Lap Splice Research Articles

Evaluation of failure mechanism in lap splices and role of stirrup confinement using 3D RBSM

The bond behavior and failure mechanisms of lap splices with multiple deformed rebars were evaluated using a Three-Dimensional Rigid Body Spring Model (3D RBSM) with beam element. Previous studies have shown the applicability of the method in simulating the bond behavior of single deformed rebar. In this study, we validated the applicability of the numerical method in the simulation of bond stress-slip behavior in unconfined and confined lap splices with various parameters. Then, in unconfined lap splices, we investigated the simulated detail internal crack development considering the strut crack propagation between the individual rebar of lap splices and around the rebars, phenomena that cannot be observed in test. It was found that at the failure section, the strut cracks interlink and propagate at an incline relative to the side surfaces, causing significant bond and concrete stress loss in the lap splice span. As a result, we investigated the failure mechanism and the roles of the geometric and material characteristics of stirrups in improving the performance of lap splices.

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.

Analysis of Reinforcement Overlapping on Retrofit Reinforced Concrete Beams of Bending Behavior

The length of reinforced concrete blocks varies widely, while in general the reinforcement produced in Indonesia is 12 m. Therefore, the use of reinforcement in a long stretch is done to be connected. The through connection is the most economical connection [2]. Lap splice can be made by overlapping the reinforcement which is touching or separate [3]. Splicing reinforcement can cause the strength of reinforced concrete beams to be reduced or even damaged so that rehabilitation measures are needed which can be in the form of retrofit (repair). Retrofitting with wiremesh and self compacting concrete (SCC) is considered to improve building structures. Reinforcement overlapping on reinforced concrete beams retrofit with wiremesh and self compacting concrete can be analyzed by numerical methods to determine their effect on bending behavior. Now, to analyze a structural behavior, it can be done using finite element method based program. The application of the finite element method is used in several programs, including ABAQUS, ADINA, Atena, ANSYS, etc. This study aims to analyze the overlapping of reinforcement in retrofit reinforced concrete beams against the flexural behavior, overlapping is made at one-third and one-third of the beam span using finite element method based analysis software.

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.

나선철근 또는 U철근으로 횡보강된 SD400 D10 철근 겹침이음 실험

신구 슬래브의 접합을 위해서는 슬래브 철근의 이음이 필요하다. 철근을 겹침이음하기 위해서는 기존 슬래브 끝단의 콘크리트 파쇄가 불가피하다. 콘크리트 파쇄는 기존구조물의 손상을 야기하고 공사비 또한 매우 높다. 신구 슬래브 접합은 주로 응력이 낮은 위치로 설계하므로 SD400 D10 철근이 사용된다. 이 연구에서는 나선철근 또는 U철근으로 횡보강한 SD400 D10 철근의 이음실험을 수행하였다. 실험변수는 콘크리트 압축강도, 겹침이음 길이, 주철근의 간격, 철근의 위치 그리고 이음구간의 횡보강 형태로 설정하여 총 32개 실험을 수행하였다. 대부분의 실험체에서 예상강도보다 높은 강도를 발현하였다. 나선철근 또는 U철근으로 횡보강된 SD400 D10 철근은 10의 짧은 이음길이에서도 설계 항복강도 400 ㎫를 발현하였다. 단면해석을 통하여 이음철근에 발현된 응력을 계산하고, 이 연구와 유사한 조건을 갖는 ACI 408 위원회 DB의 2개 자료를 포함하여 총 26개 실험결과를 4가지 제안식과 비교하였다. ACI 408 위원회 식이 [실험값]/[예측값] 비가 1.12로 1.0에 가장 가깝고, 변동계수가 12 %로 가장 낮아 신뢰성이 높았다. 다른 식보다 많은 설계 변수를 고려하는 ACI 408 위원회 식은 철근 지름의 영향도 고려하여 이 연구의 대상인 SD400 D10 철근의 이음강도를 비교적 정확히 평가하였다. ACI 408 위원회 식에 5 % 분위수 안전율을 적용하여 나선 철근 또는 U철근으로 횡보강된 SD400 D10 철근의 이음길이 설계식을 제안하였다.

