Impact Stiffness of the Contact-Element Models for the Pounding Analysis of Highway Bridges: Experimental Evaluation

For the requirement of pounding analysis of highway bridges, how to properly choose the impact stiffness has become a primary issue for an achieving accurate result. This article presents an evaluation test of the impact stiffness of four types of contact-element models based on the shaking table test results of a steel highway bridge model. The analytical results indicate that the theoretical impact parameters are significantly larger than the identified values because the assumptions for deriving those models cannot match the actual impact conditions. The possible reasons causing those differences are discussed at the end of this study.     

Population–Employment Models: Stationarity, Cointegration, and Dynamic Adjustment

Abstract.  Population and employment in the 50 United States are found to be non‐stationary and cointegrated. Vector error correction (VEC) models exhibit dynamics with adjustment to shocks essentially completed in 30–35 years . This contrasts with adjustment periods between one and two centuries for non‐stationary models specified in levels. These dynamic adjustment patterns support the hypothesis that relatively long adjustment periods and slow dynamics are probably the spurious results of using non‐stationary levels of population and employment outside of a VEC model framework. Recommendations for modeling the population–employment relationship are offered based on the findings reported.     

The Net Effects of Large Plant Locations and Expansions on County Employment*

This paper argues that the net economic impact of new firm locations or expansions is determined by a multitude of opposing forces. Using a unique database, I set out to evaluate the net effects of these opposing forces by looking at the net change in local employment and population arising from large (greater than 300 new jobs) firm locations or expansions in the State of Georgia. The analysis suggests that the employment multipliers associated with new firm locations are much less than one; that is, the net employment effect of a large firm opening is smaller than the gross employment impact. This result is consistent with other empirical economic impact studies, which find multipliers much smaller than those of typical input–output models, often less than unity, and a previous study showing little net effect of large plant openings. Expansions of existing establishments are shown to have substantial multiplicative effects, however, with an average employment multiplier of 2.0. I discuss possible reasons for differential impacts across new and expanding firms, focusing on the nature of the firms. Differences in net impact across industries and high‐tech versus low‐tech firms also is evaluated. I find that the impact of large firm locations or expansions on population in the resident county generally is negative, but positive for the broader region encompassing the county of location and its contiguous neighbors.     

Point-to-Surface Pounding of Highway Bridges with Deck Rotation Subjected to Bi-Directional Earthquake Excitations

Post-earthquake survey of several strong earthquakes demonstrated that pounding between the neighboring civil infrastructures, such as building and highway bridge, would induce significant structural damage, even collapse, of the structures. This article presents a pounding experiment of highway bridge, especially focused on the point-to-surface pounding of bridge decks due to torsional rotation, when subjected to extreme bi-directional earthquake excitations. To experimentally investigate the point-to-surface pounding between the neighboring bridge segments, a base-isolated highway bridge model, in which the mass centers of the bridge decks do not strictly coincide with the corresponding stiffness centers, is manufactured. A series of shaking table tests of the highway bridge model are carried out for the structural model with large and small separations of the expansion joint to investigate the dynamic responses of the bridge model with and without including the pounding effects, respectively. An analytical model of the highway bridge, in which the point-to-surface pounding is represented by using a modified contact-friction element, is also established based on the lump mass model with three degrees of freedom for each segment. Based on the test results, the model parameters of the modified contact-friction element are identified, and the analytical responses of the highway bridge model with pounding effects are compared with the experimental data. The results show that the highway bridge is vulnerable to the deck rotation, and point-to-surface pounding should be considered in the structural design to lighten the pounding damage of the highway bridge under strong earthquake excitations.     

THE 1987 STOCK MARKET CRASH AND NEW YORK CITY EMPLOYMENT: AN INTERVENTION-MULTIPLIER ANALYSIS*

ABSTRACT. Intervention analysis is used to assess the impact of the October 1987 stock market crash upon employment in the securities industry in New York City. The results indicate that the crash has led to a gradual, but permanent reduction of approximately 25,000 jobs in this industry through July 1990. Using a dynamic location quotient methodology to measure basic employment, an estimate of a partial-adjustment economic base multiplier suggests that total New York City employment is likely to decline by over 100,000 as a result of the crash and subsequent adjustments in the securities industry.     

