Inducing recovery stress of NiTiNb SMA wires using heat of hydration for confining concrete

2011 ◽  
Vol 22 (17) ◽  
pp. 1949-1957 ◽  
Author(s):  
Eunsoo Choi ◽  
Baik-Soon Cho ◽  
Joonam Park ◽  
Kyoungsoo Park
Keyword(s):  
Residual Stress ◽  
Shape Memory ◽  
Concrete Beams ◽  
Plain Concrete ◽  
Heat Of Hydration ◽  
Reinforced Concrete Beams ◽  
Recovery Stress ◽  
Concrete Cylinders ◽  
Temperature Window ◽  
Compressive Tests

This study suggests the utilization of heat of hydration of concrete to activate the shape memory effect (SME) of shape memory alloy (SMA) wires embedded in concrete and produce recovery and residual stress on the wires. This method is more convenient than the previous electronic resistance heating. For the purpose, this study prepares NiTiNb SMA wires that show appropriate temperature window for the use of heat of hydration. Axial compressive tests of concrete cylinders confined by the NiTiNb SMA wire jackets are used to prove that the utilization of heat of hydration is valid to generate recovery and residual stress in the SMA wires. The confined cylinders show increased peak strengths and much larger failure strains than those of the plain concrete. The general behavior of the SMA wire-confined specimens in this study is similar to that of specimens heated by electronic heating jacket. Also, this study explains two examples for the utilization of heat of hydration for the SME in reinforced concrete beams and columns.

Recovery and Residual Stress of Shape Memory Alloy Wires and Its Application

2009 ◽  
Author(s):  
Eunsoo Choi ◽  
Tae-hyun Nam ◽  
Man-Cheol Kim ◽  
Jong Wan Hu ◽  
Bak-Soon Cho ◽  
...  
Keyword(s):  
Residual Stress ◽  
Reinforced Concrete ◽  
Shape Memory Alloy ◽  
Shape Memory ◽  
Residual Deformation ◽  
Concrete Columns ◽  
Recovery Stress ◽  
Reinforced Concrete Columns ◽  
Concrete Cylinders ◽  
Active Confinement

Two kinds of shape memory alloy wires, NiTiNb and NiTi, are manufactured and pre-elongated during the manufacturing process. After fixing the pre-elongated wires, heating on the wires induces recovery stress on them. Several tests to measure the recovery stress are conducted with varying initial strains. Stress-reduction of the recovery stress is observed after the temperature of the wires is cold down; the remaining stress is called residual stress that is also measured. Also, this study measures the stress-strain curves of the SMA wires under the state that the residual stress is working. The tension behavior of the wires under residual stress is very unique. The NiTi is martensitic state at room temperature, thus a residual deformation remains after applying a large strain. However, under residual stress, the tensile behavior of the wire does not remain residual deformation and return to the original position by unloading; this looks like viscoelastic behavior. The residual stress of the SMA wires can be used as active confinement for civil structures and the behavior under residual stress can be used as like an elastic spring with hysteretic damping. This study confines concrete cylinders and reinforced concrete columns using the pre-elongated SMA wires to introduce an active confinement on them. The SMA wire jackets on concrete cylinders increase the peak strength and the ductility so much comparing to the plain concrete cylinders. Also, the wires on reinforced concrete columns increase the ductility so much without the reduction of flexural strength.

Determination of Creep Behavior of Concrete Beams Made with Rice Husk Ash

2021 ◽  
Vol 15 (1) ◽  
pp. 339-346
Author(s):  
Winfred Mutungi ◽  
Raphael N. Mutuku ◽  
Timothy Nyomboi
Keyword(s):  
Prediction Model ◽  
Rice Husk ◽  
Creep Behavior ◽  
Rice Husk Ash ◽  
Concrete Beams ◽  
Plain Concrete ◽  
Reinforced Concrete Beams ◽  
Partial Replacement ◽  
Design Strength ◽  
Concrete Production

