Erica C. Fischer

Experimental Investigation of Composite Beams with Shear Connections Subjected to Fire Loading

AbstractThis paper presents the results from experimental investigations focused on the thermal and structural behavior of composite beams with shear connections subjected to fire conditions. Five partial composite beams with flat, lightweight concrete slabs were designed according to current U.S. codes and standards. Vertical loading was applied to the composite beams, and the surfaces of the steel and concrete were heated using high-temperature ceramic radiant heaters. Variations in the loading and heating protocol provided insight into the mechanical response and failure modes of composite beams and connections. There was an overall reduction in the composite beam load-carrying capacity due to heating, both at elevated temperatures as well as postfire ambient conditions. Concrete compression failure occurred at moderate steel temperatures (350–500°C) combined with overloading. In cases where service level loading was applied, the composite beams and connections sustained the loading and heating up to s...

Investigation of Cylindrical Steel Tank Damage at Wineries during Earthquakes: Lessons Learned and Mitigation Opportunities

AbstractThe moment magnitude scale (Mw) 6.0 South Napa earthquake caused damage to stainless steel cylindrical tanks used for wine storage and fermentation. The damage observed to the tanks included local buckling of the tank walls, anchorage failure, and damage at the top of the tanks as a result of the catwalk system. Inspections of these tanks after the South Napa earthquake provided the motivation and the basis for investigating the seismic behavior of stainless steel cylindrical tanks used for liquid storage. This investigation focused on (1) the behavior of stainless steel cylindrical tanks in previous earthquakes around the world, and (2) research performed to mitigate this damage. The damage to cylindrical steel tanks after the South Napa earthquake was found to be identical to damage documented by postearthquake reconnaissance reports from around the world. Large-scale experimental research (by other researchers) has already demonstrated the inadequacy of cylindrical tank anchorage details for th...

Closure to “Experimental Evaluation of the Fire Performance of Simple Connections” by Erica C. Fischer, Kristi L. Selden, and Amit H. Varma

The writers thank the discusser for his interest in the paper. The discusser presents four pertinent points in his discussion. The following presents closure for each point: 1. The discusser indicates that there is some lack of clarity between the maximum bottom flange temperatures in Tables 2 and 3 of the original paper. To further clarify, the “Maximum bottom flange temperature” values presented in Table 3 are the target temperature values for each of the experiments. The “Maximum bottom flange temperature” values presented in Table 2 are the measured maximum temperature values for the bottom flange in each experiment; 2. The discusser indicates that there are differences between the measured connection temperatures (for the north and south connections) for each experiment, and inquires about which connection temperature history was presented in Table 3 and Figs. 6(a), 7(a), 8(a), 10(a), 12(a), and 14(a) of the original paper. To further clarify, the temperature history curves shown in these plots are for the connection that has the maximum temperature throughout the experiment. Please refer to Fischer and Varma (2015) for additional connection temperature history data; 3. The discusser inquires about the exact time when cooling was implemented in the testing protocol. In response, the testing protocol outlined within the paper states that the cooling phase was implemented immediately when the target temperature was reached. The steel beam was heated at 7°C=min, but this heating rate should not be used to estimate the time when cooling was implemented, as the steel beam temperature history was nonlinear as a result of conduction, convection, and radiation losses. The onset of cooling is shown by the connection temperature histories. Cooling is initiated when the connection temperature begins to decrease. The writers request the discusser to read Selden (2014), Fischer (2015), Selden et al. (2016), and Fischer and Varma (2015) for additional information on the steel beam temperature history; and 4. The writers provide a discussion of the observed connection behavior and the axial force in the connection. Additional discussion of the axial force history at the connections of the specimens is provided in Fischer and Varma (2015). Further discussion is also provided in Fischer (2015) and Fischer and Varma (2017). These discussions focus on the axial force history during both the heating and cooling phases, and explain how it depends on the heating, cooling, and loading protocols. The discusser is comparing the axial force histories of the connections in specimens CB-2, CB-5 and CB-6, but this direct comparison is inappropriate and inapplicable, because these three specimens have very different heating, cooling, and loading protocols. This paper is part of a larger research program conducted on the behavior, analysis, and design of composite steel beams and connections under realistic fire scenarios (including cooling). The results from this research program are summarized in a series of related dissertations, namely, Selden (2014) and Fischer (2015). The discusser is requested to review the following publications (based on the dissertations) for a comprehensive understanding of the tests, results, analysis, and design implications: Agarwal et al. (2014), Selden et al. (2016), Fischer and Varma (2015), and Fischer and Varma (2017).

Experimental Evaluation of Single-Bolted Lap Joints at Elevated Temperatures

AbstractIn U.S. building construction, typical simple (shear) connections are often bolted for flexibility during fabrication and construction. This paper summarizes the results of experimental inv...

Sustainability and Structural Fire Engineering

Many buildings in the U.S. are vulnerable to natural and man-made disasters due to the increased popularity of sustainable building infrastructure. Life cycle assessment (LCA) analyses are required to design and achieve “green” building status. These analyses do not require evaluations of building performance during natural or man-made hazards. Increases in labor and material caused by robust and resilient systems also often increase embodied energy and carbon dioxide emissions. Those LCA analyses which do consider seismic performance of a building many times do not take into account the seismic performance of the non-structural secondary systems (partition walls, drop ceilings, etc.). In the particular case of fire hazards, automatic sprinkler systems add 30-40kg of embodied carbon to a building; however, reduce the risk factor for fire during the life span of a building. To prevent post-fire repairs, which would increase the embodied energy and carbon of the building more, hazard mitigation needs to be integrated with sustainability. The development of performance-based design standards helps this integration; however, the lack of risk factors incorporated into life cycle assessments needs to be remedied, not just for seismic design, but all natural disasters. This paper references previous developments in the marriage between natural hazard mitigation and sustainability as well as the limitations of the tools available to structural engineers. Advancements in the development of a risk factor for fire is discussed as well as the increased carbon emissions and embodied energy of buildings without active fire protective measures.

Advanced Fire Testing of a Composite Beam with Shear Tab Connections

This paper presents the results of a full-scale experimental test on a composite floor beam designed according to American codes and standards that was subjected to elevated temperatures. The test focused on the fundamental behavior and mechanics of a composite beam with end shear connections that was subjected to combined gravity loads and thermal loading, simulating realistic fire effects that included both heating and cooling. The test was conducted on a 3.80m long composite beam that consisted of a steel beam that was composite with a flat, lightweight concrete slab through the use of shear studs, and the beam was connected to a portal frame using shear tab connections. High temperature ceramic radiant heaters with independent temperature control were used to heat the steel and concrete portions of the specimen. Results from the experimental test provide insight to the behavior of composite beams and the beam-tocolumn connections at elevated temperatures. The composite beam and connection survived heating to 600°C, but the shear tab connection fractured during cooling.