Tension Lap Splice Research Articles

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.

The cyclic performance of reinforced concrete columns using the lap‐spliced crosstie and lap‐spliced inner hoop

A lap‐spliced crosstie consists of two J‐shaped steel bars (rebars) that have a straight end and an end featuring a 180° hook. A lap‐spliced inner hoop is the lap splice of two U‐bars. In this study, cyclic load test was conducted on four large‐sized reinforced concrete (RC) columns to investigate the cyclic performance of RC columns comprising lap‐spliced crossties and lap‐spliced inner hoops. The research results are presented as follows: (a) The ductility of the specimens that adopted the lap‐spliced crossties and lap‐spliced inner hoops was significantly superior to that of the specimens using conventional crossties and crossties featuring a 180° hook on the two ends. (b) The use of the lap‐spliced crossties and lap‐spliced inner hoops may significantly improve the constructability of crossties over the conventional crossties; however, the amount of transverse reinforcement used is most likely to increase. (c) The lap‐spliced crosstie and lap‐spliced inner hoop were formed on the basis of the tension lap splice of rebars. Therefore, column size has to be large enough to meet the minimum requirement for tension lap splice of rebars when lap‐spliced crosstie or lap‐spliced inner hoop is to be used.

Bond strength prediction of tension lap splice for deformed steel bars in recycled aggregate concrete

Splice strength of deformed steel bars embedded in recycled aggregate concrete was experimentally investigated using 48 bottom-cast scaled splice beam specimens detailed with unconfined contact lap splices and tested under four-point bending. The following variables were investigated: concrete grade (normal- and medium-strength), recycled concrete aggregate replacement level (0, 50 and 100%), rebar diameter (12 and 20 mm), splice length (15 and 25 d b), rebar surface characteristics and concrete cover to rebar diameter (c/d b = 1.25 and 2). Bond behaviour and failure modes were noted to be similar in the natural and in the recycled aggregate concrete and a regression analysis of the results shows that f′ c 3/4 provides a good representation of the influence of recycled aggregate concrete grade on splice strength. A descriptive bond strength equation has been proposed for recycled aggregate concrete and it is noted that the MacGregor model (for conventional concrete) gave relatively the most accurate and conservative bond strength predictions for the recycled aggregate concretes under investigation. Bond strength is predicted based on analytical model available in literature.

Experimental investigation of bond behavior with tension lap splice for deformed steel bars in recycled aggregate concrete

Splice strength of deformed steel bars embedded in recycled aggregate concrete (RAC) was experimentally investigated using 48 bottom-cast scaled splice beam specimens detailed with unconfined contact lap splices and tested under four-point bending. The following variables were investigated: concrete grade (normal- and medium-strength), recycled concrete aggregate replacement level (0, 50, and 100%), rebar diameter (12 and 20 mm), splice length (15 and 25 db), rebar surface characteristics, and concrete cover to rebar diameter (c/db = 1.25 and 2). Bond behavior and failure modes were noted to be similar in the natural and in the RAC and a regression analysis of the results shows that f′c3/4 provides a good representation of the influence of RAC grade on splice strength. A descriptive bond strength equation has been proposed for RAC.

Experimental Research on Tension Lap Splice in Reactive Powder Concrete Beams Exposed to Repeated Loading

This research is a part of an experimental study to examine the effect of lap splicing tension steel bars reactive powder concrete (RPC) beams under repeated loads. Eight RPCbeams whose tension steel bars were spliced at mid-span for a length equals 20 times the bar diameter and one RPC beam without lap splice were casted and tested. These beams were simply supported and tested up to failure under the action of two point repeated loads. The studied parameters were: the steel fiber volumetric ratio (1.5%,1.75% and2%), diameter of tension steel bars (12mm, 16mm and 20mm) and the repeated loading regime in which three types of loading were used depending on the minimum to maximum ratio of the applied load. The first loading regime with ratio of 0% with 0 kN for the minimum load while the maximum was the load beyond that causes yielding of steel bars and this is determined from the previous monotonic load test. The second type with 27% ratio (30 kN for the minimum and 105-110 kN for the maximum). The last type was with 20% ratio (the minimum12 kN and the maximum 60 kN).It should be mentioned that 10mm bar diameter was used to the top reinforcement and stirrups for all beams. The mid-span deflection as well as cracks propagation were recorded for each beam throughout the test. The main results showed that the adopted spliced length of tension steel bars was sufficient in monotonic load but insufficient under the action of high number of cycles of the repeated load. In addition, there were beams of splice failure that having low steel fiber ratio or larger diameter of tension steel bars.

