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A Reinforcing Bar for Durable Concrete Constructions and Much More

276
Reinforced concrete structures
Dr. Anil K. Kar, B.Sc CE, MSCE, Ph.D
Proprietor, Engineering Services International
Email: dr_anil_kar@engineerings.in

Keywords

Concrete reinforcement, concrete structures, corrosion, ductility, durability of concrete structures, earthquake resistant structures, rebars, reinforced concrete structures, reinforcing bars

Abstract

Reinforced concrete structures have suffered early distress in recent decades.  This distress can most often be traced to excessive corrosion in ribbed rebars. In recognition of the excessive susceptibility of ribbed bars to accelerated rates of corrosion, PSWC-bar*, with its plain surface and wave-type configuration, is proposed as rebar for concrete constructions. The absence of ribs on the surface makes PSWC-bars much less susceptible to corrosion than conventional ribbed rebars are, leading thereby to several-fold enhancement in the life span of concrete structures.  Tests have revealed significantly higher load-carrying capacities for beams and columns and several-fold higher ductility for beams.

* PSWC stands for plain surface with wave-type configuration

  1. Introduction

Cement based concrete, reinforced with steel reinforcing bars (rebars), and commonly known as reinforced concrete, tops the list of materials of construction.

Construction with reinforced concrete in the past has given many graceful, robust and durable structures.  Infrastructure, in the nature of reinforced concrete bridges, buildings and other forms of constructions, have, however, fallen into disrepute in recent decades due to developing cracks  and spalling of concrete at an early age.

Papadakis, et al. [1] observed in their paper in 1991 : “The last two decades have seen a disconcerting increase in examples of the unsatisfactory durability of concrete structures, specially reinforced concrete ones.”

Sixteen years later, Swamy [2] remarked that “the most direct and unquestionable evidence of the last two/three decades on the service life performance of present constructions and the resulting challenge that confronts us is the alarming and unacceptable rate at which the infrastructure systems all over the world are suffering from deterioration when exposed to real environments.”

  1. The causes of early distress in today’s reinforced concrete constructions

Beyond recognizing the unsatisfactory performance of reinforced concrete constructions, Swamy [2], like Papadakis, et al. [1], did not identify the primary cause of the distress.

The time period, referred to by Swamy [2] and Papadakis, et al. [1], would suggest that the phenomenon of early distress in concrete structures followed the start and increasing use of ribbed rebars (Fig. 1 and Fig. 2) in concrete constructions since the 1960s.

The problem of early distress in reinforced concrete structures was studied thoroughly in Russia.  On the basis of extensive work there, Alekseev [3] went to the extent of suggesting that the durability of concrete structures, reinforced with ribbed bars (Fig. 1), would be one order of magnitude less, i.e. one-tenth of that of concrete structures, reinforced with plain bars.

A survey of many concrete bridges and buildings in the public domain in Kolkata in the year 1999 for their performance revealed that older concrete structures, which were built with plain round bars, were still performing without any apparent sign of distress, whereas all the newer concrete structures, constructed with ribbed rebars, some even on the same premises, had reached states of distress early, in some cases within a decade of construction.

As the cracking or spalling of concrete in relatively new concrete structures, built with ribbed bars, was caused by the swelling of corroding steel, rusting of steel in the case of ribbed bars was the principal event in the process of early distress in concrete structures.

Kar [4] had explained the reasons why ribbed bars were intrinsically susceptible to corrosion at accelerated rates (Fig. 2).  The reasons in short are :

  1. residual stresses develop at the bases of ribs during the manufacture of rebars
  2. cracks, which trigger corrosion, may develop at the edges of ribs at the time of manufacture, during transportation and handling
  3. inside the structure, nominal stresses under load are enhanced in keeping with the phenomenon of stress concentration due to the presence of ribs or cracks
  4. additional stresses develop in ribs due to the wedge action of such ribs against surrounding concrete
  5. the sum-total of stresses and strains in 1 to 4 approach or reach yield stress or strain levels
  6. rate of corrosion increases with increasing stress levels; the rate accelerates as the stress or strain approaches yield levels, and the surface becomes unstable once beyond yield, whereupon the process of corrosion becomes unstoppable
  7. alkaline solution of Ca(OH)2 in the pores inside concrete cannot passivate the unstable steel surface at an yield state [3] and thus cannot guard ribbed steel rebars against corrosion
  8. even without the additional stresses, which ribbed bars under service load conditions can be subjected to, the rate of both micro corrosion and macro corrosion are higher in the case of ribbed bars than in the case of plain bars [5]
  9. the rate of corrosion increases with an increase in the yield stress level, apparently because of higher carbon contents
  10. the rate of corrosion also increases where higher strengths in rebars are gained through thermal hardening, i.e., quenching, or through cold twisting beyond yield.

