High-strength Rebar Research Articles

Hollow Threaded Rebar for Cross Hole Sonic Logging Access Tubes Combined with Longitudinal Concrete Reinforcing in Drilled Shafts

AbstractCrosshole Sonic Logging (CSL) of drilled shafts requires 1.5-in (38-mm) or 2-in (51-mm) I.D. sonic access tubes to be installed inside the steel reinforcement cage. The sonic access tubes do not contribute to the structural capacity of the drilled shaft. The proposed use of Ischebeck TITAN T73/56 CSL/Hollow Threaded Rebar for Cross Hole Sonic Logging Access Tubes Combined with Longitudinal Concrete Reinforcing in Drilled Shafts (patent pending) is discussed as an alternative method of construction and CSL probe access. The T73/56 hollow threaded rebar/sonic access tube performs as a high strength rebar while at the same time creating a 2.2-in (56-mm) I.D. sonic access tube. The deformed high strength hollow bar provides better adhesion to concrete thus reducing the problem of debonding associated with smooth PVC and steel pipe. A cost comparison using conventional rebar with added sonic access tubes is discussed. The use of T73/56 CSL/Hollow Threaded Rebar as a value engineering alternative can re...

ECC와 고장력 철근으로 보강된 철근콘크리트 보의 휨 실험

ECC는 모르타르 매트릭스에 약 2% 이내 체적비의 합성 섬유를 보강하여 1축 인장 하에서 변형률 경화 거동과 다수의 미세균열을 발현하도록 제조한 높은 연성의 시멘트 복합 재료이다. 최근 ECC를 적용하는 연구가 구조물 보수보강 공법, 현장 타설 및 프리캐스트화 공법 등 다양한 형태로 진행되고 있으며, 특히 연성이 요구되는 구조 부재에 적용하고 하는 시도가 끊임없이 이루어지고 있다. 이 연구에서는 성능 저하된 철근콘크리트(RC) 보의 구조 성능 및 균열 제어 성능을 개선하기 위하여 ECC와 고장력 철근을 함께 활용하는 보강 공법을 다루고 있다. 이를 위하여 RC 보실험체를 제작·실험하여 구조 성능과 파괴 형태 등을 연구하였다. 실험 결과, ECC와 고장력 철근으로 보강된 RC보는 우수한 균열 제어 성능과 더불어 휨 내하력 및 휨 강성이 크게 향상되는 것으로 평가되었다. 이 연구 결과는 ECC와 고장력 철근을 활용한 보강 공법의 설계 및 현장 적용을 위한 기초 자료로 활용될 것이다.

Shaping high-strength rebar for redesigned ferroconcrete cross ties

Cold deformation of high-strength rebar is considered. By statistical control methods, control charts are formulated for the shaping of a periodic rebar profile by two technologies. Two-section, six-roller drawing cells prove preferable to single-section, three-roller cells.

Pseudo-dynamic test and numerical simulation of high-strength concrete frame structure reinforced with high-strength rebars

This paper describes an investigation of a high-strength concrete frame reinforced with high-strength rebars that was tested in the structure engineering laboratory at Shenyang Jianzhu University. The frame specimen was pseudodynamically loaded to indicate three earthquake ground motions of different hazard levels, after which the test specimen was subjected to a pseudo-static loading. This paper focuses on the design, construction and experiment of the test frame and validation of the simulation models. Research shows that a high-strength concrete frame reinforced with high-strength rebars is more efficient and economical than a traditional reinforced concrete frame structure. In addition to the economies achieved by effective use of materials, research shows that the frame can provide enough strength to exceed conventional reinforced concrete frames and provide acceptable ductility. The test study provides evidence to validate the performance of a high-strength concrete frame designed according to current seismic code provisions. Based on previous test research, a nonlinear FEM analysis is completed by using OpenSees software. The dynamic responses of the frame structure are numerically analyzed. The results of the numerical simulation show that the model can calculate the seismic responses of the frame by OpenSees. At the same time, the test provides additional opportunities to validate the performance of the simulation models.

A New Calculation Method for Cracking Width of Beam with High Strength Rebar

With the application of high strength concrete and rebar, the influence of concrete strength on cracking width of reinforced concrete beam with high strength rebar is becoming more and more important. To investigate the effect of concrete strength on cracking width of reinforced concrete beam with high strength rebar, the experiment including 6 simply supported T-beams with high-strength rebar and 2 beams with ordinary-strength rebar have been made. Then the relevant specifications advised in Code for Design of Concreter Structure (GB50010-2002) are revised according to the experiment results so as to considering the influence of concrete on cracking width. A new cracking width method considering the influence of concrete strength on cracking width for reinforced concrete beam with high strength rebar is proposed. Finally, the comparisons between predictions and experiment results have been conducted, which shown that the proposed new cracking width method agreed with experiment results well.

