Emidio Nigro

Behavior of FRP Reinforced Concrete Slabs in Case of Fire: Theoretical Models and Experimental Tests

Several technical codes allow concrete structures reinforced with FRP to be designed, but few calculation models taking account of fire condition are available. Assuming that the anchoring of the reinforcement is ensured in cooler zones of the structure, a calculation procedure developed by authors allows the flexural capacity of the one-way FRP reinforced concrete slabs under fire conditions to be assessed. The procedure was used for the design in the fire situation of six concrete slabs reinforced with Glass Fiber Reinforced Polymer (GFRP) bars. Such slabs were tested in case of fire by exposing them to heat in a furnace according to ISO834 standard time-temperature curve: four slabs have been tested under typical design loads in fire situation and two unloaded slabs have been tested after the cooling phase in order to evaluate their residual resistance. The experimental results confirmed that the effects of the high temperatures on both the deterioration of the material mechanical properties and the decrease of bond between FRP reinforcement and concrete are key aspects of the structural behavior of concrete members reinforced with FRP bars. Nevertheless the anchoring length at the end of the members not directly exposed to fire could ensure a fire resistance time higher than 180 minutes.

The Influence of Fire Scenarios on the Structural Behaviour of Composite Steel-Concrete Buildings

Fire Safety Engineering can be defined as a multi-discipline based on the application of scientific and engineering principles to the effects of fire in order to reduce the loss of life and damage to property by quantifying the risks and hazards involved and provide an optimal solution to risk mitigation. The correct identification of fire scenarios is the central stage in the process of the structural fire design. A design fire scenario is the description of the spread of a particular fire with respect to time and space. In the process of identification of design fire scenarios for the structural fire safety check, all fires must be assessed realistically, choosing those most severe for the structural response. This paper is devoted to evaluate the influence of fire scenarios on the structural behaviour of composite steel-concrete buildings. In order to that, an office building subjected to different fire scenarios was considered. In particular the fire scenarios were defined by both standard fire (prescriptive approach) and natural fire (performance approach). Finally, a comparison between the prescriptive approach and the FSE approach is presented.

Fire Safety Engineering for Open and Closed Car Parks: C.A.S.E. Project for L’Aquila

The Fire Safety Engineering (FSE) is a multi-discipline aimed to define the fire safety strategy for buildings under fire conditions, in which structural stability and control of fire spread are achieved by providing active and/or passive fire protection. In this paper, the aspects of FSE for the structural safety checks in case of fire are shown with reference to Italian and European standards. FSE requires the choice of a performance level, the definition of design fire scenarios, the choice of heat flows models and several numerical thermo-mechanical analyses. The information provided by a significant research, performed in Europe for open and closed car parks, are used to apply the FSE to the car parks of the new buildings of the C.A.S.E. Project for L’Aquila, characterized by steel columns supporting the seismically isolated superstructure. The results of the application of the FSE approach are reported and discussed in the second part of the paper.

Bond Between EBR FRP and Concrete

This chapter provides an overview of the debonding process between the FRP reinforcement and the concrete substrate. The main aspects of the debonding phenomenon are described and discussed, showing also mechanical interpretation of different processes. Experimental techniques to study the bond behavior between FRP and concrete are also described and corresponding available experimental results are shown to compare performances of different set-ups. Finally, an extensive description of the existing bond capacity predicting models is reported, together with the main international Codes provisions, allowing the designer for operating in common practice.

Adhesion at High Temperature of FRP Bars Straight or Bent at the end of Concrete Slabs

Confidence in the use of Fiber Reinforced Polymer (FRP) for Reinforced Concrete (RC) members in multi-story buildings, parking garages, and industrial structures is poor due to lack of provisions and calculation models taking account of fire condition. In the past, to contribute to refining existing codes for the design of FRP-RC structures, authors tested six concrete slabs reinforced with Glass FRP (GFRP) bars characterized by different values of concrete cover and anchoring length in fire condition. Recently, further three fire tests were carried out on concrete slabs reinforced with GFRP bars bent at the ends. The anchoring of the FRP bars in the zone of slab not directly exposed to fire at the end of the members revealed essential to ensures slab resistance, once in the fire exposed zone of slab the glass transition temperature was attained and the resin softening reduced the adhesion at the FRP-concrete interface.

