What Standards Govern Anchor bolt testing in China?
Anchor bolt testing in China is governed by a product standard and a design code that together define both how the anchor is tested and how its tested capacity is used in structural design. The two are not interchangeable — an anchor must be tested to the product standard and its results applied through the design code.
GB/T 37266-2018 Anchors for Structural Strengthening is the product standard. It defines the type-test requirements for anchors used in structural-strengthening applications — the tensile capacity, shear capacity, and the failure-mode classification. The type tests are run on anchors installed in standard concrete test blocks under defined conditions, and the results define the anchor's basic resistance values that feed into the design calculation.
JGJ 145-2013 Technical Specification for Post-Installed Fastenings in Concrete Structures (replacing the 2004 edition) is the design code. It is the standard the structural engineer uses to calculate the design bearing capacity of a post-installed anchor in a real concrete structure — applying reduction factors for edge distance, spacing, cracked concrete, and seismic loading to the basic resistance values from the product test. JGJ 145 contains a mandatory provision (clause 4.3.15) that must be strictly enforced, and it classifies post-installed anchors into three types by their anchoring mechanism.
JG/T 335 Test Methods for Pull-Out and Shear Resistance of Building Anchors is the test-method standard — it defines the test apparatus, loading rate, displacement measurement, and reporting for the pull-out and shear tests that GB/T 37266 invokes. JG/T 160-2017 Mechanical Anchors for Use in Concrete is the product-classification standard for mechanical anchors.
The international counterparts are ETAG 001 / EAD 330499-01 (European Technical Assessment Guideline for metal anchors), ACI 355.2 (mechanical anchors) and ACI 355.4 (adhesive anchors) in the US, ASTM E488 (test method for anchors in concrete), and ISO 22477 (international anchor test). The failure modes, the test setup, and the capacity-reduction framework are closely aligned across these standards — an anchor tested to GB/T 37266 / JG/T 335 will produce results that map to ETAG/ACI categories — but the report must cite the specific standard the project invokes.
What Are the Three Anchor Types and Their Design Implications?
JGJ 145 classifies post-installed anchors by their load-transfer mechanism, and the classification determines where the anchor may be used.
Undercut (扩底 / 切底) anchors transfer load through mechanical interlock — the drilled hole is undercut (enlarged at the bottom), and the anchor's expansion key locks into the undercut, transferring load in bearing rather than friction. Undercut anchors are the preferred type for structural-member connections because the bearing load transfer is reliable in cracked concrete and under seismic loading, where friction-based anchors lose capacity. The higher installation cost (undercutting tool required) is offset by the higher design resistance and the broader application scope.
Torque-controlled expansion (膨胀) anchors transfer load through friction — the applied torque expands the anchor sleeve against the drilled-hole wall, and the friction between sleeve and concrete carries the tension. Expansion anchors are not permitted for structural-member connections under JGJ 145 and JG/T 160 — their friction-dependent load transfer is unreliable in cracked concrete (the crack opens the hole, reducing the normal force on the sleeve) and under sustained load (the expansion force relaxes over time). Expansion anchors are used for non-structural fixings — pipe supports, façade trim, light equipment.
Adhesive / chemical (化学 / 粘结型) anchors transfer load through bond — the anchor rod is set in a drilled hole filled with adhesive (epoxy, vinyl ester, polyester), and the bond between adhesive-steel and adhesive-concrete carries the tension. Adhesive anchors can develop high capacity in good concrete and are suitable for structural connections, but their performance is installation-sensitive — hole cleanliness, adhesive mixing, curing temperature, and curing time all affect the bond. The field-failure literature documents that adhesive anchors pulled out cleanly (no concrete attached to the adhesive) almost always failed because the installer did not blow out the drill dust before injecting the adhesive.
The classification matters for the test report: an expansion anchor tested for a non-structural application cannot be re-classified for a structural application by re-testing — the classification is by mechanism, not by measured capacity. A structural anchor must be an undercut or a qualified adhesive.
How Is the Tensile (Pull-Out) Test Performed?
The tensile pull-out test is the headline anchor test — it measures the tension load the installed anchor can resist before failure. Per JG/T 335 and ASTM E488, the test applies an axial tension load to the installed anchor and records the load-displacement behaviour to failure or to a defined proof load.
Test setup: the anchor is installed in a concrete test block of defined strength (typically C20/C25 to C50/55, covering the range used in real structures) at the specified embedment depth. A hydraulic pull-tester is connected to the anchor via a threaded adapter, and the load is applied axially. The critical setup detail is the bridge placement — the reaction legs of the pull-tester must sit outside the potential concrete-cone failure zone. If the legs press on the cone that the test is trying to extract, they artificially confine the concrete and produce a falsely-high reading. The rule is: the reaction legs sit at a distance from the anchor ≥ the effective embedment depth.
