Out-of-Plane Seismic Response of Unreinforced Masonry Walls: Conceptual Discussion,Research Needs,and Modeling Issues

ABSTRACT

Modeling unreinforced masonry walls, subjected to seismic loads applied normal to their plane, has received much attention in the past. Yet, there is a general lack of conformance with regard to what aspects of seismic response a computational model should reflect. Boundary conditions are certainly an important aspect, as the response can involve two-way bending or just one-way bending and, in the second case, along vertical or horizontal directions. In this respect, flexural restraint of wall intersections can be significant in addition to size and placement of openings. Moreover, in-plane damage can modify the boundary conditions and the overall out-of-plane performance. Proper modeling of actions is also relevant, as they can be a result of distortions imposed upon wall elements and/or inertial forces along the span of a wall. Axial forces can markedly affect the out-of-plane response of the wall, particularly vertical compressive forces, which can enhance out-of-plane strength. The outcome of static verifications can be more conservative than that of dynamic analyses, but the latter are much more complex to carry out. These topics are discussed with reference to previous research, observations in the field and in the laboratory, as well as numerical analyses on three-dimensional models.     

The United States and the Middle East at the End of the Cold War

Books reviewed in this article:
Burton I. Kaufman, The Arab Middle East and the United States: Inter-Arab Rivalry and Super-Power Diplomacy
Michael W. Suleiman (ed.), U.S. Policy on Palestine from Wilson to Clinton     

Facility Location with Changing Demand Levels

The paper identifies six strategies that may be considered by a planner in the location of public facilities over time. All the strategies share the common goal of producing the optimal locational arrangement at the end of a specified planning period, where optimality is defined in terms of cost minimization. However, the paths taken by each toward the optimal arrangement differ markedly. The analysis focuses on two main questions. The first is a comparison at any given point in time of the demand levels that result from implementing the various strategies. The second is a consideration of the relative costs involved in instituting two of the strategies. The appendix supplies the proofs of the main theorems derived for the demand level comparisons.     

AN ALGORITHM FOR THE SPATIAL PRICE EQUILIBRIUM PROBLEM ON A GENERAL NETWORK IN THE SPACE OF THE PATH FLOWS*

ABSTRACT. The spatial price equilibrium on a general network may be formulated as a nonlinear-cost mathematical programming problem with simple constraints, when the decision variables are the path flows. The solution of this problem is difficult due to the very large number of variables (paths) and the impracticality of generating all the paths from all the origins to all the destinations. In this paper, we develop a Gauss-Seidel-Newton Projection algorithm and combine it with a restriction strategy. That makes it unnecessary to generate a priori all the paths. This algorithm may be further improved by exploiting the equivalence between the spatial price equilibrium on a general network and the network equilibrium. Computational results that we present in this paper demonstrate the efficiency of the proposed solution algorithms.