 

 

3. The cause of poor ductility and energy absorbing capacity

Besides the problem of early distress, today’s reinforced concrete structures suffer also from poor ductility level that could possibly be due to the inability of conventional steel rebars to intimately and sufficiently engage inherently brittle concrete; failing thereby to provide a good  resistance to the propagation of cracks across the rebars into the mass of concrete in the compression zone, leading thereby to an early and sudden failure of the member under load, as the member is found incapable of sustaining such load through continued deflection of the member once the yield load is reached as shown in Fig. 3 [6].  In sharp contrast, a ductile member continues to sustain increasing load, beyond yield, through continued deflection as shown in Fig. 4 [6].  It is noted that the rebars for the beams in Fig. 3 and Fig. 4 were the same, except that the bars for the beam, related to Fig. 4, were PSWC-bars, characterized by their plain surface and a gentle wave-type configuration.  Fig. 3 and Fig. 4 are plotted to different scales.

Observations, very much similar to those made by Aarathi [6], were earlier made on the basis of tests at the Indian Institute of Technology Kharagpur, India, and at B.S. Abdur Rahman University, Chennai, India.

  1. Greenhouse gas emission

Besides the world-wide problem of early distress in today’s concrete constructions, a far more serious environmental issue has come to the fore.

PBL Netherlands Environmental Assessment Agency [7], has reported that the making of cement, a principal constituent element of reinforced concrete, leads to 9.5 percent of the total global emission of CO2 from all sources.  Other activities, related to reinforced concrete constructions, adversely affect the environment in many other ways.

  1. Objectives of a solution to the problems of (a) early distress (b) lack of ductility and (c) excessive greenhouse gas emission

Three serious problems with today’s reinforced concrete constructions have been identified. These are:

  1. excessive rates of corrosion in today’s ribbed rebars, leading to early distress in concrete constructions
  2. lack of ductility and energy absorbing capacity in reinforced concrete, leading to frequent failure of concrete structures during earthquakes
  3. very high contribution to greenhouse gas and global warming due to the needs for early and more frequent repairs and construction of replacement structures for the shortcomings in items 1 and 2.

May not be in the initial construction, but in the long run, durable constructions with the use of  rebars, which will corrode less, bond well and engage intimately with concrete, will automatically help cut down avoidable wastage of cement for repairs and replacement constructions, and therewith lower the total emission of CO2 and other greenhouse gases as well as global warming, both directly and indirectly.

It will be an added plus if the object of the solution to the problems of excessive rates of corrosion in rebars and CO2 emission would also lead to an enhancement of strength.  It will help enormously if the same solution would also increase ductility and energy absorbing capacities of reinforced concrete flexural members.

Thus, the primary objective became one to innovate a rebar of high strength steel which, without any change in chemistry, and without any added effort or cost, would corrode much less than today’s high yield strength deformed (HYSD) rebars would.

  1. PSWC-bar: an innovative solution

The solution to a problem becomes easier once the causes of the problem are known.

Given the problems and their causes, and given the objectives and constraints, efforts led to the innovative, and yet strikingly simple, solution in the form of the PSWC-bar, in which the letter P stands for plain, S stands for surface, W stands for wave-type and C stands for configuration. The PSWC-bar is thus characterized by its plain surface and a gentle wave-type configuration (Fig. 5).

The observations and inferences, made in this article, are based on results of tests at different universities on beams and columns with different types of rebars.

