Raffaele Landolfo

Post-earthquake fire resistance of moment resisting steel frames

Fires following earthquakes are considered one major threat in seismic regions. In fact, according to modern seismic codes, ordinary structures are designed to suffer damage to some extent during strong earthquakes, exploiting the structure own ductility to avoid collapse and safeguard human lives. Then, a fire coming soon after an earthquake will find a different, more vulnerable, structure with respect to the initial, undamaged, one. Depending on the extent of damage, the fire resistance rating of the structure could be significantly reduced. This paper is devoted to obtaining some quantitative information about this topic, with reference to steel moment-resisting frames, even if the adopted methodology could also be extended to either different structural types or structural materials. As a first step, a simplified modelling of earthquake-induced structural damage, based on the superposition of geometrical and mechanical effects, is proposed. Then, a wide numerical analysis is performed with reference to a single-bay single-storey frame structure, allowing the main parameters affecting the problem to be identified. Finally, two multi-storey plane frames, designed in accordance with methods specified by Eurocodes, are analysed as a case study.

Field Testing of All-Steel Buckling-Restrained Braces Applied to a Damaged Reinforced Concrete Building

AbstractThis paper reports the results of full-scale inelastic cyclic static tests of all-steel dismountable buckling restrained braces (BRBs) applied to an existing damaged reinforced concrete (RC) building. The two concepts set as the design targets for the prototype BRBs were to minimize interference with the functions and aesthetics of the existing building and to use an all-steel dismountable solution to allow for inspection of the yielding core after earthquakes. Two masonry infill panels (typical in RC buildings) were used to hide the braces and satisfy the first objective. Specially designed steel built-up shapes with bolted connections were used to satisfy the second objective. The design criteria and procedure adopted for the retrofitting design are first described, and a description of the BRB specimens and the experimental results follows.

Seismic response of MR steel frames with low-yield steel shear panels

Non-linear dynamic analyses examining the seismic response of moment resisting (MR) steel frames enhanced with low-yield steel shear panels are presented. Shear panels, which act as damping and stiffening devices, are schematised as equivalent bracing elements having a suitable hysteretic behaviour. For this purpose, an analytical model is set up and calibrated on the basis of available experimental tests. A parametric analysis is therefore carried out varying several parameters of shear panels, namely strength, stiffness, ductility and hysteretic behaviour, aiming at determining those factors having the major impact on the seismic response of the frame. Obtained results show that the considered design procedure is really effective and convenient, low-yield steel shear panels providing an apparent reduction of storey deflection and damage level of the primary structure.

Structural Analyses of the Submerged Floating Tunnel Prototype in Qiandao Lake (PR of China)

In this paper, after a general presentation of the Submerged Floating Tunnel (SFT) as an attractive technical solution for waterway crossings, the SFT prototype to be built in Qiandao Lake (Peoples Republic of China) is introduced. The main peculiarities of such an innovative system are briefly summarized and the importance of realizing a SFT prototype is underlined. The types of action that the SFTs can be generally subjected to are illustrated and the specific load conditions for the SFT prototype in Qiandao Lake are presented. The numerical analyses carried out for investigating the system behaviour in presence of the environmental loads, such as waves, currents and earthquakes, are focused. Three cables configurations are considered for the hydrodynamic analyses, in order to select the most performing one, which is subsequently analyzed also under seismic loads. The model assumptions and the results of the performed analyses are shown and critically discussed. Finally, the displacement and strength safety checks are shown, which allow to state that the designed SFT prototype is able to withstand the environmental design actions in Qiandao Lake.

Numerical calibration of an easy method for seismic behaviour assessment on large scale of masonry building aggregates

The paper deals with the numerical calibration of a speedy procedure for large scale seismic vulnerability assessment of masonry building aggregates, which are typical building compounds diffused within historical centres of many Italian towns. First of all, based on several numerical analyses developed with the 3MURI calculation program, this simplified assessment procedure has been implemented, it being derived from the well known vulnerability form for masonry buildings integrated by five parameters accounting for the aggregate conditions among adjacent units. Later on, the set-up procedure has been validated through an application to a single building aggregate in the Vesuvius area. Since the results previously achieved have been again confirmed, subsequently the procedure has been used to investigate a wide area of the historical centre of Torre del Greco, allowing for the knowledge of the buildings most at risk under earthquake.Finally, the methodology has been applied to the historical centre of Poggio Picenze (AQ), damaged by the recent Italian earthquake (2009), in order to prove its effectiveness to foresee the damage level experienced by other types of masonry aggregates under seismic actions.

