Lap-spliced Bars Research Articles

The axial tensile performance of DSCW-RC joints with lap-spliced bars

Joints formed between double-skin concrete shear walls (DSCWs) and reinforced concrete (RC) foundations commonly utilize lap-spliced bars to transfer forces. However, the behavior and design of these critical connections have not been thoroughly investigated. This study experimentally analyzes a steel-reinforced DSCW-to-RC foundation anchorage joint under monotonic uniaxial tension loading. Seven 1:3 scale specimens were tested to examine the effects of varying lap-spliced bar diameter, steel plate thickness, and stud bolt spacing. Crack propagation, load-displacement response, and reinforcement strain were measured. The results characterize two potential failure modes: ductile steel yielding and brittle stud shearing. Steel strains developed linearly up to yielding, demonstrating uniform transmission of tensile loads. Increased plate thickness and decreased stud spacing enhanced capacity. To mitigate sudden shear failures, the number and strength of studs must exceed the expected tensile demand. New design recommendations are proposed, including minimum stud bolt shear strength and the use of confining tie bars. This study provides an improved understanding of the behavior of DSCW-to-RC foundation lap-spliced connections, enabling resistance to axial demands while avoiding brittle failure modes. The experimental data will inform future analytical models and design provisions for these critical structural joints.

Post-heating flexural behavior of reinforced concrete beam with lap-spliced bar and feasibility of improving flexural performance by adding hybrid fibers

Using bar splices in reinforced concrete structures is inevitable due to transportation and construction limitations. On the other hand, executing lap splices in flexural members such as beams allows these members to potentially fail at the splice zone before reaching their ultimate flexural capacity. The failure of the beam at the splice location results from different factors, one of which is the exposure of concrete members to elevated temperatures. To address this, the flexural behavior of beams with lap-spliced bars after exposure to heat was examined, and the feasibility of improving their flexural performance by incorporating hybrid steel-polypropylene fibers was studied in the work. Here, 24 reinforced concrete beam specimens were constructed in 12 groups and exposed to the four-point bending test. Variables considered in the manufacturing and testing of these specimens included the splicing method (continuous reinforcement, simple lap splice, and hooked-end lap splice), concrete mix type (plain and fiber-reinforced), and exposure temperature (25 and 600 °C). Parameters under study included the load–deflection behavior, crack pattern, cracking load, ultimate load, failure mode, initial stiffness, effective stiffness, energy-absorption capacity, and ductility of the beams. The results indicated that exposing the spliced concrete beams to elevated temperatures changed the failure mode from flexural to splitting; however, adding hybrid fibers to the concrete mix improved the behavior of these members, with a more pronounced improvement in the specimens with the hooked-end splice. In addition, the simultaneous use of the hooked-end splice and hybrid fibers in the beams that had been exposed to heat prevented the splitting failure mode in these members. Furthermore, splicing the bar in the heated and unheated beam specimens lowered the energy-absorption capacity and ductility of the beams. The addition of fibers improved the energy absorption and ductility of the heated and unheated specimens, and the beams with the hooked-end splice showed a more significant improvement.

Strengthening of substandard lap splices using hollow steel section (HSS) collars

Bond splitting failure of substandard lap splices have caused extensive damage to many structures during earthquakes. Existing methods to strengthen substandard lap splices primarily involve wrapping the substandard lap spliced regions with jackets possessing mainly in-plane stiffness. Hence, the efficiency of such techniques is compromised due to the lateral bulging of concrete and flexural bending of jackets. This study investigated hollow steel section (HSS) collars which offer axial and flexural stiffness in mitigating splitting failures associated with lap splices not conforming to current design codes. Three lap splice lengths, mainly 20, 28, and 35 times the bar diameter (db) were studied. Experiments were conducted on 19 beams subjected to four-point bending, with substandard lap splices within the constant moment region. Test variables involved the lap splice length, concrete cover, and spacing of HSS collars. Results revealed that HSS collars successfully prevented splitting failures resulting in ductile behavior. It was found that the bond stress of the lap-spliced bars increased till the onset of their yielding. Beyond that, the bond stress was maintained close to their peak value in the beams sufficiently confined by HSS collars. By applying HSS collars, improvements in the bond strength for beams with 20db lap splices were evident. The control beams having longer lap splice lengths exhibited yielding, and the improvement in their bond strength was limited despite showing ductile behavior. In order to capture the contribution of HSS collars to the improvement from brittle behavior to ductile behavior, the interfacial fracture energy was also used instead of the bond strength alone. An equation for the increase in the interfacial fracture energy due to the confinement by HSS collars was obtained using nonlinear regression. This equation was utilized to determine the required confinement ratio of HSS collars for a given substandard lap splice. The required confinement ratios of HSS collars obtained from the proposed equation were found to agree with the experiment while overestimation was found in some cases.