The pitch length defined as the distance between two successive peaks on the same side of the axis of the deformed configuration of the PSWC-bar (Fig. 6), is 20d to 30d (preferably 30d) where d is the diameter of the bar, and the offset or peak excursion of the axis of the PSWC-bar from its original straight line is about 4 mm to 6 mm; 5 mm for standardization.  Even though offsets, greater than 5 or 6 mm, have led to better performances under load, the recommended configurational proportions provide PSWC-bars with gentle configurations, and make the use of such bars practical.  It is recognized here that, according to provisions in some codes, 5 mm is the permissible deviation in the placement of rebars from their stated positions.

The material of PSWC-bar is steel of grades which are used in the manufacture of plain round or HYSD rebars for the construction of concrete structures, except that the yield strength of the steel may not exceed 620 MPa so that, in the event of constructions with concrete of inadequate strength, the stresses in concrete, at the interfaces with rebars, may not cross safe limits.

  1. Research significance

PSWC-bar, characterized by its plain surface and a gentle wave type configuration, is offered as a solution to the problem of early distress in concrete structures, reinforced with ribbed bars.  The absence of ribs will automatically enhance the life span of concrete structures very significantly. Numerous tests have shown that the use of PSWC-bars as rebars can enhance the load-carrying capacities of concrete beams and columns and make concrete constructions ductile. All of these can lower the cost of initial construction, and can lower the life cycle cost of construction very significantly through several-fold enhancement in the life span of structures.  While the several-fold increase in ductility and energy absorbing capacity of constructions with PSWC-bars may prevent catastrophes during earthquakes, the several-fold increase in the life span of concrete structures will help lessen 5% of the total global emission of CO2 from all sources and other environmental degradations. Also, since tests on concrete elements, reinforced with different types of rebars of the same strength while constructed with concrete of the same strength, have shown distinctly different responses under load, a knowledge of such differences in response can help proper design of reinforced concrete elements.

  1. Experimental investigation

8.1 PSWC-bar meets the tests for durability

The elegant PSWC-bar (Fig. 5), with its plain surface, is free from all of the secondary stresses which have been identified in the section on “The causes of early distress in today’s reinforced concrete constructions”. In the absence of secondary stresses, which could have arisen due to the provision and presence of the ribs on the surface, the stresses in PSWC-bars under service load conditions are thus much less than the yield stress (as per design), and such bars, with their plain surface, are thus passivated and better protected against corrosion inside concrete with the right cement, e.g., Ordinary Portland Cement.  In contrast, ribbed bars (Fig. 1 and Fig. 2), with stresses or strains at or beyond yield inside concrete, may remain unguarded against corrosion for lack of passivation.  The significant difference, these can make, can be found in the observations of Fontana [8] and Alekseev [3].

Fontana [8], in his highly acclaimed book “Corrosion Engineering”, provides an estimate of the differences in the rates of corrosion in passivated and non-passivated steel.  Fontana [8] writes : “It is important to note that during the transition from the active to the passive region, a 103 to 106 reduction in corrosion rate is usually observed.”

On the basis of extensive work in Russia, Alekseev [3] commented that the life span of concrete structures with stepped (ribbed) bars was one order of magnitude less than the life span of structures with plain bars.

Experiences with reinforced concrete structures, the old ones with plain bars and the new ones with ribbed bars, show that Alekseev’s [3] observations may not be way off the mark.

Concrete structures, built with plain bars, as PSWC-bars are, will thus have life spans many times longer than those of concrete structures, built with today’s ribbed bars (Fig. 1 and  Fig. 2).

Simultaneously, with its gentle (5 mm offset and 30d pitch length) wave-type configuration, the effective bond or engagement between PSWC-bars and the surrounding concrete is greatly enhanced, as should be evident from a comparison of the information available in Fig. 3 and Fig. 4 and also in Table 1 and Table 2. It is noteworthy that the strength properties of the bars in the beams, related to Fig. 3 and Fig. 4, are the same, and so are the properties of concrete in the two cases.

As the PSWC-bar is devoid of any surface feature, and as its use improves the load-carrying capacities of reinforced concrete elements, it fully and eminently meets the required objectives of the innovation in solving the world-wide problem of early distress in today’s reinforced concrete constructions with ribbed bars.

8.2 PSWC-bar meets the test for load-carrying capacity

It is not only that the use of PSWC-bars can eliminate the basic cause of the world-wide problem of early distress in today’s reinforced concrete constructions, it can do much more. Tests at different universities have revealed that the use of PSWC-bars increases load-carrying capacities in both beams and columns.  Table 1 and Table 2, and Fig. 3 and Fig. 4 present some of the test results.

