Experimental evaluation of changes in strain under compressive fatigue loading of brick masonry

© 2017 Elsevier Ltd Assessing the long-term performance of masonry structures and their response to increased loading conditions are critical to safety and maintenance. A series of laboratory tests have been carried out on brick masonry to assess its performance under long-term fatigue loading. The relationship between stress levels and number of cycles to failure was identified under compressive loading, together with stress-strain evolution at various stress levels. Strain evolution shows distinctive characteristics for the three stages of deterioration and increased strain for increased number of cycles. Experimental results provide useful data for developing analytical prediction models for the fatigue deterioration of masonry structures

Evaluation of the Loss of Uniaxial Compressive Strength of Sandstones Due to Moisture

The reduction in uniaxial compressive strength (UCS) was investigated for sandstones under various moisture levels. Thirty-four UK Darney sandstone samples were tested under six different moisture conditions. The time-dependent moisture gain and loss were also evaluated. For 77 sandstones identified in the literature, the loss of UCS between oven-dry and saturated conditions was up to 45%, with an average of 20%. For Darney stone, the average loss of UCS was around 20%, with UCS around 72 N/mm2 when oven-dry and 58 N/mm2 when fully saturated. During saturation, significant loss of UCS occurred soon after exposure to water with 80% of UCS being lost within the first 2.5–6 hours. For Darney stone 50% of UCS was lost at air-dry conditions. Results from the 78 sandstone types were compared with the equivalent compressive strength defined by BS EN 772–1:2011 for oven-dry, air-dry, and saturated conditions. The estimated values by BS EN 772–1:2011 for dry and saturated UCS agreed well with the available test data and indicated a lower-bound solution. For immersed conditions, BS EN 772–1:2011, however, overestimates the reduction in UCS for a large number of samples and provides an average, instead of a lower-bound solution

Strain evolution of brick masonry under cyclic compressive loading

Long-term fatigue tests in compression were performed on low-strength brick masonry prisms under laboratory conditions at different maximum stress levels. The maximum and minimum total longitudinal deformations with the loading cycles were recorded. The experimental results revealed that fatigue life is divided into three distinct stages. The recordings were further analysed to develop an analytical expression for the prediction of the development of strain during the fatigue life of masonry. A set of three mathematical equations were proposed to predict the three characteristic stages of fatigue. The developed expressions, related the normalised total longitudinal strain with the normalised maximum applied stress. The proposed model provides good agreement with the mean available data at any maximum stress level and could be used to to evaluate the remaining service life, plan maintenance works minimising life-cycle costs and prevent premature failures Continuity of the curves at the intersection points in terms of slope and numerical values ensures accuracy of the method and results to a differentiable function

Sustainability of bridge maintenance

Bridge maintenance activities are important to consider within sustainable development due to the cost and environmental impact associated with various maintenance activities. Comparisons have been made between different bridge structural forms, based on materials, components and construction method, but less information is available on bridge maintenance activities to help decide a sustainable structural form. Typical maintenance aspects of the predominant forms of bridge structure (i.e. concrete, steel and masonry bridges) were considered in this study to reveal their sustainability in terms of materials, energy, transportation, human health and ecosystems. The results indicate that concrete and steel bridge maintenance activities have an average impact of 42% and 46% compared with 12% for masonry bridge maintenance activities. It is concluded that the component parts of concrete and steel bridges should be revised as they play an integral role in the selection of maintenance options

Acoustic emission monitoring of masonry arch bridges

Acoustic emission (AE) monitoring has the unique ability to record crack propagation inside the material and indicate the condition of the structure. Although AE has been widely used for concrete and steel bridges , its use for masonry structures is currently very limited. Application of AE to masonry arch bridges has been investigated through a series of laboratory and field studies and has been found to provide useful information on the condition of masonry structures, their response to traffic loading and the efficacy of strengthening works

Long-term cyclic load capacity and residual life of masonry arch bridges

How long can existing masonry arch bridges continue to carry heavily increased traffic loading? Is there a weight limit for masonry bridges below which no long-term damage will occur to the structure? Can the life expectancy for masonry arch bridges be estimated? The present report attempts to explore some of these questions and suggest a framework to incorporate long-term life-cycle assessment into the thinking process. While the fatigue behaviour of metals and metallic structures has been widely studied, little information exists on the fatigue behaviour of masonry structures. There are no specific guidelines available to assess the fatigue limit and residual life expectancy of masonry arch bridges.Similarly to any material, masonry also deteriorates under long-term fatigue loading. The majority of masonry arch bridges were built over 100 years ago and carry far greater traffic loading than they were originally designed for. Although masonry bridges do not generally collapse or suffer visible fatigue damage, they may suffer localised deterioration under long-term service loading. Even if the ultimate capacity is not reached, localised deterioration can lead to changes in the load path and to accelerated deterioration of the overall structure. Failure under long-term cyclic loading can be different from the failure mode associated with quasi-static loading. While four-hinge mechanism is the typical failure mode under quasi-static loading, multi-ring arches are more likely to fail by ring separation under cyclic loading. Although available test data is insufficient to quantify the long-term cyclic capacity of the wide range of masonry arch bridges, the report seeks to raise awareness of potential issues associated with long-term cyclic loading and provide a methodology for identifying the remaining service life and residual capacity for masonry arch bridges. Assessing the impact of long-term cyclic loading on masonry arch bridges seeks to identify-safe long-term loading limits -expected service life -likely forms of deterioration over time-future strengthening needs

Condition monitoring of masonry arch bridges using acoustic emission techniques

40% of European railway bridges are masonry, 60% of which are over 100 years old and are still carrying traffic loading. The weight and density of traffic has increased substantially over the last century and bridge owners have the continuous responsibility to ensure safe working condition of their bridges. The condition assessment of masonry bridges generally relies on visual observation and there are limited number of techniques that provide insight into the actual condition of the masonry structure. There is an increasing need for techniques to help determine the bridge condition and predict their life expectancy. The acoustic emission technique has been applied to a series of masonry arch bridges in laboratory and in field to investigate its applicability for routine bridge assessment. The technique has shown to be able to identify damaged regions in the arch barrel, detect crack propagation and warn of residual damage occurring to the arch. It is also able, for the first time, to record the period of damage propagation which can allow sufficient time to remove critical loading and avoid crucial damage. The acoustic emission technique is simple and easy to use and has shown great potentials for assessment and monitoring of masonry arch bridges in the traffic network