Effect of Corrosion on Bond Strength of Tension Lap-Splices

This study aimed to investigate the effect of corrosion on the bond strength of tension lap splices in reinforced concrete beams. The test variables were the corrosion level (0%, 2.5% and 5.0%) and the concrete cover to bar diameter (c/d) ratio (c/d=1.5, 2.0, and 2.67). The observed failure mode was splitting of the concrete cover on the tension side. An accelerated corrosion technique was used to corrode the reinforcing lap-spliced bars in a reasonable time frame. Corrosion did not affect failure mode but caused a reduction in the ultimate strength and deflection at failure. The bond strength was reduced by 15% to 26% at 2.5% corrosion level and by 21% to 38% at 5% corrosion level depending on the c/d ratio. A model was proposed to predict the bond strength of corroded tension lap-splices in concrete. The model results correlated well with the measured bond strength.

Lap-spliced connections of steel and FRP bars in reinforced flexure concrete structures

Nowadays, the concept of energy saving is achieving more attention in building construction. As a critical element of a building, the balcony creates a discontinuity in envelope insulation and causes massive heat losses. To solve this issue, the adoption of fibre reinforced polymer (FRP) bars with the feature of low thermal conductivity in balcony insulation joints is imperative. This introduces a new lap-spliced connection between FRP bars and steel bars in the adjacent slabs. Yet, the lap-spliced connections are usually used for identical kind of rebars, for example, two steel or two FRP bars. There are scarce studies on the combined connection of a steel bar and a FRP bar. To explore this new topic, the present paper summarizes comprehensive knowledge on the tensile lap-spliced steel and FRP bars in flexure concrete specimens based on the current investigations. First, relating information regarding lap-spliced connections is summarized, for instance, connection methods, lap-spliced lengths specified in several codes. Second, important experiment results including various failure modes of flexure specimens, the distribution of tensile stresses and bond stresses along lap-spliced bars are collected and analysed. Third, different factors affecting the bond strength between lap-spliced bars and concrete are discussed. In the end, the obtained knowledge is briefly concluded.

RETRACTED: Influence of bond-slip on the flexural performance and ductility of steel fibres-reinforced RC beams with lap-spliced bars: Experimental and finite element analysis

This article has been retracted: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/about/our-business/policies/article-withdrawal). This article has been retracted at the request of the Editor-in-Chief. The Editor-in-Chief no longer has confidence in the scientific integrity of this paper as similar images have been used in various articles in multiple journals claiming varying conditions and geometries, which violates our publishing policies. Several identical images can also be found in [https://doi.org/10.1016/j.jobe.2020.102090], only for different geometric & material conditions than what are claimed in the above referenced paper. Communication with one co-author, Jorge De Brito, raised further concerns about the integrity of this work, to the extent that he expressed no longer having confidence in the content of the article.

