Strength assessment of old masonry arch bridges through moderate destructive testing methods

Abstract

This paper aims to assess the strength of a 100 + year old masonry arch bridges in Australia that are currently in operation and routinely subjected to train loadings. Towards this end, 45 cores of 150 mm diameter with varied lengths and joint configurations were drilled from a typical bridge and tested. Out of these samples, 30 were tested under direct compression and 15 were tested for tensile strength with varying bed joint angles. The samples for compression testing were regularised by developing high strength mortar capping whereas, the samples for tensile strength were tested according to Brazilian testing method commonly used for evaluating the splitting tensile strength of materials. The typical failure mode of masonry under compression was due to vertical cracking in bricks, spalling and cracking in perpend joints. The average compressive strength of masonry was determined as 10.6 MPa. Young’s modulus was also determined with a magnitude of 11,048 MPa which is comparable to an in-situ flat jack test conducted on the similar bridges. The increased number of perpend joints in masonry cores decreased the masonry compressive strength. Splitting tests revealed the average tensile strength of 1.34 MPa. From the results it can be concluded that the aged masonry used in the arch bridge has a higher strength than previously thought of and that the bridge seems to be capable of sustaining the current train loads, as observed at site.