Dynamic one-sided out-of-plane behavior of unreinforced-masonry wall restrained by elasto-plastic tie-rods

Past earthquakes have shown the high vulnerability of existing masonry buildings, particularly to out-of-plane local collapse mechanisms. Such mechanisms can be prevented if façades are restrained by tie rods improving the connections to perpendiculars walls. Whereas in the past only static models have been proposed, herein the nonlinear equation of motion of a monolithic wall restrained by a tie rod is presented. The façade, resting on a foundation and adjacent to transverse walls, rotates only around one base pivot and has one degree of freedom. Its thickness is explicitly accounted for and the tie rod is modeled as a linear elastic—perfectly plastic spring, with limited displacement capacity. The model is used to investigate the response to variations of wall geometry (height/thickness ratio, thickness), tie rod features (vertical position, length, prestress level), and material characteristics (elastic modulus, ultimate elongation, yield strength) typical of historical iron. The most relevant parameter is the steel strength, whereas other characteristics play minor roles allowing to recommend reduced values for pre-tensioning forces. The force-based procedure customary in Italy for tie design is reasonably safe and involves protection also against collapse, although probably not enough as desirable

Finite-discrete element modelling of masonry infill walls subjected to out-of-plane loads

In this paper, the out-of-plane response of infill walls is investigated by means of non-linear monotonic (push-over) analyses through a combined finite and discrete modelling approach. The model accounts for material deformability, crack formation, sliding, separa-tion and formation of new contacts. Masonry units are modelled as finite elements, and differ-ent material models are assumed for the masonry. Contact between masonry units, and between masonry and frame elements is modelled by means of interfaces, which permit tan-gential motion with frictional sliding. Frame elements are modelled by means of a linear-elastic material. The results of the numerical analyses are compared with those of experimen-tal tests available in the literature. The advantages and disadvantages of the adopted model-ling strategy are investigated

Effect of the vertical component of ground motion on a rubble masonry wall model

In this paper the influence of the vertical component of ground motion on the performance of an unreinforced masonry wall is analysed using sets of one-component and two-component ground motions. The set of motions represents the actual seismicity of L'Aquila, while the investigated wall mimics an experimental specimen with two unconnected external leaves and a rubble core. The model falls within the mixed finite element method – discrete element method and accounts for crack formation, complete separation and new contact formation. The modelling strategy is capable to simulate the out-of-plane seismic response and the progressive loss of compactness of the wall up to collapse with the separation between the two external leaves. The vertical component increases the fragility of the wall and confirms the relevance of vertical ground motion for very vulnerable constructions. Nonetheless, to worsen the response, the vertical component needs to overcome specific, non-negligible intensity measure thresholds

Dinamica non lineare fuori del piano di pareti murarie. Stato dell'arte, sperimentazione e modellazione

La tesi è articolata secondo lo schema che segue. Il capitolo 2 contiene una ricognizione dello stato dell'arte sulla modellazione della risposta dinamica fuori del piano di pareti murarie e sulle campagne sperimentali condotte al riguardo; l’attenzione è centrata sui temi più pertinenti al resto della dissertazione. Il capitolo 3 studia la formulazione analitica della dissipazione impulsiva dell'energia cinetica di una parete in oscillazioni bilaterali e di una parete in oscillazioni monolaterali. Per la seconda è proposta una formulazione originale. Entrambe le formulazioni sono messe a confronto con i risultati di una campagna di prove sperimentali di oscillazione libera, nella quale è stata valutata l’influenza di diversi parametri di interesse. Nello stesso capitolo è stata studiata l’influenza della dissipazione dell’energia sulla risposta dinamica di pareti murarie a segnali sismici naturali. Il capitolo 4 prende le mosse da una sperimentazione originale su tavola vibrante di una parete accostata a muri trasversali. Successivamente a una sintesi delle prove si propone un modello analitico di parete in oscillazione monolaterale e su fondazione inclinata, con dissipazione impulsiva dell’energia tarata sulla base delle prove del precedente capitolo. Il modello così messo a punto è confronto con codici di calcolo commerciali, con casi studio reali e con le procedure statiche equivalenti di normativa. Completano la tesi appendici sulle sperimentazioni e sulle eccitazioni sismiche impiegate

