1 ASSESSING STEEL STRAINS ON REINFORCED CONCRETE MEMBERS FROM SURFACE 1 CRACKING PATTERNS 2 R.N.F. Carmo *1,2 , J. Valença 2 , D. Silva 1 , D. Dias-da-Costa 3 3 * corresponding author (Email: carmo@isec.pt) 4 1 Polytechnic Institute of Coimbra, Rua Pedro Nunes – Quinta da Nora, 3030-199 Coimbra, Portugal. 5 2 CEris, ICIST, Av. Rovisco Pais, 1049-001 Lisboa, Portugal. 6 3 School of Civil Engineering, The University of Sydney, Sydney, NSW 2006, Australia. 7 Abstract 8 The measurement of steel strains in reinforced concrete structures is often critical to characterise stresses and 9 forces along the member. In this scope, this manuscript describes the development of a method to assess steel 10 strains inside concrete members using solely surface measurements. These measurements were obtained 11 using photogrammetry and image processing. The technique was validated using two concrete ties monitored 12 using strain gauges placed inside the steel bars. The experimental results showed that one of the most 13 important parameters affecting the accuracy of the technique is the measurement of crack widths, whereas 14 the concrete strain has little effect on the final results. The technique is particularly advantageous since it is 15 non-contact and does not impact on the bond conditions. It also does not require accessing the 16 reinforcements. As a main conclusion, this work showed the feasibility of estimating strains inside the 17 structure. This will benefit in the near future from further improvements namely in what concerns camera 18 resolutions. 19 Keywords: strains; monitoring; strain gauges; crack pattern; reinforced concrete; photogrammetry; image 20 processing. 21 1. Introduction 22 Monitoring reinforced concrete (RC) structures is an important issue not only for assessing existing 23 structures, but also to characterise the behaviour of new structures. In what regards experimental 24