Non-contact lap splice connections for steel-plate composite walls - to - reinforced concrete structures

Non-contact lap splices may be considered for connecting steel-plate composite (SC) walls to conventional reinforced concrete (RC) structures. This connection type is preferred over mechanical splice connections because of perceived construction efficiency. The primary components of the non-contact lap splice connection are the steel rebars, which are fully developed in the RC structure and extended and embedded in SC walls to transfer tensile stresses to the steel faceplates. The structural performance of a non-contact lap splice connection depends on the detailing of rebars (embedment length and location relative of stud anchors) embedded in SC walls, and the design of stud anchors (spacing and size) along the rebar length. This paper presents the results of experimental investigations conducted on SC-to-RC non-contact lap splice connections to evaluate the influence of various design and detailing parameters on structural performance, failure modes, and the ability to develop full-strength connection design. Design recommendations developed previously for SC-to-RC non-contact lap splice connections were reviewed and modified based on the results of experimental investigations.

Lateral Deformation Capacity and Plastic Hinge Length of RC Columns Confined with Textile Reinforced Mortar Jackets

This paper presents a nonlinear finite element analysis (FEA) of textiles reinforced mortars (TRM)-confined reinforced concrete (RC) columns through jacketing, under combined axial and cyclic loadings. The FEA models were validated with an experimental study in the literature that was conducted on full-scale square columns reinforced with continuous steel bars (no lap splices). Subsequently, parametric study was performed on the validated FEA models. The parameters considered include various jacket’s lengths and mortar strengths. Moreover, semiempirical models were developed to evaluate the plastic hinge length (LP) and the ultimate drift ratio of RC columns confined with TRM and FRP jackets, while considering the jacket length effect. The FEA models and experimental results were in good agreement. The finite element results revealed that the increase in the jacket length improved the lateral deformation capacity and increased the plastic hinge length linearly up to a confinement ratio of 0.2. Beyond this point, the plastic hinge length shortened as the confinement ratio raised. Moreover, mortars with higher flexural strength resulted in a slightly higher deformation capacity. However, the difference in the mortar compressive strength did not affect the ultimate lateral deformation capacity. The semiempirical models show that the average difference in the predicted LP and the ultimate drift ratio values as compared to the experimental and simulated columns was 3.19 and 16.06%, respectively.

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.

Mechanical Properties and Energy Conservation Analysis for The New Connection of The Fabricated Shear Wall

In order to investigate a reliable reinforcement connection form for the assembly nodes of the fabricated reinforced concrete shear walls with joint seams, and explore a reinforced bars lap splice method with easy control of construction quality, a new type of reinforced bars lap splice method with the additional X-shaped reinforcement at the assembly nodes is proposed. By changing the width of the assembly nodes, three fabricated shear wall models were designed. By using Abaqus finite element analysis software, the full-range numerical simulations of its mechanical properties under static load were carried out to study the behaviors of the new reinforced bars lap splice method, which were compared with the behaviors of the cast-in-place monolithic shear wall with the same design parameters and analyzed. The results show that the additional X-shaped reinforcement changed the force transmission path of the reinforced bars lap splice at the assembly nodes and reduced the cross-sectional stress of lap splice area, and improved the reliability of the weak part of the fabricated shear walls. The method also reduced the difficulty of assembling fabricated shear wall structure. Comparing the fabricated shear walls in the same assembly position, the analyses show that the reinforced bars lap splice with the additional X-shaped reinforcement is not sensitive to joint seam width, which can realize the shear walls can assemble with small seam width, and effectively improves prefabrication rate.

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.

Evaluation of seismic performance of as‐built and retrofitted reinforced concrete frame structures with LAP splice deficiencies

AbstractSeveral studies have looked at the development of hinge models to simulate the hysteretic response of flexure‐ and shear‐critical reinforced concrete (RC) beam‐column components from damage initiation to onset of gravity collapse. However, few studies have been conducted to develop similar models for older type bond‐critical beam‐column components. First, using existing experimental data, this paper describes the calibration of simple and efficient hinge models to simulate the inelastic hysteretic response of as‐built and retrofitted splice‐deficient columns. Subsequently, to demonstrate the applicability of the hinge models, the seismic performance of as‐built and fibre‐reinforced polymer (FRP) ‐retrofitted two‐ and four‐story nonductile RC frame buildings with splice‐deficient columns are assessed using nonlinear dynamic analysis procedures. The results show that buildings with bond‐critical columns may have a lower collapse potential than buildings with shear‐critical columns, implying that in certain cases a longer splice length may actually worsen performance. According to the analyses, local retrofitting of the columns can significantly improve the seismic performance of the buildings. Contrary to results presented in this study, a significant U.S. evaluation methodology for RC frame buildings, FEMA P‐2018, indicates that buildings with bond‐critical columns have similar collapse potential as buildings with shear‐critical columns. Modifications are proposed to improve the FEMA P‐2018 provisions. The modelling approach presented in this paper are recommended for incorporation into ASCE/SEI 41, engineering practice and future research.

