Abstract
The steel sheet metal diaphragm used in AWWA D110, Type III, prestressed concrete tanks on the outside face of the precast concrete tank wall serves a dual purpose as a liquid barrier and as vertical reinforcement. Seismic restraint cables, located on the outside face of the diaphragm, are fully encapsulated in shotcrete before applying prestressing wires on the tank wall. Seismic load path from the center of gravity of precast concrete core wall to the base cables generates vertical shear stresses at the diaphragm-shotcrete interface, which are resisted by the bond strength of shotcrete–diaphragm interface. The concept of “development surface” of the diaphragm is presented based on the “diaphgram surface pull-out” tests in response to the concern that diaphragm-shotcrete interface may not have sufficient bond strength to develop full capacity of restraint cables. A design procedure based on bond strength test results ensures a ductile failure mode as specified in ASCE 7-05.
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