microstructure [1–3]. A torturous microstructure will reduce the drying rate and the ingress of fluids and external ions. This means that curing can improve the long-term durability of concrete [4–6]. Wet curing continuously supplies moisture to the surface of the concrete [1,2]. However, there are challenges in curing concrete elements that dry from one side, such as pavements [2,7,8]. For example, concrete pavement in a dry environment can suffer from large differential drying shrinkage after the termination of wet curing which can lead to dimensional instability, called curling [9–13]. Some have suggested that a possible alternative could be to use curing compounds instead of wet curing. While wet curing must be removed from the surface to allow traffic on the structure, curing compounds can stay in place until they are worn off the concrete surface [14,15]. Curing compounds have their own challenges. For example, the amount of curing compound needed depends on the ambient conditions, surface texture, and product being used [16]. Therefore, it has been suggested to apply them in two layers to ensure a uniform coverage [17–20]. Two recently developed curing compounds are investigated in this paper. The first is based on Poly(alpha-methylstyrene) or PAMS, which has been reported to be very effective in reducing the moisture loss and drying shrinkage induced curling [16,21]. This work also investigates a lithium silicate curing compound that has been reported to cure concrete and reduce the cracking in bridge decks [22]. The lithium silicates are reported to react with calcium hydroxide to generate calcium silicate hydrates and cause a densification near the surface [23,24].