application of high-strength and corrosion-resistant … · 05/02/2004 · threshold of this...

CTBUH 8th World Congress 2008 �

Salem FazaDr. Faza has more than 20 years experience in the concrete industry specializing in conventional and advanced reinforcing products. He has been involved in the development and code acceptance of advanced reinforcing products at the national and international levels. Dr. Faza has been a member of the American Concrete Institute for the past 15 years, and served as co-chairman of the ACI 440-H and 440-K subcommittees on advanced reinforcing materials and currently serves on the ACI 439 steel reinforcing committee. He also serves on the American Society of Testing Materials and the American Society of Civil Engineering committees. Through his involvement with concrete reinforcements, he planned, supervised, and coordinated all phases of application engineering including research programs at over 20 institutions worldwide. In his role as the President of Middle East Operations for MMFX Technologies Corporation, Dr. Faza has been instrumental in the development and acceptance of the newest ASTM reinforcing bar specification for the high strength steel (ASTM A1035) in the Middle East. Dr. Faza is currently coordinating code development for concrete designs with MMFX steel reinforc-ing bars. Dr. Faza received his Ph.D. from West Virginia University in Advanced Composite Applications in Construction with emphasis on rebars for concrete application, design, and analysis. He has published over 30 papers related to concrete reinforcement and construction and has been a reviewer for leading engineering technical journals.

Johnny KwokMr. Kwok has more than 13 years of structural design experience in California. He received his undergraduate and graduate degrees from the University of California, Berkeley, and Master of Business Administration from the Anderson School at UCLA. Over his career, Mr. Kwok has completed structural design for over $1 Billion worth of building structures, includ-ing regional mall expansion, new airport terminal, high-rise structures, as well as seismic retrofit using high-tech damping devices. His expertise has been in seismic design of structures, and specialized in reinforced concrete and structural steel design. Mr. Kwok serves as the chief structural engineer at MMFX, presenting and educating structural engineering firms on the specialized rebar product, assisting engineers with design and technical support, and working closely with building officials and code authorities to approve the use of MMFX rebars in construction projects both in the U.S. and overseas.

[email protected]@mmfx.com

Application of High-Strength and Corrosion-Resistant ASTM A1035 Steel Reinforcing Bar in Concrete High-Rise Construction

S. Faza1, J. Kwok1 and O. Salah2

1MMFX Technologies Corporation, Irvine, California, U.S.A, Email: [email protected] 2Zamil Holding Group, Al Khobar, Saudi Arabia, Email: [email protected]

Abstract Concrete reinforcing steel congestion in high-rise structures is a major concern to design engineers. Congestion of the reinforcing steel decreases the efficiency of construction and adds greatly to the cost of construction of high-rise structures. MMFX Microcomposite steel bars (MMFX 2), conforming to ASTM A1035 specification, have high-strength properties that can be utilized to combat this problem. In addition, ASTM A1035 steel bar’s distinct microstructure technology provides an answer for the worldwide corrosion problem. The technology that gives ASTM A1035 steel bar its mechanical properties also make it very corrosion resistant. Independent tests show that the chloride threshold of this uncoated steel is 5 to 6 times greater than that of conventional A615 steel bars and 1.75 greater than 2101 solid stainless steel bars. This paper presents the economical analysis done on the design and construction of different high-rise structures and make recommendations to designers on where cost savings can be realized. The use of ASTM A1035 steel bar reduced the amount of steel in some areas by up to 40% while providing a reduction in the installed cost of the material by 15-25% in the highly congested areas.

Keywords: High-Strength Steel, Corrosion Resistance, ASTM A1035, High-Rise Construction

Introduction One of the major issues currently facing the

concrete construction industry is the congestion of reinforcing steel in structural components. Rebar congestion complicates steel placement, hinders concrete placement, and as a result leads to improper consolidationof concrete around rebar, affecting the integrity of the structure.

