Flexural Strength Of Beams Research Articles

Flexural Capacity of Full-Depth and Two-Lift Concrete Slabs with Recycled Aggregates

Full-depth and two-lift concrete slabs were cast with fractionated reclaimed asphalt pavement and recycled concrete aggregate as partial and full replacements of the coarse aggregate in a ternary blend concrete containing cement, slag, and fly ash. These large-scale slabs were monotonically loaded at the edge to quantify the effect of recycled aggregates on the slab's flexural capacity. Although the introduction of these recycled aggregates into the concrete reduced the compressive, split tensile, and flexural strengths as well as the elastic modulus of the concrete relative to virgin aggregate concrete, fracture testing demonstrated that recycled concrete aggregate can have fracture properties statistically similar to those of virgin aggregate concrete. Testing of the flexural capacity of the slabs revealed that concrete with recycled aggregates had peak loads at failure similar to or greater than those of virgin aggregate concrete despite a significant difference in beam flexural strength. The calculated tensile stress in the slab at flexural failure was underpredicted by the beam flexural strength by a factor of 1.5 for virgin aggregate concrete and 1.9 to 2.7 for concrete with recycled aggregates; these findings demonstrate that the beam flexural strength results are not always reliable predictors of slab capacity, especially with recycled aggregates. Because of lower beam flexural strengths with recycled aggregates, pavement engineers should compare the fracture properties of concrete containing recycled aggregate with those of typical virgin aggregate concrete before deciding whether to increase the required concrete slab thickness.

Fracture Properties of Roller-Compacted Concrete with Virgin and Recycled Aggregates

Roller-compacted concrete (RCC) pavement has renewed interest among designers as a sustainable pavement option with the potential to lower total cement content, incorporate recycled aggregates, reduce road closure time, and decrease total project costs. One main design challenge is whether RCC can achieve the same performance life as conventional portland cement concrete (PCC) pavement with similar slab thickness. This research investigated the strength and fracture properties of RCC containing virgin aggregates and fractionated reclaimed asphalt pavement (FRAP) relative to conventional PCC to address this design challenge. The compressive and split tensile strengths of the RCC mixes showed similar strengths to the same constituents in PCC. RCC containing FRAP had lower strengths than did RCC with virgin aggregates. The critical stress intensity factor and the initial and total fracture energies were not statistically different between the RCC mixes containing virgin and FRAP aggregates. Overall, the RCC fracture properties were found to be significantly higher than those of conventional PCC. At lower stress ratios, RCC fatigue data from laboratory beam tests predict lower fatigue life relative to PCC; this result translates to a thicker RCC pavement. Large-scale testing has shown that the flexural capacity of PCC slabs is strongly related to the concrete fracture properties despite differences in beam flexural strength. Because these RCC fracture properties were shown to be higher than similar constituents used in conventional paving concrete, RCC designs could employ similar PCC fatigue curves for certain conditions, such as when the RCC fracture properties are equivalent to or greater than those of conventional PCC.

Minimum column-to-beam strength ratios for beam–hinge mechanisms based on multi-objective seismic design

The current strong-column weak-beam design criterion presents a single value as the acceptance limit of strength ratios for Special Moment Resisting Frames (SMRFs). However, previous research efforts have shown that the required column–beam flexural strength ratios of joints in SMRFs vary with the factors such as the height of frames. Therefore, in this paper, the multi-objective seismic design method based on nonlinear static analysis is proposed and applied to find optimal column-to-beam strength ratios required for ensuring the beam–hinge mechanism. In this formulation, the optimal method is to minimize the two objective functions of the structural weight as well as the column-to-beam strength ratio while satisfying the constraints. Based on multiple Pareto-optimal solutions with beam–hinge mechanisms, the relationship between the structural weights and optimal strength ratios is provided. Using the well-known two moment resisting example structures, instead of suggesting a specific single value as a limit for the column–beam flexural strength ratio, a common tendency is identified through investigating the relationships between optimal strength ratios and structural weights.

