Lap Splice Region Research Articles

Finite element analysis on non-contact lap splice connections in ultra-high-performance concrete

This study investigates the stress characteristics and failure modes of the lap splice region for non-contact lap-spliced rebar embedded in Ultra-High-Performance Concrete (UHPC), as well as the influence of lap parameters on these aspects. A series of refined finite element models of non-contact lap-spliced rebars embedded in UHPC were established and validated. The influences of UHPC mechanical properties, splice length, and clear spacing on lap region and the failure modes of specimens were studied. As the lap clear spacing increases from 0.5d to 4d, the ratio of principal compressive stress to principal tensile stress in the lap region of the elastic model decreases from 2.36 to 0.36. This trend indicates that with increasing clear spacing, the force transfer between rebars shifts from being dominated by compressive stress to tensile stress within the UHPC lap region. Consequently, the maximum load of the specimen transitions from being governed by compressive strength to being governed by tensile properties. With a clear spacing of 2d, the maximum load of the specimen increases with the splice length. The maximum load of 8d splice length specimen was increased by at least 27 % compared to the specimen with 0d splice length.

Structural behavior of jointed precast concrete beams reinforced with GFRP bars

This experimental research aims to reduce the joint length between the precast concrete elements reinforced with GFRP bars. The experimental work was divided into two stages. Stage (I) consists of twelve specimens made from GFRP bars and jointed together using GFRP or steel sleeves filled with epoxy resin. The specimens were tested under tension up to failure to investigate the tensile capacity of splice bars taking into consideration different parameters such as sleeve type, embedment length, bar size, and sleeve radial stiffness. While Stage (II) consists of ten reinforced concrete beams measuring 200 × 350 × 3300 mm. All beams were tested under a four-point bending load up to failure. The connection types for GFRP bars were investigated using two methods; (i) the optimum sleeve connector selected from stage I, (ii) using lap splice with different parameters such as splice length, joint compressive strength, and confinement lap-splice region with GFRP sheets. The test results show that an adequate bar embedment length and sleeve radial stiffness are required to achieve bar tensile strength. Whereas lap splice length can be reduced by increasing confinement of lap splice region with GFRP sheets. Finally, precast elements' joint length can be minimized by using a sleeve connector with adequate radial stiffness and embedment length equal to 15-times bar diameter or by confinement of the lap splice region to minimize its length to 40-times bar diameter.

FATIGUE BOND LIFE OF REINFORCED CONCRETE BEAMS WITH LOW REINFORCEMENT CORROSION

Corrosion in reinforced concrete elements can result in a decrease in cross-sectional area and loss of bond between steel and concrete. The cumulative effects of fatigue loading can exacerbate the adverse impact on the bond characteristics between steel and concrete. In this study, the impact of reinforcement corrosion on the fatigue bond life of reinforced concrete members using lap-splice specimens is investigated. The beams are designed such that the failure of the control specimen occurs due to bond failure in the lap-splice region. Stirrups are provided in the lap-splice region to consider the influence of stirrup confinement on bond behavior. The longitudinal rebars and stirrups in the lap-splice region are subject to accelerated corrosion using the impressed current technique, respectively achieving approximately 5% and 15% mass loss. Subsequently, the beam specimens are tested under four-point loading, such that the lap-splice region falls under a constant moment zone. Under monotonic loading, the control specimen experiences abrupt failure due to bond failure. In fatigue loading, the corroded specimen exhibits a significant reduction of 98% in its fatigue life.

FATIGUE BOND LIFE OF REINFORCED CONCRETE BEAMS WITH LOW REINFORCEMENT CORROSION

Corrosion in reinforced concrete elements can result in a decrease in cross-sectional area and loss of bond between steel and concrete. The cumulative effects of fatigue loading can exacerbate the adverse impact on the bond characteristics between steel and concrete. In this study, the impact of reinforcement corrosion on the fatigue bond life of reinforced concrete members using lap-splice specimens is investigated. The beams are designed such that the failure of the control specimen occurs due to bond failure in the lap-splice region. Stirrups are provided in the lap-splice region to consider the influence of stirrup confinement on bond behavior. The longitudinal rebars and stirrups in the lap-splice region are subject to accelerated corrosion using the impressed current technique, respectively achieving approximately 5% and 15% mass loss. Subsequently, the beam specimens are tested under four-point loading, such that the lap-splice region falls under a constant moment zone. Under monotonic loading, the control specimen experiences abrupt failure due to bond failure. In fatigue loading, the corroded specimen exhibits a significant reduction of 98% in its fatigue life.