500MPa Seismic Rebars Developed by Nitrogen-Rich and Vanadium-Microalloyed, Controlled Cooling Technology

500MPa high-strength seismic rebars was developed by nitrogen-rich & vanadium -microalloyed, controlled cooling technology in domestic steel plant of china, microalloy precipitates, microstructure, mechanical properties, welding performance and aging properties of rebars were researched by using metallographic microscopy, scaning electron microcopy, transmission electron microscopy, x-ray diffraction apparatus, flash-butt welding and mechanical properties testing. The results show that a large number of the dispersed V (C, N) precipitates are precipitated in the grain boundary, dislocation line and the ferrite matrix, precipitation size in the ferrite matrix is 10~ 20nm, V(C,N) precipitates amount accounts for 67.54% of the total amount of vanadium in steel, effect of precipitation strengthening is remarkable; when termination temperature after controlled cooling for rebars is controlled at 710°C ～750°C , the core microstructure is polygonal ferrite and pearlite, ferrite grain grade is 11.0, outer layer microstructure is acicular ferrite, pearlite and a small amount of bainite, good effects on fine-grain strengthening and seismic performance are obtained; rebars have low strain aging and good welding performance; production cost is reduced by RMB 100 Yuan per ton steel compared with VN micro-alloyed and hot-rolling process, benefit is obvious.

STUDY ON ULTIMATE STRENGTH OF PRECAST PRESTRESSED BEAM WITH MULTIPLE LARGE OPENINGS EXPOSED TO FIRE HEATING

In order to investigate shear and bending behavior of prestressed precast concrete (PCaPC) beams with high-strength rebars and multiple large openings, three specimens for PCaPC beams were tested. Test parameters are the level of vertical loading and the quantity of shear reinforcement. It was confirmed from the test results that PCaPC beams are able to resist the allowable permanent during 3 hours standard fire. The evaluation method for bending and shear strength of PCaPC beams at high temperature, as well as the results of the fire experiment will be presented. In this analytical method of shear strength, the truss mechanism across openings in addition to at opening and between openings was considered. This new shear strength mechanism is proposed to calculate with a good accuracy taking into account of the temperature of longitudinal and shear rebars.

Effect of different cooling rates on thermomechanically processed high-strength rebar steel

The present article is dealing with 0.2% C, 0.1% V and 0.02% Nb steel. Billets with 130 mm × 130 mm cross-section were austenitized and hold at 1080 °C. The billets were hot rolled to 22 mm bar diameter. Hot rolling was finished at 980–1000 °C. The final bars were air-cooled. On a parallel way, an experimental hot deformation investigation, on the same steel, was carried out at deformation temperature range 1200–800 °C with the same amount of deformation (97% reduction in area). However, cooling regimes after deformation were air cooling, water quenching to 600 °C followed by air cooling, and water quenching to room temperature. Microstructure investigation was done using both optical and scanning electron microscopes. Further evaluation was done using mechanical testing. The industrial trial has unsatisfied results with poorer yield strength with higher ultimate strength. Bainitic aggregates are detected in the hard phases islands. Air cooling after pilot hot deformation creates banded ferrite–pearlite microstructure with 9.11 μm ferrite grains. However, quick water quenching to 600 °C followed by air cooling develops tempered and softened coarse bainite phase. On the other hand, water quenching to room temperature develops fine bainite texture. Water quenching to 600 °C followed by air cooling is the best regime creating accepted mechanical properties.

Research Development and Production of V-N Microalloyed High Strength Rebars for Building in China

The research, production, and application of V-N microalloyed high strength rebars in China were reviewed. Enhanced nitrogen in vanadium-containing rebars promotes the precipitation of fine V(C, N) particles, and markedly improves the precipitation strengthening effectiveness of vanadium. Therefore, vanadium added to V-N microalloyed rebars can be reduced by 40% compared to the same strength level of vanadium-containing rebars.

HIGHLY EFFECTIVE THERMOMECHANICALY REINFORCED REBAR

The article investigates the structure, mechanical and services characteristics of high-strength rebar, thermomechanically strengthened under different cooling modes.

Effects of Microalloying Elements on Mechanical Properties of Reinforcing Bars

Reinforcing steel bars are an important material for construction. The strength level of rebar has been increased to as high as, for example, 345, 390 and 490 grade. In order to produce high-strength rebar, V microalloying technology has been successfully applied, while Nb application to reinforcing bars has been tried energetically recently. However, exact discussions about the effect of hot-rolling and cooling condition in Nb microalloyed steel on mechanical properties have not been reported exactly.This paper reports on the experimental results of the effects of reheating temperature and cooling rate after hot-rolling on the microstructure and mechanical properties of 0.25C–0.5Si–1.2Mn steel and 0.25C–0.5Si–1.2Mn–0.05Nb(+0.05V) steel (mass%).0.05% Nb and 0.05% Nb+0.05% V additions to 0.25C–0.5Si–1.2Mn steel (mass%) led to an effective increase in strength, especially at high reheating temperature. This strengthening is caused by precipitation hardening and grain refinement hardening. Accelerated cooling after hot-rolling to 700°C was effective in increasing strength and yield point elongation.

고강도 콘크리트 및 고강도 철근을 사용한 중실교각의 내진거동에 관한 실험적 연구

The purpose of this study is to investigate the structural behavior of RC Piers using high strength concrete and high strength rebars. The high strength concrete offers many advantages such as enhanced mechanical performance and durability, in addition to member size reduction. The high strength rebars are used here to reduce the amount of rebars, which facilitates the placement of concrete and labor works. Five RC piers were tested under a constant axial load and a cyclically reversed horizontal load. The seismic design of piers were implemented, according to the current Korean Bridge Design Code. The test variables include concrete compressive strength, steel strength, and steel ratio. The test results indicate that RC piers using the high strength concrete and high strength rebars exhibit ductile behavior and appropriate seismic performance, in compliance with the design code. The present study allows more realistic application of high strength rebars and concrete to RC piers, which will provide enhanced durability as well as more economy.