Punching shear strength of reinforced concrete transfer slab-column connections with shear reinforcement

At RC transfer slab system, the load transfer from the above vertical members to the bottom columns is significantly changed, which requires two-way shear action. For structural safety, a reasonable design for two-way shear strength of RC transfer slab systems is of importance. To improve the two-way shear strength, stirrups are generally used for shear reinforcement in RC transfer slabs. However, unlike conventional structural members using single leg stirrups, lap spliced stirrups are used in the RC transfer slab due to construction difficulty. In the present study, concentric compression tests were performed on four RC transfer slabs with small shear span-to-depth ratio and shear reinforcement to investigate the two-way shear strength. The test parameters were the conventional stirrups, lap splice of stirrups, and steel truss for shear reinforcement. The two-way shear strength, failure mode, and strain distribution of reinforcement of the slab specimens were evaluated. The test results showed that the use of spliced stirrups increased the two-way shear strength of the transfer slab specimen. The two-way shear strengths of the test specimens were compared with the predictions of the current design method and the strut-tie model.

A Case Study on Comparison of Column reinforcement with Couplers and without couplers as Lap Splices

Regular construction practices focus makes use ofreinforcing bars for transferring forces. Method of lap Splice isgenerally used for ensuring continuity of reinforcement steel.However, this method results in minor defects such as jointfailure, inadequate length for lapping, improper welding ofbars, increased cost of labor etc.A comparative study of column reinforcement with couplersand without couplers as lap splices was carried out through acase study of an under construction building. Initially thequantity of reinforcing bars required for conventional lapsplicing of columns was estimated. The value of steel forproviding lap splices within the columns was also determined.Finite element analysis of coupled rebar is carried out to checkfor the yielding and ultimate stresses developed. These valuesare verified with that specified in the code. The use of couplerssignificantly decreases construction time and quantity of steelrequired in lapping.The use of couplers as lap splices provides an economic wayof connecting reinforcement without adversely affecting thestrength of the joint.

Cutting Waste Minimization of Rebar for Sustainable Structural Work: A Systematic Literature Review

Rebar, the core resource of reinforced concrete structures, generates more carbon dioxide per unit weight than any other construction resource. Therefore, reducing rebar cutting wastes greatly contributes to the reduction of greenhouse gas (GHG). Over the past decades, many studies have been conducted to minimize cutting wastes, and various optimization algorithms have been proposed. However, the reality is that about 3 to 5% of cutting wastes are still generated. In this paper, the trends in the research on cutting waste minimization (CWM) of rebar for sustainable work are reviewed in a systematic method with meta-analysis. So far, the literature related to cutting waste minimization or optimization of rebar published has been identified, screened, and selected for eligibility by Preferred Reporting Items for Systematic Reviews and Meta-Analyses, and the final 52 records have been included in quantitative and qualitative syntheses. Review by meta-analysis was conducted on selected literatures, and the results were discussed. The findings identified after reviewing the literature are: (1) many studies have performed optimization for the market length, making it difficult to realize near-zero cutting wastes; (2) to achieve near-zero cutting wastes, rebars must be matched to a specific length by partially adjusting the lap splice position (LSP); (3) CWM is not a one-dimensional problem but an n-dimensional cutting stock problem when considering several rebar combination conditions; and (4) CWM should be dealt with in terms of sustainable value chain management in terms of GHG contributions.

Post-fire performance of RC beams with critical lap splices – Numerical parametric study

The paper presents and discusses the results of a numerical study on post-fire (residual) behavior of reinforced concrete (RC) beams with critical tension lap splices. It is based on the experimental findings and the validation of the numerical approach in the accompanying paper and further analyzes the residual performance by varying most influencing parameters such as bond length, fire duration and concrete cover to the spliced reinforcing steel. Three-dimensional numerical (FE) analysis is performed employing the temperature dependent microplane model for concrete in the framework of the smeared crack approach. The numerical results show that the exposure to fire can change the strength hierarchy of the flexural member such that the splice lengths required to develop the bar under ambient (unheated) conditions may not be sufficient to develop the bar in residual (post-fire) conditions due to the preceding bond splitting failure. It is further found that increased concrete cover does not significantly enhance the post-fire flexural capacity. In closing, a design concept for the determination of the required bond length in case of fire loads is presented.