A comparison of test results, offered by Aarathi [6] in Fig. 3 and Fig. 4, shows that when plain round bars are converted into PSWC-bars, there can be a sea-change in the structural performance of reinforced concrete flexural elements.

In the particular case of the two beams, for which test results are given in Fig. 3 and Fig. 4, the ultimate load-carrying capacity of the conventional beam was 237.10 kN, whereas the ultimate load-carrying capacity of the beam with PSWC-bars was 330.60 kN, indicating an increase of 39% in the load-carrying capacity, that was achieved simply by giving a gentle wave-type configuration to the bars.

A comparison of the test results in Fig. 3 and Fig. 4 also shows a dramatic increase in the ductility and energy absorbing capacity.  It is noted that the plots in Fig. 3 and Fig. 4 are drawn to different scales.

These significant improvements in the nature of load-carrying capacity, ductility and energy absorbing capacity could be attributed to an increase in the engagement or effective bond between rebars and concrete when PSWC-bars are used as rebars.

Very significant increases in load-carrying capacities of beams, with a switch over from conventional plain bars to PSWC-bars as rebars, was also observed in other tests at B.S. Abdur Rahman University, Chennai, and at the Indian Institute of Technology Kharagpur, India.

Results from a few of the many tests involving under-reinforced beams, performed by Patel [9] at Nirma University, can be found in Table 1. The increase in the load-carrying capacity of a beam with PSWC-bars was

(154.67 – 109.00) x (100.0 ÷ 109.00) or 42% over the load-carrying capacity of a beam with plain round bars. This 42% increase in the load-carrying capacity, observed by Patel [9], compares with the 39% increase as per Fig. 3 and Fig. 4, observed by Aarathi [6].

The 42% increase is highly conservative as the limitations of the test facilities did not permit Patel to study the post-yield response.

Similarly, a comparison of the load-carrying capacities, given in Table 1, shows that when ribbed bars may be replaced with PSWC-bars, having the same yield strength for both types of rebars, there may be an increase of about

(274.12 – 238.33) x (100.0 ÷ 238.33) or 15%

The increase of 15% does not take into account the fact that the real ultimate load in the case of the beams with PSWC-bars at their post-yield state can be much higher than the normalized load of 274.12 kN at yield as could be seen from a comparison of results in Fig. 3 and Fig. 4.

A comparison of normalized results from some of the tests on columns by Varu [10], reported in Table 2, shows that the use of PSWC-bars could lead to the highest load-carrying capacities for columns.

If PSWC-bars in the columns in Sl. No. 2 would have steel of fy 435 MPa and if concrete would be of 37.78 MPa as in the case of columns in Sl. No. 3, the test load of columns with PSWC-bars could have been even higher at 1635 kN instead of 1586.67 kN.

The results of column tests (Table 2, and additional tests by Varu [10] on columns with PSWC-bars, but without any ties, suggest that (a) there may not be any premature buckling of the wave-type PSWC-bars under compression inside columns, and (b) as in the case of beams, the quality of engagement between concrete and rebars influences the load carrying capacity of columns, and the use of PSWC-bars gives the highest load-carrying capacity of columns.

Tests by Varu [10] showed that (a) if there would be no ties around the vertical rebars, the bursting load would be less, and (b) with increasing offsets in the configuration of PSWC-bars, i.e., with increasing engagement with concrete, the bursting load would increase when ties were not provided.

Many studies on beams and columns were made at different universities. In the tests, many types of bars of different diameters, different steel grades and surface conditions were used.  Tests consistently showed better structural performances with the use of PSWC-bars.

Since PSWC-bars have a plain surface and thus their susceptibility to corrosion is much less than the susceptibility (to corrosion) in today’s ribbed bars, and since, in terms of load-carrying capacity, beams and columns, reinforced with PSWC-bars, outperform beams and columns, reinforced with conventional rebars, whether plain or ribbed, PSWC-bar not only meets the test for durability, which is the primary objective behind the development of PSWC-bar, it also meets the test for load-carrying capacity.

