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Papers by Alex Li

World Journal of Engineering, 2012

Bonded steel-concrete is one new type composite structure in civil engineering domain. Generally,... more Bonded steel-concrete is one new type composite structure in civil engineering domain. Generally, for steel-concrete composite structures, the steel beam and the concrete are connected by means of shear connectors. This work consists in analyzing the design ...

2011 International Conference on Electric Technology and Civil Engineering (ICETCE), 2011

Abstract—The steel-concrete composite beam bonded by adhesive has its particular advantages over ... more Abstract—The steel-concrete composite beam bonded by adhesive has its particular advantages over the traditional composite beam. Based on the experimental observation of push-out test, the shear connection behaviour of concrete-adhesive interface is modelled by ...

Journal of Adhesion Science and Technology, 2000

J. Adhesion Sci. Technol., Vol. 14, No. 13, pp. 1639–1656 (2000) © VSP 2000. ... In uence of the ... more J. Adhesion Sci. Technol., Vol. 14, No. 13, pp. 1639–1656 (2000) © VSP 2000. ... In uence of the adhesive thickness and steel plate thickness ... ALEX LI¤, TCHAO ASSIH and YVES DELMAS Laboratory of Mechanics, Materials and Structures, Université de Reims Champagne-...

Computers & Structures, 2008

In traditional steel–concrete composite beam, the connection between steel beam and concrete slab... more In traditional steel–concrete composite beam, the connection between steel beam and concrete slab is ensured by steel shear studs. This paper studies the nonlinear mechanical behavior and failure process of a bonded steel–concrete composite beam by using finite element method. A three-dimensional finite element (FE) model has been developed in this work. The results indicate that there are three major reasons for failure of the composite beam: cracking of the concrete by the local tensile stress, crushing of the concrete by the compressive stress and extensive yielding of the steel beam under the global bending moment.

Computers & Structures, 2009

This paper investigates the reliability assessment of structures exhibiting both stochastic and b... more This paper investigates the reliability assessment of structures exhibiting both stochastic and bounded uncertainties by using a probability and convex set mixed model. The safety measure of a structure is quantified by a reliability index defined by a nested minimization problem. An iterative procedure is developed for seeking the worst-case point and the most probable failure point in the standard uncertainty space. Numerical examples are given to demonstrate the applicability of the probability and convex set mixed model representation in the structural reliability assessment, as well as to illustrate the validity and effectiveness of the proposed numerical method.

Engineering Structures, 2008

Bonding connection in steel–concrete composite beams is investigated in the case of static loadin... more Bonding connection in steel–concrete composite beams is investigated in the case of static loading and high-strength concrete. The 3-point bending test performed on a large beam confirms that bonding is very efficient: the elastic domain is followed by a non-linear behaviour with noticeable ductility. The measurements are generally close to the numerical results provided by beam models or the FE model. The composite beam model which does not take into account slip and shear deflection could be used for engineering design purposes. However all the studied beam models do not allow a very accurate prediction of the behaviour close to the interface and the behaviour at failure in the case of shear failure. Non-linear FE approach may be more suitable but requires realistic failure criterion for all the materials.

Engineering Structures, 2003

The present work deals with shear performance of reinforced concrete (RC) beams with rectangular ... more The present work deals with shear performance of reinforced concrete (RC) beams with rectangular section. The RC beams are designed with shear deficiencies and strengthened by externally bonded carbon fibre fabrics. Four different configurations of externally bonded carbon fibre fabric strips are used to strengthen the reinforced concrete beams in shear. The carbon fibre fabric, is a dry bi-directional impregnated (epoxy resin) on site, supplied and installed by Freyssinet (TFC®). The experimental programme consists of two control beams and eight strengthened RC beams. The reinforced concrete beams are strengthened with carbon fibre fabric vertical strips and 45° inclined strips in the form of U-wrap or in the form of a ring. The objectives of this study are to investigate the influence of parameters like carbon fibre fabric span and wrapping manners on the shear capacity of strengthened RC beams. A mechanical formula is used to predict the contribution of carbon fibre fabric to shear capacity of strengthened RC beams. The results obtained by using the mechanical formula have been compared with theses obtained by test.

