You are the safety manager for a company that erects steel frame structures. A common method that your company uses to provide fall protection is to weld an L5x3.5×1/4 section of angle that is 8” long to the WF beams that are used in the construction of the building. The angles have an eye that has been welded to them (See Figs. 1 and 2). The eye provides an anchor point for the lanyard of a PFA to be attached to. The angle is welded to the beams on the ground, so that it will be in place and ready for immediate use as soon as the beam is set. This design was approved by a P.E.
For the current jobsite you are on, this design has been modified. Workers at heights of 10-50 feet were found not affixing the PFA to an anchor point. After analysis, it was determined the reason was the workers were not able to reach the anchor point to attach the vertical lifeline. Therefore, your director decided to modify the anchor point design and have a section of flat bar bolted to the angle to provide an extension (See Fig. 3). A D-ring plate is then bolted to the extension (See Fig. 4).
You are concerned that the modification has negatively impacted the strength of the anchorage point. You raise this concern to your director, but he rebuffs your concern stating that the same size angle that was approved by the P.E. is being used, and the flat bar that is bolted on as an extension is thicker and of higher strength material than the angle. Furthermore, he states that the D-ring plate being used is a special, high strength product rated at 15,000 lbs of fall protection- which he states is over what OSHA requires. He also informs you that the D-ring plate is bolted on using ¾” bolts, which is what the manufacturer specifications require.
You are particularly concerned with the bolts— and bolt holes—- that the modification requires. You point out to the director that when the bolts were added, holes were drilled that removed material, hence weakening the design. The director, now concerned that a serious error has been made, asks you to investigate your concerns by compiling a report by doing the following:
⦁ Determine the need for fall protection.
⦁ Determine how many pounds an anchorage is required to support.
⦁ Determine if the bolts used are of adequate strength/size.
⦁ Determine if the angle will experience tensile failure.
⦁ Determine if the angle will experience block shear rupture.
NOTES: Be sure to state specific regulations where applicable. Figs. 1-3 are not to scale, nor do they reflect the bolt sizes, spacing, or patterns unique to each group. Please refer to Figs. 6 for specific information. Fig. 7 provides an orthographic drawing of the bolt holes.
The written report should contain the following:
⦁ Title Page
⦁ Executive Summary
⦁ Table of Contents
⦁ List of Figures (If Applicable)
⦁ List of Tables (If Applicable)
⦁ Methodology
⦁ Results and Conclusions
⦁ References (If Applicable)
⦁ Appendices
⦁ Essay on Ethical Implications—
⦁ BCSP Code of Ethics
⦁ Actions to be Taken
⦁ Need for a P.E. ?
Additional Information:
⦁ The PFA system uses a full body harness, a non-shock absorbing lanyard, a mechanical lever fall arrester, 5/8” diam. 3 strand, nylon rope, a 3’ lanyard w/ 6’ fall distance.
⦁ For the Angle:
⦁ Fy= 36,000 psi
⦁ Fu= 58,000 psi
⦁ For the Extension:
⦁ Fy= 42,000 psi
⦁ Fu= 60,000 psi
⦁ Design the system based on a worker + tool weight of 290 lbs.
⦁ There are three workers attached to each anchor point.
⦁ The extension is bolted on using 1/2” diam. GR 5 bolts.
⦁ The bolt hole pattern for attaching the extension to the angle is given in Figure 6.
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