8.3  PSWC-bar meets the test for increased ductility and energy absorbing capacity

Tests on beams have revealed  that  the  use of  PSWC-bars  not  only leads  to  increased  load-carrying capacities, as given in Table 1, it also increases ductility and energy absorbing capacities very significantly, as shown in Fig. 3 and Fig. 4.

While the displacements at yield and at failure in the case of the control beam with conventional plain round bars were 5.39 mm and 6.97 mm as per Fig. 3, the corresponding figures for the beam with PSWC-bars of the same material were 5.42 mm and 21.5 mm as per Fig. 4.

The comparisons show that while the ductility became higher at 3.1 times, the energy absorbing capacity increased to a level that was higher at 6.0 times when PSWC-bars, with their wave-type configurations, were used as reinforcing bars.

Fig. 4, depicting the load-displacement curve for a concrete beam, reinforced with PSWC-bars, represents a typical ductile response.  Tests on beams, reinforced with conventional plain bars and PSWC-bars at IIT Kharagpur, India too, have shown responses very similar in nature to the curves in Fig. 3 and Fig. 4 even when the rebar diameters in the tests at two centers were significantly different.

Tests on many more beams, straight and cambered, at B.S. Abdur Rahman University, Chennai, India showed similar trends.

The use of PSWC-bars as rebars thus transforms traditionally non-ductile reinforced concrete into ductile reinforced concrete, thereby making concrete structures much better resistant to forces during earthquakes and other dynamic loadings.  This transformation in reinforced concrete elements is achieved at no additional effort or cost.

8.4  PSWC-bar meets the test for earthquake resistant constructions

Tests have shown that, besides significantly higher load-carrying capacities beyond yield, concrete beams, reinforced with PSWC-bars, have ductility several times that of concrete beams, reinforced with rebars of other known forms. The relative increase in energy absorbing capacities is even higher.

The use of PSWC-bars virtually makes concrete constructions ductile.

These greater ductility’s and energy absorbing capacities are very important elements in minimizing the damaging effects of earthquakes.

Among reinforcing bars of different types, PSWC-bar thus admirably satisfies the test for earthquake resistant constructions.

8.5  PSWC-bar meets the test for lower life cycle cost

By virtue of the fact that constructions with PSWC-bars can be made at lower cost by taking advantage of (a) the increased load-carrying capacities of concrete flexural and compression elements, and (b) much greater ductility and even greater energy absorbing capacity of concrete flexural elements, reinforced with PSWC-bars, and most significantly, (c) by virtue of the fact that concrete structures, reinforced with PSWC-bars, will have much greater life spans, constructions with PSWC-bars will have significantly lower life cycle costs.

8.6  Test for ease of design and construction 

Students at different universities have successfully designed and constructed numerous beams and columns with PSWC-bars as with conventional plain bars and ribbed bars using the Indian standards.  They encountered no difficulties, either in design or in construction with PSWC-bars.

For positional locations, (e.g., effective depth) in design, the PSWC-bars were considered as if there was no deformation of the axis.

Most of the tests with beams and columns had multiple samples of the same design. Though the performances of multiple beams and columns of the same design varied with expected minor variations in the construction details, the load-carrying capacities of multiple elements of the same design were very much similar, and the results had small standard deviations.

This should suggest that the use of PSWC-bars is not beset with any unusual problem in design and construction.

8.7  PSWC-bar meets the test for sustainability

By virtue  of  the  fact  that  the  use of  PSWC-bars  as rebars  in  concrete  constructions has the capacity to enhance the life span of such constructions several fold, by virtue of the fact that such constructions will have greater resistance to earthquakes and other dynamic forces, by virtue of the fact that increased load-carrying capacities will permit the use of smaller sections, and by virtue of the fact that durable constructions with PSWC-bars will be much less damaging to the environment in the long run than constructions with other rebars, it can be said more easily in the case of PSWC-bars, than in the case of any other rebar, that the use of PSWC-bars makes concrete constructions sustainable.

8.8  PSWC-bar meets the test for Green Technology

The manufacturing of cement leads to CO2 emission of about 9.5% of the total global emission from all sources [7].

Thus, any possible lessening of the need for the manufacturing of cement, without any reduction in the availability of constructed facilities, will truly be a green technology.

