Experimental study of composite concrete cellular steel beams

The main objective of this study is to compare the structural behavior of composite steel– concrete beams using cellular beams with and without steel ring stiffeners placed around the web openings. An IPE140 hot rolled I-section steel beam was used to create four specimens: one without openings (control beam); one without shear connectors (non-composite); a composite steel–concrete beam using a cellular beam without strengthening (CLB1); and a composite steel–concrete beam using a cellular beam (CLB4-R) with its openings strengthened by steel ring stiffeners with geometrical properties Br = 37mm and Tr = 5mm. CLB1 was fabricated with openings of 100mm diameter and a 1.23 expansion depth ratio, while CLB4-R was fabricated with openings of 130mm diameter, a 1.42 expansion depth ratio. Both beams were 1700mm in length with ten openings. The results of this experiment revealed that the loads applied to CLB1 and CLB4-R at deflection L/360 exceeded the load applied to the control specimen at the same deflection by 149.3% and 177.3%, respectively. The results revealed that the non-composite beam had an ultimate load 29% lower than that of the control beam. The ultimate load on CLB1 was 5.3% greater than that of the control beam, and failure occurred due to web-post buckling. While the ultimate load of the CLB4-R beam was 18.43% greater than that of the control beam, the Vierendeel mechanism was indicated as the failure mode.

The effect of different levels of pre-damage loading on the strength and structural behavior of CFRP strengthened R.C. beams: Experimental and analytical investigation

In order to investigate the effect of pre-loading damage on the structural performance of Carbon Fiber Reinforced Polymer (CFRP) strengthened Reinforced Concrete (R.C.) beams, experimental and Finite Element Modelling (FEM) investigation was carried out on six R.C. beams. Five of the R.C. beams were damaged up to different levels of strain in the main steel bars before Flexure CFRP strengthening. One of the R.C. beams loaded up to failure and was kept as a control beam for comparison. The experimental results showed that the failure mode of the CFRP strengthened specimen was controlled by CFRP debonding followed by concrete crushing; however, the control beam failed in concrete crushing after yielding the steel bars, which is a ductile failure. The CFRP sheet increases the strength and initial stiffness of the R.C. beams and reduces ductility and toughness. Also, CFRP application increases the first crack and yielding steel bars load by 87.4% and 34.4%, respectively. Furthermore, the pre-damage level does not influence the strength and ductility of the strengthened R.C. beams except for the highest damage levels, which experienced a slight decrease in load capacity and ductility. However, the initial stiffness decreases with increasing pre-damage levels by 40%. Design guideline ACI 440.2R (2004) predicts the ultimate load capacity marvelously for externally bonded Fiber-Reinforced Polymer (FRP) beams compared to the experimental maximum load capacity. The excellent agreement between experimental and FEM results indicates that the constitutive models used for concrete and reinforcement and the cohesive interface model can well capture fracture behavior. However, The FEM analysis predicts the beam to be slightly stiffer and more robust, probably because of the assumed perfect bond between concrete and reinforcement. The developed FEM can be used for further parametric study.

Flexural Behaviour of RC Beams with a Circular Opening at the Flexural Zone and Shear Zone Strengthened Using Steel Plates

In this paper, an investigation on the behaviour of RC beams with circular openings in the flexural zone and shear zone strengthened using steel plates is presented. Totally seven beams were cast: a control beam, one beam with a circular opening of size of one-third the depth of the beam (100 mmϕ) in the flexural zone, one beam with opening strengthened using the steel plate, one beam with a circular opening of size of 100 mmϕ in the shear zone, one beam with an opening in the shear zone strengthened using the steel plate, one beam with two circular openings of size of 100 mmϕ in the shear zone, and another beam with two openings in the shear zone strengthened using the steel plate. The experiments were conducted in a loading frame of 400 kN capacity. The beams were subjected to two-point loading. The ultimate load carrying capacity reduced marginally by 1.78% and 2.8% compared to that of the control beam when a circular opening of 100 mmϕ was provided in the flexural zone and shear zone, respectively, and when the opening was strengthened with steel plates, it reduced by 3.04% and 25%, respectively, but the ductility increased when steel plates were provided. Beams with an opening of size of one-third the depth of the beam (100 mmϕ) in the flexural zone strengthened with the steel plate can be provided, as the load carrying capacity is only marginally reduced compared to the control beam, and the ductility is more when compared with beams with unstrengthened openings.

