1. Working Principle Difference
Chemical anchors rely on cured resin to form a bonding layer between threaded rod and concrete borehole. It produces no outward expansion stress on base concrete, suitable for heavy static load, wind load and vibration working conditions.
expansion anchor belongs to mechanical friction anchoring. It depends on sleeve expansion and extrusion against hole wall to create friction force for load transfer. It can bear load right after installation, but the friction connection will gradually weaken under long-term vibration and repeated load.
2. Main Failure Causes of Wrong Selection
Using expansion anchor on curtain wall main keel and heavy steel structure anchoring. Friction slips under wind alternating load, causing pull-out.
Drilling hole diameter, depth, edge distance and spacing do not match the anchor specification. Insufficient embedment depth is the top reason for unqualified pull-out test.
Confusion of application substrate: expansion anchors are not fit for cracked concrete, low-strength lightweight concrete.
Construction omission: hole dust not fully cleaned, resin injection insufficient or curing time not respected for chemical anchors.
Non-compliant substitution in drawing requirements, resulting in direct rejection by third-party supervisors.
3. Selection Reference for Curtain Wall & Steel Structure
Item | Chemical Anchor | Expansion Anchor |
Load level | Heavy load, curtain wall main anchor, steel embedded part | Light auxiliary fixing, non-structural connection |
Concrete state | Allowed for cracked concrete (certified type) | Require intact, solid plain concrete |
Edge distance | Smaller allowable edge spacing | Need larger edge distance, easy to split concrete |
Load characteristic | Resist cyclic wind vibration well | Poor anti-vibration performance, easy loose |
Construction demand | Need curing waiting time, strict hole cleaning | Immediate loading after tightening |
4. On-site Pull-out Test & Acceptance Rule
Pull-out test is mandatory before batch construction of post-installed anchors. The test load shall meet design requirement. If the anchor slips, pulls out or concrete breaks during loading, the batch is unqualified and needs replacement and re-test.
Supervisors will check product certificates, drilling record, curing record and pull-out report together. Simple replacement of anchor type without design approval will lead to whole batch rejection and project delay.
5. Standard Operation & Risk Prevention
Follow construction drawing requirement strictly. Do not replace chemical anchors with expansion anchors for structural load-bearing points.
Confirm drill bit diameter, effective embedment depth, edge distance and center spacing before drilling.
For chemical anchors: blow and brush hole repeatedly to remove dust; control injection volume and full curing time.
For expansion anchors: control tightening torque, avoid over-torque splitting concrete or under-torque insufficient expansion.
Reserve sampling test points in advance, arrange pull-out inspection before mass installation.
FAQ
Q1: Can expansion anchors be used for curtain wall auxiliary brackets? A1: It is permitted only when the design clearly marks non-structural light load, and complete pull-out verification is finished. Main force-bearing curtain wall anchors generally adopt certified chemical anchors.
Q2: If pull-out test fails, can we deepen the hole and reinstall? A2: Not recommended. Failed boreholes shall be abandoned at proper spacing, re-drill new holes and re-construct anchoring.
