Publications

Composite Actions of Steel-Fibre Reinforced Polymer Composite Beams

No abstract is provided for this article.

Effects of the corrosion of main bar and stirrups on the bond behavior of reinforcing steel bar

Pull-out tests have been carried out to study the combined effects of corrosion of main bar and stirrups on the bond behavior. The main experimental variables included concrete cover thickness, stirrup spacing, and corrosion levels of main bar and stirrups. It was found that the corrosion of stirrups could lead to serious cover cracking and the way of stirrup corrosion influencing the cover cracking patterns was affected by the stirrup spacing. Moreover, the test results showed that the propagation of transverse cracks was similar to that of longitudinal cracks. In comparison to the case that merely main bar was corroded, the coupled corrosion of main bar and stirrups exacerbated bond deterioration. It was also found that the frictional bond stress was negatively affected by the corrosion of stirrups. Based on the experimental results and previous studies, a bond stress-slip model for RC with corroded main bar and corroded stirrups was for the first time proposed. The effectiveness of the proposed bond-slip model was finally validated by FE modelling.

Strengthening of steel members in compression by mortar-filled FRP tubes

A strengthening approach to improve the buckling resistance of steel members in compression is introduced in this paper, where a mortar-filled FRP tube is sleeved outside the steel member and wrapped with FRP fabrics at the ends of the tube. Through axial compression tests on 18 specimens with bi-axial symmetrical cross-section, the load–strain development and failure modes were obtained and improved load bearing capacity and ductility were evidenced. The effects of the cross-section of core steel, slenderness and FRP fabric layers wrapped at the ends of specimens were investigated. It was found that, after strengthening, the failure modes changed from steel yielding at the mid-height of the steel member due to global buckling to local damage at the steel end. As a result, the load bearing capacity increased by 44–215% and ductility increased by up to 877%. The segmentation model was developed for strengthened specimens, by which the calculated load bearing capacity agrees well with the experimental result.

A high efficiency charge pump circuit for low power applications

No abstract is provided for this article.

FRP-confined concrete core-encased rebar for RC columns: Concept and axial compressive behavior

In the ultimate failure mode of columns in RC structures under seismic load, the longitudinal reinforcement generally suffers from severe buckling due to the axial compressive load, spalling of concrete cover and dilation of concrete core. Proper configuration of RC columns to postpone or prevent the buckling phenomenon can enhance the seismic performance and make full use of the strength of steel reinforcement. In this paper, a new concept and configuration of FRP-confined concrete core-encased rebar (FCCC-R) for RC columns is proposed. The concrete surrounded the longitudinal rebar is confined by an FRP tube, which can prevent the rebar from premature buckling. The axial compressive behavior of the hybrid bar considering different parameters, including the slenderness ratio, FRP tube diameter, mortar strength, and bar position was studied experimentally. Furthermore, finite element (FE) simulation was carried out and calibrated by test results. Based on the FE model, additional discussion and a parametric study was performed. Finally, the minimum FRP tube diameter required for the FCCC-R considering the compressive behavior enhancement effect was calculated, and design curves for 3 types of steel bars with nominal yield strengths of 400 MPa, 800 MPa, and 1100 MPa were proposed.

Experimental Study of FRP-Reinforced Slotted RC Shear Walls under Cyclic Loading

The seismic performance of slotted reinforced concrete walls strengthened with fiber-reinforced polymer (FRP) was investigated. This reinforcement method aims to increase the ultimate deformation capacity and avoid compressive damage to the concrete. To compare the performance of the slotted RC walls with and without FRP reinforcement, pseudostatic tests were conducted on two conventional slotted RC walls and two FRP-reinforced slotted RC walls. The slotted RC walls reinforced with FRP exhibited significantly improved deformation capacity and were able to sustain a 1∶30 drift ratio without obvious damage, while the ultimate deformation of the slotted RC wall without FRP reinforcement could only sustain a drift ratio of about 1∶50. Furthermore, a partial FRP retrofitting method can fully recover the load-bearing capacity of the wall. The results confirm the effectiveness of FRP reinforcement in a slotted RC wall. However, the initial stiffness and energy dissipation capacity were not regained completely through the FRP reinforcement.

