I missed the beginning of this sub-thread, but hear are some comments: Factors of safety for building structures are in the range of 1.4 for=20 dead load (the structure and none moving load), and 1.7 for live loads,=20 and a 0.9 factor applied to the material for defects, tolerances, etc.=20 For lifting equipment like cables and chains, the factor of safety is in=20 the 3 - 4 range. The structural engineer also needs to be concerned with=20 the dynamic loading and resonant frequency of the structure. Some floor=20 structures a few years back were light weight, long spans, and a walking=20 person would cause noticeable deflections (vibration) of the floor.=20 Today that issue is addressed by many building codes. If the reference below to the killing of numerous people is to the=20 Kansas City Holiday Inn walkway collapse. The structural engineer design=20 indicated hanger rods through steel channels, continuous for several=20 levels, with a nut at each level below the channel for support. This=20 would have entailed the rod being threaded nearly full length, which the=20 architect would have not liked the aesthetics. The steel detailer (makes=20 a drawing of every piece to be used for piece fabrication) changed the=20 detail, to have one piece of rod for each level (there were numerous=20 rods, spaced the length of the walkway) with a nut below the channel for=20 the rod going up, and a nut on top the channel for the rod going down.=20 The rods were inches apart. With this detail, for the top level walkway,=20 all load was transferred into the channel, and then to the rod going up.=20 The channel needed stiffener plates to be able to carry this load, and=20 they were not provided. There was a concert happening in the area, there=20 were numerous people on the walkway, and it was reported they were=20 moving in time to the beat of the music. Probably the loading with out=20 the music beat loading was into the factor of safety area of the=20 furnished detail. The engineer should have noticed the detail change=20 during the drawing approval process, or if he was engaged to inspect the=20 construction (should have been), then seeing the detail should have set=20 a flag. One of the hardest items for a structural engineer is, a structure has=20 been performing well for many years, and the owner wants to change the=20 loading or modify slightly something. The calculations show that the=20 structure is in the factor of safety area, and requires reinforcement.=20 The owner will, argue that the building is fine, has been for years. In=20 Ohio, the registered engineer is personally liable for his actions. On 9/8/2010 11:02 AM, Olin Lathrop wrote: > RussellMc wrote: > =20 >> In that case overloading a nut by a factor of two (more or less) >> killed a number of people. >> I'd feel that less than a factor of two over maximum possible loading >> is excessively low for a walkway - that's the sort of margins that you >> go to space on. And, when you DO go to space on a 1.5:1 safety margin >> (or 1.2:1 in some cases) , you find people doing up nuts with a force >> calibrated certified traceable nut driver, counting the turns and >> recording them in a log. >> =20 > I only got a vague verbal description of the cause once from a structural > engineer. There may well be reasons the actual stress factor was > considerbly more than 2x the design load. If I remember right, it was th= e > bracket that actually failed, which was built differently than designed. = I > also don't know the load of the lower structure compared to the upper one= .. > Possibly it was several times higher. > > There must be references web references you can find to this incident if = you > really want to know the details. > > > ******************************************************************** > Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products > (978) 742-9014. Gold level PIC consultants since 2000. > =20 --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .