Self-centering using Shape Memory Alloys


Shape Memory Alloy Publications are listed below. They cover the utilization of Shape Memory Alloys to achieve self-centering structures. This includes: experimental tests, modeling aspects, and design criteria. You can also check our engineering tools and/or submit your engineering inquiry.

 

Shape Memory Alloy Publications (SMA RC Joint)

 

Elfeki M.A., Youssef M.A., 2017, “Shape Memory Alloy Reinforced Concrete Frames Vulnerable to Strong Vertical Excitations”, Journal of Building Engineering. 

Reinforced concrete (RC) framed buildings dissipate the seismic energy through yielding of the reinforcing bars. This yielding jeopardizes the serviceability of these buildings as it results in residual lateral deformations. Superelastic shape memory alloys (SMAs) can recover inelastic strains by stress removal. This paper extends previous research by the authors that optimized the use of SMA bars in RC frames considering the horizontal seismic excitation by addressing the effect of the vertical seismic excitation. A steel RC six-storey building designed according to current seismic standards is considered as case study. Five different earthquake records with strong vertical components are selected for the nonlinear dynamic analysis. The results were used to evaluate the effect of the vertical excitation on the optimum locations of SMA bars.

 

Youssef M.A., 2016, “Reducing Seismic Residual Deformations in Civil Structures using Superelastic Shape Memory Alloys”, keynote speech, 2nd International Conference on Civil, Structural and Transportation Engineering (ICCSTE’16), Ottawa, ON, May 5-6. (Invited) 

The uniqueness of superelastic Shape Memory Alloy (SMA) bars lies in their ability to undergo large deformations and return to their undeformed shape through stress removal. In conventional seismic design of civil structures, inelastic deformations are allowed to dissipate the seismic energy. Such design philosophy results in permanent residual deformations, which complicate the post-earthquake retrofitting efforts. This keynote lecture summarizes Dr. Youssef’s research that utilizes superelastic SMA bars to reduce or eliminate seismic residual deformations. The lecture will summarize the characteristics of superelastic SMA bars and highlight challenges facing their implementation in future construction projects. It will then cover research addressing their use in Reinforced Concrete (RC) moment frames. Experimental tests of RC beam-column joints provided the initial proof that superelastic SMA bars can upgrade our RC framed structures to sustainable ones that can be easily repaired following a strong seismic excitation. Incremental dynamic analysis identified the optimum locations of superelastic SMA bars in a typical RC frame. Other applications including the use of superelastic SMA bars in brace members, RC walls, steel frames, and modular steel buildings will also be presented.

 

Sultana, P., Youssef M.A., 2016, “Seismic performance of steel moment resisting frames utilizing superelastic shape memory alloys”, Journal of Constructional Steel Research, 125: 239-251. 

Steel structures dissipate the seismic energy through steel yielding, which results in residual deformations. Although conventional earthquake-resisting structural systems provide adequate seismic safety, they experience significant structural damage when exposed to strong ground shaking. Seismic residual drifts complicate the repair of damaged structures or render the structure as irreparable. Therefore, systems that can minimize the seismic residual deformations are needed. Superelastic shape memory alloys (SMAs) have the ability to undergo large deformations and recover all plastic deformations upon unloading. Their utilization in steel structures can significantly reduce seismic residual deformations, which will facilitate post-seismic retrofitting. Although the literature provides few research data on using SMA in steel beam-column connections, previous research did not address their optimum use. This paper identifies the required locations of SMA connections in a typical steel moment resisting frame to enhance its seismic performance in terms of maximum inter-storey drift, residual deformations, and damage scheme.

Meshaly M.E., Youssef M.A., Abou Elfath H.M., 2014, “Use of SMA Bars to Enhance the Seismic Performance of SMA Braced RC Frames“, Earthquakes and Structures, 6(3): 267-280. 

Shape Memory Alloy (SMA) braces can be used to reduce seismic residual deformations observed in steel braced Reinforced Concrete (RC) frames. To further enhance the seismic performance of these frames, the use of SMA bars to reinforce their beams is investigated in this paper. Three-story and nine-story SMA-braced RC frames are designed utilizing regular steel reinforcing bars. Their seismic performance is examined using twenty seismic ground motions. The frames are then re-designed using SMA reinforcing bars. Different design alternatives representing different locations for the SMA reinforcing bars are considered. The optimum locations for the SMA bars are identified after analysing the design alternatives. The seismic performance of these frames has indicated better deformability when SMA bars are used in the beams.