Journal of Structural Engineering-asce, 2001

The results of an experimental and analytical investigation of shear strengthening of reinforced ... more The results of an experimental and analytical investigation of shear strengthening of reinforced concrete (RC) beams with externally bonded (EB) fiber-reinforced polymer (FRP) strips and sheets are presented, with emphasis on the effect of the strip-width-to-stripspacing ratio on the contribution of FRP (V f ). In all, 14 tests were performed on 4,520-mm-long T-beams. RC beams strengthened in shear using carbon FRP (CFRP) strips with different width-to-spacing ratios were considered, and their performance was investigated. In addition, these results are compared with those obtained for RC beams strengthened with various numbers of layers of continuous CFRP sheet. Moreover, various existing equations that express the effect of FRP strip width and concrete-member width and that have been proposed based on single or double FRP-to-concrete direct pullout tests are checked for RC beams strengthened in shear with CFRP strips. The objectives of this study are to investigate the following: (1) the effectiveness of EB discontinuous FRP sheets (FRP strips) compared with that of EB continuous FRP sheets; (2) the optimum strip-width-to-strip-spacing ratio for FRP (i.e., the optimum FRP rigidity); (3) the effect of FRP strip location with respect to internal transverse-steel location; (4) the effect of FRP strip width; and (5) the effect of internal transverse-steel reinforcement on the CFRP shear contribution.

Engineering Structures, 2001

An experimental investigation was conducted to study the effect of composite carbon fabric shear ... more An experimental investigation was conducted to study the effect of composite carbon fabric shear reinforcement on the ultimate strength and behaviour of a reinforced concrete beam in the absence of the stirrup in the shear span. A total of fourteen reinforced concrete beam with or without composite carbon fabrics were tested in a load system by a point load at one-third of the clear span. The results indicate that the ultimate strength of the beam increased with an increase of the strengthening surface. The effect of the composite fabric reinforcement on the reinforced concrete beam was variable. The shear capacity of strengthened reinforced concrete beam is not the simple superposition of the shear strength due to concrete plus the shear strength due to steel stirrups and the additional shear capacity due to the composite fabrics. Almost all the beams failed in shear but the beams strengthened by composite fabrics at full depth of the beam failed in flexure. After analysing the experimental results, an analytical model to predict the shear contribution of the strengthened RC beam was proposed in this work. The values obtained by the analytical model have shown a close agreement to experimental results.

Review of Scientific Instruments, 2010

Glass transitions in confined polystyrene films on a silicon substrate were studied using atomic ... more Glass transitions in confined polystyrene films on a silicon substrate were studied using atomic force microscopy incorporating a thermal tip. Three-dimensional spatial nanoconfinements were achieved by controlling size and boundary conditions of small heated volumes of polymer nanostrands drawn from the polymer surface with the thermal tip, using appropriate loads and temperatures at the tippolymer contact. Finite element analysis was performed to model mechanical contact and thermal transport, including the effects of contact radius, film thickness, and load on temperature and pressure distributions in the confined volume at the contact. The glass transition temperature (T g ) was measured by observing the softening of polymers with increasing temperature. The measured surface T g exhibited a strong size dependence, while the subsurface T g increased with decreasing the distance to the substrate. A large increase in the surface T g was observed when the radius of contact was reduced below about 10 nm. The increase in the glass transition temperature at the surface was attributed to the presence of surface and line tension at the nanometer contact, while the enhanced T g near the substrate was attributed to the pinning effects that reduces the mobility of the polymer molecules in the film over several hundreds of nanometers away from the polymer-substrate interface.

Nanoscale, 2013

We report the nanorobotic in situ formation and characterization of memristors based on individua... more We report the nanorobotic in situ formation and characterization of memristors based on individual copper oxide nanowires (CuO NWs) and their potential applications as nanosensors with memory function (memristic sensors or "memsensors"). A series of in situ techniques for the experimental investigations of memristors are developed including nanorobotic manipulation, electro-beam-based forming, and electron energy loss spectroscopy (EELS) enabled correlation of transport properties and dopant distribution. All experimental investigations are performed inside a transmission electron microscope (TEM). The initial CuO NW memristors are formed by localized electron-beam irradiation to generate oxygen vacancies as dopants. Current-voltage properties show distinctive hysteresis characteristics of memristors. The mechanism of such memristic behavior is explained with an oxygen vacancy migration model. The presence and migration of the oxygen vacancies is identified with EELS. Investigations also reveal that the memristic behavior can be influenced by the deformation of the nanowire, showing that the nanowire memristor can serve as a deformation/force memorable sensor. The CuO NW-based memristors will enrich the binary transition oxide family but hold a simpler and more compact design than the conventional thin-film version. With these advantages, the CuO NW-based memristors will not only facilitate their applications in nanoelectronics but play a unique role in micro-/nano-electromechanical systems (MEMS/NEMS) as well.

Structural and Multidisciplinary Optimization, 2009

Using a quantified measure for non-probab ilistic reliability based on the multi-ellipsoid convex... more Using a quantified measure for non-probab ilistic reliability based on the multi-ellipsoid convex model, the topology optimization of continuum structures in presence of uncertain-but-bounded parameters is investigated. The problem is formulated as a double-loop optimization one. The inner loop handles evaluation of the non-probabilistic reliability index, and the outer loop treats the optimum material distribution using the results from the inner loop for checking feasibility of the reliability constraints. For circumventing the numerical difficulties arising from its nested nature, the topology optimization problem with reliability constraints is reformulated into an equivalent one with constraints on the concerned performance. In this context, the adjoint variable schemes for sensitivity analysis with respect to uncertain variables as well as design variables are discussed. The structural optimization problem is then solved by a gradient-based algorithm using the obtained sensitivity. In the present formulation, the uncertain-but bounded uncertain variations of material properties, geometrical dimensions and loading conditions can be realistically accounted for. Numerical investigations illustrate the applicability and the validity of the present problem statement as well as the proposed numerical techniques. The computational results also reveal that non-probabilistic reliability-based topology optimization may yield more reasonable material layouts than conventional deterministic approaches. The proposed method can be regarded as an attractive supplement to the stochastic reliability-based topology optimization.

Engineering Structures, 2011

It is meaningful to account for various uncertainties in the optimization design of the adhesive ... more It is meaningful to account for various uncertainties in the optimization design of the adhesive bonded steel–concrete composite beam. Based on the definition of the mixed reliability index for structural safety evaluation with probabilistic and non-probabilistic uncertainties, the ...

Engineering Structures, 2001

An experimental investigation was conducted to study the effect of composite carbon fabric shear ... more An experimental investigation was conducted to study the effect of composite carbon fabric shear reinforcement on the ultimate strength and behaviour of a reinforced concrete beam in the absence of the stirrup in the shear span. A total of fourteen reinforced concrete beam with or without composite carbon fabrics were tested in a load system by a point load at one-third of the clear span.

Engineering Structures, 2012

The steel-concrete composite beam bonded by adhesive has particular advantages over the tradition... more The steel-concrete composite beam bonded by adhesive has particular advantages over the traditional composite beam. Based on the experimental push-out test, this paper proposes a three-dimensional nonlinear finite element model for the mechanical behaviour simulation of bonded steel-concrete composite beams. The proposed numerical model is validated through comparisons between numerical results and experimental data. The effects of certain parameters, including the elastic modulus of adhesive, the adhesive layer's thickness, the concrete strength, the bonding strength and the bonding area, are investigated. Numerical results show that the influence of most investigated parameters on the response of the bonded composites is very notable, while that of the adhesive layer's thickness (variation within 3-15 mm) is relatively small.

Computers & Structures, 2008

In traditional steel–concrete composite beam, the connection between steel beam and concrete slab... more In traditional steel–concrete composite beam, the connection between steel beam and concrete slab is ensured by steel shear studs. This paper studies the nonlinear mechanical behavior and failure process of a bonded steel–concrete composite beam by using finite element ...

Computers & Structures, 2009

This paper investigates the reliability assessment of structures exhibiting both stochastic and b... more This paper investigates the reliability assessment of structures exhibiting both stochastic and bounded uncertainties by using a probability and convex set mixed model. The safety measure of a structure is quantified by a reliability index defined by a nested minimization problem. An iterative procedure is developed for seeking the worst-case point and the most probable failure point in the standard uncertainty space. Numerical examples are given to demonstrate the applicability of the probability and convex set mixed model representation in the structural reliability assessment, as well as to illustrate the validity and effectiveness of the proposed numerical method.

World Journal of Engineering, 2012

Bonded steel-concrete is one new type composite structure in civil engineering domain. Generally,... more Bonded steel-concrete is one new type composite structure in civil engineering domain. Generally, for steel-concrete composite structures, the steel beam and the concrete are connected by means of shear connectors. This work consists in analyzing the design ...

2011 International Conference on Electric Technology and Civil Engineering (ICETCE), 2011

Abstract—The steel-concrete composite beam bonded by adhesive has its particular advantages over ... more Abstract—The steel-concrete composite beam bonded by adhesive has its particular advantages over the traditional composite beam. Based on the experimental observation of push-out test, the shear connection behaviour of concrete-adhesive interface is modelled by ...

Journal of Adhesion Science and Technology, 2000

J. Adhesion Sci. Technol., Vol. 14, No. 13, pp. 1639–1656 (2000) © VSP 2000. ... In uence of the ... more J. Adhesion Sci. Technol., Vol. 14, No. 13, pp. 1639–1656 (2000) © VSP 2000. ... In uence of the adhesive thickness and steel plate thickness ... ALEX LI¤, TCHAO ASSIH and YVES DELMAS Laboratory of Mechanics, Materials and Structures, Université de Reims Champagne-...

Computers & Structures, 2008

In traditional steel–concrete composite beam, the connection between steel beam and concrete slab... more In traditional steel–concrete composite beam, the connection between steel beam and concrete slab is ensured by steel shear studs. This paper studies the nonlinear mechanical behavior and failure process of a bonded steel–concrete composite beam by using finite element method. A three-dimensional finite element (FE) model has been developed in this work. The results indicate that there are three major reasons for failure of the composite beam: cracking of the concrete by the local tensile stress, crushing of the concrete by the compressive stress and extensive yielding of the steel beam under the global bending moment.

Computers & Structures, 2009

This paper investigates the reliability assessment of structures exhibiting both stochastic and b... more This paper investigates the reliability assessment of structures exhibiting both stochastic and bounded uncertainties by using a probability and convex set mixed model. The safety measure of a structure is quantified by a reliability index defined by a nested minimization problem. An iterative procedure is developed for seeking the worst-case point and the most probable failure point in the standard uncertainty space. Numerical examples are given to demonstrate the applicability of the probability and convex set mixed model representation in the structural reliability assessment, as well as to illustrate the validity and effectiveness of the proposed numerical method.

Engineering Structures, 2008

Bonding connection in steel–concrete composite beams is investigated in the case of static loadin... more Bonding connection in steel–concrete composite beams is investigated in the case of static loading and high-strength concrete. The 3-point bending test performed on a large beam confirms that bonding is very efficient: the elastic domain is followed by a non-linear behaviour with noticeable ductility. The measurements are generally close to the numerical results provided by beam models or the FE model. The composite beam model which does not take into account slip and shear deflection could be used for engineering design purposes. However all the studied beam models do not allow a very accurate prediction of the behaviour close to the interface and the behaviour at failure in the case of shear failure. Non-linear FE approach may be more suitable but requires realistic failure criterion for all the materials.

Engineering Structures, 2003

The present work deals with shear performance of reinforced concrete (RC) beams with rectangular ... more The present work deals with shear performance of reinforced concrete (RC) beams with rectangular section. The RC beams are designed with shear deficiencies and strengthened by externally bonded carbon fibre fabrics. Four different configurations of externally bonded carbon fibre fabric strips are used to strengthen the reinforced concrete beams in shear. The carbon fibre fabric, is a dry bi-directional impregnated (epoxy resin) on site, supplied and installed by Freyssinet (TFC®). The experimental programme consists of two control beams and eight strengthened RC beams. The reinforced concrete beams are strengthened with carbon fibre fabric vertical strips and 45° inclined strips in the form of U-wrap or in the form of a ring. The objectives of this study are to investigate the influence of parameters like carbon fibre fabric span and wrapping manners on the shear capacity of strengthened RC beams. A mechanical formula is used to predict the contribution of carbon fibre fabric to shear capacity of strengthened RC beams. The results obtained by using the mechanical formula have been compared with theses obtained by test.

