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