I've never been a fan of dobies for rebar support. I prefer metal or plastic chairs. I feel like the dobies create too much of a discontinuity in the concrete with increased potential for cracking. Am I being to restrictive?
I have a 4-foot tall retaining wall that has a point load surcharge at the top which is 2 feet from inside face of wall. How do you calculate the vertical pressure on the heel of the retaining wall due to the point surcharge load?
I'm reviewing a foundation design from another engineer. The foundation is a 24" thick pad for support of an antennae tower. The tower feet are anchored to the pad using an anchor bolt assembly composed of four threaded rods bolted to a steel plate and the whole thing embedded into the...
We have an existing sanitary force main that I'm evaluating. The 8" main terminates at a manhole with the crown of the force main at the same elevation as the crown of the 8" gravity line leaving the manhole. This is per City code.
I have seen other municipalities require that the crown of...
I'm designing a structure to support WWR 4x4-W4xW4 wire grid over a 42'x 85' mechanical yard which has 15' tall solid screen walls on three sides and the building on the fourth side (85-foot dimension). The steel structure to support the wire grid includes moment frames for both directions...
My client purchased an aircraft jack test stand. The manufacturer of the test stand provided an installation drawing which shows the two posts embedded in a concrete pad that is 5' thick x 20' x 20' with two mats of #8's at 6" o.c.b.w. located 5 inches from top and bottom. I asked if they...
I have a 20ft tall structure with walls on two sides which are all glass. As such, I was checking serviceability wind drift. I used the AISC 7 commentary with 10yr MRI which gives me a wind pressure qz of 10psf. According to AISC commentary, this pressure (Wa) is non-factored, so the full...
I'm designing a canopy structure composed of open web steel joists with roof deck on the top chord and soffit panels on the bottom chord. The canopy would be an open building, monoslope free roof per ASCE 7-10. I need to figure out the wind pressure on the soffit panels. I noticed that ASCE...
I need to design a moment frame using HSS10x10x1/2 columns and W12x16 beam. The problem: I can't have anything additional on the exterior face of the beam flanges.
Has anyone ever done a moment connection by using attachment plates on the interior face of the beam flange? See attached...
A contractor installed a new HVAC unit in an existing building, which hangs from the inside roof structure. The roof structure has horizontal cross bracing and each set of cross braces has a sag rod in the middle. The cross bracing bay size is 16'x16'. The new HVAC unit will prevent...
A long time ago, in a galaxy far, far, away (like 2009), I posted a question about building owners complying with posted floor load limits (IBC section 106). The question was, how do laymen figure out if they are staying under the posted limit. For example, the recent inquiry to me from an...
I'm designing a new 3-0x7-0 personnel door in an existing exterior wall to go out onto a flat roof off of a second level hallway. The balanced snow depth here is 14 inches. The drift from the upper roof would make the total snow depth at the door 38 inches. I'm concerned that this door is...
I'm reviewing an exterior stair design. The rise of the stairs is 16', the run is 25', and the stair width is 3'. There is no intermediate landing, so the stringers are continuous. This is an industrial stair, so the live load is 100psf x 5 per OSHA. The fabricator wants to use C12x20.7...
I'm trying to use Table 8.1, case 2, Partial distributed load. The formulas use what is called a "unit step function". I looked on page 131 for the definition.
If x < a, then <x-a> = 0. If x > a, then <x-a> = (x-a).
OK, I get that. But what about when x=a? It says it's undefined. I have...
I'd like someone to double check my calcs on a tied arch. I'm using Roark, Table 9.3.1.h. The arch has the following:
Span = 100'
Radius = 97.7'
Theta = 31 degrees = 0.54 rad
w = 625 plf
The top chord of the arch is 2-L5x3-1/2x1/2 angles, so this would be a thin arch.
I assumed k1 and k2 to...
I need to analyze an existing bowstring truss in a hangar built in 1928. See attached. These trusses are at 20 foot on center.
There's a lot of tension members and not a whole lot of compression members. It seems like it is broken down into three sub-arches on the top chord, which transfer to...
I am designing a new 30'x30' hip roof canopy to be built next to an existing 20'x20' hip roof canopy. Both canopies have a 12 foot eave height. This is in Colorado, so snow load is a big factor. The new canopy eave will be 1.5 feet away from the existing canopy eave. The new canopy will be...
I have a 24'Wx72'Lx12'H building that is supported on columns elevated 16' above grade, so a building on stilts. The floor of the building will be conform deck with concrete supported by OWSJ's. The bottom of the OWSJ's will have a metal soffit panel to enclose the building, similar to a gas...
Sometimes, we engineers do design "by inspection". If something looks obvious, then we skip the calcs and just say "by inspection". Wind versus seismic is an example. But how far do you take this and how legal is it? It seems to be a judgement call on the part of the EOR, who is ultimately...