Another major issue currently facing the concrete construction industry is the corrosion of steel reinforcing in concrete members subjected to corrosive environment. Corrosion of steel reinforcing leads to reduction in strength of the concrete member, and causes the deterioration of the surrounding concrete, further damaging the concrete member. Repair and maintenance cost is enormous to address the corrosion issue.

Proposed Resolution Utilizing the higher yield strength of rebar in

designing various structural components, such as mat foundations, shearwalls, etc., the amount of reinforcing steel required would be reduced and thus relieving the rebar congestion. Reduced congestion facilitates concrete consolidation around the rebar, and results in safer structures.

Besides the ease of placement of rebar and concrete, the use of higher strength steel reinforcing can be an economical method of construction, by reducing the total tonnage of steel reinforcing, the placement labor, and

time, etc.

The inherent corrosion resistance property of ASTM A1035 reinforcing steel would also improve the long-term durability of the structure. If water penetrates the waterproofing membrane or if the reinforced concrete strucural member is exposed to water, the water can reach the reinforcing through the anticipated micro-cracks that are inevitable with concrete. ASTM A1035 rebar provides much better performance under these conditions.

ASTM A1035 Steel Reinforcement The strength of ASTM A1035 steel rebars far

surpasses conventional steel. The high-strength corrosion-resistant steel bars are produced in 12 and 18m (40 and 60 ft) stock lengths. Alternatively, longer lengths can be produced by using mechanical splices that develop the full strength of the reinforcing bars. Stock 12 and 18 m (40 and 60 ft) length material is generally available in bar sizes [#10 (#3) through #36 (#11)]. Stock material for #10 (#3) through #15 (#5) bars are available in coils commonly used by fabricators for fabrication of ties and spirals. Bar sizes #43 (#14) and #57 (#18) are generally available, but these bar sizes are not usually kept in fabricator’s inventory.

Material Composition One of the unique features of the ASTM A1035

steel rebar is the chemical composition. The maximum chemical constituent requirements of the ASTM A1035 reinforcing bars are illustrated in Table 1:


Application of High-Strength and Corrosion-Resistant ASTM A1035 Steel Reinforcing Bar in Concrete High-Rise Construction

S. Faza1, J. Kwok1 and O. Salah2

1MMFX Technologies Corporation, Irvine, California, U.S.A, Email: [email protected] 2Zamil Holding Group, Al Khobar, Saudi Arabia, Email: [email protected]

Abstract Concrete reinforcing steel congestion in high-rise structures is a major concern to design engineers. Congestion of the reinforcing steel decreases the efficiency of construction and adds greatly to the cost of construction of high-rise structures. MMFX Microcomposite steel bars (MMFX 2), conforming to ASTM A1035 specification, have high-strength properties that can be utilized to combat this problem. In addition, ASTM A1035 steel bar’s distinct microstructure technology provides an answer for the worldwide corrosion problem. The technology that gives ASTM A1035 steel bar its mechanical properties also make it very corrosion resistant. Independent tests show that the chloride threshold of this uncoated steel is 5 to 6 times greater than that of conventional A615 steel bars and 1.75 greater than 2101 solid stainless steel bars. This paper presents the economical analysis done on the design and construction of different high-rise structures and make recommendations to designers on where cost savings can be realized. The use of ASTM A1035 steel bar reduced the amount of steel in some areas by up to 40% while providing a reduction in the installed cost of the material by 15-25% in the highly congested areas.

Keywords: High-Strength Steel, Corrosion Resistance, ASTM A1035, High-Rise Construction

Introduction One of the major issues currently facing the

concrete construction industry is the congestion of reinforcing steel in structural components. Rebar congestion complicates steel placement, hinders concrete placement, and as a result leads to improper consolidationof concrete around rebar, affecting the integrity of the structure.

Another major issue currently facing the concrete construction industry is the corrosion of steel reinforcing in concrete members subjected to corrosive environment. Corrosion of steel reinforcing leads to reduction in strength of the concrete member, and causes the deterioration of the surrounding concrete, further damaging the concrete member. Repair and maintenance cost is enormous to address the corrosion issue.

