Spray-applied Fire-resistive Material Research Articles

Fires Following Earthquake Fragility Functions for Protected Steel Braced Frames

The paper describes the outcomes of the analysis of a steel braced frame protected with spray-applied fire resistive material and subjected to fires following earthquake (FFE). Nonlinear time-history analyses were performed in order to evaluate the seismic response. Then, the post-earthquake fire ignitions within selected compartments were considered based on the damage suffered by the structure, which was estimated according to the inter-storey drift ratio and floor acceleration. Natural fire curves were determined by means of zone models. Thus, compartmentation and opening characteristics were included in the analysis. Finally, thermomechanical analyses were completed and failure criteria based on the column and beam displacement and rate of displacement were investigated. The results of the probabilistic analyses were used to produce fragility functions to evaluate the probability of exceeding a limit state conditioned on an intensity measure in the context of FFE.

The role of a novel coating of SFRCR-ECC in enhancing the fire performance of CFST columns: Development, characteristic and ISO-834 standard fire test

The conventional spray-applied fire-resistive material meets the basic fire resistance requirements. However, it has limited strength and ductility, and poor bonding with the substrate, consequently, it will not deform with the main structure and reduces the fire resistance performance. A multifunctional spray-applied, fire-resistive and corrosion-resistive Engineered Cementitious Composites (SFRCR-ECC) has been developed to overcome these defects. Material properties of SFRCR-ECC coating were initially investigated, as well as the ISO-834 standard fire test of CFST columns sprayed with SFRCR-ECC coating were carried out. The effects of SFRCR-ECC coating thickness and the load ratio of the columns to the fire resistance limit were preliminarily explored, while the damage of the specimens after the open fire test, the temperature distribution and the axial deformation of CFST columns were obtained. The open fire test results also proved that SFRCR-ECC has excellent fire resistance performance as a new sprayable fire resistant material.

Comparative response of tiled finishes and bonded fire resistive coatings for normal weight concrete tunnel liners under high-intensity one-sided heating

Experimental tests were performed to examine the relative fire resistance provided by several bonded coatings for normal weight concrete (NWC) panels that emulate a tunnel liner: ceramic tiling on mortar, spray-applied fire resistive material (SFRM), and intumescent paint (IP). Sixteen panel specimens (150-mm [6-in.] thick, 457-mm [18-in.] wide, and 610-mm [24-in.] tall) were subjected to one-sided heating using a gas-fired radiant panel, which can apply heat flux at intensities similar to hydrocarbon fuel fire. All specimens were cast from a single batch of NWC (approx. 40 MPa compressive strength) with a single curtain of steel reinforcing bars at 38-mm (1.5-in.) cover to the heated face. All specimens were vertically loaded to a service level of compressive uniaxial stress (approx. 14% of ambient specified compressive strength), which remained relatively constant during each test. Four bare concrete panel specimens were tested as a control group, and a ceramic tile finish was installed on six specimens in accordance with a current state department of transportation specification. The other six specimens were coated with fire resistive material (three each with SFRM and IP) at thicknesses corresponding to a 1-hr fire resistance rating per manufacturer specifications. Thermally-induced explosive concrete spalling was observed in 3 of 4 control specimens, 4 of 6 tiled specimens, and none of the 6 SFRM/IP coated specimens. The tiled finishes delaminated and eventually became fully detached from the concrete surface, thus providing negligible fire resistance compared to that provided by the SFRM or IP. Temperature time histories recorded within the outer 25-mm (1.0-in.) thickness of the heated concrete were used to evaluate the relative thermal resistance of each surface finish, as well as to validate a simplified thermal numerical model used for a brief parametric study. Post-fire removal of the surface finishes is also demonstrated.

Modeling delamination of fire insulation from steel structures subjected to blast loading

This article presents a fracture mechanics-based numerical approach for quantifying delamination of spray-applied fire-resistive material (SFRM) from a steel beam–column subjected to a blast loading. In the numerical model, cohesive zone model is employed to simulate interfacial crack initiation and propagating at the interface of SFRM and steel. Three types of SFRM, widely utilized in the practice namely, mineral fiber-based, gypsum-based and Portland cement-based SFRM are considered in the analysis. The numerical model is validated against two sets of experiments; a full scale blast test on a steel beam–column and a drop mass impact test on a steel beam insulated with SFRM. The verified numerical model is subsequently utilized to carry out extensive parametric study to quantify critical factors that can influence the extent of delamination of SFRM from a steel beam–column, namely fracture energy at steel-SFRM interface, elastic modulus of SFRM, thickness of SFRM, and the level of blast overpressure. Results from parametric studies show that Portland cement-based SFRM can provide the highest level of resiliency in terms of withstanding the applied blast overpressure, while mineral fiber-based SFRM shows the lowest level of endurance. Further, the outcomes obtained from parametric study demonstrate that the extent of delamination can directly be related to blast overpressure and thickness of SFRM, whereas it can inversely be related to elastic modulus and fracture energy of SFRM. Based on the results of parametric study, a delamination characteristic parameter, which incorporates the major factors influencing the delamination, is defined and the extent of delamination is expressed as a function of this parameter.

