The natural bond between FRP (fiber reinforced polymer) profile and concrete is quite weak, additional measures for improving the FRP-concrete interface should be taken to ensure the hybrid FRP-concrete members work compositely. There are several methods for interface improvement, and this paper focuses on the sand-coating method. Experimental tests including pull-out tests and push-out tests were conducted on sand-coated FRP-concrete interface. Test results revealed that the interfacial behavior included two stages. In the first stage, the concrete surrounding the plate failed in shear, which was similar to the adhesive bonding FRP-concrete interface. In the second stage, interfacial dilatation was induced and significant friction took place between fractured concrete surfaces. The adhesive-FRP interface and adhesive-sand aggregates interface were further damaged. Based on test results and numerical analysis, the variation of the interfacial dilatation and friction coefficient with the interfacial slip were determined. Finally, a pressure-dependent bond stress-slip model which was suitable for both active and passive confinement conditions was developed. This model can be implemented into commercial FE software and used for FE analysis of structural members. Comparisons with test results of the present paper and those from the literature indicate that the proposed model can provide reliable predictions.
No abstract is provided for this article.
Current design manuals for fiber-reinforced polymer (FRP) structures only allow limited application of FRP in high-temperature environments. However, the residual mechanical properties of FRP composites at high service temperatures should be considered. This paper presents the results of bending tests on FRP coupon specimens at temperatures from 25 to 120°C and of compression tests on FRP components at temperatures from −40 to 90°C. Although the mechanical properties decrease with increasing temperature, they retain residual strength and stiffness at high service temperatures. The influence of subzero temperatures on the mechanical properties is negligible. Additionally, the flexural properties of the coupon specimens and the compressive properties of the components were experimentally investigated after high-normal temperature cycles, which alternated between 45 and 135°C every 12 h. The results show that repeated high-normal temperature cycles have little effect on the mechanical properties. The simultaneous effects of loading and high-temperature environments on FRP structures should be considered during design. Thus, this paper proposes a design method for calculating the loading capacity of FRP members at different temperatures. Experimental data from literature and this study were normalized and compared with the results predicted by this method. As expected, the proposed method provides a lower envelope of experimental data for both strength and modulus. Thus, the design method can conservatively estimate various mechanical properties of FRP structural members under different loading conditions at high service temperatures. Additionally, the method can be conveniently established and applied in design.
Conference paper written by Peng Feng, Lieping Ye, Rui Bao, Asad Ullah Qazi and Jin-Guang Teng presented at IABSE Symposium: Metropolitan Habitats and Infrastructure, Shanghai, China, 22-24 September 2004.
Most stress-strain models of FRP-confined concrete under uniaxial loading only consider FRP in tension in the hoop direction.This paper presents a model which takes into account the reduction in confinement modulus of FRP tube under combined axial compression and lateral tension.The results of this model agree well with test results.A parametric study is presented based on the model in this paper.
以252Cf中子源驱动噪声分析测量法为依据,利用中子脉冲信号自相关函数与被测核材料（252 U）质量的关系,设计了一种基于神经网络的核材料质量识别方法,探索借助时域特征进行质量识别的有效性。利用平稳小波变换抑制中子统计涨落对自相关函数带来的影响,利用分布式Elman神经网络对不同质量核材料的自相关函数样本进行训练和识别,并研究了有限样本前提下不同子网个数对最终识别结果所造成的影响。对4种核材料质量共计120组样本进行的实验,结果表明：在理想实验条件下,平稳小波变换抑制了统计涨落对信号自相关函数的影响;分布式Elman神经网络能够较好地识别自相关函数的特征,分辨不同质量的核材料,平均识别误差小于0.1。
Fiber reinforced polymer (FRP) bars have been proposed for use in ultra-high performance concrete (UHPC) as the reinforcement to mitigate/avoid the post-peak strain softening of UHPC under tension and to reduce the fiber dosage used in UHPC. The so-formed FRP-reinforced UHPC plates could be adopted for both structural strengthening and constructing novel structural elements. In this paper, a novel connection based on FRP bars and steel grouting sleeves has been developed for prefabrication construction of FRP bar-reinforced UHPC structures. Flexural tests were conducted to gain understandings of the effects of the connection mode (the staggered connection and the horse tooth connection) and reinforcing fiber type (polyethylene (PE) fibers and steel fibers) in the UHPC on the flexural behavior of connected FRP bar-reinforced-UHPC composite plates. The test results revealed that the proposed connection system is reliable since the composite plates always failed outside the connection zone, and most of the crack opening displacements at the interface of the connection are smaller than 0.2 mm at ultimate. The connection mode and the fiber type had little influence on the first cracking load and the initial bending stiffness of the FRP bar-reinforced UHPC plates, while the horse tooth connection led to a better ductility of the composites plates than the staggered connection mode. At given tolerable deflection of 1/200 span (about 5 mm), the longitudinal strains developed in the CFRP bars were about 2000 με for all specimens.
