High Strength Rods in Modern Construction
Limited Space and Population Density in Bangladesh
Bangladesh is a country of 15,980,140,000 square feet, where approximately 169,608,636 people reside, meaning each person has just over 9,421 square feet allocated to them. Within this limited space, they must manage housing, food production, sports, and all other necessities of life.
The Necessity of High-Rise Infrastructure for Economic Growth
Among the 195 countries rising through continuous economic development, Bangladesh ranks as the 32nd strongest in terms of economy, but 8th in terms of population density. To sustain both economic growth and social standing, our beloved motherland has no alternative but to build high-rise infrastructure.
The Role of Rebar in Infrastructure Construction
In infrastructure construction, rebar is one of the most crucial elements. Although Bangladesh ranks 29th globally in steel production, it has an annual rebar production capacity of nearly 9 million metric tons, which surpasses the demand of Poland, ranked 22nd.
Record Rebar Demand and Domestic Production Capacity
In the 2022-2023 fiscal year, Bangladesh’s steel producers met a record demand of over 6.3 million tons of rebar, the highest to date. According to my available statistics, this demand will likely exceed 6.662 million tons in the 2023-2024 fiscal year, Inshallah.
Contributions of Leading Rebar Companies in Bangladesh
This remarkable milestone in rebar supply for construction, solely based on domestic companies, owes much to eight major rebar companies in the country. Notably, thanks are due to the top four—BSRM, AKS, GPH Steel, and KSRM.
Progression in Rebar Strength Grades
Due to their relentless efforts, research, and dedication, Bangladesh has progressed from the era of 40-grade rebar to 60-grade, followed by 72.5-grade initially, then its advanced version, ductility class D’s B500DWR, the strong 80-grade, and most recently, South Asia’s strongest 87-grade B600C-R and ductility class D’s B600D-R rebars have entered Bangladesh.
Market Share Dominance by Leading Companies
It is noteworthy that, due to this continuous success, only these four companies had a market share of 55.35% in the last fiscal year.
Code Acceptance Challenges with High-Strength Rebar
Although Bangladesh National Building Code (BNBC) and associated agencies like the Public Works Department and House Building Research Institute warmly welcome 60-grade rebar, they hesitated with 72.5-grade and only included 80-grade with reluctance in the latest BNBC-2020 version.
The Long Wait for Higher Grade Recognition
Notably, it took almost a decade for 72.5 to get official recognition, and years for 550 MPa to be adopted. Interestingly, it took BNBC itself nearly 27 years to revise and update!
Confusion in the BNBC and BSTI Manufacturing Codes
Even though 80-grade rebar has been included in the BNBC code, BSTI’s manufacturing code does not recognize it, because the Bangladesh Standards and Testing Institution follows the BDS 6935-2 code, which does not include 550 MPa.
The Role of International Standards in Testing Rebar
This has put manufacturers in a bind, forcing them to market under different names. However, this 80ksi strength is well-established in the ASTM code, which is used for most mechanical testing of rebar in Bangladesh. It’s also referenced in the ACI code, the basis for BNBC. It’s a situation akin to “mix-and-match” rules.
How BNBC Relies on International Design Codes
As I mentioned earlier, the BNBC code is merely a shadow of the ACI code. This isn’t a flaw, but it becomes an issue when newly developed, research-backed products face resistance or non-acceptance.
BNBC and the Lag Behind ACI Code Updates
The BNBC-2020 code is based on ACI 2008. However, ACI has since independently updated itself three times in 2011, 2014, and 2019. Meanwhile, the shadow code remains stagnant, lacking any self-reflection.
Higher Yield Strength Allowances in Other Codes
The American Concrete Institute’s Building Code 318-19 states that reinforcement for flexural and axial members can be used up to 690 MPa. In Europe, the Eurocode 8 for earthquake-resistant structure design supports the use of 600 MPa reinforcement in flexural and axial members.
International Codes in Earthquake-Prone Regions
The American Association of State Highway and Transportation Officials (AASHTO), known for bridge and highway design codes, allows 690 MPa for flexural members and 550 MPa for axial members. The Korean Concrete Institute, in 2012, supported 600 MPa reinforcement for building design in flexural and axial members.
ACI Code 318-2014 and Seismic System Recommendations
Returning to ACI code 318-2014, it clearly states in Table 20.2.2.4A that in special seismic systems and other places with flexure, axial force, shrinkage, and temperature, reinforcement of 80,000 psi and spiral seismic systems up to grade 100 are encouraged.
Manufacturing Codes from Various Standards Bodies
The Bangladesh Standards and Testing Institution, which follows the code BDS:ISO-6935-2:2019(E), recognizes rebar with a maximum strength of 700 MPa or grade 100. The American Society for Testing and Materials (ASTM) codes A615/A615M-20 and A706/A706M-22 recognize a maximum grade of 100.
Maximum Strength Standards in Seismic Zones
Japan, one of the world’s most earthquake-prone countries, has JIS G 3112:2020, which allows rebar with a maximum strength of 785 MPa or grade 113 and ductility of 1.17. Yes, in Bangladesh’s very severe and severe seismic zones, we need rebar that reaches at least 60,000 psi.
High-Strength Rebar Standards in Bangladesh and Other Countries
China, which most Bangladeshi mega constructions follow, gives its highest rebar recognition to HRB600 in its GB/T 1499.2-2018 code. Australia and New Zealand’s AS/NZS 4671:2019 code allows a maximum rebar strength of 750 MPa.
BNBC-2020 Code and Yield Strength Specifications
Returning to our BNBC code-2020, Part 6, Chapter 5 on concrete materials, Section 5.3.2.2 states: “Deformed reinforcing bars with a specified yield strength fy exceeding 420 N/mm² shall be permitted, provided fy is the stress corresponding to a strain of 0.35 percent.”
The Preface of BNBC’s 1993/2006 Edition on Code Updates
The preface of BNBC’s 1993/2006 edition states: “Technology is a dynamic field with continuous advancements and innovations, so is a building code. The code will require continuous updates and periodic revisions to keep pace with developing technology and the changing needs of the times.”
The Need for Continuous Monitoring and Code Revisions
After the National Building Code has been used and tested in the field, many issues will have the opportunity to be judged in practice, and the need for revision of specific requirements will be felt. Updates and revisions of the code will have to become a routine affair eventually.
Observations on Code Enforcement and Structural Integrity
Since the publication of the BNBC 1993/2006 Gazette in 2006, from 2008 until February 11, 2021, despite the use of 500 MPa or 72.5 grade rods in millions of buildings in Bangladesh, the authorities have taken no action against a single structure.
Reflections on the BNBC 2020 Preface and New Material Standards
The preface of BNBC 2020 states, ‘Since its publication in 1993, the BNBC has been referred to and consulted by professionals and designers in the field of building design and construction. After the endowment of legal status, the importance of the BNBC 2006 has further enhanced.’
“This article was published on September 13, 2023, in the online version of the Daily Kaler Kantho under the title ‘আধুনিক নির্মাণে উচ্চশক্তির রড ব্যাবহারে কোড কি সত্যিই অন্তরায় ?”