Reinforced Lightweight Concrete Beams Research Articles

Improvements in lightweight concrete T beams CFRP strengthened and anchored with U‐wraps

AbstractThis research provides a study for an experimental program using sand‐perlite‐lightweight reinforced concrete (RC) beams strengthened and anchored with carbon fiber reinforced polymer (CFRP) materials. The main objective of this work is to showcase the efficiency of using U‐wrap anchors to secure the externally applied CFRP sheets on lightweight RC beams. A series of six full‐scale T‐beams with an increasing number of CFRP U‐wraps per shear span was prepared and tested. The use of U‐wrap anchorage enhanced the flexural performance of the sand‐lightweight concrete beams by progressively delaying the premature debonding of CFRP sheets as a direct function of the number of U‐wraps used per shear span. The beam flexural capacity gradually improved from 116 kN without the use of U‐wrap anchors to 182 kN when using six U‐wraps per shear span, which reflects a significant enhancement. Similarly, the ultimate deflection gradually improved from 56 mm for the beam without U‐wrap anchors to 94 mm when applying six U‐wraps per shear span. A design model established earlier, for normal weight concrete, has been successfully qualified to yield accurate findings against the experimental results. Also, the outcome of this study interestingly showed that the ultimate strength results of the anchored beams were close to their counterparts of normal weight concrete conducted on identical beams. This finding shows that U‐wrap anchors performed efficiently despite the lack of coarse aggregate interlock in the concrete mix.

Influence of Steel and Polypropylene Fibers on the Structural Behavior of Sustainable Reinforced Lightweight Concrete Beams Made from Crushed Clay Bricks

Structural lightweight concrete is preferred over traditional concrete due to its ability to reduce the dead load, minimize the size of load-bearing structural members, and provide more economical solutions for foundation deteriorations. This research sheds light on sustainable lightweight concrete using waste crushed clay bricks (CCB) as a lightweight aggregate. To reduce micro-crack propagation of the developed concrete, two types of fiber were implemented and investigated. Steel fibers (SF) with amounts of 0.5% and 1.0% by volume of concrete, and polypropylene fibers (PPF) with amounts of 0.1% and 0.2% by volume of concrete, were employed. Five reinforced concrete beams were made and tested in order to precisely evaluate the structural behavior of the proposed lightweight CCB concrete. Additionally, ABAQUS software for nonlinear finite element analysis has been utilized to simulate the tested beams and compare the numerical model predictions with the experimental findings. The findings revealed that the addition of SF and PPF exhibited a notable influence on enhancing the mechanical characteristics of lightweight CCB concrete. Adding 0.2% PPF increased the ultimate load and deformation capacity at failure by approximately 16% and 24%, respectively. Furthermore, after 28 days, the addition of 0.5% and 1.0% SF enhanced the compressive strength by around 11.7% and 17.6%, respectively. Moreover, a significant level of consistency between the results obtained from the numerical model and the experimental findings was observed. In general, the use of SF and PPF in CCB concrete successfully produced high-quality lightweight concrete with interesting results for use in reinforced concrete beams.

The behavior of reinforced lightweight concrete beams with initial cracks

This research examines the performance of reinforced lightweight concrete beams subjected to several degrees of damage (50%, 60%, 70%, and 100%). It can use a sheet made of Carbon Fiber Reinforced Polymer (CFRP) to reinforce. The Full U-wrapping rehabilitation method was tested in the presented experimental program. In this method, CFRP sheets are attached to the bottom only and the side and bottom of the beam section. Experiments proved that the service load (Ps) increases by 7.06 % from a damage level of 50 % to 70 %, rises by 1.21 % from a damage level of 60 % to 70 %, and falls by 3.07 % from a damage level of 100 %. The result also rose for the fortified sample by 11.99%. Increases of 42.67 %, 33.07 %, and 23.73 % in the stiffness ratio (k) were observed at damage intensities of 50, 60, and 70 %, respectively. Damage at lower severity levels is increasing at a faster rate. The ductility of the restored LWC beams is more excellent than the control, as with the stiffness. Damage levels of 50%, 60%, and 70% saw increased ductility of 35.60, 34.92, and 34.69 %, respectively.

