Methods and Approaches for Blind Test Predictions of Out-of-Plane Behavior of Masonry Walls: A Numerical Comparative Study

ABSTRACT

Earthquakes cause severe damage to masonry structures due to inertial forces acting in the normal direction to the plane of the walls. The out-of-plane behavior of masonry walls is complex and depends on several parameters, such as material and geometric properties of walls, connections between structural elements, the characteristics of the input motions, among others. Different analytical methods and advanced numerical modeling are usually used for evaluating the out-of-plane behavior of masonry structures. Furthermore, different types of structural analysis can be adopted for this complex behavior, such as limit analysis, pushover, or nonlinear dynamic analysis.

Aiming to evaluate the capabilities of different approaches to similar problems, blind predictions were made using different approaches. For this purpose, two idealized structures were tested on a shaking table and several experts on masonry structures were invited to present blind predictions on the response of the structures, aiming at evaluating the available tools for the out-of-plane assessment of masonry structures. This article presents the results of the blind test predictions and the comparison with the experimental results, namely in terms of formed collapsed mechanisms and control outputs (PGA or maximum displacements), taking into account the selected tools to perform the analysis.     

NEW FRONTIERS OF IMMIGRATION RESEARCH: CITIES AND FIRMS*

ABSTRACT The increase in international migration to rich countries during the last two decades has spurred research and policy questions. The economic determinants of national and international migrations and the impact of immigrants on labor markets have been investigated by economists, geographers, and regional scientists for a long time. Recently, however, the availability of new and detailed individual data on migrants across regions and localities in several countries has made it possible to analyze the impact of immigration on a richer set of socio‐economic outcomes. Two avenues of research have emerged as particularly interesting and are the focus of this special issue. First, international migrants are particularly concentrated in urban areas but their impact on some outcomes that are particularly relevant in cities (such as crime and housing markets) are not well understood yet. Second, immigrants not only increase labor supply but also affect firms’ productivity, survival and growth through their impact on localized externalities. These two themes link all the contributions of this special issue and show new directions for future research on the impact of immigration.     

INTRODUCTION: WHITHER SPATIAL ECONOMETRICS?

ABSTRACT Spatial econometrics has become a mainstay for regional scientists aiming to estimate geographic spillovers in regional outcomes. Yet, many remain skeptical, especially urban economists who prefer natural experimental approaches. Their concerns revolve around identification and a general lack of a theoretical foundation in the estimation of spatial econometric models. This theme issue includes three papers from leading regional scientists to appraise the status of spatial econometrics. The outcome is sweeping proposals from (1) abandoning standard spatial econometrics because it cannot identify causality, (2) using nonparametric approaches, and (3) implementing more nuanced changes revolving around better theoretical and empirical modeling.     

OPENNESS TO TRADE AND INDUSTRY COST DISPERSION: EVIDENCE FROM A PANEL OF ITALIAN FIRMS*

ABSTRACT We use Italian firm‐level data to investigate the impact of trade openness on the distribution of firms across marginal cost levels. In so doing, we implement a procedure that allows us to control not only for the standard transmission bias identified in firm‐level TFP regressions but also for the omitted price bias due to imperfect competition. We find that more open industries are characterized by a smaller dispersion of costs across active firms. Moreover, in those industries the average cost is also smaller.     

On economic geography in economic theory: increasing returns and pecuniary externalities

Our objective is twofold. First, we show why there is a spatialquestion in economic theory – why a free competitive marketis unable to cope with agglomeration and regional imbalancein the absence of market distortions. Second, using a new andsimple model, we review what has been accomplished in economictheory during the 1990s when due allowance is given to increasingreturns, while market structure is given by monopolistic competition.     

An analytically solvable core-periphery model

We develop an analytically solvable version of the central modelof ‘new economic geography’, the so called core-peripherymodel by Krugman. While the modified model reproduces all theappealing features of the original one, it also allows us toobtain additional analytical results that are out of reach inKrugman's set-up. First, we are able to assess the exact numberof equilibria and their global stability properties. Second,we are able to investigate the implications of exogenous asymmetriesbetween countries. This is achieved by introducing heterogeneitybetween high-skill mobile and low-skill immobile workers, whichmay also be an empirically attractive property.     

