concrete frame joints; specific design

[jfmann]

I am interested in discussing the design of beam-column joints with any structural engineers who design reinforced concrete building frames. I am thoroughly familiar with the design issues...........but am seeking to find out if, and under what conditions, practicing engineers are using the design recommendations in ACI 352 for buildings that do not have to be designed for seismic loading. <br>
<br>
Specifically...........are the provisions for joint shear in ACI 352 used to size the columns??.........are designers considering shear reinforcing even though it is not recommended by the standard??

 

[hasanh]

I am also a practicing engineer, mainly reinforced concrete structures. In areas not subjected to seismic activities,column shear forces rarely play a role when sizing or designing a column.

 

[merbas]

I agree with hasanh. column shear forces rarely play a role during the calculation.but this is a fact also. Praticaly we dont add siesmic loads which they are impuls load. They are short time but contains high energy.Looks like knock-out<br>
<br>
If you give residual strengh which is most important for concrete, pratically I advice to use fiber reinforced concrete.Fibers provide three dimentional micro reinforcement to concrete.<br>
<br>
When you use fiber reinforced concrete, if any impuls power occures like earthquerck, beams or coloumns deformed and first creack will appears.But fibers still hold the concrete together and supports the bars.therefore the building will not sunk at least untill you leave the building.<br>
<br>

 

[jfmann]

hasanh and merbas......thanks for the replies!........the issue is not so much shear in the columns .......it is horizontal joint shear within the beam column joints (between the Tension and Compression resultants of the negative beam moments).........I am investigating severe diagonal cracking problems in the beam-column joints of a building under construction........we know it was not designed properly ...columns are much too small.....poor reinforcing details........however I am interested primarily in determining if engineers in non-seismic areas are using the code standards in typical design.......at least running the calc for joint shear.........column shears are not a problem.......

 

[hasanh]

Hi jfmann,<br>
<br>
If I recall correctly, from my college days, diagonal joint cracking usually result from overstresses during seismic activities. Rarely have I seen that happen in areas not subjected to dynamic loads, although I live in a part of the world were construction quality is shabby and over 50% of the structural designs are below average(i.e. nothing is checked, joints, reinforcement anchorage,...,etc.). But thank god, this region is not exposed to earthquakes.<br>
<br>
Anyway, shouldn't a plastic hinge have occured in the column before diagonal cracks appearing in the joint, and if so, wouldn't that have transformed the joint to a pinned one?<br>
<br>
Regarding what merbas mentioned, fiber reinforced concrete, I believe that good design and detailing in non-seismic areas is enough. The added cost of fiber reinforced concete is not warranted.<br>
<br>
Regards,<br>
<br>
Hasan

 

[ishvaaag]

My bet is that in Spain if no seismic provision asks for seismic design, for ordinary RC buildings no one is looking about anything pertaining to in-joint shear. Contrarily most surely for steel is done quite commonly by conscious designers out of mere necessity of checking if the panel zone is strong enough. Also in 24 years of building practice never saw but in EQ photos RC in-joint failures.