Background: Creep in concrete is a long-term deformation under sustained loading. It is influenced by many factors, including constituent materials, environmental conditions, among others. Whenever there is an alteration in the convectional concrete preparation process, the creep characteristics need to be realistically assessed. In the present construction, rice husk ash has been used for partial replacement of cement in concrete production. This is because its properties of both tensile and compressive strength in concrete have been tested and found comparable with plain concrete. However, durability characteristics such as creep, which take place in the long run, have not been realistically assessed. Therefore, it is important to study the creep of rice husk ash concrete, which will further help in the development of a creep prediction model for such concrete for use by design engineers. Objectives: Rice husk ash was used as supplementary cementitious material in concrete, and the creep behavior was studied with the aim of producing a creep prediction model for this concrete. Methods: The cement was replaced with 10% of rice husk ash in concrete with a design strength of 30MPA. Reinforced concrete beams were cast and loaded for flexural creep 35 days after casting. The loading level was 25% of the beam’s strength at the time of loading. The creep observation was done for 60 days. The rice husk used was obtained locally from Mwea irrigation scheme in Kenya. The experiments were carried out in our school laboratory at Jomo Kenyatta university of Agriculture and Technology. Results: The creep strain data of rice husk ash concrete beams was obtained with the highest value of 620 micro strain for 60 days. The results were used to develop a creep prediction model for this concrete. Conclusion: A creep prediction model for rice husk ash concrete has been developed, which can be adopted by engineers for class 30 of concrete containing rice husk ash at a 10% replacement level.

Flexural Tests of Fiber-Reinforced-Concrete Beams Reinforced with FRP Rebars

2012 ◽  
Vol 166-169 ◽  
pp. 1797-1800
Author(s):  
Hong Chang Qu ◽  
Hong Yuan Li ◽  
Xuan Zhang
Keyword(s):  
Concrete Beams ◽  
Plain Concrete ◽  
Fiber Reinforced Concrete ◽  
Reinforced Concrete Beams ◽  
Flexural Behavior ◽  
Test Results ◽  
Flexural Performance ◽  
Flexural Tests ◽  
Hybrid Reinforcement ◽  
Brittle Mode

This paper investigates the flexural performance of FRP/FRC hybrid reinforcement system as well as FRP/plain concrete beams. Test results showed that the crack widths of FRP/FRC beams were smaller than those of FRP/plain concrete beams at the different corresponding load. With the increase of load, the crack spacing slightly decreased. The plain concrete beams failed in a more brittle mode than the FRC beams. Once they reached their ultimate moments, the load dropped fleetly. Compared to the companion beam, the addition of fibers improved the flexural behavior.

scholarly journals Performance of Cement-Based Patch Repair Materials in Plain and Reinforced Concrete Members

2016 ◽  
Vol 13 (2) ◽  
pp. 160
Author(s):  
A.H. Al-Saidy
Keyword(s):  
Mechanical Properties ◽  
Reinforced Concrete ◽  
Concrete Beams ◽  
Plain Concrete ◽  
Reinforced Concrete Beams ◽  
Patch Repair ◽  
Concrete Members ◽  
Repair Materials ◽  
Superior Mechanical Properties ◽  
The Cost

Structural elements such as beams, slabs, and columns may require strengthening or repair during their service life. Different repair materials (RMs) are available and it is usually difficult to choose the best ones, especially when considering the cost of such materials. This paper presents the results of an experimental investigation of patch RMs on plain concrete prisms as well as on reinforced concrete beams. Three cement-based RMs available in the market with different mechanical properties and an ordinary Portland cement (OPC) mix produced in the lab were used in the study. Damage was induced in prisms/beams and then repaired using different materials. The experimental work included assessment of the flexural strength of damaged/repaired plain concrete prisms; slant shear (bond) strength between the concrete and the RM; axial strength of damaged/repaired plain concrete prisms and bond of the repair materials in damaged/repaired reinforced concrete beams loaded to failure. The test results showed that all RMs performed well in restoring the strength of damaged plain concrete. Compatibility of the RMs with substrate concrete was found to be more important in the behavior than superior mechanical properties of the RMs. No difference was noted in the behavior between the RMs in repairing reinforced concrete beams at the tension side. 