An Experimental Study on Flexural Behavior of Reinforced Concrete Beams with GFRP Bars and Recycled Coarse Aggregate

This study evaluates the flexural performance of reinforced concrete beams with GFRP(Glass Fiber Reinforced Polymer) bars and RCA(Recycled Coarse Aggregates). A total of four specimens with various replacement ratios of RCA (0%, 30%, 50%, and 100%) were tested. An investigation was performed on the influence of RCA with various replacement ratios on load-carrying capacity, post cracking stiffness, cracking pattern, and ductility. The test results showed that replacement ratios of RCA had not a bad effect on concrete compressive strength or flexural strength of beams. They were compared with the design flexural strength and the nominal moment predictions of ACI Code.

전단스프링과 섬유요소를 이용한 철근콘크리트 전단벽의 비선형 해석모델에 관한 연구

철근콘크리트 전단벽을 모델링하기 위해서 섬유요소와 전단스프링을 사용한 모델을 개발하였다. 섬유요소는 전단벽의 휨변형을 나타내며, 전단스프링은 전단변형을 나타낸다. 섬유요소는 단면치수와 비선형 재료성질을 입력하여 모델링되며, 전단스프링은 섬유요소모델과 VecTor2프로그램의 해석 결과로부터 그 변수들을 선정한다. 전단스프링은 전단변형에 의한 강도ㆍ강성 감소, 핀칭효과, 그리고 슬립현상을 모사할 수 있는 OpenSees의 Pinching4 모델을 사용하였다. 전단스프링의 변수선정과정은 복잡하고 시간이 오래 걸린다. 따라서 섬유요소모델의 사용성을 검토하기 위해 전단벽의 형상비(H/L), 보의 높이변화, 그리고 보와 전단벽의 강성비ㆍ휨강도비를 변수로 하여 전단벽 건물에 동적해석을 수행하였다. 전단벽의 형상비는 섬유요소모델을 사용한 모델과 섬유요소와 전단스프링을 함께 사용한 모델의 층간변위비 오차와 일정한 관계를 가진다. 하지만 보의 높이변화와 강성비ㆍ휨강도비 변화에 두 모델의 오차는 일정한 관계를 보이지 않는다.

FLEXURAL STRENGTH OF CFRP BOX BEAMS WITH DIFFERENT LAMINATE STRUCTURES

This paper presents an experimental study on the flexural strength of CFRP box beams with two laminate structures: a cross-ply (CP) and a quasi-isotropic (QI). Three specimens were prepared for each laminate structure. The specimens were tested under four point bending, and the material tests of each laminate structure were conducted. The bending tests showed that QI exhibited higher flexural strength than CP and that they had different failure configurations. Also, flexural strength is calculated based on beam theory with Tsai-Wu criterion or maximum stress criterion to be compared with the experimental one. Moreover, in order to discuss a buckling behavior, buckling stress is calculated. It is shown that the calculated flexural strength based on Tsai-Wu criterion agrees well with the experimental one and that the buckling stress exhibits higher value than compressive stress at the flexural strength in the bending test.

Experimental Investigation on the Seismic Performance of Large-Scale Interior Beam-Column Joints with Composite Slab

The experimental and analytical investigations carried out on large-scale interior precast beam to column joints with composite slab are presented in this paper. Four specimens were tested under reversed cyclic loading that simulated earthquake-type motions. The most relevant feature of the joint is that the beam reinforcement on the bottom was formed and installed with anchor head, rather than bent to form stand 90-degree hooks or closed loops. The performance of the precast concrete connection was compared with that of the monolithic connection, and the failure pattern, hysteretic characteristic, skeleton curve, displacement ductility and energy dissipation, were analyzed. The test results provided some information about the seismic behavior of the large-scale joint. In general, the performance of the joint was satisfactory. No bond problem and obvious pinching effect were observed in the test, and specimen behavior was ductile and joint strength was almost equal to that of monolithic reinforced concrete construction, however, the ductility of the specimens was affected by the ratio of column to beam flexural strength, and the scope of application was recommended.

