Browsing by Author "Lakhani, Hitesh"

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Open Access
Concrete cone failure of post installed fasteners during fire
(2023) Lakhani, Hitesh; Hofmann, Jan
The fire resistance of fasteners needs to be verified for all failure modes applicable at ambient conditions. Generally, in most cases, for unprotected fasteners loaded in tension, steel failure mode is decisive. But for fasteners made of stainless steel and/or larger (bolt) sizes, concrete cone failure may be the decisive failure mode for small anchorage depths. Due to practical difficulties associated with loading an anchor during a fire test, very limited experimental data is available in literature and that to for relatively small embedment depths. The paper presents the results (6 nos) of the fire tests conducted on expansion anchors (made of stainless steel) with sizes M12 (hef = 70 mm) and M20 (hef = 100 mm). Moreover, the paper also compares the reduction in the concrete cone capacity with exposure duration, predicted as per the current design guidelines and the new set of experimental data obtained in this study.
Open Access
Coupled thermo-mechanical inelastic analysis of reinforced concrete flexural members subjected to fire loads
(2016) Lakhani, Hitesh; Sharma, Akanshu; Hofmann, Jan
A simplified procedure to evaluate the complete-load-deflection time response of Reinforced Concrete (RC) flexural members subjected to fire loads is presented in this report. The proposed approach is extendable for performance evaluation of RC structures at all three levels of complexity namely member level (e.g. beams, columns), sub assembly level (e.g. beam-column joints) and as well as the structural level. This approach involves the determination of moment-curvature characteristics for the critical sections of the fire affected structural member and performing nonlinear static analysis to determine the load-deflection response of the member exposed to fire loads. The thermal analysis is first performed to determine the temperature distribution across the section, for a given fire duration. Temperature-dependent stress-strain curves for concrete and steel are then utilized to perform a moment-curvature analysis. The moment-curvature relationships are obtained at regular intervals of the fire exposure. These are then utilized to obtain the load-deflection plots following nonlinear static analysis (Pushover Analysis). The load-deflection plots obtained for the different exposure duration's are then used to obtain the deflection-time plots for a particular load level. Moreover, one of the important issues of modeling the initial stiffness giving due consideration to stiffness degradation due to material degradation and thermal cracking has been addressed in a rational manner. The approach is straightforward and can be easily programmed in spreadsheets. Implementation and validation of the proposed approach with various experiments available in literature has been discussed in detail in this report. The report also discusses the in-house code developed for carrying out 2D transient heat transfer analysis and obtaining moment-curvature relationships.