Analysis of Challenges and Countermeasures for Glass Curtain Walls

Glass curtain walls represent an aesthetically pleasing and innovative method of architectural facade decoration, serving as a defining characteristic of the era of modernist high-rise buildings; however, if poorly constructed, glass curtain walls can give rise to a multitude of problems.

 

 

1. The quality of the materials used does not meet the requirements.
Glass curtain walls are exposed to the air and are affected by sunlight and corrosive media. Materials that comply with relevant national regulations must be used to ensure project quality. However, in actual construction, many curtain wall aluminum profile columns and beam walls do not meet the requirements of the regulations. Some aluminum profiles are made of ordinary grade materials and the thickness of the anodized film is less than 15 μm, which does not meet the anti-corrosion requirements; some engineering designs require tempered glass, but semi-tempered or ordinary coated glass is selected. The strength of the glass is insufficient and there are safety hazards; the stainless steel sliding braces selected for the opening fans of some projects have insufficient stiffness and can easily cause serious deformation.

 

2. The production quality of components does not meet the requirements
The production quality of components does not meet the requirements, which is an important reason for the unqualified construction quality of the glass curtain wall. For example, the cutting accuracy of some aluminum alloy profiles is poor, and the assembly gap between adjacent components is too large or too small; after cutting some curtain wall glass, due to the lack of chamfering, it is easy to cause stress concentration at the corners and cause the glass to break; some hidden frame glass curtain walls use the method of gluing on the construction site, but there are no purification measures, which can neither guarantee the relative humidity and temperature requirements nor avoid contamination at the bonding point between the structural glue and the glass, making it difficult to ensure production quality.

 

3. Problems with quality assurance data
Most glass curtain wall projects have problems such as incomplete and non-standard information, and many missing items. For example, the imported materials used have no commodity inspection reports, and some structural adhesive materials have no validity period certificates and compatibility test reports; most projects lack aluminum profile quality certificates and high-precision indicators and oxide film thickness inspection certificates, and lack factory certificates for building sealing materials and fireproof materials; some concealed project acceptance forms lack detailed records of fireproof nodes, lightning protection nodes, and movable joint nodes.

 

 

Based on the various construction-related problems outlined above, the following section focuses primarily on proposing prevention and control measures for commonly encountered quality issues, offered here for reference.

 

(I) Omission and Misalignment of Curtain Wall Embedded Parts

1. Analysis of Causes

1) During the construction of the main civil structure, the contractor responsible for glass installation may not yet have been selected; consequently, the embedding of parts may be impossible due to the absence of design drawings specifically for the curtain wall embedded components.

2) The original architectural design may not have incorporated a plan for glass elements. If a glass curtain wall is subsequently adopted for exterior decoration, the structural framework may lack the necessary embedded parts.

3) During the construction of the main building structure, adequate fixing measures may not have been implemented for the embedded parts, resulting in their displacement during the pouring and vibrating of concrete.

2. Remedial Methods

1) For main structures lacking embedded parts, the specifications and methods for retrofitting these parts must be determined prior to the installation of the glass curtain wall. This determination requires joint consultation and agreement among the design, civil construction, and installation contractors. It is impermissible to rely solely on expansion bolts for connecting to the main structure; instead, supplementary anchorage components should be installed at intervals of every 3 to 4 stories, with expansion bolts serving only as localized, supplementary connection measures. Any expansion bolts utilized must be positioned to primarily bear shear loads.

2) In cases where the misalignment of embedded parts occurs, a thorough inspection of the extent of the deviation must be conducted first, followed by the snapping of reference lines (chalk lines) to facilitate correction. If the misalignment exceeds 20 mm, splicing measures must be implemented. If an embedded part is recessed (set back) by more than 10 mm, a steel plate must be welded onto it to bring it up to the specified elevation before installation can proceed.

3. Preventive Measures

1) Before the embedding of parts, a specialized technical briefing should be conducted to ensure the correctness of the specifications, models, and positioning of the embedded components. Measures must be taken to prevent displacement during concrete vibration, thereby guaranteeing the quality of the embedded parts' installation.

