The cyclic behaviour of plain cylindrical concrete subjected to multidirectional compression was ... more The cyclic behaviour of plain cylindrical concrete subjected to multidirectional compression was investigated experimentally. A total of 42 cylindrical concrete specimens from three different concrete mixes were tested. This test program was particularly focused on the strength and deformation aspects of the concrete response and the process of damage build-up. From this study, it was found that the most important response index for concrete subjected to cyclic loading was the history of damage accumulated in the microstructure which was measured in terms of volumetric strain. The degradation of the elastic stiflhess due to cyclic loads was found to be primarily a function of geometrical change and insensitive to the type of concrete considered. The comparison with the monotonic response of concrete which was also investigated in this study suggests that the cyclic nature of the load promotes damage build-up at faster rates than the monotonic loading, and the path-dependence in the ...
With the advent of strain-hardening cementitious composites (SHCC), an opportunity for alternativ... more With the advent of strain-hardening cementitious composites (SHCC), an opportunity for alternative jacketing solutions is presented, where the internal confinement exerted by the fibers in the material may effectively encase the structural component, thereby enhancing the strength and deformation capacity in the critical regions. This concept is explored in the present paper through testing of four pre-damaged prismatic flexural reinforced concrete members with various reinforcing deficiencies. Thin SHCC jackets constituted of a fiber-reinforced Engineered Cementitious Composite (ECC) are used to replace the damaged cover without any additional confining reinforcement. An advantage of cover replacement is that strengthening is achieved without altering the dimensions of the members. The experimental results documented the SHCC jackets’ effectiveness as a rehabilitation strategy, enhancing both the strength and ductility of the retrofitted elements and mitigating the deficiency in tr...
Recent developments in the area of ultra-high-performance steel fiber reinforced concrete (UHP-SF... more Recent developments in the area of ultra-high-performance steel fiber reinforced concrete (UHP-SFRC) has enabled a reduction in the use of steel reinforcement and has led to enhanced ductility and toughness of structural components owing to its resilient tensile behaviour. This paper presents the results of an experimental study that was conducted to investigate the tensile behaviour of UHP-SFRC. Four commercial mixes and two in-house mixes were evaluated using the procedures prescribed in the 2019 edition of Annex U of CSA-A23.1 and in Annex 8.1 of CSA-S6 2018. The tensile strength of UHP-SFRC was quantified and correlated through the direct tension test, splitting test, inverse analysis of four-point bending tests using either code expressions or nonlinear finite element analysis, and a calibrated empirical expression that links this property to the cylinder compressive strength. In addition, the effect of important parameters on flexural strength including casting methodology, vo...
The experimental response of a single‐story, indeterminate reinforced concrete (RC) frame with fl... more The experimental response of a single‐story, indeterminate reinforced concrete (RC) frame with floor slabs is investigated in this paper. The frame was quarter‐scale and tested under static lateral‐load reversals simulating earthquake load. The internal force redistribution occurring within the inelastic range of response and the beam flexural overstrength resulting from slab contribution are evaluated. It is shown that the pattern of lateral‐load distribution in indeterminate structures is severely affected by the partial restraint that continuity imposes on the inelastic member expansion, particularly at large levels of lateral displacement. Specimen behavior is characterized in terms of strength, stiffness, lateral drift ratio, and plastic hinge‐formation. The mechanism by which shear is introduced to beam‐column joints of connections with floor slabs is examined. The performance of the current code recommendations for design of beam‐column joints is investigated in view of the combined effects of cont...
Results of an experimental investigation of the lateral load behavior of antifriction slide beari... more Results of an experimental investigation of the lateral load behavior of antifriction slide bearings used in bridge foundations are presented. The tests are performed under quasi-static lateral loads, and are intended to provide estimates for the average coefficient of friction of the bearings when they are subjected to slow rates of lateral movement, such as those occurring in bridge foundations due to support settlement, thermal expansion, and creep effects. During the experiments, the bearings are subjected to a constant vertical load simulating the weight of the assumed superstructure, while the lateral load is increased at a constant rate. The lateral load resistance of the bearings is found to be in excess of 5% of the applied confining pressure. Furthermore, the resistance increased with the rate of applied loads, but it was drastically reduced with increasing accumulated damage of the bearings (velocity and history-dependent friction mechanism).