Loading regimes — proof load vs failure:
- Proof load test: load is applied to a defined percentage of the design load (typically 1.5× or 2× the working load) and held for a defined duration (typically 60 seconds for adhesive anchors, to catch viscoelastic creep). The anchor passes if it holds the proof load without excessive displacement or failure. This is the non-destructive test used for in-situ quality verification.
- Destructive test: load is increased until the anchor fails, recording the maximum load and the failure mode. This is the test that defines the anchor's ultimate capacity for type certification.
Displacement measurement: throughout the test, the anchor's displacement (pull-out movement) is recorded against the applied load, producing a load-displacement curve. The curve shape is diagnostic — a sudden drop indicates brittle failure, a gradual softening indicates ductile yield, and continuing displacement at constant load indicates creep (the failure mode that catches under-cured adhesive).
What Are the Three Failure Modes and What Do They Mean?
The failure mode — not just the peak load — is what a qualified anchor test report records, because the mode determines whether the result is usable for design.
Steel failure (锚栓钢材破坏): the anchor rod itself fractures in tension. This occurs when the embedment is deep and the concrete is strong, so the steel's tensile capacity is exceeded before the concrete or the bond fails. Steel failure is the desired failure mode for a ductile structural anchor — it is predictable (the steel's tensile strength is known), it is ductile (steel yields before fracture, giving warning), and it means the anchor has developed its full material capacity. The field literature notes that a steel-failure result from a high-strength adhesive anchor is technically a "good failure" — the installation held to the limit of the metal.
Concrete cone failure (混凝土锥体受拉破坏): a cone-shaped volume of concrete pulls out of the substrate with the anchor. This occurs when the concrete's tensile capacity is exceeded before the steel or the bond — the concrete is weaker than the fastener. Concrete cone failure is governed by the concrete strength, the embedment depth, and the edge distance / spacing. It is the failure mode that the design code (JGJ 145) calculates explicitly, with reduction factors for edge distance, spacing, and cracked concrete. A concrete-cone failure at a load below the expected value typically indicates the concrete was weaker than specified, the embedment was shallower than specified, or the anchor was too close to an edge.
Pull-out / bond failure (拔出 / 粘结破坏): the anchor slides out of the hole, leaving the concrete largely undamaged. For adhesive anchors, this means the bond between adhesive and steel, or between adhesive and concrete, failed. For expansion anchors, it means the friction was overcome. Pull-out failure almost always indicates installation deficiency rather than product deficiency — for adhesive anchors, the root cause is typically inadequate hole cleaning (the adhesive bonded to dust, not concrete); for expansion anchors, insufficient torque or an oversized hole.
Splitting failure (劈裂破坏): the concrete cracks and splits along the anchor axis. This occurs when the anchor is placed too close to an edge or too close to a neighbouring anchor, and the tension load creates a tensile stress in the concrete that exceeds its splitting capacity. Splitting failure is what the edge-distance and spacing requirements in JGJ 145 are designed to prevent — the critical edge distance is 1.5 × effective embedment depth (hef).
The diagnostic logic: a report that records only the peak load, without the failure mode, is not usable for design — the same peak load reached by steel failure vs pull-out failure means completely different things for the anchor's reliability in service.
How Do Edge Distance and Spacing Affect Capacity?
An anchor's capacity is not a single number — it depends on where the anchor is placed relative to the concrete edge and to neighbouring anchors. JGJ 145 defines the reduction factors that account for this.
Edge distance effect: an anchor placed near a free edge of the concrete has a reduced concrete-cone failure capacity, because the cone cannot develop its full volume — part of the cone is "missing" where the edge cuts through. JGJ 145 clause 6.1.6 defines the edge-distance reduction factor, and the critical edge distance — the distance beyond which the edge no longer reduces the capacity — is 1.5 × hef. An anchor placed closer to the edge than 1.5 × hef has its concrete-cone capacity reduced proportionally.
Spacing effect: when two or more anchors are placed close together, their concrete cones overlap, and the combined capacity is less than the sum of the individual capacities. JGJ 145 defines the spacing reduction factor similarly — the critical spacing, beyond which the cones do not overlap, is typically 3 × hef. A group of anchors placed closer together than this spacing has the per-anchor capacity reduced.
Cracked concrete effect: the concrete in a real structure is often cracked — shrinkage cracks, thermal cracks, flexural cracks. A crack that passes through the anchor's concrete cone reduces the cone's capacity, because the crack plane is a plane of weakness. JGJ 145 specifies whether the anchor's capacity is assessed for "uncracked" or "cracked" concrete, and the cracked-concrete capacity is lower — typically by 30–50 % for concrete-cone failure. An anchor qualified only for uncracked concrete cannot be used in a location where cracking is expected, which in practice means most structural locations.
