Flexure-shear Failure Mode Research Articles

Structural behavior of S-UHPC-S composite wall strips with waved tie bars: Experiment, simulation, and design

In this paper, novel steel waved tie bar shear connectors were developed in conjunction with ultra-high-performance-concrete (UHPC) core to obtain lightweight, high-strength, and easy-construction steel-UHPC-Steel (S-UHPC-S) composite structures. To study the structural behavior of S-UHPC-S composite wall panels with waved tie bars subjected to out-of-plane loads, seven 1/2 scaled S-UHPC-S composite beams were extracted and tested under three-point bending. Test variables included longitudinal and transverse reinforcement ratios, and shear span ratio. Experimental results indicated that S-UHPC-S composite beams failed in flexure mode under the shear span ratios of 2.5 and 3.5 and in flexure-shear mode under the shear span ratio of 1.5. Increasing the longitudinal reinforcement ratio from 1.0 % to 1.5 % and 2.0 % increased the peak load capacity of the S-UHPC-S composite beams by 16.5 % and 43.6 %, respectively, but increasing the transverse reinforcement ratio had a marginal effect on the load resistance because the S-UHPC-S composite beams were dominated by flexure or flexure-shear failure mode. Full-scale models were built with the finite element (FE) software LS-DYNA. After being validated with the test results, the FE model is used to conduct extended studies. Numerical results indicate that the contribution proportion of each component to the bending moment capacity of the S-UHPC-S composite beam can be sorted in a descending order, namely, steel faceplates > UHPC > ribs > tie bars. A method was proposed to predict the failure mode of the S-UHPC-S composite beams in accordance with shear span ratios and mechanical reinforcement ratios. Finally, computation methods for flexure strength and the maximum stud spacing were developed.

Experimental investigation of the effects of concrete strength and axial load ratio on the performances of CFRP-wrapped and externally collared RC short columns

In this study, the seismic performances of 18 full-scale reinforced concrete short columns were evaluated under cyclic quasi-static loading. Concrete strength and axial load ratio were considered as parameters in performance tests of the columns. Based on these parameters, there were used six reference columns without any strengthening application. CFRP wrap and steel collar strengthening were applied to the other twelve columns. Longitudinal reinforcements of all test columns were the same. In order to demonstrate the efficiency of the strengthening applications more clearly, Ø10/100 stirrups were used in reference columns, while Ø10/150 stirrups were used in strengthened columns. The effectiveness of the applied strengthening methods based on changes in the concrete strength and axial load ratio, which are the two important parameters affecting the behaviour of RC short columns, were investigated. Reference columns were called as ideal columns with well transverse reinforcement detail. The performances of the strengthened columns were compared with ideal reference columns. The performances of the columns were examined in terms of crack development, hysteretic behaviour, strength, ductility, and energy dissipation. Increasing the concrete strength and axial load ratio increased the strength of the columns and directed the columns toward brittle behaviour. The columns were governed by a flexure-shear failure mode and the strengthening solutions herein were adopted aim at avoiding the shear interaction in order to achieve the ductile behaviour of the members. CFRP wrap and Collar strengthening applications significantly improved the performance of the columns. CFRP wrap and Collar strengthening increased the mean ductility values of the columns by 38.8%-108.6% and 61.7% −100.8%, respectively, compared to Reference columns. This resulted in an increase in energy dissipation values of up to 347.2% in the CFRP-wrapped columns and 379.3% in the collared columns.

Analysis of seismic performance and research of load capacity of steel reinforced high strength concrete columns with rectangular helical hoops

This paper mainly focused on the seismic performance and shear calculation method of steel reinforced high-strength concrete (SRHC) columns with rectangular helical hoops. An experimental investigation was performed in this paper. Eleven SRHC columns with rectangular helical hoops and one with ordinary hoops were constructed at the laboratory of Guangxi university. The failure modes, hysteresis loops, envelope curves, characteristic loads and displacements and cumulative damage analysis are presented and investigated. It can be seen from the test results that the failure modes of SRHC columns can be divided into three types with the shear span ratio increased, namely, shear baroclinic failure mode, flexure-shear failure mode and flexure failure mode. In addition, the specimens with rectangular helical hoops have plumper hysteretic loops. Shear span ratio is the main influencing factor of characteristic load; the axial compression ratio and concrete strength have less influence on characteristic load, while stirrup ratio has little effect on the characteristic load. Finally, a calculation method for shear capacity of SRHC columns under shear baroclinic failure and flexure-shear failure mode is proposed.

Flexural behaviour of ambient cured geopolymer concrete beams reinforced with BFRP bars under static and impact loads

The applications of GeoPolymer Concrete (GPC) with basalt-fiber-reinforced-polymer (BFRP) reinforcements could be alternative for conventional structural designs with Portland Cement Concrete reinforced with steel bars for green and sustainable constructions. Very limited studies, however, have been carried out to investigate the performance of GPC beams reinforced with BFRP bars subjected to static loads, and no study of their performance under impact load is available in open literature yet. In this study, ambient-cured GPC beams reinforced with BFRP bars were tested under static and impact loads. Their damage modes, static and dynamic responses were recorded and analysed. The test results showed that the beams experienced flexural failure mode under static load while combined flexure-shear failure mode was observed under impact load. The impact-loading tested beams were further statically loaded to examine their residual capacities. Additionally, numerical models of the tested GPC beams were developed adopting the commonly used concrete material model *Mat_072R3 (KCC model) in LS-DYNA with modified parameters based on the GPC material testing data. The calibrated numerical model was used for parametric simulations. The results showed that with the increased impact velocity, failure mode of the beam shifted from the flexure-governed to punching-shear-governed along with the rupture of longitudinal BFRP bars.