Youssef M.A., Elfeki M.A., 2012, “Seismic Performance of Concrete Frames Reinforced with Superelastic Shape Memory Alloys”, Smart Structures and Systems, 9(4): 313-333. 

Reinforced concrete (RC) framed buildings dissipate the seismic energy through yielding of the reinforcing bars. This yielding jeopardizes the serviceability of these buildings as it results in residual lateral deformations. Superelastic Shape Memory Alloys (SMAs) can recover inelastic strains by stress removal. Since SMA is a costly material, this paper defines the required locations of SMA bars in a typical RC frame to optimize its seismic performance in terms of damage scheme and seismic residual deformations. The intensities of five earthquakes causing failure to a typical RC six-storey building are defined and used to evaluate seven SMA design alternatives.

Nehdi M., Alam M.S., Youssef M.A., 2011, “Seismic Behaviour of Repaired Superelastic Shape Memory Alloy Reinforced Concrete Beam-Column Joint”, Smart Structures and Systems, 7(5): 329-348. 

Large-scale earthquakes pose serious threats to infrastructure causing substantial damage and large residual deformations. Superelastic (SE) Shape-Memory-Alloys (SMAs) are unique alloys with the ability to undergo large deformations, but can recover its original shape upon stress removal. The purpose of this research is to exploit this characteristic of SMAs such that concrete Beam-Column Joints (BCJs) reinforced with SMA bars at the plastic hinge region experience reduced residual deformation at the end of earthquakes. Another objective is to evaluate the seismic performance of SMA Reinforced Concrete BCJs repaired with flowable Structural-Repair-Concrete (SRC). A -scale BCJ reinforced with SMA rebars in the plastic-hinge zone was tested under reversed cyclic loading, and subsequently repaired and retested. The joint was selected from an RC building located in the seismic region of western Canada. It was designed and detailed according to the NBCC 2005 and CSA A23.3-04 recommendations. The behaviour under reversed cyclic loading of the original and repaired joints, their load-storey drift, and energy dissipation ability were compared. The results demonstrate that SMA-RC BCJs are able to recover nearly all of their post-yield deformation, requiring a minimum amount of repair, even after a large earthquake, proving to be smart structural elements. It was also shown that the use of SRC to repair damaged BCJs can restore its full capacity.

Alam M.S., Youssef M.A., Nehdi M., 2010, “Exploratory investigation on mechanical anchors for connecting SMA bars to steel or FRP bars”, Materials and Structures, 43: 91-107. 

Using superelastic shape memory alloys (SMAs) as reinforcing bars in concrete structures proved to have a great potential in seismic areas because of its recentering capability. However, using them in an entire structure is generally not economically feasible due to their high cost. Therefore, it is more practical to limit their use to the plastic hinge zones, while regular steel can be used in the other regions of the structure. Connections between SMA and steel are critical, and need to be strong enough to transfer the full force from SMA bars to steel bars. Various mechanical couplers are available in the market to splice bars in reinforced concrete (RC) structures, each of which has several advantages and disadvantages. The efficiency of these couplers for connecting steel bars is tested and reported in this paper. Since these couplers are intended for connecting steel bars only, another experimental investigation has been performed to determine the suitability of these couplers for connecting SMA with steel bars. Commercially available screw-lock couplers are found to be unsuitable for connecting SMA to steel bars. An existing coupler has been modified for SMA–steel splicing to allow SMA bars to achieve their full superelastic strain. Additional tests have also been performed for connecting FRP bars to SMA bars. A new generation mechanical-adhesive type coupler has been developed for splicing FRP to SMA bars.

Nehdi M., Alam M.S., Youssef M.A., 2010, “Development of corrosion-free concrete beam-column joint with adequate seismic energy dissipation”, Engineering Structures, 32(9): 2518-2528. 

The use of Fibre-Reinforced Polymer (FRP) as reinforcement in concrete structures has received much attention owing to its higher resistance to corrosion compared to that of regular steel reinforcement. Since FRP is a brittle material, its use in seismic resisting structural elements has been a concern. FRP RC structures can be made ductile by utilizing a ductile material such as steel at the plastic hinge regions. However, the use of steel negates the corrosion resistance purpose of FRP. On the other hand, Nickel–Titanium (Ni–Ti) shape memory alloy (SMA) is highly resistant to corrosion. It also brings about an added advantage in seismic regions since it has the unique ability to undergo large deformation, but can regain its undeformed shape through stress removal. In this study, a SMA–FRP hybrid RC beam–column joint has been proposed to address not only corrosion resistance, but also seismic related problems. This joint is reinforced with a super-elastic Ni–Ti SMA bar at the plastic hinge regions of the beam and FRP in the other regions of the beam and column. To validate the proposed joint, an experimental investigation has been carried out to develop such a joint and test it under reversed cyclic loading. The results are compared in terms of load–storey drift, moment–rotation and energy dissipation capacity to those of a similar RC beam–column joint specimen reinforced with conventional steel. The SMA–FRP beam–column joint proved to have adequate energy dissipation under earthquake type loading.