Local Behavior of Lap-Spliced Deformed Rebars in Reinforced Concrete Beams.

Twelve full-scale reinforced concrete beams with two tension lap splices were constructed and tested under a four-point loading test. Half of these beams had shorter lap splices than that recommended by American Concrete Institute Building Code ACI 318-19; they failed by bond loss between steel and concrete at the lap splice region before rebar yielding. The other half of the beams were designed with a lap splice length slightly exceeding that recommended by ACI 318-19; they failed by rebar yielding and exhibited a ductile behavior. Several strain gauges were attached to the longitudinal bars in the lap splice region to study the local behavior of deformed bars during loading. The strain in a rebar was maximum at the loaded end of the lap splice and progressively decreased toward the unloaded end because the rebar at this end could not sustain any load. Stress flow discontinuity occurred at the loaded end and caused stress concentration. The effect of this concentration was investigated based on test results. The comparison of bond strengths calculated by existing equations and those of tested specimens indicated that the results agreed well.

Cyclic Performance of RC Columns with Inadequate Lap Splices Strengthened with CFRP Jackets

The cyclic performance of non-seismically designed reinforced concrete (RC) columns, strengthened with carbon fiber reinforced polymer (CFRP) jackets, was analytically and experimentally investigated herein. Three cantilever column specimens were constructed, incorporating design parameters of the period 1950s–1970s, namely with concrete of a low compressive strength, plain steel bars, widely-spaced ties and inadequate lap splices of reinforcement. The specimens were strengthened using CFRP jackets and were subsequently subjected to cyclic inelastic lateral displacements. The main parameters examined were the length of the lap splices, the acceptable relative bar slipping value and the width of the jackets. The hysteresis behaviors of the enhanced columns were compared, while also being evaluated with respect to those of two original columns and to the seismic performance of a control specimen with continuous reinforcement, tested in a previous work. An analytical formulation was proposed for accurately predicting the seismic responses of the column specimens, comparing the actual shear stress value with the ultimate shear capacity of the concrete in the lap splice region. The test results verified the predictions of the analytical model, regarding the seismic performance of the strengthened columns. Moreover, the influences of the examined parameters in securing the ductile hysteresis performance were evaluated.

Methodology for Regularization of Force-Based Elements to Model Reinforced Concrete Columns with Short Lap Splices

In reinforced concrete structures built before the 1970s, it was common for columns to be constructed with short lap splices and widely spaced transverse bars at the column base, leading to increased likelihoods of pull-out failures and structural collapse during seismic events. In the modeling and analysis of reinforced concrete columns with short lap splices, several challenges arise, particularly with softening behavior that leads to strain localization and scaling and convergence issues in analyses. This research presents a methodology to regularize force-based beam-column elements with softening lap-splice material response. In the methodology, a constant energy release criterion is imposed with the constant postpeak energy of the lap-splice region determined from relevant experimental data. With the proposed regularization, the numerical model shows objective results that are independent of the length of the element and number of integration points used. Whereas the accuracy in estimating, for example, the displacement at 20% strength drop using existing nonregularized models changes with the number of integration points, the accuracy using the proposed model remains constant across numbers of integration points used with a mean accuracy of 94% compared with experimental tests. Results from static pushover and cyclic analyses show an order of magnitude decrease in standard deviation of the response using the regularized model. Increased accuracy and increased convergence for the method across the number of integration points used is shown in static and dynamic analyses. The proposed regularization approach is able to alleviate strain localization issues and facilitates the scaling of analyses from small-scale to full-scale structures.