Improvements of IS 1343-2012 Shear Design Provisions Using a New Traditional Shear Database of Prestressed Concrete Members with Stirrups

Various national codes of practice play a crucial role in the development of the country’s infrastructure and should be developed based on principles of mechanics and experimental verification. Continuous monitoring of infrastructure and updating of relevant codes of practice at regular intervals is essential to withstand the ever-increasing demand of the country’s infrastructure. In the present study, the shear design provisions of prestressed concrete (PC) in IS 1343-2012 have been reviewed. The assumptions used in the formulations of the existing shear design equations in IS 1343-2012 have been discussed. The present study reveals that the IS 1343-2012 shear design provisions, which are based on old test data, are too conservative and are unable to distinguish the two major modes of traditional shear failure, namely web-shear and flexure-shear. Modifications for the existing IS 1343-2012 shear design equations have been proposed to improve the shear strength estimation of PC members and also to distinguish between the web-shear and flexure-shear failure modes. A detailed comparison of existing IS 1343-2012 shear design provisions with the proposed modified shear strength equations has also been made with the help of a traditional shear database on PC members with stirrups.

Comparison of available shear strength models for non-conforming reinforced concrete columns

Field surveys in the aftermath of major seismic events, laboratory tests and numerical studies outlined that existing reinforced concrete (RC) structures are likely to exhibit premature shear failures. However, a proper quantification of the shear capacity of existing members with seismic details non-conforming to current seismic code is still a challenging task. Several models based on mechanical approaches or experimental observations are available in literature, current standards and guidelines. Nevertheless, the lack of a widely accepted theory often results in the use of old formulations, mainly developed for design purposes, to assess the shear strength of non-conforming RC members. This study investigates the available shear strength formulations. Eight capacity models commonly adopted in the current practice and worldwide standards or guidelines have been assessed comparing the model predictions with a unique database of 180 experimental tests properly selected to be representative of non-conforming RC members. Members with rectangular or circular cross-section, different aspect ratio (i.e. slender or squat) and shear or flexure-shear failure mode have been investigated. Meaningful statistics have been used to quantify the accuracy and the level of safety of each formulation. Several criticisms in the use of the available formulations are herein outlined. Suggestions for the model applicability have been provided in order to drive the reader to select the most appropriate shear strength formulation for assessment purposes. Finally, corrective factors have been calibrated to allow the use of the selected models with specific levels of safety.

Experimental study on the seismic performance of existing reinforced concrete bridge piers with hollow rectangular section

Experimental tests on typical existing reinforced concrete bridge piers with hollow rectangular section were carried out. The specimens were designed and realized (scale 1:4) with material and reinforcement characteristics representative of the Italian bridge structures realized prior to 1980. Four specimens were tested, with different shear span-to-section depth ratio. Cyclic tests under displacement control with constant axial load were performed. Flexure and flexure-shear failure modes were observed. Design criteria and adopted setup are described. Experimental global response and observed damage evolution are presented. Results about local response and hysteretic energy dissipation are analysed. A database of tests on elements of the same typology tested in this work and subjected to shear or flexure-shear failure mode is collected from literature, and a comparison with shear strength capacity models from literature and codes is carried out.

Simulation of Prestressed Steel Fiber Concrete Beams Subjected to Shear

This paper developed an analytical software, called Simulation of Concrete Structures (SCS), which is used for numerical analysis of shear-critical prestressed steel fiber concrete structures. Based on the previous research at the University of Houston (UH), SCS has been derived from an object-oriented software framework called Open System for Earthquake Engineering Simulation (OpenSees). OpenSees was originally developed at the University of California, Berkeley. New module has been created for steel fiber concrete under prestress based on the constitutive relationships of this material developed at UH. This new material module has been integrated with the existing material modules in OpenSees. SCS thus developed has been used for predicting the behavior of the prestressed steel fiber concrete I-beams and Box-beams tested earlier in this research. The analysis could well predict the entire behavior of the beams including the elastic stiffness, yield point, post-yield stiffness, and maximum load for both web shear and flexure shear failure modes.

Predicting the Response of Shear-critical Reinforced Concrete Beams using Response-2000 and SNI 2847:2013

This study investigates the accuracy of Response-2000 in predicting the response of shear-critical reinforced concrete beams. The experimental data selected was that obtained by Vecchio and Shim in 2004 on twelve reinforced concrete beams which sought to replicate beams originally tested by Bresler and Scordelis in the early 1960s. This study also aims to compare the results obtained to the predictions of SNI 2847:2013. It is demonstrated that Response-2000 is capable of providing accurate predictions of load-deflection responses up to the peak load, but underestimates the ductility of beams that exhibit a mixed flexure-shear failure mode. It is also shown that both methods provide conservative predictions of the shear strength of beams with no shear reinforcement, with the software providing more consistent and reliable predictions of shear strength of beams containing shear reinforcement.

