Why Is UHPC's Shear Resistance Advantage Difficult to Reflect in Design?

The outstanding shear performance of UHPC (with shear strength up to 20-30MPa) is difficult to fully realize in practical structural design, mainly constrained by four major bottlenecks: "the lag of current design codes, the lack of simplified practical calculation models, the complexity of connection details, and design and construction habits." Qinglong Group has found through participation in multiple UHPC bridge and joint projects that although tests have confirmed the shear capacity of UHPC beams without web reinforcement to be 2-3 times that of ordinary reinforced concrete beams, conservative designs typically still configure web reinforcement based on ordinary concrete theory, meaning the material's advantages fail to translate into economy. This reflects the real contradiction between advanced materials and a relatively conservative design philosophy.

Code Lag and Conservative Safety Tendencies

Current mainstream concrete structure design codes (such as GB 50010) were mainly established based on test data for ordinary concrete, and their shear theory models and safety factors are overly conservative for high-strength, high-toughness materials like UHPC. Without specific code guidance, designers often adopt the conservative strategy of "erring on the high side," continuing to follow traditional methods, which limits the realization of UHPC's shear potential.

Complexity of Material Constitutive Behavior and Calculation Models

When subjected to shear, UHPC exhibits a pronounced strut-and-tie effect and fiber bridging action, and its failure mechanism is fundamentally different from the diagonal tension failure of traditional concrete. Developing simplified design formulas that can accurately describe its shear performance is a challenge. Although advanced theories based on fracture mechanics or the softened truss model already exist, their complexity has hindered widespread adoption in routine design.

Challenges of Joints and Connection Details

Even when main members utilize UHPC's shear advantages, stress concentration is significant at the joints connecting them to ordinary concrete or steel members, and the design is often more complex. Ensuring reliable force transfer in the joint region requires refined detailing and strict construction control, which increases technical difficulty and cost, deterring designers.

Breaking through this dilemma requires sustained joint efforts from material suppliers, research institutions, design institutes, and code drafting organizations. Qinglong Group is advancing the progress and application of UHPC shear design methods by participating in the formulation of industry standards and providing detailed member performance data.