Proposed Resolution Utilizing the higher yield strength of rebar in

designing various structural components, such as mat foundations, shearwalls, etc., the amount of reinforcing steel required would be reduced and thus relieving the rebar congestion. Reduced congestion facilitates concrete consolidation around the rebar, and results in safer structures.

Besides the ease of placement of rebar and concrete, the use of higher strength steel reinforcing can be an economical method of construction, by reducing the total tonnage of steel reinforcing, the placement labor, and

time, etc.

The inherent corrosion resistance property of ASTM A1035 reinforcing steel would also improve the long-term durability of the structure. If water penetrates the waterproofing membrane or if the reinforced concrete strucural member is exposed to water, the water can reach the reinforcing through the anticipated micro-cracks that are inevitable with concrete. ASTM A1035 rebar provides much better performance under these conditions.

ASTM A1035 Steel Reinforcement The strength of ASTM A1035 steel rebars far

surpasses conventional steel. The high-strength corrosion-resistant steel bars are produced in 12 and 18m (40 and 60 ft) stock lengths. Alternatively, longer lengths can be produced by using mechanical splices that develop the full strength of the reinforcing bars. Stock 12 and 18 m (40 and 60 ft) length material is generally available in bar sizes [#10 (#3) through #36 (#11)]. Stock material for #10 (#3) through #15 (#5) bars are available in coils commonly used by fabricators for fabrication of ties and spirals. Bar sizes #43 (#14) and #57 (#18) are generally available, but these bar sizes are not usually kept in fabricator’s inventory.

Material Composition One of the unique features of the ASTM A1035

steel rebar is the chemical composition. The maximum chemical constituent requirements of the ASTM A1035 reinforcing bars are illustrated in Table 1:


Table 1. Max. Chemical Constituents (Weight %).

*Maximum unless range indicated.

Element

ASTM A1035 MaximumAmount *

Typical MMFX 2

Carbon 0.15% 0.08% Chromium 8 to 10.9% 9% Manganese 1.5% 0.5% Nitrogen 0.05% Phosphorus 0.035% Sulfur 0.045% Silicon 0.50%

Tensile Properties The ASTM A1035/A1035M steel bars are of two

minimum yield strength levels: namely, 100 000 psi [690 MPa], and 120 000 [830 MPa] designated as Grade 100 [690] and Grade 120 [830], respectively. The yield strength is determined by the offset method (0.2 % offset), described in Test Methods and Definitions ASTM A370 (ASTM 2004). In addition, the stress corresponding to a tensile strain of 0.0035 shall be a minimum of 550 MPa [80 000 psi], and a minimum of 620 MPa [90 000 psi] for Grade 100 and Grade 120 respectively. The mechanical properties are summarized in Table 2.

Corrosion Properties Many highly credible institutions and government

agencies have tested the corrosion resistance of ASTM A1035 steel bars. Substantial documented test results have been published to validate the corrosion resistance of this innovative steel product. The high-corrosion resistance provides increased service life to the steel before its structural carrying capacity has dissipated leading to reduced serviceability of reinforced concrete structures, damage to structural load carrying capacity or loss of aesthetic appeal. ASTM A1035 steel bars’ corrosion resistance is 5 to 6 times better than the corrosion resistance of conventional carbon steel (ASTM A615) as measured by its critical chloride threshold level, CCTL (Clemena, G.G. 2004).

Flexural Tension Applications Practical application of ASTM A1035 steel rebars

to high-rise construction includes, but is not limited to, tension piles, mat foundations, shearwalls and moment frames, etc. These structural components designed with the higher yield strength property of ASTM A1035 steel rebars have been demonstrated to be cost effective, improve constructability, and shorten construction schedules. An example of this type of design and construction is illustrated in figures 1 and 2 for a Miami, FL High-Rise tower.