Experimental investigation of bond stress distribution and bond strength in unconfined UHPFRC lap splices under direct tension

Several studies on tension lap splices have shown the improvement of bond strength using Ultra-high performance Fibre Reinforced Concrete (UHPFRC). The bridging effect of fibres on cracks improves the bond splitting strength substantially in comparison to normal concrete. This paper investigates the influence of fibre content on the strength of tension lap splice of reinforcing bars in UHPFRC without additional transverse reinforcement. Different splice lengths and UHPFRC mixes were tested. Internal strain measurements were used to capture the force transfer mechanism and the evolution of longitudinal strain distribution and associated bond stresses. The bond performance is clearly related to the pre- and post-cracking tensile capacity of UHPFRC. At a distance exceeding 2 db from bar extremities, bond stress distribution at failure displayed a quasi-constant value regardless of the lap splice length up 10 db. This reveals for short lap splices that the bearing action of all ribs along the splice length contributes equally in resisting the applied force. This experimental program provides experimental results for understanding the local force transfer mechanism in UHPFRC lap splice and contribute for further developments on bond in UHPFRC.

Behavior Of A Confined Tension Lap Splice In High-Strength Reinforced Concrete Beams

Abstract The results of an experimental program conducted on seventeen simply supported concrete beams to study the effect of transverse reinforcement on the behavior of the lap splice of a steel reinforcement in tension zones in high-strength concrete beams are presented. The parameters included in the experimental program were the concrete compressive strength, the lap splice length, the amount of transverse reinforcement provided within the splice region, and the shape of the transverse reinforcement around the spliced bars. The experimental results showed that the displacement ductility increased and the mode of failure changed from a splitting bond failure to a flexural failure when the amount of the transverse reinforcement in the splice region increased, and the compressive strength increased up to 100 MPa. The presence of the transverse reinforcement around the spliced bars had a pronounced effect on increasing the ultimate load, the ultimate deflection, and the displacement ductility. The prediction of maximum steel stresses for spliced bars using the ACI 318-05 building code was compared with the experimental results. The comparison showed that the effect of the transverse reinforcement around spliced bars has to be considered into the design equations for lap splice length in high-strength concrete beams.

Bond strength of tension lap splice specimens in UHPFRC

Outstanding tensile properties of ultra-high performance fibre reinforced concrete (UHPFRC) initiate innovative applications that take advantage of the bond improvement with reinforcement (precast element connections, seismic strengthening of deficient lap splices, etc.). Tests on lap splice specimens under direct tension were performed to investigate the influence of UHPFRC fibre content on bond strength. Three fibre contents (Vf) were examined with large reinforcing bar diameter (db) and multiple splice lengths. According to strain hardening response of UHPFRC under direct tension, results show a considerable improvement of bond performance and splitting crack control. For UHPFRC mix with Vf=4% per volume, a splice length of 12 db was found sufficient to achieve yielding of 400MPa reinforcement; with 10 db length a bond stress around 10MPa is reached. The contribution of the fibres was clearly highlighted through this experimental study, a strong relationship between the bond performance and both the maximum tensile strength and strain ductility of UHPFRC was noted.

Flexural behaviour and ductility of high strength concrete (HSC) beams with tension lap splice

An experimental program has been conducted in order to investigate the flexural behaviour of concrete beams with variable length of tension reinforcement lap splice. A test series of eighteen simple beams containing different lap splice length (0, 300, 500 and 700mm) had been conducted in this investigation. The tested beams are of 2200mm total length and 200×150mm cross-section, loaded at the middle third with two equal concentrated loads. The parameters included in the experimental program are the splice length, the bar diameter (12, 16mm), the amount of transverse reinforcement provided within the splice zone, the shape of the anchor at the splices end and the concrete cover (20, 35mm). The test program has been performed on two grades of high strength concretes (0%, 15% silica fume); 55, 65MPa. Two deformed bars of tension reinforcement were spliced in the constant moment zone. The effect of splicing tension reinforcement on the response, cracking load, crack propagation, deflection, ultimate capacity, mid-span reinforcement strain, failure mode and beam ductility, is examined. Results show that by introducing an appropriate amount and distribution of transverse reinforcement, a satisfactory ductility response can be obtained (91% of reference beam).