Advanced Composite Retrofit of RC Columns and Frames with Prior Damages—Pseudodynamic Finite Element Analyses and Design Approaches

This study develops three-dimensional (3D) finite element (FE) models of composite retrofits in deficient reinforced concrete (RC) columns and frames. The aim is to investigate critical cases of RC columns with inadequate lap splices of bars or corroded steel reinforcements and the beneficial effects of external FRP jacketing to avoid their premature failure and structural collapse. Similarly, the RC-frame FE models explore the effects of an innovative intervention that includes an orthoblock brick infill wall and an advanced seismic joint made of highly deformable polymer at the boundary interface with the RC frame. The experimental validation of the technique in RC frames is presented in earlier published papers by the authors (as well as for a four-column structure), revealing the potential to extend the contribution of the infills at high displacement ductility levels of the frames, while exhibiting limited infill damages. The analytical results of the advanced FE models of RC columns and frames compare well with the available experimental results. Therefore, this study’s research extends to critical cases of FE models of RC frames with inadequate lap splices or corroded steel reinforcements, without or with brick wall infills with seismic joints. The advanced pseudodynamic analyses reveal that for different reinforcement detailing of RC columns, the effects of inadequate lap-spliced bars may be more detrimental in isolated RC columns than in RC frames. It seems that in RC frames, additional critical regions without lap splices are engaged and redistribution of damage is observed. The detrimental effects of corroded steel bars are somewhat greater in bare RC frames than in isolated RC columns, as all reinforcements in the frame are considered corroded. Further, all critical cases of RC frames with prior damages at risk of collapse may receive the innovative composite retrofit and achieve higher base shear load than the original RC frame without corroded or lap-spliced bars, at comparable top displacement ductility. Finally, the FE analyses are utilized to propose modified design equations for the shear strength and chord rotation in cases of failure of columns with deficiencies or prior damages in RC structures.

RETRACTED: Effect of different fibre types on the structural performance of recycled aggregate concrete beams with spliced bars

Abstract Providing a sufficient lap length to spliced bars plays a vital role to provide an adequate flexural strength and flexibility to reinforced concrete (RC) beams. This study intends to assess the influence of polypropylene fibres (PPF) and steel fibres (SF) on the flexural behaviour of recycled aggregate reinforced concrete (RARC) beams with spliced bars. For this purpose, 40 specimens with a cross-section 150 mm wide and 200 mm high, and a length of 1500 mm with different lap lengths in spliced bars, were cast and tested. One specimen was selected as a control beam with no fibres, recycled aggregate (RA) and spliced bars. Then, RA was replaced at 100% mass replacement ratio. Furthermore, to increase the cohesiveness between bars and concrete, which affect the flexural behaviour of RC beams, SF and PPF were added at 0%, 1% and 2% (by volume) separately. Four-point bending tests were performed to measure the load-bearing capability, ultimate deformation, flexibility and stiffness of RARC beams with different lap lengths. The influence of the fibres and of the lap length on the structural performance of RARC beams was the main aim of this investigation. Experiments indicated that the lap-spliced bars length could be reduced by 40% when both RA and 2% fibres are used with no reduction of the flexural strength of the beams, and the influence of 2% SF is higher than that of PPF.

철근콘크리트 보의 열화 및 겹침이음부 거동특성 예측

이 연구에서는 철근콘크리트 보의 열화 및 겹침이음부 거동특성 예측을 위해 비선형 유한요소해석 기법을 제시하였다. 이를 위해서 비선형 해석프로그램인 RCAHEST가 사용되었으며 손상 모델링을 통해 부식과 이로 인한 철근의 단면감소, 그리고 철근의 연성능력 및 콘크리트 강도 저하 등을 고려하였다. 열화된 겹침이음 철근의 거동을 예측하기 위해서 열화를 고려할 수 있는 겹침이음 철근요소를 개발하였다. 이 연구에서는 철근콘크리트 보의 열화 및 겹침이음부 거동특성 예측을 위해 제안한 해석기법을 신뢰성 있는 실험결과와 비교하여 그 타당성을 검증하였다.