Application of Stochastic Finite Element Modeling to Reinforced Lightweight Concrete Beams Containing Expanded Polystyrene Beads

Limited investigations have evaluated the effect of expanded polystyrene (EPS) beads on the structural lightweight concrete properties. EPS offers many features compared to natural or artificial lightweight aggregates including the elimination of aggregate saturation prior to concrete batching, ability to be fabricated on site, consistency in size and quality, and reduced cost. The main objective of this paper is to assess the suitability of finite element (FE) modeling based on deterministic and stochastic approaches to predict the shear strength behavior of reinforced concrete (RC) beams containing EPS additions. Test results showed that the experimental load-deflection properties recorded at failure can be well reproduced using both FE approaches. Nevertheless, the damaged-zone distribution and crack patterns that occur during the loading stages of RC beams cannot be approximated using the deterministic FE approach. In contrast, the stochastic method was quite suitable as it accounted for the concrete heterogeneity and altered spatial mechanical properties (such as compressive strength, splitting tensile strength, and Young’s modulus) due to EPS additions. Such data can be of interest to civil engineers seeking to predict the failure patterns and performance of structural lightweight members while reducing the time and resources needed to account for the concrete’s strength variability during experimental testing.

Experimental study on flexural behavior of reinforced lightweight concrete beams strengthening with a slurry infiltrated fiber concrete (SIFCON)

Experimental study on flexural behavior of reinforced lightweight concrete beams strengthening with a slurry infiltrated fiber concrete (SIFCON)

Flexural Strengthening of Light Weight Reinforced Concrete Beams by Using Glass Fiber Reinforced Polymer

The use of Lightweight concretes has gained acceptance and popularity worldwide in the recent years in the construction and development of both the infrastructure and residential buildings. Light weight aggregate concrete has become more popular in recent advancements owing to the tremendous advantages it offers over the conventional concrete but at the same time light in weight and strong enough to be used for structural purposes. Replacement of natural aggregate with concrete such as light weight concrete by using sintered fly ash aggregate (natural aggregate), The main disadvantage of conventional concrete it is high self -weight. This heavy self-weight will make it to some extent an uneconomical structural material. Light weight concrete having low density facilitates reduction of dead load and to increase thermal insulation.

Flexural response of FRP-strengthened lightweight RC beams: hybrid bond efficiency of L‐shape ribbed bars and NSM technique

This paper presents the results of an experimental study on employing near surface mounted (NSM) fiber-reinforced polymer (FRP) reinforcement technique, and L‐shape ribbed bars, for flexural strengthening of lightweight reinforced concrete (RC) beams. 18 RC beams including 14 lightweight RC beams and four normal-weight concrete beams were designed. The beams were strengthened with glass fiber-reinforced polymer (GFRP) bars and carbon fiber-reinforced polymer (CFRP) laminate in bending tests. Test parameters included: (1) different FRP materials (glass bars and carbon sheets), (2) longitudinal steel reinforcement ratio, and (3) type of strengthening technique used (NSM reinforcement or hybrid). The ultimate tensile strength, deflection, compressive and tensile strain of concrete, and failure mode of the beams were examined under four-point flexural test. Results showed that the ultimate strength of all RC beams increased between 33 and 105% compared to the control beam. The ultimate strength of beams reinforced with CFRP in the mid-span region was 10% higher than that of beams strengthened at both ends, although the former exhibited 28% lower ultimate deflection. The ultimate strength and deflection of RC beams strengthened with combined steel reinforcing bars and GFRP bars were 10% and 108% higher, respectively, compared to those of RC beams strengthened with GFRP bars only. Hybrid L‐shape ribbed bars beams showed a considerably higher ductility (up to 170% increase in the ultimate deflection) compared to other beams. The comparison of the experimental results of the ultimate strength of the beams with ACI440-2R guidelines indicated a reasonable and conservative prediction of the code expression.

Numerical Investigation on the Behavior of Reinforced Lightweight Concrete Beams at Elevated Temperature

In this paper, the response of lightweight reinforced concrete (LWRC) beams under elevated temperature is numerically investigated using the nonlinear finite element software ABAQUS. Firstly, a numerical model is suggested and validated against experimental tests conducted by the authors. The validation results have shown the accuracy and reliability of the suggested numerical model. Thereafter, the validated numerical model was utilized in conducting a comprehensive parametric study to investigate the effects of several important parameters on the behavior and failure of normal and lightweight RC beams at elevated temperature. These parameters include the effect of the high ranges of elevated temperatures; the effect of heating rate; and the effect of thermal distribution along the beam length and around the beam section. The parametric study results have indicated that the distribution of the temperature along the beams length and around the beams section can affect the ultimate load resistance up to 5 and 4.93% for LWRC and NWRC beams, respectively.

