Diagonal Shear Cracks Research Articles

Experimental investigation on the behaviour of reinforced concrete slabs strengthened with ultra-high performance concrete

Nine rectangular specimens were tested to investigate the behaviour of composite reinforced concrete (RC) slabs strengthened with ultra-high performance concrete (UHPC). The specimens were two series with various UHPC strengthening configurations. The first, a rehabilitation series, tested UHPC as patch material for repairing deteriorated concrete structures. The second, a UHPC overlay series, was used to retrofit soffits of RC members. The results showed that using the rehabilitation series, the UHPC reduced diagonal cracking and developed more flexural cracks as compared to RC slabs with no UHPC strengthening. The UHPC exhibited excellent energy absorption with extensive deflection hardening and ductility during the post cracking range. In the UHPC overlay series, each slab showed diagonal shear cracks and debonding modes. The UHPC overlay delayed the development of shear cracking. As the overlay thickness increased, the ultimate load increased; but the tendency for the UHPC to undergo fracture failure also increased.

Shear strength modelling of deep beam reinforced with high-strength steel without stirrups

Non-linear finite-element analyses were performed to model the shear behaviour of deep beams with high-strength reinforcement and grade-60 conventional reinforcement, without stirrups. The FE model was compared with experimental results from recent tests of deep concrete beams reinforced with both types of reinforcement and loaded until failure. A detailed comparative study of the FE and experimental results is presented, which demonstrates the capability of the analytical model to describe the observed experimental behaviour. The shear behaviour of beams reinforced with high-strength steel (HSS) was compared with that of beams reinforced with grade-60 steel to demonstrate the benefits of using high-strength reinforcement. The shear design provisions of current codes and mechanics-based models were also compared with the results from the analytical model. The findings of the study showed that diagonal shear cracking strength is independent of the type of reinforcement, while beams reinforced with HSS exhibited higher post-cracking shear strength than beams with conventional reinforcement. Strut-and-tie modelling is recommended for the design of deep beams reinforced with HSS since this method accounts for high strains in reinforcement and accounts for large-size effects. The current code provisions are suitable for slender beams regardless of type of reinforcement.

Tracking multi-directional intersecting cracks in numerical modelling of masonry shear walls under cyclic loading

In-plane cyclic loading of masonry walls induces a complex failure pattern composed of multiple diagonal shear cracks, as well as flexural cracks. The realistic modelling of such induced localized cracking necessitates the use of costly direct numerical simulations with detailed information on both the properties and geometry of masonry components. On the contrary, computationally efficient macro-models using standard smeared-crack approaches often result in a poor representation of fracture in the simulated material, not properly localized and biased by the finite element mesh orientation. This work proposes a possible remedy to these drawbacks of macro-models through the use of a crack-tracking algorithm. The macro-modelling approach results in an affordable computational cost, while the tracking algorithm aids the mesh-bias independent and localized representation of cracking. A novel methodology is presented that allows the simulation of intersecting and multi-directional cracks using tracking algorithms. This development extends the use of localized crack approaches using tracking algorithms to a wider field of applications exhibiting multiple, arbitrary and interacting cracking. The paper presents also a novel formulation including into an orthotropic damage model the description of irreversible deformations under shear loading. The proposed approach is calibrated through the comparison with an experimental test on a masonry shear wall against in-plane cyclic loading.

Post‐cracking shear strength and deformability of HSS‐UHPFRC beams

AbstractEleven T‐beams, reinforced with high strength steel, were tested to failure to investigate the effect of shear span to depth ratio, fibre ratio, fibre type, concrete strength and stirrup ratio on the shear behaviour, especially post‐cracking shear strength and deformability, of ultra‐high performance fibre reinforced concrete (UHPFRC) beams. Test results indicated that fibres were efficient not only in enhancing the post‐cracking shear strength, but also in improving the post‐cracking deformability of UHPFRC beams. In addition, fibres could bridge the cracks and help in redistributing and homogenizing the concrete stress beside the cracks, allowing more short fine diagonal shear cracks with small spacing to develop around the existing cracks. A moderate amount of stirrups can effectively restrain shear cracks and allow more parallel diagonal shear cracks to develop and propagate thoroughly within the shear span. The stiffness of the UHPFRC beams at ultimate state was about 50 % of initial beam stiffness, which was considerable in strength calculations and ductility analysis, especially in seismic performance evaluation. Lastly, the current shear provisions were evaluated using the experimental results.