The effect of span length to height ratio of reinforced concrete slabs on pressure-impulse diagram with multiple failure modes under blast loading

In this paper, two loosely coupled single degree of freedom (SDOF) systems are used to generate pressure-impulse diagrams (P-I) with the flexural and direct shear responses of one-way reinforced concrete slabs subjected to blast loading. The effect of span length to height ratio in P-I diagrams is investigated. The numerical calculation results indicate that a slab tends to fail in a direct shear mode if the blast load amplitude is high but of short duration. It tends to fail in flexural failure mode if load amplitude is relatively low and duration is relatively long. And the failure of the slab might be a combination of shear and flexural damage in the dynamic loading region. Based on numerical results, different failure modes are got with different the span length to height ratio on the P-I diagrams. Results indicate that there is only shear failure mode in the P-I diagrams when L/h 24.89, there are two damage mode in the P-I diagrams with flexure failure mode and flexure-shear failure mode. When 10.9 < L/h < 24.89, there are three damage modes in the P-I diagrams: shear failure mode, flexure failure mode and flexure-shear failure mode.

Experimental research and finite element analysis of bridge piers failed in flexure-shear modes

In recent earthquakes, a large number of reinforced concrete (RC) bridges were severely damaged due to mixed flexure-shear failure modes of the bridge piers. An integrated experimental and finite element (FE) analysis study is described in this paper to study the seismic performance of the bridge piers that failed in flexure-shear modes. In the first part, a nonlinear cyclic loading test on six RC bridge piers with circular cross sections is carried out experimentally. The damage states, ductility and energy dissipation parameters, stiffness degradation and shear strength of the piers are studied and compared with each other. The experimental results suggest that all the piers exhibit stable flexural response at displacement ductilities up to four before exhibiting brittle shear failure. The ultimate performance of the piers is dominated by shear capacity due to significant shear cracking, and in some cases, rupturing of spiral bars. In the second part, modeling approaches describing the hysteretic behavior of the piers are investigated by using ANSYS software. A set of models with different parameters is selected and evaluated through comparison with experimental results. The influences of the shear retention coefficients between concrete cracks, the Bauschinger effect in longitudinal reinforcement, the bond-slip relationship between the longitudinal reinforcement and the concrete and the concrete failure surface on the simulated hysteretic curves are discussed. Then, a modified analysis model is presented and its accuracy is verified by comparing the simulated results with experimental ones. This research uses models available in commercial FE codes and is intended for researchers and engineers interested in using ANSYS software to predict the hysteretic behavior of reinforced concrete structures.

형상비 2.5의 RC 교각의 내진 곡률연성도

Due to the 1989 Loma Prieta, 1995 Hyogoken Nambu earthquakes, etc, a number of bridge columns were collapsed in flexure-shear failures as a consequence of the premature termination of the column longitudinal reinforcement. Nevertheless, previous researches for the performance of bridge columns were concentrated on the flexural failure mode. It is well understood that the seismic behaviour of RC bridge piers was dependent on the performance of the plastic hinge of RC bridge piers, the ductility of which was desirable to be computed on the basis of the curvature. Experimental investigation was made to evaluate the variation of the curvature of the plastic hinge region for the seismic performance of earthquake-damaged RC columns in flexure-shear failure mode. Seven test specimens in the aspect ratio of 2.5 were made with test parameters: confinement ratios, lap splices, and retrofitting FRP materials. They were damaged under series of artificial earthquakes that could be compatible in Korean peninsula. Directly after the pseudo-dynamic test, damaged columns were retested under inelastic reversal cyclic loading under a constant axial load, $P

鉄筋コンクリート柱の崩壊変形に関する研究

This study is intended to grasp general nature of column collapse. Half-scale model specimens with shear or flexure-shear failure modes simulating RC columns designed by the old code were tested until they came to be unable to sustain axial load. Test variables were longitudinal reinforcement, axial load and transverse reinforcement. Using results from this test and past tests, the general nature of column collapse, especially lateral drift associated with collapse is discussed. Some structural indices that are considered to govern the amplitude of collapse drift are also discussed.

Nonlinear finite element modelling of failure modes in RC slabs

With the development of generalized nonlinear finite element modelling, this paper delineates the various failure modes of a RC slab in terms of damage dominated either by tension cracking in concrete or plastic yielding leading to concrete crushing. Commonly observed failure modes of such slabs are classified according to the level of each damage component. Such a classification helps separate the flexure-shear failure mode of RC slabs from the true punching or shear mode of collapse. The influence of main tensile reinforcement on the metamorphosis in failure modes is highlighted by the nonlinear finite element model, using as an illustration, patch loads whose size bear a similar ratio to the size of the slab as the ratio of the print of a wheel to the size of a deck slab. Also the beneficial effect of edge restraint on punching capacity is highlighted.