Download Design and Construction of a Full-scale 5

Design and Construction of a Full-scale 5-story Base Isolated Building outfitted
with Nonstructural Components for Earthquake Testing at the UCSD-NEES
Facility
Chen, M.1, Pantoli, E.1, Wang, X.1, Espino, E.2, Mintz, S.1, Conte, J.1, Hutchinson,
T.1, Marin, C.3, Meacham, B.4, Restrepo, J.1, Walsh, K.2, Englekirk, R.5, Faghihi, M.5,
and Hoehler, M.6
1
Department of Structural Engineering, University of California, San Diego, 9500
Gilman Drive, Mail Code 0085, La Jolla, CA 92093; email:
{mcchen,epantoli,xiw002,sjmintz,jpconte,tara,jrestrepo}@ucsd.edu.
2
Department of Civil, Construction, and Environmental Engineering, San Diego
State University, 5500 Campanile Dr., San Diego, CA 92182; email:
[email protected], [email protected]
3
Department of Civil Engineering, Howard University, 2300 Sixth Street, NW
Washington, DC 20059; email: [email protected]
4
Department of Fire Protection Engineering, Worcester Polytechnic Institute, 110
Institute Road, Worcester, MA 01609; email: [email protected]
5
Englekirk Structural Engineers, 2116 Arlington Avenue, Los Angeles, CA 90018;
email: {robert.englekirk, mahmoud.faghihi}@englekirk.com
6
Hilti Corporation, Corporate Research and Technology, Feldkircherstrasse 100,
Schaan, 9494, Liechtenstein; email: [email protected]
Abstract
This project involves earthquake and post-earthquake fire testing of a fullscale five-story building furnished with nonstructural components and systems
(NCSs). A broad array of NCSs are incorporated in the test building, including a
functioning passenger elevator, stairs, exterior walls, interior partition walls, piping,
HVAC, ceiling, sprinklers, building contents, as well as passive and active fire
systems. The NEES-UCSD outdoor shake table facility is utilized to support this fullscale testing program. In this paper, the design and construction of the test building
and its NCSs are summarized. Testing is projected for March 2012, and pending this
progression, preliminary data may be presented at the conference. Data obtained from
this program will be used to evaluate and refine current code assumptions and
computer models regarding nonstructural components and systems, and to find ways
to minimize undesirable damage to NCSs during an earthquake.
Introduction
Seismic damage induced on nonstructural components and systems (NCSs)
continues to plague society, leading to undesirable consequences including excessive
economic losses, downtime, and harm to humans. For example, the 2010 Baja
California earthquake resulted in four fatalities and 100 injuries mostly from falling
nonstructural components in buildings (Hutchinson et al., 2010). Observed NCS
damage included collapsed parapets, damage to glazing, cracked walls, fallen soffits,
failure of unreinforced masonry walls, and partial collapse of roofs. Damage
extended to schools in the U.S., and included damage to doors, fallen bookshelves,
light fixtures and ceilings, some remaining out of service for months with costly
repairs. Likewise, the 2010 Chile earthquake imposed significant nonstructural
damage to all types of buildings (Moehle et al., 2010). The closure of airports due to
nonstructural damage cost the airline $25 million in downtime, while 62% of the
hospitals in the affected regions of Chile suffered from nonstructural damage, causing
most of the hospitals’ economic losses, evacuations, and closures.
Regardless of the continued evidence of their vulnerability, to date, only a
handful of building-NCS system level experiments have been conducted. This has
been largely due to cost and scale limitations (limited funds to support such extensive
full-scale tests, and limited availability of facilities to support adequately sized test
structures). With NCSs encompassing around 80% of the total investment in building
construction (Miranda and Taghavi, 2003), and with the majority of earthquakeinduced direct losses in buildings attributed to NCS damage, it is important to
complement our existing experimental database with full-scale integrated tests. By
conducting an integrated (building-NCS) test, inertial forces and deformations
generated by the earthquake motion to the building will be transferred to the attached
and unattached NCSs. Amplified forces generated by the dynamic response of the
building can be detrimental to the NCSs, even at levels that do not damage the
structure itself.
