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Re: more aci 318 -- CMU v. CIP

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Wow, what a creative solution!  I say this with very mixed emotions, because I consider CMU walls to be *much* less dependable than CIP concrete walls.  Too dependent on field conditions and workmanship.  Yes, I know that CMU CAN be built properly, it's just that I believe it is much less likely to actually be built properly.  After I've checked the rebar I feel fairly confident that the typical CIP concrete house foundation is built properly -- and big deficiencies can be seen when the wall is stripped, and repaired as necessary.  OTOH everything about CMU depends on the quality of the field work step-by-step, and cannot be verified later without demolition.  (I'm reminded of the short parking lot dividers I sometimes see, after they've been bashed by a car, breaking open the cell and exposing grout extending only halfway down the cell, with rebar hanging bare in the cell.)  Yes, CMU can be built properly, but in the house-building, minimum-oversight, low-bidder situation I don't have much faith that it will be.  I avoid CMU as much as possible. 

I see this as the code *forcing* us to use worse construction in its misguided zeal.  "The perfect is the enemy of the good."

Ralph Hueston Kratz, S.E.
Richmond CA USA

In a message dated 8/5/08 9:21:06 AM, rgarner(--nospam--at) writes:

To deal with ACI Appendix D, I am using CMU stem walls and installing anchor bolts to the requirements of Chapter 2 of ACI 530.

Bob Garner, S.E.

From: Mark D. Baker [mailto:shake4bake(--nospam--at)]
Sent: Tuesday, August 05, 2008 9:10 AM
To: seaint(--nospam--at)
Subject: more aci 318

This bolt thing is becoming more frustrating.

I have been doing anchor bolt shear/tension calc for a 1000# piece of electrical equipment mounted on a pad with” dia. anchor bolts (manufacturers frame provides holes for” dia bolts). The pad is 8’ by 8’.

I have found that a 14” deep concrete pad with cast in place bolts embedded 8” is required for ductile failure, my closest edge distance is 18”. I cannot have brittle failure due to seismic category D.

What used to be a 30 minute calc for loading and bolt design has turned into hours of *&^$%#@ and a pad design that is embarrassing to provide the client and contractor.

Aaaargh !!

Mark D. Baker
Baker Engineering

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