Publications

Study of GFRP Steel Buckling Restraint Braces

Buckling-restraint braces (BRBs) are used extensively in seismic-resistant structures. They consist of a core energy dissipation and external restraining component. A novel glass fiber–reinforced polymer (GFRP) steel BRB is proposed. In the GFRP steel BRB, four GFRP pultruded tubes, which are tied together by GFRP wrapping layers, are used to restrict core steel component buckling instead of conventional steel tube and infilled concrete or mortar. This GFRP steel BRB is extremely lightweight. Techniques for manufacturing GFRP steel BRB were developed for convenient large-scale industrialized production. Quasi-static tests were carried out to validate the performance of the GFRP steel BRB under cyclic loading. The tests focused mainly on energy dissipation capacity and ultimate failure mode of the proposed GFRP steel BRB. The effect of applying additional reinforcements to the GFRP external restraining component on the performance of GFRP steel BRB was also investigated. The performance of the appropriately designed GFRP steel BRB was satisfactory; however, it is prone to damage from local failure of external restraining GFRP components and additional reinforcements may enhance its performance.

Column base joint made with ultrahigh-strength steel bars and steel tubular: An experimental study

The use of ultrahigh-strength steel in civil, bridge, and offshore engineering is increasing rapidly. In this study, the seismic behavior of a concrete-filled steel tubular (CFST) column base joint with implanted ultrahigh-strength reinforcing bars has been investigated. The steel tubular and the implanted reinforcing bars are made of ultrahigh-strength steel. Four column base joints with square and circular cross-sections and with 0 and 0.25 axial force ratios have been tested to discuss the hysteretic capacity, deformation, ductility, failure modes, and energy dissipation. The axial force is the main parameter to improve the flexural capacity of the column base joints. Owing to the slip between the infilled concrete and the steel tubular columns, the hysteresis loops show an obvious pinch phenomenon. The tested specimens demonstrate good ductility behavior. Finally, the flexural capacity of the CFST column base joint has been determined by analyzing the failure characteristics and stress of the CFST columns. The flexural capacity of the CFST column base joints determined by the calculation formulae matches well with the test results. The ratio of the calculated and tested flexural capacity is between 0.967 and 1.059, and the absolute relative error is between 0.131% and 5.595%.

Experimental Investigation on Performance of Pultruded Planks Laminated Structures for Wind Turbine Blades

Compressive bearing capacity of CFRP–aluminum alloy hybrid tubes

Combining Al (namely, aluminum alloy) and CFRP (carbon-fiber-reinforced polymer) jackets to form structural members can yield many advantages and a bilinear behavior, which can enhance their advantages and mitigate any disadvantages. CFRP–Al hybrid tubes, which are used as axial load members in spatial structures, are investigated in this study by using compression experiments and a theoretical analysis. Formulas that describe the compressive bearing capacity with and without local buckling before yielding are proposed for stub hybrid tubes. In addition, their compressive behaviors are simulated by using the finite element method (FEM). A good agreement in the test results is achieved. The effect of the number of pairs of CFRP layers, the diameter-thickness ratio (DT ratio) and width-thickness ratio (WT ratio), and the fiber direction are described based on finite element analysis (FEA). Finally, a design approach for compressive CFRP–Al hybrid stub tubes is proposed.

Novel joint for pultruded FRP beams and concrete-filled FRP columns: Conceptual and experimental investigations

A novel joint, inspired by ancient mortise-and-tenon joints in timber structures, was proposed for pultruded FRP beams and concrete-filled FRP columns. FRP structures are widely known to lack appropriate joint solutions. In this regard, the proposed joint effectively provides a feasible solution for FRP frame structures. In this work, the conceptual development of this joint was first addressed. Then, the construction schemes were presented in detail, and a total of four full-scale joints were tested. To assess the structural behavior of the proposed joint, experiments including four specimens were conducted under symmetric and anti-symmetric load, i.e. the loading conditions in sway and non-sway frames. The typical failure modes were identified, including pull-out or tensile fracture of the tensile flanges and end crushing of the compressive flange. Additionally, an analytical study is carried out to develop the design method for this joint. The predicted moment capacity is found to have an excellent accuracy as compared to the experimental results. Moreover, the proposed joint can be classified as the rigid and full-strength joint based on the classifications prescribed by the European design code. It is noted that the proposed joint is completely composed of FRP composites and concrete (i.e., a steel-free joint). Thus, the joint is expected to exhibit excellent corrosion resistance, which is of particular interest for marine structures on/near oceans.

