How to Select UHPC Strengthening Components for Old Building Renovation?

In old building renovation and strengthening projects, UHPC has become a highly advantageous strengthening material thanks to its ultra-high strength, excellent bonding performance, and convenient construction technology. Component selection must be based on a comprehensive analysis of “defect types of the original structure, strengthening objectives, construction conditions, and cost-effectiveness.” Drawing on engineering practice, Qinglong Group has summarized the main selection options for UHPC strengthening components into several forms, such as “UHPC thin plate/layer strengthening, precast UHPC shell jacketing, and UHPC prestressed plate strengthening.”

For beam and slab members with insufficient flexural or shear bearing capacity, UHPC composite layer/thin plate strengthening is a common method. After roughening the surface of the existing concrete and planting reinforcement bars, a UHPC layer 20-50mm thick is cast or sprayed, or precast UHPC thin plates are bonded, forming an integral structure with the original one through bonding and shear keys so that they bear loads together. This method can greatly improve the flexural and shear stiffness and bearing capacity of the section, with minimal added thickness and little impact on space. The key to selection lies in determining the optimal thickness of the UHPC layer and the connection details with the original structure (such as whether short rebar studs are used to enhance shear resistance).

For strengthening columns under compression or bridge piers, precast UHPC shell jacketing delivers remarkable results. After treating the column surface, prefabricated segmented UHPC shells are installed (usually two semicircular halves or multiple pieces), and high-strength grout or UHPC is cast at the joints and between the shell and the original structure to form a solid jacket. This not only provides additional load-bearing area, but its circumferential confinement effect can also greatly increase the ultimate compressive strain and ductility of the core concrete, with a marked improvement in seismic performance. Precast shells can be produced with high quality in the factory and installed quickly on site, making them suitable for renovation projects requiring rapid construction.

For long-span members or cases requiring a substantial increase in bearing capacity while controlling deformation, externally bonded prestressed UHPC plate strengthening can be selected. Precast UHPC plates with prestressing tendons are anchored in the tension zone of the structure using the post-tensioning method, actively applying prestress to offset part of the load. UHPC plates themselves have high strength and good durability, effectively protecting the prestressing tendons. Selection requires precise calculation of the required prestress magnitude and application position. Regardless of the form adopted, the substrate of the original structure must be thoroughly treated, and reliable bonding between the UHPC and the old concrete must be ensured—this is the prerequisite for successful strengthening.