Splice Length Research Articles

Behavior of Lap-Spliced Plain Steel Bars

Fifteen lap splice specimens reinforced with plain steel bars were tested under four-point loading to investigate bond resistance as a function of development length and bar diameter. Three of these specimens were instrumented with both steel and concrete strain gages to examine bond loss within the lap splice length. All of the specimens failed in bond. Splice specimens reinforced with plain bars are capable of resisting maximum loads that are approximately 60% of those recorded for two similar specimens that were reinforced with deformed bars. An analysis of 11 of the splice specimens tested shows that CEB-FIP Model Code provisions for average bond stress underestimates the prediction of the maximum load by 16% on average. A flexural analysis conducted for the instrumented specimens showed that strain compatibility did not exist for much of the loading range.

Bond strength of glass fibre-reinforced polymer bars in unconfined concrete

Glass fibre-reinforced polymer (GFRP) bars can be used to avoid steel reinforcement corrosion in bridge decks, which usually have no transverse reinforcement. In this study, 35 flexural tests of beams and slabs were carried out to experimentally determine the bond strength of spliced GFRP bars with no transverse reinforcement. The test variables included splice length, cover thickness, and bar spacing. The splice lengths were relatively large to test realistic splice lengths used in the field (longer than 30 d b in most tests). In addition, four beams with conventional steel rebar splices were also tested to compare their bond strengths with those of the GFRP bars. Test results showed that the bond strengths of the specimens with GFRP bars were lower than those of the steel rebars. Although the average bond strength of the GFRP bars decreased with increasing splice length and decreasing cover thickness/bar spacing, the bond strength of the long splice increased when c/ d b ⩾ 2.5, in which c denotes the smaller of the minimum concrete cover and 1/2 of the bar clear spacing. Two equations for predicting the average bond strength of GFRP bars in unconfined concrete are proposed based on the regression analysis of the 33 test results from the beams and slabs that failed by concrete splitting.

Flexure of pultruded glass-fibre-reinforced polymer beams with bonded splice joints

Elastic moduli of pultruded glass-fibre-reinforced polymer beam and plate profiles are presented. The method used to fabricate three beams, each with a six-plate bonded splice joint at mid-span, is outlined. Details of the instrumentation used to measure deflections, etc. during three-point flexure tests on the beams are given. Deflections, support rotations and mid-span strains recorded during the tests are presented. Formulae, based on shear deformation beam theory, are presented for predicting the centre deflection and the support rotations of the beams. It is shown that they predict deflections and rotations with a maximum error of about 10%, provided the elastic moduli are derived from coupon tests rather than the manufacturer's minimum values. The theory is extended to provide a simple method, based on the solution of a quadratic equation, for determining the optimum and limiting splice length ratios for particular values of the additional cross-sectional area and additional second moment of area factors and the shear flexibility parameter. Finally, the theory is used in three parameter studies to assess the effects of splice length ratio, adhesive thickness and modulus, splice plate thickness and splice joint layout on the normalised mid-span deflections of spliced beams.

SD600 철근의 B급 겹침 이음에 대한 현행설계기준의 적용성

이 연구에서는 SD600 철근 B급 이음에 대한 현행 설계기준의 적용성 평가를 위하여 실험적 연구가 수행되었다. 단순 지지된 12개의 B급 겹침 이음 실험체에 단순 증가 하중을 가하여 실험하였다. 주요 변수는 겹침 이음 철근 직경, 콘크리트 피복 두께, 콘크리트 강도, 횡보강 철근 간격이다. 콘크리트는 24 MPa의 보통 강도 콘크리트와 60 MPa의 고강도 콘크리트를 사용하였다. 대부분의 실험체는 현행 설계기준의 B급 이음 길이를 만족하도록 설계하였다. 실험에서 발현된 철근 응력의 평균을 현행 KCI설계기준의 예측 철근 응력과 비교하였으며, 그 결과를 통하여 SD600 철근에 대한 현행 설계기준의 적용성을 평가하였다. 현행 설계기준은 모든 D13 겹침 이음과 횡보강 철근이 배치된 D22, D32 겹침 이음에 대하여 안전측이었다. 직경 D22 이상 철근의 겹침 이음은 횡보강 철근의 사용이 권장되는 결과를 나타내었다. 고강도 콘크리트를 사용한 D22, D32 철근의 겹침 이음은 안전한 경향성을 보였으나, 확실한 검증을 위하여 추가적인 연구가 필요하다.

