Large Diameter Bars Research Articles

Splice Length of Large Diameter Reinforcing Bars in Ultra-High-Performance Concrete

Potential exists for construction time savings through replacement of cast-in-place substructure columns, piers, or both, with prefabricated bridge elements and systems. Cast-in-place substructure construction requires forming, placing steel, and pouring concrete at the construction site. Using prefabricated elements would decrease the extent of work required at the site and potentially reduce concrete curing time. This research furthers the effort to use ultra-high-performance concrete (UHPC) as a joining material for prefabricated bridge substructure elements. UHPC has a high early strength, requires less development or splice length than conventional concrete, and has been used previously for accelerated construction projects, such as bridge deck replacement with precast units. UHPC also has a discontinuous pore structure that reduces liquid ingress, significantly enhancing durability compared to conventional concrete. Although UHPC has been researched extensively, previous research for reinforcing bar splice and development lengths has focused on #9 and smaller diameter bars. Typically, larger diameter bars are used for substructures. This research determined the required splice lengths for large diameter steel deformed reinforcing bars embedded in UHPC based on 127 individual tests. Three primary variables were included in the testing matrix: bar size, bar spacing, and concrete cover. To achieve at least 75 kips per square inch (ksi) (517 MPa) reinforcing bar stress in UHPC with an early age strength of 14 ksi (97 MPa), the required embedment length ranges from 8 to 13 times the bar diameter and the corresponding splice length varies from 6 to 11 times the bar diameter, depending on the bar size and concrete cover.

Performance of high strength steel bar splice with novel grouted deformed sleeve under tensile load

High-strength steel (HSS) bars can solve bar congestion problem in beam-column joints of monolithic precast concrete frame structure. Unfortunately, its application in precast concrete structures is greatly hindered by few researches on HSS bar grout splice. In this paper, utilizing large-diameter HRB600 reinforcements with specified yield strength of 600 MPa, 34 splice specimens were prepared considering the parameters of embedded length, grout strength and inner cavity structure of sleeve. Through uniaxial tension test, it is shown that the embedment length has the greatest effect on the structural performance of grouted splice. For the d28 bar grout splice, 8db is the minimum embedded length to ensure bar fracture failure, which is longer than the normal-strength steel bar grout splice. For the splices with embedded length not smaller than 5db and concentric ribs not less than five, excessive ribs set on the sleeve cannot significantly increase the tensile strength of the grouted splice, but further adding one rib still can effectively reduce the elastic residual deformation. Similar test results have been observed for the effect of grout strength. As the compressive strength increases from 95.3 MPa to 118.2 MPa, the tensile strength improves only by about 2.52%, but the residual deformation decreases significantly by 11.68% on average. For a high-strength large-diameter bar grout splice, it is recommended to set six concentric ribs at each side of the sleeve, and select 8db as the minimum embedded length to achieve reliable performance.

Seismic performance of precast concrete walls with grouted sleeve connections using large-diameter bars

This paper proposes an innovative assembly technique using large-diameter bars anchored in several single-row, widely spaced grouted sleeves at the keyway-type horizontal joint to realize an indirect vertical connection between adjacent precast concrete (PC) walls, which has the advantages of high efficiency and ease of construction. To examine the effect of vertical connection strength (rebars' diameter at horizontal joints) on the seismic performance of PC shear walls, quasi-static cyclic loading tests on five full-size wall specimens, including one cast-in-place specimen and four PC specimens with grouted sleeve connections, are carried out. Seismic performance indicators in terms of failure modes, hysteresis characteristics, energy dissipation, ductility, and stiffness degradation of PC walls are investigated and compared with those of the cast-in-situ wall. Meanwhile, the method for predicting the bearing capacity of PC walls with large-diameter rebars is developed. The results show that the failure modes of cast-in-situ and precast walls are controlled by bending instead of shear, but there is an obvious difference in the crack propagation between the two types of walls. Carrying capacity, ductility factor, stiffness, and energy dissipation of PC walls are significantly enhanced by increasing the connection strength, by 44.1%, 23.9%, 72.1%, and 24.0%, respectively, when the connection strength reaches around 90%. Particularly, the PC wall's seismic performance is comparable to that of the cast-in-situ wall when the connection strength is 90%. The calculated results are well-matched with the experimental results, the proposed calculation method reliably predicts the bearing capacity of PC walls with large-diameter rebars. The assembly technique can be safely applied to multi-story PC wall panel structures in seismic zones.

