PSI - Issue 64

Asad-ur-Rehman Khan et al. / Procedia Structural Integrity 64 (2024) 1065–1072 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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2.2. Application of TRM on Beams Concrete used in the casting of RC beams had a compressive strength of 20.7 MPa, whereas longitudinal reinforcement and transverse reinforcement had tensile strengths of 500 MPa and 414 MPa respectively. Properties of basalt fibres based TRM determined through tests include the compressive strength and tensile strength, which came out to be 26.2 MPa and 2.7 MPa after 28 days of curing. The pull-out strength of concrete-TRM interface was found to be 0.3 MPa. The three-point bending strength for one, two, and three basalt fibre rovings was noted to be 0.34 MPa, 0.45 MPa, and 0.53 MPa, respectively. Three samples for each test were used. Table 2 enlists the properties of the TRM system (mortar + basalt mesh) provided by the manufacturer of TRM material. The surface of the beams was prepared for the application of TRM as suggested by the material provider. Matrix was applied in a layer of 2 mm thickness on the face of concrete already prepared with a trowel. The basalt fibre grid was trimmed according to the desired length and then applied through hand compression, cautiously placing it onto the already applied mortar and levelling it to ensure that straight-oriented fibres were placed that were well infused with the matrix. A second coating of cementitious mortar was installed on the fibre to wholly embed the fibre within the mortar, resulting in 5 mm thick TRM. The TRM in strengthened beams was cured for 28 days.

Table 2: Properties of TRM System Material Property

Experimental Value

Suggested Value for Design

Depth of Layer, mm Elongation at failure, %

5

5

1.62%

1.62%

Ultimate strength (tensile), MPa

6.00 0.37

5.10 0.31

Tensile Modulus, GPa

The length of all control and strengthened beams of analogous a/d ratios to be tested is reflected in Table 1. Figure 4 presents the test setup. Application of load was at a distance ‘ a ’ from the left support as identified in Table 1 and shown in Figure 2. LVDTs were used at the location of the point load application and were imitated on the far end to monitor deformations. Surface strain gauges were applied to the compression face, flexural reinforcement level, farthest TRM fibre, and location of the expected shear crack to monitor strains. Testing of the beams was carried out in deflection control mode. Loading rate was maintained at 0.01 mm/sec.

(a) Supports

(b) Test assembly

(c) Placement of LVDT

Figure 4: Testing setup of control and strengthened beams

3. Results and Discussion Following subsections presents and discusses results of the experimental investigation for all the control and strengthened beams, in terms of ultimate load carrying capacities, cracking pattern, loads at the initiation of initial crack and load-deflection curves. 3.1 Experimental Load Carrying Capacity Table 3 represents a succinct list of the highest values of failure loads sustained by both control and strengthened beams. The table also reports the increase in the percentage of failure loads for strengthened beams and their respective modes of failure. All the beams were designed to fail in flexure. This was achieved by designing the transverse reinforcement in the shear span to avoid failure in shear, although the a/d ratios are shear critical ratios.