What Are the Reinforcement Design Principles for UHPC Load-Bearing Members?

Reinforcement design for UHPC load-bearing members must follow four core principles: "strength matching, crack control, durability assurance, and rational detailing." It differs significantly from traditional concrete reinforcement concepts, placing greater emphasis on leveraging UHPC's inherent high strength and fiber toughening effects. Based on 28 years of structural design and project practice (such as the UHPC beams for the Shenzhen Yirui Biotechnology Building and the UHPC roof trusses for the Hainan Convention and Exhibition Center), Qinglong Group has summarized the keys to reinforcement: the ordinary steel reinforcement ratio should be controlled at 1-2%, mainly serving detailing and crack distribution functions; fibers (with a steel fiber volume content of 2-3%) take on the primary tensile resistance and toughening roles; prestressing technology can further exploit the material's strength (compressive strength ≥150MPa). For the long-span UHPC trusses of the Wuhan Han Show Theatre, through finite element analysis, we adopted a combined reinforcement scheme of 1.5% non-prestressed steel + 2.5% steel fibers + partial prestressing tendons (tensioning control stress 0.6fptk), keeping crack width within 0.05mm while the members met load-bearing capacity requirements. Reinforcement design is the safety core of UHPC load-bearing applications.

Synergistic Working Mechanism of Fibers and Steel Reinforcement

In UHPC, fibers form a micro-reinforcement network that suppresses microcrack propagation, giving members strain-hardening behavior under tension (cracking without shattering). Steel reinforcement mainly provides backup load-bearing capacity after macro-cracks appear. In design, the fiber volume content should be no less than 2%, and the steel reinforcement ratio no less than 0.8%, to ensure safety redundancy. Qinglong Group determined the optimal fiber aspect ratio (60-80) through splitting tensile tests.

Crack Control Is the Primary Goal of Reinforcement

UHPC itself has high tensile strength (8-12MPa), so the purpose of reinforcement is more about controlling crack width (≤0.1mm) than preventing cracking. We use dispersed small-diameter bars (8-12mm in diameter) at close spacing (≤100mm) to effectively constrain cracks. In the Nanning Wuxiang China Resources MixC project, the measured maximum crack width of the UHPC beams was 0.06mm.

Durability Design Considers Reinforcement Cover

Although UHPC has excellent impermeability, cover thickness still needs to be ≥20mm (indoors) or ≥30mm (outdoors in severe environments) to prevent potential carbonation or chloride ion attack. Qinglong Group uses epoxy-coated rebar or stainless steel rebar for critical members as double insurance.

Detailing Ensures Smooth Force Flow

Anchorage lengths can be halved compared to ordinary concrete (due to high bond strength), but must be ≥20 times the bar diameter. Joint zones require densified fibers or additional shear reinforcement. We verify joint reliability through full-scale testing to ensure design safety.

UHPC reinforcement is a fusion of materials science and structural engineering. With extensive experience, Qinglong Group customizes the optimal reinforcement scheme for every project.