FLEXURAL BEHAVIOR OF FRP BARS AFTER BEING EXPOSED TO ELEVATED TEMPERATURES

This research study investigates the flexural behavior of fiber reinforced polymer (FRP) bars after being subjected to different levels of elevated temperatures (100, 200 and 300°C). Three types of glass FRP bars (ribbed, sand coated, and helically wrapped) and one type of carbon FRP bars (sand coated) were used in this study. Two testing scenarios were used: a) testing specimens immediately after heating and b) keeping specimens to cool down before testing. Test results showed that as the temperature increased the flexural strength and modulus of the tested FRP bars decreased. At temperatures higher than the glass transition temperature (Tg), significant flexural strength and modulus losses were recorded. Smaller diameter bars showed better residual flexural strength and modulus than larger diameter bars. The immediately tested bars showed significant strength and modulus losses compared to bars tested after cooling. Different types of GFRP bars showed comparable results. However, the helically wrapped bars showed the highest flexural strength losses (37 and 60%) while the sand coated bars showed the lowest losses (29 and 39%) after exposure to 200 and 300℃, respectively. The carbon FRP bars showed residual flexural strengths comparable to those recorded for the GFRP bars; however, they showed lower residual flexural modulus after being subjected to 200 and 300℃.

Relaxation of Carbon and Stainless-Steel Threaded Bars for Posttensioning Applications

AbstractAn experimental program was conducted to investigate the stress relaxation properties of large-diameter bars [65 to 70 mm (2.5 to 2.75 in.) nominal] for posttensioning applications. This st...

Degradation of glass fiber reinforced polymer (GFRP) bars in concrete environment

Degradation of tensile, shear and flexure properties of glass fiber reinforced polymer (GFRP) bars is investigated in the paper. Glass fibre reinforced polymer bars, when used in structures exposed to aggressive environments, can significantly increase the lifetime, as compared to structures reinforced with conventional steel. However, the progress in utilization of GFRP bars in concrete structures is hampered due to limited information on durability of these materials. Since long-term durability data are not readily available, accelerated aging tests have been used in this research to study GFRP bar degradation. The bars were kept in a highly alkaline solution heated to 50, 60 and 70 °C for 1, 3 and 5 months, respectively, and after each immersion period, bars were taken out and tested in tension, shear and flexure. The experimental results show that immersion in high pH of the alkaline solution reduces the strength of the bars. The speed of degradation depends on the temperature of the solution. The degradation is then studied using the models for solution ingress into the GFRP bars. The conclusions proposed are that the shear test is a good indicator of the tensile strength degradation, bent bars deteriorate faster than straight bars, and smaller diameter bars deteriorate faster than larger diameter bars; finally, bars under flexural (tensile) strength deteriorate faster than those under direct tensile and shear strengths.

Research of an SHPB Device in Two-by-Two Form for Impact Experiments of Concrete-Like Heterogeneous Materials

A split Hopkinson pressure bar (SHPB) device in two-by-two form, including the bar bundle form and the single cylindrical bar form, was designed in response to the demand for the dynamic mechanical experiments for brittle materials such as concrete, rock, etc. The stress waveforms generated through a projectile impacting two different types of incident bars have been studied based on the one-dimensional stress wave theory and numerical simulation method. At last, based on the established two types of mesoscale concrete models with random convex polyhedral aggregates, we performed comparison analysis of SHPB numerical simulations for concrete materials with bar bundle and single cylindrical bar separately, so as to provide technical support for the manufacture and development of this experimental device. The results showed that the introduced two-by-two form SHPB device expanded the scope of practical application, and the wave dispersion effect existing in a large-diameter bar can be evidently reduced when we employed the bar bundle form, indicating its applicability to the dynamic mechanical experiments of concrete-like heterogeneous materials.

Guidelines for flexural design of FRP reinforced concrete beams

This paper investigates the effects of different parameters on the live load carrying capacity of concrete beams reinforced with FRP bars. The author performed a parametric study utilizing an innovative numerical approach to inspect the effects of multiple variables such as reinforcement ratio, concrete compressive strength, span to depth ratio, FRP type, and bar diameter on load carrying capacity of FRP reinforced concrete beams. This study concluded that unless the span to height ratio is smaller than 8, tension-controlled sections are impractical as they do not meet code requirements for serviceability. In addition, it is recommended to use higher reinforcement ratios when using larger span to depth ratios and/or when using CFRP reinforcing bars. Moreover, larger number of bars with small diameter is more practical than fewer large diameter bars. Furthermore, this research suggests that increasing the concrete compressive strength is associated with a significant increase in the ultimate flexural capacity of FRP reinforced beams.

