Ultimate Load Of Beams Research Articles

Numerical Modeling and Design Method for Reinforced Polyvinyl-Alcohol-Engineered Cementitious Composite Beams in Bending

The polyvinyl-alcohol-engineered cementitious composite (PVA-ECC) is a superior cementitious material when used for tension and flexural loading. The utilization of PVA-ECC in the tension zone can prevent the development of wide cracks and increase the flexural resistance of reinforced PVA-ECC members. In this paper, a nonlinear finite element model is established to simulate the behavior of PVA-ECC beams in bending. In the model, the constitutive models for PVA-ECC in compression and tension are employed by simplifying them as piece-wise linear models, and the bond between the reinforcing bar and PVA-ECC is also considered. The load–deflection curve and failure mode of beams can be obtained from the finite element model. Comparisons between numerical and experimental results show that the developed numerical model can estimate the ultimate load and failure mode of beams with reasonably good accuracy. After evaluating the accuracy of the finite element model, parameter analysis is conducted to investigate the effects of the reinforcement ratio, steel strength grade, and mechanical properties of PVA-ECC on the flexural behavior of reinforced PVA-ECC beams. The numerical results conclude that the effects of reinforcement ratio on the peak load, stiffness, and deflection are obvious while the influence of steel grade is mainly on the peak load. The tensile localization strain of PVA-ECC mainly affects the ductility of the beam. Furthermore, a design method is proposed based on the plane-section assumption to calculate the ultimate load of reinforced PVA-ECC beams, in which the contribution of PVA-ECC to the moment resistance of beam sections is considered. Comparisons between existing design methods and the proposed method indicate that the ultimate load of beams can be predicted more accurately by considering the tensile strength of PVA-ECC in the tension zone.

Experimental tests and analytical model for reinforced polyvinyl alcohol‐engineered cementitious composite beams in bending

AbstractPolyvinyl alcohol‐engineered cementitious composite (PVA‐ECC) exhibits strain hardening and multiple cracking characteristics under tension. Its superior tensile behavior may also influence the flexural behavior of reinforced PVA‐ECC beams. This paper investigates the load capacity and failure mode of reinforced PVA‐ECC beams in bending. Seven beams with different tensile reinforcement ratios, including six PVA‐ECC beams and one conventional concrete beam, were tested in the experimental program. The influence of reinforcement ratio on load capacity and failure characteristics was discussed in detail. Test results showed that with increasing reinforcement ratio, the ultimate load of beams was increased, but the failure mode was changed from fracture of PVA‐ECC in the tension zone to crushing in the compression zone, thereby limiting the full development of beam ductility. An analytical model is proposed to calculate the load and the vertical deflection of beams. In the model, the tension‐stiffening effect of reinforcement after cracking of PVA‐ECC is considered by defining the bond–slip relationship of reinforcement embedded in PVA‐ECC. Comparisons are made between experimental results in the literature and those calculated by using the analytical model to show the accuracy of the model in predicting the load–deflection relationship, the moment–rotation relationship, and the moment–curvature relationship.

Behavioral assessment of graphene nanoplatelets reinforced concrete beams by experimental, statistical, and analytical methods

The objective of this study was to evaluate the effect of graphene nanoplatelets (GnP) on the mechanical properties of concrete as well as the flexural performance of reinforced concrete (GnP-RC) beams. In the experimental campaign, several dosages of GnP (0.00%, 0.02%, 0.05%, 0.10%, 0.30%, and 0.50% wt of cement) were included in the concrete mixtures. First, the mechanical properties of concrete (compressive, tensile, flexural, and modulus of elasticity) were studied. A further experimental investigation was conducted on the flexural behavior of GnP-RC beams. The failure mode of beams, crack patterns, moment-curvature relationship, and ductility properties are reported. According to the observed results, GnP addition is capable of significantly improving mechanical properties. By adding 0.02% of GnP, both the compressive and tensile strengths were improved by 20.82% and 30.05%, respectively. Additionally, 0.02% of GnP also enhanced the cracking, yielding, and ultimate loads of beams by 36%, 23%, and 15%, respectively. Further, for the same concentration of GnP, the energy absorption and post-cracking ductility were improved by 25% and 20%, respectively. This report also presents analytical and statistical models for predicting the ultimate moment capacity of RC beams containing nano-reinforcement materials. The models have been demonstrated to be accurate at predicting the present and independent data.