2) For any project involving a glass curtain wall, the installation contractor must be designated during the civil construction phase, and the design drawings specifying the locations of embedded parts must be provided. A designated individual must be assigned to oversee the embedding and installation of these parts, and acceptance inspections for concealed works must be conducted promptly as they occur. Concrete pouring must be executed with meticulous care-ensuring thorough compaction via vibration-while strictly avoiding contact with the embedded parts, thereby guaranteeing the precise positioning of these components.

 

(II) Substandard Anchoring of Connectors to Embedded Parts

1. Analysis of Causes

1) During the connection process between connectors and embedded parts, detailed shop drawings were not strictly followed; in some instances, no detailed shop drawings were produced at all, and construction was carried out solely based on experience.

2) The quality of welding at the anchorage points between connectors and embedded parts is poor, failing to meet both design specifications and relevant code requirements.

2. Remedial Measures

1) Particular emphasis must be placed on the anchoring of connectors to embedded parts, as this is critical to ensuring the overall quality of the glass curtain wall. If inspections reveal that a connection point fails to meet design requirements, remedial measures-such as reinforcement or re-welding-should be implemented as appropriate; in necessary cases, the work must be completely redone.

2) If weld seams exhibit deficiencies-such as insufficient height or width, slag inclusions, or burn-throughs-they must be addressed with the utmost care. Experienced, senior-level welders should be assigned to handle the necessary re-welding and reinforcement work.

3. Preventive Measures

1) During the design phase of a glass curtain wall, detailed node drawings must be produced for every connection point to facilitate construction by the workforce. These drawings must clearly specify all technical requirements, including material specifications, model numbers, and weld parameters.

2) When performing the anchoring or welding of connectors to embedded parts, installation must strictly adhere to code requirements. The height, length, and width of all weld seams must be determined based on engineering design calculations.

3) All welders involved in the project must undergo qualification testing and possess valid certification before being permitted to perform work on-site. Quality inspection of welded components shall comply with the following requirements:
① In the heat-affected zone of the weld, the surface shall be free from defects such as cracks, porosity, and slag inclusions;
② The depth of undercut at the weld shall not exceed 0.5 mm, and the total length of undercuts on both sides of the weld shall not exceed 10% of the weld length;
③ The geometric dimensions of the weld shall conform to the design requirements.

 

 

1. Cause analysis

1) If there are no gaskets between the connectors and the columns, the components are prone to electrochemical corrosion, which will have a certain impact on the service life of the entire curtain wall.
The main reasons for missing gaskets are:
First, there is no clear annotation in the node design drawing;
Second, construction workers leaked water during construction;
Third, the construction management personnel were not serious and did not make corrections in time.

 

2. Treatment method

1) If it is found that there is no gasket between the connector and the column, a 1mm thick gasket of insulating and heat-resistant hard organic material should be immediately added to prevent electrochemical corrosion of different metals.

2) If the elastic rubber gaskets of the connectors at both ends of the columns and beams are not installed, they must be replaced and installed securely.

3. Preventive measures

1) To prevent electrochemical corrosion caused by contact between different metal materials, the specification stipulates that gaskets should be installed at the contact parts. Generally, a 1mm-thick insulating, heat-resistant, hard organic material gasket should be used, and no leakage or under-discharge should occur during installation.

2) Between the ends of the curtain wall columns and beams, to adapt to and eliminate the requirements of lateral temperature deformation and noise, the specification stipulates that an elastic rubber gasket or a gasket made of nylon sheet with one side and no glue should be installed at the connection. The elastic rubber gasket should have a compressibility of 20% to 35% and be installed at the predetermined position of the column. It should be installed firmly and its joints should be tight.

 

 

1. Cause analysis

1) When designing glass curtain walls, water leakage problems can easily occur due to poor design considerations and improper or careless handling of details.

2) The quality of the rubber strips used is substandard, or the specifications do not meet the design requirements, resulting in uneven thickness at the glue joints, thus forming water penetration channels.

