The objective of this paper is to present incremental dynamic analysis (IDA) and seismic performance evaluation results for a two‐story cold‐formed steel (CFS)–framed building. The archetype building was designed to current U.S. standards and then subjected to full‐scale shake table tests under the U.S. National Science Foundation Network for Earthquake Engineering Simulation (NEES) program. Test results showed that the building's stiffness and capacity were considerably higher than expected and the building suffered only nonstructural damage even at excitations in excess of Maximum Considered Earthquake levels for a high seismic zone. For the archetype building, three‐dimensional finite element models at different modeling fidelity levels were created using OpenSees. The models are subjected to IDA using the far‐field ground motion records prescribed in Federal Emergency Management Agency (FEMA) P695. Seismic performance quantification following the FEMA P695 procedure shows that if the modeling fidelity only follows the state‐of‐the‐practice, ie, only includes shear walls, unsafe collapse margin ratios are predicted. State‐of‐the‐art models that account for participation from CFS gravity walls and architectural sheathing have overall performance that are consistent with testing, and IDA results indicate acceptable collapse margin ratios, predicated primarily on large system overstrength. Neglecting the lateral force resistance of the gravity system and nonstructural components, as done in current design, renders a safe design in the studied archetype, but largely divorced from actual system behavior. The modeling protocols established here provide a means to analyze a future suite of CFS‐framed archetype buildings for developing further insight on the seismic response modification coefficients for CFS‐framed buildings.
Earthquake and Post-earthquake Fire Testing of a Mid-rise Cold-formed Steel Framed Building. I: Building Response and Physical Damage
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.
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- Award ID(s):
- 1663569
- NSF-PAR ID:
- 10341546
- Date Published:
- Journal Name:
- Journal of structural engineering
- ISSN:
- 0733-9445
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract A full‐scale, reconfigurable, three‐story steel building was constructed and its modal properties identified prior to shake table testing on the UC San Diego Large High Performance Outdoor Shake Table (LHPOST6). The aim of this pre‐shake table test erection was to demonstrate the rapid constructability of the building and identify construction fit issues prior to its assembly on LHPOST6. This posed a unique opportunity to characterize the building's modal properties using a variety of non‐destructive, low‐amplitude techniques. To this end, two novel, non‐destructive methods were used, namely: (1) impact tests conducted by swinging a tire from a crane to impact strategically selected locations, and (2) dynamic base vibration tests, induced by driving heavy machinery in the vicinity of the base of the structure. A system of accelerometers located throughout the structure captured waves propagating from each test to characterize the as‐built dynamic properties of the building. Results from various system identification methods are presented and compared to theoretical and numerical analysis. Comparisons indicate that the theoretical, numerical, and experimentally determined periods are nominally within 15% of each other. The erection of the structure was complete over the course of 3 days and construction fit‐up issues were addressed. The structure was then rapidly deconstructed and stored prior to erection for full‐scale shake table testing. This pre‐shake table test exercise demonstrated the viability of two, simple, low‐amplitude excitation approaches for use in the dynamic characterization of full‐scale buildings, with results consistent with theoretical and numerical models.
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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
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1061/(ASCE)ST.1943541X.0003097
