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The Shaking of a City Block: Seismic Performance in
Dense Urban Environments
Presenters: Nick Trombetta, ZhiQiang Chen, UCSDAdvisor: Prof. Tara Hutchinson, UCSDCollaborators: Prof. Jonathan Bray, Ben Mason, UCB
Prof. Gregg Fiegel, Cal PolyProf. Bruce Kutter, UCDRobert Reitherman, CUREE Prof. Andrew Whittaker, SUNY Buffalo
Test 1 – Isolated Structures – SFSI Effects
Test 2 – Interaction of SFSI Effects
Test 3 – SFSI in a City Block
Common Structures in the “City Block” – Los Angeles
Prototype Selection and Preliminary Model Design
Test Series Design and Philosophy
Introduction
Prototype Model Scale (55g)
Common Structure
Structural System
Foundation Type Structural System
5 Moment Frame (9 Stories)
Mat – Below 3 Level
Basement
Moment Frame (3 Stories)
1 Moment Frame (5 Stories)
Piles – Below 1 Level
Basement
Moment Frame (2 Stories)
6 Rocking Elastic Wall (5 Stories) Spread Shear Wall (1 Story)
1 Moment Frame (3 Stories) Spread Moment Frame (1 Story)
3, 5Dual – Moment Frame + Wall (5
Stories)Spread Moment Frame (1 Story)
+ Shear Wall
5Eccentrically
Braced Frame (5 Stories)
Mat – Below 1 Level
Basement
Moment Frame (2 stories) + Braced Frame(Perpendicular to Shaking
Axis)
Structure Description
1 Concrete Encased Semi-Rigid Steel Moment Frames with Individual Spread Footings – 3-13 Stories, possibly 1-2 Basement Levels
2 Retrofitted Unreinforced Masonry Buildings – 1-6 Stories
3 Non-Ductile Reinforced Concrete Frame with or without Shear Walls –5-10 Stories, no basements
4 Wood-Framed Apartment Buildings – 3-5 Stories, possibly above Reinforced Concrete parking structure
5 Steel Moment Frame – 5-54 Stories, possibly 1-5 Basement Levels6 Parking Structures, Reinforced Concrete Shear Walls – 5-10 Stories
Test Series Number Description
0 Soil Only – Test to confirm centrifuge’s ability to create desired ground motions.
1 Soil + 2 Isolated Structures – Structures are placed far enough apart to be considered isolated. Isolated SFSI Response and seismic performance quantified.
2Soil + 2 Interacting Structures – Structures are placed side-by-side
in order to create interaction effects during ground motion. Affects of SFSI interaction on seismic performance determined.
3Soil + City Block – All 6 Structures placed in close proximity in order to determine seismic performance of an entire city block including the interaction of various SFSI
effects.
In dense urban areas buildings are arranged in clusters (i.e., the city block). However, these buildings are designed assuming they are isolated from one another, thereby ignoring the complex effects of interactions between buildings during earthquakes. The lack of design tools is due to both an incomplete understanding of the soil-foundation-structure interaction (SFSI) and the lack of well-documented case histories that could be used to develop understanding of the interaction of closely-spaced buildings. This project aims to remedy these shortcomings by performing centrifuge tests of physical models of building clusters. Ultimately developing design guidance on the basis of both centrifuge data and numerical studies.
Research Goals
1. Investigate the interacting relationship between nonlinear soil, foundation and structural response in a dense urban environment.
2. Develop a catalog of building performance case histories, to be used to advance our understanding of SFSI and our ability to analyze it.
3. Develop and verify fully nonlinear analysis methods for SFSI interaction effects utilizing OpenSees.
4. Develop Guidance, based on (1) and (4), for the design professional community.
5. Translate the challenge of understanding this problem to undergraduates through an annual “shaking of a city block” EERI Shaking Table Competition.
Tasks and Current Progress
1. Develop a Program for Centrifuge Testing –Preliminary plan is to run 4 test series, described to the right.
2. Develop/Construct Prototype and Model Structures – Prototypes have been selected and models are currently being designed to meet various performance parameters (period, yield-drift, contact stress, etc).
3. Soil-Foundation-Structure Numerical Simulations – Models are being designed utilizing OpenSees.
4. Centrifuge Experiments5. Validation of Numerical Tools and Post-Test
Simulations6. Develop Code Guidelines for PBEE and Policy
Guidance
www.nees-cityblock.org
Locations of Non-Ductile Steel
Moment Frame Buildings in
North-West Los Angeles
Blue: Office StructuresRed: Retail
Yellow: HousingLight Blue: Hospital
Green: Other