University of California at Berkeley
Civil and Environmental Engineering
Instructor: Stephen A. Mahin
Spring Semester 2008
CEE 227 -- Earthquake Resistant Design
Term Project
This term project is intended to provide the opportunity for you to study a topic addressed
by CEE 227 in more depth, to integrate information from this course with what you have
learned in other courses, or to apply techniques in more detail than permitted within the
regular homework assignments. The term project contributes 35% of the course grade.
By March 4, provide a brief (half page) abstract of your project, indicating the subject, a
narrative paragraph describing what you hope to achieve, and some references you intend to
use. Full credit will be awarded for all submissions. I will use this abstract to help you
refine (narrow) the scope of your project and locate useful sources of information. Earlier
submissions are encouraged.
By May 8, 2006, prepare a written report on your project. This should include:
• a concise statement of objectives,
• a statement on how your topic relates to CEE 227,
• background information, citing appropriate references,
• the body of your report, and
• conclusions and observations.
Even if your project is doing a design or carrying out detailed analyses, you need to prepare
a written narrative (though this can be brief, if you organize your other material).
Reports can be done individually, or better still, in groups of two. Group projects will be
expected to demonstrate correspondingly more total work than individual projects. Groups
are particularly encouraged where one team member, for instance, has background in
nonlinear analysis and another in design, or where one has a background in geotechnical
engineering and the other in structures, or one on probabilistic methods and the other in
design. Groups of three or more are acceptable, but require prior approval of the instructor.
Ideally, we should have a very short oral presentation so everyone might benefit from what
you have learned. We will discuss this option during class.
MS students are required to take the Comprehensive Examination, unless they take at least 2
units of CE 299. Students may wish to consider adding units of CE299 with a professor of
their choice on the topic of this project. This will avoid the need to take the Comprehensive
Exam, without much work beyond that required to complete the term report.
You can pick of topic of your own choosing! To stimulate thinking, some possible topics
are listed below. You need not limit your topics to this list.
CEE 227 – Term Project
2
Related to design of new structures (See later sections on Isolation, etc.)
Redesign the class project building (or another structure you find in the literature)
and compare your redesign and its performance with those of the original structure.
Some ideas would be to consider:
• Modified moment frames for improved ductility using (FEMA350, AISC
441, AISC 353) “prequalified” details.
• Modified moment frames (configuration (number of frames, bay spacing,
member depths, etc.) and proportioning (panel zone vs. beam yielding) to
improve performance
• Modified braced frames (to help control drift), including bucking restrained
braces, friction or other types of hysteretic devices.
• Supplemental viscous damping energy dissipation systems (viscous), for
example, looking at the effect of different powers than one for velocity.
• Seismic isolation of various types to limit damage in the superstructure.
• Special bracing elements that would tend to make a structure re-center
following a major earthquake, such as hydraulic springs by Jarret, shape
memory alloys, or prestressed friction devices (e.g., see Christopolous). The
hysteretic characteristics are pinched in a flagpole shape as shown.
Use of PBE procedure in FEMA 350 to design the homework building more
rationally and evaluate the confidence we have in it. There are numerous levels of
analytical methods and performance objectives that can be addressed with this
methodology.
Application of course concepts to other types of structures (bridges, offshore
structures, etc.)
What happens if the foundations of a structure are allowed to uplift during an
earthquake. Consider a structure like a braced frame or a narrow moment frame
where there is net uplift on the footings, or a wider mat or spread foundation where
there is only partial uplift along the edges of the foundation. Recently, architects like
Renzo Piano have designed structures where this is an explicit design feature and
viscous dampers (or perhaps, as an alternative, buckling restrained braces could be
used) are included in the uplifting columns to help dissipate energy.
Application of issues related to soil-structure interaction (for example, the simplified
methods outlined in FEMA 368) to design. When is this important, does it help (yes)
or hurt?
CEE 227 – Term Project
3
What is the effect of considering vertical ground motions? Carry out analyses of
some simple building systems with different heights or floor spans considering or
ignoring the vertical component of excitation. Consider the change of the relative
character of the vertical ground motions (or spectra) with distance and earthquake
magnitude. Look at structures, such as long span systems, prestressed systems,
cantilever systems, etc., where vertical motions may generally expected to be
important.