Journal of Structural Engineering-asce, 2001

The results of an experimental and analytical investigation of shear strengthening of reinforced ... more The results of an experimental and analytical investigation of shear strengthening of reinforced concrete (RC) beams with externally bonded (EB) fiber-reinforced polymer (FRP) strips and sheets are presented, with emphasis on the effect of the strip-width-to-stripspacing ratio on the contribution of FRP (V f ). In all, 14 tests were performed on 4,520-mm-long T-beams. RC beams strengthened in shear using carbon FRP (CFRP) strips with different width-to-spacing ratios were considered, and their performance was investigated. In addition, these results are compared with those obtained for RC beams strengthened with various numbers of layers of continuous CFRP sheet. Moreover, various existing equations that express the effect of FRP strip width and concrete-member width and that have been proposed based on single or double FRP-to-concrete direct pullout tests are checked for RC beams strengthened in shear with CFRP strips. The objectives of this study are to investigate the following: (1) the effectiveness of EB discontinuous FRP sheets (FRP strips) compared with that of EB continuous FRP sheets; (2) the optimum strip-width-to-strip-spacing ratio for FRP (i.e., the optimum FRP rigidity); (3) the effect of FRP strip location with respect to internal transverse-steel location; (4) the effect of FRP strip width; and (5) the effect of internal transverse-steel reinforcement on the CFRP shear contribution.

Engineering Structures, 2001

An experimental investigation was conducted to study the effect of composite carbon fabric shear ... more An experimental investigation was conducted to study the effect of composite carbon fabric shear reinforcement on the ultimate strength and behaviour of a reinforced concrete beam in the absence of the stirrup in the shear span. A total of fourteen reinforced concrete beam with or without composite carbon fabrics were tested in a load system by a point load at one-third of the clear span. The results indicate that the ultimate strength of the beam increased with an increase of the strengthening surface. The effect of the composite fabric reinforcement on the reinforced concrete beam was variable. The shear capacity of strengthened reinforced concrete beam is not the simple superposition of the shear strength due to concrete plus the shear strength due to steel stirrups and the additional shear capacity due to the composite fabrics. Almost all the beams failed in shear but the beams strengthened by composite fabrics at full depth of the beam failed in flexure. After analysing the experimental results, an analytical model to predict the shear contribution of the strengthened RC beam was proposed in this work. The values obtained by the analytical model have shown a close agreement to experimental results.

Review of Scientific Instruments, 2010

Glass transitions in confined polystyrene films on a silicon substrate were studied using atomic ... more Glass transitions in confined polystyrene films on a silicon substrate were studied using atomic force microscopy incorporating a thermal tip. Three-dimensional spatial nanoconfinements were achieved by controlling size and boundary conditions of small heated volumes of polymer nanostrands drawn from the polymer surface with the thermal tip, using appropriate loads and temperatures at the tippolymer contact. Finite element analysis was performed to model mechanical contact and thermal transport, including the effects of contact radius, film thickness, and load on temperature and pressure distributions in the confined volume at the contact. The glass transition temperature (T g ) was measured by observing the softening of polymers with increasing temperature. The measured surface T g exhibited a strong size dependence, while the subsurface T g increased with decreasing the distance to the substrate. A large increase in the surface T g was observed when the radius of contact was reduced below about 10 nm. The increase in the glass transition temperature at the surface was attributed to the presence of surface and line tension at the nanometer contact, while the enhanced T g near the substrate was attributed to the pinning effects that reduces the mobility of the polymer molecules in the film over several hundreds of nanometers away from the polymer-substrate interface.

Nanoscale, 2013

We report the nanorobotic in situ formation and characterization of memristors based on individua... more We report the nanorobotic in situ formation and characterization of memristors based on individual copper oxide nanowires (CuO NWs) and their potential applications as nanosensors with memory function (memristic sensors or "memsensors"). A series of in situ techniques for the experimental investigations of memristors are developed including nanorobotic manipulation, electro-beam-based forming, and electron energy loss spectroscopy (EELS) enabled correlation of transport properties and dopant distribution. All experimental investigations are performed inside a transmission electron microscope (TEM). The initial CuO NW memristors are formed by localized electron-beam irradiation to generate oxygen vacancies as dopants. Current-voltage properties show distinctive hysteresis characteristics of memristors. The mechanism of such memristic behavior is explained with an oxygen vacancy migration model. The presence and migration of the oxygen vacancies is identified with EELS. Investigations also reveal that the memristic behavior can be influenced by the deformation of the nanowire, showing that the nanowire memristor can serve as a deformation/force memorable sensor. The CuO NW-based memristors will enrich the binary transition oxide family but hold a simpler and more compact design than the conventional thin-film version. With these advantages, the CuO NW-based memristors will not only facilitate their applications in nanoelectronics but play a unique role in micro-/nano-electromechanical systems (MEMS/NEMS) as well.