Cohesive zone model properties for evaluating delamination of spray-applied fire-resistive materials from steel structures

This paper presents cohesive zone model (CZM) fracture properties of spray-applied fire-resistive material (SFRM) for modeling delamination of fire insulation from steel structures. For characterizing cohesive zone properties, namely cohesive strength, cohesive fracture energy and cohesive displacement ductility, a set of experiments are conducted on three types of commercially available SFRM namely medium density Portland cement-based, medium density gypsum-based and mineral fiber-based. Data from experiments is utilized to develop a cohesive stress–displacement relationships in both mode-I and mode-II delamination. The recorded stress–displacement relationship indicates noticeable strain-softening zone verifying that SFRM is not a completely brittle material, rather, it is quasi-brittle.

Critical Factors Governing Crack Propagation at the Interface of Fire Insulation and Slender Steel Trusses

AbstractThis article presents a numerical approach in which the implicit finite element method and fracture mechanics concepts are applied to simulate crack propagation at the interface of fire insulation and truss members in steel framed buildings. An intrinsic cohesive zone model (CZM) in conjunction with contact interaction analysis is applied to model the progression of fracture at the interface of fire insulation and slender steel truss members. Experimentally determined cohesive zone properties are utilized to simulate the progressive delamination in three types of commercially available spray-applied fire-resistive material (SFRM) applied on a truss chord. The numerical model, which is initially validated against the previously conducted fracture experiments, is employed to perform a sensitivity analysis with respect to CZM parameters, SFRM elastic modulus, and thickness of SFRM. Results obtained from a sensitivity study are subsequently utilized to define a delamination characteristic parameter (d...

Development of durable spray-applied fire-resistive Engineered Cementitious Composites (SFR-ECC)

A new spray-applied fire-resistive material (SFRM) that combines the desirable thermal insulation property, sprayability, lightweightness and enhanced mechanical property is developed adopting Engineered Cementitious Composite (ECC) technology, overcoming the lack of durability issue of conventional brittle SFRM. The newly developed spray-applied fire-resistive ECC (SFR-ECC) exhibits density as low as 550kg/m3 yet with tensile strength of 0.87MPa and tensile strain capacity of 1% when spray-applied, significantly higher than those of conventional SFRM with tensile strength of less than 0.1MPa and no inelastic tensile strain. The newly developed material also exhibit significantly higher adhesion to steel than conventional SFRM. The thermal conductivity and sprayability of SFR-ECC are measured to be comparable to conventional SFRM, which ensures the proper functioning of SFR-ECC. SFR-ECC with enhanced mechanical performance is expected to improve the overall fire safety of steel structure under both service and extreme loads.

Effective properties of spray-applied fire-resistive material for resistance to cracking and delamination from steel structures

This paper presents a study on quantifying the effective properties of spray-applied fire-resistive material (SFRM) to mitigate delamination of fire insulation from steel structures. The crack development in SFRM, its propagation and then delamination is investigated for two types of structural elements; a flimsy steel truss chord, and a beam-column assembly in a moment-resisting frame insulated with three types of SFRM widely utilized in steel construction. In the truss chord, the strain ductility of steel at which delamination initiates and propagates is studied, while in the beam-column assembly, the extent of delamination over the plastic hinge region developed on the beam is monitored. A fracture mechanics-based numerical model is employed to undertake parametric studies to determine effective parameters of SFRM for minimizing delamination. In the sensitivity study, the material properties of SFRM applied on steel members are varied over a wide range. Results from the sensitivity study indicate that the elastic modulus of fire insulation (E), thickness of insulation (t) and interfacial fracture energy (Gc) are the crucial factors that govern the delamination of SFRM from the steel surface. Subsequently, results from an additional set of parametric studies, carried out on a beam-column assembly, also infer that delamination of SFRM occurs over the plastic hinge region and is mainly governed by the critical factors of E, t and Gc. Results from these studies indicate that all three governing factors play a critical role in determining the extent of delamination and such delamination can be overcome if the interface fracture energy in normal mode is enhanced to 350J/m2.

Effect of Earthquake-Induced Damage on the Sidesway Response of Steel Moment-Frame Buildings during Fire Exposure

Spray-applied fire-resistive material (SFRM) is prone to debonding, cracking, and spalling in steel moment-frame plastic hinge regions during inelastic seismic response. To evaluate the effect of experimentally observed earthquake-induced SFRM spall patterns on building sidesway response during an ensuing fire, an analytical case study is developed for a steel special moment-frame building with a seismic hazard representative of coastal California. Response data from numerical earthquake simulations indicate that damage to SFRM insulation in beam hinge regions should be anticipated following ground shaking representative of the maximum considered seismic hazard. Thermomechanical post-earthquake fire simulations demonstrate that earthquake-induced SFRM spalling significantly increases thermal degradation in the affected beam hinge regions during fire exposure, leading to pronounced softening of moment-rotation response for the beam-column assemblies. This temperature-induced moment-frame connection softening increases the flexibility of the structural system for sidesway motion and exacerbates drift demands under the action of residual destabilizing forces.

