Talking about the selection of stone curtain wall materials? (II)

3、 Stone dry pendant

Stone dry pendants, hang pieces of stone weighing dozens of kilograms high on the wall, but their quality worries people. At present, due to price factors, the market of dry pendant products is in chaos. The products sold in the market and used in the project include national standard stainless steel, 7075 aluminum silicon magnesium alloy, galvanized sheet, and stainless steel. The quality of the above products is mixed, which can also be reflected in their tensile strength. National standard stainless steel 530Mpa~620Mpa, national standard aluminum alloy 540Mpa~560Mpa, and stainless steel 160Mpa~180Mpa. Obviously, the tensile strength of stainless steel iron is less than 1/3 of that of stainless steel, so it is inappropriate to use it as a dry pendant, which is really too dangerous.

Therefore, the material selection of the dry hanging parts must be careful. Each performance index of the dry hanging parts must meet the design and specification requirements, and the test work should be done well during the construction. At the same time, the casting parts should be selected as far as possible to avoid the impact of the welding quality on safety.

4、 Embedded parts

The structural system of the stone curtain wall is finally connected to the main structure through pre (post) embedded parts, and the quality of pre (post) embedded parts is particularly important. In order to ensure the quality of embedded (post) parts, the following points shall be paid attention to in the construction of the stone curtain wall:

1. The embedded (post) parts must be strictly calculated by the designer according to the stress conditions to determine the anchor plate specification, anchor bar diameter, length, and weld thickness, among which the minimum thickness of the anchor plate, the spacing of anchor bars, and the distance from the anchor bar to the edge of the anchor plate must also meet the structural requirements of the specification.

2. The embedded (post) parts shall not be set on the light partition wall. The reliable connection point between the curtain wall embedded parts and the main structure of the building is mainly on the reinforced concrete (or steel structure) column beam slab of the main structure. For the floors with large story height, in order to solve the stress problem of the vertical pole of the curtain wall, in addition to increasing the sectional size of the vertical pole or using high-strength materials, some projects add a bearing point on the wall between the upper and lower floor beams. This bearing point should be on the reinforced concrete (or steel structure) structural beam (column) to be reliable and effective. In fact, the Code for Curtain Walls has stipulated that “light-infilled walls should not be used as the supporting structure of curtain walls”.

3. Attention shall be paid to the welding quality of embedded parts. The common form of embedded parts is composed of anchor plates welded with anchor bars. The anchor plates are usually made of Q235 high-quality carbon steel plates, and the anchor bars should also be Grade I steel bars with good welding performance. It is better to adopt groove plug welding for reliable quality. The welding quality of the anchor plate and anchor bar is the key to the quality of embedded parts. To ensure weld quality, electric welding operators must be trained and certified. However, due to the different responsibilities of electric welders, the quality of embedded iron weld must also be strictly inspected and accepted.

4. It is necessary for the pull-out test of post-embedded parts. For curtain wall projects, post-embedded parts are often used to solve the connection problem between curtain wall components and building structures due to non-embedment, repair of embedded failure, or modification of old buildings. During the inspection, whether the connection is reliable or not, the field pull-out test shall be used to determine the bearing capacity. At present, the quality hidden danger of the post anchoring construction is one of the construction operation reasons, for example, the reinforcement is often encountered in the drilling, resulting in insufficient depth or deflection of the reinforcement, and the hole dust and slag are not cleaned up; Second, the anchoring matrix is not solid and reliable. If the strength of the concrete substrate is not enough and the margin is not enough, the concrete substrate will crack and cause the anchoring failure. Therefore, the on-site construction management personnel shall carefully carry out technical disclosure, strengthen quality inspection, and conduct random sampling for the on-site pull-out test, and shall not be false or perfunctory.

5. The quality of chemical anchor bolts varies from good to bad. At present, chemical anchor bolt is the most commonly used post anchoring in the curtain wall industry. However, chemical anchor bolts have many brands and different qualities. The anchoring glue of the chemical anchor bolt plays the role of bonding the concrete substrate and the anchor bar. At present, chemical binders with various chemical compositions appear on the market, and the more common types are modified epoxy resin, vinyl acrylic resin, and unsaturated resin.

To sum up, in order to ensure the safety of dry-hanging stone curtain walls, we must start with the most basic material selection. We should not only consider immediate interests but use low-cost materials, which will bring hidden dangers to safety. At the same time, it is necessary to strengthen the construction process management, do a good job in the disclosure and training of the installation workers, enhance their quality safety awareness, and avoid the potential safety hazards to the stone curtain wall due to the non-standard operation or poor quality safety awareness of the workers. In a word, we should make stone curtain walls become beautiful scenery lines of urban buildings, rather than time bombs.

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