Anchorage and laps of plain surface bars in R.C. structures

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Nowadays virtually all-concrete construction uses reinforcement with deformations rolled or indented on the bar surface to improve bond between bar and concrete, but many older structures built with plain surface bars remain in service. The increasing need for assessment of existing construction means there is a continuing need for information on their performance. Research into plain surface bars essentially ceased when ribbed bars became established, and plain bars have consequently been bypassed in developments in understanding and modeling of bond since 1960. The profession's ability to numerically model behavior of concrete structures has expanded dramatically since plain surface reinforcement was discontinued. The option of numerically modeling may be particularly important for assessment of existing structures with noncompliant details. Although the fib Model Code 2010 includes a local bond-slip model for plain surface bars, information on the derivation of the model and supporting evidence of its validation are not available. The current paper analyses data on bond-slip behavior of plain surface bars and demonstrates shortcomings in the fib model. An improved model is proposed and verified against test data from an independent source. K E Y W O R D S anchorage, assessment, bond slip, local bond, plain bars 1 | INTRODUCTION Code committees have responded to the increasing requirement to verify capacity of existing structures by developing codes oriented toward assessment as well as new design. The American Concrete Institute (ACI) first published its Code Requirements for Evaluation, Repair, and Rehabilitation of Concrete Buildings in 2013. 1 The version of EN1992 currently under development will include content on assessment, as will the fib Model Code

Section: Evaluation Of Peak Bond Stress τ Bmaxmentioning

confidence: 89%

“…The evaluation proceeds by considering the influence of bond length, cover ratio, and concrete strength successively to build an expression for τ bmax . The sequence follows that selected by Palmisano et al 14 to obtain a fit to lap and anchorage data.…”

Section: Evaluation Of Peak Bond Stress τ Bmaxmentioning

confidence: 99%

Local bond–slip model for plain surface reinforcement

Cairns

2020

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“…A total of 16 pairs of results from two studies conducted by Feldman and Pouydal are available, half for bars classified as in a 'good' casting position and half for bars cast near the top of 400 mm deep specimens and which would be classified as in a 'other' casting position according to major international design Codes. Secondly, lap strength of square twisted bars is compared with strengths estimated by semi‐empirical expressions derived by Palmisano et al 9 for lap/anchorage capacity of plain surface bars.…”

Section: Analysis Of Test Datamentioning

confidence: 99%

“…For reasons outlined earlier, the parameters influencing bond resistance of square twisted bars are expected to be the same as those for plain bars and to influence resistance in a similar way. In the second approach to evaluating anchorage of square twisted bars, measured resistance is compared with mean strength ( f stm ) estimated by Equation proposed by Palmisano et al 9 for plain bars in a 'good' casting position, and similar to that suggested by Cairns & Feldman 21 in their earlier analysis. This approach allows test specimens for which there is no matched companion to be taken into consideration.…”

Section: Analysis Of Test Datamentioning

confidence: 99%

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Anchorage and lap capacity of square twisted reinforcement for assessment of existing structures

Cairns

Feldman

Palmisano

2021

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Although square twisted section reinforcement is no longer used in new construction, there remain many older structures still in service that were built with such bars. The increasing need for assessment of existing construction means there remains a continuing need for information on performance over older types of reinforcement. Research into plain surface bars essentially ceased when ribbed bars became the norm, and plain bars have consequently been bypassed in developments in understanding of bond since 1960. The basis through which margins of safety are introduced for design has also changed as formal methods for analysis of reliability have developed. An analysis of test data on bond of square twisted bars, also termed Type 1 deformed or Ransome type bars is presented, and a new semi‐empirical formulation for anchorage capacity of straight square twisted bars in R.C. structures consistent with the reliability‐based approach included in the forthcoming second generation of Eurocodes is derived. The expression parallels that for ribbed bars in the fib Model Code 2010. A comparison with provisions of some historical international design codes suggests that in some cases the margin of safety against failure of straight plain bar anchorages may have been lower than would be required by current norms. Implications for practice are briefly discussed.

Anchorage and lap capacity of plain surface and square twisted bars in existing R.C. Structures: A comprehensive approach

Cairns,

Feldman,

Palmisano

2024

Although plain round or square section reinforcement is no longer used in new construction, there are many older structures still in service built with such bars. In recognition of the need for guidance on the assessment of load‐carrying capacity of structures reinforced with such bars, design codes are now introducing or re‐introducing provisions to assess the capacity of laps and anchorages of such reinforcement. The authors have contributed to the introduction of design rules in the fib Model Code 2020. This paper describes the derivation of these provisions. Starting from the form of expression proposed earlier by the authors, the data from which these proposals are derived is specified and modifications in interpretation preparatory to a statistical analysis are outlined. A rigorous multivariate statistical procedure is then employed firstly to determine a mean strength expression for the capacity of anchorages and laps which is then validated against test data. Further statistical analysis is subsequently used to determine a design expression using the approach outlined in EN 1990, taking appropriate account scatter in test data. Finally, some comparisons are presented between the assessment expressions proposed and design provisions that were in place when these types of bars were in common use. Areas where earlier design provisions may be non‐conservative are identified.