Experimental Study Of Simple Cyclic Testing On Reinforced Beam Using Fiber Reinforced Polymers (FRP)

The geographical location of Indonesia on the Ring of Fire makes it prone to earthquakes. Frequent earthquakes cause failures in construction. Construction failures must be repaired to restore the strength of the structures to their original or even higher levels. One type of structural reinforcement is Fiber Reinforced Polymers (FRP). FRP can enhance the strength of beams damaged by earthquakes, alter the structural failure mode, increase load-carrying capacity, and prolong plastic hinges in beam elements. This study recommends using FRP to reinforce concrete structures, particularly beams. The first stage of the research involves experimental testing on a prototype not wrapped with FRP. After reaching peak strength and experiencing failure, then the prototype is covered with FRP. Subsequently, the prototype is retested until it gets peak strength and experiences failure again. Both specimens are subjected to monotonic loading, which is simulated as cyclic loading. Data processing is performed by analyzing the results of the experimental testing on both prototypes. The processed data includes crack patterns in the beams, cyclic load capacity, displacement, strain of concrete, strain in the primary reinforcement, and strain in the stirrup reinforcement.


Introduction
Indonesia is an area frequently struck by earthquakes.This is due to its geological location at the convergence of three major lithospheric plates: the Eurasian Plate, the Pacific Plate, and the Indo-Australian Plate.Earthquake disasters in Indonesia result in significant material losses and loss of life.To reduce casualties, earthquake-resistant buildings should be constructed.Additionally, structural strength should be restored or reinforced in buildings that experience varying degrees of failure.
In construction, concrete is a composite material composed of various combinations of fine aggregates, coarse aggregates as fillers, and cement as a binder.Concrete exhibits characteristics of high compressive strength but is weak in tension.Moreover, concrete is brittle in nature.
According to Ir. Mardiana Daoed, a senior structural planner at PT. Ingenium Consultants, a good building construction must meet three criteria: strength, stiffness, and stability.Therefore, a building is considered defective or experiencing construction failure if its structural elements do not meet one or more of these criteria.Construction failures occur in every construction project, making it essential to address this issue, as buildings are used by humans and can pose dangers if damaged [1].In addition to natural disasters, construction failures can also occur during the construction phase due to issues with compaction using vibrators.Construction workers in Surabaya have insufficient knowledge about compaction using vibrators [1].One way to restore or enhance the strength of concrete structures is by providing structural reinforcement, such as using steel plates or Fiber Reinforced Polymers (FRP).
Reinforcement of beams is carried out to strengthen structures that have suffered damage from earthquakes, ensuring that if another earthquake occurs, the structure remains undamaged as before the reinforcement (Bahraq et al., 2021).In other research, beam-column connections reinforced with Fiber Reinforced Polymers (FRP) and subjected to cyclic loads showed improved structural integrity and loadcarrying capacity [2]).Reinforcement using Fiber Reinforced Polymers (FRP) improves the performance of beam-column connections in cyclic load conditions [3] It also changes the failure mode of the structure from brittle failure to a more ductile failure mode [3] Reinforcing beam-column connections with FRP also results in longer plastic hinge zones [4].In another study, reinforcing with Carbon Fiber Reinforced Polymers (CFRP) coated with high-quality cement and mortar modified the failure mode of specimens by shifting the eccentricity of loading from the joint to the beam.This improved the overall strength and ductility of the specimens (Lim et al., 2022)

Beam flexural analysis
Composite reinforced beams are beams that have both tensile reinforcement (As) and compressive reinforcement (A's) in their cross-section.Fundamentally, concrete possesses high compressive strength, and the primary role of compressive reinforcement is to control deformation, reduce the effects of creep and shrinkage in the beam, and enhance the ductility of the beam's structure.In the design of composite reinforcement, the process is similar to that of single reinforcement design.However, the key difference lies in the contribution of strength from the compressive reinforcement in the compression zone of the beam, denoted as "Compression of Steel" (Cs).Meanwhile, the compressive strength of the beam is adjusted from "C" to "Cc" (Compression of Concrete) to account for the contribution of the compressive reinforcement in the structural design.This adjustment is made to ensure that the calculations accurately consider the influence of the existing compressive reinforcement.As can be seen in Figure 1, composite reinforced beams have tensile reinforcement (As) in the tensile stress region and compressive reinforcement (A's) on the compressive stress side.The distance from the center of gravity of the compressive reinforcement (A's) to the outermost compressive fiber of the beam cross-section is denoted as d'.With the presence of compressive reinforcement, the strain of the compressive reinforcement is also calculated using the notation ε's.To facilitate the analysis of composite reinforcement, here is the stress-strain mechanism of composite reinforced beams.

Structural Strengthening
Strengthening joints in beam-column connections under both monotonic and cyclic loading is aimed at achieving enhanced structural behavior using Fiber Reinforced Plastics (FRP).The method employed in this research involves reinforcement using FRP materials.The application of FRP is modeled with various configurations and types of FRP.The results from these different experiments indicate that reinforcement using FRP can increase the shear force capacity that the beam-column structure can withstand.This leads to improved ductility in beam-column structures, preventing sudden and brittle failures.
Beam-column connections were externally strengthened using Kevlar fiber wraps.The configurations used can be observed in Figure 2.