Splice strength of large diameter, high strength steel reinforcing bars

The results of an experimental program conducted to study the splice strength of large diameter, high strength reinforcing bars, either No. 20 (63.5 mm diameter) or No. 9 (28 mm diameter), are presented. The parameters included in the experimental program are the bar size, splice length, concrete compressive strength, and the amount of transverse reinforcement provided within the splice zone. The ability of several models including the current ACI 318 Building Code, to predict the maximum steel stresses at the onset of splitting failure was examined for these high strength, large diameter bars. The influence of the moment of inertia of the bar on the induced splitting stresses was evaluated numerically using finite element analysis. Test results showed that the presence of transverse reinforcement has a more pronounced effect for large diameter spliced-bars compared to regular size bars. It is also shown that the current ACI 318 Building Code provided more conservative bond strength predictions for regular bars compared to large diameter bars.

철근 마디 형상에 따른 RC 휨부재의 부착강도 평가

최근 구조물 설계개념의 변화로 사용응력 수준이 높아지고, 시공 및 경제성의 이유로 고강도 재료의 활용이 증가되고 있다. 그러나 고강도 철근을 사용하면 정착 및 이음 길이가 증가하게 되어 시공성이 저하되고 상세 설계의 어려움을 유발할 수 있다. 이에 따라 이 연구에서는 고강도 철근의 정착 및 이음 길이를 단축시키기 위하여 철근 마디형상의 변화가 부착 성능에 미치는 효과를 분석하도록 하였다. 기존 철근을 포함하여 마디의 형상을 개선한 총 5개의 단순보형 실험체를 제작하여 실험하였으며, 각 실험체는 경간 중앙부에서 겹침 이음되어 부착 파괴를 유도하도록 설계하였다. 실험의 결과는 부착강도, 하중-처짐 관계 및 균열의 관점에서 분석하였으며, 기존 연구자들의 부착강도 관련 설계 및 제안식과 비교·분석하였다. 실험 결과 마디면적비가 증가된 철근은 보통 철근보다 약 11%의 부착강도 향상을 나타내었으며, 마디면적비가 같더라도 높고 낮은 마디를 혼합한 경우에는 23%의 강도 증가를 나타내었다. 또한, 부재의 처짐, 균열의 개수 및 균열폭 등 사용성 관점에서 살펴볼 때, 개선된 형태의 철근은 보통 철근과 유사한 거동을 나타내어 현장적용에 큰 문제가 없을 것으로 분석되었다.

Image analysis of the elastane position effect on the appearance of wet pneumatic spliced elastic core-spun yarn

This work discusses the contribution of the elastane filament (Spandex©) on the appearance of wet pneumatic elastic denim core-spun yarn. The cross-section views of the splice region were investigated using the image analysis method. In fact, this work also defines developed parameters such as the cover factor and the relative distance for quantifying the contribution of Spandex©filament position to the spliced yarn appearance. To improve the objective method (the image analysis), the subjective one (the expert’s rating and the composite desirability) was discussed. Compared to the computer image analysis results, the desirability function provides nearly identical results and proves that appearance can be evaluated objectively. However, compared to the expert’s rating which can complete the computer results, it remains insufficient to subjectively classify the splice appearance. Hence, our findings show that the Spandex©filament angular position is influenced by the important splicing conditions (splice length and duration of water joining). By providing the adequate splicing condition adjustments high splice physical performance is given and a particularly good appearance.