Gender, space, and the location changes of jobs and people: a spatial simultaneous equations analysis

This article summarizes a spatial econometric analysis of local population and employment growth in the Netherlands, with specific reference to impacts of gender and space. The simultaneous equations model used distinguishes between population- and gender-specific employment groups, and includes autoregressive and cross-regressive spatial lags to detect relations both within and among these groups. Spatial weights matrices reflecting different bands of travel times are used to calculate the spatial lags and to gauge the spatial nature of these relations. The empirical results show that although population–employment interaction is more localized for women's employment, no gender difference exists in the direction of interaction. Employment growth for both men and women is more influenced by population growth than vice versa. The interaction within employment groups is even more important than population growth. Women's, and especially men's, local employment growth mostly benefits from the same employment growth in neighboring locations. Finally, interaction between these groups is practically absent, although men's employment growth may have a negative impact on women's employment growth within small geographic areas. In summary, the results confirm the crucial roles of gender and space, and offer important insights into possible relations within and among subgroups of jobs and people.     

The minimum wage and seasonal employment: Evidence from the US agricultural sector

Nearly 40% of agricultural workers in the United States earn an hourly wage that is within 10% of the prevailing state-level minimum wage. We evaluate the impact of the minimum wage on farm employment using county-level data from the United States Census of Agriculture. We employ long-differences specifications and find evidence of a dynamic, negative effect of the minimum wage on seasonal agricultural employment, but no effect on year-round agricultural employment. We estimate a long-run elasticity of total agricultural employment with respect to the minimum wage of about −0.40, which is both statistically and economically significant. Employers’ total expenditures on hired agricultural workers are not affected by the minimum wage. Finally, our analysis suggests that increases in minimum wages may lead to higher capital investment as well as the consolidation of farming operations in the agricultural sector.     

REGIONAL POPULATION–EMPLOYMENT DYNAMICS ACROSS DIFFERENT SECTORS OF THE ECONOMY*

ABSTRACT An important subset of the literature on agglomeration externalities hypothesizes that intrasectoral and intersectoral relations are endogenously determined in models of local and regional economic growth. Remarkably, structural adjustment models describing the spatio‐temporal dynamics of population and employment levels or growth traditionally do not include intersectoral economic dynamics. This paper argues and shows that allowing for economic linkages across sectors in these models adds considerable value, especially in forecasting. An econometric model of population–employment dynamics, in which sectoral variations in economic development are explicitly taken into account, is applied to a large urban planning policy proposal in the Netherlands. The empirical analyses suggest that population dynamics are largely exogenous, population changes drive employment in particular in the industry and retail sectors, and employment in all sectors depends strongly on intersectoral dynamics. Intersectoral dynamics appear as important drivers of regional sectoral employment changes; they are even more important than population changes, and their effect shows up clearly even within the Dutch institutional context where strict regulatory housing and planning restrictions are enforced.     

SPATIAL DISCONTINUITY FOR THE IMPACT ASSESSMENT OF THE EU REGIONAL POLICY: THE CASE OF ITALIAN OBJECTIVE 1 REGIONS*

The economic impact of the Regional Policy of the European Union is still controversial. This paper exploits administrative boundaries as spatial discontinuity to estimate the causal effect of this policy on the Italian Objective 1 regions’ employment. The analysis, developed both in a border strategy framework (municipalities contiguous to the policy‐change boundary) and with more traditional RDD models balanced by spatial forcing variables (centroids’ distance and coordinates), shows that the EU Regional Policy produced a positive impact on employment levels, without any displacement of economic activities away from nontreated regions and a concentration of the impact in key economic sectors.     

WHEN AND HOW DOES COMMUTING TO CITIES INFLUENCE RURAL EMPLOYMENT GROWTH?