Elbahy Y.I., Nehdi M., Youssef M.A., 2010, “Artificial Neural Network Model for Deflection Analysis of Superelastic Shape Memory Alloy RC Beams”, Canadian Journal of Civil Engineering, 37(6): 855-865. 

The need for a new model capable of accurately predicting the deflection of shape memory alloy (SMA) reinforced concrete (RC) beams is clear from the results obtained in the companion paper. In the present paper, artificial neural networks (ANNs) are utilized to develop such a model. The objective is to create a design tool for computing a reduction factor β to be used in the calculation of the effective moment of inertia for SMA RC beams. First, a database was developed using the results obtained from the parametric study reported in the companion paper. The main factors affecting the moment of inertia have been considered. The network architecture that results in the optimum performance was selected and trained. After demonstrating the network’s ability to predict output data for unfamiliar input data, the network was used to develop a design chart that provides the reduction factor β as a function of the reinforcement ratio and the reinforcement modulus of elasticity. A design example is discussed to illustrate the advantages of using the developed design chart over existing models.

Elbahy Y.I., Youssef M.A., Nehdi M., 2010, “Deflection of Superelastic Shape Memory Alloy Reinforced Concrete Beams: Assessment of Existing Models”, Canadian Journal of Civil Engineering, 37(6): 842-854. 

This paper investigates the load–deflection behaviour of shape memory alloy (SMA) reinforced concrete (RC) beams through a parametric study. The effects of the cross-section height, cross-section width, reinforcement ratio, reinforcement modulus of elasticity, and concrete compressive strength were considered. The sectional analysis methodology was adopted to predict the moment–curvature relationship for the considered sections. Deflection was then estimated using the moment–area method. The applicability of this method for SMA RC beams was demonstrated through comparisons with available experimental results. Based on the results of the parametric study, an assessment of the available models for deflection analysis of SMA RC beams was conducted. The accuracy and reliability of the different models were evaluated, and suitable models were recommended. A companion paper provides the development of an artificial intelligence based model that can predict the deflection of SMA RC beams more accurately than existing models.

Alam M.S., Nehdi, M., Youssef M.A., 2009, “Seismic Performance of Concrete Frame Structures Reinforced with Superelastic Shape Memory Alloys”, Smart Structures and Systems, 5(5): 565-585. 

Superelastic Shape Memory Alloys (SMAs) are gaining acceptance for use as reinforcing bars in concrete structures. The seismic behaviour of concrete frames reinforced with SMAs is being assessed in this study. Two eight-storey concrete frames, one of which is reinforced with regular steel and the other with SMAs at the plastic hinge regions of beams and regular steel elsewhere, are designed and analyzed using 10 different ground motion records. Both frames are located in the highly seismic region of Western Canada and are designed and detailed according to current seismic design standards. The validation of a finite element (FE) program that was conducted previously at the element level is extended to the structure level in this paper using the results of a shake table test of a three-storey moment resisting steel RC frame. The ten accelerograms that are chosen for analyzing the designed RC frames are scaled based on the spectral ordinate at the fundamental periods of the frames. The behaviour of both frames under scaled seismic excitations is compared in terms of maximum inter-storey drift, top-storey drift, inter-storey residual drift, and residual top-storey drift. The results show that SMA-RC frames are able to recover most of its post-yield deformation, even after a strong earthquake.

Elbahy Y.I., Youssef M.A., Nehdi M., 2009, “Stress Block Parameters for Concrete Flexural Members Reinforced with Shape Memory Alloys”, Materials and Structures, 42(10): 1335-1351. 

The unique properties of superelastic shape memory alloys (SMAs) have motivated researchers to explore their use as reinforcing bars. The capacity of a steel reinforced concrete (RC) section is calculated by assuming a maximum concrete strain εc-max and utilizing stress block parameters, α1 and β1, to simplify the non-linear stress–strain curve of concrete. Recommended values for εc-max, α1, and β1 are given in different design standards. However, these values are expected to be different for SMA RC sections. In this paper, the suitability of using sectional analysis to evaluate the monotonic moment–curvature relationship for SMA RC sections is investigated. A parametric study is then conducted to identify the characteristics of this relationship for steel and SMA RC sections. Specific mechanical properties are assumed for both steel and SMA. Results were used to evaluate εc-max, α1, and β1 values given in the Canadian standards and to propose equations to estimate their recommended values for steel and SMA RC sections.

