Calculating requirements for a steel chair

by coldsquid
Tags: chair, requirements, steel
 P: 2 Hi, I found this forum while looking for a formula online and am hoping someone here can help me. I'm having chairs built from sheet steel for a public art display and need to decide the thickness of sheet steel to use. The job shop is suggesting 1/4" steel (either A36 or stainless), but before I pay to have prototypes built I want to compare the estimated performance of 1/4" to 3/8" plate to see if I should use 3/8" instead. The chairs will be made from a single piece of laser cut steel, bent using a press brake into a form similar to that shown in the attached images, and secured to the floor. I want to calculate two figures: First, how much drop would there be at the back of the seat (due to the bend at the front of the seat) for a given maximum weight of say, 600 pounds, for either 1/4" or 3/8" steel. Second, for a given tolerance for the seat to drop at the back (such as a 1/4" drop between unweighted and weighted), what would be the maximum allowable weight? For these purposes I'm content to assume that all of the weight is placed about 80% of the distance from the seat front to seat back and, unless someone here suggests otherwise, for my current purposes I'm content to focus solely on the strain on the bend at the seat front and to ignore the strain on the bent support underneath the seat. The front bend will be the weak link. Finally, is there a formula to estimate the longevity of a steel bend? For example, I imagine that repeatedly placing 500 pounds on the seat would strain the front bend, and that the cumulative strain would eventually result in the back drop increasing to 1/2", and eventually failing altogether. Is there a way to estimate if the number of repeated 500 pound weightings before an additional drop of 1/4" would be closer to 10k, 100k or 1000k? All feedback and assistance is greatly appreciated. Thanks! Matt Attached Thumbnails
 Sci Advisor HW Helper P: 2,097 coldsquid: What is the exact width of the chair at the front bend?