Crack Spacing Prediction of Fibre-Reinforced Concrete Beams with Lap-Spliced Bars by Machine Learning Models

Reduction of spaces between flexural cracks is one of the crucial factors in protecting reinforcements from corrosion. Different parameters, such as concrete cover, concrete compressive strength, specimens’ dimension and spacing of longitudinal and transverse reinforcements, influence the crack spacing. Insufficient lap-spliced length reduces the strength and increases the crack spacing. In this study, the effects of lap-sliced length, a cyclic number, steel fibre percentage, longitudinal rebar diameter, concrete compressive strength, cross-section height and width on flexural crack spacing are investigated. Multilayer perceptron (MLP) neural network, adaptive neuro-fuzzy inference system, support vector regression and least mean squares regression are utilized to predict the flexural crack spacing. The obtained results illustrate that the MLP model yields better accuracy compared to other ones in the prediction of cracking spacing. The proper features for predicting crack spacing are prioritized based on mutual information between features. Furthermore, it is found that the available codes are unable to determine the crack spacing within reinforced concrete beams with lap-spliced bars.

RETRACTED: Influence of steel fibres on the flexural performance of reinforced concrete beams with lap-spliced bars

Abstract In reinforced concrete structures, providing sufficient anchorage length in the connections and lap-spliced bars (LSB) is essential. In this research, LSB in steel fibre-reinforced concrete (SFRC) beams under static and loading/unloading cycles are investigated. The ductility of fibre-reinforced concrete (FRC) beams with LSB is also studied. For that purpose, ten beams (width, height and length of 150 mm 200 mm and 2300 mm, respectively) with different lap-spliced length (LSL) of tension rebars and different percentages of steel fibres (SF) were manufactured and tested. Four beams are tested under static loads and six others under loading/unloading cycles. Also, one specimen was selected as control, with no LSB and SF. Other nine specimens were made using SF at 0%, 1% and 2% by volume. In these tests, the flexural resistance, maximum displacement at mid-span, ductility and dissipated energy were evaluated. It was found that by adding 2% SF, the LSL could be reduced by at least 20%, without a reduction of the ductility and bearing-capacity. The behaviour of SFRC-beams with LSB was superior to that of beams with no SF and LSB.

Large-scale quasi-static testing of precast bridge column with pocket connections using noncontact lap-spliced bars and UHPC grout

A novel pocket connection was put forward to be utilized in both ends of a precast bridge column to connect cap beam and foundation, respectively. The pocket connection adopted noncontact lap-spliced bars and ultra-high performance concrete (UHPC) grout. One 1:2.5 scale specimen was fabricated and tested to investigate the seismic performance of the precast bridge column with the proposed pocket connections. Based on OpenSees platform, a verified finite element model was utilized to simulate cyclic behavior of a monolithic reinforced concrete companion. The comparison was carried out to evaluate the precast bridge column in a comprehensive way. The results show that drift capacities of the two bridge columns are up to 5% and controlled by lateral force degradation. The lapped length of five times diameter is feasible when UHPC grout is used for longitudinal bars with a diameter no more than 32 mm. For the precast bridge column, the joint opening between column and foundation contributes over 30% to total lateral displacement and traditional equivalent plastic hinge model may be not suitable. With drift ratio over 1.5%, the precast specimen has larger secant stiffness than that of the monolithic companion, owing to the shorter shear length of the precast specimen caused by moving up of the actual plastic hinge region. The precast and monolithic bridge columns have good energy dissipation capacity, and the maximum damping ratios reach up to 19.8% and 22.6% at 5% drift ratio, respectively. The precast specimen has 18.8% less residual drift ratio at 5% drift ratio than the monolithic companion.

Improvement of the cyclic response of RC columns with inadequate lap splices-Experimental and analytical investigation