A Parametric Study of the Reinforced Concrete Slab Subjected to Dynamic Excitation

The width of effective slab to estimate the beam flexural strength at the beam ends in structures subjected to lateral loading, such as earthquake, is not explicitly addressed in design codes. As a result, designers often ignore the contribution of floor slabs to the lateral load resistance. There is a need for a simple model to assess the slab contribution to beam strength for analysis and design. General expressions for the yield loading and stiffness characteristic of the slab element have been developed which is more sensitively depend on yield line theory beside other parameters such as spacing, yield strength, area of reinforcement, and the span length. A model considering beam growth, bending effects and the slab effect is being considered in the present work. The results of the analytical investigation are compared with experimental results. The slab element model is then used to conduct a parametric study aiming to investigate the effect of the distribution and strength of the slab steel. It is shown that the performance of the unit is directly related to this steel.

Flexural performance of CFRP strengthened RC beams with different degrees of strengthening schemes

Externally bonded carbon fiber reinforced polymer (CFRP) composite laminates have been successfully applied to reinforced concrete (RC) beams and other structural elements for the purpose of increase load carrying capacity of such elements. This paper presents the experimental results on the flexural strengthening of reinforced concrete beams by CFRP laminates attached to the tensile soffit of the beams by epoxy adhesive. A total of six reinforced concrete beams having different degrees of strengthening scheme were tested to failure under transverse bending over an effective span length of 1900 mm. The increase of ultimate strength provided by the bonded carbon fiber was assessed by varying the layers of composite laminates. The results indicate that the flexural strength of beams was significantly improved as the layers of laminate increased. No de-lamination of the superimposed CFRP plates was observed from the test. However, de-bonding of CFRP laminates from concrete surface was observed for the case of multi-layer strengthening of beam. It is concluded that the attachment of CFRP laminates with edge strip plates has substantially influenced the performance of CFRP strengthened beams. The paper also highlighted the beams failure modes due to the different level of strengthening scheme.

Simplified method for the analysis of externally prestressed steel–concrete composite beams

The ultimate capacity of beams prestressed with external slipping tendons cannot be evaluated by a local analysis of the critical sections and a nonlinear analysis of the whole beam-tendon structural system is required. Since this type of analysis is complex, simplified approaches are of great assistance to engineers in the design process. In this work a new simplified method is introduced for evaluating the tendon traction increment at collapse and consequently the beam flexural strength without requiring a nonlinear analysis of the whole beam-tendon structural system. A detailed description of the proposed approach is given and some applications of practical interest to externally prestressed steel–concrete composite beams are discussed.

Various Fatigue Testing of Polycrystalline Silicon Microcantilever Beam in Bending

With the vast potential of micro-electro-mechanical systems (MEMS) technology, the reliability is essential for the successful applications of microdevices. Polycrystalline silicon is one of the most often used structural materials in microdevices. Tension testing for fatigue life of this material has been investigated since past years. This paper presents a micro-actuator-based bending testing system as well as a MTS Tytron250 micro-tensile-force testing machine to study the fatigue of microbeams in bending. The polycrystalline silicon microcantilever beams are fabricated on silicon wafer. The influence of various dimensions and stress on the fatigue endurance is studied when an external force is loaded on the microcantilever beam. The flexural strength of beams are calculated by the ANSYS. Based on the experimental results and ANSYS analysis, it shows that the longer specimen reduces the stresses when the displacement, width and thickness are kept the same. When the width varies, the larger width results in higher stresses. The fatigue life lies between 9.1 ×105–1.53 ×107 cycles in use of the testing machine. For microactuator testing experiment, the fatigue life persists up to million cycles without failure. The obtained results are compared with the references of different testing methods.

A Method for Predicting the Flexural Strength of RC Beams Strengthened with Carbon Fiber Reinforced Polymer