scholarly journals Strengthening of Reinforced Concrete Beams with Externally Mounted Sequentially Activated Iron-Based Shape Memory Alloys

Materials ◽  
2019 ◽  
Vol 12 (3) ◽  
pp. 345 ◽  
Author(s):  
Emanuel Strieder ◽  
Christoph Aigner ◽  
Gabriele Petautschnig ◽  
Sebastian Horn ◽  
Marco Marcon ◽  
...  
Keyword(s):  
Reinforced Concrete ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Reference Beam ◽  
Reinforced Concrete Beams ◽  
Rc Beams ◽  
Recovery Stress ◽  
Strengthened Beam ◽  
Iron Based ◽  
Stress States

Iron based shape memory alloys (Fe-SMA) have recently been used as active flexural strengthening material for reinforced concrete (RC) beams. Fe-SMAs are characterized by a shape memory effect (SME) which allows the recovery of previously induced plastic deformations through heating. If these deformations are restrained a recovery stress is generated by the SME. This recovery stress can be used to prestress a SMA applied as a strengthening material. This paper investigates the performance and the load deformation behavior of RC beams strengthened with mechanical end anchored unbonded Fe-SMA strips activated by sequentially infrared heating. The performance of a single loop loaded and a double loop loaded SMA strengthened RC beam are compared to an un-strengthened beam and a reference beam strengthened with commercially available structural steel. In these tests the SMA strengthened beam had the highest cracking load and the highest ultimate load. It is shown that the serviceability behavior of a concrete beam can be improved by a second thermal activation. The sequential heating procedure causes different temperature and stress states during activation along the SMA strip that have not been researched previously. The possible effect of this different temperature and stress states on metal lattice phase transformation is modeled and discussed. Moreover the role of the martensitic transformation during the cooling process on leveling the inhomogeneity of phase state in the overheated section is pointed out.

Self-Post-Tensioning for Concrete Beams Using Shape Memory Alloys

2014 ◽  
Author(s):  
Muhammad Sherif ◽  
Osman Ozbulut ◽  
Asheesh Landa ◽  
Reginald F. Hamilton
Keyword(s):  
Corrosion Resistance ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Shape Memory Effect ◽  
Memory Effect ◽  
Concrete Beams ◽  
Heat Of Hydration ◽  
Image Correlation ◽  
Temperature Hysteresis ◽  
Post Tensioning

This study explores the use of shape memory alloys for self-post-tensioning concrete beams. SMAs have the ability to regain their original shape after being deformed up to 6–8% strain. This shape recovery is a result of an underlying reversible solid-solid phase transformation, which can be induced by either a stress (superelastic effect) or a temperature change (shape memory effect). The shape memory effect can be exploited to prestress concrete. The heat of hydration of grout can thermally activate SMA tendons to obtain self-post-tensioned (SPT) concrete. NiTi-based SMAs are promising due to their corrosion resistance and resistance against low frequency/cycle fatigue failure. NiTiNb alloys are a class of SMAs that exhibit a wide temperature hysteresis and transformation temperatures near the service temperatures required for practical application. Here, NiTiNb shape memory alloys are studied to design an optimized SMA that can be activated using hydration heat. The material design and characterization of the SMA tendons are discussed. The temperature increase due to the heat of hydration of four commercially available grouts is investigated. The bond behavior of SMA tendons is evaluated through pullout tests. Digital Image Correlation method is used for monitoring the slippage of the SMA tendons. The feasibility of developing SPT concrete is assessed through experimental studies. The use of SMAs, which possess high fatigue and corrosion resistance, as post-tensioning tendons in concrete members will increase the service life and provide life cycle cost savings for concrete bridges. The replacement of steel tendons with SMA prestressing tendons will prevent corrosion-induced deterioration of tendons in concrete structures. The use of heat of hydration of grout to activate the shape memory effect of SMA tendons will provide self-stressing capability. This will greatly simplify the tendon installation. The need for jacking equipment or electrical source will be eliminated.

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