Papers by Author: Gaetano Manfredi

Abstract: Design provisions for the repair, retrofitting, and rehabilitation of existing masonry structures are not always available and included in International and National Building Codes. Due to the extremely large variability in masonry performances, equations of general validity cannot be provided, namely relationships suitable for confinement of every masonry type, as it is done for concrete. Large amount of results obtained for concrete led to consolidated design guidelines. Despite the great research effort in the experimental field on masonry, considerable theoretical work is still needed to fully outline a definitive analytical model to predict the behavior of FRP confined masonry. In this study, a mechanically based confinement model is proposed based on mechanical parameters able to differentiate similar masonry types and to highlight that they present different confinement performance. The most relevant parameters are the compressive and tensile strength of unconfined masonry and they are discussed in the framework of solid mechanic based models based on triaxial plasticity and calibrated experimentally. The proposed approach can then be extended to other masonry types.

Abstract: 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.

Abstract: 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.

Abstract: Extreme loading conditions such as man-made malicious actions, fires or natural events could induce local failure mechanisms (e.g., a loss of a member) which may trigger progressive collapse. The design or the assessment of a critical infrastructure needs to address the possibility of such an extreme circumstance taking place during its effective life-time. It is observed that blast-induced progressive collapse mechanisms involve non-linear structural behavior similar to that due to earthquakes. This work focuses on probabilistic analysis of progressive collapse of a typical RC structure, induced by a blast event. The objective is to verify the effectiveness of seismic retrofitting schemes against explosions and the eventual progressive collapse. The probabilistic analysis is performed by taking into account the uncertainties in loading such as planar configuration and amplitude of the blast loading. A standard Monte Carlo simulation method is employed to generate various realizations of the uncertain parameters within the problem. For a given realization, various component-level dynamic analyses are preformed within a certain range of distance, in order to quantify and locate the damage induced by shock wave on structural elements. As a case study, a 5-storey reinforced concrete frame structure designed for gravity loading only is considered. As possible retrofitting schemes, steel bracing, FRP wrapping and RC jacketing are compared. The probability of collapse considering both blast and earthquake for the structure before and after retrofit are compared.