Lap Splice Length Research Articles

Macro and micro polypropylene fiber effect on reinforced concrete beams with insufficient lap splice length

For longer spans of reinforced concrete elements, design codes dictate the use of sufficient lap splice length. Insufficient lap splice length decreases the flexural strength and ductility of reinforced concrete (RC) beams, while fiber addition improves their load-carrying capacity, ductility, and durability. The main purpose of this study was to examine the effects of micro and macro fibers on the lap splice length of RC beams. In this regard, the effect of fiber addition on RC beams having insufficient lap splice length under bending test has been studied in detail. Mixtures were prepared with different fiber ratios (0.5% micro polypropylene (PP), 0.25% micro polypropylene-0.25% macro-synthetic polypropylene (MS), 0.5% macro-synthetic polypropylene by volume of concrete) and performed on half-scale RC beams with various lap splice lengths. In beams with insufficient lap splice length, the addition of MS fiber improved the energy absorption capacity at around 30% and the load-carrying capacity at about 18%, while the effect of PP was limited. Damage analysis of the beam illustrates that MS fiber addition on RC beams inhibits crack propagation and improves load-carrying capacity.

New Model for the Lap-Splice Length of Tensile Reinforcement in Concrete Elements

In this study, a model is proposed to determine the required lap-splice length in RC beams using a multilayer genetic programming machine learning (MLGPML) algorithm. This model was obtained from the study of the bond stress between concrete with normal and high compressive strength and tensile reinforcement. Previous models were used to estimate this bond stress, taking into account different parameters. In this study, using the results of 386 experimental tests on reinforced concrete beams, the lap-splice length and the required transverse reinforcement over that length were calculated. The proposed model to determine the bond stress is very well suited to the design purposes by comparison with various experimental campaigns’ results.

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.

Tensile Performance, Lap-Splice Length and Behavior of Concretes Confined by Prefabricated C-FRCM System

Results of an experimental study aimed to evaluate tensile performance, lap-splice length of carbon fabric-reinforced cementitious matrix system (C-FRCM), and performance of concretes confined by C-FRCM are presented. Green high-strength mortar was used in this study which actively utilized recycled fine aggregate and fine waste glass powder to partially substitute cementitious binder. Test plans were developed in due consideration of prefabricated C-FRCM for strengthening concrete columns: 14 tensile tests, 12 lap-splice tests, and 6 uniaxial compression tests of plain concrete specimens confined by C-FRCM were performed. Test variable for the tensile test was number of fabric layers (one or two layers). Nominal strength of the C-FRCM with two fabric layers was 11.0 MPa while it was 7.4 MPa with one fabric layer in tension. Full strength of the carbon fabric was developed in all tensile tests while the C-FRCM with two fabric layers (with axial fiber amount = 0.59% by vol.) showed pseudo-ductile behavior. From the lap-splice tests in direct tension, an increased lap-splice length was required for the double fabrics over that for the single fabrics. The required splice length was about 170 mm for the single fabrics and it was about 310 mm for the double fabrics. Plain concrete cylinders and prismatic specimens were laterally confined by C-FRCM and subjected to uniaxial compression. All test results showed strain-softening behavior. Compressive strength increased by 10–41% while ductility also increased by 6–45% indicating applicability of the prefabricated type C-FRCM in the future.

Experimental study on seismic behavior of precast concrete beam-column joints using UHPC-based connections

Ultra-high performance concrete (UHPC) with high bond characteristics with reinforcing bars could significantly shorten the lap splice length of rebars. UHPC-based rebar lap splice connections offer larger tolerance and simpler operation than traditional rebar connection approaches, which could ease and accelerate the on-site construction process of precast concrete structures. This paper characterizes the seismic behavior of precast beam-column joints where the longitudinal rebars of columns are connected using UHPC with a lap length of 15 times rebar diameter (15db). Full-scaled cyclic tests on two precast joints and two corresponding monolithic joints to compare were carried out keeping a high axial compression ratio (n) at 0.5. It was demonstrated that the beam-column subassemblies failed characterized by flexural failure of beam end instead of the column or joint core. The arch-like load–displacement curves and stable hysteretic behavior were still captured considering the p-delta effect. The proposed precast beam-column joints with UHPC-based connections could achieve similar bearing capacity, ductility and stiffness degradation rule to the monolithic counterparts. The degenerated four-linear restoring force model was presented and verified. Moreover, the numerical simulation was also performed, and the predicted structural behavior was in agreement with the experimental results.

