Steel Support Testing

Steel support inspection mainly conducts scientific testing and analysis on the geometric dimension testing, appearance quality testing, material mechanical property testing, surface anti-corrosion coating testing and connection node 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

Geometric dimension testing: Mainly testing the lengths, section dimensions (such as the section heights, web thicknesses, flange widths and thicknesses), straightness and end flatness of the steel supports. The precise geometric dimensions are the basis of ensuring the supports to be installed in place and bear the loads uniformly. Any out-of-tolerance may lead to the loss of the pre-stresses of the support systems or the local stress concentrations.

Appearance quality testing: Checking the defects such as the rust, cracks, lamination, scars, laps and bubbles on the steel support surfaces. The key checks are whether the welds and heat-affected zones have the welding defects such as the cracks, undercuts, lack of penetration and slag inclusions, as well as whether the base metals have the mechanical damages caused by the transportation and hoisting. These defects will seriously affect the load-bearing capacities and fatigue lives of the components.

Material mechanical property testing: Through the sampling testing or non-destructive methods, the key mechanical indicators such as the yield strengths, tensile strengths, elongations and impact toughness of the steel are verified. This testing aims to confirm whether the used material meets the design-required designations (such as Q235 and Q355), and is the core basis of evaluating the load-bearing capabilities and safety reserves of the steel supports.

Surface anti-corrosion coating testing: For the steel supports with the anti-corrosion requirements, the coating types (such as the paints and hot-dip galvanizing), coating thicknesses, adhesion and surface treatment grades (such as the Sa2.5 grade rust removal) are tested. The coating qualities directly affect the durability and service lives of the steel supports in the humid and corrosive environments.

Connection node testing: The key testing is carried out on the connection nodes between the steel supports and the wales, columns or embedded parts. The connection plate dimensions, bolt hole position precision, bolt specifications and tightening torques, welding qualities, as well as the fit clearances of the pin connections are checked, ensuring the reliable force transfer of the nodes and avoiding them from becoming the weak links of the structures.

Testing Scope

Deep foundation pit engineering supports: Suitable for the steel supports in the deep foundation pit engineering such as the building foundation pits, subway stations and underground pipe galleries (including the opposite supports, corner supports and truss-type supports, etc.). The testing runs through the whole process from the raw material incoming, component processing, on-site installation to before the demolition, ensuring their stability under the complex earth pressures and water pressures.

Tunnel and underground cavern support: Covering the support structures such as the steel arches and lattice girders used in the underground engineering such as the mining method tunnels and hydraulic tunnels. The testing emphatically focuses on the bonding tightness with the initial support concrete, installation clearances, as well as the load-bearing states under the high ground stress or weak surrounding rock conditions.

Temporary structure support systems: Including the support systems of the bridge construction, formwork support systems of the building construction, and temporary top supports of the large equipment installation. The testing of this type of supports emphasizes their overall stability, settlement deformations and connection structure safety, belonging to the key link of the construction safety control.

Existing structure reinforcement supports: For the permanent or temporary reinforcement supports that need to be added due to the renovation, functional changes or damages. The testing needs to evaluate the connection reliability between the new and old structures, the effects of the supports on the original structures, as well as the long-term properties of the supports themselves, ensuring the reinforcement effects.

Prefabricated components and finished products: Covering the standardized steel support products prefabricated in the factories. The testing scope ranges from the raw material incoming inspection, production line process quality control to the finished product factory delivery inspection, ensuring the quality consistency and traceability of the batch products.

Testing Methods

Dimension and geometric tolerance measurement: The tools such as the steel tapes, vernier callipers, ultrasonic thickness gauges, laser distance meters and total stations are used for the direct measurement. For the geometric tolerances such as the straightness and flatness, the wire-pulling method, optical levels or laser leveling instruments can be used for the testing, ensuring that the installation precision meets the design requirements.

Non-destructive testing (NDT): Widely applied to evaluate the internal and surface defects. Including the magnetic particle testing (MT) or penetrant testing (PT) for the surface crack testing; the ultrasonic testing (UT) for the detection of the internal defects (such as the lamination and lack of fusion) and weld quality evaluation; the radiographic testing (RT) for the precise imaging of the internal quality of the important welds.

Material property testing: Mainly according to the standards such as GB/T 228.1 (Metallic materials — Tensile testing), the tensile, bending and impact testing are carried out on the specimens cut from the components on the universal testing machines. For the in-service supports, the Leeb hardness testers, etc. can be used for the hardness testing, indirectly estimating the material strengths.

Coating testing method: The magnetic or eddy current thickness gauges are used to measure the dry film thicknesses; the cross-cut method or pull-off adhesion testers are used to evaluate the coating adhesion; the appearance defects such as the coating uniformity, gloss, missed coating and sagging are checked through the visual inspection.

Installation quality and monitoring testing: The total stations are used to monitor the plane positions and elevations of the support axes; the hydraulic jacks combined with the pressure gauges are used for the verification of the pre-stress application values and locking forces; the stress gauges or strain gauges are installed for the real-time monitoring of the axial forces of the supports during the earth excavation, preventing the overload.

Testing Standards

Domestic Standards:

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

2. GB 50755, Code for construction of steel structures

International Standards:

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

2. ISO 8501, Preparation of steel substrates before application of paints and related products — Visual assessment of surface cleanliness

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

Geometric measurement equipment: Including the high-precision steel tapes (such as the 5m and 50m), digital callipers, outer diameter micrometers, ultrasonic thickness gauges (used to measure the web and flange thicknesses), laser distance meters and total stations. These equipment are the basis of obtaining the accurate geometric data of the steel supports, and themselves need to be regularly verified to ensure the accurate quantities.

Non-destructive testing instruments: The magnetic particle flaw detectors (portable or mobile) and contrast enhancement agents; color penetrant testing kits; digital ultrasonic flaw detectors, equipped with the angle-beam probes and straight-beam probes of the different angles; for the important projects, the X or γ-ray flaw detectors may be used for the film testing. The operators need to hold the corresponding qualification certificates.

Material mechanical testing equipment: The universal material testing machines (used for the tensile and bending testing), pendulum impact testing machines (used for the Charpy V-notch impact testing), Leeb hardness testers or Brinell/Rockwell/Vickers hardness testers. The laboratory environments, equipment precision and testing methods all need to strictly follow the relevant national standards.

Coating testing instruments: The magnetic/eddy current coating thickness gauges (need to be selected according to the substrate and coating types), cross-cut testers, coating adhesion pull-off instruments and gloss meters. In addition, the standard reference pictures (such as ISO 8501) and roughness comparison blocks used to evaluate the surface cleanliness are also included.

Installation and monitoring instruments: The total stations (used for the spatial positioning and deformation monitoring), precision levels, hydraulic jack systems (with the precision pressure gauges or transducers, used for the axial force application and verification), vibrating wire or fiber Bragg grating axial force gauges (used for the long-term automated monitoring), and static or dynamic data acquisition instruments.