春栽果树保成活 严用“三水”是关键

No abstract is provided for this article.

Noise Rejection Using Variable-Height Timing-Window Technique for Pulse Signals With Variable S/N Ratio

This paper proposes a novel technique, known as the variable-height timing window (TW), for rejecting noise in an active source detection system. The basic principle of a TW and a methodology of using a microprocessor to dynamically adjust the height of the TW are presented. This variable-height TW technique has been applied to a laser-based detection system (LBDS) for detecting vehicle information on highways. Field-test results of the LBDS showed that the adaptive nature of the proposed TW approach can effectively reject various types of noise under different environmental conditions. This variable-height TW technique can also be used to remove out-of-window noise and suppress the effect of in-window noise in various field environments in which the signal/noise (S/N) ratio is variable.

Long-term behavior of CFRP plates under sustained loads

This paper studies the long-term behavior of carbon fiber–reinforced polymer (CFRP) plates under sustained loads. Two typical loading conditions, CFRP plate loading controlled by displacement constraints and force constraints, are studied. The first section investigates the prestress loss of the CFRP plate when it is loaded via displacement constraints, which serves as a prestressed system applied for prestressed structures. Short- and long-term measurements show that the prestress loss of CFRP is caused by material creep, temperature change, and CFRP and anchorage slippage. When the CFRP prestress level is 5.0%–12.3%, the average prestress loss after 42 days is 5.1%. The second section investigates the permanent deformation of the CFRP plate with curved anchorages caused by creep under a certain sustained load (i.e., controlled by force constraints), which serves as a suspension bar or cable applied for determinate structures. The creep strain-to-time relationship, creep rate, and residual strength were obtained. The creep strain-to-time relationship strongly depends on the stress level applied; the creep coefficient is less than 10.94% and the residual strength is greater than 80% of the initial tensile strength after 1000 h. The findings show the effectiveness and reliability of these two typical cases of CFRP plates under long-term sustained loads.

Mechanical and Durability Properties of Coral Aggregate Concrete

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Shear-dilation model for the sand-coated FRP-UHPC interface under lateral confinement

Accounting and Recommended Values for Carbon Emission Factors of Structural Steel

A Large-Span Woven Web Suspension Roof System Made of High-Strength FRP

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.

Characterizing pseudo-ductile behavior of pultruded and pullwound GFRP composites: Box-section short columns subjected to axial compression

GFRP composites are known to suffer from the “sudden-brittle failure”, while this work demonstrates a different behavior, namely pseudo-ductile behavior. A total of 28 pultruded and pullwound GFRP composite short columns having two heights were tested in axial compression. Stable pseudo-ductile behavior was observed in all tests, and it was realized by the progressive failure of GFRP composites. The residual strength of GFRP columns could be maintained at a high stress level, ranging from 50 % to 83 %. In order to quantify the pseudo-ductile behavior, FE model was developed within Abaqus, and a VUMAT subroutine incorporated with 3D Hashin damage criterion was used to predict the progressive failure of materials. Developed FE model was able to satisfactorily simulate the entire progressive failure process of pultruded and pullwound GFRP short columns. As a result, predicted peak strengths showed excellent agreement with experimental results, with average strength ratio of 1.00 (COV = 0.04), and the predicted residual strengths at the deformations of interest were generally conservative, with average strength ratio of 0.85 (COV = 0.24). The experimental and numerical results obtained in this work successfully show that pultruded and pullwound GFRP short columns could exhibit stable progressive failure at a high stress level. The finding is aimed to shed light on the future acknowledgement of the pseudo-ductile behavior as well as to promote the performance-based design of GFRP composite structures.

