Non-Linear Analysis for Residential TowerAug 01 2014 · 0 comments · NISHKIAN MENNINGER, Residential ·0
The renovation of the tower at 100 Van Ness has been no ordinary task. The existing building in the San Francisco Civic Center neighborhood stands at 415 feet tall, and was once home to 29 stories of offices. Constructed in 1972, the building featured a steel moment frame structure and was clad with heavy precast concrete exterior panels. National Real Estate Advisors, Emerald Fund, with Solomon Cordwell Buenz Architects, Nishkian Menninger, and Plant Construction Company are close to completing the conversion of this office building into a total of 418 residential and retail units, totaling over 400,000 square feet of livable space, including a rooftop garden with stunning 360 degree views.
Since the building is undergoing a complete renovation from top to bottom as well as an occupancy change, the San Francisco Building Code requires that the structure be analyzed and proven to meet the performance requirement of the current building code. Nishkian Menninger utilized performance based design to evaluate and analyze the existing structure. Working with the San Francisco Department of Building Inspection, and an independent 3rd party peer reviewer, Nishkian Menninger developed the following four-part system to evaluate the existing structure:
– A static code level analysis
– A static service level earthquake analysis
– A non-linear dynamic analysis
– Testing of existing moment frame weld quality
The two static analyses are typical for new structures. The results from these analyses showed that the structure fully complies with the existing code for member strength and stiffness. However, the structural steel moment frames have joint connection type that predates the current requirements for a special moment resisting steel frame, Welded Unreinforced Flange (WUF) connections. Therefore, special performance requirements and testing is required to ensure an acceptable performance during an earthquake.
The Non-Linear Dynamic analysis provides detailed results from subjecting the recorded ground motions through a 3-D computer model of the building. Ground motion records that are similar to the types of earthquakes typical to San Francisco were chosen for this analysis, including the Loma Prieta earthquake. The building code provides acceptance criteria for the WUF connections, indicating where any modifications are necessary.
Based on the analysis, along with a non-destructive testing program on the existing WUF welds, the existing structure steel frame was validated to meet the performance requirements of the current building code.
With this knowledge, we could show that the overall structure was fully code compliant; however our work was not over. As work progressed, issues had to be analyzed, the tower crane had to be located and erected above a road (click here), and constant coordination was required with the construction crews. An example of one issue was the way of removing the large precast panels from the exterior of the building. Restrictions on the methods of removal meant that it would be faster to remove all the panels from one side of the building, before moving on. However, the weight of these panels was significant enough to warrant an analysis on the foundations, to make sure the large mat of concrete would not rotate under the imbalance of load. The outcome of this analysis showed that the majority of these panels could be removed from one side without causing any unwanted imbalance.
The renovation at 100 Van Ness is nearing completion. The new façade is in place and the interior work is near its end. The building is slated to open in 2015.