Flexural behavior of reinforced concrete beams strengthened by carbon fiber reinforced polymer using different strengthening techniques

The externally bonded reinforcement on grooves (EBROG) method is increasingly recognized as an alternative strengthening method that can overcome the debonding problem. This study aims to experimentally investigate the effectiveness of EBROG as compared to the conventional externally bonded reinforcement (EBR) method in strengthening reinforced concrete (RC) beams. Twelve RC beams have been tested under four point load bending. One of these beams has been designated as a reference beam, seven beams have been strengthened with carbon fiber reinforced polymer (CFRP) sheets, and four beams have been strengthened with CFRP laminates using EBROG or EBR methods. The effect of CFRP type, number of layers, as well as the type of strengthening methods on the flexural performance have been also investigated. The load, deflection, stiffness, and failure modes were recorded and discussed intensively. Overall, test results indicated that the flexural strength and stiffness of the strengthened specimens using EBR or EBROG methods increased compared to the control beam, where the increase in the load carrying capacity of beams strengthened using the EBR method ranged between 24.8 and 48.2% and by the EBROG method ranged between 31.7 and 76.7% of the control beam. The most interesting result obtained is that the failure mode of beams has been changed from debonding of CFRP material to rupture of CFRP in some samples strengthened by EBROG, which demonstrates the superior behavior of this strengthening technique as compared to the traditional strengthening using EBR.

Shear Behavior of Steel-Fiber-Reinforced Recycled Aggregate Concrete Deep Beams

Results of an experimental investigation aimed at studying the effect of steel fibers on the shear behavior of concrete deep beams made with a 100% recycled concrete aggregate (RCA) are presented in this paper. The study comprised testing of seven concrete deep beam specimens with a shear span-to-depth ratio (a/h) of 1.6. Two beams were made of natural aggregates (NAs) without steel fibers, two beams were made of a 100% RCA without steel fibers, and three beams were made of RCA-based concrete with steel fibers at volume fractions (vf) of 1, 2, and 3%. Two of the beams without steel fibers included a minimum shear reinforcement. Test results showed that the beam with a 100% RCA without steel fibers exhibited a lower post-cracking stiffness, reduced shear cracking load, and lower shear capacity than those of the NA-based control beam. The detrimental effect of the RCA on the shear response was less pronounced in the presence of the minimum shear reinforcement. The addition of steel fibers significantly improved the shear response of the RCA-based beams. The post-cracking stiffness of the RCA-based concrete beams with steel fibers coincided with that of a similar beam without fibers containing the minimum shear reinforcement. The use of steel fibers in RCA beams at vf of 1 and 2% restored 80 and 90% of the shear capacity, respectively, of a similar beam with the minimum shear reinforcement. The response of the RCA specimen with vf of 3% outperformed that of the NA-based control beam with the minimum shear reinforcement, indicating that steel fibers can be used in RCA deep beams as a substitution to the minimum shear reinforcement. The shear capacities obtained from the tests were compared with predictions of published analytical models.

Experimental Ductility of Compression-Controlled Flexural Members Using CFRP Grid to Confine Concrete

Concrete members are typically designed so that flexural failure initiates with steel yielding and ends with concrete crushing in compression in order to take advantage of the yielding property of steel that allows for large deformations prior to any fracture of the material. On the other hand, if a large percentage of steel or linear elastic non-yielding reinforcement (i.e., FRP composite) is used, the member flexural failure typically initiates and ends with concrete crushing in compression. These members are known as compression-controlled members and typically exhibit brittle behavior. This study proposes a new approach in improving the flexural behavior of over-reinforced members through concrete confinement using carbon fiber reinforced polymer (CFRP) grid tubes in the compression zone. The concept was experimentally tested using rectangular beams. Beam 1 (control beam) had no grid reinforcement and beam 2 (tube beam) had two 152 mm grid tubes embedded in its compression zone. Experimental results indicate improvement in the ductility of the tube beam compared to the control beam of approximately 20–30% depending on the criteria used. Considering the low amount and mechanical properties of the CFRP grid, the improvement is significant, which shows that the proposed approach is valid and improves the ductility of compression-controlled members.

