Strengthening of concrete, metallic and timber construction materials with FRP composites

KeynoteThis paper provides a review of research being conducted at The University of Hong Kong (HKU) on the strengthening of concrete, metallic and timber construction materials with externally bonded fibre-reinforced polymer (FRP) composites. The motivation of such research is to enhance our understanding of the interfacial behaviour between the FRP and the three different substrate materials via FRP-to-concrete, -metal, and-timber joint tests. Of the three substrate materials, concrete has clearly experienced the most research activity to date by the wider research community, followed by that of metal and then that of timber. In order to progress the extensive knowledge base of FRP-to-concrete behaviour, research at HKU is aimed at enhancing the bond strength of the FRP via the addition of anchorage. The anchor of choice is the so called FRP anchor and its effectiveness in anchoring FRP flexural strengthening applied to reinforced concrete (RC) slabs is also presented. For the metal and timber substrate materials, HKU research is more focused at this stage on understanding the influence of key fundamental variables affecting interfacial behaviour such as FRP geometry, surface preparation and substrate material characteristics.postprintThe 5th International Conference on FRP Composites in Civil Engineering (CICE 2010), Beijing, China, 27-29 September 2010. In Proceedings of the 5th CICE, 2010, p. 13-1

FRP anchors: recent advances in research and understanding

The effectiveness of strengthening reinforced concrete (RC) members with externally bonded fibre-reinforced polymer (FRP) composites may be compromised by premature debonding failure of the FRP prior to its ultimate strength being reached. An anchorage system which can delay or even eliminate debonding failure is therefore of most importance in order to improve the efficiency, reliability and safety of FRP strengthening. Anchors made from FRP (known as FRP anchors) are an attractive form of anchorage as they are non-corrosive and can be applied to a wide variety of structural elements. Surprisingly, little research has been undertaken on the characterisation of such anchors though and it is this limitation in knowledge which is prohibiting their rational design and wide-scale use. This paper in turn presents recent advances in research and understanding of the strength and behaviour of FRP anchors. In addition, future research needs are also identified.published_or_final_versionThe 2nd Official International Conference of International Institute for FRP in Construction for Asia-Pacific Region (APFIS 2009), Seoul, Korea, 9-11 December 2009. In Proceedings of the 2nd APFIS, 2009, p. 35-4

Transformation Optics with Photonic Band Gap Media

We introduce a class of optical media based on adiabatically modulated, dielectric-only, and potentially extremely low-loss, photonic crystals. The media we describe represent a generalization of the eikonal limit of transformation optics (TO). The foundation of the concept is the possibility to fit frequency isosurfaces in the k-space of photonic crystals with elliptic surfaces, allowing them to mimic the dispersion relation of light in anisotropic effective media. Photonic crystal cloaks and other TO devices operating at visible wavelengths can be constructed from optically transparent substances like glasses, whose attenuation coefficient can be as small as 10 dB/km, suggesting the TO design methodology can be applied to the development of optical devices not limited by the losses inherent to metal-based, passive metamaterials.Comment: 4 pages, 4 figure

Strengthening of RC slabs with large penetrations using anchored FRP composites

Large penetrations are routinely made in existing reinforced concrete (RC) slabs due to structural and/or functional changes. Externally bonded fibre-reinforced polymer (FRP) composites can in turn be bonded to the tension face of the slab in the immediate vicinity of the penetration in order to restore the strength of the slab due to the lost internal steel reinforcement. In order to prevent premature debonding failure of the FRP strengthening, anchors can be applied. The results of tests on the strength and behaviour of one-way spanning RC slabs with large central penetrations which have been strengthened with unanchored and anchored FRP composites are presented in this paper. The FRP strengthening was found to be effective in strengthening penetrated slabs and the anchors were found to be effective in controlling the propagation of debonding cracks.published_or_final_versionThe 2nd Official International Conference of International Institute for FRP in Construction for Asia-Pacific Region (APFIS 2009), Seoul, Korea, 9-11 December 2009. In Proceedings of the 2nd APFIS, 2009, p. 111-11

Concerns with AED conversion: comparison of patient and physician perspectives.

