A proposal to modify the moment coefficient in Eurocode 2 for predicting the residual strength of corroded reinforced concrete beams

Ultimate limit state (ULS) criteria are used to design reinforced concrete beams which give a ductile behaviour at failure. This means the resisting moment, M t , is less than the resisting moment in compression, M c . Since steel reinforcement is susceptible to corrosion, the ultimate capacity can be seriously affected as the degree of corrosion increases. The impact of corrosion to the main steel reinforcement on the flexural performance of reinforced concrete beams is investigated. Beams measuring 100 mm wide × 150 mm deep with differing levels of under-reinforcement (M t /M c ratios) were tested under four-point bending. Although the design code for reinforced concrete beam design has gone through various changes over the years, the fundamentals for design has broadly remained the same in that the beam is designed with an ultimate moment-coefficient (K=M/f c bd 2 ) with sufficient capacity to be able to easily carry the service loads it is exposed to. However, the long term influence of corrosion on the steel reinforcement is not considered at the design stage although a manufacturing factor of safety is applied. The analysis in this paper uses a modified-moment coefficient (K corr =M corr /f ck bd 2 ) based on EC 2 ultimate limit state design guidelines to predict the residual flexural strength of reinforced concrete beams suffering from main steel corrosion. Two grades of concrete (>C35/45 and C35/45. The analysis is then extended to include test data from other researchers to develop a similar simplified empirical analytical expression for beams with concrete grades <C35/45, thereby enabling a prediction of residual strength due to corrosion to be made for any beam size or concrete strength grade

Analysis of stray current induced by cathodic protection on steel-framed masonry structures

Cathodic protection (CP) has been successfully employed to protect steel-framed masonry buildings from corrosion related damage. When a CP system is installed to protect the structural members, other metallic items which are within the fabric of the structure but are not in direct electrical continuity may suffer from stray current interactions, resulting in accelerated corrosion of the discontinuous items. Therefore, these must be considered when CP systems are designed prior to installation. This paper presents both experimental and numerical studies into the risk and extent of stray current corrosion in steel-framed masonry structures when subject to impressed current cathodic protection. The objective is to allow CP systems to be optimised so that interference is minimised without compromising the technical or cost benefits of this method of corrosion control

Influence of constituents on the properties of self compacting repair materials

The paper presents the results of laboratory tests and field application in a highway bridge of self compacting repair materials. Three commercially available repair materials and one specially designed self compacting concrete were used in the study. The properties investigated were shrinkage, creep, elastic modulus and modulus of rupture. In addition, the field investigation determined flowing characteristics, compactibility and placing procedure of the flowing materials. The laboratory results show that the constituents of the mixtures greatly influence the basic properties of the materials. Inclusion of coarse aggregate in the mixture generally lowered the free shrinkage and modulus of rupture. Creep was highest in the material with polymer modification but creep recovery was lowest where large size aggregate was present. The elastic modulus was also influenced by the addition of coarse aggregate and copolymers The field results show that the materials can be placed and compacted satisfactorily without the aid of mechanical equipment

Thermal characterisation of Composite Insulation Panels using a vacuum insulated core

Composite Insulation Panels (CIPs) are used in building envelopes due to their thermal insulation properties, lightweight, aesthetics and ease of production and installation. In this paper, an advanced thermal insulation core material (vacuum insulation) with a thermal conductivity of 5-8 mWm-1K-1 has been investigated as core material for enhancing the thermal insulation performance of CIPs. Results revealed a significant reduction in heat loss and improvement in thermal performance of the vacuum insulation compared to that of the conventional extruded polystyrene (XPS) core material. It was determined that the CIP with a vacuum insulation core had a thermal transmission of 0.38 Wm-2K-1 compared to 0.78 Wm-2K-1 for XPS core of equivalent thickness at the centre of the panel. This represents a 51% reduction in heat loss through the vacuum insulated CIP

Efficacy of different materials and methods of repair in highway bridges

Repairs were carried out on three highway bridges using repair materials of higher elastic modulus than the substrate, Erm>Esub and materials with ErmEsub perform efficiently. Hand applied repairs act as cosmetic repairs with no significant load transfer. Application of repair to propped structures leads to unpredictable stress redistribution in the long-term