Design by Testing and Statistical Determination of Capacity Models

In this chapter, the procedure proposed in EN1990 is adopted and extended to the case of EBR FRP systems, with the aim of attaining a uniform reliability level among all equations developed in this technical report. This approach will allow comparing experimental results and theoretical predictions in a consistent manner, and also identifying possible sources of error in the formulations. Any capacity model should be developed on the basis of theoretical considerations and subsequently fine-tuned through a regression analysis based on tests results. The validity of the model should then be checked by means of a statistical interpretation of all available test data. The formulation should include in the theoretical model a new variable that represents the model error. This variable is assumed to be normally distributed whit unit mean and standard deviation to be evaluated from comparison with experimental results. Once the statistical parameters of the model error are known, it is possible to define the statistical parameters of the capacity model and to evaluate its characteristic value, which is the aim for application in design. Some applications are shown to prove the feasibility of the proposed procedure.

Calibration of a simplified method for fire resistance assessment of partially encased composite beams

Purpose This paper aims to deal with the evaluation of the bending moment resistance of partially encased composite beams, heated from below by the standard-time temperature curve (ISO 834). Design/methodology/approach EN 1994-1-2 provides two calculation models for evaluating the sagging and hogging moment resistance: the “general simplified rules” and the “simplified models” proposed in the Annex F. Findings In this paper, these simplified calculation models were implemented on several partially encased composite beams, by means of a parametric analysis. Then, the results were compared to those obtained through an advanced calculation model, such as the Moment–Curvature model, by means of a comparative analysis. Originality/value The aim of the “parametric-comparative” analysis is the evaluation of the reliability of the Annex F simplified models. This analysis was conducted by means of both numerical-numerical and numerical-experimental comparisons. This paper provides an alternative simplified calculation model, which is easy to implement and very reliable.

INVESTIGATION ACTIVITY ABOUT A COLLAPSED STEEL STRUCTURE SUBJECTED TO A REAL FIRE, Fire scenarios and structural behaviour of a real steel structure

The paper describes the behaviour ofa real steel structure collapsed under a fire event. 3D structural analyses were performed with SAFIR program (J-M Franssen, 2005). Different modellingare implemented with some fire load models and analyses of thebehaviour of the whole structure. The main purpose of this work was to investigate the failure types of a warehouse structure under fire conditions. Different fire conditions were applied to the steel frame sections, with ISOcurve (ISO EN 834-8:2002) and zone model approach. The analyses show that with unprotected steel sections, horizontal structures are more critical than columns. Trough applying a performance basedapproach,structure has 30 minutes of fire resistance.

Bond Models for FRP Bars Anchorage in Concrete Slabs under Fire

Experimental tests were recently performed to evaluate resistance and deformability of nine concrete slabs reinforced with Fiber Reinforced Polymer (FRP) bars in fire situation by varying (a) external loads in the range of the service loads, (b) concrete cover in the range of usual values (30-50mm), (c) bar end shape (straight or bent) and its length at the end of the concrete members, namely in the zone not directly exposed to fire (250-500mm). Experimental results showed the importance of concrete cover in the zone directly exposed to fire for the protection provided to FRP bars, due to its low thermal conductivity. Moreover, the length of the FRP bars in the zone of slab not directly exposed to fire and its shape at the end of the members was crucial to ensures slab resistance once the resin softening reduced the adhesion at the FRP-concrete interface in the fire exposed zone of slab. In particular the anchorage obtained simply by bending bars at the end of member in a short zone (250mm) allowed attaining a good structural behavior in case of fire equivalent to that showed by slabs characterized by a large anchoring length (500mm). Tests results are briefly compared and discussed in this paper, whereas the behavior of the bar anchorage is carefully examined based on both the results of numerical thermal analysis and the predictions of a bond theoretical model adjusted for fire situation.