It is my understanding that properly vibrated/consolidated concrete has the vibrator inserted at each location for a few seconds at the most. The operator then pulls it out and inserts it adjacent to the prior insertion to get some minimal overlap in the zones (circles) of consolidation. If...
Excellent earlier responses! May also want to find out where the rebar was placed in the slab.
Sounds like the slab was not wet cured or protected from the drying elements.
I find it easier to put in wide spaced #4 rebar on bricks and then put the WWF on top of it. I use the rebar grid on bricks to hold up the WWF at the proper elevation. Bends a little bit when walking, but it bends back up when you step off.
LPPE,
The operative words are "bearing connection as designed." Sometimes slip critical connectors are installed because it is easier and faster. BUT, the number of connectors typically required for a truly slip critical connection are more than for a bearing connection. Thus, the slip...
Welding can definitely distort the steel after it cools. If you are putting a cover plate on, I normally require both sides of the cover plate to flange weld to be welded at the same time with the maximum difference in longitudinal location not to be more than 2'. Otherwise, the cover plate...
If it was steel framing, it could be that slip-critical connections were made by the erector and the connections are slipping into a bearing configuration. Sometimes when a connection "goes", it sounds like a small gunshot. This is ussually not a problem, just a little unnerving until you find...
gb238,
You may find the following of interest:
http://www.nrmca.org/aboutconcrete/cips/CIP%2010p.pdf
http://www.cement.org/tech/faq_rebound_hammers.asp
BigH,
The latest copy of ACI 228.1 that I have is 1995 with a total of 41 pages. The copy I had originally referred to was 20 plus. The 1995 version has the calculation in chapter 6, table 6.2; rather than the 3.5 and table 3.3 that I referred to in an earlier post.
If you want, let me...
Lastly, sometimes it does not matter to the homeowner that the concrete foundation is structurally adequate. In their mind, they paid for a 3000 psi of 3500 psi mix. That is what is shown on the drawings. Why should they settle for an average strength of 2000 psi? They paid for the higher...
BiGH
The difference in this case is not a design or the testing of cylinders, it is the evaluation of concrete in place. ACI 228.1 is entitled as "In-Place Methods for Determination of Strength of Concrete." Some cylinder sitting in a curing box is not representative of a core taken from a...
gp238
You may want to do the rebound hammer at the core locations prior to taking the cores. That way, when the cores are tested, you can get some sort of correlation between the rebound value and the actual strength for the cores.
Next, since you are in New York, you need to check the NYS...
Lots of questions:
1. What type of pressure treated wood was used? Is it the new stuff? If yes, you almost have to use stainless steel for fasteners.
2. What is the maximum vertical load on any column?
3. What is the maximum horizontal load on any column due to: wind on the cabin, water force...
I have used Azek material in the past to form stairs like that, that were wider than 8'. Makes a nice smooth finish with easy release from the concrete.
You could use a concrete rebound hammer. Core those areas. Then test for compressive strength. Determine a correlation between the rebound and the compressive strength. Then go back and use the rebound hammer on the rest of the structure to test strengths.
If that is not good, you could use...
DRC1,
You have been fortunate in your past experiences. We have tried the low speed routine; didn't work, still ended up with a weaker deck at those locations.
As for the dowels, you must have a real stiff superstructure, otherwise, the dowels in the already cast deck will "move" upwards in...
If you weld the plates together, you should check the shear stress to insure that the weld is adequate to insure composite action for the two plates. Just a simple matter to check the shear forces along the length of the plate and then calcuate the VQ/It value.
Crossframe has it correct. Most states use closure pours to isolate the stages. The diaphragms are then bolted solid in the closure pour bay to try to limit the differential vibrations/deflection due to one stage having live load.
Another option is to close the bridge over a weekend using...
Depends on how much funding you have available, and your construction schedule. You could do a "launched" type structure using precast elements, with a cased drilled shaft substructure; depends on soil conditions.
