truss bars

[dtvankirk]

I have a set of drawings from the 1970's which shows a cast in place concrete beam. The beam is 25-Ft long, 1'-9" deep, and 1'-6" wide. The beam is integral with the concrete slab.

The section thru the beam does not show the reinforcing layout, but there is a note describing the reinforcing as follows:

3-#7 straight-bottom bars
3-#7 truss bars
3-#7 extra-top bars
#3 stirrups @ 4"

Any ideas as to what the truss bars are and where they might be located within the beam? I am sure they are not referring to the shear reinforcing since they specifically call out stirrups. I believe that the truss bars must be some sort of flexural reinforcing, since the beam is under-designed for moment if I neglect the truss bars.

 

[JAE]

Here are some similar threads you can review:

thread507-14653

thread507-91262

The bars are bent continuous bars that start out at one end of the span (over the support) as top bars, extend out to about the inflection point or so and then bend down at a diagonal to become bottom bars in the central region of the span, then turn up diagonally at the other inflection point and become a top bar again. Very common in older concrete structures.

So at the supports, you have an As value that is the sum of the bent and top straight bars at that support.

At the midspan, you have the sum of the bent and bottom straight bars in that span.

 

[jike]

At the support, the truss bars from each span typically overlap. The As negative is commonly the sum of the truss bars from each span plus any supplement straight top bars

 

[dik]

and early design also recognized the contributing shear resistance provided by truss bars...

Dik

 

[civilperson]

The current design standard also recognizes the contribution of bent longitudinal bars. (ACI 318-05 11.5.1.2)

 

[dtvankirk]

Thanks guys that was very helpful!