Papers by Δέσποινα Συντζιρμά
The inventory of structures that could be classified as old or substandard construction with refe... more The inventory of structures that could be classified as old or substandard construction with reference to modern seismic design standards is vast throughout the world. For this reason development of methods for seismic assessment of such structures is a great and pressing priority for the earthquake engineering community. In the present work, an experimental research has been conducted in order to identify the interacting strength mechanisms that may develop leading individual structural components to failure, including the influence of load history on the sequence of failure. A series of component tests that comprise sixteen (16) specimens modelling reinforced concrete columns with substandard details representative of former construction practices have been tested. Columns are cantilevers with a square cross section and lap-splices in the critical region. Specimens are tested in single curvature under constant axial load and cyclic lateral load reversals simulating earthquake effects. Detailing of the specimens was done so as to develop closely interacting modes of failure (shear failure after flexural yielding, lap splice failure accompanied by shear or flexural failure, etc.). This was done because based on previous research it was shown that apriori identification of the prevailing mode of failure and the associated deformation capacity is the most critical benchmark test of analytical assessment procedures of substandard reinforced concrete elements . From the experimental evidence it becomes apparent that the load history played a determining role both in terms of available deformation capacity and the mode of failure that eventually prevails. The various response mechanisms such as flexure, shear, lap-splice and bar buckling undergo different levels of strength degradation with increasing displacement demand and number of loading cycles.
jackets in upgrading the seismic behaviour of substandard reinforced concrete prismatic members. ... more jackets in upgrading the seismic behaviour of substandard reinforced concrete prismatic members. The experimental program comprised sixteen (16) square cross section cantilever specimens representative of a typical building column from column mid–height between floors to the beam-column connection at a scale of 1:2 to 1:3. Due to lack of adequate seismic detailing the specimens were susceptible to various modes of failure such as shear failure, reinforcement buckling or failure in the lap splice region. The as-built specimens were first damaged to failure after being subjected to simulated seismic loading. In the next phase, the specimens were retrofitted with composite jackets and then loaded again under cyclic lateral displacement reversals simulating earthquake effects under constant axial load. The efficiency of composite jackets as an intervention method for seismic upgrading of substandard reinforced concrete members was investigated considering the design parameters of the in...
Geotechnical, Geological and Earthquake Engineering, 2010
Displacement-based codes for assessment of existing structures ride on the ability of the user to... more Displacement-based codes for assessment of existing structures ride on the ability of the user to establish the deformation capacity of the individual members of the structure in order to compare with the so called acceptance-criteria. The paper summarizes the first principles underlying the mechanical problem of deformation capacity calculation, discusses highlights of the basic Code Models in the US and
Journal of Structural Engineering, 2010
Post earthquake reconnaissance reports illustrate that failure of reinforced concrete (R.C.) memb... more Post earthquake reconnaissance reports illustrate that failure of reinforced concrete (R.C.) members often involve buckling of reinforcement, an observation suggesting that this phenomena is prerequisite for the necessary reduction of member length (shortening) that marks failure under transverse cyclic displacement reversals. From previous experimental research it is known that occurrence of buckling is linked to displacement history. In the present paper the problem of bar buckling in the plastic hinge region as a limiting factor of deformation capacity of reinforced concrete members is expressed, using as a vehicle the hysteretic stress−strain model of the reinforcement, in terms of the imposed displacement amplitude under cyclic reversals. Through the derived analytical expressions it is shown that when controlled by bar buckling, deformation capacity cannot be defined uniquely as it varies with the path of applied load. This explains in part the wide scatter of experimental results regarding drift capacity, which is particularly intense in cases where premature modes of failure are suppressed and the response is controlled by flexure. A corollary to this finding, which refers to the established procedures of displacement−based design, is that quantifiable indices of deformation capacity, associated with the various failure modes, need be expressed as lower bounds, to reflect the wide range of expected values as these might be limited by the occurrence of buckling of compression reinforcement under realistic earthquakes.
The inventory of structures that could be classified as old or substandard construction with refe... more The inventory of structures that could be classified as old or substandard construction with reference to modern seismic design standards is vast throughout the world. For this reason development of methods for seismic assessment of such structures is a great and pressing priority for the earthquake engineering community. In the present work, an experimental research has been conducted in order to identify the interacting strength mechanisms that may develop leading individual structural components to failure, including the influence of load history on the sequence of failure. A series of component tests that comprise sixteen (16) specimens modelling reinforced concrete columns with substandard details representative of former construction practices have been tested. Columns are cantilevers with a square cross section and lap-splices in the critical region. Specimens are tested in single curvature under constant axial load and cyclic lateral load reversals simulating earthquake effects. Detailing of the specimens was done so as to develop closely interacting modes of failure (shear failure after flexural yielding, lap splice failure accompanied by shear or flexural failure, etc.). This was done because based on previous research it was shown that apriori identification of the prevailing mode of failure and the associated deformation capacity is the most critical benchmark test of analytical assessment procedures of substandard reinforced concrete elements . From the experimental evidence it becomes apparent that the load history played a determining role both in terms of available deformation capacity and the mode of failure that eventually prevails. The various response mechanisms such as flexure, shear, lap-splice and bar buckling undergo different levels of strength degradation with increasing displacement demand and number of loading cycles.
Geotechnical, Geological and Earthquake Engineering, 2010
Displacement-based codes for assessment of existing structures ride on the ability of the user to... more Displacement-based codes for assessment of existing structures ride on the ability of the user to establish the deformation capacity of the individual members of the structure in order to compare with the so called acceptance-criteria. The paper summarizes the first principles underlying the mechanical problem of deformation capacity calculation, discusses highlights of the basic Code Models in the US and
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Papers by Δέσποινα Συντζιρμά