Experimental characterization of concrete beams elements reinforced by long fiber chips

This work deals with the experimental study of the mechanical behavior by three-point bending tests and shear (fracture shear) of concrete beam elements reinforced by long fibers. These fibers come from machined steel parts waste. Bending and shear tests are conducted on prismatic specimens [10 × 20 × 120] cm3. Compressive strength tests are carried out on cylinders of 16 cm diameter and 32 cm height. The fibers are characterized in terms of mechanical strength and tear strength. The composition of the concrete is determined by the experimental method called ‘Dreux-Gorisse.’ Two different fiber contents were used for this study (W = 0.6%, 0.8%) and a control concrete BT (W = 0%) of the same composition as the matrix is prepared as a reference. The comparison of the different results obtained shows that long fibers provide a significant ductility to the material after concrete cracking. Also, the used fibers limit diagonal shear cracks and improve the strength and rigidity in bending and shear.

Premature Failure and its Prevention in Flexural Beams Retroftted by GFRP Fibers

Nowadays, retroftting reinforced concrete with FRP fbers is regarded as a globally signifcant issue. In reinforced concrete beam, the shear failure mode is more dangerous than fexural failure mode. Because this thin and sudden mode occurs without any pre-warning, diagonal shear cracks are wider than fexural cracks and preventing their expansion is rather diffcult. In the present study, the concrete beams are retroftted with GFRP fbers through a common method. Then, the beams have four- point bending test until the premature failure occurs. This phenomenon is relatively prevented through retroftting along the shear. The failure of beams are examined here.Journal of the Institute of Engineering, 2015, 11(1): 12-19

Influence of longitudinal bar corrosion on impact behavior of RC beams

To investigate the influence of longitudinal bar corrosion on impact behavior of RC beams, four RC beam specimens with varied corrosion rate were tested under falling-weight, impacting the specimens at the mid-span. Four corresponding specimens were also tested under static loads to determine their static properties and behavior. Reinforcement was corroded by means of immersing the specimens in 3 % sodium chloride solution and applying a current density of 3 mA/cm2. The test results indicate that corrosion of longitudinal bars decreases the impact force and reaction force, and increases mid-span displacement of RC beams under impact load and the beam’s capacity of absorbing energy. Corrosion-induced cracks in concrete have been shown as the most relevant damages in the tested beams. All specimens, regardless of their corrosion rate, failed in shear-critical mode and presented severe diagonal shear cracks under the impact point.

Cyclic Loading Tests for Shear Strength of Low-Rise Reinforced Concrete Walls with Grade 550 MPa Bars

In the construction of nuclear power plants using massive walls, the use of high-strength reinforcing bars for shear design is necessary to enhance the constructibility and economy. In this study, low-rise walls (aspect ratio of 1.0) with Grade 550 MPa (80 ksi) reinforcing bars were tested to investigate the shear capacity and deformation capacity under cyclic loading. The test parameters were the grade of horizontal reinforcement, concrete strength, web bar ratios, use of boundary hoop, shape of cross section, and failure mode. The failure mode of the walls with 550 MPa (80 ksi) bars was diagonal shear cracking, followed by web crushing, which was the same as that of the wall with 420 MPa (60 ksi) bars. In the shear failure mode specimens, the ratio of the peak shear strength to the prediction of ACI 349 was 1.33 to 1.99 for the shear provision and 1.27 to 1.73 for the seismic provision, respectively.