Observations by Alekseev [3] and Fontana [8] would suggest that, compared to the life span of constructions with today’s ribbed rebars, the life span of constructions with PSWC-bar, with its ability to be used as high strength steel rebar, should be about ten times as high. Very conservatively, this enhanced life span can be suggested to be at least two to three times as high.

Besides the CO2 emission and direct warming of the environment in the process of making cement, there are other gaseous emissions and direct warming of the environments related to quarrying, steel (rebar) making and transportation.

Thus, because of the enhancement (say, doubled) of life span of concrete structures, reinforced with PSWC-bars, the effective reduction in CO2 emission, as a percentage of the total global emission of CO2 can be thought of as 5.0% annually after an initial period of construction. With decreased cement productions, decreased rebar productions therewith, and reduced quarrying and hauling of materials there will also be a reduction in the direct warming of the environment.

Since all of the benefits of lower CO2 emission and lower direct warming of the environment can be had without any extra effort or cost, since there are very considerable increases in the different performance parameters of concrete elements, reinforced with PSWC-bars, since PSWC-bar helps to make concrete constructions more sustainable than any other rebar can, and since the manufacture of PSWC-bars requires no additional effort or cost beyond what it takes to make conventional rebars with surface ribs, PSWC-bar truly offers a green technology in the field of concrete  construction.  This green technology is strengthened by the fact that lengthened life span of concrete structures, reinforced with PSWC-bars, will also lead to lowered demands on natural resources, including water.

  1. Teachings in reinforced concrete

Tests show:

  1. The effective bond (not to be confused with resistance to pull-out forces which is generally treated as bond in the case of ribbed bars) or the quality of engagement between rebars and the surrounding concrete has an important bearing on the performance of reinforced concrete beams in terms of load-carrying capacity, shear strength, ductility and energy absorbing capacity.
  2. Configurations and surface conditions of rebars can have an important bearing on the load bearing capacity of columns.
  3. The effectiveness of ties in confining concrete, and thereby in inhibiting bursting of concrete, can have an important bearing on the load-carrying capacity of columns.
  4. Proposed Theory

On the basis of tests at different universities, it is recognized and theorized that:

Besides depending upon the strengths and dimensions of concrete and rebars, and the disbursement of the rebars inside concrete, the performance of reinforced concrete elements under load is greatly influenced by the quality of effective bond or engagement between rebars and their surrounding concrete, in which the engagement can be governed, besides the quality of concrete, by the surface features, surface textures and conditions as well as physical configurations of rebars.

This influence of effective bond or engagement between rebars and the surrounding concrete can be accounted for by incorporating an influence factor for bond, ß, for different types of rebars in determining the load-carrying capacities of reinforced concrete elements as could be determined following today’s design practices.

Until  the  time  values of ß for different types of rebars will be  determined through more  detailed work, guides for design of concrete structures with PSWC-bars are given in APPENDIX-I.

  1. Concluding remarks
  2. The use of PSWC-bars (characterized by their plain surface and a gentle wave-type configuration), in lieu of ribbed bars, can raise the durability of reinforced concrete elements several fold, thereby significantly lowering the life cycle cost of construction and reducing demands on natural resources, including construction quality water.
  3. Compared to the case of beams and columns with conventional rebars, the use of PSWC-bars raises the load-bearing capacities of such beams and columns very significantly. It raises the ductility and energy absorbing capacities of flexural elements by several hundred percent, thereby offering the potential to save lives and properties during earthquakes.
  4. The advantages of using PSWC-bars include lowering of the total global emission of CO2 from all sources by at least 5%, and lowering direct warming of the environment.
  5. The making and use of PSWC-bars require no special technology, effort or cost.
  6. The steel material can have any chemistry/metallurgy of choice for reinforcing bars, but the yield stress is not to exceed 620.00 MPa and the diameter of the rebar may not exceed 40 mm unless when the concrete will have sufficiently high strength, such that stresses in concrete surrounding the rebars may not cross safe limits for concrete.
  7. PSWC-bar outperforms all known forms of steel rebars for concrete construction.
  8. Standard provisions in codes can be followed in the design and construction with PSWC-bars; however, advantage can be taken of the increased load-carrying capacities, ductility and energy-absorbing capacity of reinforced concrete elements which will be constructed with PSWC-bars.
  9. It may be reasonable, and desirable for economy, to account for the influence of bond explicitly in the design for flexure, especially at the ultimate load or ultimate state condition. Similarly, economy can be achieved in the design and construction of columns through a recognition of the superior bond or engagement between rebar and concrete.

