Report - PEER - University of California, Berkeley

Ideally, the preliminary design of step 2 would satisfy, or come close tosatisfying, the performance objective(s) selected for the building to avoid multipledesign iterations. Assuming that fragility functions are developed in sufficient numberand detail to characterize the vulnerability of NCCs for common buildingoccupancies, guidance will be required to assist the structural engineer to select thestructural system type (incl. material, seismic framing system, strength, ductility) thatwill deliver the intended building performance.Studies are under way at the University at Buffalo to aid in the identification ofoptimal structural framing systems, noting that the optimal solution will vary as afunction of the performance objectives. Weak and flexible, strong and stiff, andprotected framing systems are being studied. A hospital structure was chosen for thebaseline building because of the high value (measured as a percentage of the totalinvestment) of the nonstructural components and building contents in such buildings(see Figure 1). Sample preliminary results from these studies are presented in thefollowing sections with emphasis on demands on acceleration- and drift-sensitiveNCCs. Results for velocity-sensitive components will be presented in Astrella (2004).3. NORTHRIDGE HOSPITAL ASSESSMENTThe MCEER demonstration hospital is sited in Northridge, California, close to theepicenter of the 1994 Northridge earthquake. The building is a four story rectangularstructure with a penthouse; the building was constructed in the early 1970s. Thelateral-load resisting system is composed of perimeter steel moment-resisting framesand two interior moment-resisting frames in the transverse direction.To facilitate analysis of the hospital building, a simplified mathematical model ofthe building was prepared: the penthouse was eliminated, the chamfered southwestcorner of the building was eliminated and the framing was made both regular andsymmetric about each horizontal axis. Two views of the building are presented inFigure 3: a building elevation and a plan view showing gridlines. The plandimensions of the building are 83.8 m by 17.2 m and the story heights (1st to 4th) are4.1 m, 3.8 m, 3.8 m and 3.8 m. In the transverse direction, the width of the exteriorbays is 4.9 m and the width of the interior bay is 7.4 m. The moment-resisting framesare located on grids B, F, J, N, 2 and 5. All remaining frames were constructed withsemi-rigid seat angle beam-to-column connections.To illustrate the impact of structural-system choice on the response ofacceleration- and drift-sensitive NCCs, the building was further simplified andanalyzed in the north-south direction only. Specifically, the building was sliced alonggrid line H (the building centerline) and the moment frame of grid line F wasrelocated to grid lines H and B: producing a regular and symmetric building with notorsional response. Column bases on grid lines H and B were fixed, reflecting the insituconditions; all remaining column bases were pinned.115