Concrete is the most ubiquitous construction material. Apart from the fresh and early age properties of concrete material, its condition during the structure life span affects the overall structural performance. Therefore, development of techniques such as non-destructive testing which enable the investigation of the material condition, are in great demand. Tomography technique has become an increasingly popular non-destructive evaluation technique for civil engineers to assess the condition of concrete structures. In the present study, this technique is investigated by developing reconstruction procedures utilizing different parameters of elastic waves, namely the travel time, wave amplitude, wave frequency, and Q-value. In the development of algorithms, a ray tracing feature was adopted to take into account the actual non-linear propagation of elastic waves in concrete containing defects. Numerical simulation accompanied by experimental verifications of wave motion were conducted to obtain wave propagation profiles in concrete containing honeycomb as a defect and in assessing the tendon duct filling of pre-stressed concrete (PC) elements. The detection of defects by the developed tomography reconstruction procedures was evaluated and discussed.

With the growing trend in industry towards zero carbon construction, mass timber structures are becoming more accepted globally. Beam-to-column connections in mass timber buildings are currently designed to carry shear actions. However, the connections may be considered to take moment actions and large rotations to comply with ductility and robustness requirements of the building standards. The current study deploys finite element analysis (FEA) to investigate the failure due to large deformation and rotation of a typical bolted beam-to-column connection and provides an economic retrofitting design solution using self-tapping screws (STS). The FEA is validated against current or published experimental results and is used to conduct a thorough assessment of the retrofitted connection. It is shown that a proper arrangement of screws can delay the brittle failure, develop significant moment-resisting capacity, and enhance the rotational ductility of the connection.