A review on FRP-concrete hybrid sections for bridge applications

Development of durable, cost-effective bridges is a pressing research topic. Previous research and field applications have shown that fiber reinforced polymer (FRP)-concrete hybrid sections, including beams and decks, are attractive options for bridge superstructures. To date, there have been many experimental results, analytical approaches, and field applications scattered in the literature. This paper aims to review and evaluate FRP-concrete hybrid sections in the context of bridge engineering. Two databases of flexural tests and push-out tests of shear connections are developed, respectively. The paper is organized as follows: First, the characteristics of materials and structural configurations are introduced according to the database of flexural tests. Then, six typical types of shear connections from the database of push-out tests of FRP-concrete shear connections are compared. Next, three typical failure modes and deformation of FRP-concrete hybrid sections are separately analyzed with necessary design equations. Finally, case studies and perspective future development are discussed.

不同栽培因子对‘绥杂7号’产量的影响

为了明确不同栽培因子对‘绥杂7号’产量影响的综合效应,采用三因素二次通用旋转组合设计方法,建立了栽培密度、施肥量、播种日期与粒用高粱‘绥杂7号’产量之间的效应模型,经DPS统计软件检验,二次回归模型拟合度较好。建立的回归模型为：Y=8218.18312-446.78324X12-287.68422X22-567.34494X32。试验结果表明：密度、施肥量、播期3因子对产量的增产作用依次为播期〉密度〉施肥量,对密度与肥料、密度与播期、肥料与播期之间的交互效应分析得出：以上两两因子之间存在一定程度的正交互效应。模型经计算机模拟寻优,得到’绥杂7号’获得7330 kg/hm2以上产量的栽培因子组合方案为栽培密度17.154~18.846万株/hm2,施肥量为211.8~150.7 kg/hm2,播种日期为5月7号—5月12号。

Experimental Study on Uniaxial Compression of Bamboo Poles with Different Reinforcements

The natural round bamboo is a kind of ecological building material with many excellent physical and mechanical characteristics, such as fast growth, high strength and good environmental performance. However, the natural round bamboos were barely used for its worse durability and easiness to crack compared other bamboo productions after secondary operation. In order to improve the safety and durability of the round bamboo structure, the axial compression test of the GFRP (glass fiber-reinforced polymer) and/or mortar reinforcing cracked bamboo was conducted. The 20 cm tall round bamboo column specimens were divided into five categories: the first without cracks and reinforcement, the second with cracks but without reinforcement, the third with cracks and full GFRP reinforcement, the forth with cracks and fulfil of cement motrar, and the last with cracks and reinforced using both GFRP and cement mortar. The bearing capacity and the failure modes were observed and studied. It was found that the composite reinforcement of GFRP and mortar could significantly increase the bearing capacity of the cracked round bamboos, and avoid brittle failure through improving the ductility of the specimens.

Design Methodology of Bamboo-Raft-Type Floating Structure (BRT-FS)

3D printed concrete walls reinforced with flexible FRP textile: Automatic construction, digital rebuilding, and seismic performance

