Shear Resistance Of Concrete Research Articles

Assessment of concrete shear resistance of lightweight SCC beams containing scoria aggregates

Lightweight self-consolidating concrete (LWSCC) has become a construction material that combines the benefits of lightweight concrete (LWC) and self-consolidating concrete (SCC). However, this combination may affect the shear resistance of structural members made with such concrete. This paper evaluates the shear resistance and performance of LWSCC beams. Eight full-scale beams without stirrups were fabricated and tested to failure. Seven beams were constructed using LWSCC and one was cast using normalweight self-consolidating concrete (NWSCC). Natural lightweight coarse and fine scoria aggregates were used in preparing the concrete mix. The beams were tested over a simply supported span in a two-point loading configuration. The test parameters comprised the type of aggregates, the reinforcement ratio of longitudinal steel bars, the shear span-to-depth ratio, and the depth of the beam. The experimental results showed that employing scoria aggregates in the mix resulted in beams with a reduced self-weight, where the obtained unit weight of LWSCC was 1800 kg/m3. Compared to the beam with NWSCC, the counterpart beam with LWSCC showed 25% lower shear strength. Additionally, the LWSCC beam experienced a reduction of 20% in the flexural cracking load while the beam showed a larger number of cracks at failure. The shear strength of the beams was predicted using the relevant shear design provisions of the American Concrete Institute building code ACI 318, the Canadian standard CSA-A23.3, and Eurocode 2. The ACI 318 method provided more reliable and conservative estimates for the shear capacity of the tested beams.

Punching shear strength under static and dynamic loads

Modern domestic calculation methods and developed countries for determining the bearing capacity of monolithic reinforced concrete slabs for punching do not fully take into account all factors of design solutions and operating conditions. The available design provisions are made for the static operation of structures and there are no recommendations for taking into account the features of the dynamic impact on the overlap and the nature of the work of the node interfaces. The accepted empirical assumptions of the calculation, based on numerous experimental data, do not take into account the features of the stress-strain state of the coupling of the overlap with the column during destruction according to the punching scheme. This is due to the lack of computational models in which all the acting internal forces ensuring the resistance of the interface to penetration would be considered comprehensively. The complexity of the problem is due to the fact that the sections of the nodal interface are in an inhomogeneous stressed state. The stress-strain state of plates for punching under dynamic load is currently little studied. This article proposes a method for determining the bearing capacity of a symmetrical nodal coupling of a column with an overlap for punching under static and short-term dynamic loading. The proposed design model of the punching strength is based on the following prerequisites: the resistance to punching of a monolithic reinforced floor consists of the shear resistance along the surface of the reduced punching pyramid formed by the height of the compressed concrete zone; the strength of the concrete shear resistance increases due to volumetric compressive forces on the surface of the reduced punching pyramid; the angle of inclination of the faces of the punching pyramid depends on the loading speed. The obtained theoretical dependences are applicable under static and dynamic loading and are in satisfactory agreement with experimental data.

Shear Resistance of Low Height Precast Concrete Lintels

The scope of the paper is to investigate analytically and determine experimentally the shear resistance of low height reinforced precast concrete lintels. The chosen procedures included in national and international standards applied for the design of structural concrete elements to an estimation of shear behaviour of reinforced concrete elements are described. The characteristic and designed shear strength of precast concrete lintels are determined and compared with experimentally obtained results. The shear resistance for precast concrete lintels was determined by laboratory tests according to a European standard. The assessment of the in-situ compressive strength of concrete in precast concrete lintel is specified. The designed compressive strength class is confirmed. The real reinforcement distribution is verified to assess the wide scatter of experimentally obtained failure forces. A short literature outlook of the papers concerning investigations on lintels and shear resistance of concrete is given also. The paper can provide scientists, engineers, and designers a theoretical and experimental basis in the field of precast concrete lintels shear resistance.

Bending and shear behaviour of two layer beams with one layer of rubber recycled aggregate concrete in tension

This paper presents the results of an experimental, numerical and analytical study of bending and shear behaviour of simply supported reinforced concrete beams with two layers of different grades of concrete. The top layer (1/3rd) concrete, mainly in compression, is higher grade, and the bottom (2/3rd) layer, in tension, is lower grade using rubber recycled aggregate concrete. A total of 8 tests were conducted. The results confirm that the two layer beam achieves the same bending resistance as the control reinforced concrete beam made entirely of the higher grade concrete.In beams without shear reinforcement, the two layer beam attained lower shear resistance than the control beam. This was attributed to the unzipping effect: once the lower strength concrete has failed in shear, it loses its shear resistance and transfers the shear force from the failed lower strength concrete to the control concrete. Further FE simulations reveal that the top layer higher grade concrete plays no role in influencing the beam's shear resistance. Therefore, when calculating shear resistance of concrete of the two layer beam, the lower concrete grade should be used. However, since the shear force in reinforced concrete beams is mainly resisted by shear links, the lower shear resistance of rubber recycled aggregate concrete has very minor implication on beam shear resistance.The proposed construction facilitates wider adoption of recycled concrete without having to undergo expensive processes to achieve the same mechanical properties of concrete made of fresh aggregates.