Cyclic Load Tests of SFRM-Insulated Steel Gravity Frame Beam-Column Connection Assemblies

AbstractEarthquake-induced damage to structural components and spray-applied fire-resistive material (SFRM) in steel gravity frame beam-column connection regions can impact connection performance during an ensuing fire. Bolted connections are particularly susceptible to failure at elevated temperatures due to a rapid loss in bolt capacity with increasing temperature, which occurs at an accelerated rate compared to the thermal degradation of structural steel. In order to characterize structural and SFRM damage over a range of seismic drift demands, two large-scale SFRM insulated beam-column connection assemblies utilizing single-plate and unstiffened seated connection designs, with composite floor slabs, were tested under combined gravity and lateral loading. SFRM cracking, debonding, and spalling were observed during both tests, exposing critical connection elements. In addition, the single-plate connection assembly, which was developed in accordance with U.S. national guidelines but contained design feat...

Feasibility Study on Fire-Resistive Engineered Cementitious Composites

Spray-applied fire-resistive material (SFRM) is one of the most commonly used fire protection materials for steel structures. The commonly observed delamination and detachment of SFRM, however, significantly reduces the overall effectiveness of fire protection. Engineered cementitious composites (ECCs) are a special family of high-performance, fiber-reinforced Cementitious composites featuring very high ductility under tension, bending, and impact loads. This study investigates the feasibility of developing a new version of fire-resistive ECC that combines the fracture-resistant property of the ECC family of materials and the excellent insulation property of SFRM. The study shows that ECC with similar or even better insulation property compared with conventional SFRM can be developed, and the intrinsic high ductility of ECC improves the overall effectiveness and durability of fire protection.

Effect of earthquake-induced damage to spray-applied fire-resistive insulation on the response of steel moment-frame beam-column connections during fire exposure

Spray-applied fire-resistive material (SFRM) is prone to debonding, cracking, and spalling in steel moment-frame beam hinge regions during inelastic seismic response. This article presents an analytical case study designed to evaluate the effect of experimentally observed SFRM spall patterns on the thermomechanical response of a steel moment-frame beam-column assembly during post-earthquake compartment fire exposure. Earthquake-induced SFRM spalling is shown to significantly increase thermal degradation in the beam hinge region during fire exposure, leading to considerable temperature-induced softening of moment-rotation response for the beam-column assembly. This reduction in rotational stiffness increases the flexibility of the structural system for sideway motion, and exacerbates drift demands under the action of residual (post-earthquake) destabilizing forces. Language: en

Structural Analysis of Impact Damage to World Trade Center Buildings 1, 2, and 7

The National Institute of Standards and Technology (NIST) conducted an extensive investigation of the collapse of World Trade Center towers (WTC 1 and WTC 2) and the WTC 7 building. This paper describes the reconstruction of impact damage to each of the WTC buildings, as well as analytical studies related to the WTC building collapses. In addition, data and evidence that were collected, tests of the floor truss systems in the WTC towers that were conducted, the overall structural analysis approach, and the development of the collapse hypotheses are discussed to provide a basis for the impact analyses and the fire and structural response analyses in a companion paper. Three companion papers address the primary structural systems of the WTC towers and WTC 7, the effects of fire on the three buildings, and how these events contributed to building collapse. The papers provide an overview of the complex and extensive investigations undertaken by NIST at a level of detail that has scientific merit but presents key aspects from the voluminous official reports at a level suitable for the technical literature. The aircraft impact damage to structural members and their passive fire protection in WTC 1 and 2 were estimated through detailed aircraft impact simulations. The impact damage to WTC 7 was estimated from photographs after the collapse of WTC 1, where falling debris damaged the southwest corner of WTC 7. Based on the aircraft impact simulation, over half of the exterior columns on the north face of WTC 1 were severed and approximately 20% of the core columns were severed or heavily damaged. Spray-applied fire resistive material (SFRM) was dislodged by direct debris impact over five floors (Floors 94 to 98). WTC 2 structural damage was concentrated on the east side of the building. Over half of the exterior columns on the south face were severed and approximately 25% of the core columns were severed or heavily damaged. SFRM was dislodged by direct debris impact over six floors (Floors 78 to 83). WTC 7 was structurally damaged by debris from the collapse of WTC 1. Photographic evidence showed that seven exterior columns were severed near the southwest corner at the lower floors. Unlike the towers, the SFRM in WTC 7 likely remained intact except for local areas around the debris impact damage at the southwest corner. All three buildings were stable with the impact damage, but the WTC 2 building section above the aircraft impact damage leaned to the east and south.