The overall seismic performance of existing pre 1960-70s reinforced concrete (RC) structures is significantly affected by the inadequate length of columns\' lap-spliced reinforcement. Due to this crucial structural deficiency, the cyclic response is dominated by premature bond - slip failure, strength and stiffness degradation, poor energy dissipation capacity and low ductility. Recent earthquakes worldwide highlighted the importance of improving the load transfer mechanism between lapspliced bars, while it was clearly demonstrated that the failure of lap splices may result in a devastating effect on structural integrity. Extensive experimental and analytical research was carried out herein, to evaluate the effectiveness and reliability of strengthening techniques applied to RC columns with lap-spliced reinforcement and also accurately predict the columns\' response during an earthquake. Ten large scale cantilever column subassemblages, representative of columns found in existing pre 1970s RC structures, were constructed and strengthened by steel or RC jacketing. The enhanced specimens were imposed to earthquake-type loading and their lateral response was evaluated with respect to the hysteresis of two original and two control subassemblages. The main variables examined were the lap splice length, the steel jacket width and the amount of additional confinement offered by the jackets. Moreover, an analytical formulation proposed by Tsonos (2007a, 2019) was modified appropriately and applied to the lap splice region, to calculate shear stress developed in the concrete and predict if yielding of reinforcement is achieved. The accuracy of the analytical method was checked against experimental results from both the literature and the experimental work included herein.

Seismic retrofitting of damaged RC columns with lap-spliced bars using FRP sheets

In many cases, existing reinforced concrete (RC) columns have been designed according to old seismic recommendations and present inefficient seismic behavior. Moreover, they usually have prior damages due to moderate earthquake excitations. Therefore, it is necessary these columns to be retrofitted. Many researches concern the seismic strengthening of RC columns with fiber reinforced polymers (FRP) and models have been proposed for calculating shear strength (VR) and ultimate chord rotation capacities (θu). This paper focuses on columns with lap-spliced bars, with or without previous damages, externally confined with FRPs. The accuracy of KANEPE and EC8.3 equations for estimating VR and θu is investigated as well as reasonable modifications are proposed to improve the accuracy of predictions.

Evaluation of load–deformation behavior of reinforced concrete shear walls with continuous or lap-spliced bars in plastic hinge zone

This article presents an analysis procedure for evaluation of load–deformation behavior of reinforced concrete shear walls with continuous or lap-spliced bar connections in plastic hinge zones under horizontal loads. For the shear walls with continuous bars, the lateral deformations caused by flexure, shear, and reinforcement slip are evaluated by considering their interaction. The flexural deformation is calculated by conventional fiber model. The shear mechanism is based on modified compression field theory with a softened smeared cracked reinforced concrete membrane element. Both the flexural and shear deformations are estimated separately in the plastic hinge and non-plastic hinge regions. In addition, an approach is proposed for analysis of plastic hinge length based on fracture energies of materials. For the shear walls with lap-spliced bars, due to its complicated behavior and mechanism, a simple way to deal with the lap splice is proposed. The equations regarding bond-slip of the lap splice with minimum spliced length are established and the stress and strain states of lap splices with different spliced lengths are analyzed on the basis of equilibrium of forces with a mean bond stress model. Finally, the validity of the proposed analysis procedure is confirmed by comparing the analytical results with previous experimental data.

Lapped-steel effects on bridge pier behavior under moderate near-fault motions

Extensive research for the Far Fault Ground Motion (FFGM) has been carried out in strong seismic regions, but limited research has been done for the Near Fault Ground Motion (NFGM) because of very few records. Shake table tests for NFGM were conducted to investigate the seismic behavior of Reinforced Concrete (RC) bridge columns with lap-spliced longitudinal bars that are designed in low or moderate seismic region. Seven RC column specimens with a height of 1400 mm (55.2 in) and a diameter of 400 mm (15.8 in) were tested on a shaking table, and one alike specimen was quasi-statically tested. The effect on lap-spliced longitudinal reinforcing steel was investigated. Shaking test results are compared to those of the quasi-static test. The displacement ductility was significantly decreased in RC column specimens with lap-spliced longitudinal reinforcing bars. The effect of NFGM is compared to that of FFGM. The NFGM specimen showed somewhat less seismic capacity than the FFGM model from Fig. 4(d). Decrease of displacement ductility and energy dissipation was observed in the shake table test specimens in comparison with the quasi-static model.