Constrained Rationality: Formal Value-Driven Enterprise Knowledge Management Modelling and Analysis Framework for Strategic Business, Technology and Public Policy Decision Making & Conflict Resolution

The complexity of the strategic decision making environments, in which busi- nesses and governments live in, makes such decisions more and more difficult to make. People and organizations with access to the best known decision support modelling and analysis tools and methods cannot seem to benefit from such re- sources. We argue that the reason behind the failure of most current decision and game theoretic methods is that these methods are made to deal with operational and tactical decisions, not strategic decisions. While operational and tactical decisions are clear and concise with limited scope and short-term implications, allowing them to be easily formalized and reasoned about, strategic decisions tend to be more gen- eral, ill-structured, complex, with broader scope and long-term implications. This research work starts with a review of the current dominant modelling and analysis approaches, their strengths and shortcomings, and a look at how pioneers in the field criticize these approaches as restrictive and unpractical. Then, the work goes on to propose a new paradigm shift in how strategic decisions and conflicts should be modelled and analyzed. Constrained Rationality is a formal qualitative framework, with a robust method- ological approach, to model and analyze ill-structured strategic single and multi- agent decision making situations and conflicts. The framework brings back the strategic decision making problem to its roots, from being an optimization/efficiency problem about evaluating predetermined alternatives to satisfy predetermined pref- erences or utility functions, as most current decision and game theoretic approaches treats it, to being an effectiveness problem of: 1) identifying and modelling explic- itly the strategic and conflicting goals of the involved agents (also called players and decision makers in our work), and the decision making context (the external and internal constraints including the agents priorities, emotions and attitudes); 2) finding, uncovering and/or creating the right set of alternatives to consider; and then 3) reasoning about the ability of each of these alternatives to satisfy the stated strategic goals the agents have, given their constraints. Instead of assuming that the agents’ alternatives and preferences are well-known, as most current decision and game theoretic approaches do, the Constrained Rationality framework start by capturing and modelling clearly the context of the strategic decision making situation, and then use this contextual knowledge to guide the process of finding the agents’ alternatives, analyzing them, and choosing the most effective one. The Constrained Rationality framework, at its heart, provides a novel set of modelling facilities to capture the contextual knowledge of the decision making sit- uations. These modelling facilities are based on the Viewpoint-based Value-Driven - Enterprise Knowledge Management (ViVD-EKM) conceptual modelling frame- work proposed by Al-Shawa (2006b), and include facilities: to capture and model the goals and constraints of the different involved agents, in the decision making situation, in complex graphs within viewpoint models; and to model the complex cause-effect interrelationships among theses goals and constraints. The framework provides a set of robust, extensible and formal Goal-to-Goal and Constraint-to Goal relationships, through which qualitative linguistic value labels about the goals’ op- erationalization, achievement and prevention propagate these relationships until they are finalized to reflect the state of the goals’ achievement at any single point of time during the situation. The framework provides also sufficient, but extensible, representation facilities to model the agents’ priorities, emotional valences and attitudes as value properties with qualitative linguistic value labels. All of these goals and constraints, and the value labels of their respective value properties (operationalization, achievement, prevention, importance, emotional valence, etc.) are used to evaluate the different alternatives (options, plans, products, product/design features, etc.) agents have, and generate cardinal and ordinal preferences for the agents over their respective alternatives. For analysts, and decision makers alike, these preferences can easily be verified, validates and traced back to how much each of these alternatives con- tribute to each agent’s strategic goals, given his constraints, priorities, emotions and attitudes. The Constrained Rationality framework offers a detailed process to model and analyze decision making situations, with special paths and steps to satisfy the spe- cific needs of: 1) single-agent decision making situations, or multi-agent situations in which agents act in an individualistic manner with no regard to others’ current or future options and decisions; 2) collaborative multi-agent decision making situ- ations, where agents disclose their goals and constraints, and choose from a set of shared alternatives one that best satisfy the collective goals of the group; and 3) adversarial competitive multi-agent decision making situations (called Games, in gamete theory literature, or Conflicts, in the broader management science litera- ture). The framework’s modelling and analysis process covers also three types of con- flicts/games: a) non-cooperative games, where agents can take unilateral moves among the game’s states; b) cooperative games, with no coalitions allowed, where agents still act individually (not as groups/coalitions) taking both unilateral moves and cooperative single-step moves when it benefit them; and c) cooperative games, with coalitions allowed, where the games include, in addition to individual agents, agents who are grouped in formal alliances/coalitions, giving themselves the ability to take multi-step group moves to advance their collective position in the game. ...

