The reasons for this are:

(1) The embedded parts were already buried during civil construction, but due to changes or alterations in the curtain wall design grid, they cannot be used.

(2) The embedded parts are not securely tied, causing displacement and deviation during concrete pouring and compaction during construction.

Article 10.2.3 of the Technical Code for Glass Curtain Wall Engineering JGJ102-2003: The embedded parts connecting the glass curtain wall and the main structure should be buried according to the design requirements during the construction of the main structure, and the position deviation of the embedded parts should not exceed 20mm.

3. Construction quality issues with rear anchor components

1) Install anchor components on lightweight walls after installation

Some engineering projects have large floor spans, and the deflection or strength calculations of the columns cannot be passed. Therefore, some designers add a support point between the upper and lower beams. If this support point is effective on reinforced concrete (or steel structure) constructed beams (columns). Some frame structure buildings usually use lightweight infill walls for their masonry. If the added support points are placed on the lightweight infill walls, even if steel plates and through wall bolts are used, they cannot provide effective support. So the standard stipulates that curtain walls should not be connected to masonry, let alone to lightweight walls.

2) The anchoring substrate is not solid and reliable. If the strength of the concrete substrate is insufficient and the edge distance is not enough, it will cause the concrete substrate to crack and lead to anchoring failure.

3) The rear anchor is misaligned. Drilling often results in misalignment and deviation when encountering steel bars, as well as incomplete removal of powder and debris from holes, leading to loosening of anchor components during use.

According to regulations, individual pull-out tests and node (group) pull-out tests must be conducted on site for post added bolts. The load applied in the test should reach 1.5 times the design load without significant slippage. If necessary, ultimate pull-out tests should be conducted at the testing unit.

The results of the experiment should be verified with the design calculations, and it is required that the design value of the anchor bolt bearing capacity should not exceed 50% of its ultimate bearing capacity.

4) The burial depth of the rear embedded parts is insufficient. The rear embedded parts should ensure their minimum effective burial depth and should be the depth after removing the paint layer.

As shown in the picture, the depth of the anchor component is insufficient if the thickness of the paint layer (about 20mm) is removed.

Construction of pre embedded parts for building curtain walls and related issues

4) The quality of chemical anchor bolts is not high

Chemical bolts are commonly used for embedded parts in the curtain wall industry. In the 1990s, chemical bolt products were introduced from abroad and applied in construction projects. In recent years, many domestic manufacturers have followed suit and produced in large quantities, with market prices ranging from tens of yuan to two or three yuan. It can be said that there are many brands, mixed fish and pearls, and varying quality. The anchoring adhesive of chemical bolts plays a role in bonding the concrete substrate and anchor bars. At present, there are various chemical anchoring agents with different chemical compositions on the market, among which modified epoxy resin, ethylene acrylic resin, and unsaturated resin are commonly used. The physical and chemical properties of anchoring adhesive directly affect the anchoring effect. Except for a few well-known imported brands that have testing indicators such as durability, temperature resistance, freeze-thaw resistance of anchoring adhesive in their promotional materials, most manufacturers only have vague statements such as "acid and alkali resistance, heat and fire resistance, low temperature sensitivity" in their product introductions. Although the on-site pulling force test meets the design requirements, due to the fact that the durability of the anchoring adhesive can only be predicted through laboratory testing, and the impact of high welding temperatures on the anchoring agent is unclear, it is no wonder that industry insiders have questioned the durability of the anchoring adhesive and expressed concerns about the widespread use of certain low-cost products.

Stainless steel bolts for rear embedded parts should provide a certificate of conformity, material mechanical performance report, and undergo mechanical performance retesting.

In the review of the National Building Engineering Decoration Award (Building Curtain Wall category), it was found that there were still problems with the construction and on-site tensile testing of the rear anchor components in some of the inspected projects.

(1) Some projects do not have pre embedded parts and use various specifications of chemical bolts as post-treatment preparation. In observable areas, the exposed length of the bolts varies, and some clearly feel that the effective contact length between the bolts and the concrete substrate is insufficient. When renovating an old building, if there is a paint layer on the wall (usually 20mm), the effective depth of bolt embedding should also consider the thickness of the paint layer. If there is an old building renovation project where the original walls were tiled, in order to compensate for the non verticality of the structural structure, the method of increasing the thickness of the wall painting layer is adopted, so that the maximum thickness can reach 7-10mm. If chemical bolts are used as rear embedded parts in this project, great caution should be taken, and through wall bolts with anchor plates or other reliable connection methods should be used.

(2) Some projects only conduct tensile force testing on test blocks in the laboratory, without on-site tensile force testing, or only perform 1-2 types of bolt testing. For example, a certain project uses 4 different specifications of chemical bolts, but only 2 types of bolts are tested.

(3) The number of on-site bolt pulling force tests is insufficient, and some projects only conduct one set (3 pieces) of symbolic testing.

According to regulations, on-site bolt pulling force testing should form an inspection batch in the same model, specification, and basically the same part. The sampling quantity should be 1 ‰ of the total number of bolts in each batch, and each batch should not be less than 3.

(4) The test results were not verified against the design calculations. Ensure that the design value of anchor bolt bearing capacity should not exceed 50% of its ultimate bearing capacity.