Acknowledgement

The innovative idea of PSWC-bar as a simple solution to a worldwide problem was arrived at working over a long period of time as proprietor of Engineering Services International, Kolkata, India, which provided not only the time but also resources for tests during the period of development of PSWC-bar. This writer would like to acknowledge the help he received from the work of A R V Aarathi under the guidance of Professor M S Haji Sheik Mohammed at B S Abdur Rahman University, Chennai (for basic information in Fig. 3 and Fig. 4), from N A Patel (for basic data in  Table 1), and from R S Varu (for basic data in Table 2) under the guidance of Professor Urmil V Dave at the Institute of Technology, Nirma University, Ahmedabad, both in India. This writer also acknowledges the generous help by their universities in providing resources and permitting the use of their facilities in carrying out the cited work.

References

  • [1]         G. Papadakis et al, Physical and Chemical Characteristics Affecting the Durability of Concrete,  ACI Materials Journal, American Concrete Institute, March – April, (1991) 186-196.
  • [2]         N. Swamy, Infrastructure Regeneration : the Challenge of Climate Change and Sustainability – Design for Strength or Durability, The Indian Concrete Journal, The ACC Ltd., Vol. 81, No. 7, July , (2007) 7-13.
  • [3]         N. Alekseev, Corrosion of Steel Reinforcement, Durability of Reinforced Concrete in Aggressive Media, Oxford & IBH Publishing Co. Pvt. Ltd., (Translation of : Dolgovechnosti zhelezobetona v aggressivnikh sredakh, Stroiizdat, Moscow), (1990), Chapter 7.
  • [ 4] K. Kar, Concrete structures – the pH potential of cement and deformed reinforcing bars, Journal of the Institution of Engineers (India), Civil Engineering Division, V. 82, June,  (2001) 1-13.
  • [5] U. Mohammed, N. Otssuki, and M. Hisada, Corrosion of steel bars with respect to orientation, ACI Materials Journal, American Concrete Institute, March-April, (1999) 154-159.
  • [6] R.V. Aarathi, Optimisation of C-bars, for enhanced flexural performance of RCC beams,  M. Tech Thesis, B. S. Abdur Rahman University,  Chennai (2014).
  • [7]         PBL Netherlands Environmental Assessment Agency, Trends in Global CO2 Emissions, Report — Background Studies, (2014)
  • [8] G. Fontana, Corrosion Engineering, Third Edition, McGraw Hill Education (India) Private Limited, New Delhi (2005).
  • [9]         A. Patel, Study on PSWC-bar as reinforcement for beam, M. Tech project, Nirma University, Ahmedabad (2015).
  • [10] R.S. Varu, Studies on C-bar as reinforcement for column, M. Tech project, Nirma University, Ahmedabad (2014).

(Note: In [6] and [10] PSWC-bar was initially named as C-bar)

Appendix

Appendix I- Design of Concrete Structures with PSWC-Bars

Tests at different universities have shown improved performances of beams and columns, when reinforced with PSWC-bars of gentle wave-type configurations. Expectedly, enhancement in performance is sensitive to the offset and pitch length in the configuration pattern of PSWC-bars.

As an interim and a conservative measure, it is suggested that all the tables and provisions/ recommendations in ACI-318, IS 456 and other similar or related standards/guides/ handbooks/books be followed for the design  and  construction of  reinforced  concrete  elements and  structures  while using  PSWC-bars,  except  that

  • The ultimate strength in flexure in beams/slabs, etc. will be 10.0% (ten percent) higher when constructed with PSWC-bars
  • The available shear and torsional strength will be 5.0% (five percent) higher when constructed with PSWC-bars
  • Capacities of columns will be 5.0% (five percent) higher when constructed with PSWC-bars
  • For the design of flexural members, subjected to vibratory, impact and impulsive loads, advantage may be taken of  the idealized load-deformation curve as shown in Fig. 7.

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