인장력을 받는 확대머리 이형철근의 겹침이음에 관한 실험적 연구

현행 콘크리트구조기준 (KCI2012) 및 ACI318-11에서 B급이음된 일자형 이형철근에 대하여 인장력에 대한 겹침이음길이를 정착길이의 1.3배로 산정하고 있다. 동일 기준에서 확대머리 이형철근의 정착길이를 제시하고 있지만 겹침이음상세에 대한 규정은 없다. 이에 본 연구에서는 400MPa과 500MPa 설계기준항복강도를 가지는 확대머리 이형철근의 겹침이음실험을 실시함으로써, 기준의 정착길이식을 겹침이음설계에 적용가능한 지를 평가하고자 하였다. 실험결과, SD400과 SD500의 설계기준항복강도를 적용한 확대머리 이형철근에 대하여 겹침이음길이를 정착길이의 1.3배로 산정할 경우, 실험 최대휨강도가 공칭휨강도에 비하여 16~31% 크게 평가되었고 연성적인 휨파괴 거동을 나타내었다. 따라서, 이들 철근에 대해 정착길이 1.3배의 겹침이음길이로 설계함으로써 강도 및 변형성능 측면에서 겹침이음 성능을 확보할 수 있는 것으로 사료된다. In tension lap splices of straight deformed bars, KCI Code (KCI2012) and ACI Code (ACI318-11) requires that the lap lengths for class B splice are 1.3 times as development length. KCI2012 contains development length provisions for the use of headed deformed bars in tension and does not allow their tension lap splices. The purpose of this experimental study is to evaluate that KCI2012 equation for the development length, <TEX>$l_{dt}$</TEX>, of headed bars can be used to calculate the lap length, <TEX>$l_s$</TEX>, of headed deformed bars in grade SD400 and SD500, having specified yield strength of 400 and 500 MPa. Test results showed that specimens with <TEX>$l_s$</TEX> equal to <TEX>$1.3l_{dt}$</TEX> had maximum flexural strengths as 1.16~1.31 times as the nominal flexural strengths, flexural failure mode, and ductility. These observations indicate that <TEX>$1.3l_{dt}$</TEX> is suitable to the tensile lap length of headed deformed bars in grade SD400 and SD500.

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...

Effect of tension lap splice on the behavior of high strength self-compacted concrete beams

Construction using concrete is spreading widely and there is a need for concrete that is capable of flowing under its own weight without mechanical vibration or compaction and fill the places between reinforcement and the complicated form shapes. From here, Self-Compacted Concrete (SCC) appears for the first time. Limited attention has been directed toward the bond between High Strength Self-Compacted Concrete (HSSCC) and spliced bars in beams [1–8].This research studies the bond between HSSCC and spliced tension bars in beams. It is focused on observing the effect of some factors such as; reinforcement bar diameter and ratio, splice length and casting position on the beam flexural behavior. An experimental program consisting of sixteen simply supported beams divided into four groups is considered. All beams are of 1800mm span and 200×400mm cross-section cast with HSSCC. In twelve beams, the tensile steel was spliced in the constant moment zone, and four control beams without splice for comparison purpose. During testing; ultimate capacity, deflection, crack pattern and mode of failure have been recorded. Test results had been compared with proposed values in the Egyptian code of practice, other international design codes and recorded values of other researchers.

Effect of tension lap splice on the behavior of high strength concrete (HSC) beams

In the recent years, many research efforts have been carried out on the bond strength between normal strength concrete (NSC) and reinforcing bars spliced in tension zones in beams. Many codes gave a minimum splice length for tension and compression reinforcement as a factor of the bar diameter depending on many parameters such as concrete strength, steel yield stress, shape of bar end, shape of bar surface and also bar location. Also, codes gave another restriction about the percentage of total reinforcement to be spliced at the same time. Comparatively limited attention has been directed toward the bond between high strength concrete (HSC) and reinforcing bars spliced in tension zones in beams. HSC has high modulus of elasticity, high density and long-term durability. This research presents an experimental study on the bond between high strength concrete (HSC) and reinforcing bars spliced in tension zones in beams. It reports the influence of several parameters on bond in splices. The parameters covered are casting position, splice length as a factor of bar diameter, bar diameter and reinforcement ratio. The research involved tests on sixteen simply-supported beams of 1800mm span, 200mm width and 400mm thickness made of HSC. In each beam, the total tensile steel bars were spliced in the constant moment zone. Crack pattern, crack propagation, cracking load, failure load and mi span deflection were recorded and analyzed to study the mentioned parameters effect.