An experimental study on the influence of incorporating lap or forging (GPW) splices on the cyclic performance of RC columns

Bar splices play an important role on the performance of RC structures by transferring loads from one bar to another. Therefore, applying an appropriate method to achieve satisfactory stress transmission has become a major concern for structural designers. In the present study, the application of lap and forging splice methods in RC columns is evaluated experimentally. Four 1/3 scale RC columns were fabricated and examined under cyclic and axial loads: the reference column with non-spliced bars, one specimen with lap splices at the middle of column and two other specimens with forging splices at two different positions of longitudinal bars. Force-displacement hysteresis curves and crack propagation of the specimens are presented and discussed. Moreover, the specimens are compared together in terms of ductility, absorbed energy, stiffness and curvature to find out the influence of applying forging splice method. An equation is also proposed to calculate plastic hinge length of RC columns. Results indicated that using forging splices either at the middle or at the bottom of columns can increase displacement ductility, curvature ductility and plastic hinge length while lap splices can decrease mentioned seismic parameters. Moreover, incorporating forging splices at the bottom of columns may increase stiffness and ultimate moment. Overall, it was concluded that forging splices can be considered as a reliable method for bar splicing under cyclic and axial loads.

Seismic Performance Enhancement of RC Columns Using Thin High-Strength RC Jackets and CFRP Jackets

The existing non-ductile RC structures built prior to the 1960s–1970s were mainly conceived to carry only vertical loads. As a result, the columns of these structures demonstrate poor overall hysteresis behavior during strong earthquakes, dominated by brittle shear or/and premature excessive slipping of the inadequately lap-spliced reinforcement. In the present study, the effectiveness of two different strengthening systems (including either the wrapping of the columns by carbon-fiber-reinforced polymer textile or the use of thin high-strength reinforced concrete jackets), was experimentally and analytically investigated. The main variables examined were the strengthening material, the length of the lap splices and the amount of confinement provided by the jackets. Three cantilever column specimens were constructed without incorporating modern design code requirements for preserving seismic safety and structural integrity. Subsequently, the specimens were strengthened and subjected to earthquake-type loading. Their hysteresis performances were compared, while also evaluated with respect to the response of two similar original specimens and the behavior of a control one with continuous reinforcement, tested in a previous study. The predictions of the proposed analytical formulation for the hysteresis behavior of the strengthened specimens were satisfactorily verified by the experimental results.

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.

Seismic assessment of reinforced concrete columns with short lap splices

Existing reinforced concrete (RC) columns with short splices in older-type frame structures are prone to either a shear or bond mechanism. Experimental results have shown that the force–displacement response of columns exhibiting these failure modes are different from flexure-critical columns and typically have lower deformation capacity. This article presents a failure mode-based approach for seismic assessment of RC columns with short splices. In this approach, first, the probable failure mode of the component is evaluated. Subsequently, based on the failure mode, the force–displacement response of the component can be predicted. In this article, recommendations are proposed for evaluating the probable failure mode, elastic rotation, drift at lateral failure, and drift at axial failure for columns with short splices experiencing shear, flexure, or bond failures.

EXPERIMENTAL STUDY ON PULLOUT BEHAVIOR OF LAP SPLICE CONNECTIONS BETWEEN DOUBLE-STEEL-PLATE COMPOSITE WALLS AND RC RAFT FOUNDATION IN NUCLEAR ENGINEERING

Combining the advantages of steel and concrete, the double–steel-plate composite (DSC) structures exhibit the advantages of high bearing capacity, good seismic performance and durability, and convenient construction, and they have been increasingly used in nuclear engineering projects. The connection between DSC walls and reinforced concrete raft foundation is the key to make full use of the aforementioned advantages. Compared with the traditional embedding connection and anchoring connection, the lap splice connection can greatly improve the construction efficiency, which gains more and more attention. However, there is few research on such connection. Therefore, in this paper, four 1∶2 scaled lap splice connections between double-steel-plate composite wall and RC foundation are designed, and the static monotonic loading tests are carried out. Through the observation of bearing capacity, stiffness, crack pattern and strains of steel plate and rebar, the influences of the arrangement of lapped bars and tie bars on the mechanical performance of the connections are explored. The test results show that this kind of connection can achieve equal strength and shows satisfactory ductility. Transverse bars can control the crack development effectively and improve the integrity of the connection greatly; in addition, the tie bar strain along the lap length is not linearly distributed. The higher eccentricity of the lapped bars, which means larger unbalanced moment between the reinforcement and the steel plate, will result in lager strains of the transverse bars and lower slip of lapped bars. This paper provides experimental basis for the design of lap splice connections.