Model development and seismic performance evaluation of rectangular reinforced concrete columns with short lap splices in existing building frames

Numerous existing building structures around the world were constructed without seismic provisions. Reinforced concrete columns in these buildings feature shortcomings (e.g., shorter lap splices, splices located in the plastic hinge zone, and minimal confinement) which increase their seismic vulnerabilities. To assess the seismic risk associated with these structures, this study proposes a numerical model to capture the nonlinear behavior of bar-slip in lap splices and applies the model to non-ductile building frames. To this end, an experimental database consisting of 28 rectangular specimens exhibiting lap-splice failure prior to yielding is constructed and then used to calibrate the numerical model to optimize the model parameters. The proposed model correlates strongly with the existing experimental data. The seismic damage potential of non-ductile frames is evaluated by developing their fragility curves. The selected building frames feature three stories with different lap-splice lengths and continuous longitudinal reinforcement in the plastic hinge zone. Fragility results indicate that increasing the lap-splice length in the plastic hinge zone decreases the frame vulnerability.

Reinforced Concrete Slabs Strengthened with Lap-Spliced Carbon TRC System

Construction with precast or prefabricated elements requires the connecting of structural joints. This study presents an accelerated construction method to strengthen reinforced concrete (RC) slab-type elements in flexure using precast lap-spliced textile-reinforced concrete (TRC) panels. The objectives of this study are to identify the tensile behavior of a TRC system with lap-spliced textile, and to experimentally validate the performance of the proposed connecting method by flexural failure test for the concrete slabs strengthened by TRC panels with lap-spliced textile. Twenty-one coupon specimens were tested in tension with two different matrix systems and three different lap splice lengths. The influence of the lap splice length and matrix properties on the tensile performance of the TRC system was significant. Five full-scale RC slabs were strengthened by the precast TRC panels with and without the lap splice, and was tested in flexure. The results of the failure test for the strengthened specimens showed that the ultimate load of the strengthened specimen with the TRC panel increased by a maximum of 24%, compared to that of the unstrengthened specimen. Moreover, the failure-tested specimens were re-strengthened by a new TRC panel system and tested again in flexure. The objective of the re-strengthening of the damaged RC slabs by the TRC panel is to investigate whether the yielded steel reinforcement can be replaced by the TRC panel. The initial cracking load and the stiffness of the re-strengthened specimens were significantly increased by re-strengthening.

Bond of recycled coarse aggregate concrete: Model uncertainty and reliability-based calibration of design equations

This paper concerns the design of lap splice lengths for ribbed steel reinforcement bars embedded in concrete produced with coarse recycled concrete aggregates. Recycled aggregates are weaker and typically lead to concrete with lower tensile strength. Both aspects change the model uncertainty of bond strength formulae and a major topic of the paper is the influence of recycled aggregates on the model uncertainty of the bond strength model of fib Bulletin 72. A stochastic model for this model uncertainty is developed from a meta-analysis. The model uncertainty, estimated from analogue specimens made with either natural aggregate concrete or recycled aggregate concrete, is compared and the incorporation of recycled aggregates was indeed found to have a detrimental influence on the model uncertainty. A partial factor for lap splice length design is calibrated through reliability analyses so that the probability of failure of the bond length design of recycled aggregate concrete is equivalent to that of natural aggregate concrete. Two design equations were studied: that of the fib Bulletin 72 and that of the D6 draft of the second generation of Eurocode 2.

