GRIFFITH PARK

In the late 1800s, wealthy landowner and bachelor Don Antonio Feliz contracted a deadly case of smallpox. When his niece Petranilla discovered she was left out of the will, rumor has it she put a curse on the land her family had owned for generations. All subsequent owners have met untimely deaths or misfortune, including Griffith J. Griffith, who sold the land to the City before going to prison for shooting his wife. The ghost of Petranilla is said to haunt the Feliz Adobe at Crystal Springs, staring out the window at night.

KPFF LA holds our annual summer party at Crystal Springs. While we have yet to encounter Petranilla, a Pokemon piñata did suffer an untimely demise this year. Additionally, KPFF LA has provided civil engineering services to the LA Zoo, located in the heart of Griffith Park.

HOLLYWOOD ROOSEVELT HOTEL

KPFF LA provided structural engineering services for the existing stair #6 and lowered landing demolition, a new raised stair and landing connected to the Upper Ground Floor level. We hope the ghost of Marilyn Monroe appreciates this new staircase to help her revisit her old stomping grounds.

COLORADO STREET BRIDGE

The hauntingly beautiful Colorado Street Bridge in Pasadena was completed in 1913, claimed its first life in 1919, and has been the backdrop to a string of untimely deaths ever since. KPFF LA provided peer review services for the structural support and anchorage of a proposed new perimeter iron fence to increase bridge safety.

Additionally, we have been a trusted advisor to the City for years, including serving as the on-call structural engineer since 2018. As part of our on-call contract, KPFF provided a structural engineering evaluation of the Pasadena Central Library, an Unreinforced Masonry (URM) building initially constructed in 1925. URM buildings are known to be collapse prone during earthquakes, requiring seismic strengthening to meet life safety standards. The City plans to rehabilitate and retrofit the Library so the historic building can safely reopen in time for its centennial celebration.

ELSEWHERE IN TOWN

We’ve also helped build some other scary haunts in town, but we’ve been sworn to secrecy for those, so we’ll take those details to our graves.

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The age of the construction inherently presents a lateral resisting system (consisting of perimeter concrete walls at the basement and concrete frames above grade) that lacks adequate detailing for a ductile seismic response. Preliminary retrofit schemes, developed by another firm, incorporated conventional strengthening approaches, including the addition of exterior braced frames or moment frames. The initial project scope as envisioned by UCLA was the selection and implementation of one of the preliminary schemes. Recognizing that such a retrofit would have significantly impacted the architectural nature of the building, as well as presenting significant cost, construction duration, and disruption to ongoing research within the building, the project team explored potential retrofit alternatives that would work in concert with the existing architecture and alleviate negative impacts.

The prominent façade consists of tightly spaced, uniquely profiled concrete beams and columns that support the gravity load from the exterior structural bays. The primary deficiency identified in prior seismic evaluations was an apparent shear failure at the beam/column joints, colloquially referred to as the “fin column” and “ledge beam” system, initiating at extremely low drift ratios on the order of 0.1% to 0.25%. Recognizing that this conclusion was based on existing ASCE 41-13 component models that were developed for conventional concrete frames with larger dimensions and spans than those occurring in this building, we hypothesized that the inherent redundancy from the numerous columns and the potential for load sharing between the ledge beams and the interior waffle slab floor system would significantly enhance the ductility of the system, and accommodate drift ratios on the order of 1% or more at the collapse prevention performance objective. As the specific details could not be precisely modeled with existing ASCE 41 guidelines, and a literature search did not reveal any prior research into similar structural systems, our team identified the “knowledge gap” between the analytical models and the intuition, and conceived of a component testing program to test this hypothesis and develop a better model of the seismic response of the façade structural system, thereby bridging the knowledge gap and supporting the development of a more elegant seismic retrofit solution.

The component testing program was developed in collaboration with Dr. John Wallace at UCLA, and consisted of the construction and testing of 2/3 scale component models to explicitly determine the deformation capacity of the façade structure. The specimen was designed by Dr. Wallace, and PhD Candidate Ellie Moore with the UCLA Civil and Environmental Engineering Structural Design and Testing Laboratory, and constructed by PCL Construction’s Special Projects Group. The test specimen was based on a location at the base of the tower where fixity imposed by the large transfer girder resulted in the highest deformation demands on the system. The final test specimen included five columns, extended vertically for one and a half stories and included one-half of an interior floor framing bay. Inclusion of the interior bay was critical to impose the appropriate rotational restraint on the columns for out-of-plane deformations, and to simulate the load sharing between the ledge beams and the waffle slab gravity framing. Gravity and overturning axial demands were applied to the columns by a system of actuators while biaxial lateral deformations were imposed on the specimen. A figure-eight displacement pattern was utilized, with increasing displacement amplitudes applied on each cycle. The tests were conceived to be conducted until a loss in axial capacity was realized in the columns, however the tests were eventually limited by the lateral displacement limitations of the actuators and no loss of vertical capacity was observed in the testing.