Some architects are building new structures that are not uniform with height.
Explore design issues related to these systems. For instance, see the figures below.
Similarly, many architects are building systems that are not typical rectangular
frames. Explore design issues related to such systems. For instance, see the figures
shown below.
Elevation
No Vertical Columns
Plan View
CEE 227 – Term Project
4
For high-rise structures, a number of structural features are used to help reduce
lateral displacements. These include truss belts, outriggers and mega-trusses (see
below). How do such structures behave compared to traditional strong-column,
weak girder designs? What approaches are can be used to design these for ductile
behavior?
Often tall buildings in the US like the ones shown above are designed such that they
are relatively non-redundant and a single concrete core provides lateral load
resistance. What special requirements might someone use to improve confidence in
achieving acceptable performance?
Tuned mass dampers have been suggested for improving seismic response. However,
it is difficult or costly to add sufficient mass and damping for the tuned mass.
Recently, several projects have been built around the world where the design places
a plane of seismic isolation at about two thirds the height of the building, and the top
third of the building is used as the tuned mass and the isolators allow lateral
movement of the upper mass and provide damping. Are there special requirements
for the period range of the overall structure (limited to low rise or to very tall
buildings), does the upper part of the structure need to be stiff and elastic, can the
two parts of the structure yield (in one instance, lower part was allowed to yield
significantly, and it was shown that the lower part performed better than if the upper
part of the structure were not there).
Seismic
Isolators
Fluid sloshing dampers are used at the top of tall buildings to control vibrations due
to wind and small earthquakes. How do these work? Can they be used for larger
earthquakes?
CEE 227 – Term Project
5
Related to detailed evaluation procedures for existing buildings: FEMA
356/351
Review methodology and comment on how it relates to class. Compare two or more
analysis methods described, such as elastic versus nonlinear static methods,
nonlinear static and dynamic methods, etc. Compare methodology in FEMA
356/ASCE 41 and FEMA 351 for establishing acceptance criteria and for describing
acceptability of structure. Note you cannot do all of this. Buildings available may
include:
•
1994 UBC designed SAC buildings (3, 9 or 20 stories) located in Seattle,
Boston or Los Angeles
•
Soda Hall (pre-Northridge welded steel moment frame, lots of data and some
OpenSEES models exist)
•
Van Nuys Holiday Inn (reinforced concrete frame, a PEER testbed with
considerable information on it)
•
McLaughlin Hall (a preliminary seismic report exists)
•
Sather Tower (whoops, it sits on a mat foundation only as wide as the tower,
plus some other issues. A report exists on a preliminary investigation and
additional professional help is available from recent CE 227 grads)
•
What about the early seismic retrofits on campus (do the student housing
units (retrofit to 3/4 of the 1988 UBC need to be re-retrofit?)
•
Applications of bracing, supplemental viscous damping or seismic isolation
as a retrofit of steel or reinforced concrete frames.
•
Addition of tuned mass dampers or sloshing dampers to add “damping” to the
structure to improve response.
•
Preservation of historic monuments and structures. For example,
preservation of European cathedrals or monuments located around the world
(Tikal, Pompei, Stonehenge, etc.). Cyark is working to move from scanning
of these structures to automatically make analysis models, and from there to
evaluate monuments (and figure out how to fix them so they will not collapse
in earthquakes). See http://archive.cyark.org/index.php
Drawings of buildings on the Berkeley campus are available through capital
projects
FEMA 547 discusses techniques for retrofitting various systems like those
described above.
Analytical / behavior related studies (can be analyses you do, a critical review
of literature, or a combination of both)
•
Assess methods to predict and improve response of structures, which exhibit strong
geometric nonlinearities (P-Δ effects) - SDOF or MDOF systems.
•
Effect of strong motion duration and aftershocks on structural response.
CEE 227 – Term Project
6
•
Identification of damaging features of ground motions (how to measure damage
(peak displacement, drift, cumulative plastic displacement, Park-Ang models,
fracture mechanics/low cycle fatigue, etc.), and what aspects of a ground motion can
be used as an index of damage potential (peak acceleration, peak velocity, total
energy input, instantaneous power, etc.)