Table 2. Tensile properties of ASTM A1035 high strength steel bars.Property GRADE

100 GRADE

120 Tensile strength, min, MPa [psi]

1030 [150

000]

1030 [150 000]

Yield strength (0.2 % offset), min, MPa [psi]

690 [100

000]

830 [120 000]

Stress corresponding to an extension under load of 0.0035 mm/mm. (0.0035 in/in), min, MPa [psi]

550 [80 000]

620 [90 000]

Elongation in 203.2 mm [8 in.] min. %: #10 through #36 [#3 through #11]

7 7

#43, #57 [#14, #18]

6 ---

The design of concrete members reinforced with ASTM A1035 steel rebars for flexure is analogous to the design of concrete reinforced with conventional steel bars. Experimental data of concrete members reinforced with ASTM A1035 steel bars show that flexural capacity can be calculated based on similar assumptions for members reinforced with ASTM A615 carbon steel rebars, taking into account the higher strength of the ASTM A1035 steel bars.

Designers need to be aware that typical design standards limit the design strength to 550 MPa [80,000 psi], and that the use of deformed reinforcing bar with a material specified yield strength fy exceeding 420 MPa [60,000 psi] is permitted, providing fy is the stress corresponding to a strain of 0.35%. Based on the experimental results and the analysis conducted, the design of a concrete section reinforced with ASTM A1035 steel bars can be simplified by using the ACI 318 design philosophy and 690 MPa [100,000 psi] in tension, while limiting the stresses in compression up to 550 MPa [80,000 psi]. However, well-confined concrete, such as that used in seismic-resisting columns and shear walls, has a compressive strain capacity much greater than that of unconfined concrete. So, the 80,000 psi and 0.35 percent limits in steel compression strength may be unnecessary for well-confined concrete.


Figure 1. The use of ASTM A1035 in Flexural Design in a Miami

High-Rise Structure

Calculations involved in control of cracking should be made for the service load level. Research have shown that, in spite of service load steel stresses as high as 60,000 psi, the width of individual cracks can be held down to hair-line size by proper distribution of the bars (Malhas, F. 2002, El-Hasha, R. and Rizkalla, S. 2002). The strength characteristics of high quality concretes along with the high corrosion resistance properties of the high strength steel will complement the structural properties of the ASTM A1035 steel bars, thus facilitating design development of attractive and economical structures.

Figure 2: ASTM A1035 in Mat Foundation

Transverse Reinforcement Applications One of the applications that high-strength

reinforcing steel achieved code recognition and market acceptance is for use as transverse reinforcement in columns and comparable vertical elements. There are indications worldwide that increased design requirements for transverse reinforcing steel especially in concrete columns and piles, are either exceeding the practical capacity of mild steel reinforcing bars, or are causing such a great amount of steel congestion that correct placement and consolidation of concrete is becoming complex.

There are further indications that this burden is adversely affecting the market for such reinforced concrete structures by making them prohibitively more

expensive. As a result, alternative members such as structural steel rolled sections have replaced reinforced concrete as the material of choice. It appears that in some regions, design engineers are seriously questioning the ability of reinforced concrete members utilizing mild steel reinforcement to perform with structural integrity under certain types of anticipated loading conditions. In one western state in the United States, prestressed concrete piles are no longer doable under the current code restraints.

As a result, the newly published American Concrete Institute, ACI, 318-05 building code includes a new provision for allowing the use of higher design stresses for spiral transverse reinforcement in section 10.9.3 of the building code.

The American Concrete Institute’s ACI 318-05 building code commentary provides the following explanation for the acceptance of the use of the high strength steel bars with yield strength of 100,000 psi for spiral reinforcement: "Confinement reinforcement often creates congestion in reinforced concrete structures. Research shows that 690 MPa (100,000 psi) yield strength reinforcement can be used for confinement (ACI, 2005). This will reduce congestion, thereby making structures safer, because concrete can be consolidated more easily, and will make structures more economical".

Furthermore, the upcoming ACI 318-08 building code extends the use of ASTM 1035 steel in transverse reinforcement ties for confinement purpose, for structural components subjected to high seismic load as illustrated by recently designed and constructed Escala’s high-rise in Seattle, Washington shown in Figure 3.