Alam M.S., Youssef M.A., Nehdi M., 2008, “Analytical prediction of the seismic behaviour of superelastic shape memory alloy reinforced concrete elements”, Engineering Structures, 30(12): 3399-3411. 

Superelastic shape memory alloys (SMAs) are unique materials that have the ability to undergo large deformations, but can return to their undeformed shape by the removal of stress. If such materials can be used as reinforcement in plastic hinge regions of beam–column elements, they will not only experience large inelastic deformations during strong earthquakes, but can potentially recover their original shape. This behaviour will allow mitigating the problem of permanent deformation. Hence, this study aims at establishing guidelines for predicting the seismic behaviour of concrete beam–column elements reinforced with superelastic SMAs. The paper identifies the disparities in moment–curvature relationship between SMA and steel reinforced sections. Then it examines the applicability of existing methods developed for steel reinforced concrete (RC) members to predict the length of the plastic hinge, crack width, crack spacing, and bond-slip relationship for superelastic SMA RC elements. Existing superelastic SMA models are discussed and the application of one of the models in a finite element (FE) program is presented. This FE program is used to simulate the behaviour of an SMA RC column and a beam–column joint. The predicted load–displacement, moment–rotation relationships and energy dissipation capacities have been found to be in good agreement with experimental results.

Youssef M.A., Alam M.S., Nehdi M., 2008, “Experimental Investigation on the Seismic Behaviour of Beam-Column Joints Reinforced with Superelastic Shape Memory Alloys”, Journal of Earthquake Engineering, Vol. 12, No. 7, pp. 1205-1222. 

Superelastic Shape Memory Alloys (SE SMAs) are unique alloys that have the ability to undergo large deformations and return to their undeformed shape by removal of stresses. This study aims at assessing the seismic behavior of beam-column joints reinforced with SE SMAs. Two large-scale beam-column joints were tested under reversed cyclic loading. While the first joint was reinforced with regular steel rebars, SE SMA rebars were used in the second one. Both joints were selected from a Reinforced Concrete (RC) building located in the high seismic region of western Canada and designed and detailed according to current Canadian standards. The behavior of the two specimens under reversed cyclic loading, including their drifts, rotations, and ability to dissipate energy, were compared. The results showed that the SMA-reinforced beam-column joint specimen was able to recover most of its post-yield deformation. Thus, it would require a minimum amount of repair even after a strong earthquake.

Alam M.S., Nehdi M., Youssef M.A., 2008, “Shape Memory Alloy-Based Smart RC Bridge: Overview of State-of-the-Art”, Smart Structures and Systems, 4(3): 367-389. 

Shape Memory Alloys (SMAs) are unique materials with a paramount potential for various applications in bridges. The novelty of this material lies in its ability to undergo large deformations and return to its undeformed shape through stress removal (superelasticity) or heating (shape memory effect). In particular, Ni-Ti alloys have distinct thermomechanical properties including superelasticity, shape memory effect, and hysteretic damping. SMA along with sensing devices can be effectively used to construct smart Reinforced Concrete (RC) bridges that can detect and repair damage, and adapt to changes in the loading conditions. SMA can also be used to retrofit existing deficient bridges. This includes the use of external post-tensioning, dampers, isolators and/or restrainers. This paper critically examines the fundamental characteristics of SMA and available sensing devices emphasizing the factors that control their properties. Existing SMA models are discussed and the application of one of the models to analyze a bridge pier is presented. SMA applications in the construction of smart bridge structures are discussed. Future trends and methods to achieve smart bridges are also proposed.

Alam M.S., Youssef M.A., Nehdi M., 2007, “Utilizing Shape Memory Alloys to Enhance the Performance and Safety of Civil Infrastructure: a Review”, Canadian Journal of Civil Engineering, 34(9): 1075-1086. 

