Structural Fire Performance of Fiber Reinforced Polymer (FRP) Strengthened high Strength Concrete Beams Using Opensees Software

Abstract

Analysis of structures subjected to extreme static and dynamic loads (such as earthquake, impact, wind and snow) using finite-element software are common and extensively being used in construction industry. However, to study the structural response under fire conditions, highly tedious nature of modeling involving full (often coupled) hydro-thermal-mechanical properties as a function of time under realistic fire scenario is required. OpenSees (Open System for Earthquake Engineering Simulation) developed initially by McKenna (Buchanan 2002; McKenna et al. 2000; Mckenna 1997) at the university of California, Berkeley, USA, is an object-oriented software framework used to create finite element applications to simulate the response of structural systems subjected to an earthquake. OpenSees consists of wide variety of material models which can be customized to one’s own material in its ever-growing library. A structural fire research group in School of Engineering, University of Edinburgh (Jiang and Usmani 2013) successfully conducted the research to add structures-in-fire modeling capability into the OpenSees framework by utilizing its well-designed software architecture. By adopting object-oriented programming paradigm, the software structure is consistent with that of the official OpenSees platform, which made it possible to reuse some of the existing components of software whereby introducing fire related components in it. At present, the use of high-strength concrete (HSC) is becoming popular due to the improvements in structural performance such as high strength and durability that it can provide compared to conventional normal strength concrete (NSC) (Kodur and Dwaikat 2008). However, OpenSees analysis module lacks material properties of many concrete types such as high strength concrete (HSC) and fiber reinforced concrete (FRC). Thus, there is a dire need to incorporate such material properties in existing OpenSees software so that realistic analytical simulations can be performed in predicting the fire response of infrastructure made of a peculiar concrete. In this research, material models based on mechanical and thermal properties of HSC (Kodur and Khaliq 2010) along with carbon fiber reinforced polymer (CFRP) (Ahmed and Kodur 2010) were added in OpenSees material library for thermal and structural analysis. OpenSees material library was updated for tracing the response of HSC beams strengthened with CFRP under realistic fire, loading and restraint conditions. All of the critical factors, namely; high-temperature material properties, axial restraint force, and different strain components that have a significant influence on the fire behavior of HSC beams strengthened with CFRP were incorporated in the model. For validation of this modification, developed code was validated against previous available studies and data. The validated model was then applied to conduct a set of parametric studies to quantify the influence of various factors, such as fire scenario, load level, axial restraint and concrete strength; on the fire response of HSC beams strengthened with CFRP. Results from parametric studies with OpenSees numerical simulations show that fire resistance of CFRP strengthened HSC beam is enhanced under design fire exposures. Different fire scenario has varying impact on fire performance of HSC beam strengthened with CFRP. Provision of insulation of CFRP can enhance the fire resistance of CFRP strengthened HSC beams. Higher load levels decrease time to reach failure state under fire exposure and thus affect fire performance. End boundary conditions also affect the fire performance, lower restraint forces lead to a lower fire resistance in CFRP strengthened HSC beams whereas lower compressive strength of concrete increases the fire performance.