... for new and existing Structures Project) frame which was tested at full-scale in European Lab... more ... for new and existing Structures Project) frame which was tested at full-scale in European Laboratory for Structural Assessment (ELSA) [Pinto et ... For the latter reason the Yield Point Spectrum (YPS) format was used to quantify the intensity of seismic demands [Aschheim and Black ...
The concept of three-field displacement finite element formulations of constrained problems is ex... more The concept of three-field displacement finite element formulations of constrained problems is explored in this paper. The approach studied uses collocation within the element domain to enforce the constraints of the problem and resembles mixed formulations because in addition to the approximation of the displacement field, all other auxiliary deformation variables that enter the constraint conditions are interpolated independently. Plate-bending as described by the Reissner–Mindlin theory is used as a model problem for the development of the approach. Two triangular plate elements are formulated based on this methodology, and their performance is investigated using several patch tests. Numerical examples are also considered to study the element behavior under locking conditions (which occur with the classical displacement approach at the thin plate limit). The ability of the elements to overcome locking is established using mathematical arguments and practical examples. The influen...
An existing highway overpass located on a major motorway in Europe is examined on account of exte... more An existing highway overpass located on a major motorway in Europe is examined on account of extensive longitudinal cracking on the lower face and sides of the deck, and signs of sustained damage in the piers. Material analysis reports have validated the existence of ASR activity in fine aggregates. The deck comprises a well reinforced hollow-core prestressed system, however longitudinal cracks penetrate to the interior of the hollow cores. The extent of damage is heavy considering that the laboratory values for free ASR expansion are below the threshold limits, suggesting that there may be underlying structural causes related to the response of the deck under traffic. Objective of the study is to interpret the reported damage, reproduce computationally the mechanics that led to the observed crack pattern and assess the residual structural capacity of the bridge. Detailed nonlinear finite element analysis is conducted to evaluate the structure and study the synergistic effects of st...
This paper examines the seismic behavior of three typical traditional houses in the old city of X... more This paper examines the seismic behavior of three typical traditional houses in the old city of Xanthi using simulation models and the possibilities of restoration and optimization of the Local Historical Structural System used. For this purpose the function of their existing structural system is analyzed and their seismic behavior examined and evaluated using simulation models and time history analysis of the dynamic response to a series of ground motions. Simple, noninvasive structural interventions are selected for restoration and optimization. The seismic behavior of the improved structural system is subsequently re-evaluated using the same modeling procedures. A comparative evaluation of the results obtained from the initial and the postintervention models is used to assess the global modification of the dynamic characteristics and the anticipated performance effected by the types of interventions examined. The variability of the results owing to parameter changes enables a fir...
The sequence of failure in reinforced concrete (RC) prismatic members is used in this paper as a ... more The sequence of failure in reinforced concrete (RC) prismatic members is used in this paper as a tool for estimating dependable deformation capacity. Response mechanisms that may limit the response leading to damage localization are identified in the paper, such as: web diagonal cracking, bar buckling, disintegration of compressive struts due to load reversal, and anchorage failure of primary reinforcement. Deformation components are additive only if stable hysteretic response controlled by flexure prevails. In all other cases, the deformation component associated with the controlling mode of failure dominates the overall deformability of the member. Because the sequence of failure depends to a large extent on load history, deformation attained at any particular level of load is also load history dependent. This is why experimental values for deformation capacity reported in international literature are characterized by excessive scatter. The methodology proposed in this paper is ap...
Objective of the present work is to establish a framework for seismic assessment and retrofit of ... more Objective of the present work is to establish a framework for seismic assessment and retrofit of traditional unreinforced masonry structures. Both demand indices and acceptance criteria are geometric variables related through derived expressions with the fundamental response of the building. These include drift ratios that quantify the intensity of out of plane differential translation and in plane shear distortion of masonry walls oriented transversally to and along the seismic action, respectively, for in plane and out of plane deformation. This framework is particularly useful for setting retrofit priorities and for management of the collective seismic risk of historical settlement entities. A characteristic Balkan type of traditional building is used in the study as a model structure for illustration of concepts. The structure represents the construction methods and building characteristics of the historical town of Xanthi (Greece).