Concrete-filled steel tubular (CFST) columns have been extensively studied and widely used in practice. Existing research has shown that non-circular CFST columns is much less ductile than their circular counterparts, particularly when thin/high strength steel (HSS) tubes and high-strength concrete are used. To address this problem, a new form of CFST columns has recently been proposed by the first author. The new column consists of a steel tube filled with concrete that is confined with HSS spiral reinforcement typically with a yield stress exceeding 1000 MPa. These columns, referred to as confined concrete-filled steel tubular (CCFST) columns, also maintain the ease for connection to CFST or steel beams. This paper presents the results of a series of concentric axial compression tests on such columns of square cross-section to demonstrate their advantages. The experimental program included 13 CCFST columns, four CFST columns without internal spiral confinement, two hollow steel tube (HST) columns, and 11 circular HSS spiral-confined concrete columns. Three different compressive strengths and three HSS spiral pitches were examined in the experimental program. The CFST columns, HST columns, and HSS spiral-confined concrete columns were all tested under axial compression to gain a good understanding of the confinement mechanism in a CCFST column. The test results show that the new columns possess much greater ductility than those without internal spiral confinement, although the use of HSS spirals increases the steel volume by only a small percentage. It is also shown that the axial load-axial strain curve of a CCFST column can be conservatively predicted by summing the axial load-axial strain curves of the hollow steel tube without local buckling, the HSS spiral-confined concrete core, and the sandwiched concrete between the two.
The concept of multiscale fibrous reinforcements in cementitious matrices is characterized by a wide range of scales from distributed nanomaterials and chopped short fibers to continuous fibrous reinforcements. Based on fibrous reinforcements at multiple scales, this study elaborately optimizes mechanical behavior by tailoring the types and volume fraction of fibers and develops a cementitious composite, flexible ultra-high performance reinforced cementitious composite (FHPRC), with 160 MPa compressive strength, 36 MPa tensile strength, over 1% ultimate tensile strain, less than 0.1 mm crack width, and significant post-yield stiffness. FHPRC combines the superior strength and durability of ultra-high performance concrete (UHPC) with the high ductility and crack control capacity of engineered cementitious composite. We demonstrated the effectiveness of the material design strategy through experimental and numerical examinations. The effects of the types of short fibers (steel with a designed length of 13 mm and glass with a length of 50 mm), fiber-reinforced polymers (FRPs) (carbon and glass), and textile configuration on the flexural behavior were analyzed. To capture their flexural behavior, several numerical models have been developed to optimize FHPRCs. Furthermore, the layered shell finite element model (FEM) based on the smeared crack approach considerably simplifies the numerical effort required to simulate intense matrix cracking. However, no realistic constitutive model for any composite containing one or more reinforcing fibers for layered shell FEMs has been developed. Hence, an equivalent constitutive model for layered shells was established to analyze the flexural behavior of FHPRCs. The model proved that the combination of UHPC and carbon FRP textiles yielded a superior composite. The research results provide valuable insights into the evolving field of advanced construction materials and engineering.
Biology has been a brilliant teacher and a precious textbook to man-made construction for thousands of years, because it allows one to learn and be inspired by nature's remarkable and efficient structural systems. However, the emerging biomimetic studies have been of increasing interest for civil engineering design only in the past two decades. Bridge design is one of aspects on structural engineering of biomimetics that offers an enormous potential for inspiration in various aspects, such as the geometry, structure, mechanism, energy use and the intelligence. Recently built bridges and design proposals in which biological systems have produced a range of inspiration are reviewed in this paper. Multidisciplinary cooperation is discussed for the implementation of bio-inspired methods in future design. A case study about using bio-inspired strategy is trying to present a problem-solving approach, yet further cooperation is still needed to utilize biomimetic studies for design inspiration. This paper aims to call a close multidisciplinary collaboration that promotes engineers to build more sustainable and smart structural systems for bridges in the 21st century.