Shape memory alloys (SMAs) are special materials with a substantial potential for various civil engineering applications. The novelty of such materials lies in their ability to undergo large deformations and return to their undeformed shape through stress removal (superelasticity) or heating (shape-memory effect). In particular, SMAs have distinct thermomechanical properties, including superelasticity, shape-memory effect, and hysteretic damping. These properties could be effectively utilized to substantially enhance the safety of various structures. Although the high cost of SMAs is still limiting their use, research investigating their production and processing is expected to make it more cost-competitive. Thus, it is expected that SMAs will emerge as an essential material in the construction industry. This paper examines the fundamental characteristics of SMAs, the constitutive material models of SMAs, and the factors influencing the engineering properties of SMAs. Some of the potential applications of SMAs are discussed, including the reinforcement and repair of structural elements, prestress applications, and the development of kernel components for seismic devices such as dampers and isolators. The paper synthesizes existing information on the properties of SMAs, presents it in concise and useful tables, and explains different alternatives for the application of SMAs, which should motivate researchers and practicing engineers to extend the use of SMAs in novel and emerging applications.Key words: shape memory alloy, superelasticity, shape-memory effect, construction, retrofitting.

 

Palermo, D, Youssef MA, Alam MS, Winter 2013, “Pushing the Envelope in Structural Concrete Design: Applications of Superelastic Shape Memory Alloys”, Canadian Civil Engineer, Vol. 30.5, pp. 26-29.

 

Shape Memory Alloy Publications (Mechanical Coupler Usage)

 

Abraik, E, Youssef, MA, 2016, “Performance Assessment of Three-Story Shape Memory Alloy Reinforced Concrete Walls“, CSCE 5th International Structural Specialty Conference, London, ON, Canada, Paper #852. 

The need for sustainable structures, that provide adequate ductility without experiencing major damage, has led researchers to develop methods to achieve self-centering structures. One of these methods involves the use of superelastic Shape Memory Alloy (SMA) bars. This study assesses the seismic performance of a three-story SMA Reinforced Concrete (RC) shear wall considering different potential locations for the SMA bars. The maximum inter-story drift, residual drift, and damage scheme are evaluated using Incremental Dynamic Analysis (IDA). The use of SMA bars at the plastic hinge of the first floor was found to significantly reduce the residual drifts and associated damage.

Abraik EA, Youssef MA, 2015, “Cyclic Performance of Shape Memory Alloy Reinforced Concrete Walls“, Proceedings of PROTECT2015 Conference on Response of Structures under Extreme Loading, Michigan State University, Paper ID 1354, pp. 326-333, 28-30 June 2015, Lansing, Michigan, USA. 

Concrete walls are commonly used to resist lateral loads. Their relatively high stiffness limits the inter-story drifts and minimizes damage to other structural and nonstructural elements. However, significant structural damage to the walls is expected during seismic events. This study investigates numerically the effectiveness of using Superelastic (SE) Shape Memory Alloy (SMA) bars to improve the seismic performance of moderate and squat concrete walls. The used analytical model was validated using experimental results by others. It was then utilized to investigate the cyclic load-displacement response of one-intermediate and two-squat walls while incorporating SMA bars. Results of this study led to identifying the location of SMA bars that result in best seismic performance

Youssef M.A., Mashaly M.E., Abou-Elfath H, 2010, “Use of SMA and Buckling Restrained Braces to Reduce Seismic Residual Deformations in Low-Rise RC Frames”, Proceedings of the 9th U.S. National and 10th Canadian Conference on Earthquake Engineering, July 25-29, 2010, Toronto, Ontario, Canada, Paper No 544, 10 pp, DOI: 10.13140/2.1.1826.0488. 

Concentric bracing systems have proven to be effective in limiting the lateral drifts of Reinforced Concrete (RC) frames. One of the known deficiencies for these systems is the expected residual deformations following a seismic event. This paper focuses on evaluating the effect of using Buckling Restrained Braces (BRBs) and Shape Memory Alloy Braces (SMABs) on the seismic performance of a three-storey RC building. Two RC frames are designed utilizing both BRBs and SMABs and analyzed using pushover and dynamic analyses. The SMAB system is found to significantly reduce seismic residual deformations. However, this advantage is lost at peak ground accelerations close to the peak ground acceleration causing failure of the frame.

Elfeki M.A. and Youssef M.A., 2010, “Seismic Performance of Shape Memory Alloy Reinforced Concrete Frames”, Proceedings of the 9th U.S. National and 10th Canadian Conference on Earthquake Engineering, July 25-29, 2010, Toronto, Ontario, Canada, Paper No 488, 10 pp, DOI: 10.13140/2.1.4447.4888. 