An experimental study on bond behavior of tensile lap spliced FRP in aggressive environments

This paper investigates the tensile performance of single lap-spliced fiber reinforced polymer (FRP) coupons subjected to harsh environments. Uniaxial tensile tests were performed on 945 specimens after 2, 4, 12, 20, 28, 36, and 48 weeks of exposure to various conditions, including acidic, alkalis, distilled water, and seawater solutions. The experiment results indicated that a solution with a pH of 12.5 had the highest impact on the deterioration of all joints, regardless of the FRP type and bond length. The bond strength reduction was approximately 18% in glass specimens exposed to the acidic solution and less than 10% in aramid specimens. Joints made of carbon showed excellent resistance against all the conditions. The change in failure mode and the minimum lap splice length were investigated for different types of FRPs. Finally, the effects of parameters on the bond strength of FRP were statistically analyzed using ANOVA analysis, and recommendations for minimum lap splice length were presented based on the analyzed data.

Effect of Inadequate Lap Splice Length on the Seismic Fragility of Ground Soft-story Reinforced Concrete Frames

In this study, numerical analysis was used to derive seismic fragility curves for 3-, 6- and 9-story reinforced concrete (RC) frame with inadequate lap splice length and ground soft-story condition. The structural models were subjected to 15 far-field natural earthquake records. The peak ground acceleration (PGA) of the selected records was scaled in the range of 0.05g to 0.50g with an increment of 0.05g. Incremental dynamic analysis was employed to determine their inter-story drift demand and capacities. The obtained results indicated that the probability of severe damage to the RC frames increased as the number of stories decreased. It was also observed that the RC frames with inadequate lap splice length exhibited significantly higher probability of collapse when compared with RC frames with adequate lap splice length.

Strengthening of Lap-Spliced RC Beams Using Near-Surface Mounting Method

An adequate bond between concrete and reinforcement along lap-splice length is necessary to prevent bond failure in lap-splice zone. Sometimes, lap splice has insufficient bond due to such various reasons as design and construction errors and needs strengthening. NSM and FRP confinement are highly promising methods compared to other available methods. NSM and NSM–CFRP confinement methods used for this purpose, and bonded length and concrete cover were considered as variables. The results reveal that the specifications of lap-spliced RC beams (load-bearing capacity, energy dissipation capacity, and ductility) are increased using strengthening methods. In the NSM, the lap-spliced beam’s strength would be increased, while CFRP leads to more ductility. Besides, load-bearing capacity and ductility led to more values when the concrete cover is increased.

A drift capacity prediction model for retrofitted reinforced concrete columns

Seismic assessment of reinforced concrete (RC) buildings heavily relies on the deformation capacity predictions of members. Similarly, the prediction of the deformation capacity of retrofitted RC columns has the utmost importance for seismic retrofit design. In this paper, a new unified drift model is proposed in order to estimate the rotation capacity of RC columns retrofitted with concrete jacketing, steel jacketing and fibre-reinforced polymer (FRP) wrapping. In order to generate the model, an extensive database was compiled consisting of 269 columns composed of 39 concrete-jacketed, 91 steel-jacketed and 139 FRP-wrapped RC columns failing in flexure mode. In the proposed drift model, the key model parameters are the confinement stress ratio, the axial load ratio and the lap splice length. The accuracy and scatter of the estimations with regard to the previous models were studied. For all of the column retrofitting options, the proposed unified model was observed to have rotation predictions better than the previous models in terms of the mean of the predicted to experimental rotation capacity ratios and with a reduced standard deviation.

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.

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.

On lap splice length of lap-spliced crossties for reinforced concrete columns under cyclic loading

A lap-spliced crosstie comprises two J-shaped rebars, each with a 180° hook at one end and straight at the other end. Six large reinforced concrete columns subjected to lateral cyclic loading were tested. The results indicated the following: (1) the confining effect of horizontally lap-spliced crossties is similar to that of vertically lap-spliced crossties. (2) Splice length of the lap-spliced crossties that is smaller than the code requirement can also provide sufficient concrete confinement. (3) A method for determining required lap splice length for lap-spliced crossties is proposed. (4) The lap-spliced crosstie can considerably improve the constructability of the crossties. Furthermore, the construction quality of reinforced concrete column reinforcement and the seismic resistance capability of reinforced concrete structures can be significantly upgraded.

