Question
In designing of corbel beams in a pump station, why are shear links designed in top 2/3 of section? What is general advice on designing?
Answer
Corbel beams are definite as z/d<0.6 where z is distance of bearing load to beams fixed end and d is depth of beams. Design philosophy is base on strut and tie structure. To set up design model, it is initially assumed failure surface such as shear cracks extending to 2/3 of depth of beam. Test results verified that failure cracks extended only to 2/3 of beam as remaining 1/3 depth of concrete contributed as existing strut to provide compressive strut force to bearing loading.
Horizontal links are usually provided to corbel beams as experimental results indicated that horizontal links were extra effective than vertical links while shear span/depth is a smaller amount than 0.6. For shear span/depth>0.6, it have to be not considered as corbel beams but as cantilevers.
During design corbel beams, care must be taken to avoid bearing load to extend beyond straight portion of tie bars, otherwise corners of corbel beams are possible to shear off.