The issue of upgrading existing structures is of great importance due to their deterioration (ageing, environmental induced degradation, lack of maintenance, need to meet the current design requirements). Recently, an innovative structural material, the so-called Textile-Reinforced Mortar (TRM), was successfully developed for structural retrofitting of deficient masonry and concrete structures. TRM is an advanced sustainable material which offers well-established advantages (good behaviour at high temperature, compatibility to concrete or masonry substrates material high strength to weight ratio, corrosion resistance, ease and speed of application, minimal change of cross section dimensions) at a low-cost. Over the last decade it has been reported in the literature that TRM is a very promising alternative to the FRP (Fibre Reinforced Polymers) retrofitting solution.
A few researchers have studied the use of TRM on shear strengthening of reinforced concrete beams concluding that TRM is a very promising alternative to the FRP retrofitting solution. However, development of reliable and accurate design models for shear strengthening of RC members with TRM is required for enabling their wide use in real applications. The available experimental data in the literature are limited and in most cases, a detailed description of the failure modes observed at the TRM jackets and information related with the characteristics of the textile material and the mortar strength are missing, complicating the development of design models. In this project, all the well reported available data on shear strengthening of reinforced concrete beams with TRM are used for developing design models to calculate the contribution of the TRM jacket to the total shear resistance.
Fig.1 - Typical textile configurations
Aim of this project is the development of design models for the calculation of the contribution of the TRM jacket to the total shear resistance, Vf. A variety of TRM systems have been widely studied so far, including carbon, glass, basalt and PBO textile reinforcements combined with different mortar mixes. The textile geometry and the mortar strength significantly varies at the TRM jackets applied so far on beams strengthened in shear with TRM and therefore different failure modes have been experienced.
To achieve this aim, the following objectives should be satisfied:
The methodology used to develop the design models for the calculation of the contribution of the TRM jacket to the total shear resistance involves initially the collection of the available data from literature. Data of specimens strengthened in shear with TRM jackets or counterpart FRP jackets included in the same studies are collected, reporting all the information related with the concrete member (dimensions, internal reinforcement, shear span to-depth-ratio and concrete strength), the TRM jacketing (strengthening configuration, number of layers and textile and mortar properties) and loading conditions (monotonic or cyclic load). Data of bond tests on TRM jackets are also collected as they can release useful information and contribute to better understanding of the failure modes.
The most common failure modes of reinforced concrete beams strengthened in shear with FRP jackets are: (a) debonding of the FRP jackets and (b) fracture of FRP jacketing. The aforementioned failure modes were also observed in reinforced concrete beams strengthened in shear with TRM jackets. However, in case of TRM jacketing, local damage of the jacket including slippage of the vertical fibres through the mortar constitutes a recurring failure mode. Based on the available data, TRM is as effective as FRP jacketing in increasing the shear capacity of reinforced concrete beams when failure is associated with debonding of the jacket. Therefore, in this case the models that are available in the literature for the contribution of FRP jackets to the total shear resistance can be also used for TRM jackets. However, TRM is less effective than equivalent FRP system when failure is attributed to local damage of the jacket instead of debonding. In this case, a reduction factor should be introduced taking into account the characteristics of TRM system. Finally, when failure of specimens is attributed to fracture of TRM jackets, the results of tensile tests on TRM coupons can be used.
So far all data of tests on concrete beams strengthened in shear with TRM have been collected and grouped based on their failure mode.
Conferences and meetings