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<p>Ultra-high-performance concrete (UHPC) provides excellent crack resistance due to its dense microstructure and steel fiber reinforcement, but its high cost limits full-section application. An economical alternative is to cast UHPC only in the tensile zone of beams, forming UHPC-normal concrete (NC) composite sections. This study experimentally investigates the flexural behavior of seven reinforced UHPC-NC composite beams, focusing on the effects of UHPC casting height (0&#xa0;mm, 100&#xa0;mm, 200&#xa0;mm, 300&#xa0;mm) and longitudinal reinforcement ratio (0.63%–1.44%) on crack development. Crack patterns, cracking load, crack spacing, crack width, load–deflection response, and reinforcement strain were systematically analyzed. Results show that composite beams exhibit markedly better crack resistance than ordinary NC beams, with higher cracking loads, finer and more evenly distributed cracks, and clear formation of dominant main cracks at failure. The UHPC–NC interface remained fully composite throughout loading, with no delamination or slip observed. Reinforcement ratio significantly influences crack behavior, whereas UHPC casting height plays a limited role beyond 100&#xa0;mm. Based on the test results and theoretical analysis, a crack width calculation method for composite beams is proposed, modifying the GB50010-2015 code framework to account for UHPC tension-stiffening and composite section characteristics. The proposed model shows good agreement with experimental measurements within the serviceability range (crack width ≤ 0.4&#xa0;mm).</p>

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Experimental and theoretical investigation on crack resistance of UHPC- normal concrete composite beams

  • 期刊论文

  • 发表日期：

    2026年6月1日

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  • Xiang Liu,
  • Dan-Ling Lin,
  • Wei Zhang,
  • Yu-Lu Chen

摘要

Ultra-high-performance concrete (UHPC) provides excellent crack resistance due to its dense microstructure and steel fiber reinforcement, but its high cost limits full-section application. An economical alternative is to cast UHPC only in the tensile zone of beams, forming UHPC-normal concrete (NC) composite sections. This study experimentally investigates the flexural behavior of seven reinforced UHPC-NC composite beams, focusing on the effects of UHPC casting height (0 mm, 100 mm, 200 mm, 300 mm) and longitudinal reinforcement ratio (0.63%–1.44%) on crack development. Crack patterns, cracking load, crack spacing, crack width, load–deflection response, and reinforcement strain were systematically analyzed. Results show that composite beams exhibit markedly better crack resistance than ordinary NC beams, with higher cracking loads, finer and more evenly distributed cracks, and clear formation of dominant main cracks at failure. The UHPC–NC interface remained fully composite throughout loading, with no delamination or slip observed. Reinforcement ratio significantly influences crack behavior, whereas UHPC casting height plays a limited role beyond 100 mm. Based on the test results and theoretical analysis, a crack width calculation method for composite beams is proposed, modifying the GB50010-2015 code framework to account for UHPC tension-stiffening and composite section characteristics. The proposed model shows good agreement with experimental measurements within the serviceability range (crack width ≤ 0.4 mm).