The American Concrete Institute (ACI) has released a paper called Axial Load-Bending Moment-Interaction Diagram of Partially Composite Precast Concrete Sandwich Panels.
The document, written by Douglas Tomlinson and Amir Fam, explores the axial load-moment interaction diagram for a 2.7 m (106 in.) long partially composite precast concrete sandwich panel – developed by using five full-scale tests and nine stub specimens.
ACI says the load-bearing sandwich panel comprised ribbed structural wythe and a façade wythe connected through angled steel shear connectors passing through a layer of insulation.
These panels were subjected to axial compression loads applied to the structural wythe only, then loaded transversely in flexure while subjected to the various levels of axial loads. One panel was loaded axially to failure.
“At axial loads between the classical tension- and compression-controlled failure regions in the interaction curve, a third failure mode unique to sandwich panels was observed—namely, shear connection failure by excessive slip and yielding of connectors,” ACI adds.
This failure mode dissipated energy which is similar to conventional flexural tension failure. The interaction curve of the panel was compared to analytical interaction diagrams developed for the cases of fully composite and noncomposite panels.
This study considered second-order effects from the slenderness of the panel. Also, the location of the effective centroid of the partially composite panel was established to calculate the end eccentricity of the axial load, which contributes to the total moment.
The level of composite action was assessed using a range of methods.
“Based on the strength method, composite action decreased from 87% in pure flexure to 11% at an axial load equal to 31% of the pure axial capacity of the structural wythe,” ACI concludes.