Seismic reduction: under seismic loading, the anchor's capacity is further reduced by the seismic reduction factor k (JGJ 145 clause 4.3.9). The k value is determined from the anchor product's certification report, or from the standard table if no certification exists. The seismic case also requires the anchor to be placed outside the plastic-hinge region of the structure, because in the hinge region the concrete itself will be damaged and the anchor's support is lost.
Why Can Torque Not Replace Pull-Out Testing?
A common field question — raised in the Hilti technical correspondence and in many project disputes — is whether an installed anchor can be verified by applying a torque (with a torque wrench) rather than by pulling it (with a pull-tester). The answer is no, and the reason is that torque measures a different thing.
Torque measures the friction in the threads and under the nut, not the anchor's tension capacity. The relationship between applied torque and resulting tension in the bolt is approximate, varies with lubrication, thread condition, and bearing-surface condition, and cannot reliably confirm that the anchor's embedment or bond is adequate. An anchor with an inadequate bond (adhesive not cured, hole not cleaned) can still accept full installation torque without any sign of deficiency — the torque is resisted by the thread friction, not by the anchor's pull-out capacity.
Pull-out testing measures the anchor's actual resistance to axial tension — the property the anchor was installed to provide. A proof-load pull test to 1.5× or 2× the working load, held for 60 seconds, directly verifies that the anchor can carry the design tension. This is why the IBC Special Inspection framework, the European ETA framework, and the Chinese JGJ 145 acceptance framework all require pull testing (not torque verification) for structural anchors.
The only role of torque in anchor verification is confirming that the installer applied the specified installation torque to a torque-controlled expansion anchor — and even that is an installation control, not a capacity verification.
How Is Ultrasonic Testing Used for In-Service Anchor Bolts?
For anchor bolts already installed in service — particularly the large-diameter foundation bolts on highway sign structures, traffic signals, and cantilever poles — destructive pull testing is not possible, and the non-destructive option is ultrasonic testing (UT). The UT method detects cracks in the anchor bolt steel that are not visible at the surface.
Method: a longitudinal-wave ultrasonic transducer (typically 0°, 5 MHz, 12.7 mm diameter) is placed on the ground-flat top of the anchor bolt, and the ultrasonic pulse travels down the bolt length. A crack in the bolt reflects the pulse back to the transducer, producing an indication on the UT screen. The indication's position on the timebase gives the crack's depth below the top surface, and the indication's shape distinguishes a crack (tall, sharp, tight — large acoustic-impedance difference between steel and air) from corrosion (short, fat, sloppy — small impedance difference between steel and corrosion product).
Application: UT anchor-bolt inspection is used on highway sign structures where wind-induced fatigue has caused documented bolt failures. The most common crack location is just below the top of the base plate or the foundation — the location of maximum bending stress under wind load. The UT procedure must account for the bolt's thread engagement (a nut with < 75 % thread engagement reduces the scanable area on the bolt top), the bolt type (straight-end vs hook-end, which have different UT signatures), and the range setting (which must cover the projection length plus ~50 mm to catch the critical crack zone).
UT anchor-bolt testing is a specialised NDT application — it is not the same as the pull-out test, and it answers a different question (is the bolt cracked?) rather than (what is the bolt's capacity?). For in-service structures where pull testing is impossible, UT is the primary inspection method.
How Does the Chinese Framework Map to International Anchor Standards?
| Scope | China | Europe (ETA / EAD) | US (ACI / ASTM) |
|---|---|---|---|
| Product standard (mechanical) | JG/T 160 / GB/T 37266 | EAD 330499-01 (ETAG 001) | ACI 355.2 |
| Product standard (adhesive) | GB/T 37266 | EAD 330499-01 / 330987-01 | ACI 355.4 |
| Test method | JG/T 335 | ETAG 001 Annex B | ASTM E488 |
| Design code | JGJ 145-2013 | EN 1992-4 (Eurocode 2 Part 4) | ACI 318 Chapter 17 |
| Seismic | JGJ 145 clause 4.3.9 | EN 1992-4 seismic category | ACI 318 seismic |
| In-service NDT | UT per project procedure | — | ASTM E114 |
The test methods (JG/T 335, ASTM E488, ETAG Annex B) are closely aligned — all apply axial tension to an installed anchor in a concrete block and record load-displacement to failure. The failure-mode classification (steel / cone / pull-out / splitting) is common across all three frameworks. The design codes (JGJ 145, EN 1992-4, ACI 318 Ch. 17) use different reduction-factor formulas but the same physical model — the capacity is the minimum of the steel capacity, the concrete-cone capacity (reduced for edge, spacing, cracking), and the bond/pull-out capacity. For multi-market product, the anchor must carry certification for each destination framework — a Chinese JGJ 145 design calculation is not cross-accepted in a US ACI 318 jurisdiction.