Evaluation of tension lap splices for code provisions

Six real-size beams were tested in order to examine the reliability of tension lap splices for the minimum requirements of clear cover, spacing between bars and transverse reinforcement. The beams were prepared in accordance with the minimum provisions of the American Concrete Institute building code requirements for structural concrete (ACI 318–08) and the Turkish standards on requirements for design and construction of reinforced concrete structures (TS 500). Results showed that all beams prepared in accordance with ACI 318–08 showed satisfactory behaviour. Since the specimen prepared according to TS 500 with 26 mm diameter bars failed due to bond, it can be concluded that the TS 500 clear cover is insufficient for spliced bars equal to or greater than 26 mm in diameter. In order to evaluate the ACI Committee 408 new proposal and Eurocode 2 provision for tension lap splices, a case study was also conducted. According to the results of the case study, while the ACI 318–08 requires unnecessarily longer splice lengths for bars of greater than 19 mm diameter, Eurocode 2 always gives the smallest lap splice length which leads to safety concerns.

100 MPa 이하 콘크리트의 철근 압축 이음 강도와 이음 길이 설계

Although a compression splice length does not need to be longer than a tension splice length due to end bearing effect, current design codes impose a longer compression lap splice than a tension lap splice in high strength concrete. Hence, new criteria for the compression lap splice including concrete strength effect need to be found for economical design of ultra-high strength concrete. An experimental study has been conducted using column specimens with concrete strength of 80 and 100 MPa with transverse reinforcement. The test results showed that splice strengths improved when the amount of transverse reinforcement increased. However, end bearing strength did not increase when larger amount of transverse reinforcement is provided within the spliced zone. Therefore, the splice strength enhancement was attributed to the improvement of bond. From regression analysis of 94 test results including specimens made with concrete strength of 40 and 60 MPa, a new design equation is proposed for compression lap splice in the concrete compressive strength ranging from 40 to 100 MPa with transverse reinforcement. By using the proposed equation, the incorrect design equations for lap splice lengths in tension and compression can be corrected. In addition, the equation has a reliability equivalent to those of the specified strengths of materials.

횡보강근이 없는 100 MPa 이하 콘크리트의 철근 압축이음 강도와 이음길이

Although the compression splice needs not be longer than the tension slice due to existence of end bearing, current design codes impose a longer compression lap splice than a tension lap splice in high strength concrete. Hence, new criteria for the compression lap splice including the effects of concrete strength need to be sought for economical design involving ultra-high strength concrete. An experimental study has been conducted with column specimens in concrete strength of 80 and 100 MPa. Test results show that the splice strength can be evaluated to be proportional to square root of compressive strength of concrete. Bar stress developed by end bearing is not affected by splice length and is expressed with a function of the square root of concrete strength. Mean value of stresses developed by end bearing is 16.5 square root of fck. The stresses developed by bond in compression splices are nearly identical to those in tension splices and, therefore, strength increment of compression splices is attributed to end bearing only. From regression analysis of 58 tests, a design equation is proposed for compression lap splice in 40 to 100 MPa of compressive strength of concrete. By the proposed equation, the anomaly of lap lengths in tension and compression is got rid of. In addition, the equation has a reliability equivalent to those of the specified strengths of materials.

40-70 MPa 콘크리트에서의 철근 압축이음 길이

초고강도콘크리트의 개발에 따라 철근 압축이음에 대한 연구 필요성이 높아지고 있다. 40여년 전의 연구를 바탕으로 한 현재의 압축이음 설계기준으로는 향상된 강도를 제대로 활용할 수 없으며, 특히 압축이음길이가 인장이음길이보다 길어지는 기현상(奇現象)이 발생되어 실무의 혼란을 초래하기도 한다. 이러한 현상은 현행 설계기준에서 콘크리트 강도와 횡보강근의 영향을 고려하지 않기 때문이다. 본 연구에서는 51개 실험체의 결과를 바탕으로 40부터 70MPa까지 콘크리트에 대한 압축이음길이 설계식을 제안하였다. 실험 결과를 통해 도출된 압축이음의 영향 인자들을 분석하여 이음강도식의 기본형을 만들었다. 실험 결과에 대한 비선형 회귀분석을 통해 압축이음강도 평가식을 마련하고, 5% 분위수 개념을 통해 설계기준이음강도를 설정하고 압축이음길이 설계식을 도출하였다. 이 연구에서 제안된 압축이음길이 설계식을 이용하여 고강도콘크리트에서 압축이음길이가 인장이음길이보다 길어지는 이상 현상을 해소할 수 있다. 더불어 제안된 압축이음길이 설계식은 통계적 기법에 기반을 두어 재료강도와 동일한 수준의 신뢰성을 확보할 수 있다.