The cyclic behaviour of plain cylindrical concrete subjected to multidirectional compression was ... more The cyclic behaviour of plain cylindrical concrete subjected to multidirectional compression was investigated experimentally. A total of 42 cylindrical concrete specimens from three different concrete mixes were tested. This test program was particularly focused on the strength and deformation aspects of the concrete response and the process of damage build-up. From this study, it was found that the most important response index for concrete subjected to cyclic loading was the history of damage accumulated in the microstructure which was measured in terms of volumetric strain. The degradation of the elastic stiflhess due to cyclic loads was found to be primarily a function of geometrical change and insensitive to the type of concrete considered. The comparison with the monotonic response of concrete which was also investigated in this study suggests that the cyclic nature of the load promotes damage build-up at faster rates than the monotonic loading, and the path-dependence in the ...
With the advent of strain-hardening cementitious composites (SHCC), an opportunity for alternativ... more With the advent of strain-hardening cementitious composites (SHCC), an opportunity for alternative jacketing solutions is presented, where the internal confinement exerted by the fibers in the material may effectively encase the structural component, thereby enhancing the strength and deformation capacity in the critical regions. This concept is explored in the present paper through testing of four pre-damaged prismatic flexural reinforced concrete members with various reinforcing deficiencies. Thin SHCC jackets constituted of a fiber-reinforced Engineered Cementitious Composite (ECC) are used to replace the damaged cover without any additional confining reinforcement. An advantage of cover replacement is that strengthening is achieved without altering the dimensions of the members. The experimental results documented the SHCC jackets’ effectiveness as a rehabilitation strategy, enhancing both the strength and ductility of the retrofitted elements and mitigating the deficiency in tr...
Recent developments in the area of ultra-high-performance steel fiber reinforced concrete (UHP-SF... more Recent developments in the area of ultra-high-performance steel fiber reinforced concrete (UHP-SFRC) has enabled a reduction in the use of steel reinforcement and has led to enhanced ductility and toughness of structural components owing to its resilient tensile behaviour. This paper presents the results of an experimental study that was conducted to investigate the tensile behaviour of UHP-SFRC. Four commercial mixes and two in-house mixes were evaluated using the procedures prescribed in the 2019 edition of Annex U of CSA-A23.1 and in Annex 8.1 of CSA-S6 2018. The tensile strength of UHP-SFRC was quantified and correlated through the direct tension test, splitting test, inverse analysis of four-point bending tests using either code expressions or nonlinear finite element analysis, and a calibrated empirical expression that links this property to the cylinder compressive strength. In addition, the effect of important parameters on flexural strength including casting methodology, vo...
The experimental response of a single‐story, indeterminate reinforced concrete (RC) frame with fl... more The experimental response of a single‐story, indeterminate reinforced concrete (RC) frame with floor slabs is investigated in this paper. The frame was quarter‐scale and tested under static lateral‐load reversals simulating earthquake load. The internal force redistribution occurring within the inelastic range of response and the beam flexural overstrength resulting from slab contribution are evaluated. It is shown that the pattern of lateral‐load distribution in indeterminate structures is severely affected by the partial restraint that continuity imposes on the inelastic member expansion, particularly at large levels of lateral displacement. Specimen behavior is characterized in terms of strength, stiffness, lateral drift ratio, and plastic hinge‐formation. The mechanism by which shear is introduced to beam‐column joints of connections with floor slabs is examined. The performance of the current code recommendations for design of beam‐column joints is investigated in view of the combined effects of cont...
Results of an experimental investigation of the lateral load behavior of antifriction slide beari... more Results of an experimental investigation of the lateral load behavior of antifriction slide bearings used in bridge foundations are presented. The tests are performed under quasi-static lateral loads, and are intended to provide estimates for the average coefficient of friction of the bearings when they are subjected to slow rates of lateral movement, such as those occurring in bridge foundations due to support settlement, thermal expansion, and creep effects. During the experiments, the bearings are subjected to a constant vertical load simulating the weight of the assumed superstructure, while the lateral load is increased at a constant rate. The lateral load resistance of the bearings is found to be in excess of 5% of the applied confining pressure. Furthermore, the resistance increased with the rate of applied loads, but it was drastically reduced with increasing accumulated damage of the bearings (velocity and history-dependent friction mechanism).