As numerous impressive large-scale 3D printed concrete structures have been built with 3D concrete printing (3DCP) technology, more attention has been given to the automation, accuracy and reliability of this technology. The concept of Brain-Eyes-Hands Loop (BEH Loop) is defined for use in automatic construction, describing the relationships among design, evaluation, and construction. In this paper, an innovative continuous reinforcement method with fiber reinforced polymer (FRP) flexible textile and Engineered Cementitious Composite (ECC) is presented, that offers an effective solution for the lack of tensile reinforcement and corrosion of steel bars in 3D printed concrete structures. The reinforced 3D printed concrete walls were constructed, evaluated, and tested under quasi-static cyclic loading. By digital rebuilding and geometric evaluation, the printing quality of wall specimens was accessed and ensured. Based on the mechanical tests, the seismic performances of the wall specimens were obtained and found to be mainly bending failure. The proposed reinforcement method was demonstrated for delaying crushing and improving mechanical behaviors. The end column and smaller height-width ratio also showed much improvement in mechanical performance. Compared with the conventional cast concrete wall, the 3DCP wall specimens reinforced by the proposed reinforcement method showed better material utilization efficiency and mechanical properties. Therefore, the 3DCP structures reinforced with flexible FRP textile show great potential for the future use in fully automatic construction of large-scale complex architectures according to the frame of the BEH Loop.

An Exposure-Aware Self-Attention Method for Enhanced Self-Supervised All-Day Depth Estimation

Response of continuous cropping cowpea and root-zone soil to composite microbial agents: plant growth promotion and nitrogen-fixing bacterial community regulation

Continuous cropping obstacle of cowpea is an urgent problem to be solved for its sustainable production. A field experiment was performed from April to June 2024 to study the effects of four commercially microbial agents on the growth and yield of continuously cropping cowpea plants and nitrogen-fixing bacterial community structure in root-zone soil by high-throughput sequencing technology. Four commercially microbial agents used were BS (Bacillus subtilis), TH (Trichoderma harzianum), AB (Bacillus amyloliquefaciens, Brevibacillus laterosporus, Bacillus mucilaginosus and Enterobacter ludwigii), and CP (T. harzianum, B. amyloliquefaciens, Bacillus licheniformis and B. laterosporus). The results showed that four microbial agents enhanced soil organic matter, nitrate nitrogen and available potassium content in soil. The application of BS resulted in an increase in the relative abundance of Proteobacteria in root-zone soil of cowpea, while Actinobacteria and Firmicutes showed a downward trend compared to the control (CK). The treatments of BS, TH and AB significantly increased the relative abundance of Bradyrhizobium in soil by 109.4%, 38.5%, and 20.6% compared with CK, respectively. Furthermore, TH and CP increased the relative abundance of Halorhodospira in soil by 47.4% and 98.5%, respectively. The yield of cowpea plants increased by 9.6% with CP treatment compared to CK (P < 0.05). The BS treatment significantly promoted the main stem width of cowpea plants. The AB treatment enhanced protein, vitamin C and organic acid contents in cowpea plants. Overall, CP treatment is a better choice, as it has potential advantages over other agents in terms of cowpea growth and yield, and can improve the structure of the soil nitrogen-fixing bacterial community.

Behavior analysis of FRP tube/filling strengthened steel members under axial compression

This study presents a new fiber reinforced polymer tube/filling strengthening method (i.e., FRP tube/filling strengthening) that creates a new composite compression member with a novel mechanical behavior, “bilinear behavior.” Previous experimental and theoretical studies have been conducted based on the ultimate state of the section. To thoroughly study the stiffness and entire loading process of this novel member, finite element analysis (FEA) models are built in this paper. First, the model development process considers the initial defections and interface properties, and these models are verified by the experimental results. Two models of typical load-axial displacement curves describe the experimental results: a Bilinear model and a Trilinear model. Second, finite element modeling (FEM) is used to conduct a parametrical analysis that considers 7 parameters, and the results identify the mechanism of the strengthened member. Specifically, the Bilinear model corresponds to an unreinforced or relatively weakly reinforced specimen, and the Trilinear model corresponds to a relatively strongly reinforced specimen. If the exterior restraint system is weak, then the core steel buckles and subsequently yields; this behavior is described by the Bilinear model. If the exterior restraint system is strong (e.g., the length or the bending stiffness of the exterior restraint system is great), then the specimen can continue to bear a higher force after steel yielding until elastic-plastic buckling occurs; this behavior is described by the Trilinear model. Third, the FEA results and previous experimental and theoretical studies are used to obtain the stiffness and load-axial displacement curves, which are helpful for the design process. In general, relatively accurate FEA models are built in this paper that are capable of describing the mechanical behaviors of the novel member.