횡보강근이 없는 40, 60 MPa 콘크리트에서 철근 압축이음의 거동과 강도

현행 기준식에 따르면 초고강도콘크리트에서는 철근 인장이음길이보다 압축이음길이가 더 길어지는 현상이 발생된다. 초고강도콘크리트의 경제적 실용화를 위해 합리적인 압축이음강도의 평가가 필요하다. 이를 위해 압축이음의 거동 특성을 분석하고 영향인자를 도출하였으며, 설계강도 40, 60 MPa 콘크리트에 대한 압축이음 실험을 수행하였다. 압축이음강도는 부착과 지압으로 구성되고, 부착과 지압의 복합 거동에 의해 발현되므로, 압축이음 거동특성 및 강도평가를 위해서는 부착과 지압이 함께 존재하는 상태에서의 연구가 수행되어야 한다. 인장이음과 달리 압축이음은 이음길이가 짧고 지압의 존재로 인해 콘크리트 강도의 영향이 크다. 실험결과 압축이음강도는 콘크리트의 제곱근에 비례하는 것으로 평가되었다. 부착과 지압 모두 주변 콘크리트의 응력상태에 따라 결정되는데, 콘크리트의 축방향 응력이 높기 때문에 철근 순간격 증가에 따른 이음강도 증가는 거의 없다. 지압강도는 이음길이와 철근 순간격에 무관하며, 콘크리트 강도의 제곱근의 함수로 표현할 수 있다. 파괴양상이 측면파열파괴와 유사하므로 지압강도는 앵커의 측면파열파괴강도식을 활용하여 평가가 가능하다. 부착에 의해 발현되는 강도는 인장이음의 경우와 유사하므로, 인장이음강도에 비해 향상된 압축이음강도는 단부 지압효과로 설명될 수 있다.

Discussion of “Comparison of Roles of FRP Sheets, Stirrups, and Steel Fibers in Confining Bond Critical Regions” by Bilal S. Hamad and Ahmad A. Rteil

Studies on confinement of tension lap splices and comparison of confinement provided by various techniques such as FRP wrapping, the use of fiber-reinforced concrete and the use of transverse steel have been very meticulously done by the authors. The authors are to be commended for their contribution to the understanding of bond performance with various levels of confinement. The discusser would like to highlight the effect of the size of the specimen on the results reported by the authors. The following points may be taken for discussion. 1. The length of the splice is fixed as 300 mm irrespective of the diameter of the bar. However, the amount of transverse reinforcement needed to provide adequate ductility depends on the splice length Azizinamani et al. 1999 . Because the length of the splice depends on the bar diameter, testing the confinement with a fixed splice length of 300 mm may not give the required results. 2. When the diameter of the bar being tested is varied, the size of the specimen tested must be proportional to the bar diameter Azizinamini et al. 1993 . In the investigations done by the authors, the depth of the beam is kept constant for all the specimens with different bar diameters. This makes the sec-

Comparison of Roles of FRP Sheets, Stirrups, and Steel Fibers in Confining Bond Critical Regions

Based on experimental data of tension lap splices confined with fiber reinforced polymer (FRP) sheets in normal and high strength concrete (HSC) specimens, a new FRP confinement parameter, Ktr,f , was recommended. It accounts for the increase in bond strength due to the presence of FRP sheets. In this paper, a correlation is presented between the confining effects of FRP flexible sheets, transverse reinforcement, and steel fibers to improve the bond capacity and ductility of the mode of failure of tension lap splices. The correlation is based on research programs conducted at the American University of Beirut in recent years using identical specimens except for the confinement method used: FRP sheets, transverse steel stirrups, or steel fibers. Other variables included the amount of confinement provided and concrete strength. Analysis of test results indicated that an equivalent improvement in bond strength of tension lap splices in normal and high strength concrete specimens is provided by an amount of F...