Diagonal Shear Cracks and Size Effect in Concrete Beams Reinforced with Glass Fiber Reinforced Polymer (GFRP) Bars

Removed at authors request

Tests on anchorage of naturally corroded reinforcement in concrete

Many studies on the structural effects of corrosion in reinforcement have been conducted. However, most of them are based on artificially corroded test specimens. Thus, the knowledge available entails one major uncertainty, i.e. whether the results are reliable enough to be used for naturally corroded structures. The purpose of this study was to develop a test method and carry out experiments on naturally corroded specimens taken from an existing structure to investigate the anchorage capacity. Beam specimens were taken from the edge beams of a bridge at repair. The specimens showed corrosion-induced damage to a varying extent from no sign of corrosion to extensive cracking and spalling of the concrete cover. A four-point bending test indirectly supported by suspension hangers was chosen. The beams were strengthened with transverse reinforcement around the suspension hangers to avoid premature failure. Eight successful tests were carried out; in all these tests, diagonal shear cracks preceded a splitting induced pull-out failure; i.e. anchorage failure was achieved as intended. The results showed around 10 % lower capacity for the corroded specimens than for the reference ones. The average bond stress in the anchorage zone was estimated based on the applied load and available anchorage length. The stress was about 16 % lower in the beams with corrosion cracks, and 9 % lower in the beams with cover spalling compared to the reference specimens; there was also a larger variation among the damaged specimens than for the reference specimens. The results extend our knowledge concerning the structural behaviour of corroded reinforced concrete structures during field conditions.

In-plane strengthening of clay brick unreinforced masonry wallettes using ECC shotcrete

New Zealand’s stock of unreinforced masonry (URM) bearing wall buildings was principally constructed between 1880 and 1935, using fired clay bricks and lime or cement mortar. These buildings are particularly vulnerable to horizontal loadings such as those induced by seismic accelerations, due to a lack of tensile force-resisting elements in their construction. The poor seismic performance of URM buildings was recently demonstrated in the 2011 Christchurch earthquake, where a large number of URM buildings suffered irreparable damage and resulted in a significant number of fatalities and casualties. One of the predominant failure modes that occurs in URM buildings is diagonal shear cracking of masonry piers. This diagonal cracking is caused by earthquake loading orientated parallel to the wall surface and typically generates an “X” shaped crack pattern due to the reversed cyclic nature of earthquake accelerations.Engineered Cementitious Composite (ECC) is a class of fiber reinforced cement composite that exhibits a strain-hardening characteristic when loaded in tension. The tensile characteristics of ECC make it an ideal material for seismic strengthening of clay brick unreinforced masonry walls. Testing was conducted on 25 clay brick URM wallettes to investigate the increase in shear strength for a range of ECC thicknesses applied to the masonry wallettes as externally bonded shotcrete reinforcement. The results indicated that there is a diminishing return between thickness of the applied ECC overlay and the shear strength increase obtained. It was also shown that, the effectiveness of the externally bonded reinforcement remained constant for one and two leaf wallettes, but decreased rapidly for wall thicknesses greater than two leafs. The average pseudo-ductility of the strengthened wallettes was equal to 220% of that of the as-built wallettes, demonstrating that ECC shotcrete is effective at enhancing both the in-plane strength and the pseudo-ductility of URM wallettes.

Size effect on shear strength of FRP reinforced concrete beams

This paper presents test results of six concrete beams reinforced with longitudinal carbon fiber reinforced polymer (CFRP) bars and without vertical shear reinforcement. All beams were tested under a two-point loading system to investigate shear behavior of CFRP reinforced concrete beams. Beam depth and amount of CFRP reinforcement were the main parameters investigated. All beams failed due to a sudden diagonal shear crack at almost 45°. A simplified, empirical expression for the shear capacity of FRP reinforced concrete members accounting for most influential parameters is developed based on the design-by-testing approach using a large database of 134 specimens collected from the literature including the beams tested in this study. The equations of six existing design standards for shear capacity of FRP reinforced concrete beams have also been evaluated using the large database collected. The existing shear design methods for FRP reinforced concrete beams give either conservative or unsafe predictions for many specimens in the database and their accuracy are mostly dependent on the effective depth and type of FRP reinforcement. On the other hand, the proposed equation provides reasonably accurate shear capacity predictions for a wide range of FRP reinforced concrete beams.