3) The construction of weather-resistant silicone sealant is not standardized, and the installation of opening windows does not meet the design requirements.

 

2. Treatment method

1) First, we must carefully identify the cause of water leakage, and then take corresponding treatment methods. If water leakage occurs due to cracks in the sealant shell, the sealant in the shell and the cracks must be removed, scrubbed clean, and then sealed tightly with a qualified weather-resistant silicone sealant. After testing, it is considered qualified if there is no more leakage.

2) A waterproof strip should be added to the upper opening of the window.

 

3. Preventive measures

1) When designing a glass curtain wall, a drainage channel should be designed so that water can be collected and discharged through pipes, so that a large amount of water can be drained away from the curtain wall promptly and reduce the chance of water seeping into the curtain wall.

2) Before filling in the sealant, clean the contact area and wipe it with solvent before filling in the sealant. The thickness should be greater than 3.5mm and the width should be greater than 2 times the thickness.

3) The rubber strips should be selected according to the materials and specifications specified in the design, and the inlay must be smooth and tight; the glass installed in the open window should be on the same level as the curtain wall, and no indentation should be allowed.

 

 

1. Cause analysis

1) When designing some glass curtain walls, fireproof partitions were not considered, resulting in omissions in the design and making the glass curtain walls unable to be fireproof.

2) Some floor contact beams are not provided with curtain wall beams, the position of the fire protection layer is incorrect, and there is no design drawing of the node.

3) The quality of the fireproof materials used does not meet the requirements of the specification.

 

2. Treatment method

1) After inspection, if the glass curtain wall does not have a fireproof barrier in the original design, the design unit and the construction unit should study and make a supplementary fireproof plan.

2) Some glass curtain wall fireproof partitions are closed with wooden materials, which must be replaced with fireproof materials and anchored firmly. When it is impossible to replace wooden materials, fire-retardant paint should be painted on the surface of the wooden materials.

 

3. Preventive measures

1) When designing the glass curtain wall, the design of the fireproof barrier must not be omitted. When dividing the facade in the preliminary design, the fire safety design should be considered simultaneously, and a large node diagram should be drawn. The specifications of the materials and anchoring requirements should be noted on the diagram.
2) When designing the glass curtain wall, the layout of the beams should be coordinated with the floor height. Generally, each floor is an independent fire protection zone, and beams and fire protection partitions must be set on the floor.

3) The gaps between the glass curtain wall, floors and partitions should be filled with fire-resistant or non-combustible materials. However, the partition materials used for the fire-proof layer should not be in direct contact with the curtain wall glass. The gaps should be filled with fire-resistant insulation materials, and the surface seams should be tightly filled with sealants.

 

 

1. Cause analysis

1) When designing the glass curtain wall, the lightning protection system was not considered at all, so this part was missed, which seriously affected the safety of the curtain wall.

2) Some construction workers are not familiar with the installation regulations of lightning protection systems and are unable to construct lightning protection systems, resulting in non-installation or unqualified installation.

 

2. Treatment method

1) For projects without lightning protection facilities on the glass wall, lightning rods must be installed and connected to the lightning protection system of the main structure. Generally, one is installed every three floors so that the lightning protection system forms the curtain wall itself.

2) Carefully check the installed lightning protection system, including its material specifications, connectors, lightning protection down conductors, grounding devices, etc. The grounding resistance shall not be greater than 10Ω.

 

3. Preventive measures

1) When designing the glass curtain wall, there must be a design plan for the lightning protection system, and there must be construction drawings of the lightning protection system during construction so that workers can construct according to the drawings.

2) The glass curtain wall should be equipped with flat iron or round steel lightning protection rings every three floors. The lightning protection rings are connected to the lightning protection system of the main structure, so that the lightning protection system of the glass curtain wall forms its own system.

3) The materials used for lightning protection rings, lightning protection wires, down conductors, grounding devices, etc. must meet the design requirements and lightning protection specifications.