Enterobiasis among Pre-School Children in Gaza Strip, Palestine.

Background: Enterobius is one of the common nematode causing health problem in developing countries. The aim of the present study was to estimates the prevalence of Enterobius vermicularis in Gaza Strip. Methods: This is a cross-sectional study which included 149 pre-school children who are residing in four Governorates in Gaza Strip; north Gaza, Gaza, mid zone and Khanyounis in Gaza Strip. Scotch tape preparation (STP) was used for the detection of E. vermicularis eggs. Results: Children with employee father had high prevalence of E. vermicularis with a percentage of (47.3%) while those with un-employee father had a percentage of (45.7%) but there was no significant difference. The same results were found with working mother. Families with low family income had children with low rate of E. vermicularis (40.5%) but families with high family income had children with high rate of E. vermicularis (52.8%). Children who are drinking water from filters had high rate of E. vermicularis than others who are drinking from other sources (65%) with a significant difference (p= 0.003). Conclusion: The study concluded that enterobiasis constituted a high prevalence among pre-school children in Gaza strip (46.3%). These results may shed the light on an infectious disease in Gaza Strip and help health authorities to take serious measures for prevention and control, and educate peoples towards the biology of Enterobius

Non-linear dynamic model of a two-bodies vertical spanning wall elastically restrained at the top

Understanding the out-of-plane behavior of unreinforced masonry walls is crucial in seismic assessment of existing buildings. Here, the dynamic response of a vertical spanning strip wall, connected to a flexible diaphragm at the top, is investigated. Despite the simplicity of the model, two rocking rigid bodies elastically restrained at the top, the dynamic response is highly nonlinear. This behavior is due to different phenomena: when in motion the system may assume different configurations, with the transition between them due either to impacts or crack opening caused by ground acceleration. An analytical model capable to capture the complex dynamic response of the system is implemented. The equations of motion are first derived, using variational methods, then the events that the system can undergo during motion are studied. Finally, in order to show the potential of the model, some numerical exemplifications are presented applying an earthquake record and a sine pulse to the system

Shake table testing of a low-impact technology for the seismic protection of stone masonry

This paper presents a novel low-impact technique for the seismic protection of fair-face masonry walls. The proposed strengthening solution involves the use of carbon-fibre reinforced polymer (CFRP) connectors installed from the outside by perforating the stone elements, combined with grout injections. The connectors cover ¾ of the wall thickness, so as to leave the inner surface undisturbed. Once the work is completed, they are also substantially invisible. Shake table tests were carried out under natural accelerograms on two full-scale irregular multi-leaf stone masonry wall specimens. In order to replicate materials and construction technique of the Apennine historical buildings, the prototypes were made from stones recovered from the debris of a settlement in the municipality of Accumoli (RI, Italy), and the mortar was designed to reproduce lime-poor mortars surveyed in the field. The experimental setup was designed to induce out-of-plane vertical bending under base seismic motion, while allowing the vertical displacement of the wall top. One specimen was tested “as-built” and the other one was tested strengthened, to investigate the gain in seismic performance, the limitation of progressive damage accumulation and the effects on dynamic properties

Comparison between rocking analysis and kinematic analysis for the dynamic out-of-plane behavior of masonry walls

This paper provides a contribution to the rocking analysis of masonry walls by making a comparison with the kinematic analysis suggested by the Italian code. It is shown that the latter approach is generally over-conservative and therefore potentially inappropriate for historic buildings, where rehabilitation can be expensive and can affect their cultural value. The equation of motion given by the Housner formulation, corresponding to the movement of a rigid block, is here modified to account for different boundary conditions at different heights of the wall. These boundary conditions, or horizontal restrainers, can represent vaults, transverse walls or retrofitting devices such as steel tie-rods. A systemic analysis of walls having different dimensions and slenderness is performed, and the results from the Italian code and rocking analysis are compared. Finally, the improvement in the response offered by retrofitting devices is discussed in terms of reduction of amplitude ratio