Lap splices in steel fiber-reinforced reactive powder concrete beams under dynamic loading

Reactive powder concrete is a new cement-based composite with ultra-high strength and performance that has been recently used in many structural elements. This study is focused on studying the effect of lap splices in reinforcing bars on the behavior, strength and deflection of steel fiber-reinforced reactive powder concrete beams under dynamic-harmonic loading. The models were simulated using finite elements approach by ANSYS software with different parameters such as compressive strength of concrete, lap splices length of reinforcing bars, steel fiber percentage and the presence of stirrups in the lap splices zone. Data from experimental test by others were adopted as input data such as loading and mechanical properties of concrete and reinforcements. Total eight beam models were analyzed and two of them were compared with the experimental tests. The analysis results indicate that the criteria based on the ACI code for lap splices is enough in the case of splices in reinforced concrete beam under the effects of harmonic loadings under low and medium frequency ranges, and showed that the increase in lap splice length under the effect of harmonic loading resulted in a decrease in the deflection of beams, especially in case of medium frequency.

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.

An Evaluation of Lap Splice Length of Epoxy Coated Reinforcements Using Beam-End Test

An Evaluation of Lap Splice Length of Epoxy Coated Reinforcements Using Beam-End Test

Performance of non-contact lap splices in geometrically dissimilar bridge column to drilled shaft connections

It is often required to provide a reinforcing steel splicing arrangement with non-contact lap splices due to the limitation of internal space or geometric irregularity for the connection of non-circular bridge columns interfacing directly with circular drilled shafts. But there are concerns regarding the safety and cost-effectiveness of such non-contact lap splices at bridge column to drilled shaft connections because the guidelines in AASHTO LRFD Bridge Design Specifications (2017) and studies on this type of connection are limited. This paper presents an experimental investigation of non-contact lap splices in non-circular bridge column to circular drilled shaft connections. A total of seven large-scale column-drilled shaft specimens were tested to investigate the effects of the critical parameters affecting the performance of such non-contact lap splices. The investigated parameters were the non-contact splice distance between the spliced bars, the lap splice length and the amount of transverse reinforcement in the non-contact lap splice zone. The specimens were subjected to flexure action with both monotonic and cyclic loading. The results of this study provide a basic understanding of the behavior of non-contact lap splices in non-circular columns to circular drilled shaft connections. Based on the findings from the experimental investigation, a set of design recommendations is provided for the design of non-contact lap splices in geometrically dissimilar bridge column to drilled shaft connections. All in all, with the consideration of the current AASHTO LRFD code and the design recommendations from this study, a safe non-circular column to circular drilled shaft connection can be constructed.

Compression Splices of Reinforcing Bars in Reactive Powder Concrete

Compression splices are widely used in compression members such as columns in multi- story buildings. There are efficient design equations for compression splice of reinforcement embedded in conventional concrete proposed by design codes of practice. However, there is no design equation for compression splice in compression members made of reactive powder concrete (RPC). So, it is required to introduce a design equation to calculate the steel bars lap splice length of RPC compression members. In this study, an experimental work was conducted to investigate the effect of different variables on compression splices strength. These variables were compressive strength of concrete, transverse reinforcement amount, splice length, yield stress of reinforcement and spliced rebar diameter. The experimental results showed that; Increase in the yield stress of reinforcing bars, length of spliced bars and compressive strength of concrete result in increasing in splice strength. Meanwhile, increase in diameter of reinforcing bars result in decreasing in compression splice strength. The increase in the amount of transverse reinforcement has insignificant effect on compression spliced strength of rebar. Finite element analysis was used to analyze the tested specimens and compared between numerical and experimental result was carried out. The numerical and experimental ultimate load and load-deflection behavior is very close to each other. Finite element method was used to investigate a wide range of experimental variables values through a parametric analysis. A new proposing equation for compression splicing of rebar in RPC column is presented in this research.