CBlair
Structural
- Sep 19, 2012
- 3
An issue for my client came up while testing their fencing product for state approval thru Miami Dade NOA. By 2010 F.B.C. fencing that is not greater than 6' from ground elevation in height, shall be designed for 115 mph 3-sec gust or 75 mph fastest mile. Upon testing the product, the fence support post failed under the 24 hour gravity load testing. This was due in part to an increase of loading applied to the 2 panel condition, where the middle post would see the full loading(half from each fence panels tributary area). Upon reviewing the calcs provided by the testing lab, i noticed that they are using a Kd factor of 1.0 when calc'ing out the velocity pressure (q) as well as multiplying by 0.6 after. I assumed that he was using the ASD load combination factor here from the ASD Basic Combination #5 or one of them because of the 0.6 multiplier.
In a discussion with my client and the testing lab, they are actually not using any load combination as they feel none of them apply. As by ASCE, it states that the Kd factors are calibrated to be used in conjunction with load combination from chapter 2. Because they feel that none of the combinations apply, the Kd is equal to 1.0. The lab stated that because the fences dead load is low, they are considering it to be equal to zero. The 0.6 multiplier is actually the effect of the squaring of the nominal wind speed factor of 0.6^0.5 from the Florida Building Code. That threw me even more off as the velocity pressure (q) is to be calculated using basic wind speed (3 sec gust) only. The justification is that he is taking it from strength design to allowable stress design by multiplying the 115 mph by 06^0.5 when calc'ing out the velocity pressure. I became lost in the conversation and the understanding of the explanation as we were all on the phone it can be difficult to get across a point in conferences. In the end, the testing lab agreed to allow me to submit my own load pressures that i want the various fence panels to be tested too. This is typical practice for them, with say a window manufacturer wanting their product to meet say 50 psf loading...
I have discussed this with my boss and brother who are both structural P.E.'s, and they agree with me. I am submitting calcs and wanted to see if someone out there disagrees with me as i am moving forward using a Kd factor of 0.85, V of 115 mph, and ASD load combination #5 when applying my velocity pressure into a force to be applied as it proves to be the most critical.
Thanks for the input
In a discussion with my client and the testing lab, they are actually not using any load combination as they feel none of them apply. As by ASCE, it states that the Kd factors are calibrated to be used in conjunction with load combination from chapter 2. Because they feel that none of the combinations apply, the Kd is equal to 1.0. The lab stated that because the fences dead load is low, they are considering it to be equal to zero. The 0.6 multiplier is actually the effect of the squaring of the nominal wind speed factor of 0.6^0.5 from the Florida Building Code. That threw me even more off as the velocity pressure (q) is to be calculated using basic wind speed (3 sec gust) only. The justification is that he is taking it from strength design to allowable stress design by multiplying the 115 mph by 06^0.5 when calc'ing out the velocity pressure. I became lost in the conversation and the understanding of the explanation as we were all on the phone it can be difficult to get across a point in conferences. In the end, the testing lab agreed to allow me to submit my own load pressures that i want the various fence panels to be tested too. This is typical practice for them, with say a window manufacturer wanting their product to meet say 50 psf loading...
I have discussed this with my boss and brother who are both structural P.E.'s, and they agree with me. I am submitting calcs and wanted to see if someone out there disagrees with me as i am moving forward using a Kd factor of 0.85, V of 115 mph, and ASD load combination #5 when applying my velocity pressure into a force to be applied as it proves to be the most critical.
Thanks for the input
