Expansion Bolt Testing

Expansion bolt inspection mainly conducts scientific testing and analysis on the tensile strength testing, shear strength testing, slip displacement testing, fatigue performance testing, installation torque and preload testing, and fire resistance performance testing, objectively assessing the product quality grade and issuing a detailed test report, providing a basis for manufacturers' quality control and downstream users' product acceptance.

Testing Items

Tensile strength testing: Evaluating the capability of the expansion bolts to resist the fracture under the axial tensile forces. This testing simulates the working conditions when the bolts vertically suspend the heavy objects or bear the vertical pull-out forces, and is the key indicator of measuring their core load-bearing performance, directly related to the safety of the anchorage systems. The testing results are usually expressed as the maximum tensile loads (kN).

Shear strength testing: Determining the maximum loads that the expansion bolts can withstand under the transverse shear forces perpendicular to the axes. This testing simulates the stressed states of the bolts when the relative displacement occurs between the structural members. It is crucial for resisting the horizontal loads such as the earthquakes and wind loads, and is the main basis of evaluating their capability to resist the structural lateral displacements.

Slip displacement testing: Measuring the displacements of the expansion bolts relative to the substrates (such as the concrete) under the sustained or cyclic loads. The smaller slip displacements mean that the anchorage systems have the better stiffness and stability, and can effectively control the structural deformations. This parameter is particularly important for the precision equipment installation and seismic structures.

Fatigue performance testing: Evaluating the durability and fatigue damage resistance of the expansion bolts under the long-term cyclic alternating loads. Through the repeated loading simulating the conditions such as the wind-induced vibration and machine vibration, whether the sudden fracture caused by the material fatigue occurs is tested. This is indispensable for the safe applications in the dynamic load environments.

Installation torque and preload testing: Verifying whether the torques applied during the installation can be converted into the preloads required by the designs, and ensuring that the force values are uniform and stable. The appropriate preloads are the premise of ensuring that the expansion sleeves are fully expanded, tightly fitted with the substrates and exert the designed load-bearing capabilities. The excessively large or small torques will both lead to the anchorage failures.

Fire resistance performance testing: Under the standard fire temperature rise curve conditions, the capability of the expansion bolts to maintain their load-bearing capacities within a certain time is tested. The high temperatures will lead to the decreased metal strengths and the decomposition of the chemical adhesive colloids. This testing is of great significance for evaluating the overall stability of the building structures and the escape time in the fire situations.

Testing Scope

Under-cut mechanical anchors: Suitable for the anchors of this type which form the under-cuts at the bottoms of the drilled holes in the concrete substrates through the dedicated under-cutting tools, and bear the loads by relying on the mechanical interlocking principle. The testing emphases are their under-cut forming qualities, tensile and shear properties of the interlocking parts, as well as the applicability in the high-strength concrete.

Torque-controlled expansion anchors: Covering the anchors which realize the expansion sleeve expansion by controlling the installation torques. The testing needs to verify the accuracy of their torque-preload relationships, the uniform expansion of the expansion sleeves, as well as the displacement control capabilities in the cracked concrete, ensuring their installation reliability and repeatability.

Displacement-controlled expansion anchors: For the anchors which realize the expansion through the displacement of the expansion sleeves caused by the impact or hammering. The testing needs to pay attention to the relationships between the installation striking times and final expansion states, vibration and relaxation resistance, as well as the applicable lower limits in the concrete of the different strength grades.

Chemical anchors: Suitable for the anchorage systems which bond the threaded rods with the concrete substrates by relying on the chemical adhesives (such as the epoxy resins and vinyl esters). The testing core includes the bonding strengths of the colloids, relationships between the curing times and temperatures, durability (heat and humidity resistance, freeze-thaw resistance), as well as the performance under the different hole cleanliness conditions.

Anchors for the special substrate applications: The testing scope extends to the special expansion bolts used in the non-dense or low-strength substrates such as the hollow blocks, lightweight concrete, stone and brick walls. The anchorage mechanisms adapting to the substrate characteristics, the special tensile and shear properties, as well as the adaptability of the installation processes need to be additionally evaluated.

Stainless steel and anti-corrosion anchors: For the austenitic stainless steel or hot-dip galvanized anchors used in the corrosive environments (such as the coastal areas, chemical plants and swimming pools). In addition to the mechanical properties, the salt spray testing, stress corrosion cracking testing, etc. also need to be carried out according to the relevant standards, to verify their long-term anti-corrosion effectiveness.

