keatinij
Structural
- Mar 19, 2018
- 1
A “Micro Look” at single angle lattice tower members for fall arrest conditions.
Please See associated Photo/Sketch.
Loading on a single angle as shown in the photo/sketch is applied from a large rigid hook (OSHAs 5,000 pound anchorage point loading condition). I am attempting to examine the suitability of various single angle members. My question specifically refers to the examination of shear stress on single angles as shown (outstanding leg on top). Shear stress is grouped with torsional stress and therefore I am obtaining highly non-favorable results when including torsional effects (say applying the load with 1” or less of eccentricity). This is a unique loading scenario as it could be acceptable for the outstanding angle leg to deflect / yield (similar to a cantilever beam), if the member does not fracture / separate. The thought is under this unique loading condition, it would be acceptable replace damaged members after the loading event. Under this acceptability, if the outstanding leg deflects / yields, would the deflection relieve the member of torsional effects and therefore the vertical leg be examined only for shear stresses only.
My thought is that the hook, when the significant load is applied acts similar to a pin as it desires vertical downward direction only. (i.e., it is NOT a condition as if a force is applied with static eccentricity such as a force applied on a welded stud on one of the angle legs).
I have calculated the deflection of the outstanding angle leg (i.e., looking (6” long) angle leg as a very short cantilevered beam). I have examined bending stress under this same method. If half of the 5K load is applied to the end of the angle, the localized stress in the leg would be very high, well enough to yield I believe. If a “bar” (or as if there were no horizontal angle leg at all), centric shear stress would be much more suitable. A sincere thank you for any direction, input, or thoughts with this unique scenario.
Please See associated Photo/Sketch.
Loading on a single angle as shown in the photo/sketch is applied from a large rigid hook (OSHAs 5,000 pound anchorage point loading condition). I am attempting to examine the suitability of various single angle members. My question specifically refers to the examination of shear stress on single angles as shown (outstanding leg on top). Shear stress is grouped with torsional stress and therefore I am obtaining highly non-favorable results when including torsional effects (say applying the load with 1” or less of eccentricity). This is a unique loading scenario as it could be acceptable for the outstanding angle leg to deflect / yield (similar to a cantilever beam), if the member does not fracture / separate. The thought is under this unique loading condition, it would be acceptable replace damaged members after the loading event. Under this acceptability, if the outstanding leg deflects / yields, would the deflection relieve the member of torsional effects and therefore the vertical leg be examined only for shear stresses only.
My thought is that the hook, when the significant load is applied acts similar to a pin as it desires vertical downward direction only. (i.e., it is NOT a condition as if a force is applied with static eccentricity such as a force applied on a welded stud on one of the angle legs).
I have calculated the deflection of the outstanding angle leg (i.e., looking (6” long) angle leg as a very short cantilevered beam). I have examined bending stress under this same method. If half of the 5K load is applied to the end of the angle, the localized stress in the leg would be very high, well enough to yield I believe. If a “bar” (or as if there were no horizontal angle leg at all), centric shear stress would be much more suitable. A sincere thank you for any direction, input, or thoughts with this unique scenario.
