Papers by S. Pantazopoulou
Geotechnical, Geological and Earthquake Engineering, 2012
ABSTRACT As part of the preparation for the fib Model Code for Concrete Structures 2010, task gro... more ABSTRACT As part of the preparation for the fib Model Code for Concrete Structures 2010, task group 4.5 Bond Models undertook a major review of rules for bond and anchorage of reinforcement in the CEB-FIP Model Code 1990. This bulletin presents the outcome of that review, describes the rationale for the revisions and presents the evidence on which the revisions are based. The principle changes in MC2010 include raising the limit on concrete strength that may be used when determining bond resistance to 110MPa, introduction of a coefficient η4 to cater for different reinforcement Classes, and coverage of new construction materials including epoxy coated and headed bars. The format of design rules has been changed to permit more rational treatment of confinement from concrete cover and transverse reinforcement, the contribution of end hooks and bends for tension bars, and end bearing to compression laps. New guidance is provided covering a range of construction techniques and service environments and the influence of long term degradation. Analyses of various aspects of detailing on performance of laps and anchorages have resulted in discontinuation of the ‘proportion lapped’ factor α6, alterations to requirements of transverse reinforcement at laps, and have resolved inconsistencies in provisions for bundled bars between major national codes. Apparent inconsistencies in existing rules for lapped joints and anchorages and between the local bond/slip model and design rules are also resolved, thus allowing integration of application rules and modelling. Finally, the basis for an attempt to introduce simple detailing rules for laps and anchorages is described.
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.
Journal of Structural Engineering, 1998
Journal of Structural Engineering, 1991
Journal of Structural Engineering, 1991
Journal of Engineering Mechanics, 1992
Journal of Composites for Construction, 2008
Performance of near-surface mounted ͑NSM͒ bars as additional reinforcement in strengthening of ex... more Performance of near-surface mounted ͑NSM͒ bars as additional reinforcement in strengthening of existing reinforced-concrete construction largely depends on the development capacity of the bar inside the groove. This is controlled primarily by the surface characteristics of the bar and its interaction with the surrounding groove filler and the cover concrete. In this paper, the bond strength of short NSM-bar anchorages is explored experimentally, using a modified eccentric pullout test specimen designed to alleviate some of the deficiencies associated with bond testing. A total of 45 tests were conducted to study the influence of the most important technological parameters of this upgrading method, namely the groove dimensions, the embedment length, and the surface pattern of the bars. NSM bars were 12 mm diameter rods: CFRP bars used had a sandblasted surface and winding helical lengthwise indentations. Steel bars were either standard deformed bars or smooth reinforcement. The variety of bar type considered was intended to highlight and to quantify through the tests the bond strength that may be mobilized by postinstalled reinforcement according to surface profile and stiffness. Test results are used to establish a limit-state bond-slip model for near-surface mounted bars, so as to enable implementation of this emerging technology in practical design.
Construction and Building Materials, 2007
Performance of near-surface mounted (NSM) bars as additional reinforcement in strengthening of ex... more Performance of near-surface mounted (NSM) bars as additional reinforcement in strengthening of existing reinforced-concrete construction largely depends on its development capacity, controlled by the surface characteristics of the bar, and its interactions with the surrounding epoxy paste filler and the cover concrete. In this paper, the bond strength of short NSM-bar anchorages is explored experimentally, using a novel test specimen
Canadian Journal of Civil Engineering, 1995
Engineering Structures, 2015
ABSTRACT
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
Proceedings of 13th International Conference on Digital Signal Processing, 1997
... The user can get, separat,e plot,s of the st,raiii dah , t,lic spect,rum vs. ... decompositio... more ... The user can get, separat,e plot,s of the st,raiii dah , t,lic spect,rum vs. ... decomposition using (,he Daulmdiies order 5 Wavelet,s is shown for the same data record iis in figure 4. The t,op left, figure shows t,he decornposit,ion tree, and the t,op right. the original signal. ...