... for new and existing Structures Project) frame which was tested at full-scale in European Lab... more ... for new and existing Structures Project) frame which was tested at full-scale in European Laboratory for Structural Assessment (ELSA) [Pinto et ... For the latter reason the Yield Point Spectrum (YPS) format was used to quantify the intensity of seismic demands [Aschheim and Black ...
The concept of three-field displacement finite element formulations of constrained problems is ex... more The concept of three-field displacement finite element formulations of constrained problems is explored in this paper. The approach studied uses collocation within the element domain to enforce the constraints of the problem and resembles mixed formulations because in addition to the approximation of the displacement field, all other auxiliary deformation variables that enter the constraint conditions are interpolated independently. Plate-bending as described by the Reissner–Mindlin theory is used as a model problem for the development of the approach. Two triangular plate elements are formulated based on this methodology, and their performance is investigated using several patch tests. Numerical examples are also considered to study the element behavior under locking conditions (which occur with the classical displacement approach at the thin plate limit). The ability of the elements to overcome locking is established using mathematical arguments and practical examples. The influen...
An existing highway overpass located on a major motorway in Europe is examined on account of exte... more An existing highway overpass located on a major motorway in Europe is examined on account of extensive longitudinal cracking on the lower face and sides of the deck, and signs of sustained damage in the piers. Material analysis reports have validated the existence of ASR activity in fine aggregates. The deck comprises a well reinforced hollow-core prestressed system, however longitudinal cracks penetrate to the interior of the hollow cores. The extent of damage is heavy considering that the laboratory values for free ASR expansion are below the threshold limits, suggesting that there may be underlying structural causes related to the response of the deck under traffic. Objective of the study is to interpret the reported damage, reproduce computationally the mechanics that led to the observed crack pattern and assess the residual structural capacity of the bridge. Detailed nonlinear finite element analysis is conducted to evaluate the structure and study the synergistic effects of st...
This paper examines the seismic behavior of three typical traditional houses in the old city of X... more This paper examines the seismic behavior of three typical traditional houses in the old city of Xanthi using simulation models and the possibilities of restoration and optimization of the Local Historical Structural System used. For this purpose the function of their existing structural system is analyzed and their seismic behavior examined and evaluated using simulation models and time history analysis of the dynamic response to a series of ground motions. Simple, noninvasive structural interventions are selected for restoration and optimization. The seismic behavior of the improved structural system is subsequently re-evaluated using the same modeling procedures. A comparative evaluation of the results obtained from the initial and the postintervention models is used to assess the global modification of the dynamic characteristics and the anticipated performance effected by the types of interventions examined. The variability of the results owing to parameter changes enables a fir...
The sequence of failure in reinforced concrete (RC) prismatic members is used in this paper as a ... more The sequence of failure in reinforced concrete (RC) prismatic members is used in this paper as a tool for estimating dependable deformation capacity. Response mechanisms that may limit the response leading to damage localization are identified in the paper, such as: web diagonal cracking, bar buckling, disintegration of compressive struts due to load reversal, and anchorage failure of primary reinforcement. Deformation components are additive only if stable hysteretic response controlled by flexure prevails. In all other cases, the deformation component associated with the controlling mode of failure dominates the overall deformability of the member. Because the sequence of failure depends to a large extent on load history, deformation attained at any particular level of load is also load history dependent. This is why experimental values for deformation capacity reported in international literature are characterized by excessive scatter. The methodology proposed in this paper is ap...
Objective of the present work is to establish a framework for seismic assessment and retrofit of ... more Objective of the present work is to establish a framework for seismic assessment and retrofit of traditional unreinforced masonry structures. Both demand indices and acceptance criteria are geometric variables related through derived expressions with the fundamental response of the building. These include drift ratios that quantify the intensity of out of plane differential translation and in plane shear distortion of masonry walls oriented transversally to and along the seismic action, respectively, for in plane and out of plane deformation. This framework is particularly useful for setting retrofit priorities and for management of the collective seismic risk of historical settlement entities. A characteristic Balkan type of traditional building is used in the study as a model structure for illustration of concepts. The structure represents the construction methods and building characteristics of the historical town of Xanthi (Greece).
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