Upon completion of the testing program, the instrument data was used to develop hysteresis loops that were further distilled into a backbone curves for the façade components. The resulting data successfully bridged the “knowledge gap” by showing a nearly tenfold increase in allowable deformation at the Life- Safety and Collapse-Prevention performance objectives. Preliminary 3-dimensional nonlinear analytical models were refined through incorporation of the experimentally derived backbone curves. Analysis was performed with Perform3D software using the nonlinear dynamic procedure in ASCE 41-.-13. GeoPentech conducted a site-specific seismic hazard analysis to obtain seven pairs of ground motion records representing a uniform hazard spectra for 225 year (20% in 50 years), 475 year (10% in 50 years), 975 year (5% in 50 years), and 2475 year (2% in 50 years) return-period earthquakes.

The nonlinear analysis demonstrated that the addition of supplemental damping was an effective means to reduce interstory drift to the order of 1% to 2% at the 475 year and 2475 year return-period earthquakes representing the BSE-1N and BSE-2N hazard levels. As these drift levels were comfortably under the Life Safety and Collapse Prevention limits derived from the experimental results, the retrofit objective was set at achieving a SPL III rating under the UC Seismic Safety Policy through the introduction of supplemental damping. Analysis also demonstrated that a limited number of interior columns required the addition of confining FRP wraps to meet the required ductility demands.

The damping system developed for the project utilized fluid viscous damper devices installed in-line with steel drivers placed on primary grids between beam and column joints. Analysis demonstrated that the addition of four damper devices per floor from grade to Level 6 effectively limited the building drifts sufficiently to meet the SPL III rating objective. At the lower levels, dampers were implemented in discrete locations at the building perimeter, while dampers on the upper stories were located on interior grid lines and incorporated into a full interior remodel designed by CO Architects. Meticulous attention was given to details that subtly reveal the presence of the dampers while seamlessly integrated into the building architecture. Most notably, the exterior braces were connected to the structure using a discrete, bespoke picture frame gusset plate conceived by CO Architects, demonstrating their high level of attention to design details. The remodel also included opening the original lobby into a two-story space by removing a portion of the mezzanine level. The overall retrofit scheme was designed to minimize the impact on the exterior and historical aspects of the building, and preserving maximum usable space in the interior.

Our collaboration with Rudolph and Sletten, the general contractor, included an early procurement package for the viscous damping devices, which were manufactured by Taylor Devices. The project team understood that the lead time for the dampers, estimated at six months, was a critical path that needed to be addressed as soon as the testing phase was complete. Additionally, the retrofit scheme minimized the number of attachment points to the structure in order to reduce vibrations that could disrupt ongoing research within the basement levels which would remain occupied. Extensive preconstruction investigations helped ensure that unforeseen conditions were minimized and the high level of attention on detailing and the commitment from all of the team members to deliver a great final product resulted in smooth construction and installation.

The preservation of this architectural gem is inherently the most sustainable outcome for the UCLA campus. The ability to continue using an existing building significantly reduces the use of new materials, waste from demolition, and develops a sense of place for the students on campus. The retrofit scheme required only 20 new bracing elements which minimized the introduction of new materials and the carbon emissions associated with the manufacture and transport of major structural elements, and particularly with the introduction of new concrete. In addition to preserving a part of the campus culture, the cost savings and construction schedule improvements demonstrate that this retrofit scheme successfully integrated new research, nonlinear analysis and viscous damping technologies to provide another 50 years of service for this campus landmark.

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The building architecture lent itself to a unique retrofit solution that included advanced analysis and laboratory testing to prove out a concept using viscous fluid dampers. The long spans and large open bays on the first floor gave our engineering team the opportunity to seek alternative retrofit methods including installing discrete viscous damping elements to lessen the seismic demands transmitted up to the non-ductile columns making up the façade above. Traditionally retrofits include column and beam strengthening as well as new connections between floors and walls that overlay on top of existing structural elements. These methods are costly, time consuming and often change the character of a building. With the fluid viscous dampers, KPFF was able to minimize the impact on the architectural intent as well as drastically reducing the construction cost and schedule.

To prove the retrofit concept, KPFF worked with the engineering department at UCLA itself to conduct component testing in a laboratory setting. The research team recreated key portions of the existing structure within the lab where key structural components were subjected to simulated seismic loading experiments. The testing allowed the engineering team to gain better insights to how the building reacts to seismic loading in as-built conditions.

The nonlinear dynamic procedure in ASCE 41 was used to determine the code requirements for this retrofit. Using parametric studies, the engineering team used the information gleaned from component testing as well as ground motion reports to optimize the supplemental damping system. The critical building behavior occurred in the non-ductile concrete columns above the 3rd floor, and therefore the retrofit was tailored to modulate the seismic actions on these elements so they remained safely within the limits determined by the testing program.

The minimally invasive retrofit will leave the architectural integrity of Franz Hall intact, while allowing our partners, CO Architects, the opportunity to upgrade and refresh the building with thoughtfully designed interiors reflecting the needs of today’s students and faculty. The first phase of construction currently underway includes outfitting the viscous dampers on the upper floors of the building. The second phase of construction will include additional viscous dampers on the first floor as well as the renovation of the interior of the tower.

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