Self-Monitoring of Reinforced Concrete Beam Bending with Carbon Nanofiber Polyurethane Composite

To examine the intelligent sensing properties of polyurethane cement mixed with carbon nanofiber and used as beam reinforcement material, 7 reinforced concrete T-beams were made and reinforced with carbon nanofiber polyurethane cement material (CPUC). Four-point bending tests were conducted. Reinforcing concrete beams with CPUC material might increase the yield load and ultimate load of beams significantly. The overall stiffness of the reinforced beam was enhanced. CPUC played a significant inhibitory role in the formation and development of beam cracks. A sudden change in the rate of CPUC resistance can be used to monitor the yield of a steel bar, and then, a safety warning for the components can be launched. By establishing a model of the relationship between the resistance change rate and the external load, the bearing capacity of the beam is evaluated in real time, and the dual effects of reinforcement and health monitoring of the beam are realized simultaneously.

Behaviour of self-repaired reinforced concrete beams made using smart materials under static cyclic loads (shear study)

The aim of the study is to work on developing a pump automatic system capable of supplying the repair materials into expected cracks in shear or tension zones by internal injection epoxy materials. It functions once it receives the signal from crack sensors to measure (crack width and strains) in order to commence the injection after any sudden impact in the structure occurs. The new strengthening methods were experimentally investigated for simply supported concrete beams with internal injected ducts and /or super elastic Nitinol bars under static load in two cycles (loading – off loading) up to failure with different shear reinforcement ratio. The studied parameters were the type of strengthening technique and shear reinforcement ratios.This is in addition to their effect on the loads, deflections, concrete, steel and Nitinol smart bar strain as well as ductility and stiffness that were also analyzed for all tested beams. Results elucidated that the ultimate load of beams having both internal injected ducts and super elastic Nitinol bars has increased by 12% compared with the reference beams; moreover, the deflection and concrete strain at the ultimate load decreased by 31% and 30% respectively. Furthermore, steel and Nitinol strains had small recovery behavior passed 85% of the ultimate load up to the failure due to the effect of the strain recovery of the smart bars.

Effect of Large Openings on the Behavior of Reinforced Concrete Continuous Deep Beams under Static and Repeated Load

This paper aims to investigate the behavior of the existence of large openings on reinforced concrete continuous deep beams (RCCDBs) under static and limited cycles of repeated load. The experimental work included testing seven RCCDBs. One of these beams was solid subjected to static load, while the other beams having external shear spans, internal shear spans, and mid-span openings subjected to static and fifteen cycles of repeated loading. The range of the repeated loading was varied between a lower level and an upper level, equal to 30 and 70 percent, respectively, of the ultimate load of the beam subjected to static load. All test specimens were tested under five-point bending. For beams with large openings, 160×160 mm (which represents 40% of the overall depth of the section) openings were created symmetrically at various locations. Experimental results showed that the maximum ultimate loads of beams with large openings were decreased by about 36% for beams with large openings locating at interior shear spans compared to a solid beam. However, the maximum reduction in ultimate load of the beam with a large opening subjected to repeated load was about 6%.

Effect of small transverse service holes on shear strength of reinforced concrete slender beams

This paper presents the results of a study conducted to investigate the effect of small transverse hole on the shear capacity of slender beams. A total number of ten beams were cast, with concrete grade of C13.02. The cross -sectional dimensions of the beams were 100mm x 150mm, with an effective span of 560mm. The tested beams consisted of two control beams. The experimental beams consisted of eight beams, four of the beams were with 20mm service hole (two beams with holes at the centre and two beams with holes at 220mm from both ends), while the other four had 25mm service holes, with two of beams had holes at the centre, while the other two beams had holes at 220mm from both ends. The beams were subjected to both point load and load at third points. The study shows that the ultimate load of beams with service holes depends on the size of holes, position of holes, and of type loading. Keywords: Slender beam, Concrete, Compressive strength, Control beam, Service hole