Behavioral Study of RC Beams Designed for Shear Using CFP and ACI Code Models

Compressive Force Path concept is a proposed shear design method to explain shear behavior in reinforced concrete beams. This concept identifies 04 behaviors based on the shear span to beam depth (a/d) ratio and provides detailed shear design and transverse reinforcement detailing procedure for each behavior. Therefore, author of this paper intended to use this concept as a practical tool for the designing of RC beams particularly for Type II (2 ≤ a/d < 5) and Type III (1 < a/d < 2) behaviors to validate the concept. Total 08 beams of 100×200×1800 mm size beams were cast; out of which, 04 beams were designed according to ACI Code approach while, rest were designed and detailed using CFP concept strategy. The beam sizes in this study are identical and all parameters are constant except shear span 'a'. The two-point loading test results of RC beams showed that the shear resistance of concrete is better estimated by the CFP concept with a good prediction of cracks pattern, load carrying capacity and actual behavior of the beams in shear as compared to the beams designed according to ACI Code approach. However, most of the beams, particularly a/d ratio less than 4.44 were observed to be deficient in serviceability and failed in shear in spite of attaining theoretical predicted loads.

SHEAR MECHANISM AND SHEAR STRENGTH PREDICTION OF REINFORCED CONCRETE T-BEAMS

Shear failure in reinforced concrete beams are sudden failures and should be avoided at all times. However, the shear behaviour of a reinforced concrete beam is a complex mechanism and requires in-depth study. To understand the shear mechanism, two (2) simply supported reinforced concrete T-beams, BEAM1 and BEAM2 were tested until failure subjected to a 4-point bending test. Both beams were designed to the recommendations and specifications of two (2) established design codes by ACI318-08 and Eurocode2 (EC2). The study comprises of two reinforced concrete T-beams having similar variables and parameters with longitudinal reinforcement of ρ = 2.15% and shear span-to-effective depth ratio (av/d) of 3.5. Shear reinforcement or stirrups has been added to the specimen and its spacing of stirrups has been provided with the provisions of the codes. The findings from the study indicate that ACI318-08 and EC2 design codes shows significant differences in determining its shear strength capacity Vn and concrete shear resistance Vcof the T-beams. However, both results were less conservative in its prediction when compared to the experimental results.

Shear enhancement in RC beams with multiple point loads

Eurocode 2 (EC2) allows short shear spans in reinforced concrete beams with loads near supports to be designed using either its shear provisions or strut and tie models (STM). In the case of beams with loads applied on their upper side within a distance av⩽2d from the edge of supports, EC2 allows the contribution of these loads to the design shear force to be reduced by the multiple β=av/2d⩾0.25 (where d is the beam effective depth). Conversely, the previous UK code BS8110 increases the shear resistance provided by the concrete within 2d of supports to vc/β (in which vc is the concrete shear resistance in MPa) up to a maximum shear resistance of 0.8fcu or 5MPa. The two methods are only equivalent for beams without shear reinforcement and single point loads within 2d of supports. However, there is a lack of test data to assess the comparative merits of the two methods and STM for beams with multiple point loads within 2d of supports. Therefore, twelve beams were tested with up to two point loads within 2d of supports. Significantly, BS8110 is found to give better estimates of shear resistance than the EC2 shear provisions. STM gives good predictions of shear resistance if strut strengths are calculated in accordance with the recommendations of the modified compression field theory (MCFT) but some unsafe predictions are obtained when using EC2 strut strengths.

Rational Approach to Prediction of Shear Capacity of RC Beam-Column Elements

This paper presents a new predictive formula for the shear capacity evaluation of reinforced concrete members subjected to combined axial, bending, and shear forces. The formula is based on a tensorial approach to concrete shear resistance that is very similar to the one used in the shear-enhanced fiber beam element. The total shear resistance is broken down into the contribution of concrete and contribution of shear reinforcement. The concrete contribution to the shear resistance is calculated using a normal-shear stress failure envelope. Normal (longitudinal) stresses are calculated from axial and bending forces acting on the concrete member. In the formulation, a number of simplifications are made to keep the formula as simple as possible but still sufficiently accurate. The resulting formulation, although capable of accounting for all of the major variables that influence the shear strength, including size effect, remains particularly simple and with a compact notation. The predictions of the proposed formula are compared with those used by the American Concrete Institute (ACI), the European Committee for Standardization (CEN) Eurocode, and the International Federation for Structural Concrete (fib) model code, and its accuracy is checked against a vast experimental database available in the literature. Results and comparisons are very encouraging and confirm the soundness of the underlying mechanical model. The capability of this model to provide a unified approach for reinforced and unreinforced members opens up the possibility to extend the application of the proposed formula to engineered cementitious composites, such as fiber-reinforced concrete.

