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Re: Masonry Expansion Joints

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This is a question that I am sure most engineer's have thought about or have
encountered on a project. First, I must assume that you are talking about masonry
control joints, not expansion joints. As you correctly point out, with many
openings in a wall to contend with, it seems more logical to locate the joint at
the edge of an opening, since this is the weak point.

The lintel will try to prevent the joint from working since it bears on both sides
of the joint. How much restraint the lintel may provide is unknown. Is there a
detail that can be provided that will reduce this restraint?  I haven't seen one.

My concern is that as the block tries to shrink, it tries to pull on the lintel
which may cause a diagonal crack to form below the lintel bearing. This piece
would be lose and the lintel will lose it's vertical support as well. I suppose
this can be detailed to prevent this failure with a horizontal hairpin bar.

If I was going to use this method (which I don't), I would also provide twice as
C. J.'s as a wall with no openings. The reason for this would be that the C.J.'s
may only be partially effective due to the lintel restraint.

 I would think that a reinforced masonry wall with block lintels would provide
more restraint across the joint than an unreinforced masonry wall with a short
steel lintel.

Jim Kestner, P.E.
Green Bay, Wi.

BSmithSE(--nospam--at) wrote:

> The discussion of masonry reinforcing reminded me of expansion joint I saw in
> Mesa Arizona while visiting folks who retired there.  It was at a tract of new
> single family residences built with masonry exterior walls and wood roofs.  I
> noticed that the vertical expansion joints were located at one end of sliding
> glass door openings.  The location made sense since this is at the weak link
> of thermal contraction.  But how do lintels for the openings find bearing with
> the expansion joint at the end?
> Perhaps the expansion joints I saw aren't true expansion joints and that all
> the horizontal reinforcing continues through?
> In my practice, vertical expansion joints are indicated on masonry wall
> elevations (I use 2x wall height as the maximum spacing as Jim Amhrein once
> recommended).  However, when there are numerous door and window openings,
> locating the expansion joint between the openings seem futile.  I should like
> to locate the expansion joint at the edge of an opening.
> Any thought?
> Brad Smith