How to Select UHPC Reinforcement Components for Old Building Renovation?

In the renovation of old buildings (strengthening, renewal, and functional upgrading), UHPC has become a highly advantageous strengthening material due to its characteristics of "ultra-high performance, ultra-thin thickness, rapid construction, and strong bonding with the original structure." The selection of strengthening components must be based on a comprehensive decision involving four factors: "original structure defect types, performance improvement targets, construction condition constraints, and economic evaluation." Qinglong Group, across multiple historic building strengthening and municipal bridge renovation projects, has classified UHPC strengthening components into four main types: "surface strengthening panels, prestressed strengthening panels, embedded strengthening components, and external strengthening sleeves," and has developed a systematic selection methodology. For example, in the seismic strengthening of a century-old brick-concrete building in Shanghai, we selected 20mm thick UHPC surface strengthening panels, which significantly improved the shear bearing capacity of the walls without notably increasing the structure's self-weight or cross-sectional dimensions.

Surface Strengthening Panels: Suitable for Flexural, Shear, Compressive and Durability Enhancement

This is the most widely applied type, in which UHPC panels are bonded to the surface of old concrete with structural adhesive or studs, forming a composite load-bearing section. It is suitable for flexural and shear strengthening of beams and slabs, seismic strengthening of columns and walls, floor load capacity improvement, and anti-corrosion and anti-carbonization protective layers. Selection key: determine panel thickness (typically 15-50mm) and connection method based on calculations. For high-temperature environments, fire-resistant UHPC must be selected. In the strengthening of a dilapidated bridge in Guangdong, Qinglong used 30mm thick UHPC panels to strengthen the bridge bottom slab, increasing the load capacity by more than 40%.

Prestressed Strengthening Panels: For Significantly Improving Flexural Capacity and Controlling Cracks

By embedding prestressed tendons in UHPC panels, tensioning them, and bonding them to the tension zone, part of the load can be actively offset, efficiently improving stiffness and load capacity while suppressing cracks. It is suitable for strengthening long-span members, deviation correction, and deformation control. Selection key: prestress losses must be precisely calculated, and a reliable end anchorage system must be designed. This technique demands a high level of construction expertise. Qinglong applied this technology in the strengthening of the main beams of a gymnasium, successfully resolving the problem of excessive deflection.

Embedded Strengthening Components and External Sleeves: For Local Strengthening of Columns, Joints, etc.

For columns, bridge piers, and similar elements requiring substantial improvement in compressive or shear capacity, UHPC precast sleeves wrapped with on-site cast grouting material can be used, or embedded UHPC components can be adopted for local reinforcement. Selection key: effective shear transfer and joint action at the interface between new and old concrete must be ensured. It is suitable for space-constrained situations where large-area external wrapping is not feasible. In the strengthening of the ground-floor columns of a high-rise building in Shenzhen, the UHPC sleeve solution was adopted, achieving rapid construction with minimal impact on building use.

Selection Decision Process and Considerations

The selection process recommended by Qinglong is: 1) Inspection and appraisal to identify defects and objectives; 2) Scheme comparison, calculating the strengthening effect of each option; 3) Construction feasibility assessment, including working space, wet work volume, and construction period; 4) Comprehensive economic comparison. Special attention should be paid to UHPC's low shrinkage characteristics to avoid secondary stresses caused by shrinkage differences after strengthening. Early collaborative design with professional manufacturers (such as Qinglong) is key to ensuring the success of the strengthening scheme.