Our Testing Capabilities
Beijing ZKGX Research provides anchor bolt testing against GB/T 37266, JG/T 335, and the JGJ 145 design framework, with cross-reference to ETAG / ACI / ASTM.
Type tests (GB/T 37266 / JG/T 335):
- Tensile pull-out capacity (in concrete blocks of defined strength, uncracked and cracked)
- Shear capacity
- Failure-mode classification (steel / concrete cone / pull-out / splitting)
Installation verification:
- Proof-load pull test (1.5× / 2× working load, 60-second hold)
- Torque-vs-pull diagnostic (confirming that torque cannot substitute for pull)
- Adhesive-anchor installation quality (hole cleanliness, cure verification)
Capacity reduction assessment:
- Edge-distance effect (critical edge 1.5 × hef)
- Spacing effect (critical spacing 3 × hef)
- Cracked-concrete capacity
- Seismic reduction factor (JGJ 145 clause 4.3.9)
In-service NDT:
- Ultrasonic crack detection on installed anchor bolts (0° 5 MHz longitudinal, crack-vs-corrosion discrimination)
Anchor-type scope: cast-in-place, post-installed mechanical (undercut, expansion), post-installed adhesive (epoxy, vinyl ester); structural and non-structural applications.
If you need a GB/T 37266 type-test report for a structural anchor product, a JGJ 145 design-capacity calculation, a site proof-load verification for installed anchors, an adhesive-anchor installation-quality audit, or an ultrasonic crack inspection of in-service foundation bolts — contact our laboratory with the anchor type, base material (concrete strength, cracked/uncracked), embedment depth, edge distance, and the applicable standard, and we will scope the test plan.
FAQ
What is the difference between a pull-out test and a proof-load test?
A pull-out (destructive) test loads the anchor to failure and records the maximum load and failure mode — it defines the anchor's ultimate capacity but destroys the installation. A proof-load (non-destructive) test loads the anchor to a defined percentage of the design load (typically 1.5× or 2× working load) and holds for 60 seconds — it verifies the anchor can carry the design tension without damaging the installation. Proof-load testing is used for in-situ quality verification; pull-out testing is used for type certification and for anchor design in uncertain base materials.
Why does the failure mode matter as much as the peak load?
Because the failure mode determines whether the result is usable for design. A steel failure means the anchor developed its full material capacity and the result is predictable and ductile. A concrete-cone failure means the concrete (not the anchor) limited the capacity, and the result depends on concrete strength and geometry. A pull-out failure means the installation was deficient (bond or friction inadequate) and the result does not represent the product's capability. A report that records only the peak load, without the failure mode, is not usable for JGJ 145 design.
Can an expansion anchor be used for a structural connection?
No — JGJ 145 and JG/T 160 both restrict torque-controlled expansion anchors to non-structural applications. The restriction is because expansion anchors transfer load through friction, which is unreliable in cracked concrete (the crack reduces the normal force on the sleeve) and under sustained load (the expansion force relaxes). For structural connections, the specification must be an undercut anchor (mechanical interlock) or a qualified adhesive anchor (bond) — both of which have load-transfer mechanisms that remain reliable in the conditions a structural anchor will see.
Why cannot torque verification replace pull-out testing?
Because torque measures thread friction, not anchor capacity. An anchor with an inadequate bond (adhesive not cured, hole not cleaned) can accept full installation torque without any sign of deficiency — the torque is resisted by the threads, not by the anchor's embedment. A proof-load pull test directly measures the anchor's resistance to axial tension, which is the property the anchor was installed to provide. Every international anchor-acceptance framework (IBC Special Inspection, European ETA, Chinese JGJ 145) requires pull testing, not torque, for structural anchors.
How does cracked concrete affect anchor capacity?
A crack passing through the anchor's concrete-cone failure zone reduces the cone's capacity — the crack is a plane of weakness that the cone breaks along prematurely. The cracked-concrete capacity is typically 30–50 % lower than the uncracked capacity for concrete-cone failure. JGJ 145 specifies whether an anchor is assessed for uncracked or cracked concrete, and in most structural locations cracking must be assumed (shrinkage, thermal, flexural cracks are normal in service concrete). An anchor qualified only for uncracked concrete cannot be used where cracking is expected.