Long-term performance of high-stiffness repairs in highway structures

This paper presents the results of field monitoring of repair patches in two reinforced concrete highway bridges, Lawns Lane Bridge on the M1 and Gunthorpe Bridge across the River Trent. The repairs were applied by spraying (guniting) repair materials to compression members of the bridges. The structural members were unpropped during repair and throughout the 60 week monitoring period. The strains in the repair patches were monitored with vibrating-wire gauges. Four different repair materials were investigated whose elastic modulus was greater than that of the substrate concrete (E-rm > E-sub). The results show that efficient repairs are achieved with E-rm> E-sub, the optimum relationship being E-rm > 1.3E(sub). This enables the repair material to shed a significant proportion of its shrinkage strain to the substrate, thereby reducing restrained-shrinkage tension. It also enables the repair to attract externally applied load from the substrate in the long term. The effect of creep and shrinkage on the performance of the repair patch is also determined. Overall, the results show that current repair standards have limitations with respect to repair material specifications

Influence of acoustic membrane on sound and thermal properties of building façade panels

This paper compares the acoustic and thermal insulation performance of an extruded polystyrene (XPS) sandwich panel with either one or two additional layers of acoustic membrane of similar overall thickness of 28mm. Samples were prepared by bonding single and double layers of mass-loaded vinyl (MLV) membrane between extruded polystyrene (XPS) core and aluminium facings. Results show that the presence of a single MLV sound barrier layer resulted in a three dB improvement in weighted sound reduction index (Rw) over one-third octave band centre frequency of 100 Hz - 3150 Hz, Rw increasing from 35 dB to 38 dB. The addition of two layers led to an Rw increase of only a further dB to 39 dB. However, the weight of the panel increased from 9.4 kg/m2 to 13.8 kg/m2 for the single MLV layer and to 19.2 kg/m2 for the double MLV layer. The thermal transmission (U-value) with one layer of MLV membrane increased from 1.08 Wm-2K 1to 1.14 Wm-2K 1, an increase of 6% whereas a 12% increase in the U-value was found for the double MLV membrane (1.21 Wm-2K 1) as a result of reducing the thickness of the XPS to accommodate the MLV layers. The addition of MLV membranes, therefore, enhances the sound insulation performance but to the detriment of weight and thermal characteristics

Influence of shear reinforcement corrosion on the performance of under-reinforced concrete beams

The in-service performance of reinforced concrete beams can be severely affected through cor-rosion of the steel reinforcement when it becomes subjected to harsh corrosive environments containing chlo-rides and carbon dioxide. In such instances, corrosion is likely to occur in the steel reinforcement, with the expansive nature of the corrosion products likely to induce cracking and spalling of the concrete. A loss of structural integrity (stiffness) will occur and this can severely influence the serviceability of the member. The purpose of this paper is to investigate the relationship between degree of corrosion and loss of stiffness in corrosion damaged under-reinforced concrete beams. Beams (100mm x 150mm cross section) were subjected to accelerated corrosion in the laboratory and subsequently tested in flexure to failure. The paper reports on the results of these tests and relates the degree of corrosion in the main steel to the percentage loss in stiffness in the concrete beams

Factors affecting the efficiency of repair to propped and unpropped bridge beams

This paper presents the results of laboratory and field investigations of bridge beams repaired both under propped and unpropped conditions. In the laboratory beams were repaired using hand-applied repairs. Repairs to beams in two highway, bridges were carried out using both hand-applied and flowing repairs. The repair materials used were commercial products of wide-ranging properties (shrinkage, creep and elastic modulus). Both low stiffness repair materials of elastic modulus, E-rm, less than the substrate E-sub, and high stiffness repair materials (E-rm > E-sub) were used. The repairs were applied in the tensile zone of the beams. Strain distributions in the different phases of repair patches were monitored under service loading for a period of up to 240 weeks. The results show that high structural efficiency is achieved with repairs having E-rm > E-sub, other properties (shrinkage and creep) being within reasonable limits. Such repairs ave less plane to restrained shrinkage cracking and show a capacity for load redistribution into the repair patch. Low stiffness repairs (E-rm < E-sub), on the other hand, are prone to restrained shrinkage cracking and are ineffective in load-sharing with the substrate. Repairs to propped flexural members developed erratic and non-uniform load distribution in the different phases upon reapplication of load. Composite action between the repair patch and the substrate results in cracking in the repair patch, rendering the repairs structurally inefficient