To address the shortcomings in knowledge, to-date several full-scale buildings
have been tested at the E-Defense shake table in Japan and the NEES@UCSD shake
table in the United States. In a few of these, NCSs were implemented, however, the
inventory and scope of the NCS was secondary to other objectives of the test
program. For example, a full-scale four-story steel building tested at E-Defense
included lightweight concrete external cladding panels, aluminum sash, glass
windows, gypsum board partition walls, a hanging ceiling system and more
(Matsuoka et al., 2008). In addition, a full-scale five-story steel moment frame
building tested at E-Defense was outfitted with interior walls, ceilings, piping, and
concrete cladding panels. This test focused on displaying the effectiveness of using
friction pendulum isolators to protect the structure and its contents during extreme
ground shaking (Dao et al., 2011). Another full-scale test performed at E-Defense
included the testing of a four-story base isolated RC hospital building. Nonstructural
components, including a variety of furniture, medical appliances and service utilities,
representing typical hospital layouts were placed in this structure. The purpose of this
test was to demonstrate the effectiveness of protecting medical facilities using base
isolators (Sato et al. 2011). The seven-story RC building tested at the NEES@UCSD
facility incorporated a suspended pipe system and evaluated the forces transferred to
the system’s anchorage during seismic motions (Hoehler et al. 2009). In conventional
nonstructural test setups, the components are either tested individually or in
subsystems, and are mounted directly to the shake table and subjected to anticipated
floor accelerations and deformations (e.g. Mosqueda et al. 2009).
Scope of this Work
This landmark project involves the testing of a full-scale five-story building
subjected to a range of earthquake motions. By constructing a full-scale building, a
broad variety of NCSs, which would commonly be installed to support the services
and occupancies of a building, are implemented into the structure. With the full-scale
and integrative nature of the project, the outcome is a unique investigation of the
interaction between the structural and nonstructural components in realistic seismic
conditions. The testing sequence will consist of first isolating the building, subjecting
the structure to a series of serviceability-level earthquake motions, then jacking the
entire building up and removing the isolators. The test program will continue by
lowering the building and post-tensioning the foundation down to the table to support
seismic testing in a fixed base configuration.
Testing is conducted at the NEES site at the University of California, San
Diego (Figure 1). This site provides the opportunity to construct tall, full-scale
structures due to its outdoor nature. The outdoor shake table is the first and largest in
the United States and can impose a lateral acceleration of 4.2g with no load. A fullscale testing site is essential for capturing responses that cannot be captured with a
smaller scale.
(a)
(b)
Figure 1. (a) View of NEES site @ UCSD and (b) shake table specifications
(NEES@UCSD, 2011)
By achieving a better understanding of the total building systems performance
during an earthquake, data obtained in this test can be used to evaluate nonlinear
simulation tools and current code assumptions regarding nonstructural components
and systems, as well as develop a more precise and specific set of performance
objectives that cater to the clients’ exact needs. There is a strong need to evaluate and
refine current design limit states for different performance objectives. By monitoring
the performance of the NCSs during a series of ground motions, we will obtain the
needed data to accomplish these goals. This paper will present an overview of the
building design and construction, and a description of nonstructural components and
systems.
Building Design
The building is designed assuming a high seismic zone in Southern California,
namely downtown Los Angeles, with site class D soil conditions corresponding to
“stiff soil.” Using global and system level performance criteria, seven MCE ground
motions and three serviceability motions based on the site criteria are spectrally
matched and chosen for the design of the fixed base structure. The building is
designed based on a performance target of around 2.5% maximum lateral interstory
drift ratio with a maximum peak floor acceleration of around 0.7g-0.8g. Figure 2a
shows the spectral acceleration graph for the seven MCE ground motions used for
design of the structure, however the building will be tested for only one of the MCE
motions. Figure 2b shows the acceleration time history for the Denali motion, which
is preliminarily selected in the test program as the maximum motion due to its long
duration of strong shaking and broad spectral characteristics.
(a)
(b)
Figure 2. Elastic 5% damped spectral acceleration of the seven MCE level
design motions.
