Bradley Crumb, Engineering Technical Resources, Canada Masonry Design Centre, 360 Superior Blvd., Mississauga, ON, Canada, Bcrumb@canadamasonrycentre.com
In the process of updating the masonry design software Masonry Analysis Structural Systems (MASS) to include the added scope of the seismic design in Clause 16 of CSA S304-14, several technical issues arose related to performing and satisfying the ductility verification for moderately ductile and ductile shear walls. To deal with the prohibitively long calculation times associated with repeating ductility verification attempts for each failing cross section, a methodology was developed to allow the software to design shear walls that satisfy the ductility verification. For cases where increasing compressive strain is not an available option for a shear wall cross section, the software determines a target neutral axis depth to compare for future design iterations. Following this, MASS increments cross sectional properties and compares the neutral axis depth to reach the saved target value. Alternately, a failure message is displayed if the target value can not be reached within the user defined cross-section parameters. In the case of shear walls containing boundary elements that initially fail a ductility verification attempt, it is possible for the maximum compressive strain to be increased to improve ductility without changing cross sectional geometric or material properties. The software first determines the required increase in compressive strain that must be achieved, before comparing that value to other potential limiting factors. These factors include code minimums and maximums, strain within the shear wall web, confinement from ties within the boundary element, and the interaction of any strain increase with neutral axis depth. This methodology is valuable for addressing ductility verification failures by reducing the number of ductility verification iterations from the tens of thousands down to single digits, making substantial improvements in calculation times and more easily allowing engineers to find workable designs. Additional recommendations are made for designers to consider that fall beyond the scope of the software.
KEYWORDS: seismic design, software, ductility verification, shear walls