Structural and Multidisciplinary Optimization, 2009

Using a quantified measure for non-probab ilistic reliability based on the multi-ellipsoid convex... more Using a quantified measure for non-probab ilistic reliability based on the multi-ellipsoid convex model, the topology optimization of continuum structures in presence of uncertain-but-bounded parameters is investigated. The problem is formulated as a double-loop optimization one. The inner loop handles evaluation of the non-probabilistic reliability index, and the outer loop treats the optimum material distribution using the results from the inner loop for checking feasibility of the reliability constraints. For circumventing the numerical difficulties arising from its nested nature, the topology optimization problem with reliability constraints is reformulated into an equivalent one with constraints on the concerned performance. In this context, the adjoint variable schemes for sensitivity analysis with respect to uncertain variables as well as design variables are discussed. The structural optimization problem is then solved by a gradient-based algorithm using the obtained sensitivity. In the present formulation, the uncertain-but bounded uncertain variations of material properties, geometrical dimensions and loading conditions can be realistically accounted for. Numerical investigations illustrate the applicability and the validity of the present problem statement as well as the proposed numerical techniques. The computational results also reveal that non-probabilistic reliability-based topology optimization may yield more reasonable material layouts than conventional deterministic approaches. The proposed method can be regarded as an attractive supplement to the stochastic reliability-based topology optimization.

Engineering Structures, 2011

It is meaningful to account for various uncertainties in the optimization design of the adhesive ... more It is meaningful to account for various uncertainties in the optimization design of the adhesive bonded steel–concrete composite beam. Based on the definition of the mixed reliability index for structural safety evaluation with probabilistic and non-probabilistic uncertainties, the ...

Engineering Structures, 2001

An experimental investigation was conducted to study the effect of composite carbon fabric shear ... more An experimental investigation was conducted to study the effect of composite carbon fabric shear reinforcement on the ultimate strength and behaviour of a reinforced concrete beam in the absence of the stirrup in the shear span. A total of fourteen reinforced concrete beam with or without composite carbon fabrics were tested in a load system by a point load at one-third of the clear span.

Engineering Structures, 2012

The steel-concrete composite beam bonded by adhesive has particular advantages over the tradition... more The steel-concrete composite beam bonded by adhesive has particular advantages over the traditional composite beam. Based on the experimental push-out test, this paper proposes a three-dimensional nonlinear finite element model for the mechanical behaviour simulation of bonded steel-concrete composite beams. The proposed numerical model is validated through comparisons between numerical results and experimental data. The effects of certain parameters, including the elastic modulus of adhesive, the adhesive layer's thickness, the concrete strength, the bonding strength and the bonding area, are investigated. Numerical results show that the influence of most investigated parameters on the response of the bonded composites is very notable, while that of the adhesive layer's thickness (variation within 3-15 mm) is relatively small.

Computers & Structures, 2008

In traditional steel–concrete composite beam, the connection between steel beam and concrete slab... more In traditional steel–concrete composite beam, the connection between steel beam and concrete slab is ensured by steel shear studs. This paper studies the nonlinear mechanical behavior and failure process of a bonded steel–concrete composite beam by using finite element ...

Computers & Structures, 2009

This paper investigates the reliability assessment of structures exhibiting both stochastic and b... more This paper investigates the reliability assessment of structures exhibiting both stochastic and bounded uncertainties by using a probability and convex set mixed model. The safety measure of a structure is quantified by a reliability index defined by a nested minimization problem. An iterative procedure is developed for seeking the worst-case point and the most probable failure point in the standard uncertainty space. Numerical examples are given to demonstrate the applicability of the probability and convex set mixed model representation in the structural reliability assessment, as well as to illustrate the validity and effectiveness of the proposed numerical method.