The cast-in-place reinforced concrete test building has a plan dimension of
21.5 feet by 36 feet and is composed of two bays in the shaking direction and one in
the non-shaking direction (Figure 3). The floor-floor height is 14 feet with a total
height of the bare structure being 75 feet above the shake table (~88’ including the
roof mounted equipment). A pair of moment resisting frames is incorporated on the
longitudinal ends of the building. The moment resisting beams are designed with
equivalent moment capacities, however different types of detailing are used at
different levels. Floors two and three have high strength steel (MMFX) frame beams,
with a yield strength of 120ksi. Floor four has an upturned hybrid SMF beam with
four post-tensioned tendons and Dywidag ductile rod connectors. The fifth floor has a
Dywidag Ductile Connector (DDC) frame beam, which utilizes ductile rod
connectors. Details adopted on levels one through five articulated stable ductile
performance in previous test programs (Warcholik and Priestley, 1998a,b; Chang et
al., 2009) and have since observed use in practice. Lastly, the roof level, which
expects the lowest forces, is detailed using current special moment resisting frame
detailing of ACI. Strain gauges are placed on select beam ends where the highest
strains are expected. An 8” thick cast-in-place slab provides the floor support at each
level. The columns are detailed with a prefabricated hoop and transverse
reinforcement grid. Using this technique, time is saved in assembling the column
cages.
Openings of 7’-8”x13’-9¼” and 6’-11”x8’-8” are provided in the floor
diaphragm to accommodate full-height stairs and an elevator, respectively. Nominal
(4”-10” diameter) penetrations for building services (plumbing, fire sprinklers, etc.)
are also provided. A 6” thick concrete wall is constructed on either side of the
elevator opening running transversely to provide gravity support for the elevator
guiderails and torsional stability during the seismic tests (Figure 3b).
(a)
(b)
Figure 3. Schematic overview of (a) building elevation and (b) plan view.
The foundation is designed with a unique solution using a combination of
post-tensioned rods and tendons (Figure 4). The foundation is designed to remain
elastic such that its dynamic behavior does not affect the performance of the
nonstructural components and systems. A rigid foundation is also important for being
able to make direct comparisons between the base-isolated and fixed-base conditions.
Figure 4. Reinforcement details of the longitudinal foundation beams.
Construction
Construction commenced in early May 2011 with the foundation formwork.
Temporary rigid steel tubes were used below the building for its support during
construction in lieu of the rubber isolators. Following placement of foundation
formwork, tendons, rods, reinforcement, and the temporary support blocks, one
hundred cubic yards of foundation concrete were poured. A shoring system was then
assembled and reinforcing steel placed at each floor at a rate of approximately two
weeks per floor between concrete placements. Each floor’s concrete pour was divided
into three days, the first day being the slab pour, the second including the two
elevator walls and interior columns, and the third including the four corner columns.
Concrete pours were divided due to the physical characteristics of the formwork and
the layout of the structural elements. Figure 5 shows images of construction of the
building at various stages.
(a)
(b)
(c)
Figure 5. Photographs of test building during construction (a) foundation beams
and level 1 columns, (b) level 3 deck, and (c) level 5 deck.
The general contractor used one floor of shoring, and two floors of reshores
immediately below. Once concrete reached five-day strength, the reshores were
removed and placed on the active slab above to begin the next level’s shoring. This
process was supported with an onsite mobile crane, used for both jumping the
scaffolds and concrete placement via a bucket. The scaffolding system used for the
project was a floating system. The scaffolding was attached to the columns, and was
lifted up with a crane as a unit as the construction progressed (Figure 6). The bare
structure was completed on September 23, 2011. System identification using white
noise tests conducted on the bare structure indicate the first and second modes of the
bare structure were longitudinal and transverse with values of 0.57 and 0.53 seconds
and 4.08% and 1.04% damping, respectively.
(a)
(b)
Figure 6. Photographs of the construction process: (a) floating scaffolding and
(b) moving scaffolding system to next level.
Nonstructural Components and Systems
Each level of the building is designated with a different occupancy and as
such is outfitted with different types of nonstructural components and systems. The
first floor is considered the utility floor and also has several systems that represent
typical “East Coast” construction practices. The second floor has both a home office
and a laboratory environment area. Some nonstructural components on this level are
anchored whereas others are unanchored for comparison. The third floor has a server
room layout (Figure 7a). Sensitive electronic equipment is often damaged or nonfunctional after a major quake and the explicit focus of this floor is to investigate the
performance of computer equipment in such a setting. Since essential facilities such
as hospitals have a critical need to be operational after an earthquake, levels four and
five are designated as hospital floors. The fourth floor represents an intensive care
unit (ICU) layout and the fifth floor represents a surgery suite. The ICU and surgery
suite are outfitted with large medical equipment typical to those rooms. The reason
for having different architectural floor plans on each floor was to observe the
behavior of nonstructural components and systems during ground motions in a wide
variety of occupancy scenarios and to take advantage of the space available.