The Structural Characteristics of Lightweight Aggregate Concrete Beams

This paper aims to investigate the structural behavior of reinforced lightweight concrete beams. Attapulgite aggregate and crushed clay brick aggregate were used as coarse lightweight aggregate to produce structural lightweight aggregate concrete with 25 Mpa and 43.6 Mpa cube compressive strength and 1805 Kg/m3 and 1977 Kg/m3 oven dry density respectively. The result of reinforced lightweight concrete beams compared with reinforced normal weight concrete beams, which have 50.5 Mpa cylinder compressive strength and 2317 Kg/m3 oven dry density. For each type of concrete two reinforced concrete beams with (1200 mm length × 180 mm height × 140 mm width), one of them tested under symmetrical two-points load STPL (a/d = 2.2) and another one tested under one-point load OPL (a/d=3.3) at 28 days. The experimental program shows that a structural lightweight aggregate concrete can be produced by using Attapulgite aggregate with 25 MPa cube compressive strength and 1805 Kg/m3 oven dry density and by using crushed clay brick aggregate with 43.6 MPa cube compressive strength and 1977 Kg/m3 oven dry density. The weight of Attapulgite aggregate concrete and crushed clay bricks aggregate concrete beam specimens were lower than normal weight aggregate concrete beams by about 20.56% and 13.65% respectively at 28 days. As for the ultimate load capacities of beam specimens, the ultimate load of Attapulgite aggregate concrete beams tested under STPL were lower than that of crushed clay bricks aggregate concrete beams and normal weight aggregate concrete beams by about 4.85% and 5% respectively. While the ultimate load capacities of reinforced Attapulgite concrete beams tested under OPL were lower than that of reinforced crushed clay bricks aggregate concrete beams and reinforced normal weight aggregate concrete beams by about 10.3% and 10.5% respectively. Finally, Attapulgite aggregate concrete and crushed clay bricks aggregate concrete showed ductility and toughness less than that of Normal weight aggregate concrete.

Energy Absorption Capacity Of Layered Lightweight Reinforced Concrete Beams With Openings In Web

This research presents the flexural behavior on reinforced concrete beam with transverse web opening constructed from layered concrete. The layered concrete combining normal concrete and lightweight aggregate concrete (LWC) are depended in present study. In the experimental program, 13 models of normal and layered reinforced concrete beams are tested under the effect of four-point loads. All beams had the same overall geometrical dimensions and main longitudinal top and bottom with internal diagonal reinforcement provided around the openings. One of the beam specimen is tested as control beam and the other specimens are divided into three groups [G1, G2, and G3] to study the effects of the following variables: effect of presence of web openings, layered system, lightweight aggregate (partially volumetric replacement of normal aggregate by thermostone) on the ultimate load, cracking load, cracking pattern and energy absorption capacity. The existing of an opening in beam specimens reduced the flexural capacity of beams with a percentage depending on the size of opening and opening number. The test data obtained from the adopted layered technique of (NEW) and (LWC) have shown that for beams constructed from two layered concrete (LWC with thermostone in the web and bottom flange of I-beam section) ultimate load is decreased about (9.3%-48.8%). It has also, the beams constructed from three-layered of concrete (LWC with thermostone in the web of I-beam section), their ultimate load is decreased about (25.6%-58.1%). On the other hand, magnitude increased of energy absorption capacity are achieved by the decreased opening size, introducing the full size opening of dimension (100×1000) mm reduces the energy absorption capacity of the RC I-section beams at least 80% compared to solid beam while the beam with opening size (100×100) mm decrease up to 16%. In the case of the layered concrete beams specimen, the real influence of lightweight concrete (LWC) type in the layered reinforced concrete is observed significantly after increasing the length of opening more than 100 mm.

Cracking Behavior of Reinforced Lightweight Concrete Beam Using Hot Water Pre-treated Oil Palm Shell Coarse Aggregate

As one of the largest palm oil producers in the world, by-products of this commodity are also produced in Indonesia. One of the solid by-products that are obtained from palm oil production is called Oil Palm Shell (OPS). These days, this material is interesting to be studied as it has a lightweight but sufficiently tough and rough outer surface. In previous studies done in laboratory, OPS was used as alternative coarse aggregate in concrete mix proportion. The designed compressive strength of OPS concrete is in the range of 20-23 MPa. In this research, the authors are interested in studying the crack behaviour of reinforced lightweight concrete beams using OPS replacing natural coarse aggregates. First, pre-treatment of OPS is performed by using hot water at 50-°C as based on previous studies. Second, two samples of identical beam with 15 × 25 × 300 cm3 of dimension were cast and tested under four-point loading using force control hydraulic actuator. Third, crack opening evolution due to flexural test that occurs in OPS lightweight concrete beam is measured, to be precise, on the pure bending area. The crack opening is compared to service limit cracks from building code to find the corresponding loading application.