Structures 2004, 2004
The paper presents an analytical model for estimating the composite action of prismatic reinforce... more The paper presents an analytical model for estimating the composite action of prismatic reinforced concrete (r.c.) members repaired/strengthened by r.c. jacketing. The model considers the slip at the interface between the existing member and the jacket and establishes the mechanisms mobilized to resist this action thereby supporting composite behavior. An algorithm has been developed for calculating the response taking into account the shear phenomena that appear due to sliding at the interfaces as well as the spacing and penetration of flexure-shear cracks. Results calculated using the analytical model are corroborated with selected experiments from the international literature.
Journal of Structural Engineering, 2015
Design requirements for development length of lap-spliced reinforcing bars in concrete refer to t... more Design requirements for development length of lap-spliced reinforcing bars in concrete refer to the associated rules for anchorage, 5 practically treating the two problems as one. This was based on the empirical observation that development capacity of reinforcement ob-6 tained from both lap-splice and anchorage tests converge to the same experimental values. Nevertheless, from a theoretical viewpoint the 7 similarity between the states of stress of these two problems is not well addressed. In order to trace the underlying relationship between these 8 two bond conditions, the field equations governing lap-splice behavior are established and solved from first principles using simplified 9 constitutive relationships for steel and bond between reinforcement and concrete; the state of stress thus estimated is subsequently compared 10 with the state of stress that occurs along an anchorage of the same length. Because lap splices occur in the clear span of members in the 11 presence of flexural moment, an essential point in the solution of the differential equations of bond is the onset of crack stabilization in the 12 splice region. Both longitudinal and transverse concrete cover cracking is considered in solving for the associated bond stress distribution, 13 whereas debonding that initiates at the lap ends and spreads inward to cross inner flexural cracks is reproduced in the solution. Model 14 verification is based on comparisons with indicatively selected published data from elastic lap-splice tests. The main conclusion derived 15 from the model is the confirmation of the empirical rule embedded in the Code Design procedures, namely that bond in lap-splice regions 16 behaves exactly the same as in the anchorage.
Structural Concrete, 2007
This paper presents the results of a recent experimental research study where metallic (high-stre... more This paper presents the results of a recent experimental research study where metallic (high-strength steel cord) fabric jackets (MF jackets) were utilised for the seismic upgrading of substandard reinforced concrete members. The proposed intervention method and its practical application are described in detail. Specimens were cantilevers with a square cross-section, representing a typical building column at half scale. The length of the test region corresponded to half the span of a typical storey building column under lateral sway. Due to lack of adequate seismic detailing the specimens were susceptible to various modes of failure such as web shear failure, buckling of compression reinforcement or failure in the lap splice region. The as-built specimens were first damaged up to failure after being subjected to combined axial loading and cyclic lateral displacement reversals simulating seismic loading. In the next phase, specimens were retrofitted with both composite and metallic fabric jackets and then tested again under the same load history. The results of this preliminary experimental research programme show that the metallic fabric jackets performed in an excellent way compared to glass-and carbon-fibre reinforced polymer jackets, increasing substantially both the strength and the deformation capacity of the repaired members. The excellent mechanical performance of the metallic fabrics combined with many of the advantages of the synthetic wraps (easy handling, no change in member dimensions) and the intrinsic favourable properties of steel (fire resistance), underline the potential of this novel material in repair/strengthening of reinforced concrete as an alternative option for jacketing applications.
Magazine of Concrete Research, 2008
ABSTRACT Detailed non-linear three-dimensional (3D) finite-element analyses of the behaviour of r... more ABSTRACT Detailed non-linear three-dimensional (3D) finite-element analyses of the behaviour of reinforcing bars in compression were conducted for different slenderness ratios and for two different nominal strengths of steel. An equivalent engineering stress-strain response is determined for the bars, based on results obtained in natural coordinates. Approximate expressions to represent the equivalent engineering stress-strain response were fitted to the computed results. The approximate expressions are intended for use in moment-curvature analyses of reinforced concrete sections, where the contribution of the reinforcement is considered in the monotonic response of the cross-section, in cases where spalling of cover concrete allows the reinforcement to buckle. An example of moment-curvature analysis is carried out using the stress-strain relationship presented in this paper.
Journal of Structural Engineering, 1988
Journal of Structural Engineering, 2009
ABSTRACT
Uploads
Papers by S. Pantazopoulou