Seismic analysis of MR steel frames based on refined hysteretic models of connections

Abstract Evaluation of seismic performance of moment-resisting (MR) steel frames is usually carried out assuming the elastic-perfectly-plastic type of hysteresis model for plastic zones (in particular for beam-to-column connections). This type of model is associated with a conventional available ductility, giving an indication of the maximum deformation beyond which strength degradation is likely to occur. This methodology leads to conservative results and the elastic-perfectly-plastic type of hysteresis model is certainly adequate in obtaining reliable information on deformation when the above ductility limits are not exceeded. However, the safety of the frame at ‘collapse’ remains unknown. The analyses presented in this paper show that safety margins against global collapse of the structure can be predicted only by considering more realistic hysteresis behaviour, i.e. using mathematical models able to take account of strength degradation and pinching phenomena. Moreover, it is shown that the design of conventional steel building systems according to the European seismic code may lead to over-resistant structures, due to the limitation on inter-storey drift angles for non-structural damage control under frequent earthquakes. It is also noticed that this result is inevitable, owing to the indications provided by Eurocode 8 in terms of both prescribed inter-storey drift limits and assumed base shear-force demand under frequent earthquakes.

Modelling of lightweight sandwich shear diaphragms for dynamic analyses

Abstract A procedure interpreting the behaviour of screwed lightweight sandwich shear walls is presented in this paper. The study is part of a general research project aimed at the development of a suitable methodology of analysis, which should allow the effect of cladding panels on the structural response of steel frames to be properly accounted for. Firstly, the monotonic behaviour of panels in shear is predicted by means of an adequate finite element model, whose reliability is checked on the basis of available experimental results. Then, the cyclic response of the system is established through a purposely-developed analytical hysteretic model. Appropriate strength degradation functions are introduced, aimed at simulating the cyclic response of the system as experimentally stated. On the whole, the proposed methodology is profitable for predicting the seismic response of steel frames, accounting for the contributing effect due to infill sandwich panels.

Different approaches in the design of slender aluminium alloy sections

The possibility of local buckling in members classified as slender is kept into account in the most up-to-date codes by replacing the true section with an effective one. This can be done via several approaches. In order to compare these approaches a comprehensive parametric analysis is presented in this paper, applying different design criteria to a set of sections which adequately represent the most important types of slender aluminium alloy sections. The obtained results allow one to check the reliability of the procedures proposed by the codes considering also the different computational cost required by each method.

Behaviour of aluminium alloy structures under fire

Abstract In the paper the attention is focused on the influence of high temperatures on the mechanical properties of the aluminium alloys selected by Eurocode 9 for structural uses. Therefore, based on the analysis of existing data taken from technical literature, the variation of the Youngs modulus, the conventional yielding strength, the ultimate strength, the hardening factor and the material ultimate strain are represented as a function of the temperature. A mechanical model, based on the well‐known Ramberg‐Osgood formulation, which appropriately takes into account the peculiarities of such materials at high temperatures, is provided. In particular, the combined influence of the hardening factor and temperature on the material stress‐strain relationship is considered and analysed. Then, the proposed model has been introduced in a finite element program, devoted to the global analysis of structures under fire. Finally, the results obtained for a simple portal frame structure, designed with different a...

Design of Metallic Cold-Formed Thin-Walled Members

This book approaches cold-forming techniques and the specific problems of cold-formed thin-walled members. It discusses the problems that may be covered in the evaluation of the strength of cross-sections and the buckling resistance of members, and highlights the theoretical basis and the design approach necessary to overcome them. Of particular benefit is a Windows-based program accompanying the book that allows the reader to easily evaluate the strength of a cross-section and the buckling resistance of a member for both steel and aluminum.