CULTURAL IDENTITY AND KNOWLEDGE CREATION IN COSMOPOLITAN CITIES*

ABSTRACT We study how the city system is affected by the possibility for the members of the same cultural diaspora to interact across different cities. In so doing, we propose a simple two‐city model with two mobile cultural groups. A localized externality fosters the productivity of individuals when groups interact in a city. At the same time, such interaction dilutes cultural identities and reduces the consumption of culture‐specific goods and services. We show that the two groups segregate in different cities when diaspora members find it hard to communicate at distance whereas they integrate in multicultural cities when communication is easy. The model generates situations in which segregation is an equilibrium but is Pareto dominated by integration.     

Methods and Challenges for the Seismic Assessment of Historic Masonry Structures

ABSTRACT

Despite the high vulnerability of historic structures to earthquakes, the approaches for evaluating seismic demand and capacity still appear inadequate and there is little consensus on the most appropriate assessment methods to use. To develop an improved knowledge on the seismic behavior of masonry structures and the reliability of analysis tools, two real-scale specimens were tested on a shake table, and several experts were invited to foresee failure mechanism and seismic capacity within a blind prediction test. Once unveiled, experimental results were simulated using multi-block dynamics, finite elements, or discrete elements. This article gathers the lessons learned and identifies issues requiring further attention. A combination of engineering judgment and numerical models may help to identify the collapse mechanism, which is as essential as it is challenging for the seismic assessment. To this purpose, discrete modeling approaches may lead to more reliable results than continuous ones. Even when the correct mechanism is identified, estimating the seismic capacity remains difficult, due to the complexity and randomness of the seismic response, and to the sensitivity of numerical tools to input variables. Simplified approaches based on rigid body dynamics, despite the considerable experience and engineering judgment required, provide as good results as do advanced simulations.     

The District and the Global Economy: Exportation Versus Foreign Location

We depict an industrial district as a center of innovation where positive local spillovers sustain the endogenous invention of new goods by profit-seeking firms. After invention, firms face a crucial choice between reaching distant markets by export or plant delocation. Attempts by firms to circumvent trade barriers through delocation slow down the pace of innovation and harm the welfare of the district.     

A Bayesian C chronology of Early and Middle Bronze Age in Sicily. Towards an independent absolute dating

This paper proposes a Bayesian model for the ¹⁴C chronology of Sicilian Early and Middle Bronze Age, with a specific focus on the northeastern sector of the island. Building on the available ¹⁴C determinations, the model allows addressing a number of chronological questions left open in literature, making a first step towards an independent absolute chronology. The analysis put the start of the earlier part of Early Bronze Age (Capo Graziano 1-Casa Lopez phase) between 2400 and 2175 cal BC, and the end at about 1960 cal BC. The advanced stage of the same period (Capo Graziano 1-Filo Braccio phase) is likely to have started and ended around 1960 and 1730 cal BC respectively. The model indicates that the time slot with the highest posterior probability for the start of the Middle Bronze Age–Milazzese (Portella phase) is between 1490 and 1460 cal BC. This turns up to be earlier than held to date. Notably, the model enables for the first time to bracket the development of the later stage of Early Bronze (Capo Graziano 2-M. di Capo Graziano phase) between 1730 (end of Filo Braccio phase) and 1490/60 cal BC (start of Middle Bronze Age–Portella phase). The latter date is earlier than usually held for the end of Capo Graziano 2. The existence of a narrow gap between the end of the latter and the start of Middle Bronze Age-Portella phase is tentatively proposed only on stratigraphic grounds. Further, the analysis enables for the first time to pinpoint and quantify the lag that is likely to have existed between the start of those Sicilian prehistoric phases and the appearance of Late Helladic imports. The comparison with the Aegean ¹⁴C Bayesian chronology indicates that a time lag (about 45 yr) is likely to have occurred between the start of Capo Graziano 2 and of the Late Helladic period. A time lag between 20 and 70 yr is likely to have existed between the start of the Sicilian Middle Bronze Age and of the Late Helladic III. Arguments tentatively supporting the narrower interval are also discussed.