Fire resistance of reinforced concrete (RC) columns in design codes is based on concentric loading conditions. The effect of eccentric loads on spalling and fire resistance of RC columns is a matter of investigation. The present study, therefore, broadly aims to determine the influence of relative levels of spalling under eccentric loads on fire resistance of RC columns. Experimental investigation is done on 3.15 m long column specimens. The experimental results indicate that the increase in load eccentricity (from 20 mm to 40 mm) increases the amount of spalling leading to exponential decrease in fire resistance (by 43%). Spalling is restricted by increase in longitudinal bars, particularly mid-perimeter bars, contributing to increase in fire resistance by 100% with doubling of number of longitudinal bars. Even the decrease in spacing of transverse reinforcement (from 300 mm to 150 mm) for eccentric loads leads to 123% increase in fire resistance. However, this advantage is limited by greater amount of compression face spalling (400% more) under eccentric loads, which is seen to increase with the density of reinforcement. For explosively spalled high strength columns, further reduction in fire resistance occurs on account of local softening of longitudinal reinforcement due to early (10 min) and protracted (up to 58 min) deep spalling. The chances of global column element buckling become more dominant with increase in load eccentricity around 40 mm. It is concluded that spalling levels change with relative change in reinforcement detailing with other parameters under eccentric loads. From this study, it is concluded that the feasibility of existing methods of determination of fire resistance for eccentrically loaded columns are inadequate and need to be revised to as per the results of this study.

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INTRODUCTIONCurrent codes for fire design of structures in the United States are still based on design at the component level using prescriptive requirements, although performance-based approaches can provide efficient alternatives for designing modern buildings with cost-effective solutions. To promote the use of performance-based approach in practice, there is a need not only to develop the necessary knowledge and modeling tools, but also to demonstrate and exemplify the benefits of this approach on the fire design of typical structures.This study compares the fire design of a typical office building using prescriptive and performance-based designs. The U.S. prescriptive approach is used as a benchmark for fire safety. This approach specifies the fire resistance rating required for each individual building structural elements, where the fire resistance rating is defined as the amount of time the element has to withstand when exposed to the standard fire. Then, alternative designs based on performancebased approach are studied. Evaluating the validity of the alternative designs requires the definition of a clear performance target. Here, it is assumed that the acceptable level of performance is the one that corresponds to the fire safety of the same structure designed based on the U.S. prescriptive guidelines. Under standard fire, the global stability of the structure should be ensured for at least the amount of time specified in the codes. Under natural fire, it is assumed that the global stability of the structure should be ensured until complete burnout of the fire.A 9-story office building with steel frames and regular plan configurations with a composite floor system is used as the prototype structure. In the first part, the International Building Code is used to obtain the required fire resistance rating for the building structural elements based on current practice. The Underwriters Laboratory publications (UL, 2003) ABSTRACT: Performance-based structural fire design provides a rational methodology for designing modern buildings with cost-effective solutions. However, in the United States, fire design still largely relies on design at the component level using prescriptive approaches. With performance-based approaches, there is an opportunity to benefit from increased flexibility and reduced cost in the design, but these advantages need to be explicitly described and disseminated to promote this shift in paradigm. In this paper, a comparative analysis is conducted on multi-story steel-concrete buildings designed following performance-based and U.S. prescriptive approaches. The steel-concrete composite structure allows taking advantage of tensile membrane action in the slab during fire, and therefore removing the fire protection on secondary beam elements. The nonlinear finite element software SAFIR ® is used to model the behavior of the buildings under the standard ASTM fire and a natural fire determined using the two-zone fire model CFAST. The numerical simulations show that performance-based design c...

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