•
Why is response relatively insensitive to various hysteretic characteristics (strength,
pinching during loading, etc.) and sensitive to others (negative post-yield stiffness,
unloading stiffness)
•
Sensitivity of computed response to modeling assumptions (steel: modeling of panel
zones, floor systems, inclusion on frames not intentionally expected to be part of the
lateral load resisting system, material property variability, etc.; reinforced concrete:
EIeff, slab effects, etc.)
•
Effect of bidirectional excitations on inelastic response. Effect of vertical ground
motions on structural response. For example, what are the forces in a column where
the column is part of braced frames running in orthogonal directions? What are the
forces in columns in moment frames where the column is part of frames running in
two directions? What are the forces where the column is only part of one frame, but
must move in the other direction due to compatibly of motion imposed by the floor
diaphragms?
•
Assessment or studies related to collapse prediction of structures (incremental
dynamic analysis methods in FEMA 350-352, fragility curves from PEER/ATC 58)
•
Damage associated with nonstructural components. Methods to limit damage to
various types of nonstructural elements, components and contents. Damage cost
estimates. Numerical models for various types of nonstructural elements.
•
Dynamic response of heavy equipment resting on a floor slab, like large refrigerators
or computer stands.
•
Detailed probabilistic methods for characterizing performance and loss.
•
Dynamic response of long period structures to near fault motions (i.e., wave
propagation effects that may concentrate damage near the top or bottom of a
structure (or elsewhere) as waves start or reinforce one another).
Programming
•
Develop a program to carry out simple analysis of multiple degree of freedom shear
buildings (an extension of BiSpec)
•
Web-based Java (script) tools to implement various parts of course (like the attenuation
tool on the course web site)
•
Optimization
Seismic Isolation
CEE 227 – Term Project
7
1. Investigate the effects of various nonlinear models on the floor spectra observed in a
generic multi-story isolated building, subjected to a suite of acceleration records.
Possible nonlinear models include bilinear, Bouc-Wen, viscoplastic Kelvin-type model,
etc. Of interest would be the effect of changing parameters of these models on frequency
content of acceleration histories at different floor levels.
2. Complete the design of the building represented in the homework assignments using
nonlinear response history analysis, which is how virtually isolated buildings are
ultimately designed. Make this design for a specific isolation system, and select bearings
based on actual axial loads in the building. This involves the selection of a suite of
acceleration records compatible with a site-specific design spectrum.
3. Current building code provisions mandate the scaling of ground motions to 1.3 times the
design spectrum to account for bidirectional loading. This is likely quite conservative,
and of interest would be the development of an appropriate scaling factor based on a set
of recorded ground motions (i.e. what is the increase in peak isolator displacement when
bidirectional excitation is applied compared to unidirectional.)
4. The building code requires isolated buildings to be designed such that the bearings can
resist displacement resulting from a 2500-yr return period seismic event. This forces the
designer to use either a) stiff bearings, thereby reducing the isolation effect or b) large
amounts of hysteretic and/or viscous damping. These adversely effect the performance
in small and moderate seismic events. Investigate methods of achieving superior
performance under moderate levels of seismic excitation without having detrimental
performance of the isolation system in a very rare event.
5. Near fault effects have long been considered to be potentially detrimental to isolated
buildings, and probabilistic spectra for near fault sites estimate very large spectral
displacements in the long period range. Using a suite of near fault motions from the
PEER Strong Motion Catalog (http://peer.berkeley.edu/smcat) investigate the response
of a bilinear SDOF model of an isolated building.
6. Investigate the effect of variability in isolator properties on the response of the
superstructure. This could be from Monte Carlo Simulation
7. Perform a literature review of isolation devices with respect to velocity dependence.
Discuss potential nonlinear viscous models to capture this behavior.
8. Typically, isolation is recommended for relatively stiff, short period structures, and
isolator properties are selected so that the isolated period and fixed base period of the
system are well separated. This clearly is not necessary, and in Japan, there is
considerable isolation of tall buildings, where the fixed base period of the building is
longer than the effective period of the structure.