Numerical study on seismic behavior of precast bridge columns with large-diameter bars and UHPC grout considering the bar-slip effect

A novel connection adopting lap-spliced large-diameter bars and ultra-high performance concrete (UHPC) grout was developed to accelerate the assemble progress of precast bridge columns. The precast bridge column adopting the connections was testified to be on a par with the monolithic concrete counterpart in terms of seismic performance in previous research. This paper aims to develop a numerical model to further investigate the seismic behavior of the proposed bridge column considering the bar-slip effect. A finite element model was established for the bridge columns considering deformation components of flexure, shear, and bar-slip. The bond behavior between the deformed bar and UHPC was defined using a new practical model, which was developed based on a pullout test including five specimens in this research. The established finite element model was verified by the cyclic loading test in literature in terms of the overall hysteretic curve and local responses. The validated model was used to conduct parametric analysis to study the contributions of the different deformation components to lateral deformation as well as the effects of large-diameter bars on seismic performance. Results show that all the pullout specimens have the tensile fracture of bars, which indicates that the development length of 5 times bar diameter is sufficient for deformed bars in UHPC when the bar diameter is no more than 32 mm. The practical model is effective to consider the effects of the slip between the deformed bar and UHPC. The finite element model can predict the overall hysteretic curve and local responses at different drift ratios. The bar-slip has a considerable even dominative contribution to the lateral deformation of the proposed bridge column. Larger bar diameter can enhance deformation capacity as well as reduce energy dissipation and residual drift ratio.

Bar size effect on long-term durability of sand-coated basalt-FRP composite bars

Recently, the use of basalt fiber-reinforced polymer (BFRP) bars as a reinforcing material has gained increasing interest worldwide. In the last decade, the durability of BFRP bars has been the concern of the researchers, however, the effect of bar size or diameter have not yet been addressed. This paper investigates the effect of bar size on the physical, mechanical, and durability characteristics of newly developed sand coated BFRP bars conditioned for 3 months at 60°C in an alkaline solution simulating a concrete environment. Five diameters of BFRP bars (nominal diameters of 9.5, 13 mm, 12.7 mm, 15.9 mm, 19.0 mm, and 25.0 mm) were investigated before and after conditioning. In addition, the microstructure of the BFRP bars—both conditioned and unconditioned specimens—was investigated with scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) to assess any changes or degradation. The results revealed that the physical and mechanical properties of the reference BFRP bars were significantly affected by the cross-sectional size of the bar. The higher probability of defects contained in the larger diameter bars may have caused the lower interlaminar and transverse shear strength, and flexural strength in comparison to the smaller diameter bars. On the other hand, the conditioning in the alkaline solution had a greater negative effect on the mechanical properties of the larger BFRP bars than on the smaller ones. According to the finding of this research, there were variations between the physical and mechanical properties of the BFRB bars of different diameters.

Structural Behavior of Precast Reinforced Concrete Shear Walls with Large Diameter Bars

Structural Behavior of Precast Reinforced Concrete Shear Walls with Large Diameter Bars

Axial performance of hollow concrete columns reinforced with GFRP composite bars with different reinforcement ratios

A hollow concrete column (HCC) is a structurally efficient construction system and uses less material. Conventionally, HCCs are reinforced with steel bars, which are prone to corrosion. This study explored the use of glass-fiber-reinforced-polymer (GFRP) composite bars as reinforcement for HCCs and evaluated the effect of the reinforcement ratio on HCC structural behavior. A total of six HCCs reinforced longitudinally with GFRP bars with different reinforcement ratios (1.78%, 1.86%, 2.67%, 2.79%, 3.72, and 4.00%) were prepared and their behavior was investigated. The different reinforcement ratios were achieved by changing the bar diameter (12.7 mm, 15.9 mm, and 19.1 mm) and number of bars (4, 6, 8, and 9 bars). The results show that increasing the diameter and number of bars enhanced the strength, ductility and confinement efficiency of HCC. For columns with equal reinforcement ratios, using more and smaller-diameter GFRP bars yielded 12% higher confinement efficiency than in the columns with fewer and larger-diameter bars. The crushing strain of the GFRP bars embedded the HCC was 52.1% of the ultimate tensile strain. Lastly, the axial-load capacity of the GFRP-reinforced HCC can be reliably predicted by considering the contribution of the concrete and up to 3000 με in the longitudinal reinforcement.