When discussing AED conversion in the clinic, both the patient and physician perspectives on the goals and risks of this change are important to consider. To identify patient-reported and clinician-perceived concerns, a panel of epilepsy specialists was questioned about the topics discussed with patients and the clinician's perspective of patient concerns. Findings of a literature review of articles that report patient-expressed concerns regarding their epilepsy and treatment were also reviewed. Results showed that the specialist panel appropriately identified patient-reported concerns of driving ability, medication cost, seizure control, and medication side effects. Additionally, patient-reported concerns of independence, employment issues, social stigma, medication dependence, and undesirable cognitive effects are important to address when considering and initiating AED conversion

High-resolution X-ray spectroscopy reveals the special nature of Wolf-Rayet star winds

We present the first high-resolution X-ray spectrum of a putatively single Wolf-Rayet star. 400 ks observations of WR 6 by the XMM-Newton-telescope resulted in a superb quality high-resolution X-ray spectrum. Spectral analysis reveals that the X-rays originate far out in the stellar wind, more than 30 stellar radii from the photosphere, and thus outside the wind acceleration zone where the line-driving instability could create shocks. The X-ray emitting plasma reaches temperatures up to 50\,MK, and is embedded within the un-shocked, "cool" stellar wind as revealed by characteristic spectral signatures. We detect a fluorescent Fe line at approx 6.4 keV. The presence of fluorescence is consistent with a two-component medium, where the cool wind is permeated with the hot X-ray emitting plasma. The wind must have a very porous structure to allow the observed amount of X-rays to escape. We find that neither the line-driving instability nor any alternative binary scenario can explain the data. We suggest a scenario where X-rays are produced when the fast wind rams into slow "sticky clumps" that resist acceleration. Our new data show that the X-rays in single WR-star are generated by some special mechanism different from the one operating in the O-star winds.Comment: ApJL, Figure 3 is update

Ultimate strength equation for pultruded CFRP plates in fire

The paper presents a model for the ultimate strength calculation of fibre-reinforced polymer (FRP) pultruded plates in fire. The model is calibrated from a series of coupon tests on pultruded CFRP plates carried out using steady state and transient state test methods. In the steady state tests, temperatures ranging from ambient to approximately 700℃ were considered. The test specimens were heated to a specified temperature then loaded until failure while the same temperature was maintained throughout the test. Different periods of times of 5 and 30 minutes were maintained to investigate the effect of heating duration. In the transient state tests, the test specimens were loaded to a specified stress level prior to heating, and then the temperature was increased until failure of the test specimens. Three different stress levels applied to the pultruded CFRP plates were considered. Based on the test results, an ultimate strength equation is proposed which has been inspired from a model developed for metallic materials subjected to elevated temperatures. Application of the model is finally demonstrated in a worked example.postprin

Effect of surface preparation on the strength of FRP-to-mild steel and FRP-to-stainless steel joints

A detailed understanding of the strength and behaviour of the bond between fibre-reinforced polymer (FRP) composites to metals is an ongoing field of research. The many different geometrical and ma-terial parameters make for extensive research demands. This paper in turn reports a series of tests on the shear strength and behaviour of FRP-to metal joints in which the main test parameters, which have received limited attention to date, consists of (i) type of metal (i.e. non-galvanised mild steel and stainless steel), and (ii) sur-face preparation technique (i.e. different mechanical abrasion methods). All specimens are loaded in dis-placement control which enables the failure process to be followed and identification of different failure modes to be made. The results enable the effectiveness of different surface preparation techniques upon the bond of FRP to different types of metals to be made.postprintThe 5th International Conference on FRP Composites in Civil Engineering (CICE 2010), Beijing, China, 27-29 September 2010. In proceedings of the 5th CICE, 2010, p. 869-87

Mechanical behaviour of sustainable concrete with waste ceramic aggregate replacement

Sustainability and material use have been becoming increasingly important in industry and academia in recent years, prompting investigations for ways to improve sustainability in construction materials. Past studies have investigated natural aggregate replacement in concrete with a variety of materials, including recycled concrete, glass, bricks, ceramics, and even automobile tires. These studies have produced varied results. Ceramic materials are a great prospective material for aggregate replacement due to their desirable mechanical properties and availability in waste streams worldwide. This study focusses on coarse aggregate replacement with ceramic tile materials of virgin and waste origins, reaching as high as 100% replacement. To limit the variability experienced in previous studies, great emphasis was placed on limiting parameters tested between series to the physical properties of the replacement ceramic materials alone. Test results thus far have shown that natural coarse aggregate can be replaced in ratios as high as 100%, with only minimal effects on the mechanical properties of the resulting concrete. Compressive, tensile, and flexural strengths have shown minor change, with only a slight increase in elastic modulus. This study shows that ceramic waste material has great potential for use in concrete when a suitable preparation method is used.published_or_final_versio