Influence of Stirrup Corrosion on Shear Strength of RC Beams

There have been few reports on shear behavior of reinforced concrete (RC) beams with corroded stirrups, and the influence of stirrup corrosion has yet to be identified. Given this background, experience was carried out to investigate the shear behavior of RC beams containing corroded stirrups. Investigation results indicate that if the percentage local maximum mass loss is below 35%, there is little influence on the load-carrying mechanism. The concrete shear resistance seems to change little and the shear capacity can be calculated by just taking into consideration the reduction in stirrup shear resistance. It is also found that the anchorage conditions of the stirrups have a predominant influence on the shears of RC beams.

Effects of Continuity Plate and Transverse Reinforcement on Cyclic Behavior of SRC Moment Connections

Two exterior moment connections with a steel-encased reinforced concrete (SRC) column and a steel beam were tested to evaluate the cyclic performance. Continuity plates were eliminated in the first specimen, and about 60% of the transverse reinforcement as specified in the ACI 318 was used in the connection region. Two steel doubler plates offsetting from the column web were used to enhance the shear resistance of the connection. The second specimen used a steel jacket to confine the concrete in the connection region and continuity plates were extended from the steel column to the steel jacket to mobilize the shear resistance of the latter; no transverse reinforcement was used. Full-scale test results showed that both specimens were able to reach an interstory drift ratio in excess of 4%. An analytical model was developed for the concrete shear force transfer mechanism in the connection of the second specimen. This study showed that: (1) using either doubler plates or jacket plates was effective to enhance the shear capacity in the connection, (2) concrete shear resistance degraded before the maximum applied load was reached in the first specimen, (3) the concrete was mobilized to resist shear in the second specimen, and (4) transverse reinforcement as required by the ACI 318 (1995) can be relaxed as long as another shear-resisting mechanism such as doubler plates or jacket plates is provided.

Shear resistance of self-consolidating concrete beams — experimental investigations

Self-consolidating concrete (SCC) is a new generation of high performance concrete known for its excellent deformability and high resistance to segregation and bleeding. Lack of information regarding in situ properties and structural performance of SCC is one of the main barriers to its acceptance in the construction industry. There is some concern among researchers and designers that SCC may not be strong enough in shear because of some uncertainties in mechanisms resisting shear — notably the aggregate interlock mechanism. Because of the presence of comparatively smaller amount of coarse aggregates in SCC, the fracture planes are relatively smooth as compared with normal concrete (NC) that may reduce the shear resistance of concrete by reducing the aggregate interlock between the fracture surfaces. The paper compares the shear resistance of SCC and NC based on the results of an experimental investigation on 18 flexurally reinforced beams without shear reinforcements. The test parameters include concrete type, maximum size of coarse aggregate, coarse aggregate content, and beam shear span-to-depth ratio. Shear strength, shear ductility, crack patterns, and failure modes of all experimental beams are compared to analyze the shear resistance mechanisms of SCC and NC beams in both pre- and post-cracking stages. The recommendations of this paper can be of special interest to designers considering the use of SCC in structural applications.Key words: self-consolidating concrete, shear resistance, shear resistance factor, aggregate interlock, dowel action.

Punching Shear Behavior of Fiber Reinforced Polymers Reinforced Concrete Flat Slabs: Experimental Study

This paper presents the results of a two-phase experimental program investigating the punching shear behavior of fiber reinforced polymer reinforced concrete (FRP RC) flat slabs with and without carbon fiber reinforced polymer (CFRP) shear reinforcement. In the first phase, problems of bond slip and crack localization were identified. Decreasing the flexural bar spacing in the second phase successfully eliminated those problems and resulted in punching shear failure of the slabs. However, CFRP shear reinforcement was found to be inefficient in enhancing significantly the slab capacity due to its brittleness. A model, which accurately predicts the punching shear capacity of FRP RC slabs without shear reinforcement, is proposed and verified. For slabs with FRP shear reinforcement, it is proposed that the concrete shear resistance is reduced, but a strain limit of 0.0045 is recommended as maximum strain for the reinforcement. Comparisons of the slab capacities with ACI 318-95, ACI 440-98, and BS 8110 punching shear code equations, modified to incorporate FRP reinforcement, show either overestimated or conservative results.

Behaviour of Beams Without Transverse Reinforcement

To deepen the understanding of shear behaviour in beams without transverse reinforcement, the relative importance of five contributing factors to concrete shear resistance(), which are i)flexural compression zone, ii)friction at crack faces, iii)dowel action, iv)arch action and recently identified, v)residual tensile stresses across cracks, was explained physically using two analytical methods based on the truss concept. One is called Modified Compression Field Theory(MCFT) considering ii) and v) explicitly, and the other Crack Friction Truss Model(CFTM) more dominantly ii) in determining concrete resistance. To verify their effectiveness, the predictions using MCFT and CFTM were also made for twenty KAIST beam tests(=53.7Mpa), designated more likely to the development of the size effect law based on the fracture mechanics concept. Experimental findings with varying of a/d, longitudinal reinforcement ratios, and obtained from MCFT enabled additional explanations for some phenomena which were difficult to measure in tests. However, MCFT seemed somewhat conservative for beams with higher longitudinal reinforcement, while somewhat unsafe for beams with larger depths. More tests are necessary leading to firm conclusions in these areas.