This paper estimates the influence that rural‐to‐urban commuting has on rural employment growth, and whether the strength and spatial reach of this effect depend on commuters’ levels of education. A main finding is that rural‐to‐urban commuting has a robust positive impact on rural employment growth in services and retail. There is no significant difference in how far these effects reach into rural Sweden for commuters with different levels of education. These results suggest that a viable policy for local employment growth in rural areas with reasonable commuting times to urban centers is to improve the commuting to urban centers.     

Airport delays and metropolitan employment

This study provides the first empirical assessment of the impact airline delays have on urban employment. While previous works have suggested that road congestion can slow down regional development, the influence of air traffic delays on metro‐level jobs has not been examined comprehensively. The present study uses a nine‐year panel of quarterly data, which covers passenger airline traffic and delays at airports across urban areas in the United States. The panel also includes data on total and industry‐specific employment at the metropolitan‐area level. Our empirical estimates of the impact of air traffic on total employment are comparable to previously reported measures in the literature. However, we find that service‐sector employment is less sensitive to air traffic than other studies suggested. We provide new evidence confirming that delays have a negative effect on employment, a finding that is robust to various specifications of our empirical model. Our results indicate that a 10 percent increase in the number of delayed flights leads to up to a 0.15 percent decrease in total and service‐sector employment, a 0.47 percent decline in leisure and hospitality employment, and a 0.7 percent reduction in the employment level of goods‐producing jobs.     

A few “big players”: Systems approach to immigrant employment in a mid-sized city

Canada's immigration policy is regarded globally as a best practice model for selecting highly skilled migrants. Yet, upon arrival many immigrants face challenges integrating into employment. Where immigrants settle is one factor that has been shown to impact on employment integration. In Canada, regionalization policies have resulted in more immigrants settling in small to mid-sized cities. It is important to understand how these local systems are organized to promote immigrant integration into employment. Using a systems approach, this paper presents a case study of immigrant employment in a mid-sized city in Ontario, Canada. Through a document review and stakeholder interviews, a systems map was developed, and local perspectives were analyzed. Results demonstrate that in a mid-sized city, few organizations play a large role in immigrant employment. The connections between these core organizations and the local labour market are complex. Any potential challenges to the system that interfere with these connections can cause a delay for newcomers seeking employment. As cities begin to experience growth driven by immigration, there is a need to ensure local services are not only available but also working effectively within the larger employment system.     

THE IMPACT OF LOCAL DECENTRALIZATION ON ECONOMIC GROWTH: EVIDENCE FROM U.S. COUNTIES*

ABSTRACT We analyze the impact of fiscal decentralization on U.S. county population, employment, and real income growth. Our findings suggest that government organization matters for local economic growth, but that the impacts vary by government unit and by economic indicator. We find that single‐purpose governments per square mile have a positive impact on metropolitan population and employment growth, but no significant impact on nonmetropolitan counties. In contrast, the fragmentation of general‐purpose governments per capita has a negative impact on employment and population growth in nonmetropolitan counties. Our results suggest that local government decentralization matters differently for metropolitan and nonmetropolitan counties.     

Modeling Micro-Spatial Employment Location Patterns: A Comparison of Count and Choice Approaches

This article studies employment location patterns in the Puget Sound Region of Washington State at a micro level of geography. Traditional discrete choice modeling using multinomial logit (MNL) models may be problematic at a micro level of geography due to the high dimensionality of the set of alternative locations and the likely violations of the independence from irrelevant alternatives (IIA) assumption. Count models are free from the IIA assumption and, unlike logit models, actually benefit from large numbers of alternatives by adding degrees of freedom. This study identifies the best-fitting count model as the zero-inflated negative binomial (ZINB) model, because this model more effectively addresses the large number of cells with no jobs and reflects a dual process that facilitates the identification of threshold clustering effects such as those found in specialized employment centers. The estimation and prediction results of ZINB are compared with those of MNL with a random sampling of alternatives estimated on an equivalent data set. The ZINB and MNL models largely agree on major trends, with the ZINB model providing more insightful details, but with less capacity to predict large count situations.     

