CFRP-Steel hybrid retrofitting of steel-concrete composite structures

Carbon fiber reinforced polymer (CFRP) is found to be an effective material for the retrofitting of both reinforced concrete (RC) and steel structures. However, retrofitting such structures using CFRP alone is shown to exhibit a premature failure due to early de-bonding of the CFRP laminates from the hosting sur-faces. On the other hand, steel plates are also used separately for the steel and RC structures. However, steel plates usually add the self-weight to the structures whereas CFRP is known for its high strength to weight ra-tio. In the present study, the advantages of both steel plates and CFRP is used to form a hybrid retrofitting sys-tem that is able to withstand the existing load to prevent the failure of the structures. In order to improve the retrofitting efficiency of a steel-concrete composite structures, an experimental investigation is carried out to examine the use of effectiveness of CFRP-steel hybrid retrofitting system.

Interface slip control for CFRP-concrete composite beams

Carbon fibre reinforced polymer (CFRP) has been used frequently to retrofit concrete structures. Strengthening efficiency is related to the CFRP application process and the characteristics of the bonding agent. In this paper the mechanism of interface shear behaviour in CFRP to concrete beams is discussed considering previous test observations and mathematical models. This paper then discusses the consequences of introducing interface slip which reduces the integrity of the composite section, however improve ductility and delay debonding failure. The paper suggests that using softer bonding agent as well as setting limits on the interface slip could ensure acceptable serviceability and ductile behaviour.

Monitoring the corrosion of concrete reinforcement using control curves

Corrosion testing (half-cell and LPR) was carried out on a number reinforced concrete panels which had been taken from the fascia of a twenty five year old high rise building in Melbourne, Australia. Corrosion, predominantly as a result of carbonation of the concrete, was associated with a limited amount of cracking. A monitoring technique was established in which probe electrodes (reference and counter) were retro-fitted into the concrete. The probe electrode setup was identical for all panels tested. It was found that the corrosion behaviour of all panels tested closely fitted a family of results when the corrosion potential is plotted against the polarisation resistance (Rp). This enabled the development of a so-called 'control curve' relating the corrosion potential to the Rp for all of the panels under investigation. This relationship was also confirmed on laboratory samples, indicating that for a fixed geometry and experimental conditions a relationship between the potential and polarisation resistance of steel can be established for the steel-concrete system. Experimental results will be presented which indicate that for a given monitoring cell geometry, it may be possible to propose criteria for the point at which remediation measures should be considered. The establishment of such a control curve has enabled the development of a powerful monitoring tool for the assessment of a number of proposed corrosion remediation techniques. The actual effect of any corrosion remediation technique becomes clearly apparent via the type and magnitude of deviation of post remediation data from the original (preremediation) control curve.

Cost performance of multi-rise structures in Australia

The article discusses the findings of research on the cost performance of structural frames. The analysis conducted is based on a range of designs that are commonly found in 10-storey buildings in Australia. The study explored the best cost solutions for any particular project through generic cost models of steel, concrete, and formwork systems used in commercial buildings. The research concluded that the most important factor in choosing structural building frames would be the unique characteristics of individual projects.

Experimental study on strength and ductility of steel tubular stub columns filled with geopolymeric recycled concrete

Geopolymeric recycled concrete (GRC) is a new construction material which takes environmentalsustainability into account, by using alkali solution and fly ash to completely substitute Portland cementas well as by replacing natural coarse aggregate with recycled coarse aggregate. GRC could be used togetherwith steel hollow sections to form composite section. There is very limited study on such GRC filledtubular sections. This paper presents an experimental study on GRC filled tubular stub columns. A total of 12specimens were tested. The main parameters varied in the tests are: (1) two section sizes of square hollow sections(B × t) with 200mm×6mm and 150mm×5mm; (2) different concrete types: GRC and recycled aggregateconcrete (RAC); (3) different recycled aggregate (RA) replacement ratios of 0%, 50% and 100%. The relationshipof load versus axial strain was recorded and analysed to compare the ultimate strength and failuremechanism. Meanwhile, the ductility of the columns was investigated by a ductility index (DI). The resultsshow that the ultimate strength decreased with increasing RA contents for both GRC and RAC filled columns.The influence of RA content on the strength was greater in GRC than that in RAC. The effect of RA contenton the ductility of the columns was further investigated. Simulation method for predicting load versus strainrelationship is discussed for RAC and GRC filled steel tubular columns with different RA replacement ratios.