Effectiveness of R/C jacketing of substandard R/C columns with short lap splices

The effectiveness of a retrofitting method for concrete columns with particular weaknesses is experimentally evaluated and presented in this paper. Structural deficiencies namely the inadequacy of transverse reinforcement and short length of lap splices are very common in columns found in structures built prior to the 1960s and 1970s. Recent earthquakes worldwide have caused severe damages and collapses of these structures. Nevertheless, the importance of improving the load transfer capacity between the deficiently lap-spliced bars is usually underestimated during the strengthening procedures applied in old buildings, though critical for the safety of the residents\' lives. Thus, the seismic performance of the enhanced columns is frequently overestimated. The retrofitting approach presented herein involves reinforced concrete jacketing of the column sub-assemblages and welding of the lap-spliced bars to prevent the splice failure and conform to the provisions of modern design Codes. The cyclic lateral loading response of poorly confined original column specimens with insufficient lap splices and the seismic behavior of the retrofitted columns are compared. Test results clearly demonstrate that the retrofitting procedure followed is an effective way of significantly improving the seismic performance of substandard columns found in old buildings.

Flexural ductility of reinforced concrete beams with lap-spliced bars

In this paper, the flexural ductility of lap-spliced reinforced concrete (RC) beams is experimentally investigated. Twenty-four specimens were designed and manufactured for laboratory experiments. Concrete compressive strength, amount of transverse reinforcement over the splice length, and the diameter of longitudinal bars were selected as the main variables. The ductility of tested specimens is evaluated based on a previously defined ductility ratio. Results show that concrete strength and amount of transverse reinforcement over the splice have major effects on ductility. With an appropriate amount of transverse reinforcement, a satisfactory ductility response for different concrete strengths can be obtained. The CSA-A23.3-04 Standard provisions on bond strength and ductility of lap-spliced RC beams are evaluated and discussed. This study shows that the provisions in predicting the bond strength of lap-spliced concrete beams are adequate but may not achieve a satisfactory performance for ductility. An equation is proposed to achieve the appropriate ductility.

Seismic performance investigation of RC piers with lap-spliced longitudinal bars as to aspect ratio

A survey of previous studies for the seismic performance investigation of existing non-seismic bridges in Korea revealed that numerous studies have been made on piers failing in bending, but studies on piers failing in shear were rather neglected despite their large presence. Accordingly, full scale specimens with aspect ratios of 2.67 and 2.25, being prone to behave respectively in flexure-shear and shear modes, and reduced scale specimens with an aspect ratio of 2.67 were fabricated and subjected to a seismic performance test. The failure behaviour of the specimens was then examined with respect to the amount of lap-spliced longitudinal steels in the plastic hinge region, the aspect ratio, and the scale factor. Test results verified that piers with an aspect ratio expecting flexure-shear behaviour showed flexure failure mode due to the reduced scale factor, and also showed the flexural failure or bond failure of the longitudinal steels according to the lap-spliced details. Based on the experimental results, formulas for the yield and ultimate displacements of circular reinforced concrete bridge piers without seismic details are proposed to evaluate the seismic performance of existing non-seismic bridge piers. These formulas will be useful for the repair and strengthening of non-seismic bridge piers by rationally evaluating their seismic performance.

Models for FRP-wrapped rectangular RC columns with continuous or lap-spliced bars under cyclic lateral loading

A large database of cyclic tests on rectangular reinforced concrete (RC) columns wrapped with Fiber Reinforced Polymers (FRP) is used to develop or calibrate simple rules for the calculation of the column’s: (a) yield moment; (b) chord rotation at yielding; (c) secant stiffness to the yield point; (d) flexure-controlled ultimate chord rotation in cyclic loading and (e) cyclic shear resistance after plastic hinging. Two models are proposed for the ultimate chord rotation: the first one is based on a plastic hinge model which employs a plastic hinge length, the yield and the ultimate curvatures of the end section and the fixed-end-rotation due to slippage of bars from their anchorage zone beyond the column length; the other is an empirical extension of a previous model for rectangular RC columns without FRP-wrapping. The models cover seamlessly columns with vertical bars continuous or lap-spliced in the plastic hinge and FRP wrapping of the lap-splice region.