Shear Capacity of Reinforced Lightweight Concrete Beams: Concrete Recipes and Experimental Results

Shear Capacity of Reinforced Lightweight Concrete Beams: Concrete Recipes and Experimental Results

Evaluation of shear-deficient lightweight RC beams retrofitted with adhesively bonded CFRP sheets

A series of twenty-two shear-deficient lightweight reinforced concrete (LWRC) beams were casted and tested under four-point flexural loading to investigate the structural behaviour of shear-deficient LWRC beams retrofitted with adhesively bonded carbon fibre reinforced polymers (CFRP) sheets. The variables investigated in the study include as follows: shear-span to effective-depth ratio and different retrofitting schemes. The overall response of the LWRC beams, the onset of cracking, crack development and ductility were investigated. The experimental results indicated that the contribution of the CFRP to restore the shear capacity of the shear-deficient LWRC beams was significant. The ultimate shear strength of the retrofitted LWRC beams increased significantly (23–96%) depending on the technique used. The use of the CFRP transformed the mode of failure of some LWRC beams into a more ductile flexural one. The most effective technique for enhancing the shear capacity of the LWRC beams was the CFRP jacketing, followed by the U-strips, inclined strips, and side strips, respectively. The dominant failure mode for the retrofitted LWRC beams was the CFRP debonding from the beams surface by shearing of the concrete skin. An analytical model was developed and showed good correlation with the test results of this investigation.

Satisfactory margin of safety against shear failure of lightweight reinforced concrete beams: 3D finite element modeling

In concrete structures a satisfactory margin of safety should be ensured against shear failure that might occur under the forces that act upon the structure during its lifetime. Therefore, knowledge of the design and construction guidelines for shear of normal and high strength Lightweight Concrete (LWC) beams is desirable to better understand the structural design and performance of LWC beams. Thus, research is required to address and investigate the contribution of concrete compressive strength, shear span to depth ratio, tensile reinforcement ratio, and shear stirrups spacing as well as the failure mechanisms in situation of using LWC beams. As a result, this paper presents Nonlinear Finite Element Analysis (NLFEA) results of reinforced LWC beams because of the main benefits of NLFEA by providing substantial savings in the cost, time, and effort compared with the fabrication and experimental testing of structure elements as well as the ability to change any parameter of interest and the capability of demonstrating any interesting behavior at any load value and at any location in the system. After reasonable validation of NLFEA with the experimental test results, the NLFEA was expanded to provide a parametric study of fourteen hundred LWC beams that correlates the ultimate shear stress to studied parameters. Results indicated that the lower bound was for the beams with shear span to depth ratio, concrete compressive strength, and tensile reinforcement ratio of 5, 27.5 MPa, and 0.71%, respectively, and the upper bound was for the beams with shear span to depth ratio, concrete compressive strength, and tensile reinforcement ratio of 1, 68.8 MPa, and 2.21%, respectively. In addition, the performance of simulated models was investigated in terms of ultimate load capacity, ductility and energy absorption. Finally, a new parametric model is introduced in this paper to compute the shear strength of reinforced LWC beams without stirrups. The proposed equation was compared with numerous previous analytical models and founded that some models to be in a good agreement.

Ductility of reinforced lightweight concrete beams and columns

This paper presents analytical and experimental results on ductility of reinforced lightweight concrete beams and columns in the form of moment curvature relationships, and compares the response with that of normal reinforced concrete members. The experimental part is limited to flexural tests on beams made of lightweight concrete. The latter is obtained with natural lightweight aggregates. Concrete and steel stress-strain models in compression and tension are integrated analytically through the section in order to derive the resulting moment and axial force. Lightweight concrete beams and columns showed a more ductile behavior than normal concrete members and the analytical model reproduced the response with very good accuracy. The lightweight ductility was more pronounced in columns subjected to axial compression forces and bending.