Experimental Investigation of Using PET Wastes as Tension Bars in Reinforced Concrete Beams

This research is aimed to study the possibility of recycled the PET wastes by forming the PET wastes as plastic semi-bars and used it as tension bars in simply supported reinforced concrete beams . Twelve beams specimens with dimension of (150*200*1400) mm are casted and tested to monitoring the effecting of these wastes as tension bars on the strengths and serviceability of reinforced concrete beams. The mechanical properties (compressive, splitting tensile and flexural strength) are evaluated in which specimens tested in age of 28 days. The tests results showed that all presented plastic semi-bars are failed except one case in which the deformed steel bar are used with additional layer of PET bottle cut into two parts which showed an increment in ultimate failure load and deflection of 3.03 % and 213.83 % respectively, larger than the reference beam specimens. Negatively effect of PET semi-bar on ultimate load of beams is due to bonding failure between PET bars and surrounding concrete, which made the PET bars as voids or weak region within beam cross section.

Finite element modelling of composite castellated beam

Nowadays, castellated beam becomes popular in building structural as beam members. This is due to several advantages of castellated beam such as increased depth without any additional mass, passing the underfloor service ducts without changing of story elevation. However, the presence of holes can develop various local effects such as local buckling, lateral torsional buckling caused by compression force at the flange section of the steel beam. Many studies have investigated the failure mechanism of castellated beam and one technique which can prevent the beam fall into local failure is the use of reinforced concrete slab as lateral support on castellated beam, so called composite castellated beam. Besides of preventing the local failure of castellated beam, the concrete slab can increase the plasticity moment of the composite castellated beam section which can deliver into increasing the ultimate load of the beam. The aim of this numerical studies of composite castellated beam on certain loading condition (monotonic quasi-static loading). ABAQUS was used for finite element modelling purpose and compared with the experimental test for checking the reliability of the model. The result shows that the ultimate load of the composite castellated beam reached 6.24 times than the ultimate load of the solid I beam and 1.2 times compared the composite beam.

Investigation on Flexural Performance of RC Beams Flexurally Strengthened by Soffit-Bonding and Side-Bonding CFRP Sheets

It is an effective way to increase the flexural performance of reinforced concrete (RC) beam by externally bonding fiber reinforcement polymer (FRP) laminate on the soffit of the beam. However, there is little investigation on flexural behavior of RC beam by side-bonding FRP laminates. To investigate the difference of flexural behavior between soffit-bonding and side-binding FRP laminates RC beams, a total of 9 RC beams were tested, including 8 strengthened beams and 1 control beam. The test results showed that: the first crack load of RC beam strengthened by side-bonding CFRP laminates is much bigger than that of RC beam strengthened by soffit-bonding CFRP laminates.The first crack load of side-bonding CFRP laminates beams improved significantly;side-bonding and soffit-bonding methods have the same effect on the flexural stiffness of RC beams with same quantity of CFRP laminates before tension steel rebar yielding. However, side-bonding can remarkably decrease the crack width and change the crack pattern.Side-bonding of CFRP laminates can extend the pre-crack stage of the strengthened beam;the first yielding load and the ultimate load of beams cannot be improved significantly by side-bonding FRP laminates.

