Retrofitting of 10-storey steel frame building with concentric braces (LRFD)

In this study we retrofit a 10-storey steel framed building which is designed under gravity and wind loads according to ASCE 7-10 following ANSI/AISC 341-10. In addition drawing and cost analysis has been carried out separately Building is residential and in accordance with ASCE 7-10, table 1.5-1 categorized as III occupancy category. Seismic importance factor is 1.25 from table 1.5-2. Situated in San Francisco Bay area specified as seismic zone 1( with Risk category III) which consider as most vulnerable area in which most earthquake may occur in United States according Uniform building code. Site class is E (soft soil profile-soft clay chapter 20.3.2) table 20.3-1 site classification with soil safe/allowable bearing capacity which presumed 100 kN/m² referring to table IBC 1806.2 (presumptive load bearing values) modulus of subgrade reaction taken 10000 kN/m³ according to Joseph E. Bowles foundation design and analysis page 505 table 9-1. Structure is steel framed 10-story building comprise of a ground floor, 8 normal floors and a rooftop with 13, 10.5 and 8.5 feet in height respectively. Composite slab type chosen for slab system. Structure elements such as plates comply ASTM A830 / A830M-14 and slabs concrete controlled over ACI 318-11. Structure has designed under gravity and wind loads. Preliminary design has been done with SAP 2000 program. İn addition, in order to verifying the results from program hand calculation for random connection and members has been done. While designing, structure elements, column and beam defined as frame, slab as shell. Afterward, retrofitting applied in order to fortify building against earthquake loads. Retrofitting executes with applying braces in some sections X and Y directions. The structure is regular and analyzed using three techniques: equivalent lateral force analysis, modal response spectrum analysis and modal response history analysis. In each case, the structure is modeled in three dimensions and only linear elastic response is considered. The results from each of the analyses are compared and the accuracy and relative merits of the different analytical approaches are discussed.