Figure 3: Escala’s concrete frame with 100 ksi confinement steel (Photo

courtesy CKPS)


Structures Exposed to Corrosive Environment The corrosion-resistant ASTM A1035 steel rebars

are also ideal for structural members and systems exposed or in direct contact with corrosive environment, such as humid atmosphere, high foundation water table, and corrosive soil condition. Possible application would be in foundation piles, foundation systems, marine structures, exposed balconies, etc. ASTM A1035 was used in the construction of the California Academy of Sciences exhibition, education and research center in the foundation and aquarium tanks as shown in Figure 4.

Figure 4: California Academy of Sciences – Exhibition, Education and

Research Center – San Francisco, CA Foundation and Aquarium

Tank

Structural systems reinforced with ASTM A1035 steel rebars have shown to provide extended service lives of 75 to 100 years, depending on the severity of the exposure.

Lowest Construction System The effectiveness of reinforcement in strengthening

a concrete member is generally almost proportional to the product of bar area and yield strength, Asfy. The economies of high strength steels may therefore be estimated in terms of costs per ton per psi yield strength. Relative costs of reinforced concrete structures depend on several factors in addition to the cost of reinforcing steel. The reduction of steel area which accompanies an increase in fy often facilitates concrete placement by eliminating steel congestion.

The technology behind ASTM A1035 steel bars can change the way high-rise buildings are designed. ASTM A1035 steel products provide the designer with higher grade steel along with the corrosion-resistant properties, at a lower overall cost. The added strength of ASTM A1035 steel rebars results in an incremental decrease in the amount of conventional steel necessary to accomplish the same task. High-rise structures can be designed with less congestion without adding additional concrete cover. By specifying ASTM A1035 steel rebar, the high-rise owner will experience upfront cost savings, as well as lower life cycle costs.

Projects using ASTM A1035 steel rebars can be completed with up to 40% less steel resulting in less congestion and up to 50% lower labor costs (Fig. 5). Stronger, more corrosion resistant, and with faster construction build times, ASTM A1035 steel bar is truly a key component of the lowest cost construction system.

Figure 5. Side by side ASTM A1035 (MMFX) vs. ASTM A615.

Practical example 1: Parking structure in Las Vegas, NV (mat foundation application)

The proposed project is located in Las Vegas, Nevada, U.S.A. The structure consists of 12 levels of steel parking decks, supported on a 5’-0” thick concrete mat. The original design was completed using ASTM A615 Grade 60. A preliminary redesign was performed using ASTM A1035 steel bars using 690 MPa [100 ksi] design to provide the equivalent steel strength in the mat. The redesign led to significant savings in total weight of reinforcing, pieces of steel to be placed, as well as overall installed cost. A summary of the potential savings is listed in the Table 3 below:

Table 3. Potential project savings (A1035 vs. A615) – Mat Foundation.

Further analysis was performed to include the use of high-strength mechanical couplers in reinforcing splice locations. The purpose of the exercise was to illustrate further potential savings by eliminating long reinforcing splices and replacing with mechanical couplers. Again, the result of the analysis indicated further savings as illustrated in Table 4 below:

Table 4. Potential project savings (A1035 w/ couplers vs. A615) – Mat Foundation.

Practical example 2: High-rise condominium tower in Las Vegas, NV (shearwall application)

The proposed project is a 50 story tall condominium tower in Las Vegas, Nevada. The building system consists of post-tensioned concrete flat plates,

Bar Type Cost ($) Weight (tons) Placing (pieces)

A615 Gr.420 [60 ksi]

$1,793,572 1,121 13,478

A1035 690 MPa[100ksi] w/ couplers

$1,521,533 644 9,765

$272,039 477 3,713 Savings15% 43% 28%

Bar type Cost ($) Weight (tons) A615 Grade 420 [60]

$2,709,290 1,500

A1035 690 MPa [100ksi]

$2,160,540 1,097

$548,750 403 Savings20% 27%


concrete shearwalls, and mat foundation. The high aspect ratio of the building causes the flexural reinforcing, also known as jamb reinforcing, to be very substantial with Grade 420 [60] reinforcing. Due to the high flexural reinforcing and congestion in the shear wall boundary zones, an alternate reinforcing scheme was considered using ASTM A1035 steel reinforcing. Shear walls of the tower were redesigned using ASTM A1035 steel from foundation through the roof level. The use of ASTM A1035 in the flexural reinforcing of the tall shear walls effectively reduced the amount of congestion in the shear wall boundary zones. The following Table 5 illustrates the savings realized:

Table 5. Potential project savings (A1035 vs. A615 Grade 60) – Shearwall Jamb Reinforcing.

