**3.1 Specimen details and test matrix**

RC beams having an effective length of 2000 mm with an overhang of 50 mm on each side with 150 mm 230 mm cross-sectional dimensions were cast (**Figure 2**) using design mix proportions of 1:1.47:2.54 of cement, sand, and coarse aggregates with water-cement ratio of 0.46 using IS code method [30, 31]. The average compressive strength of the concrete used in both steel and GFRP reinforced concrete beams was experimentally obtained as 35.9 MPa. Moreover, mechanical properties of steel [32] and GFRP bars [33] were determined experimentally using Universal Testing Machine (Hung Ta Make, Taiwan with 1000 kN capacity) as shown in **Table 1**.

In the present study, two sets of beams were cast-one reinforced with traditional steel bars of Fe-500 grade bars denoted as (S-series) and the other reinforced with GFRP bars denoted as (G-series). It is important to note that S-series beams had both longitudinal as well as transverse reinforcement made of Fe 500 steel whereas

**Figure 2.** *Longitudinal and X-section details [29].*

*Crack Classification in Steel-RC and GFRP-RC Beams with Varying Reinforcement Ratio Using… DOI: http://dx.doi.org/10.5772/intechopen.101305*


**Table 1.**

*Mechanical properties of the reinforcing bars.*


### **Table 2.**

*Reinforcement details in the steel-RC and GFRP-RC beams.*

G-series beams had both longitudinal as-well-as transverse reinforcement entirely made of GFRP bars.

The design of RC beams is based on the [8]. Steel-RC beams were designed as under reinforced [34] whereas GFRP-RC beams were designed as over reinforced [8]. The reinforcement ratio (ρ = 100Ast/bd%) for each set of beams was varied as 0.33, 0.52, and 1.1% based on volumetric calculations. The steel-RC and GFRP-RC beams were identified according to the series. The arrangement is in the form of A-B-C, where A is the steel or GFRP-RC beam type, B is the steel or GFRP reinforcement ratio, and C is the name of the specimen which is denoted as numeric numbers 1, 2, 3. The reinforcement details of both S- and G-series are shown in **Table 2**. Three specimens of each beam series were cast to ensure repeatability of results but only one beam per type of each reinforcement ratio is explained in this research effort.

The experimental investigation involves testing of steel and GFRP reinforced concrete beams in four-point flexural loading which was displacement controlled at a rate of 0.01 mm/s (**Figure 3**). The loads were applied at L/3 from both supports using a steel spherical roller with a hydraulically controlled load cell (**Figure 3**). Mid-span deflections were measured using a Linear variable differential transformer (LVDT) attached underside of the RC beam and the load-deflection data was recorded by a high, speed data acquisition system. Before the actual AE monitoring, the AE sensors were checked for sensitivity using the pencil lead break test (PLB). After a successful PLB test, the wave velocity of concrete was set to 3.5 <sup>10</sup><sup>6</sup> mm/s. To acquire AE signals, a threshold of 45 dB was set initially with a preamplifier gain of 40 dB as input. AE-win software was used to acquire the signals originating due to bending and subsequent cracking. The mechanical performance of the steel and GFRP reinforced beams was compared by studying load-deflection characteristics, failure modes, and the progression of visible cracking patterns and moment carrying capacity. For AE monitoring of the steel and GFRP-RC beams, six AE sensors (R6α, PAC Make) with a resonant frequency of 60 kHz were attached to the front (3 Nos) and the back-face surface of the beam (3 Nos) as shown in **Figure 3**. The AE sensors were attached to the beams using a Vaseline gel and held

**Figure 3.**

*Acoustic emission monitoring setup [29]. (a) Schematic. (b) Actual beam with AE sensor.*

in position using cello tape till the end of the experiment of steel and GFRP-RC beams. AE signals were recorded continuously during the entire duration of the loading of the beam. From the recorded AE signals, various AE waveform parameters of amplitude and number of AE hits, their expanse, and spread obtained using AE X-Y event plots have been used to study the variation in fracture and failure pattern of steel-RC and GFRP-RC beams. The speckle pattern shown in **Figure 3**, is used for digital image correlation (DIC) analysis which is the future scope of the work.
