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SAE J1063-2013: Nondestructive Strain Gage Testing for Cantilevered Boom Crane Structures
SAE J1063-2013 provides a systematic, nondestructive procedure for evaluating the stresses in mobile, construction-type lifting cranes with cantilevered booms. By using resistance-type electric strain gages under specified static loading conditions, engineers can determine stress levels and verify structural integrity. The standard also mandates a 25% overload test to ensure the crane can handle extreme conditions safely.
Overview of the Standard
This SAE standard applies to load-supporting structures of cantilevered boom cranes, excluding power transmitting mechanisms. It defines key terms such as strain, stress, yield point, and critical buckling stress. The test method is static and nondestructive, requiring skilled personnel competent in structural analysis and strain measurement. The scope is limited to mobile construction-type cranes; it does not address lift capacity on tires or dynamic effects beyond static simulation.
⚠️ Important: Personnel performing these tests must be experienced in structural analysis and the use of strain-measuring instruments. Incorrect interpretation of strain readings can lead to unsafe design assumptions.
Strain Gage Testing and Stress Calculation Methodology
The test procedure involves three discrete reading stages: initial reference (zero stress), dead load stress (structure assembled and positioned without live load), and live load stress (structure supporting the specified load). Stresses are computed using the uniaxial stress equation S = E · ε within the proportional limit. However, in biaxial stress areas—common near joints and connections—the simple formula may be insufficient, and special consideration is required.
The table below summarizes the key stress types defined in SAE J1063-2013.
| Stress Type | Definition | Computation |
|---|---|---|
| Dead Load Stress (S1) | Stress from the structure’s own weight in test position | S1 = E(N2 – N1) |
| Live Load Stress (S2) | Stress induced by the rated load (including hook, block, rigging) | S2 = E(N3 – N2) |
| Resultant Stress (Sr) | Maximum stress from dead load alone or dead load plus live load | Greater of S1 or S1 + S2 |
Side loads are applied at 3% of rated load to simulate operational dynamics such as wind and swinging. These loads are applied horizontally normal to the boom plane, and readings are taken for both left and right directions.
Structural Integrity Verification and Overload Testing
The standard defines three classes of strength margins: Class I, II, and III, each with allowable ratios (n1, n2, n3) of yield strength to resultant stress. Compression members are evaluated using critical buckling stress (Scr), which depends on the effective length factor (K), radius of gyration (r), and unsupported length (L). The 25% overload test applies 125% of the rated load to prove overall integrity without permanent deformation or failure.
Design Insight: When evaluating compression members, always consider the slenderness ratio and residual stresses. The effective length factor K must be chosen based on the end conditions to correctly compute critical buckling stress.
The overload test is a requirement in Table 1 tests 5 and others. It confirms that the structure can survive short-term overloading without catastrophic failure. Only static loads are applied; dynamic effects are not captured.
Frequently Asked Questions
1. How is the 25% overload test performed?
After the standard strain gage tests at rated load, the crane is loaded to 125% of the rated load with the boom at the most unfavorable position. Strain readings are not required; the test is a visual and functional check for any permanent deformation, cracking, or instability.
2. What is the difference between dead load stress and live load stress?
Dead load stress (S1) is induced by the weight of the crane structure itself in the test position. Live load stress (S2) comes solely from the suspended load (including hook, block, and rigging). The resultant stress (Sr) is the maximum combination of these, depending on the condition.
3. Why is biaxial stress a concern in some areas?
In areas like chord-to-lacing connections, the stress state is biaxial, meaning the simple uniaxial formula S = E·ε is inaccurate. Engineers must use rosette strain gages and transformation equations to compute the principal stresses and check against yield or buckling criteria. Ignoring biaxial effects can lead to unsafe designs.
