skip to main content

Title: Probabilistic Assessment of Footfall Vibration
As one of the serviceability limit states of structural design, excessive vibration has attracted more attention in recent years, with the design trend moving toward lighter and more slender structures. Footfall vibration contains high uncertainties in nature, with significant variations in walker weight, walking speeds, and dynamic load factor. Since conservative designs can often lead to significant cost premiums, this study focuses on the stochastic assessment of footfall vibration of on a composite steel floor to better understand the variation in performance of various design factors and better inform the ultimate decision-makers. To close the knowledge gap between academia and industry in this area, San Francisco State University and the University of South Carolina partnered with Arup through an NSF-funded Research Experience for Undergraduates (REU) program. A composite steel structure was modeled to resemble a typical office bay. The model was developed and analyzed in Oasys GSA. Monte Carlo simulation was used to quantify the probability of exceeding certain common vibration criteria. The results of this study would provide actionable guidance to stakeholders to weigh the benefits and costs between performance targets.  more » « less
Award ID(s):
Author(s) / Creator(s):
; ; ; ; ; ;
Date Published:
Journal Name:
IMAC-XL Conference and Exposition on Structural Dynamics
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. To advance understanding of the multihazard performance of midrise cold-formed steel (CFS) construction, a unique multidisciplinary experimental program was conducted on the Large High-Performance Outdoor Shake Table (LHPOST) at the University of California, San Diego (UCSD). The centerpiece of this project involved earthquake and live fire testing of a full-scale 6-story CFS wall braced building. Initially, the building was subjected to seven earthquake tests of increasing motion intensity, sequentially targeting service, design, and maximum credible earthquake (MCE) demands. Subsequently, live fire tests were conducted on the earthquake-damaged building at two select floors. Finally, for the first time, the test building was subjected to two postfire earthquake tests, including a low-amplitude aftershock and an extreme near-fault target MCE-scaled motion. In addition, low-amplitude white noise and ambient vibration data were collected during construction and seismic testing phases to support identification of the dynamic state of the building system. This paper offers an overview of this unique multihazard test program and presents the system-level structural responses and physical damage features of the test building throughout the earthquake-fire-earthquake test phases, whereas the component-level seismic behavior of the shear walls and seismic design implications of CFS-framed building systems are discussed in a companion paper. 
    more » « less
  2. This research investigated experimentally the seismic performance of steel gravity framing with a concrete slab at the system level. Two half-story, two-by-three bay steel gravity frame specimens were tested under cyclic loading. Bolted-bolted double-angle connections were used for a beam-to-column gravity connection. Primary design variables and construction details include the orientation of the metal deck to the loading direction, the presence or absence of metal deck seams on secondary beams, and the contribution of additional reinforcement bars in the concrete slab. Concrete blocks were positioned at the midpoint of each bay to simulate gravity loads, and a quasi-static displacement-controlled cyclic loading protocol was applied to the specimen using three hydraulic actuators. These investigations confirmed general observations from previous subassembly testing programs that the composite steel gravity framing system can provide substantial flexural stiffness, strength, and ductility under cyclic loading. Further, the test findings showed that the primary design variables and construction details significantly affected the cyclic behavior of composite gravity connections. Comparing the test results from a multi-bay setup and a subassembly testing setup, the cyclic behavior showed remarkable differences, especially for cases with weak axis decking or strong axis decking with a seam. These large differences are attributed to a significant separation of the girder from the column in the subassembly testing setup, which may not be present in a real building. Virtually all previous cyclic loading tests on gravity connections have been conducted in subassembly test setups. These subassembly tests are therefore the basis for the models that are currently used to include gravity frame connections in the seismic performance assessment of buildings, and these models may be quite inaccurate in some cases. The data generated in this system-level testing program is intended to support efforts to develop improved models of gravity connections subject to seismic loading. 
    more » « less
  3. More than 1.6 billion people worldwide live in informally constructed houses, many of which are reinforced with concrete. Patterns of past earthquake damage suggest that these homes have significant seismic vulnerabilities, endangering their occupants. The characteristics of these houses vary widely with local building practices. In addition, these vulnerabilities are potentially exacerbated by incremental construction practices and building practices that address wind/flood risk in multi-hazard environments. Yet, despite the ubiquity of this type of construction, there have not been efforts to systematically assess the seismic risks to support risk-reducing design and construction strategies. In this study, we developed a method to assess the seismic collapse capacity of informally constructed housing that accounts for local building practices and materials, quantifying the effect of building characteristics on collapse risk. We exercise the method to assess seismic performance of housing in the US. Caribbean Island of Puerto Rico, which has high seismic hazard and experiences frequent hurricanes. This analysis showed that heavy construction, often due to the addition of a second story, and the presence of an open ground story leads to a high collapse risk. Severely corroded steel bars could also worsen performance. Although houses with infill performed better than those with an open ground story, confined masonry construction techniques produced a major reduction in collapse risk when compared to infilled or open-frame construction. Infill construction with partial height walls performed very poorly. Well-built reinforced concrete column jackets and the addition of infill in open first-story bays can reduce the greater risks of open-ground-story houses. These findings, which are quantified in the results portion of this article, are intended to support the development of design and construction recommendations for safer housing.