Testing Methods

Direct pull-out testing method: The most core testing method. The tensile loading devices are directly applied to the threaded rods of the expansion bolts, and the axial tensile forces are applied at the uniform speeds through the hydraulic or mechanical methods until the specimen failure. The load-displacement curves are recorded to determine the ultimate tensile loads, slip displacements and failure modes (such as the steel fracture, concrete cone failure and pull-out failure).

Shear testing method: The special fixtures or double-shear devices are usually used to apply the loads perpendicular to the axis directions of the bolts, to determine the shear load-bearing capacities of the bolts. The testing needs to ensure the accurate loading directions, and distinguish the single-shear and double-shear working conditions, simulating the real states of the bolts bearing the lateral forces in the actual engineering.

Long-term sustained load testing: The specimens are maintained at a certain constant high stress level (usually a certain percentage of the short-term ultimate loads) for a long time (such as several weeks to months), observing whether the creep or the time-increasing displacements occur, to evaluate their reliability and stability under the long-term static loads.

Cyclic load testing: Simulating the dynamic loads such as the earthquakes and wind-induced vibrations, the repeated tension-compression or tension-tension cyclic loads are applied to the expansion bolts. Through the recording of their performance degradation, residual displacements and final failure modes under the different numbers of cycles, their seismic resistance and fatigue resistance are comprehensively evaluated.

On-site non-destructive testing method: The sampling verification is carried out on the installed anchors at the engineering sites. The commonly used methods include using the calibrated torque wrenches to check the torques, and carrying out the small-amplitude verification pull-out testing (the loads usually not exceeding 1.25 times the design values and not causing the failure), to evaluate the consistency of the installation qualities.

Fire resistance furnace testing method: According to the standard fire temperature rise curves (such as ISO 834), the concrete components installed with the expansion bolts are placed in the fire resistance furnaces, and the constant tensile loads are applied to the bolts. The time that they can maintain until the failure is recorded, thereby evaluating their fire resistance limits.

Testing Standards

Domestic Standards:

1. GB/T 22795, Expansion anchors for use in concrete

2. GB/T 228.1-2021, Metallic materials — Tensile testing — Part 1: Method of test at room temperature

3. GB/T 10125-2021, Corrosion tests in artificial atmospheres — Salt spray tests

International Standards:

1. ISO 6892-1, Metallic materials — Tensile testing — Part 1: Method of test at room temperature

2. ISO 9227, Corrosion tests in artificial atmospheres — Salt spray tests

3. ISO 834-1, Fire resistance tests — Elements of building construction — Part 1: General requirements

Note: The applicable standard can be selected according to the product use and customer trade requirements; standards agreed in the contract take precedence over general standards.

Testing Instruments and Equipment

Universal material testing machine: The core equipment of carrying out the static mechanical property testing such as the tensile and shear. It needs to be equipped with the high-precision force transducers (the precision usually better than ±1% FS) and displacement measurement systems, which can automatically draw and record the complete load-displacement curves. The maximum load ranges need to cover the expected ultimate values of the anchors to be tested.

Dedicated pull-out tester: The portable or hydraulically driven type, mainly used for the on-site testing and engineering acceptance. Usually consisting of the hydraulic pumps, cylinders, digital pressure gauges and reaction frames, with the characteristics of the small sizes and convenient operation. It can directly read the pull-out force values, and is the key tool of the on-site quality control.

High-precision torque wrench and transducers: Used to control the installation torques and measure the preloads. The digital torque wrenches can precisely set and display the torque values; the torque-axial force transducers can measure the actual preloads generated when the torques are applied, used to calibrate the relationship curves between the torques and preloads.

Dynamic fatigue testing machine: The dedicated equipment used for the cyclic load testing, which can apply the alternating loads to the specimens at the set frequencies, amplitudes and waveforms (such as the sine waves and square waves). The equipment needs to have the high-frequency loading capabilities, precise load control and cycle counting functions.

Environmental simulation test chambers: Including the salt spray test chambers, constant temperature and humidity chambers and freeze-thaw cycling chambers, used to evaluate the durability of the expansion bolts and their chemical adhesives under the different environmental conditions. The harsh environments such as the acid salt spray, high temperature and high humidity and low-temperature freezing can be simulated, accelerating the material aging processes.

Data acquisition and analysis system: Integrated in the testing equipment or independently configured, used for the real-time acquisition of the multi-channel signals such as the forces, displacements, temperatures and deformations, as well as the data processing, storage and analysis. It can automatically generate the test reports, calculate the key performance parameters, and ensure the traceability of the testing processes.