The installation processes, design processes, materials, anchorage, and other
features of the nonstructural components are as close to actual field conditions as
possible. If a variety of materials or attachments are used in practice, the most
common are adopted, with some compliant with current code and others not.
Different materials or products are used in some cases to facilitate comparison
between different options used in practice. Industry partners designing the NCSs,
including anchorage, were each given a nonstructural design guide, with loads and
deformation distributions determined by the authors based on numerical simulations
of the test building’s response. This supports consistent design amongst the product
suppliers, while allowing for a more realistic design demand than might otherwise be
obtained with the building design code.
Mechanical-Electrical-Plumbing (MEP) Subsystems
A partial mechanical-electrical-plumbing subsystem is installed in the
building. Examples of the MEP subsystems include plumbing to support storm drain
services, an electrical distribution system to support operation of the medical
equipment, elevator, and lighting to name a few, and select levels of mechanical
ducting to mimic components installed in a functioning HVAC system. The plumbing
scope includes a 3” no-hub cast iron pipe that extends from a storm drain on the roof
to the first level. Extending from 1’ below the second floor ceiling to 1’ above the
fourth floor slab is a 4” steel pipe and a 1 ½” copper pipe. The location for these
pipes was chosen such that they extended through the floors that expected the
maximum interstory drifts. Similar strategies for the mechanical and electrical
systems are implemented (Figure 7b). The electrical scope includes outlets at
different locations on every level corresponding to the placement of equipment in
need of a power supply. In addition, fire sprinklers are installed at all levels of the
building.
(a)
(b)
Figure 7. Level 3 floor plans: (a) architectural floor plan with IT server
occupancy and burn floor and (b) MEP plan.
Largest NCSs
The largest NCSs installed in the test building include: (1) a functioning
passenger elevator, (2) prefabricated metal stairs, (3) ceiling subsystems, (4) two
pieces of roof mounted equipment and a penthouse, (5) three levels of balloon framed
metal studs overlaid with an exterior insulation finishing system (EIFS) and (6) two
levels of precast concrete cladding.
The full-scale, fully functional elevator has a 3500-pound capacity, travels all
five floors of the building for a total of 56’ in distance (Figure 8a). Its design is
compact, with no need for a mechanical penthouse as the controller is integrated with
the cab. The type of elevator installed has yet to be exposed to the seismically active
regions in the U.S. (its only market is in Europe). An elevator is an essential
component in hospitals and other emergency facilities, so it is important to
understand the exact performance of it and how it interacts with the rest of the
structure during a strong ground motion in order to find better methods to protect it
and ensure usability after a major quake. Typical seismic damage to an elevator
includes guide rail anchorage damage, bent guide rails, counterweight derailment, a
jumped or twisted rope, the collision between the counterweight and car, etc.
Likewise, the prefabricated metal stairs are installed to support access to all floors
including the roof (Figure 8b). It is also essential that stairs remain operational after a
large earthquake in any building. Damage to the stairs during an earthquake could
potentially prevent evacuation and immediate operation. The stair system installed in
the test building was previously tested by Higgins (2009) at full-scale using a onelevel configuration with hydraulic actuators at the ends.
(a)
(b)
Figure 8. NCSs providing building floor-floor access: (a) elevator rendering and
(b) photograph of the prefabricated metal stairs in the test building.
Different ceiling types including a “typical East Coast” design, code
compliant design for seismic design categories D, E & F, designs per Seismic RX
recommendations, a California Department of State Architect (DSA) drywall system,
typical Office of Statewide Health Planning and Development (OSHPD) approved
ceiling design for hospitals, and a new ceiling design are implemented on different
levels of the building.
The rooftop equipment consists of a stair penthouse, an air handling unit, and
a roof mounted cooling tower (Figure 9a, 10). The air handling unit is directly
mounted to the southwest corner of the roof using a typical anchorage design. The
cooling tower is located at the northeast corner of the roof, and sits on a steel frame
supported by vibration isolators. The isolators are bolted directly to four load cells,
which are mounted to the roof slab and measure forces in five degrees of freedom.