Superelastic Shape Memory Alloys (SMAs) are unique materials which can regain their original length upon unloading. Utilizing superelastic SMA bars in Reinforced Concrete (RC) frames results in dissipating the earthquake energy while minimizing the seismic residual deformations. In this study, the critical sections of a six-storey steel RC building are defined using five different earthquake records. The building was then redesigned using SMA bars. Seven alternative designs were explored representing using the SMA bars at the plastic hinge zones of the critical beam/column sections and/or at the beam sections adjacent to the critical columns. Each design alternative was subjected to dynamic analysis using the chosen five records scaled to the intensity causing severe damage to the steel RC frame. It was concluded that using SMA bars at the critical beam sections and at the beam sections adjacent to the critical columns results in minimal local damage and residual drifts.

Alam M.S., Youssef M.A., Nehdi M., 2010, “Cyclic Behaviour of Mechanically Spliced Shape Memory Alloy and Steel Bars”, Proceedings of the 9th U.S. National and 10th Canadian Conference on Earthquake Engineering, July 25-29, 2010, Toronto, Ontario, Canada, Paper No 435, 9 pp, DOI: 10.13140/2.1.3398.9122. 

Different types of mechanical couplers are used to splice rebars in reinforced concrete (RC) structures. The efficiency of these couplers for connecting steel rebars has been tested and reported in this paper. Recently, superelastic shape memory alloy (SMA) proves to have a great potential to be used as reinforcing bars in concrete structures in seismic areas. However, using SMA bars in entire structures is not economically feasible due to its high cost. Therefore, it is more rational to limit its use in the plastic hinge regions, whereas regular steel can be used in the other regions of the structure. The connections between SMA and steel are critical, and must be able to transfer the full force from SMA bar to steel bar. Since existing couplers have been developed for connecting steel bars, an experimental investigation was performed to determine their suitability for connecting SMA to steel bar. Commercially available screw-lock couplers were found to be unsuitable. Special treatment needs to be done to achieve the full superelastic strain of SMA while connected with steel bar. None of the available couplers provided adequate performance for SMA spliced bars. Hence, an existing coupler was modified for SMA-steel splicing.

Alam M.S., Nehdi M., Youssef M.A., 2010, “Experimental Investigation of FRP RC Sub-Assemblage with SMA Bar in The Plastic Hinge Region of Beam”, Proceedings of the 9thS. National and 10th Canadian Conference on Earthquake Engineering, July 25-29, 2010, Toronto, ON, Canada, Paper No 438, 10 pp, DOI: 10.13140/2.1.2350.3365. 

High corrosion resistance has made Fibre-Reinforced Polymer (FRP) bars increasingly accepted as reinforcement in concrete structures. However, the lack of ductility is a major concern for the use of FRP reinforcement in seismic regions. However, FRP reinforced concrete (RC) structures can be made ductile by utilizing a ductile material such as steel at the plastic hinge regions. However, the use of steel negates the corrosion resistance purpose of FRP. Nickel-Titanium (Ni-Ti) shape memory alloy (SMA) is highly resistant to corrosion and has added advantage in seismic regions since it can undergo large deformation, yet regain its undeformed shape through stress removal. In this study, an FRP RC beam-column joint with SMA bar at the plastic hinge region of the beam is proposed to address both corrosion resistance and seismic related problems. This joint is reinforced with superelastic Ni-Ti SMA bar at the plastic hinge regions of the beam and FRP in the other regions of the beam and column. The performance of the proposed joint is studied under reversed cyclic loading. The results were compared, in terms of loadstorey drift, and energy dissipation capacity, to those of the original specimen. Both the original and repaired joints proved to dissipate adequate energy under earthquake type loading. The proposed BCJ is not only corrosion resistant, but can also provide adequate energy dissipation during large earthquakes, therefore mitigating major problems related to infrastructure management.

Alam M.S., Nehdi M., Youssef M.A., 2008, “Experimental investigation on the seismic performance of SMA-FRP RC smart beam-column joint”, International Workshop on Smart Materials and Structures, Oct. 2008, Montreal, Quebec, pp. 249-258, DOI: 10.13140/2.1.2287.8721. 