Loading
Cyclic loading refers to the repetitive application of loads in both directions.The term "cyclic loading" implies a loading system characterized by regularity in both magnitude and frequency [5] In structures subjected to cyclic loading, the energy absorbed in one loading cycle is the sum of the energy absorbed when the structure is subjected to compressive loads and the energy absorbed when it experiences tensile loads.Therefore, the total energy dissipated during cyclic loading is represented by the area within the load-deflection curve loop (Rendy et al., 2015a).
Testing using cyclic loading requires specialized equipment and can incur significant costs.Due to limitations in equipment and budget for cyclic testing, it is common to utilize monotonic testing equipment to simulate cyclic loading [6].
Agarwal et al. conducted research to investigate the influence of transverse reinforcement and the application of Fiber Reinforced Polymers (FRP) under axial loading on concrete.Furthermore, this study aimed to assess the behavior of beam-column connection structures modeled as T-joints.In this research, two types of specimens were used: one specimen was not reinforced with FRP, while the other was strengthened with FRP.Both specimens were subjected to cyclic loading [7]

Fiber Reinforced Polymers (FRP)
Al-Rousan conducted a study on the effectiveness of using external fiber-reinforced polymer composites (FRP) to strengthen damaged reinforced concrete (RC) beam-column connections affected by alkalisilica reaction (ASR).To achieve this objective, two techniques were employed: experimental methods and nonlinear finite element analysis (NLFEA).Prior to conducting the experimental tests, the researcher validated the model using data from previous experimental research.The model was then subjected to axial column loading at various levels of ASR damage.For axial loading, the load was varied in increments of 25%, 50%, and 75%, and ASR damage stages included: Stage 0 (no damage), Stage 1 (45 days), Stage 2 (80 days), and Stage 3 (120 days).Different variations of each model were considered, some reinforced with FRP and others without.The results of the experiments and nonlinear finite element analysis indicated that the enhanced models exhibited improved cyclic performance, demonstrated by higher load capacities, larger horizontal displacements, greater ductility, and increased energy dissipation.. Cao et al. conducted research to investigate the effects of strengthening using Fiber Reinforced Polymer (FRP) on post-fire concrete slabs.The specimens were subjected to varying fire exposure times, including 0 minutes, 45 minutes, and 75 minutes.Nine concrete slab specimens were tested.The results revealed that the control specimens, which were not reinforced with FRP and exposed to fire, experienced flexural failure.In contrast, those reinforced with FRP failed at the FRP anchorage points.

• Types of FRP Materials • Physical Properties of Fiber Reinforced Polymers (FRP) • Mechanical Properties of FRP • Behavior Based on Time Function
In the upcoming research, a simple method of modeling monotonic loading will be employed, which will be simulated as cyclic loading.The specimens will be subjected to this loading and reinforced using FRP.

Research data
Primary data will be obtained from the testing of beam specimens subjected to monotonic loading, with the load placement modified to simulate cyclic behavior.Secondary data will be sourced from regulations and guidelines related to reinforcement, FRP, and related topics.

Research Approach
This research is conducted in several phases.The first phase involves: • Literature Review as a reference to compare previous research with the upcoming study.
• Designing the experimental testing format, including the test specimens and the testing apparatus setup.
• Experimental testing of specimens without FRP reinforcement.
• Specimens that reach peak strength and fail will be reinforced with FRP and retested under cyclic loading.Data processing occurs in several stages.The first stage involves analyzing the output data from the experimental testing of beams subjected to cyclic loading without reinforcement.The second stage entails analyzing data from the experimental testing of beams subjected to cyclic loading with FRP reinforcement.The data analyzed includes crack patterns in the beams, cyclic load-bearing capacity of the beams, displacement and strain in concrete, and strain in the main reinforcement and stirrups.The resulting data is presented in tables and graphs [8]

Specimen Configurations
The concrete grade used is 17 MPa, and the test specimen configurations can be seen in Figure 3.2 for specimens without FRP reinforcement and Figure 3.3 for specimens with FRP reinforcement.The type of FRP used is carbon fiber.The LVDT is used to measure the effective deflection that occurs in the beam, namely the deflection that occurs on both the left and right sides of the beam.Install a data logger to assist in recording each applied load and the resulting deflection.b.Apply a constant and gradual load using a hydraulic jack pump, causing the actuator to push against the load cell.Apply the planned load so that it is distributed as previously described.c.For the first test specimen, apply monotonic loading.d.During the loading process, mark each crack on the test specimen and draw the crack lines on grid paper provided.These lines serve to facilitate the observation of crack patterns.e.The applied load values will be automatically recorded by the data logger in use.f.After the beam experiences failure, observe the crack patterns.g.Summarize the load and deflection values from the data logger, then analyze and create graphs.
The Load vs. Deflection graph will provide insights into the load application stages for the subsequent testing, including the incremental loads to be applied in each loop or stage of cyclic loading on the beam.h.For the next test specimens, apply cyclic loading by relocating the setup and spreader beam.
The first position represents a positive load, and the second position represents a negative load.Increase the load value (P) gradually at each loop or stage of loading.

Conclusion
The use of a simple method for testing cyclic loading on reinforced concrete beams with Fiber Reinforced Polymers (FRP) reinforcement can be considered as an alternative approach for cyclic testing on reinforced beams.

Figure 2 .
a illustrates the beam-column connection with only laminate fibers, Figure 2.b shows the beam-column connection with laminate fibers wrapped around the joint intersection, and Figure 2.c.

Figure 3 .
Figure 3. Properties of test specimens without FRP reinforcement.

Figure 4 .
Figure 4. Properties of Test Specimens with FRP Reinforcement.