This form of isolation has many important advantages for tall buildings. Three 40 story
or more tall buildings are currently under design in California considering isolation.
Carry out a simplified (say SDOF per story) parametric study to investigate the behavior
of this type of system.
CEE 227 – Term Project
Passive Damping
1. Study the behavior of buildings equipped with linear vs. nonlinear viscous dampers.
Discuss potential benefits and drawbacks of each type of device.
2. Compare the performance of a building designed a) using steel moment frame with
linear viscous dampers and b) using steel buckling-restrained braced frames.
Specifically, look at the demand parameters of floor acceleration/spectra and peak
interstory drift.
3. Various hysteretic characteristics might be obtained for viscous dampers were Cd and
alpha depend on position and direction of the damper. For example, a damper that
makes it easier to return to the origin, and easy to initially move, but progressively
harder to move away from the origin (with a limiting force), may achieve a type of self
centering properties.
4. Viscous and hysteretic dampers are often placed in the outrigger or top cap frames
shown on page 4. What characteristics should these dampers have?
5. Some recent work has been done to design two adjacent buildings with viscous dampers
between the two, so that the relative velocity results in considerable damping. A study
on this could be quite interesting. For example, if the two buildings have identical
properties, the buildings may move in sych and there will be little supplemental
damping. Thus, there must be an optimal relation between the dynamic and mechanical
properties of the two coupled buildings.
Other dynamic loading
•
Blast-resistant design
•
Progressive collapse prevention (in Europe, this topic is now termed robust design)
•
Extreme wind storms
8
CEE 227 – Term Project
9
Recent CE 227 TERM PAPER TITLES
Subject
Impact of
nonstructural
elements
Redesign of Class
Homework Project
Building
Seismic Evaluation of
Specific Buildings
Seismic Response
Studies and Basic
Design Issues
Seismic Isolation and
Supplemental Energy
Dissipation
Seismic Hazard
Analysis
Blast, Progressive
Collapse, and Wind
Related Dynamic
Issues
Title
Reducing Nonstructural Earthquake Damage to Buildings
Homework Project Redesign (Complete confidence evaluation and
member selection for several alternative designs)
System Capacities According to Various Conditions [Pushover analyses
of 8 different redesigns considering two different computer programs]
Structural Recommendations for Design of Major Research Office
Building in High Seismic Region [13 different redesigns included]
Seismic Evaluation of the Unit Two Residence Halls
FEMA 310 Tier 1 Evaluation of UC Berkeley MLK Student Center
Union Building
Seismic Response Analysis of Sather Tower
Estimation of the Rocking Overturning of the Sather Tower
Seismic Performance Analysis and Design Verification of the EH&S
Hazardous Materials Facility
Seismic Stability of Japanese Wooden Pagodas
Mitigating Seismic Hazards in Developing Countries
Pinched Hysteresis Loops & Response Spectra
Use of Flag-Pole Shaped Hysteretic Loops to Reduce Residual
Displacements following Earthquakes
Effect of Vertical Ground Accelerations on Single Steel Moment Frames
with Varying Aspect Ratios
Improvements in Seismic Performance of Precast Segmental Bridges
[results in Flag-pole type hysteretic shapes]
Nonlinear Response of Various Offshore Jacket Platforms using Topcat
Analysis of a Three-Story Frame using Time History and Reliability
Methods
Seismic Performance Evaluation using Nonlinear Analyses of an Exterior
Frame of the Hearst Memorial Mining Building and a Three-Story Steel
Moment Frame
Base Condition Evaluation of the Berkeley Biotech Research Facility
Response of Base Isolated Bridges to Pulse Excitations
Supplemental Viscoelastic Damping in Light Frames: State of the
Technology and a Look at the Future
Passive Energy Dissipation Devices
Probabilistic Seismic Hazard Analysis
Probabilistic Seismic Hazard Analysis of 2754 Piedmont Avenue
Seismic Hazard Analysis Using a Probabilistic Approach
Blast Resistant Design
Mitigation of Blast Effects on a Building
A Comparison of Dynamic and Equivalent Static Analysis Procedures for
Typical Low- and High-rise Steel Moment Frame Buildings