1,721,476 research outputs found
FRC bending behaviour: a damage model for high temperatures
No full textPh.D. Thesis - Politecnico di Milano, Department of Structural Engineerin
Fire resistance of SFRC
No full textSteel fibre reinforcement is being increasingly considered as a profitable alternative to the traditional welded steel mesh for secondary load bearing mechanisms, such as the transversal bending of precast roof elements. An experimental investigation was carried out on HPSFRC to assess the mechanical behaviour, when subjected to high temperature. The mechanical behaviour was identified by means of bending tests, after a thermal cycle, and also for hot specimens after a fast extraction from the oven. The results were adopted to reproduce the fire behaviour of bent plates exposed to a standard fire curve
Marital fertility and exogenous contraints on child quality: a theoretical and empirical approach
No full textThis work aims to study the effect of exogenous constraints on child quality on marital completed fertility, both from a theoretical and empirical point of view. The neoclassical theory of fertility, pioneered by Becker et al., considers children in the same way as other “durable goods”: the spouses decide become parents, not only because they get utility from the number of children they bear (quantity), but also from some “desirable” child characteristics (quality). The interaction between these two dimensions gives origin to the well-known quantity/quality trade-off in the demand for children. However, it is obvious that parents do not “own” their children and cannot dispose of their offspring at their will. For instance, legislations on compulsory education and regulating the minimum age to admission to work are almost universally widespread. Furthermore, the expectations of their group of peers may be perceived by the spouses as binding as the law itself. These laws and expectations represent a binding constraint on child quality that parent are compelled to take into account in their childbearing decisions.
The first chapter proposes a theoretical approach that generalizes the classic quantity/quality trade-off model by introducing the hypothesis that couples face an exogenously determined quality constraint and taking explicitly into account that remaining childless can be optimal. The childbearing decision consists therefore in a two-stages process: in the first step, the spouses evaluate whether they can be better-off with or without children; in the second one, provided that they decide to bear children, they decide their optimal number and quality. Given the exogenous minimum quality threshold, the couple maximizes then a piecewise utility function under a budget constraint. As long as “minimum quality” (i.e. those characteristics “decided” by an entity external to the couple) and “discretionary quality” (i.e. those child characteristics that parents desire) are no perfect substitutes, the existence of an exogenous minimum quality threshold reduces both the space where becoming parents is the optimal choice and the overall number of children born to the couple. Furthermore, the quantity/quality trade-off is significantly stronger than in the standard case.
The second chapter proposes a reduced form estimation of the effect of changes in the marginal expenditures on minimum quality on the total number of children born to the couple. In fact, changes in marginal expenditures take place more often than changes in the threshold only and are easier to locate. A suitable econometric counterpart of the piecewise utility function is, in the case under examination, the complementary log-log – Poisson hurdle model. The cross-sectional dataset used in this work is built from several sweeps of the British National Child Development Study (NCDS) , while the marginal expenditures on minimum quality are proxied by the pupil/teacher ratio in primary schools observed by the partners at the time they got married. There is strong evidence that high marginal expenditures have a strongly negative effect both on the probability of becoming parents and on the overall number of children born to the couple. In turn, the overall effect of the observed income is positive but of small magnitude: in fact, a higher income reduces the predicted probability of becoming parents for nine couples out of ten (i.e. they “surrender to the suggestion” of higher own-consumption). These two results suggests therefore new insights into the interpretation of the low fertility trends experienced in most developed countries
New NDT techniques for the assessment of fire damaged concrete structures
No full textAn extensive research programme has been performed at Politecnico di Milano in order to identify quick and easy methods for the assessment of the thermal damage undergone by reinforced concrete structures in consequence of a fire. As a result, three new investigation techniques have been proposed, which allow to assess the whole thermal damage profile in one single test: a simplified interpretation technique for the indirect Ultrasonic Pulse Velocity (UPV) method (based on the refraction of longitudinal waves), an affordable approach to concrete colorimetry and the real-time monitoring of the drilling resistance. In this paper, the pros and cons of the proposed techniques are pointed out, as revealed by laboratory tests. The actual in situ viability of each method is then discussed, after the investigations conducted on two full-scale structures: a precast R/C industrial building surviving a real fire and a concrete tunnel submitted to a series of hydrocarbon-pool fire tests
Pressure–impulse diagrams for RC and FRC circular plates under blast loads
No full textIn this work, simplified models for the dynamic analysis of traditional reinforced concrete (RC) and fibre-reinforced concrete (FRC) circular plates under blast loads are proposed. The cases of plates simply supported or resting on Winkler-type soil are studied. The two cases under study intend to provide a simplified tool for predicting the response respectively for specimens subjected to blast pressure wave inside shock-tube facilities and for slabs on ground under blast loads. The second case also represents the loading conditions inside a new shock-tube facility specifically intended for the investigation of underground tunnel lining subjected to blast loads. The aim of this work is the pressure-impulse diagrams derivations for circular plates with several material characteristics, radius/thickness ratio and Winkler's constant
Nuove tecniche non distruttive per la stima del danno da incendio nelle strutture in calcestruzzo armato
No full textPressure–impulse diagrams of RC beams considering fire–blast interaction
Full text linkWhen analyzing military, defense, or structures/infrastructures deemed critical, explosion-induced actions—often associated with malicious actions—play a significant role. The combined effect of a blast and fire is not uncommon: in fact, an explosion can be the extreme consequence of a fire or vice versa, a fire can occur as the result of an explosion. Although advanced numerical approaches can be a proper solution for analyzing critical structures and infrastructures subjected to accidental actions, their complexity makes these approaches unsuitable for the analysis of ordinary buildings or even for the preliminary design of structures. A pressure–impulse diagram is an easy and common tool that can be adopted to verify the safety of structural members for a wide range of blast scenarios even considering the damage caused by a previous fire. This study aims to compare different approaches that can be adopted for the construction of pressure–impulse diagrams of reinforced concrete structures subjected to a blast and a blast preceded by fire. Taking as a reference case a statically indeterminate beam with three supports, this work presents the influence of the methods of analysis on the safety level assessed through pressure–impulse diagrams
Una lezione dal passato su rappresentanza e innovazione. Contributo allo studio del moderno apprendistato
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