Behavior of pultruded I-section GFRP profiles under restrained torsion

This work focused on restrained torsion performance and calculation methods of pultruded GFRP I-section profiles. Material shear properties were tested by V-notched tests, showing significant material nonlinearity. Restrained torsion tests were conducted for six I-section profiles. Three I-section failure modes were found: local buckling failure caused by restrained normal stress at the end, shear failure of the flange-web junction at the midspan and compression failure at the end. Subsequently, finite element analysis was conducted. UMAT based on Puck model was utilized to consider the nonlinearity of shear properties, and simulations and experiments agreed well. Shear property nonlinearity had little influence on the I-section restrained torsion behavior. Vlasov theory was extended to orthotropic materials. The formula of local buckling caused by restrained normal stress was developed based on energy theory. Furthermore, calculation methods to predict restrained torsion failure were proposed and compared; the proposed methods were the most effective.

Developing an innovative curved-pultruded large-scale GFRP arch beam

An arch glass fiber reinforced polymer (GFRP) I-beam with a 600 mm height was developed based on the latest curved-pultrusion technique to overcome the most critical design issues of large-scale GFRP beams, including excessive deflections and premature buckling failures. To achieve this goal, a review was first conducted regarding the complex buckling behaviors of pultruded GFRP beams, building a theoretical basis for the development of the curved beam. Then, a series of three-point bending tests for beams were conducted at full scale, in which the typical failure modes, load-carrying capacities and deflection and strain data were obtained. Compression flange delamination was found to be the dominant failure mode. The load–strain curves for flange and web plates demonstrated that the proposed beams were exempt from local buckling issues. Additionally, an analytical study and finite element modeling were carried out. Excellent agreement between experimental, analytical and numerical studies was observed. The design approach for conventional straight profiles is readily applicable to curved beams as the difference is limited. In the end, a 20-m-long full-scale GFRP pedestrian bridge was designed, constructed and tested. The great potential of the proposed curved-pultruded GFRP arch beam was successfully demonstrated.

LONG-TERM DEFLECTION PREDICTION OF REINFORCED CONCRETE BEAMS

Three high-strength lightweight aggregate concrete beams were tested for long-term deflections.By comparison with the test results of 3 beams in this paper and 31 beams in other references,it is found that the design methods in corresponding standards and other existing models are not consistent with the test results.Based on equivalent bending moment method,section curvature induced by shrinkage and creep is analyzed.A simplified approach to evaluate creep and shrinkage effects in cracked concrete beams is presented,which considers creep and shrinkage deflections separately.With a clear physical concept and a simple formulation,the values obtained by the proposed method are found to be in good agreement with the test results and improvement is observed in comparison with the other existing methods.

Interfacial models for FRP profile-concrete bolt connection considering shear-bending effects

Axial Compressive Behavior of Square-Section Concrete Columns Transversely Reinforced with FRP Grids

Using grid-type stirrups as transverse reinforcements in reinforced concrete (RC) columns can not only provide higher confinement of the concrete core but also lead to an improved concrete cover and better protection to longitudinal reinforcements when compared with conventional stirrups. Fiber-reinforced polymer (FRP) grids, which combine the advantages of grid-type stirrups and FRP composites, are viable for use as transverse reinforcement in square-section RC columns in corrosive environments. However, there were few researches addressing RC columns reinforced with FRP grids. To investigate the axial compressive behavior of RC columns transversely reinforced with FRP grids, experimental investigations were conducted on 17 short square-section columns in small scale (180 × 180 × 600 mm3). Columns were transversely reinforced by CFRP/BFRP grids, weld reinforcement grids (WRG), and steel hoops. The results indicate that although FRP grids could provide less confining pressure than WRG, their performance is better than that of conventional hoops. Finally, an analytical model for predicting the stress–strain behavior of concrete core reinforced with grid-type stirrups is proposed considering the arching action of the confined concrete core. The proposed model shows a good agreement with the present test results as well as those from the existing literature.