Experimental study on seismic behavior of circular RC columns strengthened with pre-stressed FRP strips

Bonding fiber reinforced polymer (FRP) has been commonly used to improve the seismic behavior of circular reinforced concrete (RC) columns in engineering practice. However, FRP jackets have a significant stress hysteresis effect in this strengthening method, and pre-tensioning the FRP can overcome this problem. This paper presents test results of 25 circular RC columns strengthened with pre-stressed FRP strips under low cyclic loading. The pre-stressing of the FRP strips, types of FRP strips and longitudinal reinforcement, axial load ratio, pre-damage degree and surface treatments of the specimens are considered as the primary factors in the tests. According to the failure modes and hysteresis curves of the specimens, these factors are analyzed to investigate their effect on bearing capacity, ductility, hysteretic behavior, energy dissipation capacity and other important seismic behaviors. The results show that the initial lateral confined stress provided by pre-stressed FRP strips can effectively inhibit the emergence and development of diagonal shear cracks, and change the failure modes of specimens from brittle shear failure to bending or bending-shear failure with better ductility. As a result, the bearing capacity, ductility, energy dissipation capacity and deformation capacity of the strengthened specimens are all significantly improved.

Experimental Investigation on the Shear Behaviour of Concrete Beams Reinforced with GFRP Reinforcement Bars

This paper presents the experimental results of shear behaviour on concrete beams longitudinally reinforced with glass fiber-reinforced polymer (GFRP) reinforcement bars. Totally sixteen concrete beams were tested under static load. Half of the tested beams were longitudinally reinforced with GFRP reinforcement bars, while, the other half were reinforced with conventional steel reinforcement bars. The beams were prepared with varying test variables, such as shear span-to-effective depth ratios (a/d), amount and types of longitudinal reinforcement bars and stirrup spacing. The experimental results show that the ratios of a/d and stirrup spacing significantly influence the ultimate capacities of the beams. Moreover, more closely spaced diagonal shear cracks were resulted in GFRP reinforced concrete (RC) beams compared to steel RC beams.

Shear behaviour of reinforced phyllite concrete beams

The shear behaviour of concrete beams made from phyllite aggregates subjected to monotonic and cyclic loading is reported. First diagonal shear crack load of beams with and without shear reinforcement was between 42–58% and 42–92% of the failure loads respectively. The phyllite concrete beams without shear links had lower post-diagonal cracking shear resistance compared to corresponding phyllite beams with shear links. As a result of hysteretic energy dissipation, limited cyclic loading affected the stiffness, strength and deformation of the phyllite beams with shear reinforcement. Generally, beams with and without shear reinforcement showed anchorage bond failure in addition to the shear failure due to high stress concentration near the supports. The ACI, BS and EC codes are conservative for the prediction of phyllite concrete beams without shear reinforcement but they all overestimate the shear strength of phyllite concrete beams with shear reinforcement. It is recommended that the predicted shear capacity of phyllite beams reinforced with steel stirrups be modified by a reduction factor of 0.7 in order to specify a high enough safety factor on their ultimate strength. It is also recommended that susceptibility of phyllite concrete beams to undergo anchorage bond failure is averted in design by the provision of greater anchorage lengths than usually permitted.

Seismic performance of masonry buildings during the 2007 Bala, Turkey earthquakes

A field investigation was conducted near the town of Bala after two strong earthquakes struck the region on December 20 and 27, 2007. The main objectives of this study are to present the results of the field investigation and examine the characteristics of the recorded ground motions and the corresponding response spectra. The focus of the research was on the causes of damage and failures commonly observed in masonry structures. This study classifies single family masonry dwellings in rural areas and investigates the seismic damage in unreinforced masonry structures. Turkish Earthquake Code requirements for masonry buildings are summarized and compared with the field observations. Our field investigation showed that there has been lack of quality control and regulation for the masonry construction. Diagonal shear cracking and out-of-plane failure were the two major factors that contributed to widespread damage in masonry structures.