An Experimental Study on Rehabilitation of RC Beam by Stitching Method

The current work presents an experimental study on rehabilitation of RC beam by stitching method. For the study, a total of Twenty-Four RC beams were casted and cured for 28 days. Among the beams casted, three is control beam. Under two point loading, the control beam was tested for ultimate failure load and remaining twenty one beams were loaded for 75% of the ultimate failure load. The damaged beams were then rehabilitated by Stitching method using two different patterns. The rehabilitated beams were tested for ultimate failure load and the results are compared with control beam and the effectiveness of the rehabilitation is determined. From the result it is observed that as the diameter is gone increasing the flexural strength of the beam is gone increasing. As the depth of insertion of the bar inside the beam is gone increasing the flexural strength of the beam is gone increasing. It is concluded from this study that stitching methods is effective to restore the flexure capacity of damaged beams. Keywords: Rehabilitation, Reinforced Concrete Beam, Stitching Method

An Experimental Study on Strengthening of Reinforced Concrete Flexural Members using Steel Wire Mesh

Reinforcing reinforced concrete (RC) beams with galvanized welded steel wire mesh is one of the latest technologies applied in retrofitting. For each sample, the experimental evaluation of 18 small reinforced concrete beam samples with a total length of 1200 mm was carried out to study the bending strength under static load conditions. Experimental testing has been carried out to the activated failure mode, with 11 reinforced samples, 4 integrally cast control beams and three original control beams. Based on the test variables, namely SWM characteristics and connection mechanism, the reinforced beams are divided into two groups A and B. This study also clarified the bending resistance, ductility, stiffness, crack width and deflection. According to the test results obtained, all reinforced beams are designed to fail ductilely. The first group of reinforced beams recovered to an average of 110% of the bearing capacity of the original control beam, while the second group of reinforced beams recovered to an average of 163%. Furthermore, it was found that the reinforcement beam functions in the same way as the general control beam and works as a unit. Therefore, the bottom line is that this reinforcement technology can be used confidently in real-life applications, especially in low- cost buildings.

Experimental Strength Evaluation of Bamboo Reinforced Concrete Beams

This paper presents the outcome of an experimental investigation of the behavior and strength of reinforced concrete beams with bamboo reinforcement. A total of five beam specimens were tested in flexural under four point (pure bending) loading. A plain concrete beam (B1) served as a control beam. Two specimens (B2 and B3) were longitudinally reinforced with four bamboo culms and steel stirrups. The last two specimens (B4 and B5) had similar longitudinal reinforcement but bamboo pieces were used as shear stirrups. The bamboo culms used in two specimens (B2 & B4) were treated with bitumen along with sprinkling of fine particles of sand to achieve rough surface for better bonding with concrete. The introduction of bamboo reinforcement increased the stiffness, strength, and ductility of beams significantly as compared to the plain concrete beam. The ultimate load carrying capacity of bamboo reinforced concrete beams was found to be 2.49 to 3.29 times that of control beam. The observed ultimate load was 25% and 13% more for specimens with coated reinforcement in case of steel stirrups and bamboo stirrups respectively. The specimen with coated bamboo reinforcementand steel stirrups achieved the highest ultimate load among all specimens.

Structural Performance of Reinforced Concrete Beams Incorporating Cathode-Ray Tube (CRT) Glass Waste

The performance of reinforced concrete beams in the presence of cathode-ray tube (CRT) glass waste is examined. Four concrete mixes containing 0%, 10%, 20%, and 30% CRT glass waste as partial replacement of sand were prepared. The compressive and flexural strength as well as the modulus of elasticity of concrete were determined. Reinforced concrete beams with varying amounts of CRT glass were prepared and the three-point bending test was conducted. The load-deflection curve as well as the strain distribution along the depth of the beams were determined. Concrete containing CRT glass showed an increase in compressive strength, flexural strength, and modulus of elasticity especially at 10% replacement level. The load carrying capacity of reinforced concrete beam is higher when 10% of sand is replaced with CRT glass compared to the control beam and the beams with 20% and 30% CRT glass substitution. The failure mode of the reinforced concrete beams is flexural failure, and the failure pattern is similar for all beams. Strain distribution showed a better ductility at control beam where the deflection was higher than the other beams at the same load. Numerical analysis was conducted, and comparison was made with the experimental results. The comparison showed the accuracy of the software used, where the results of maximum load capacity and maximum deflection were very similar, and the difference did not exceed 5%. In addition, the tensile damage generated by the numerical analysis was very similar to that obtained by the experimental study.