Extended Tension Chord Model for Boundary Elements of RC Walls Accounting for Anchorage Slip and Lap Splices Presence

This paper presents a mechanical model for the simulation of reinforced concrete (RC) wall boundary elements with lap splices, which builds on the tension chord model. The model is composed of an assembly of components, each one accounting for a different source of deformation. Namely: (i) an anchorage-slip element accounting for the strain penetration of the longitudinal reinforcement into the foundation; (ii) a basic tension chord element evaluating the response outside the lap splice zone; and (iii) a lap splice element describing the behaviour within the lap splice region. For an imposed global displacement, the model provides the steel and concrete stress and strain distributions, the crack distribution and opening, as well as the global resisting axial force. For spliced members, the ultimate displacement is computed through a semi-empirical relationship providing the average lap splice strain at failure. Validation is carried out against a series of uniaxial cyclic tests on RC wall boundary elements featuring both continuous and spliced reinforcement; different lap splice lengths and confining reinforcement are considered. Overall, a good match is obtained between numerical and experimental results in terms of crack width, rebar strain distribution along the splices and ultimate displacement.

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.

Crack growth modeling of tension lap spliced reinforced concrete beams strengthened with fibre reinforced polymer wrapping under fatigue loading

This study was aimed at increasing our understanding of the behavior of the bond between a steel bar and the concrete along a lap splice region for structures subjected to cyclic loading. An additional aim of the study was to investigate the effect of fatigue loading on the bond between concrete and steel, and the ability of the new high and low modulus fiber-reinforced polymer (FRP) sheets to enhance the fatigue performance of a tension lap splice. A crack growth model was developed to calculate the fatigue life of the bond specimens. The model results were compared with the experimental outcomes of fifty-three beams tested under fatigue and monotonic loading. There is a good agreement between the calculated number of cycles and the actual fatigue life data for all different wrapping conditions and different concrete cover thicknesses. The difference between the calculated and measured fatigue strength curves did not exceed seven percent.

Feasibility of Reduced Lap‐Spliced Length in Polyethylene Fiber‐Reinforced Strain‐Hardening Cementitious Composite

This research investigates the interfacial behavior between polyethylene (PE) fiber‐reinforced strain‐hardening cement composite (PE‐SHCC) and reinforcing bars that are spliced in the tension region to determine feasibility of reduced lap‐spliced length in PE‐SHCC. Twenty test specimens were subjected to monotonic and cyclic tension loads. The variables include the replacement levels of an expansive admixture (0% and 10%), the compressive strength of the SHCC mixtures (40 MPa and 80 MPa), and the lap‐spliced length in the tension region (40% and 60% of the splice length recommended by ACI 318). The PE‐SHCC mixture contains polyethylene fiber to enhance the tensile strength, control the widths of the cracks, and increase the bond strength of the lap splice reinforcement and the calcium sulfo‐aluminate‐ (CSA‐) based expansive admixture to improve the tension‐related performance in the lap splice zone. The results have led to the conclusion that SHCC mixtures can be used effectively to reduce the development length of lap splice reinforcement up to 60% of the splice length that is recommended by ACI 318. The addition of the calcium sulfo‐aluminate‐based expansive admixture in the SHCC mixtures improved the initial performance and mitigated the cracking behavior in the lap splice region.

Seismic Retrofitting of Rectangular Bridge Piers with Deficient Lap Splices Using Ultrahigh-Performance Fiber-Reinforced Concrete

