AASHTO LRFD Bridge Design Specifications revisions allow reinforced concrete bridges to be designed using high-strength reinforcing steels, like MMFX2 grade 100 rebar.
Photo credit: MMFX
MMFX Steel Corporation of America continues to advance infrastructure technology with the newly published 2013 Interim Revisions of the American Association of State Highway and Transportation Officials (AASHTO) Load and Resistance Factor Design (LRFD) Bridge Design Specifications. The revisions allow reinforced concrete bridges to be designed using high-strength reinforcing steels up to a 100 ksi yield, such as MMFX2 (AASHTO MP18/ASTM A1035 Grade 100 [690 MPa]).
MMFX2 is an uncoated corrosion-resistant and high-strength reinforcing steel that cuts the costs of infrastructure by decreasing steel requirements and providing lower maintenance costs over the life of the bridge. The LRFD Bridge Specification is the standard used by state departments of transportation (DOTs) to establish local bridge design codes.
“The updated specification will benefit state and federal efforts to rebuild the nation’s infrastructure with lower costs while using higher-strength reinforcing steel,” said Tom Russo, MMFX Steel Corporation of America CEO. “The expanded use of MMFX2 at its full strength will result in bridges that are not only constructed better but also offer the lowest life-cycle cost.”
High-strength rebar, such as Grade 100 MMFX2, allows DOTs to design structures to be built with 20 to 50 percent less steel that can result in up to 60 percent lower labor costs for rebar placing. By specifying high-strength steels, designers can solve costly rebar congestion problems and developers can complete structures more quickly, resulting in substantial cost savings.
“Prior to the LRFD Bridge Specification revisions, engineers were limited in their designs to only include reinforcing steel up to 75 ksi for bridge structures,” added Russo. “Now that the revisions are published, engineers and contractors have access to the new 100 ksi rebar specification and can solve difficult infrastructure design and construction issues with the best available tools and techniques.”
Made up of the chief transportation officers from every U.S. state, the District of Columbia and Puerto Rico — AASHTO is an international leader in setting technical standards for highway systems. Their approval of the 100 ksi higher-strength steel was based on the finding and recommendations of the National Cooperative Highway Research Program (NCHRP) Report 679 released in 2011.
The NCHRP report states, “…using steel with this higher capacity could provide various benefits to the concrete construction industry by reducing member cross sections and reinforcement quantities, leading to savings in material, shipping, and placement costs. Reducing reinforcement quantities also would reduce congestion problems leading to better quality of construction.”
MMFX2 high-strength reinforcing bars are also more ductile than other high-strength steels and can be fabricated using conventional fabrication equipment. MMFX2 rebar further offers superior corrosion-resistance, resulting in longer-lasting bridges without the problems and special handling requirements associated with coated rebar. The product’s combined strength and corrosion-resistance improves constructability and sustainability and is already a standard product for bridge construction in many areas of the U.S. and Canada.
MMFX2 rebar is sold in North and South America by MMFX Steel Corporation of America and in the Middle East by MMFX Steel DMCC.