An extensive experimental study has shown that the external bonding of carbon fiber reinforced polymer (CFRP) laminates or carbon fiber sheets (CFS) to the tension face of concrete beams is an effective strengthening method to increase the flexural load capacity and the stiffness. The strengthening mechanism relies on composite action between the concrete and the laminate. If composite action is not fully achieved, the strengthening effect will not be realized. Test results have indicated that the local failure of the concrete layer between the bonded laminate and longitudinal reinforcement in retrofitted beams is predominant. Premature failure due to debonding always occurs before the full composite action of the bonded laminate to the strengthened beam is reached. The ultimate tensile strength or strain of the laminate may not be fully utilized due to the debonding failure; however, through proper design of the strengthening system, an effective (maximum) laminate strain of the bonded CFS can be achieved. This effective laminate strain can be used for the prediction of the flexural behavior of the strengthened beam. A design-oriented expression for determining an effective laminate strain has been developed. This expression accounts not only for the laminate length and the laminate width but also for the stiffness of the laminate, as well as the stiffness of the member to which the laminate is bonded. Close agreement with the experimental results indicates the accuracy of the proposed method. It can predict correctly the debonding failures for all the tests in this study.

Performance evaluation of steel reduced flange plate moment connections

AbstractThis study details a new moment connection that overcomes difficulties in achieving field‐weld quality and eliminates steel beam buckling encountered in steel moment connections. This study presents cyclic test and finite element analysis results of full‐scale subassemblies using steel reduced flange plates (RFPs) to connect steel beam flanges and the column without any other direct connection. Since the RFP connection is designed as strong column‐strong beam‐weak RFPs, the RFP functions as a structural fuse that eliminates weld fractures and beam buckling. Test and analytical results show that (1) the connections transferred the entire beam flexural strength to the column and reached an interstorey drift of 4% with minor strength degradation, (2) failure of the connections was owing to buckling or fracturing of the RFP and not of the beam, and (3) the RFP connection subassembly, modelled using the nonlinear finite element computer program ABAQUS, exhibited hysteretic behaviour similar to that of the flange plate (FP) moment connection subassembly. The inelastic buckling force of the RFP was also evaluated by nonlinear regression analyses performed on a nonlinear model that relates buckling force to RFP geometries. Copyright © 2007 John Wiley & Sons, Ltd.

Impact of Reinforcement Corrosion on Ductile Behavior of Reinforced Concrete Beams

This paper reports an experimental study of concrete beams with corroded reinforcement to investigate their failure modes and ductility behavior. Before the beams were simply supported and monotonically loaded to failure, they were subjected to a process of electrochemically accelerated corrosion. The experimental results show that, in addition to reducing beam flexural strength, corrosion alters its failure modes and affects its ductile behavior substantially. When the response of a beam is dominated by cracking of its compression concrete and/or the reduction of its tension bar area, corrosion improves beam ductility. When the behavior of a beam is controlled by deterioration of its bond strength and/or the reduction of its steel ductility, however, corrosion decreases beam ductility. This raises a concern regarding the ductility of commonly used under-reinforced beams if the amount of corrosion exceeds approximately 10% because the beam could fail suddenly by the rupture of its corroded tension reinforcement due to the ultimate strain of the latter being reduced considerably.

Flexural Behavior of Two-Span Continuous Prestressed Concrete Girders with Highly Eccentric External Tendons

[Abstract]: It is generally known that the flexural strength of beams prestressed with external tendons is comparatively lower than that of members with internal bonded tendons. One possible method of enhancing the flexural strength of such beams is to place the tendons at high eccentricity. To obtain an insight into the flexural behavior of beams with highly eccentric tendons, an experimental investigation is conducted on single-span and two-span continuous beams. The test variables include external tendon profile, loading pattern on each span, casting method, and confinement reinforcements. It is found that continuous girders with linearly transformed tendon profiles exhibit the same flexural behavior irrespective of tendon layout. The presence of confinement reinforcement enhances the ductility behavior but does not increase the ultimate flexural strength. The degree of moment redistribution is affected by the tendon layout and the loading pattern on each span. The results of the experimental investigation are discussed in this paper.

Effect of Beam Growth on Reinforced Concrete Frames

In well-designed reinforced concrete frames subjected to earthquake shaking, flexural yielding and cracking occur at the ends of the beams as they undergo large lateral displacements. As the cracks form, the horizontal distance between column centerlines increases. This is known as “beam growth” and it causes an increase in member demands that is not generally taken into account in analysis used for building design. This paper describes the mechanism of beam growth, observations of it from previous experimental studies, the development and calibration of analytical models considering and ignoring beam growth, and static and dynamic inelastic frame analyses to quantify beam growth effects. Changes in beam axial forces, beam flexural strength, and column moments and shears are quantified for several frame configurations. It is shown that the column demand due to beam growth tends to be greatest at the first story level and this demand tends to be most severe in frames with deep beams and with many bays. For...