Embodied energy in buildings : wood versus concrete - reply to Börjesson and Gustavsson

We analyse the wood and concrete designs of the Wälludden building described by Börjesson et al. (Energy Policy 28 (2000) 575) in terms of their embodied energy, employing an environmentally extended input–output framework in a tiered hybrid life-cycle assessment, and in a structural path analysis. We illustrate the complexity of the inter-industry supply chains underlying the upstream energy requirements for the building options, and demonstrate that higher-order inputs are difficult to capture in a conventional process analysis. Our calculations show that Börjesson and Gustavsson's estimates of energy requirements and greenhouse gas emissions are underestimated by a factor of about 2, and that corresponding greenhouse gas balances are positive at about 30 t C-eq. Nevertheless, Börjesson and Gustavsson's general result—the concrete-framed building causing higher emissions—still holds.

Transient response analysis of steel in concrete

A new approach is presented for the analysis of galvanostatically induced transients allowing for the rapid evaluation of the corrosion activity of steel in concrete. This method of analysis is based on the iterative fitting of a non-exponential model based on a modified KWW (Kohlrausch–Williams–Watt) formalism. This analysis yields values for the parameters related to corrosion such as the concrete resistance, polarisation resistance, interfacial capacitance and β, the non-ideality exponent.

Concentration monitoring and performance of a migratory corrosion inhibitor in steel-reinforced concrete

Inhibitor concentration depth profiles for concrete samples treated with a proprietary migratory corrosion inhibitor (of the Cortec MCI range) are presented. The treated concrete was cored and these cores were then sectioned and crushed before being immersed in distilled water to extract the available inhibitor. The amine concentrations were quantified using an ammonium-sensing electrode and were then related to the inhibitor concentration present. The inhibitor examined, reported to contain a combination of volatile amines and amino carboxylate compounds, was found to readily diffuse through concrete. The inhibitor was subjected to a 5-year trial and found to be effective in suppressing corrosion of steel reinforcement in the presence of high chloride concentrations. The concentration profiles indicate that only relatively low concentrations of inhibitor were required to achieve inhibition in this case.

On the acoustic performance of a precast panel system made from environmentally sustainable concrete : application in sports hall buildings

The use of green building materials and products promotes conservation of non-renewable resources and help reduce associated environmental impacts. This article reports the acoustical performance of a precast panel system made largely from concrete waste material. Two major applications for such panels that are being investigated currently include walls and claddings to industrial and commercial buildings and sound barriers for urban freeways. In this study, the application of the concrete panels for optimizing reverberation time (RT) in sports halls is tested using numerical simulations. As an innovative approach, additional layers are added to the precast panels to improve their appearance. The absorption coefficients of the concrete panel improved significantly with the architectural finish. The material can be tuned according to the required peak frequency. The architectural finish helped reduce the RT for frequencies above 500 Hz. Its application to different types of ceilings revealed that the RT of curved ceiling reduced up to 40% compared to flat and hybrid ceiling. A comparison of wall and ceiling modifications in small, medium and large sports halls showed that medium-sized halls have better acoustical performance compared with small and large halls with ceiling as well as wall treatment.

Damage identification of slab–girder structures: experimental studies

Slab–girder structures composed of steel girder and reinforced concrete slab are widely used in buildings and bridges in the world. Their advantages are largely based on the composite action through the shear connection between slab and girder. In order to assess the integrity of this kind of structures, numerous vibration-based damage identification methods have been proposed. In this study, a scaled composite slab–girder model was constructed in the laboratory. Some removable shear connectors were specially designed and fabricated to connect the girder and slab that were cast separately. Then, a two-stage experiment including both static and vibration tests was performed. In the first stage, vibration tests were conducted under different damage scenarios, where a certain number of shear connectors at certain locations were removed step by step. In the second stage, two sets of hydraulic loading equipment were used to apply four-point static loads in the test. The loads are increased gradually until concrete slab cracked. The loading histories as well as deflections at different points of the beam are recorded. Vibration test was carried out before and after concrete cracking. Experimental results show that the changes of mode shapes and relative displacement between slab and girder may be two promising parameters for damage identification of slab–girder structures.