There are two types of exterior finishes on the building (Figure 9b, 10).
Levels one through three incorporate a metal stud balloon framing system, while
level four and five utilize a precast concrete panel system. The balloon framing
system consists of continuous metal studs extending through three levels, with king
studs framing the openings. The metal studs are connected with a clip connection for
lateral support at each floor level. The first level has openings that are governed by
the need to post tension the vertical rods connecting the foundation to the shake table
for the fixed base testing condition.
(a)
(b)
Figure 9. Photographs of (a) roof mounted NCSs and (b) installation of level 1-3
balloon framing at exterior.
The exterior cladding on the fourth and fifth floors consists of eight precast
concrete panels configured in a punch-out window floor-floor configuration. Steel
embeds supporting connection of these panels to the structure were cast with the slab,
columns and beams as would be conventionally done in practice. By using eight
panels per floor, different types of connection configurations are utilized for
comparative purposes. The system is designed to withstand an ultimate interstory
drift of 3.5%. Push-pull connections are used to allow the panels to move with the
structure, while bearing connections are utilized to support the panels at the deck
level.
(a)
(b)
Figure 10. 3D rendering of structure (a) view from northeast corner and (b) view
from southwest corner.
Instrumentation
Approximately 500 accelerometer, displacement, and strain sensors are
planned for deployment on the structure, the majority of these are dedicated to
measuring the response of the NCSs. Accelerometers are used to monitor the
behavior of the structure, including the displacement, velocity and acceleration time
history in three different directions and at every floor level. In addition, a GPS system
will be implemented, and this data will be compared with the displacements found
from the double-integration of the acceleration reading recorded by the
accelerometers. Displacement potentiometers will be placed on the structure to
measure the plastic hinge rotations, the shear deformation of the joints, and
elongations in the slab and beams. Relative motion between the structural and
nonstructural components will be captured using the analog sensors. Both the
structure and the NCSs will be monitored with an array of nearly 70 digital cameras.
Test Protocol
The building will first be tested in the base isolated configuration and
subjected to three near-serviceability level motions, two of which will be repeated
when the building is fixed to its base. White noise testing will be conducted before
and after each motion to characterize the state of the structure and the nonstructural
systems. The building will then be tested in the fixed base condition using
serviceability and a scaled MCE level motion. The scaled MCE motion will be
implemented at the end of testing and correspond to a performance target of
approximately 2-2.5% interstory drift. Following seismic shaking, local burn (fire)
tests will be conducted on designated areas of the third floor (Figure 7a). The areas
where this will occur are sealed off with typical code-compliant fireproofing prior to
the shake testing. After the earthquake simulations, controlled smoke will be released
in the places of interest, and the propagation of the smoke through any damaged
portions of the building will be monitored and recorded.
Concluding Remarks
A full scale, five-story cast-in-place reinforced concrete test building has been
constructed on the largest outdoor shake table in the United States. Unique to prior
test programs, it is fully outfitted with a wide variety of typical nonstructural
components and systems that represent different occupancy/risk categories. The
building will be shake table tested in two different configurations: first with base
isolators and then with a fixed base. After shake table testing is completed, burn tests
will be conducted in the structure, to observe the propagation of smoke through a
seismically damaged building, representing the very dangerous probable threat of
post-earthquake fires. This project will lead to breakthrough advances in the
understanding of the complete structural and nonstructural responses during
earthquakes and post-earthquake fires.
Acknowledgements
This project is a collaboration between four academic institutions (University
of California, San Diego, San Diego State University, Howard University, and
Worcester Polytechnic Institute), four government or granting agencies (the National
Science Foundation, the Englekirk Advisory Board, the Charles Pankow Foundation,
and the California Seismic Safety Commission), over 30 industry partners, and two
oversight committees. A listing of industry project sponsors may be found on the
project website: http://bncs.ucsd.edu/index.html. Through the NSF-NEESR program,
funding is provided by grant number CMMI-0936505, where Dr. Joy Pauschke is the
program manager. The above continuous support is gratefully acknowledged. In
addition, the technical support of NEES@UCSD staff, and consulting contributions
from Robert Bachman, chair of the project's Engineering Regulatory Committee, are
greatly appreciated. Opinions and findings of this study are of the authors and do not
necessarily reflect those of the sponsors.
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