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  • Users: CrabbyT
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  1. CrabbyT

    Wood Beam / Pipe Penetration / Net Section Modulus

    I'm feeling super dumb right now, I had a real heavy loss over the weekend and I just feel like I'm not thinking clearly. Can someone please help me check my work? I've got a 5.25x9.25 wood beam (three ply LVL). Contractor wants to drill a 2.125" hole through the middle of it for a pipe. Am...
  2. CrabbyT

    Tribal Knowledge

    Every now and then, I wonder how structural engineers of the previous generation used to approach the same problems that we face today. I feel like I'm losing bids on jobs because I'm somewhere between 20 - 40 years old and I lack the tribal knowledge that allows someone to design structures...
  3. CrabbyT

    Wood Shear Walls

    I'd like to have a deeper understanding of wood-frame shear walls. For context, I'm in the USA and have access to the 2015 AWC NDS and SDPWS. My background is in steel/concrete design, but lately I've been dabbling in wood design. After calculating forces, where do you usually start when...
  4. CrabbyT

    Pipe Racks vs. Atmospheric Ice

    I'm in Midwest USA, this project is about 50 miles away from the leeward side of a great lake, and I'm analyzing some existing pipe racks (a.k.a. box trusses). The old drawings show that it was designed per the UBC, so ice wasn't a consideration. Since these were engineered back in the day...
  5. CrabbyT

    Residential Snow Load (USA)

    I recently branched out and started doing some freelance engineering. The majority of my projects have been residential and have involved wood framing. With respect to snow loads, are we supposed to use the ground snow load as the design load? Or should I calculate it based on ASCE 7-10...
  6. CrabbyT

    Obtaining Existing Drawings

    I've got a prospective client who just bought an existing building, and they asked if I would be interested in helping them to determine the load capacity of some existing precast slab panels. They want to know if it's OK to drive a fork truck on them, and they span about 30'. My first thought...
  7. CrabbyT

    Stiffness of a buckled knee brace

    I'm working on a project where a girder for an existing equipment platform is bolstered by a knee brace. The knee brace was supposed to be a 2L 2.5×2.5×0.25 angle. They only installed it as a single angle. Under full design load, the angle fails but the girder has a stress ratio around 0.5...
  8. CrabbyT

    Trial Percentage of Composite Action (AISC Examples)

    I'm trying to figure out the composite strength of an existing W24x55 using the AISC 14th SCM. I started by working my way through the AISC example problems I.1 and I.2 for the 14th edition manual. They calculate the limit states of concrete crushing and tensile yielding of the steel...
  9. CrabbyT

    Adhesive Anchors for 150 HP Well Pump

    Anybody here ever spec'd (or know anyone who has spec'd) HILTI rods / adhesive for anchoring a well pump? Did it work out well? Any horror stories? I've recommended cast-in-place sleeved anchors for this project, but the PM is dead set on using post-installed HILTI's for reasons that are...
  10. CrabbyT

    Vertical Turbine Pump Foundation

    I'm working on a job that involves the installation of a 150 HP - 200 HP pump for a new well and I'm trying to understand how the foundation should be designed. For centrifugal pumps, the rule of thumb is that the base should weigh at least 3x the equipment it supports. Does anyone know if the...
  11. CrabbyT

    Wind Parallel to Box Truss

    This post mostly concerns ASCE 7-10 Chapter 29 (Wind Loads on Other Structures), but I'm curious to hear other answers if people can provide insight. For wind perpendicular to a truss, I'm familiar with using F = q∙G∙Cf∙As where Cf is based on Figure 29.5-2. For wind acting in the longitudinal...
  12. CrabbyT

    Shell Elements as Slabs

    In your structural models, what do you think about using shell elements to represent concrete floor/roof slabs? I've been hesitant to do this because the effects seem drastic. For comparison, I made two duplicate models. One uses area loads to represent a roof deck, the other uses shells. I...
  13. CrabbyT

    Concentrated load on continuous one-way slab near supporting beam

    I have a situation where I'm trying to shore up some concrete encased roof beams so that a contractor can use them to lift a tank. It's a 2-story building with a basement. The diaphragms are composed of one-way cast-in-place concrete slabs (~5" thick, no form deck). The building steel is...

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