The savings shown in the table only include the effect of ASTM A1035 reinforcing substitution for flexural reinforcing of the walls. With less flexural reinforcing, the boundary zone transverse reinforcing ties are also significantly reduced, leading to further installation savings.

In addition, the mat foundation was also redesigned using ASTM A1035 steel reinforcing to reduce the amount of horizontal flexural reinforcing. To further utilize the high strength property of ASTM A1035 steel bars, the total thickness of the mat foundation system was reduced by 3 feet on average. As a result, there is a total savings of more than 4,000 cubic yard of concrete. In additional to the steel reinforcing savings, there is significant reduction in excavation, dirt haul-out, concrete pour back, as well as construction schedule. Table 6 below summarizes the savings incurred on the project by utilizing ASTM A1035 steel reinforcing:

As illustrated in the examples above, the use of ASTM A1035 steel reinforcing is very effective in reducing overall project cost. The above examples only consider the effect of direct substitution of reinforcing. However, there are other potential savings areas including less reinforcing congestion, less placement difficulties, less plasticizer in concrete mix, more effective concrete pour, and ultimately overall project time and cost savings.

Table 6. Potential project savings (A1035 vs. A615 Grade 60) – Mat Foundation w/ Reduced Thickness.

ConclusionsConcrete reinforcing steel congestion in high-rise

structures can be addresses utilizing the high-strength corrosion-resistance MMFX 2 steel bars produced in accordance with the ASTM A1035 specification. It is apparent that the use of ASTM A1035 steel bar is extremely effective in reducing the total weight of steel for the project, providing flexibility in structural design, and at the same time achieving tremendous time and labor savings.

References ACI Committee 318, 2005. Building Code Requirements for Structural Concrete (ACI 318- 05) and Commentary (ACI 318R-05). Farmington Hills: American Concrete Institute.ASTM A1035, 2007 – “Standard Specification for Deformed and Plain, Low-carbon, Chromium, Steel Bars for Concrete Reinforcement”, ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States. ASTM A370, 2004 – “Test Methods and Definitions for Mechanical Testing of Steel Products”, ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.EL-HACHA, R. and RIZKALLA, S. 2002. Fundamental Material Properties of MMFX Steel Rebars. Retrieved February 5, 2004, from the MMFX Technologies Corporation Web site: MALHAS, F.A. 2002. Preliminary Experimental Investigation of the Flexural Behavior of Reinforced Concrete Beams Using MMFX Steel. Retrieved February 5, 2004, from the MMFX Steel Corporation of America Web site CLEMENEA, G. and VIRMANI, P. Comparing the Chloride Resistance of Reinforcing Bars”, Concrete International, November 2004, Farmington Hills, American Concrete Institute. S.K. GHOSH 2006. Application of ASTM A1035 MMFX Steel Reinforcement in Building Application: An Appraisal.

Bar Type Cost ($) Weight (tons) Placing (pieces)

A615 Gr. 420 [60 ksi]

$1,793,572 1,121 13,478

A1035 690 MPa[100ksi]

$1,570,622 714 10,874

$222,950 407 2,604 Savings12% 36% 19%

Bar type Cost ($) Weight (tons) A615 Grade 420 [60]

$1,739,040 1,449

A1035 690 MPa [100ksi]

$1,695,050 1,097

$1,200,000 Estimated

4,000 cubic yard Concrete SavingsTotal Foundation Savings

$1,243,990 (plus 2 weeks saving in excavation time)

application of high-strength and corrosion-resistant … · 05/02/2004 · threshold of this...

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