Investigation of closure-strip details for connecting prefabricated deck systems

This article describes how the Bridge Office of the Ministry of Transportation of Ontario initiated a research project to investigate the use of precast bridge technology as an innovative approach to bridge construction and rehabilitation in 2001. Two potential precast systems were investigated: precast composite slab-on-girder beam elements connected with cast-in-place concrete closure strips, and full-depth precast concrete deck slab panels laid across new or existing girders and connected with cast-in-place concrete closure segments. One of the main issues inherent in these precast systems is the presence of cold joints created by the closure pours and their potential effect on the overall deck system behavior. In addition, there is a need to develop effective connection details between the precast elements to provide continuity of reinforcement in the closure strips so that load sharing between girders is not compromised. This article presents the findings of a series of laboratory tests that were performed on 2/3-scale model of the closure strip system to study the serviceability and ultimate state behavior of the joint detail. Several types of reinforcement lapping systems were considered for the steel reinforcement in the closure strips: U-shaped bars, L-shaped bars, welded straight bars, and straight bars with full lap splice length as well as splices with reduced lap length but confined by steel spirals or stirrups. Scale models of the closure-strip connections were subjected to extensive cyclic loading and then tested to failure. Overall, the test results demonstrated the excellent performance of U-shaped, L-shaped, and welded straight reinforcing bars as connection details in the closure strips. The use of high-early-strength concrete in the closure pour was shown to have little effect on long-term performance, while a shortened lap length confined in a steel spiral was shown to be as effective as the conventional full-lap-length splice detail.

Study on spliced yarns of different spinning technologies. Part II: structural characteristics

A detailed study on structural parameters of splices of viscose staple fiber yarns made from ring, rotor, and air-jet spinning technologies are reported in this paper. All the yarns each had six different color tracers with 0.3% of total fibers. A three variable three-level factorial design approach proposed by Box and Behnken has been used to study the interactive effect of splicing parameters. The splicing parameters, such as splicing length, duration of splicing air blast, and splicing air pressure were varied to prepared spliced yarn samples. Splices were introduced at all these levels for the three different technologies. This paper deals with the structural characteristics of splice portions, i.e. splice diameter, helix angle, splicing coefficient of fiber (SCF), and fiber overlapping coefficient (FOC). The structural characteristics, such as splice diameter, helix angle, SCF, and FOC, are significantly affected by the different splicing parameters (i.e. splice length, duration of the opening air blast, and splicing air pressure). Different types of yarns (ring-, rotor-, and air-jet-spun) show different trends of structural characteristics with splicing parameters. Part I of this paper deals with the mechanical characteristics of spliced portion.

Study on spliced yarns of different spinning technologies. Part I: tensile characteristics

The details of a study on splicing behavior of viscose staple fiber yarns, prepared by ring, rotor, and air-jet spinning technologies, are reported in this paper. All the yarns had six different color tracers with each having 0.3% of total fibers. The mechanical and structural properties of splices were studied. A three-variable three-level factorial design approach proposed by Box and Behnken was used to study the interactive effect of splicing parameters. The splicing parameters such as splicing length, duration of splicing air blast, and splicing air pressure were varied to prepare spliced yarn samples. Splices were introduced at all these levels for the three different technologies. The present paper (Part I) deals with the mechanical characteristics of splice portions, i.e. retained splice strength (RSS) and retained splice elongation (RSE). It has been observed that there are significant effects of all these parameters on the tensile characteristics of spliced yarns. However, the trends are different for different spinning technologies. Part II of this paper deals with the internal structural characteristics of splices.

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.