Determining rotational stiffness of flange-web junction of pultruded GFRP I-sections

In this work, the rotational stiffness of flange-web junctions of pultruded GFRP I-sections is investigated through an experimental program. Flange-web junctions of GFRP profiles are found to be non-rigid, contradicting typical design assumptions. Accounting for flange-web rotational stiffness reduces the rotational restraint of the flange/web junction; often by 15% or more, although more modest reductions were observed in this study. A discussion of different test methods for assessing flange/web junction stiffness is provided. A simple method that mitigates unfavorable effects is recommended. The effectiveness of the selected test method is demonstrated through 25 experimental tests which also serve to augment the limited data available in this area. Finite element modeling is conducted to simulate the experimental test and investigate parameters impacting the experimentally-determined rotational stiffness. Recommendations are made to standardize test parameters. Findings from this study directly support the developments of evaluation criterion for flange-web junctions and design equations; particularly those intended to capture the local buckling behavior of pultruded GFRP beams.

Moisture diffusion in multi-layered materials: The role of layer stacking and composition

Multi-layered materials are everywhere, from fiber-reinforced polymer composites (FRPCs) to plywood sheets to layered rocks. When in service, these materials are often exposed to long-term environmental factors, like moisture, temperature, salinity, etc. Moisture, in particular, is known to cause significant degradation of materials like polymers, often resulting in loss of material durability. Hence, it is critical to determine the total diffusion coefficient of multi-layered materials given the coefficients of individual layers. However, the relationship between a multi-layered material’s total diffusion coefficient and the individual layers’ diffusion coefficients is not well established. Existing parallel and series models to determine the total diffusion coefficient do not account for the order of layer stacking. In this paper, we introduce three parameters influencing the diffusion behavior of multi-layered materials: the ratio of diffusion coefficients of individual layers, the volume fraction of individual layers, and the stacking order of individual layers. Computational models are developed within a finite element method framework to conduct parametric analysis considering the proposed parameters. We propose a new model to calculate the total diffusion coefficient of multi-layered materials more accurately than current models. We verify this parametric study by performing moisture immersion experiments on multi-layered materials. Finally, we propose a methodology for designing and optimizing the cross-section of multi-layered materials considering long-term moisture resistance. This study gives new insights into the diffusion behavior of multi-layered materials, focusing on polymer composites.

The mechanical and hydrochemical properties of cemented calcareous soil under long-term soaking

This study investigates the impact of long-term water immersion on the mechanical and hydrochemical properties of cemented calcareous soil, emphasizing the critical role of carbonate content in mechanical performance. Utilizing hydrochemical analysis and triaxial testing, the research revealed that prolonged immersion disrupts the acid-base balance of the solution, resulting in an increased concentration of ions and chemicals. Significant dissolution of carbonates and soluble minerals occurs, which reacts with carbon dioxide to generate bicarbonate ions, thereby elevating the alkalinity of the soaking solution. Additionally, the gradual dissolution of clay minerals compromises the cementitious structure, leading to particle reorientation and interlocking. The study quantitatively assesses the changes in soil properties, demonstrating a substantial reduction in soil cohesion by up to 86.1% and an increase in the internal friction angle by 37.5%. Furthermore, the gradual dissolution of clay minerals compromises the cementitious structure, resulting in particle reorientation and interlocking that contribute to the observed mechanical changes. The findings underscore the importance of understanding the effects of extended immersion on the stability and engineering applicability of cemented calcareous soils.

Development of mechanical properties of concrete in vacuum tunnel of vacuum-based maglev train

The vacuum-based maglev train is an emerging transportation system currently under development worldwide. While concrete is a technically viable material for constructing vacuum tunnels, its mechanical performance in this unique environment remains unclear. This paper investigates the behavior of concrete in vacuum using a large customized vacuum tube. The results show that concrete undergoes significant water loss in vacuum, resulting in impeded cement hydration and porous hydration products with a foam structure. Vacuum exposure during the early ages of concrete has negative effects on mechanical properties. However, once the cement hydration reaches a high level of maturity, further vacuum exposure has little influence. Compared with atmospheric conditions, the shrinkage of concrete in vacuum is significantly increased. These findings provide a valuable experimental database and new insights for the use of concrete in vacuum-based maglev trains.