Flexural behavior of reinforced lightweight concrete beams under reversed cyclic loading

This paper presents the results of an experimental investigation on the flexural behavior of doubly reinforced lightweight concrete (R.L.C.) beams tested under cyclic loading. A total of 20 beam specimens were tested. Test results are presented in terms of ductility index, the degradation of strength and stiffness, and energy dissipation. The flexural properties of R.L.C. beam were compared to those of normal concrete (R.C.) beams. Test results show that R.L.C. beam with low and medium concrete strength (20, 40MPa) performed displacement ductility similar to the R.C. beam. The ductility can be improved by enhancing the concrete strength or decreasing the tension reinforcement ratio. Using lightweight aggregate in concrete is advantageous to the dynamic stiffness of R.L.C. beam. Enhancement of concrete strength and increase of reinforcement ratio will lead to increase of the stiffness degradation of beam. The energy dissipation of R.L.C beam, similar to R.C. beam, increase with the increase of tension reinforcement ratio. The energy dissipation of unit load cycle for smaller tension reinforcement ratio is relatively less than that of beam with higher reinforcement ratio.

Concrete Shear Strength of Normal and Lightweight Concrete Beams Reinforced with FRP Bars

AbstractA new equation to predict the contribution of concrete to the shear strength of fiber-reinforced polymer (FRP) reinforced concrete beams without shear reinforcement is proposed. The new equation considers the elastic modulus ratio of the FRP bars to the steel reinforcement, the shear span to depth ratio, and the flexural reinforcement ratio, and was developed using the results of 60 concrete beam tests. The proposed equation more accurately predicted the results of various experiments available in the literature than the equations of an American Concrete Institute standard, and yielded similar degrees to the equations of a Canadian Standards Association standard, despite making somewhat higher predictions. The applicability of the proposed equation to FRP reinforced lightweight concrete beams was investigated using 24 all-lightweight concrete beam tests. The concrete shear strengths of the FRP reinforced all-lightweight concrete beams were equivalent to 75% of the strengths predicted by the propos...

Research on the Calculation Method for Diagonal Shear Capacity of Steel Reinforced Lightweight Concrete Beams

Steel reinforced lightweight aggregate concrete structure is a new type of composite structure to meet the building development trend of energy conservation and environmental protection. Based on the shear tests of steel reinforced lightweight concrete beams, according to the specifications of lightweight concrete and steel reinforced concrete, this paper established a design formula for calculating the shear capacity of steel reinforced lightweight concrete beams under the concentrated loads. The results coincided well with the tests. The calculation method is reliable, which can provide theoretical foundations for the practical engineering application of steel reinforced light aggregate concrete beam.

Flexural and Shear Resistance of Steel Fiber–Reinforced Lightweight Concrete Beams

In the present paper an analytical model is proposed that is able to determine the shear resistance of lightweight reinforced concrete beams with longitudinal bars, in the presence of reinforcing steel fibers. The model is based on the evaluation of the resistance contribution resulting from beam and arch actions. For the resistance contribution of main bars in tension, the residual bond adherence of steel bars and the crack spacing of reinforced concrete (RC) beams in the presence of fibers are considered. The contribution in terms of postcracking resistance in the tension zone of the beams is also included. The model was verified on the basis of experimental data available in the literature and is able to include the following variables in the resistance provision: diameter and number of steel bars, depth to shear span ratio, resistance of materials and fiber characteristics, crack spacing, tensile stress in main bars, residual bond resistance, postcracking tensile resistance, and size effects. Finally, some of the more recent analytical expressions able to predict the shear resistance of fibrous concrete beams are mentioned and a comparison is made with experimental data.

Flexure strengthening of lightweight reinforced concrete beams using carbon fibre-reinforced polymers

A series of 40 lightweight reinforced concrete (LWRC) beams of 1400 mm length and a rectangular cross section of 150 × 200 mm were cast, strengthened and then tested under four-point bending test to study the effectiveness of using externally applied carbon fibre-reinforced polymer (CFRP) composites as a method of increasing the flexural strength of under-reinforced LWRC beams. Parameters investigated include reinforcement ratio, ρ; ρ = 0.55ρb and ρ = 0.27ρb, CFRP sheet length; 600, 800 and 1000 mm, CFRP sheet width; beam width and half-beam width. Three types of strengthening schemes were used: jacketing covers the beam from bottom and two sides with total width of 500 mm, sheets at the tension side with width equal to beam width and sheets with width equal to half-beam width. Test results showed a limited increase in ultimate load-carrying capacity accompanied with some reduction in mid-span deflection for the strengthened beams. Among the strengthening schemes investigated, jacketing was the most effective for strength enhancement (about 41%) with respect to control beam; however, it reduced ductility significantly. An analytical model was proposed for predicting the ultimate load-carrying capacity of LWRC beams strengthened with CFRP composites.