The use of Fibre Reinforced Polymer (FRP) as reinforcement in concrete structures has received much attention owing to its higher resistance to corrosion compared to that of regular steel reinforcement, and has been a very active research area for the last two decades. Since FRP is a brittle material, ductility is considered as a major concern for FRP-reinforced concrete (RC) structures. Ductility of FRP RC structures can be achieved in conjunction with a ductile material such as steel, or shape memory alloy (SMA) which can be placed at the plastic hinge regions of a structure, while FRP bars can be used in the other regions of the structure. However, the use of steel involves the risk of corrosion. Nickel-Titanium (Ni-Ti) SMA is highly resistant to corrosion. If superelastic Ni-Ti can be used as reinforcement, it brings about added advantage in seismic regions since it has the ability to undergo large deformation, but can regain its undeformed shape through stress removal. In this research, beam-column joints reinforced with superelastic Ni-Ti SMA rebar at the plastic hinge regions of the beam and FRP in other regions of the beam and column have been tested under reversed cyclic loading. The results are compared in terms of load-storey drift and energy dissipation capacity to those of a similar RC beam-column joint specimen reinforced with conventional steel. eventually help in eliminating the majority of infrastructure management problems.

Alam M.S., Youssef M.A., Nehdi M., 2008, “Analytical Study of the Seismic Behavior of Beam-Column Elements Reinforced with Superelastic Shape Memory Alloy”, 2nd Canadian Conference on Effective Design of Structures CCEDS-II, Sustainability of Civil Engineering Structures, Hamilton, ON, Canada, pp. 663-672, DOI: 10.13140/2.1.1239.296. 

Recently two experimental investigations were carried out on beam-column elements under seismic loading, one in the University of Western Ontario and the other in the University of Nevada, Reno, where superelastic Shape Memory Alloy (SMA) rebars were used as reinforcement at their plastic hinge regions. Such SMA reinforced beam-column elements experienced reduced residual deformation at the end of seismic loading. This study aims in developing finite element (FE) models in order to simulate the seismic behaviour of SMAreinforced concrete (RC) beam-column elements. The predicted behaviour of the two specimens from FE analysis, their load-storey drift relationship, and energy dissipation ability are compared with the experimental results. The results showed that the model could predict the behaviour of both SMA-RC beam-column elements with reasonable accuracy.

Alam M.S., Nehdi M., Youssef M.A., 2008, “Exploratory Study of Seismic Behaviour of Repaired Beam-Column Joints Reinforced with Shape Memory Alloys”, Annual Conference of the Canadian Society of Civil Engineering, June 10-13, Quebec, QC, Canada, Paper GC-560, 8 pp, DOI: 13140/2.1.5040.3843. 

The objective of this study is to evaluate the seismic performance of a repaired concrete Beam-Column Joint (BCJ) specimen reinforced with superelastic (SE) Shape Memory Alloy (SMA) rebar. A large-scale BCJ reinforced with SMA rebars in the plastic-hinge zone was tested under reversed cyclic loading. Then the joint was repaired and retested. The joint was selected from an eightstorey RC building located in the high seismic region of western Canada and designed and detailed according to the NBCC 2005 and CSA A23.3-04 recommendations. The behaviour of the original and repaired joints under reversed cyclic loading, their load-storey drift, and energy dissipation ability were compared. The results demonstrate that SMA-RC BCJs are able to recover nearly all of their post-yield deformation requiring minimum amount of repairing even after a large earthquake.

Elbahy Y.I., Youssef M.A., Nehdi M., 2008, “Flexural Behaviour of Concrete Members Reinforced with Shape Memory Alloys”, 2nd Canadian Conference on Effective Design of Structures CCEDS-II, Sustainability of Civil Engineering Structures, Hamilton, ON, Canada, pp. 477-486, DOI: 10.13140/2.1.5123.3283. 

Shape Memory Alloys (SMAs) are novel materials that have many applications in different fields. The unique properties of SMA such as Superelasticity (SE) and Shape Memory Effect (SME) have made it distinctive to other metals and alloys. These unique properties have motivated researchers to utilize it in civil engineering applications. One of these applications is using SMA as reinforcing bars in Reinforced Concrete (RC) members. The lack of understanding of the behaviour of SMA RC members has limited its use as reinforcing bars. This behaviour can be understood by developing the moment-curvature relationship for SMA RC sections. Due to the unique properties of SMA and the difference in the stress-strain relationship between steel and SMA, the stress-block parameters provided by the Canadian standards to design steel RC sections might not be valid for designing SMA RC sections. In this paper, moment-curvature analyses were conducted for a range of SMA RC concrete sections. The results of these analyses allowed evaluating the capacities of SMA RC sections and the corresponding maximum concrete strain. Results were used to evaluate the validity of using the stress block parameters provided by the Canadian standards in designing SMA RC sections.

Alam M.S., Youssef M.A., Nehdi M., 2007, “Seismic Behaviour of Concrete Beam-Column Joints Reinforced with Superelastic Shape Memory Alloys”, 9th Canadian Conference on Earthquake Engineering, June 26-29, Ontario, Canada, paper 1125, 10 pp, DOI: 10.13140/2.1.4516.0966. 