Confinement device to assess dynamic crushability of wood material

Cellular materials such as wood are widely and advantageously used as shock absorbers in various transport applications. The design and manufacturing of structures made of these materials require the knowledge of their dynamic compressive properties at various strain rates and stress states. Therefore, it is challenging to conduct dynamic multiaxial stress state experiments and especially on split-Hopkinson pressure bar apparatus where stress hardening increases as a function of velocity. This paper presents the so-called verification and validation methodology for confining solutions dedicated to impact on viscoelastic split-Hopkinson pressure bar system with large diameter bars. The method is a hybrid approach combining finite element analysis and an original experimental validation. Based on finite element results, particular attention is given to the mass, the material and the geometry to minimize the confining device influence on the propagation of elastic waves and thus on the material response of the tested specimens. It is essential to avoid spurious reflected waves at the new interfaces of the system in order to ensure the validity of the experimentation. The numerically predicted solutions are experimentally validated and preliminary results in the context of dynamic loadings using wood material are presented.

51 mm 대구경 철근을 사용한 외부 보-기둥 접합부의 정착상세별 구조성능 평가

외부 보-기둥 접합부에서는 철근정착을 위해 갈고리철근 사용하고 있으며, 철근과밀배근 해소와 시공작업의 어려움으로 확대머리철근의 사용이 증가하고 있다. SD600 51 mm 확대머리철근을 사용할 경우 ACI318-14 및 KCI2012기준에서 사용을 제한하고 있다. 이번 연구에서는 외부 보-기둥 접합부 내에 고강도 대구경 철근의 확대머리 철근의 사용이 가능하도록 실험 60 MPa, 80 MPa 콘크리트강도로 제작된 실험체의 정착상세별 구조성능을 평가하였다. 모든 실험체에서는 보의 휨항복파괴가 발생하였으며, 실험체의 모멘트-변위 곡선에서 비슷한 양상을 보였다. 다른 실험체보다 갈고리가 한쪽방향으로 배근한 실험체에서는 갈고리철근 배근방향에 의해 전단저항능력이 달라지므로 3.5%변위비 이후에 부착응력 감소가 더 크게 나타났으며, 전단변형능력도 더 크게 나타났다. 실험체의 내진성능을 확인하기 위하여 ACI374.1-05기준과 비교하였으며, 실험결과 충분한 내진성능을 확보하였다. 이를 통하여 외부 보-기둥 접합부에서 SD600, 51 mm 확대머리철근의 사용이 가능한 것으로 판단된다.

Deterioration of bond–slip due to corrosion of steel reinforcement in reinforced concrete

Corrosion of steel reinforcement in reinforced concrete members is a common occurrence and a major concern, as it can significantly affect both the serviceability and ultimate limit states. In order to simulate the effects of corrosion through mechanics, it is necessary to quantify the effects of corrosion on the material bond–slip properties, which is the subject of this paper. A large database of 377 data points was used to quantify the effect of corrosion on bond strength and bond–slip in a form that can be used in numerical analyses. This research concentrates on the changes in bond strength and bond–slip due to corrosion, and hence the changes relative to the uncorroded properties because these are already well quantified. Furthermore, it does not consider the clamping action of stirrups encasing the reinforcement. As an illustration of the application of these bond properties of corroded steel reinforcement, they are used in a mechanics analysis to show that large-diameter bars are much more susceptible to the effects of corrosion than small-diameter bars.

Tension Development Length of Large-Diameter Bars for Severe Cyclic Loading

This paper presents a study on the tension development length of large-diameter reinforcing bars embedded in well-confined concrete. Pull-push tests were conducted on No. 14 and 18 (43 and 57 mm) bars to evaluate whether the development length requirements in the AASHTO LRFD (American Association of State Highway and Transportation Officials Load and Resistance Factor Design) Specifications are adequate for large-diameter bars subjected to severe cyclic loading. The data have been used to validate finite element models, which have been subsequently employed in a parametric study to establish a formula to determine the tensile capacity of a bar as a function of the embedment length, and the concrete and steel strengths. Monte Carlo simulations conducted with this formula have shown that the AASHTO requirements are adequate to develop the yield strength of a bar in tension, but they do not have the desired reliability to develop its ultimate tensile strength when uncertainties are considered. Hence, an improved development length requirement is proposed.