    more » « less
  4. This article highlights the absence of published paradigms hybridized by The Cuckoo Search (CS) and Stochastic Paint Optimizer (SPO) for optimizing truss structures using composite materials under natural frequency constraints. The article proposes a novel optimization algorithm called CSSPO for optimizing truss structures made of composite materials, known as fiber-reinforced polymer (FRP) composites, to address this gap. Optimization problems of truss structures under frequency constraints are recognized as challenging due to their non-linear and non-convex search spaces that contain numerous local optima. The proposed methodology produces high-quality optimal solutions with less computational effort than the original methods. The aim of this work is to compare the performance of carbon FRP (CFRP), glass FRP (GFRP), and steel using a novel hybrid algorithm to provide valuable insights and inform decision-making processes in material selection and design. Four benchmark structure trusses with natural frequency constraints were utilized to demonstrate the efficiency and robustness of the CSSPO. The numerical analysis findings indicate that the CSSPO outperforms the classical SPO and exhibits comparable or superior performance when compared to the SPO. The study highlights that implementing CFRP and GFRP composites in truss construction leads to a notable reduction in weight compared to using steel. 
    more » « less
  5. An eight-element oil-filled hydrophone array is used to measure the acoustic field in littoral waters. This prototype array was deployed during an experiment between Jeffrey’s Ledge and the Stellwagen Bank region off the coast of Rockport, Massachusetts USA. During the experiment, several humpback whale vocalizations, distant ship tonals and high frequency conventional echosounder pings were recorded. Visual confirmation of humpback moving in bearing relative to the array verifies the directional sensing from array beamforming. During deployment, the array is towed at speeds varying from 4-7 kts in water depths of roughly 100 m with conditions at sea state 2 to 3. This array system consists of a portable winch with array, tow cable and 3 water-resistant boxes housing electronics. This system is deployed and operated by 2 crew members onboard a 13 m commercial fishing vessel during the experiment. Non-acoustic sensor (NAS) information is obtained to provide depth, temperature, and heading data using commercial off the shelf (COTS) components utilizing RS485/232 data communications. Acoustic data sampling was performed at 8 kHz, 30 kHz and 100 kHz with near real-time processing of data and enhanced Signal to Noise Ratio (SNR) from beamforming. The electrical system components are deployed with 3 stacked electronics boxes housing power, data acquisition and data processing components in water resistant compartments. A laptop computer with 8 TB of external storage and an independent Global Positioning System (GPS) antenna is used to run Passive Ocean Acoustic Waveguide Remote Sensing (POAWRS) software providing beamformed spectrogram data and live NAS data with capability of capturing several days of data. The acquisition system consists of Surface Mount Device (SMD) pre-amplifiers with filter to an analog differential pair shipboard COTS acquisition system. Pre-amplifiers are constructed using SMD technology where components are pressure tolerant and potting is not necessary. Potting of connectors, electronics and hydrophones via 3D printed molding techniques will be discussed. Array internal components are manufactured with Thermoplastic Polyurethane (TPU) 3D printed material to dampen array vibrations with forward and aft vibration isolation modules (VIM). Polyurethane foam (PUF) used to scatter breathing waves and dampen contact from wires inside the array without attenuating high frequencies and allowing for significant noise reduction. A single Tygon array section with a length of 7.5 m and diameter of 38 mm contains 8 transducer elements with a spacing of 75 cm (1 kHz design frequency). Pre- amplifiers and NAS modules are affixed using Vectran and steel wire rope positioned by swaged stops along the strength member. The tow cable length is 100 m with a diameter of 22 mm that is potted to a hose adapter to break out 12 braided copper wire twisted pair conductors and terminates the tow cable Vectran braid. This array in its current state of development is a low-cost alternative to obtain quality acoustic data from a towed array system. Used here for observation of whale vocalizations, this type of array also has many applications in military sonar and seismic surveying. Maintenance on the array can be performed without the use of special facilities or equipment for dehosing and conveniently uses castor oil as an environmentally safe pressure compensating and coupling fluid. Array development including selection of transducers, NAS modules, acoustic acquisition system, array materials and method of construction with results from several deployments will be discussed. We also present beamformed spectrograms containing humpback whale downsweep moans and underwater blowing (bubbles) sounds associated with feeding on sand lance (Ammodytes dubius). 
    more » « less