BEHAVIOUR OF REINFORCED HIGH-STRENGTH CONCRETE BEAMS WITH OPENINGS SUBJECTED TO STATIC AND REPEATED LOADINGS

This paper presents the results of an experimental research on reinforced high strength concrete beams with web rectangular openings to determine their behaviour and ultimate strengths, and to compare these strengths with those predicted using the available equations. Test variables were length of openings, details of steel reinforcement around the openings, longitudinal main steel ratio, and type of loading (static-repeated). Test results showed that the ultimate load of beams with openings reduces by about 10 to 45% compared to similar solid beams. Provided that the same amount and scheme of reinforcement used, an increase in opening length, decreases both stiffness and strength of the beam. Diagonal bars at corners of openings results in spreading of cracking away from openings and reducing beam deflection, but it does not have significant influence on strength of the beam. The effects of transverse openings on overall response of reinforced concrete beams in shear becomes remarkable as main steel ratio (ρ) increases. Increasing shear reinforcement (stirrups) in the top and bottom chords of the openings increases slightly the cracking load; while increases significantly the ultimate load. Repeated load has no effect on either strength or mode of failure of the tested beams. The available equations do not produce satisfactory results for predicating the ultimate shear strength of highstrength concrete beams with openings.

Experimental and Theoretical St.udy on Maximum Reinforcement Ratios of High Strength Concrete Flexural Beams

In the current study, experimental and analytical analysis were carried out to propose models for the maximum reinforcement ratios for high strength concrete flexural beams and to compare the behavior of HSC beams with normal strength concrete beams with respect to this point of view. The behavior is represented by failure mode, ultimate load, deflection and strain. The failure mode of HSC beams is relatively different than that of normal strength beams and this is mainly due to the higher degree of brittleness of HSC. High strength beams require more quantity of steel reinforcement to achieve the ductility. Using HSC leads to an increase of the cracking and ultimate loads of beams and to a decrease of ductility. The steel reinforcement of HSC beams should be increased in such a way that yielding of steel should occur first before crushing of concrete to avoid brittle failure. From the given results of failure mode, load deflection relations and from recording the propagation of cracks and failure mode of beams and following the concept of the required steel reinforcement which is given by the code for normal strength concrete, the required reinforcement of HSC flexural beams is determined and given by equations 4 and 5 in the text. The equations are applicable to all grades of concrete (normal and high strength concrete). Analytical analysis is carried out to consider the effect of size of cross section on the required reinforcement. Nonlinear plane stress finite element model is utilized to give the required steel reinforcement considering the size effect. Based on experimental and theoretical results and by using parametric analysis and curve fitting, a model of the maximum required steel reinforcement of high strength concrete flexural beams considering the effect of size is recommended and represented by equation 15 in the text. The model is recommended to be used in the design of beams.

Estimate of the Ultimate Load on Structural Members Subjected to Lateral Loads

This paper examines plastic behavior of typical ship structures, specifically beams, grillages, and plates subjected to predominantly lateral loads. The ultimate loads, determined on the basis of the theorems of limit analysis [1,2], are evaluated using nonlinear finite-element plastic analysis. The relationships between analytical and finite-element models for prediction of ultimate loads of beams, stiffened panels, and grillages are illustrated. It has been shown that the ultimate loads, obtained from the theorems of limit analysis, can be successfully used for strength assessment of stiffened ship structures subjected to lateral loads. The effect of shear force on ultimate load is analyzed using the finite-element method. This paper confirms that in the case of beams and grillages under lateral loading, the ultimate load may characterize the threshold of the load at which a stiffened ship's structure fails by the development of excessive deflections. For plate elements, on the other hand, the plastic deflections represent the permissible limit of external load better than the ultimate limit load.

Prediction of the behaviour of RC beams with exposed reinforcement

The paper reports details of a fairly simple theoretical model for estimating the flexural ultimate load of reinforced concrete beam under two-point loading in which the main reinforcement over part of the span is fully exposed in a symmetrical fashion about the mid-span in the course of the patch repair process prior to the application of the repair materials. Encouraging correlations have been found between the theoretical predictions and large-scale experimental data reported by others, which covered a wide range of design parameters. Theoretical numerical results throw some light on the perhaps initially puzzling experimental observations reported previously that the ultimate loads of beams with exposed reinforcement can increase significantly if nominal top steel (in the form of, for example, 2 × 6 mm dia. bars), such as is invariably used for holding stirrups in place, is used. Numerical results are presented that show the influence of various parameters (concrete cube strength, length of exposed main reinforcement, depth of removal of concrete, etc.) on the ultimate loud-bearing capacity of beams with exposed main reinforcement.