Dynamic optimization of horticulture among the Muscogee Creek Indians of the southeastern United States

This paper reviews archaeological applications of optimization theory applied to resource use. A model of agricultural corn production is derived for a single Muscogee Creek Indian town (CA 1725–1825) which was situated in the southeastern United States. The corn productivity model is based on soil depletion, soil variation, known locations of horticultural fields, population size, and nutritional requirements. The corn productivity model shows that corn production varied significantly between 1725 and 1825. The residents of the town shifted their horticultural gardens in order to maintain a nutritional minimum. The model was compared to the marginal value theorem and expectations derived from risk minimization models. Residents of Cussetuh abandoned their horticultural fields well before the instantaneous long-term average rate of production for the habitat. The model shows that the residents of Cussetuh were risk minimizers and were not maximizing the long term average rate of corn yield in their gardens.     

Unconditional Reliability-Based Design of Tuned Liquid Column Dampers Under Stochastic Earthquake Load Considering System Parameters Uncertainties

The reliability-based design of tuned mass damper considering system parameters uncertainties is noteworthy. However, the same is not the case for liquid dampers. The present study deals with the reliability-based design of tuned liquid column dampers under random earthquake considering system parameters uncertainties. Using the conditional second-order information of response quantities, the total probability concept is applied to evaluate the unconditional failure probability which is subsequently used as the objective function to obtain the damping parameters. A numerical study elucidates the effect of system parameters uncertainties on the damper parameters optimization and safety of the structure.     

An XFEM Model for Seismic Activity in Indian Plate

Empirical approaches based on the available earthquake catalog are popular among engineers to estimate seismic hazard. The seismic activity on individual faults inferred from these approaches is associated with a large number of uncertainties, especially due to lack of data. This article proposes a mechanistic approach to quantify seismic and fault activity, thereby overcoming the difficulties in the existing empirical procedure. A finite element (FE) model for Indian Plate, with the geological ‘cratons’ is developed and subject to plate driving forces namely, the ridge push and the slab pull forces. The material properties and the thickness of both plate and cratons are obtained through inversion using the recently available Global Positioning System (GPS) data. The tectonic faults are modeled using the well-known ‘extended FE method (XFEM)’. The simulated strains at fault level are compared with the computed strain rates from the earthquake catalog. Further, the procedure to quantify fault activity is demonstrated for Gujarat, India.     

On-line Model Updating in Hybrid Simulation Tests

Hybrid simulation has emerged as a relatively accurate and efficient tool for the evaluation of structural response under earthquake loading. In conventional hybrid simulation the response of a few critical components is obtained by testing while the numerical module is assumed to follow an analytical idealization. Where there is a much larger number of analytical components compared to the experimental parts, the overall response may be dominated by the idealized parts hence the value of hybrid simulation is diminished. It is proposed to modify the material constitutive relationship of the numerical model during the test, based on the data obtained from the physically tested component. An approach based on genetic algorithms is utilized as an optimization tool to identify the constitutive relationship parameters used in updating the numerical model. The proposed model updating approach is verified through two analytical examples of steel and reinforced concrete frames. The results show the effectiveness of the updating process in minimizing the errors, compared to the assumed exact solution.     

Application of In-Test Model Updating to Earthquake Structural Assessment

Analytical methods are frequently utilized for structural assessment due to their simplicity and cost-effectiveness. However, modeling of material inelasticity and geometric nonlinearity under reversed inelastic deformations is still very challenging and its accuracy is difficult to quantify. On the other hand, realistic experimental assessment is costly, time-consuming, and impractical for large or spatially extended structures. Hybrid simulation has been developed as an approach that combines the realism of experimental techniques with the economy of analytical tools. In hybrid simulation, the structural is divided into several modules such that the critical components are tested in the laboratory, while the rest of the structure is simulated numerically. The equations of motion solved in the computer enable the integration of the analytical and experimental components at each time increment. The objective of this article is to apply a newly developed identification and model updating scheme to acquire the material constitutive relationship from the physically tested specimen during the analysis to two complex hybrid simulation case studies. The identification scheme is developed and verified in a companion article, while the two experiments presented in this article are selected such that they address different structural engineering applications. First, a beam-column steel connection with heat treated beam section is analyzed. Afterwards, the response of a multi-bay concrete bridge is investigated. The results of these two examples demonstrate the effectiveness of model updating to improve the numerical model response as compared to the conventional hybrid simulation approaches.     

南京狮子山段损伤城墙的加固对策研究

为探索南京城墙科学保护对策及加固技术方法,针对狮子山的地形特征和城墙建造特点,通过城墙本体损伤调查和山体地质勘探,对狮子山段城墙再次发生局部坍塌原因进行了分析;采用传统造城工艺与现代加固技术修复坍塌墙体,恢复了城墙与山体的排水系统;对墙体裂缝病害进行安全监测,改善了该段城墙的生存环境.此方法可为进一步研究同类城墙保护提供技术参考.     

Robust Performance-Based Design Optimization of Steel Moment Resisting Frames

The concept of performance-based design is considered in the framework of Robust Design Optimization (RDO) for the design of steel structures. The RDO problem is treated as a two-objective optimization problem where the initial construction cost and the variance of the maximum interstorey drift for the 10% in 50 years hazard level are considered as the problem objectives to be minimized. The structural performance is evaluated by means of the reliability demand and resistance methodology of the FEMA-350 guidelines in order to take into account both uncertainty and randomness in a consistent manner. The structure is designed to respond for different levels of seismic hazard levels with a desired confidence. The limit-state damage cost is used as a measure for the assessment of selected designs that have been obtained through the proposed RDO formulation. The non deterministic finite element problem encountered, is solved using the Monte Carlo Simulation method. The NSGA-II algorithm has been combined with the Evolution Strategies optimization algorithm for solving the two-objective optimization problem at hand.     

The Influence of Masonry Infill Walls in the Framework of the Performance-Based Design

In this article, a performance-based seismic design (PBD) methodology is proposed for the design of reinforced concrete buildings, taking into account the influence of infill walls. Two variants of the PBD framework are examined: The first is based on the non-linear static analysis procedure (NSP) while the second relies on the non-linear dynamic analysis procedure (NDP). Both design approaches are compared in the context of structural optimization with reference to the best possible design achieved for each case examined. Life-cycle cost analysis is considered a reliable tool for assessing the performance of structural systems and it is employed in this study for assessing the optimum designs obtained. The optimization part of the problem is performed with an Evolutionary Algorithm while three performance objectives are implemented in all formulations of the design procedures. The two most important findings can be summarized as follows: (i) if structural realization follows the design assumptions, then total expected life-cycle cost of the three type of structures, bare, fully infilled and open ground story, is almost the same and (ii) if an open ground story building is designed as bare or as fully infilled frame, real performance will be much worse than anticipated at the design stage.     

A Ground Motion Record Selection Approach Based on Multiobjective Optimization

The evaluation of the seismic safety and reliability of buildings and building contents within a probabilistic framework often requires response history analyses using site-specific ground motion records. The ground motion selection method proposed in this paper addresses this issue by a stochastic search procedure in which record sets are selected such that first- and second-order statistics (median and dispersion) satisfy predefined ground motion spectrum targets over a wide period range. Once a ground motion record set is selected, it can be used for seismic assessment of a broad class of buildings within the target period range at the given location.