프리캐스트 콘크리트 U형 쉘 공법 보-기둥 접합부의 내진성능

이 연구에서는 프리캐스트 콘크리트(PC) U형 쉘을 사용하는 PC 모멘트 골조의 일부인 보-기둥 내부접합부의 내진성능을 평가하기 위하여 실험연구를 수행하였다. 5개의 PC 보-기둥 내부접합부와 1개의 현장타설 콘크리트 보-기둥 내부접합부를 실물 크기로 제작하여 반복가력 실험을 수행하였다. 주요 변수는 보 주철근비, 보 전단철근 간격, U형 PC쉘과 기둥 모서리의 보강철물 설치 유무이다. 실험 결과, 변수에 관계없이 PC 보-기둥 접합부는 현장타설 콘크리트 보-기둥 접합부와 비교하여 유사한 하중재하능력, 연성능력을 나타냈다. 그러나 주기 하중동안 PC 보-기둥 접합부는 보-기둥 이음부에서 보 주철근의 부착파괴로 인한 미끄러짐 변형과 대각방향의 전단균열로 인하여 심한 강도 저하를 나타냈고, 이로 인해 현장타설 콘크리트 보-기둥 접합부보다 접합부의 강성과 에너지소산능력이 감소되었다.

Experimental research on square steel tubular columns filled with steel-reinforced self-consolidating high-strength concrete under axial load

A new design model for steel–concrete composite columns, namely square steel tubular columns filled with steel-reinforced self-consolidating high-strength concrete, is proposed. In this type of steel–concrete composite column, a steel section is inserted into the square steel tube and self-consolidating high-strength concrete is filled into the tube. Eighteen composite column specimens were tested under axial compression. The effects of concrete strength, width-to-thickness ratio, length-to-width ratio, and ratio of steel section on the strength and deformation characteristics of these composite columns are discussed. The experimental results indicate that the encased steel section can restrain the generation of diagonal shear cracks in the core concrete thus changing the failure mode and the post-yield behavior of short composite columns. Formulas for calculating the ultimate strength of centrally loaded composite columns are proposed. The calculated values are in good agreement with the test results.

Assessment of the Predictive Performance of Existing Analytical Models for Debonding of Near-Surface Mounted FRP Strips

The near-surface mounted (NSM) strengthening technique, in which pultruded fiber reinforced polymer (FRP) plates or bars are adhesively bonded into grooves cut in the concrete cover, has proven to overcome several of the drawbacks of externally bonded FRP plates on reinforced concrete flexural members. However, as research on the NSM technique is relatively recent, the theoretical foundation for its application is not yet as complete, and some of the debonding mechanisms are not yet fully understood. This paper presents the main findings of a literature review aimed at identifying the existing analytical models to predict the debonding strength of reinforced concrete flexural elements retrofitted with NSM FRP strips, and of a thorough assessment of the adequacy of such models by comparison with all relevant published experimental data. It is concluded that for debonding of NSM FRP strips induced by flexural (or flexural-shear) cracking or the critical diagonal shear crack of the reinforced concrete member, the currently available models capture the behavior of the debonding mechanism and provide reasonably conservative estimations of the debonding strength. However, for debonding induced by stress concentrations at the strip ends, existing models do not fully capture the debonding behavior and as such, are shown to be excessively conservative.

Towards a Unified Approach for the Analysis of Failure Modes in FRP-Retrofitted Concrete Beams

The application of the external reinforcement makes rather complex the scenario of the possible failure modes in reinforced concrete beams retrofitted with FRP. The far more commonly observed failure modes are: (i) edge debonding of the FRP sheet, (ii) intermediate crack induced debonding and (iii) beam failure due to diagonal (shear) crack propagation. In the present study we revisited the competition between all the possible failure modes that can occur in this structural element. To this aim, different analytical models based on linear and non-linear fracture mechanics are developed and harmonized. As a result, useful failure maps are analytically determined, giving, for each failure mode, the critical load of activation as a function of the main parameters governing the problem, i.e. the mechanical properties of the constituent materials, the amount of reinforcement and its bonding length, as well as the size and slenderness of the structural element. The studies presented in this paper are mainly intended to establish guidelines for the future development of these concepts towards a unified mathematical approach. Indeed, once the validity of this unified approach is confirmed, also by comparison with further experimental data, it will be possible to remove some of the simplifying assumptions we used in this analysis to reach a more comprehensive analytical formulation.