Response of lap splice of reinforcing bars confined by FRP wrapping: modeling approach

This paper presents a tri-uniform bond stress model for predicting the lap splice strength of reinforcing bar at the critical bond splitting failure. The proposed bond distribution model consists of three zones, namely, splitting zone, post-splitting zone and yielding zone. In each zone, the bond stress is assumed to be constant. The models for bond strength in each zone are adopted from previous studies. Combining the equilibrium, strain-slip relation and the bond strength model in each zone, the steel stress- slip model can be derived, which can be used in the nonlinear frame analysis of the column. The proposed model is applied to derive explicit equations for predicting the strength of the lap splice strengthened by fiber reinforced polymer (FRP) in both elastic and post-yield ranges. For design purpose, a procedure to calculate the required FRP thickness and the number of FRP sheets is also presented. A parametric investigation was conducted to study the relation between lap splice strength and lap splice length, number and thickness of FRP sheets and the ratio of concrete cover to bar diameter. The study shows that the lap splice strength can be enhanced by increasing one of these parameters: lap splice length, number or thickness of FRP sheets and concrete cover to bar diameter ratio. Verification of the model has been conducted using experimental data available in literature.

Seismic Evaluation of Reinforced Concrete Piers in Low to Moderate Seismic Regions

Evaluation of reinforcement detailing with respect to the amount and spacing of transverse reinforcement, development length, and splice length based on seismic provisions for seven Pennsylvania bridges is discussed. The selection of prototype bridges as representative of the stock of all PA bridges for the study are explained. A case study of seismic evaluation of one of the bridges selected based on finite element analysis and ductility estimation is presented as representative of the approach used to evaluate all other selected bridges.

Ultra High Performance Fibre Reinforced Concrete (UHPFRC) for connections between precast elements

The performance suitability of precast concrete structures is determined by the design and construction of connections between elements. In spite of its simplicity, the use of bond connections through bar reinforcement splices is limited by issues related to long splice lengths required and reinforcement congestion. Reinforcement splices embedded in Ultra High Performance Fibre Reinforced Concrete (UHPFRC) were tested in beam specimens, as part of an on-going investigation to develop a novel typology of beam-column connection between precast elements using UHPFRC. Elements made up of two precast elements joined through reinforcement splices in a central region poured with UHPFRC, and without using closed stirrups or vertical ties were tested in beam tests. The experimental results for splice lengths between 10 db and 20 db exhibited an adequate performance to connections undergoing load and unload cycles, being this an unfavourable condition for bond capacity, and using short covers and transversal spacing between splices, under 0.7 db. It is therefore clear that the higher tensile capacity and ductility of UHPFRC have a positive effect on confinement, bond conditions and force transference as well as a stiffness effect.

Experimental Study on Behavior of Flexural Member with Lab-Spliced GFRP Bar

The use of glass-fiber-reinforced polymer (GFRP) bars to replace steel reinforcement in concrete structures is a relatively new technique. GFRP bars possess mechanical properties different from steel bars, including high tensile strength combined with low elastic modulus and elastic brittle stress–strain relationship. Therefore, design procedures should account for these properties. This paper presents the experimental moment deflection relations of GFRP reinforced beam which are spliced. Test variables were lab-spliced length of GFRP rebar. A total of 6 concrete beams reinforced with steel and GFRP rebar tested. Three concrete beams reinforced with spliced GFRP rebar and 1 reference beams reinforced with non-spliced GFRP rebar was tested. All the specimens had a span of 4000mm, provided with 12.7mm nominal diameter steel and GFRP rebar. All test specimens were tested under 2-point loads so that the spliced region is subject to constant moment. The experimental results show that the splice length of GFRP increased with the ultimate load increasing and decreased with stiffness.

Modelling of the longitudinal structure of elastic spliced yarns

In this work, a descriptive model was established for the longitudinal structure of wet pneumatic spliced yarn. Compared to classical spliced yarns which contain a symmetrical twisting zone our microscopic analysis revealed that elastic spliced yarns present two more asymmetrical twisted zones. Our study shows that the wet pneumatic splice can be defined by six parameters which are: zones of splice, length of each zone, splice length, number of twist turns on each zone, two elastane filament ends and centre x coordinates. These parameters were tested for 167 specimens. Analysing this database, we developed a descriptive model which helps to understand the spliced elastic yarn structure.