Employment Risk in U.S. Metropolitan and Nonmetropolitan Regions: the Influence of Industrial Specialization and Population Characteristics

Abstract.  A dynamic labor market model is used to motivate the inclusion of population characteristics and industrial structure as determinants of regional employment instability. We examine how these factors influence regional employment instability using data from both metropolitan and nonmetropolitan regions in the United States. We find that population characteristics are important determinants of employment volatility and that increased industrial specialization (reduced diversification) increases employment volatility, but the magnitude of that influence drops substantially once population characteristics are considered. We also find that the influence of population characteristics and industrial specialization varies significantly across metropolitan and nonmetropolitan regions.     

Spatial Mismatch and the Structure of American Metropolitan Areas, 1970–2000

Abstract.  This paper analyzes the impact of employment and population shifts in U.S. metropolitan areas from 1970 to 2000 on a spatial mismatch index to determine how metropolitan residents reacted to changes in metropolitan employment distributions. In particular, it seeks to determine whether suburban employment growth created new areas to which access is valued or whether it repelled metropolitan residents and sparked population growth in more distant suburban locations. The results show that residents tended to move away from areas gaining jobs. Black residents, on the other hand, appeared to be attracted to areas that are experiencing employment growth.     

New Technologies,Employment and Labour Markets in Developing Countries

This article is concerned with the impact of new technologies - especially, but not entirely, those that are related to microelectronics - on employment and labour markets in developing countries. Taking the form of a literature survey it looks at those impacts that have already occurred as well as effects that seem likely to occur in the future. Both sets of issues are addressed within an analytical framework that views the impact of technical change as the end result of a process which begins with the generation and proceeds via the diffusion of new technologies. The need for so broad an approach is shown to stem from the multiplicity of ways in which the generation and diffusion of new technologies influence each other and condition the ultimate impact of these technologies on employment and labour markets. Because many such mechanisms have not yet received much attention in the literature, there appears to be substantial scope for further research.     

Analytical Modeling of Horizontally Curved Steel Girder Highway Bridges for Seismic Analysis

This article introduces a generic modeling approach that is suitable for static and dynamic analysis, and response assessment of highway bridges with varying levels of irregularities. The proposed approach and modeling recommendations are based on grillage modeling rules that allows explicit representation of various types of details and components. The validity and accuracy of the proposed approach is demonstrated against three-dimensional finite element models as well as experimentally recorded response various benchmark bridges. While achieving remarkable accuracy, the required analysis time was also reduced up to 80%, making the proposed approach suitable for computationally intensive studies.     

How does transportation shape intrametropolitan growth? An answer from the Regional Express Rail

This paper analyzes the influence of transportation infrastructure, and in particular of the Regional Express Rail (RER), on employment and population growth in the Paris metropolitan area between 1968 and 2010. In order to make proper causal inference, we rely on historical instruments and control for all other transportation modes that could be complement or substitute to the RER. Our results show that proximity to an RER station increases employment and population density and, in particular, employment and population growth. The latter effects are higher in municipalities located near RER stations and close to employment (sub)centers. They are also found to be particularly strong for jobs in the service sector, for factory workers, and for highly educated population. We find no impact of the RER expansion on employment growth during the first part of the period, while the effect on population growth appears earlier but declines over time.     

基于地铁刷卡数据的城市通勤与就业中心吸引范围研究

地理时空大数据为通勤行为和城市空间结构研究带来了新的机遇。基于一周地铁刷卡数据,采用出行链（trip-chain）数据模型对用户一天的出行进行描述,建立通勤识别规则,识别出上海市域的职住空间和通勤格局。上海市域平均通勤时间为35 分钟,通勤主流向是向心流,说明上海市域依旧表现出强单中心结构。市域就业单中心与居住郊区化并存,中心城区多核心就业已经形成。在此基础上进一步分析中心城区13 个就业（次）中心的吸引范围、模式以及在整个市域的影响力,讨论多中心发展对职住平衡与通勤消减的意义。结果表明：多中心发展有利于城市通勤的合理分配,虽然次中心的平均通勤时间不一定减少,但是就业（次）中心已经表现出对邻近地区的通勤吸引和对主中心的通勤分流。