The effectiveness of an innovative retrofitting method using ultrahigh-performance fiber- concrete (UHPFRC) was investigated experimentally on RC bridge piers with deficient lap splice details. The objective is to study the performance of the proposed retrofitting technique for eliminating the bond failure mode in lap splice regions of rectangular columns with a cross-sectional aspect ratio exceeding 2. The strengthening technique consists of substituting the normal concrete around lapped bars in the splice region by UHPFRC. The test program includes unidirectional reverse cyclic tests conducted on five rehabilitated and one control rectangular large-scale specimens. The longitudinal reinforcement ratio ranged from 1.30 to 1.67% with bar diameters (db) equal to 25, 30, 35, and 45 mm. A splice length at the column base of 24db and stirrup spacing of 300 mm were used for all specimens to replicate column design practice before the introduction of modern seismic design specifications. The selected self-compacting UHPFRC mix contained 234 kg/m3 (3% by volume) of 10 × 0.20-mm straight fibers. The failure of all retrofitted specimens was progressive and ductile because they all failed due to the successive rupture of the dowel bars in the footing at a very high displacement ductility ratio. The lapped splice splitting failure mode was eliminated, whereas no longitudinal bar buckled. The UHPFRC cover integrity contributed to eliminate all failure modes associated with concrete damage (crushing, spalling). Recommendations for applying the proposed technique to deficient column rehabilitation are suggested.

Influence of FRP wrapping on reinforcement performances at lap splice regions in RC columns

Abstract Lap-splice regions are amongst the most critical regions of Reinforced Concrete (RC) members, especially in seismic design. The goal of wrapping with Fibre Reinforced Polymer (FRP) is provide confinement to concrete, however, a further important role is either to increase the bond between the reinforcement bars (in pre-cracked conditions) or to provide for bond (in fully cracked cover conditions). The proposed study aims to quantify the beneficial effect of this retrofit technique on the performance of the longitudinal reinforcement with a first attempt to account explicitly for the pointwise variability of confining stresses. For this purpose, both the reinforcement bar working stress and the anchorage length needed to prevent the bar slippage have been analytically assessed. The model has been validated against experimental tests and a good agreement with the model predictions has been found in both the cases of square and rectangular cross sections.

Effect of the thickness of concrete cover on the fatigue bond strength of GFRP wrapped and non-wrapped reinforced concrete beams containing a lap splice

Lap splices are a common construction method for joining steel rebars in reinforced concrete beams because of their simplicity and low cost. The bond strength between the concrete and reinforcing bars in a splice is crucial to many aspects of the behaviour of a reinforced concrete member. Fatigue flexural loading imposes severe demands on the strength and ductility of the lap splice region in reinforced concrete structures and can lead to a brittle and sudden failure of the member. This paper investigates the effect of different concrete covers on the fatigue bond strength of reinforcing concrete beams containing a lap splice under a fatigue loads. It includes tests of twenty two beams divided into two groups. Each group has beams with 30mm and 50mm clear side and bottom concrete covers. The variables that were addressed where the concrete cover, the presence or absence of GFRP sheet wrapping, the type of loading (monotonic or fatigue) and the fatigue load ranges. The test results showed that an increase in the concrete cover led to an increase in the bond strength under both monotonic and fatigue loading for both the unwrapped and GFRP wrapped beams. Also, the GFRP sheets increased both the fatigue strength and the deflection for both the 30mm and the 50mm concrete covers.

Bond behavior of steel reinforcement in high-performance fiber-reinforced cementitious composite flexural members

High-performance fiber-reinforced cementitious composites (HPFRCCs) exhibit a pseudo strain hardening behavior in tension, and increased damage tolerance when loaded in compression. The unique properties of HPFRCC materials make them a viable material for increasing structural performance under severe loading conditions. In this paper, the bond performance of mild steel reinforcement embedded in HPFRCC beams is presented. Beam specimens with lap splices were tested in four-point bending to examine the bond strength and bond-slip behavior of steel reinforcement embedded in HPFRCC materials. Specimens made with three different HPFRCC mixtures, as well as a traditional normal weight concrete were tested in four point bending. The parameters investigated were the amount of concrete cover and the presence of steel confinement in the lap splice region. Experimental results show that HPFRCC normalized bond strengths increased by 37 %, on average, when compared to concrete. Furthermore, the bond-slip behavior of reinforcement in HPFRCCs had a higher toughness than observed for concrete specimens. Test results are compared with existing bond-slip models for fiber reinforced concrete from beam tests and HPFRCCs from pullout experiments, and a recommendation to modify the ascending branch of an existing bond-slip model applicable to ductile HPFRCCs is proposed.