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.

쪼갬파괴에 의한 FRP 보강근의 정착길이와 이음길이

FRP 보강근의 정착과 이음에 대한 국내외 실험을 수집하고, 정착과 이음실험을 분리한 회귀분석을 통해 쪼갬파괴에 의한 정착길이 설계식과 이음길이 설계식을 제안하였다. 이음실험에 의한 평균 부착강도는 정착실험에 의한 평균 부착강도에 비해 낮으며, C/d<SUB>b</SUB>에 크게 영향을 받는 것으로 평가되었다. 따라서 합리적인 이음길이 설계를 위해 이음실험만으로 구성된 데이터에 근거한 이음길이 설계식을 개발할 필요가 있다. 또한 부착강도의 분산(分散)이 FRP 보강근의 인장강도 분산에 비해 크므로, 정착길이와 이음길이 설계식에 이를 반영한 안전율이 요구된다. 이 연구에서는 FRP 보강 콘크리트 구조물의 하중계수와 강도감소계수가 철근콘크리트구조와 동일하다는 조건에서, 철근 품질관리에 적용되는 5% 분위수를 이용하여 경제적이면서 신뢰성 높은 정착길이와 이음길이 설계식을 개발하였다. 제안된 이음길이 설계식은 정착실험을 중심으로 개발된 ACI 440 설계식보다 C/d<SUB>b</SUB>의 영향을 정확하게 반영하여, C/d<SUB>b</SUB>가 3.0 이상인 경우 ACI 440보다 짧은 이음길이가 산정된다. FRP 보강근이 주로 활용될 것으로 기대되는 외기에 노출된 슬래브와 벽체의 배근 특성을 고려하면 이 연구에서 제안된 설계식은 매우 경제적인 이음길이 설계를 가능하게 한다.

A Study on the Loss Reduction Method of Reinforcing Bar through Case Study

Rebar work accounts for approximately 30% of the total construction costs for rebars and concrete. Recently, the high rising prices of rebars have become one of the principle factors of rising construction costs. Therefore, construction companies are putting much effort into loss reduction of rebars. Consequently, in this study, we wished to present loss reduction methods of rebars before the preparation of the placing drawings. To devise such methods, we collected previous case studies and analyzed methods that were applied for loss reduction. As a result of the analysis, we were able to find the following methods for loss reduction of rebars: method of reducing the number of splices at the mat foundation, method of reducing splice length at the internal columns or walls of the underground parking lot, method of reducing cap-ties of internal beams of basement floors excluding perimeter beams, and method of reducing anchorage length at the internal column or wall of the underground parking lot. Based on those analysis results, we presented our own loss reduction methods of rebars. Applying our methods resulted in considerable loss reduction.

Simplified Design Equation of Lap Splice Length in Compression

With the emergence of ultra-high strength of concrete, the compression lap splice has become an important area of interest. According to ACI 318-08, a compression splice can be longer than a tension splice when high-strength concrete is used. By reevaluating the test results of compression splices and performing regression analysis, a simplified design equation for splice length in compression was developed based on the basic form of design equations for development/splice lengths of deformed bars and hooks in tension. A simple linear relation between <TEX>$l_s/d_b$</TEX> and <TEX>$f_{sc}\sqrt{f'_c}$</TEX> was assumed, and yields good values for the correlation coefficient and the mean and the COV (coefficient of variation) of the ratios of tests to predictions of splice strengths in compression. By including the 5% fractile coefficient of 0.83, a design equation for splice length in compression was developed. The splice length calculated using the proposed equation has a reliability that is equivalent to other provisions for reinforcing bars.