Superelastic Shape Memory Alloys (SMAs) are unique alloys that have the ability to undergo large deformations, but can return to their undeformed shape by removal of stresses. This study investigates the seismic performance of joints reinforced with superelastic SMAs compared to regular steel. A finite element program has been validated and then used to analyze two concrete beam-column joints under reversed cyclic loading. Both joints were chosen from an eight storey-RC building located in the high seismic region of western part of Canada. The building was designed and detailed according to the NBCC 2005 and CSA A23.3-04 recommendations. The first specimen was reinforced using steel reinforcing bars. In the second specimen, SMAs were used as reinforcement at the plastic hinge region. The behaviour of the two specimens under reversed cyclic loading, their load-displacement relationship, and energy dissipation ability were compared. The SMA-reinforced specimen ductility and energy dissipation capacity were comparable to the steel reinforced specimen. The results showed that SMAreinforced specimen was able to recover most of its post-yield deformation requiring minimum amount of repair even after a strong earthquake.

Alam M.S., Nehdi M., Youssef M.A., 2007, “Development of SMA-based smart RC bridge for severe loading condition”, Proceeding of the 5th International Conference on Concrete under Severe Conditions of Environment and Loading (CONSEC’07), France, June 4-6, T2, pp. 1761-1769, DOI: 10.13140/2.1.3991.8089. 

Shape Memory Alloys (SMAs) are unique materials with high potential for various applications in bridges. The novelty of this material lies in its ability to undergo large deformations, and return to its undeformed shape through stress removal (superelasticity) or heating (shape memory effect). In particular, Ni-Ti alloys have distinct thermomechanical properties including: superelasticity, shape memory effect, and hysteretic damping. SMA can be effectively used in developing a smart Reinforced Concrete (RC) bridge which will be able to sense and detect its own damage, repair its condition, and adapt to changes in loading conditions. Existing deficient bridges can also be retrofitted by external post-tensioning using SMA. In addition, seismic retrofitting can be effectively done using various SMA dampers, isolators and/or restrainers. This paper examines the fundamental characteristics of SMA emphasizing the factors controlling its properties. The paper also presents the concept of developing a smart RC bridge with SMA applications in the construction of bridge structures along with its future trends and applications.

Alam M.S., Nehdi M., Youssef M.A., 2007, “Applications of Shape Memory Alloys in Earthquake Engineering”, 9th Canadian Conference on Earthquake Engineering, June 26-29, Ontario, Canada, paper 1124, 10 pp. 

Shape Memory Alloys (SMAs) are unique materials with the ability to undergo large deformations, and return to their undeformed shape through stress removal (superelasticity) or heating (shape memory effect). This makes them potential candidates for use in seismic resisting elements in the form of reinforcing bars, bracings, and/or connectors. Because of their high damping, they have been used as the kernel components of various damping devices, isolators and actuators for passive, semi-active and active seismic control of structures. Moreover SMAs have been efficiently used for rapid and convenient repair and strengthening of seismically damaged or deficient structures. This paper presents state-of-theart of numerous seismic applications of SMAs and their devices in various structures. The paper also reviews the fundamental characteristics of SMAs emphasizing on the factors influencing their properties.

Alam M.S., Youssef M.A., Nehdi M., 2005, “Shape Memory Alloys as a New Construction Material“, Proceedings of Cansmart 2005 – the 8th International Workshop on Smart Materials and Structures, Toronto, Ontario, Canada, pp. 123-132, DOI: 10.13140/2.1.3467.5200. 

Shape Memory Alloys (SMAs) are special materials with great potential in various civil engineering applications. The novelty of this material lies in its ability to undergo large deformations, and return to its undeformed shape through stress removal (superelasticity) or heating (shape memory effect). Among prospective SMA candidates, Ni-Ti alloys have distinct thermomechanical properties including: superelasticity, shape memory effect, and hysteretic damping. This led to numerous applications including: self-sensing, repairing of structural elements, prestressing, external post-tensioning, and developing kernel components for seismic devices (actuators, dampers, and isolators). Although the high cost of SMA is still limiting its use, researches investigating its production and processing are expected to reduce significantly its price. It is only a matter of time and SMA will emerge as an essential material in the construction industry. This paper reviews the fundamental characteristics of SMA emphasizing the factors influencing their properties and constitutive material models. The paper also presents a review of the state-of-the-art of SMA applications in the construction of civil engineering structures along with its future trends and applications.

 

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