Our top focuses when determining our design were constructability, cost effectiveness, safety, and sustainability. The use of steel framing allowed us to sufficiently satisfy all of these aspects.
Gravity loads were calculated and reduced following the guidelines from ASCE 7-16.
Wind loads were calculated using the envelope method. It was determined that they did not governing lateral force on the building.
A Response Spectrum was designed in SAP 2000 to simulate seismic loads. The height of our building gave it a large period, which fell outside of the critical zone.
Denalo Engineering used SAP 2000 to construct a 3D model of the structural frame. The model was first constructed with the member sizes from our preliminary design. After applying Live, Dead, and Seismic loads to the model, SAP 2000 allowed us to complete a full analysis. This included calculating the Demand-Capacity Ratio (DCR) and checking for compactness of each member. Through various iterations, we were able to slowly adjust member sizes to create a safe and cost effective design.
This includes analyses of:
Dead Loads
Live Loads
Seismic Loads
Wind Loads
Applied Masses
Vibrational Modes
The Deformed Shape Under Building Loads is Shown to the Left
The Structural Team chose buckling restrained bracing to reduce the acceleration during seismic response by a factor of 8. For instance, the 1st mode of vibration goes from actual (.25 g) to design acceleration (.03 g).
Buckling Restrained Braces (BRB) were chosen for our Lateral Force Resisting System (LFRS). BRB has three major components: steel core, bond-preventing layer, and casing.
The steel core resists the full axial force due to the bond-preventing layer. This causes the steel core to yield inelastically. The casing provides lateral support against flexural buckling of the core. It’s high ductility produces an energy dissipative behavior that lowers oscillations caused from seismic loads. This leads to a reduction in member size, simpler and smaller connections, and smaller foundation demands.
Since the damage from an earthquake is concentrated over a relatively small area, post-earthquake investigation and replacement are relatively easy.
The Structural Team made the following design choices from their analyses:
Design Materials Chosen: Reinforced Concrete Underground Parking Facility & Steel Framing Structure
Lateral Force Resisting System: Buckling Restrained Braces with steel core, bond-preventing layer, & casing
Design Details: Gauge 5’’ metal decking with reinforced concrete, 4 type A pretensioned single shear bolts of ⅞’’ diameter girder to column connection