Reserved Expansion Joint Width for UHPC Exterior Wall Lines and Analysis of Related Design Points

In the field of modern architectural decoration, UHPC (Ultra-High Performance Concrete) has become the ideal choice for high-end curtain wall systems thanks to its outstanding mechanical properties and artistic expressiveness. However, as an important component of building facades, the scientific design of expansion joints in exterior wall lines directly affects the safety and durability of a building. As an industry leader with 28 years of full-chain experience in UHPC/GRC/GRG/GRP materials, Qinglong Group will systematically analyze the reserved width standards and key design points for UHPC exterior wall line expansion joints from an engineering practice perspective, providing professional solutions for designers and owners.

I. Scientific Basis for the Reserved Width of UHPC Exterior Wall Line Expansion Joints

Although UHPC features low shrinkage, it still undergoes slight deformation under temperature changes, humidity fluctuations, and structural loads. According to the industry standard “General Technical Conditions for Non-Load-Bearing Components of Ultra-High Performance Concrete (UHPC)” (Plan No. 2024-0232T-JC) and the engineering practice data from over a thousand projects by Qinglong Group, the reserved width of expansion joints must be determined by comprehensively considering the following factors:

1. Temperature deformation control: In most climate zones of China, when the continuous length of a line exceeds 6 meters, the expansion joint width should be set at 10-15mm; in regions with large temperature differences (such as severely cold northern areas or scorching southern regions), it is recommended to increase the width to 15-20mm to cope with extreme temperature differences from -30℃ to 70℃.

2. Material property adaptation: The linear expansion coefficient of UHPC is approximately 12×10⁻⁶/℃. Combined with its high elastic modulus, the expansion joint spacing is typically controlled at 6-8 meters. Through BIM simulation, Qinglong Group found that adopting gradient reinforcement design can extend the expansion joint spacing to 10 meters, provided it is paired with elastic sealing materials.

3. Installation process influence: For wet installation, considering mortar shrinkage, the joint width needs to be increased by 2-3mm compared with dry installation; for irregularly curved lines, compensation joints should be added where the curvature changes most, with a width of no less than 8mm.

II. Four Core Points in UHPC Exterior Wall Line Expansion Joint Design

1. Structural node optimization: Adopt a composite design of “flexible connection + rigid restraint”. The joint is filled with EPDM rubber strips (Shore hardness 60±5), and the exterior is sealed with silicone weather-resistant sealant (movement capability ≥±25%). Qinglong Group’s patented “stepped joint mouth design” effectively avoids stress concentration; after being applied in a commercial complex project in Guangzhou, it has remained free of cracking and leakage for 5 years.

2. Drainage system integration: Expansion joints must be designed in coordination with the curtain wall drainage system, with an inclined drainage groove at the joint bottom (slope ≥3%), connected to the building’s drainage riser through concealed drainage pipes. In the Nanning ASEAN Culture and Art Center project, the Qinglong team innovatively adopted a “U-shaped water interception structure”, improving drainage efficiency by 40%.

3. Balance between aesthetics and function: Visual concealment is achieved through joint profile decoration (such as UHPC homogeneous cover plates and metal edging), with joint width errors controlled within ±1mm. For UHPC lines with stone-like textures, the joint division can be designed to align with the texture direction. For example, a landmark project in Nanjing integrated the expansion joints into the lychee-face texture, achieving the effect of “joints that are visible yet invisible”.

4. Full life-cycle consideration: Reserve maintenance access and adopt replaceable sealing systems. Qinglong Group’s maintenance plan clearly states that expansion joint sealant should be replaced every 8-10 years, with non-destructive replacement achieved through specialized tools, reducing later maintenance costs.

III. Industry Practice and Qinglong’s Technical Advantages

As an enterprise that participated in formulating the “Technical Standard for Building Applications of Glass Fiber Reinforced Cement (GRC)” (JGJ/T423-2018), Qinglong Group integrates the collaborative application experience of GRC, GRG, and other materials into its UHPC line design. For example, in a super high-rise project in Shenzhen, composite UHPC and GRG lines were used, with the expansion joint spacing breaking traditional limits to reach 12 meters; deformation was controlled through built-in carbon fiber mesh, and third-party testing showed its crack resistance was 30% better than the national standard.

In the current market, some enterprises have a “one-size-fits-all” approach to expansion joint design, ignoring regional climate differences and building functional requirements. Qinglong Group recommends that designers refer to the “Standard of Climatic Regionalization for Buildings” applicable to the project location and conduct parametric simulation together with material suppliers (such as using ABAQUS finite element analysis software) to develop customized expansion joint solutions. For overseas projects, seismic fortification intensity must also be considered. For example, in a hotel project in Malaysia, the Qinglong team raised the seismic grade of the expansion joints to C1 level based on local seismic parameters, ensuring structural safety.

The expansion joint design of UHPC exterior wall lines is an organic unity of materials science, structural mechanics, and architectural aesthetics. Supported by 28 years of full-chain experience, Qinglong Group has achieved a full-dimensional solution ranging from millimeter-level joint width control to century-long durability through in-depth design optimization, precision manufacturing assurance, and professional construction control. In the future, with the wide application of UHPC materials in green buildings, scientific expansion joint design will become a key link in improving building quality, helping to realize the industry mission of “creating aesthetically beautiful buildings”.