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

DEVELOPMENT OF A TIME-DEPENDENT STRUCTURAL RELIABILITY MODEL FOR CIVIL ENGINEERING STRUCTURES

The purpose of this paper is to outline the start of the development of a time-dependent Dynamic Structural Reliability Model for civil engineering structures. The issue of the existing extent of information for the different elements of the model is addressed together with the research required to assure a uniform reliability level for structures. A uniform reliability level provides an ethical sound method of assessment of the relative safety of the structure. Structural reliability analysis is a long-term research problem that has been aided by the development of sensitive accelerometers, capable to recording thermal vibration of structures. Changes in the natural vibration frequencies over time can be used to identify changes in the structural reliability over time based on real-time behaviour

STRUCTURAL RELIABILITY ANALYSIS FOR MASONRY BUILDINGS

The purpose of this paper is to outline the start of the development of a Dynamic Structural Reliability Model for masonry structures, although the system can be applied to a wide range of structural systems. The paper addresses the issue of the existing extent of information for the different elements of the model and considers the development of the research required to assure a uniform reliability level for each structure. A uniform reliability level provides an ethical sound method of assessment of the relative safety of the structure. Italy has been used in this paper as the loading example, which is required for all Structural Reliability Models. Italy has a long-recorded written history, which details the history of Italian earthquakes, stretching back millennia. In the central regions of Italy, such as the L’Aquila area, earthquakes are common when compared to other long settled locations, say London. Three earthquakes in the last century, in this Abruzzo Region, resulted in a significant loss of life and economic losses in terms of infrastructure. Aside from the common feature of relatively high death tolls for these earthquakes, the region has a high percentage of two storey masonry dwellings, which impact the fatality rates, due to the high collapse rates of these buildings. Masonry dwellings are dangerous in earthquakes due to the brittle nature of the walls and the connection between the walls and floor or roof. Structural reliability analysis of these masonry structures is a long-term research problem that has been aided by the development of sensitive MEMS based accelerometers, such as the Sensr CX1. A simple standard portal frame example is used to illustrate the procedure

Structural reliability for two storey Italian masonry building

Two storey masonry dwellings are a common feature of the countryside in the northern regions of Italy, they are often clumped in small groups on the hillsides, with market type gardens surrounding. This structural type represents one of the most significant contributors to deaths in earthquakes in Italy and has done so for a long time. Benedetti and Pezzoli [1] completed a series of shaking table tests on model two storey dwellings using the common characteristics of the northern Italian region. Limited work has been completed on Structural Reliability measures for masonry, with Stewart and Lawrence providing the clear starting point for walls [2]. A Structural Reliability model will be established for the key structural elements and connections for the sample two storey masonry dwellings tested by Benedetti and Pezzoli. The key objective of this paper is to determine the existing extent information for the different elements of the model and to determine the research required to provide a reasonably uniform reliability level for this type of structure. A uniform reliability level is a cornerstone of the method outlined by Melchers [3]