Tension Lap Splices Strengthened with Ultrahigh-Performance Fiber-Reinforced Concrete

AbstractThis paper presents the results of an experimental program undertaken for evaluating the effectiveness of ultrahigh performance fiber-reinforced concrete (UHPFRC) for strengthening deficient tension lap splices. A total of 18 full-scale beam specimens were tested. Tension reinforcement consisted of two deformed bars spliced at midspan. The strengthening technique consists of replacing normal concrete in the splice region with UHPFRC. One type of fiber concrete was used in this experimental program. It is characterized by a compressive strength of 130 MPa, a high tensile strength of 10 MPa, and ductile strain hardening characteristics in direct tension. The parameters considered were: splice length, bar diameter, repair depth, and bar relative position. To isolate the contribution of UHPFRC, no stirrups were used. The results clearly show the effectiveness of UHPFRC for strengthening deficient lap splices. Failure by splitting in the lap splice region was completely eliminated due to the high tensi...

Performance of RC Columns Affected by ASR. I: Accelerated Exposure and Damage

AbstractIn Texas, a number of RC bridges have developed early cracking. Most of this deterioration has been identified or suspected to be from alkali-silica reaction (ASR), and in some cases from delayed ettringite formation (DEF). An area of concern for the Texas DOT is the performance of columns, and specifically their lap-splice regions, which have varying levels of cracking primarily from ASR but also possibly from DEF. Therefore, a research program was carried out (1) to evaluate the experimental behavior of a typical column using large-scale specimens under varying levels of premature concrete deterioration and (2) to develop an analytical model that can evaluate the behavior of the column based on calibration with the experimental behavior. This paper provides a brief overview of ASR and DEF; documents the design, construction, curing conditions, and instrumentation of 16 large-scale specimens; and presents the findings on the specimen dimensional changes and cracking that occurred during the deter...

Probabilistic capacity models and fragility estimates for RC columns retrofitted with FRP composites

This paper proposes a probabilistic formulation to assess the effectiveness of the fiber reinforced polymer (FRP) retrofit schemes in enhancing the structural performance of reinforced concrete (RC) bridge columns. Two probabilistic models are proposed to predict the deformation capacities of retrofitted columns. One deformation model corresponds to the flexural failure and the other considers the bond failure in the lap-splice region. A Markov Chain Monte Carlo (MCMC) simulation method is used to estimate unknown model parameters in the context of a Bayesian updating approach. The probabilistic capacity models are used to estimate the fragility curves of three example columns. In this paper, fragility is defined as the conditional probability of failure for given deformation demand. The results compare the column fragilities before and after the application of the retrofit measure. The results from the example columns indicate that the use of FRP composites considerably reduced the fragility for the bond failure mode and is also beneficial but with a moderate impact when considering the flexural failure.

Probabilistic model for steel–concrete bond behavior in bridge columns affected by alkali silica reactions

Past research has shown that in concrete bridges, cements with high alkali content combined with reactive siliceous aggregates can result in alkali silica reaction (ASR) in the presence of sufficient moisture. There is a concern that ASR may form at the steel–concrete interface and weaken the bond behavior in RC columns. This could result in a reduction of the structural capacity of columns and overall bridge reliability. Therefore, to accurately assess the column and bridge reliability over the service life of the structure, it is important to account for the possible effects of ASR on the steel–concrete bond behavior in the lap-splice region. This paper develops a probabilistic model of the steel–concrete bond behavior that considers the effects of ASR. The proposed model is formulated starting from a currently available bond–slip model suggested by CEB-FIP. Unknown parameters in the bond–slip model and their statistics are assessed through a Bayesian approach using available data from the load testing of eight large-scale bridge column specimens constructed to study the effect of ASR on the bond behavior in the lap-splice region. The experimental data do not directly show the bond behavior, but are in terms of the force–displacement response of the full specimens. Therefore, to assess the parameters in the bond–slip model, a finite element model is constructed to obtain the force–displacement responses as a function of the parameters in the bond–slip model. The results show that the bond stiffness and strength tend to increase for the specimens exhibiting moderate ASR deterioration, but decrease as ASR deterioration reaches a certain level.

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.