Dynamic delamination of fire insulation applied on steel structures under impact loading

This paper presents an experimental-numerical approach for evaluating dynamic fracture and delamination of fire insulation from steel structures during impact loading. The experiments encompass drop mass impact tests on steel beams insulated with three types of sprayed applied fire resistive material (SFRM), namely Portland cement-based, gypsum-based and mineral fiber-based, commonly utilized in steel construction. The impact tests are conducted at two kinetic energy levels to evaluate the strain rate-dependency of fracture energy and extent of delamination at steel-SFRM interface. Results from experiments show that the cracking and delamination of SFRM is mainly localized on the bottom flange with slight extension into lower part of web of beam at the mid span. Further, Portland cement-based SFRM can withstand the applied impact energy and no delamination or substantial cracking in SFRM occurs, whereas two other types of SFRM experienced significant fracture and delamination on the bottom flange. A fracture mechanics-based numerical approach is subsequently employed to simulate the conducted experiments using LS-DYNA finite element code. In the explicit numerical model, cohesive zone approach is adopted to model fracture process zone at the interface of steel and SFRM. By quantifying and calibrating the extent of delamination on the bottom flange, the dynamic increase factor of fracture energy and stress-displacement relationships, determined through previous static fracture tests, is estimated. According to numerical simulations, extent of delamination in mineral fiber-based SFRM is not dependent on strain rate, whereas in the case of gypsum-based and Portland cement-based SFRM extent of delamination is a function of strain rate.