The Strength and Ductility of Lapped Splices of Reinforcing Bars in Tension

When designing a reinforced concrete member for strength, ductility and robustness, it is essential that the tensile reinforcement at the critical section can not only develop the yield strength of the steel f sy, but that it can sustain this level of stress as deformation increases. At a lapped splice, each bar must be fully anchored beyond the lap length. The minimum lap lengths of deformed reinforcing bars in tension specified in the Australian Standard for Concrete Structures AS3600-2009 were recently revised and a procedure similar to, but less conservative than, the provisions in Eurocode 2 was adopted. The new provisions require longer lap lengths for small diameter bars in slabs, but considerably shorter lap lengths for larger diameter bars in beams and columns. This paper reports on several series of tests that examine the efficacy of the AS 3600-2009 provisions from the perspectives of adequate strength and ductility. Over 50 specimens containing both contact and non-contact lapped splices have been tested. The aim was to assess the current Australian provisions and to examine the reliability and consistency of the factors of safety associated with lapped splices. It is concluded that the strength requirements of AS3600-2009 are adequate for small diameter bars in slabs but may not provide an adequate factor of safety for large diameter bars in beams. Also, the AS3600 provisions may not ensure sufficient ductility of a lapped splice in members that use high strength concrete. Further tests are required to investigate these aspects.

On the strength and ductility of lapped splices of reinforcing bars in tension

AbstractWhen designing a reinforced concrete member for strength, ductility and robustness, it is essential that the tensile reinforcement at the critical section can not only develop the yield strength of the steel f sy, but that it can sustain this level of stress as deformation increases. At a lapped splice, each bar must be fully anchored beyond the lap length. The minimum lap lengths of deformed reinforcing bars in tension specified in the Australian Standard for Concrete Structures AS3600-2009 were recently revised and a procedure similar to, but less conservative than, the provisions in Eurocode 2 was adopted. The new provisions require longer lap lengths for small diameter bars in slabs, but considerably shorter lap lengths for larger diameter bars in beams and columns. This paper reports on several series of tests that examine the efficacy of the AS 3600-2009 provisions from the perspectives of adequate strength and ductility. Over 50 specimens containing both contact and non-contact lapped splic...

Parametric identification for material of viscoelastic SHPB from wave propagation data incorporating geometrical effects

In the application of Split Hokinson Pressure Bar (SHPB) techniques, test bars made of viscoelastic materials are frequently used for their low impedance to test soft materials. Wave propagations in such bars are susceptible to dispersions caused by the viscoelastic effects of the bar material along with the lateral inertia of the bar particularly when large diameters are used. Thus, the time shifting of the strain signals from the recording gauges on the bars to the bar-specimen interface requires corrections based on both the material properties and the diameter of the bar. Most of the methods available in the open literature, for viscoelastic material identification using wave propagation tests, are based on one-dimensional wave propagation theory in which signal dispersions due to the lateral inertia are ignored and hence are appropriate for the bars with small diameters. A method of parametric identification is proposed in the current study, using the frequency domain information, for the viscoelastic properties of a relatively large diameter bar made from polymethyl methacrylate (PMMA). A three-dimensional wave propagation analysis is employed using recorded strain data at a single location on the PMMA bar. It is found that the proposed parametric identification procedure, compared with the results of a non-parametric identification, helps to rectify the uncertainties in the identified material characteristics in the form of a highly oscillatory trend caused by the noise in the recorded signals and by the data reduction procedures. Strain signals predicted using the identified material parameters by the proposed method correlate well with the measured experimental strains, indicating accuracy in the identified parameters and the presented procedure.

Flexural behaviour of concrete beams with large-diameter steel bars

Bending tests were performed on beam specimens reinforced with large-diameter steel bars of no. 14 (43 mm diameter) and no. 18 (57·3 mm diameter) to investigate the flexural behaviour, failure mode and bond performance at various loading stages. Attention was paid to studying the bond behaviour of the larger bar on the load resistance and failure mode of a beam made at full scale. Test results showed that the reinforced concrete beams with large-sized reinforcements of no. 14 and no. 18 steel bars exhibited a similar flexure response to the beam with steel bars of under no. 10 (32·3 mm diameter), but the samples differed from each other in the deflection behaviour at the period between yielding and ultimate stage. The ductility of the former was found to be greatly reduced. Bond strength can be increased with reinforcement with large-diameter bars until the bars yield; they are therefore adequate to predict the yielding strength using the conventional code method, but their ultimate strength will be overestimated.