6-Storey Mixed Use Building

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In order to learn how to analyze typical reinforced concrete buildings, understand their seismic behavior and to learn how guidelines such as ASCE 41, ATC-40 and FEMA could apply to buildings in Pakistan, the project team idealized a typical Karachi residential-commercial mixed use building as the pilot case study building. For simplicity, the team investigated the behavior of two-dimensional frame models with and without infill walls, and simplified certain structural details. A separate report describes a study of the three dimensional model of the building. The building upon which the idealized case study structure is based is located in Gulistan-e-Johar, a densely populated area in Karachi. This building consists of reinforced concrete framed building with five storeys including the ground floor. The building has shops located at the ground floor, while the above floors have residential apartments. The building was constructed before the 2005 Kashmir Earthquake. Project participants selected this building as the pilot case study because it has several seismic vulnerabilities common to mixed-use residential buildings in Karachi: a weak story created by open shop fronts at the ground floor, an eccentrically located reinforced concrete core, and heavy, stiff unreinforced masonry infill walls that were not considered during the structural design of the building. The case study team assessed the building’s potential seismic vulnerabilities using the US Federal
Emergency Management Agency (FEMA) Prestandard 310 Tier 1 Checklist modified for Pakistan conditions, as well as theAmerican Society of Civil Engineers (ASCE) Standard 31 Tier 2 and 3 analyses and acceptance and modeling criteria from ASCE 41. The building was found to be inadequate for seismic zone 4 and requires retrofitting to rectify the soft storey at the base and provide lateral stability to the building.

The team examined a number of potential retrofit solutions for both seismic performance and economic considerations. In order to provide a cost-effective and minimally intrusive retrofit, the
team selected a rocking spine retrofit solution. A spine of existing infill panels reinforced with shotcrete above a reinforced concrete wall at the open ground storey prevents the building from
collapsing. The spine provides stability and strength without extensive foundation work. This retrofit solution promises to be an innovative and cost-effective alternative for buildings in Pakistan. 

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6-Storey Mixed Use Building in Karachi A Pilot Case Study of Seismic Assessment and Retrofit Design
http://www.neduet.edu.pk/EQD/Publications/Building_1_Karachi6StoreyMixedUseBldg-corrected.pdf