Masonry Dowels

[Greatone76]

I am watching a project and they are laying out dowels that go from the foundation into the masonry walls. I have bars that are definitely coming up very close to webs and I feel some are in webs in my opinion using my unofficial layout. Is it legitimate to measure out every 16 inches along the wall for the block width and then measure 4 inches in where the basic middle of the core is and measure to the actual placed bar and when this dimensions exceeds 2 inches claim that it does not meet the 530 requirements of being +/- 2 in the length of the wall or does it have to be a gap between bars that exceed the spacing +/-2 requirement. Is there a different way to layout the dowel positions?

 

[concretemasonry]

Greatone76

You terms are not exactly correct. A "conventional" block is nominally 16" long (Length, not width). The ASTM C90 requirements for block do not specify the specific number or location of the size or location of "cores", but have MINIMUM thicknesses for individual face shells and webs and the equivalent web thickness/foot of the webs. This is because of the different configurations used in different area/region and preferences of contractors and engineers. - There also minor variation in units such as wider "mortar beds(wider face shells and webs) on the top of the block as laid.

Block can have a single large rectangular cores, a single large center core and two "half cores" (one at each end with webs at 8" on center), two cores with a center web and two symmetric core separated by a center web. After that there In some areas with a lot of reinforcement engineers want a single center core with webs at 8" on center that are only 4" high to allow complete grouting for situations and engineers that wear both a belt and suspenders. Those are some configurations for different areas without getting into the specialized non-symetrical shapes and those that are made for "A-shaped" units or three or more cores.

I worked for a company that had aver 1100 different drawings for "standard" 8x8x16 units and many of the same configurations is 6",10",12",14" and 16" long units.

It is a complicated system that has developed based on contractor and engineers requirements. Then you have to add the different strength requirements for individual structures. Fortunately, the manufacturing systems almost automatically produce units that are typically 30-50% over the ASTM minimums, but can exceed the requirements up to 6000 psi or 8000 psi if required to do (and color coded by certified strength level before delivery to the project).

The easiest method for most jobs is to specify the ASTM C90 block minimum specifications and find out the local block configurations. That will satisfy about 90% of the projects and projects that the ACI 530 requirements , since those units were the basis of the development of the specifications.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[hokie66]

With two core blocks in the US, if you get the first one right, then measure all others at 16", they should fall in the same place in the block.

 

[Greatone76]

Hokie66 that is exactly what the contractor says, but When I layout the block starting at a corner somewhere in the middle the cumulative effect of pulling off the last rebar dowel appears to put the dowel into the webs. I also brought this to their attention because some of the openings in the building are not masonry opening sizes and are not laid out using masonry dimensions. The contractor measured from the edge of the opening in 4 inches and did not think about the partial blocks that would exist around these non modular dimensions.

 

[hokie66]

He should have thought. But if the bars hit webs, they should cut out those webs to accommodate the reinforcement and allow the grout to flow. Don't accept bent or removed dowels.