Academic and Student Affairs Bldg (cont.)

I hope to continue a progress report on the Academic and Student Affairs Building, but this will be my last past for the BC2024 Fall class.  They are near completion of the front entrance retaining wall, which will be backfilled to street level.  Work is continuing on the foundation wall for the building's footprint and I noticed that today, concrete masonry units were delivered to the site. 

Something that I noticed along the the slab that the retaining wall sits on was a long open key hole formed out of the slab that was formed out between the vertical rebar for the wall.

Highlighted in red, which is difficult to see exactly what I'm explaining, but I'll include a sketch to give a better illustration.  Chapter 19, Concrete Construction, in the Building Construction, Principles, Materials, and Systems explains this as a relief joint because (a) it is difficult to match colors between two concrete placements, and (b) the top surface of the lower concrete may not be perfectly level, resulting in an irregular construction line, or it may be slightly out of plane with the adjacent concrete.  The latter (b) makes sense in this situation given that this will be backfilled, aesthetics do not apply.  This key will also give the concrete a good seat to set in when it is poured and the connection will be better than that of a flat connection.  Below the key joint is a horizontal dowel joint which will connect the existing slab to the newly poured slab.  Usually spacing for these joints is between 10-15 feet.

Upon further examination, I determined that this was a shear key that resists lateral forces such as earth and water pressures, wind, and earthquakes, ensuring wall stability.  Rebar is placed vertically on both sides of the shear key.  See illustration below.

http://www.concretees.com/people/bruce/pubs/C870620.pdf