Behavior of CFRPC strengthened reinforced concrete beams with varying degrees of strengthening

This paper summarizes the results of experimental and analytical studies on the flexural strengthening of reinforced concrete beams by the external bonding of high-strength, light-weight carbon fiber reinforced polymer composite (CFRPC) laminates to the tension face of the beam. Four sets of beams, three with different amounts of CFRPC reinforcement by changing the width of CFRPC laminate, and one without CFRPC were tested in four-point bending over a span of 900 mm. The tests were carried out under displacement control. At least one beam in a set was extensively instrumented to monitor strains and deflections over the entire range of loading till the failure of the beam. The increase in strength and stiffness provided by the bonded laminate was assessed by varying the width of laminate. The results indicate that the flexural strength of beams was significantly increased as the width of laminate increased. Theoretical analysis using a computer program based on strain compatibility is presented to predict the ultimate strength and moment-deflection behavior of the beams. The comparison of the experimental results with theoretical values is also presented, along with an investigation of the beam failure modes.

Retrofitting reinforced concrete beams by bolting steel plates to their sides -Part 1: Behaviour and experiments

A procedure has been developed for bolting steel plates to the sides of existing reinforced concrete beams which can be used to increase the shear strength of beams, increase the flexural strength of beams with enhanced ductility or with only a small loss of ductility, and increase the stiffness of beams in order to reduce deflections and crack widths. It will be shown in this paper, through a qualitative analysis and through the results of testing eight large scale beams, that standard rigid plastic analysis techniques which are commonly used in the design of reinforced-concrete, steel, and composite steel and concrete beams cannot be used directly to design composite bolted-plated reinforced-concrete beams. In the companion paper, quantitative procedures will be used to adapt the standard rigid plastic analysis techniques for this relatively new form of retrofitting.

高速載荷を受けるポストテンションPRCはりの動的曲げじん性に関する実験的考察

This paper presents an experimantal study on the dynamic flexural toughness of post-tension prestressed reinforced concrete beams. The elastic plastic behavior and the flexural toughness of the pretension prestressed concrete beam, the pretension prestressed reinforced concrete beam and the post-tension prestressed reinforced concrete beam were evaluated and compared by the static and high speed loading tests. Under the static loading condition and the same flexural strength of beams, the ultimate deformation of the post-tension prestressed reinforced concrete beam is clearly larger than those of the pretension prestressed reinforced concrete beam and the pretension prestressed concrete beam. On the other hand, although the order of the ductility in case of high speed loading test is not different from that of static loading test, the ultimate deformations in the high speed loading became smaller than those of the static loading.

Processing and Properties of IM7/PETI Composites

A phenylethynyl terminated imide (PETI) oligomer from the reaction of 3,3',4,4'-biphenyltetracarboxylic dianhydride, an 85:15 molar ratio of 3,4'-oxydianiline and 1,3-bis(3-aminophenoxy)benzene and 4-phenylethynylphthalic anhydride as the end-capper at a theoretical number average molecular weight (Mn) of - 5,000 g/mol was evaluated as a composite resin matrix. Unidirectional prepreg was made by coating an N-methylpyrrolidinone solution of the amide acid oligomer onto unsized IM7. The thermal and Theological properties and the solvent/volatile depletion rates of the amide acid/NMP system were determined. This information was used to successfully design a molding cycle for composite fabrication. Composites molded under 1.38 MPa at 371°C consistently yielded good consolidation as measured by C-scan and optical photomicrography. Composite mechanical properties at various temperatures included short beam shear strength, flexural strength and modulus, longitudinal compression strength and modulus (IITRI), longitudinal tensile strength and modulus and open hole compression (OHC) strength. These composites exhibited excellent resin dominant properties. The OHC strength values, in particular, suggested that PETI composites have excellent damage tolerance.