Dimos C. Charmpis

Overview of the Pathology, Repair and Strengthening of Adobe Structures

Adobe construction is considered to be an important feature of the international architectural heritage. To achieve the effective preservation of culturally significant adobe structures, the factors that cause their deterioration should be recorded and understood and the result of potential restoration interventions should be evaluated. This study reviews the pathology of adobe structures and the various restoration methods currently in use. Focus is given on the main agents of adobe deterioration and commonly encountered decay mechanisms. The applicability and efficiency of several repair and strengthening techniques currently used in practice or proposed by academic researchers is critically discussed and the gaps that occur in the field of earthen masonry retrofitting are highlighted. An extensive list of references, which reflects the international knowledge and experience on the topic, is also provided.

A heuristic approach for the generation of multivariate random samples with specified marginal distributions and correlation matrix

SummaryThis paper presents a heuristic approach for multivariate random number generation. Our aim is to generate multivariate samples with specified marginal distributions and correlation matrix, which can be incorporated into risk analysis models to conduct simulation studies. The proposed sampling approach involves two distinct steps: first a univariate random sample from each specified probability distribution is generated; then a heuristic combinatorial optimization procedure is used to rearrange the generated univariate samples, in order to obtain the desired correlations between them. The combinatorial optimization step is performed with a simulated annealing algorithm, which changes only the positions and not the values of the numbers generated in the first step. The proposed multivariate sampling approach can be used with any type of marginal distributions: continuous or discrete, parametric or non-parametric, etc.

Optimized retrofit of multi-storey buildings using seismic isolation at various elevations: assessment for several earthquake excitations

This work is concerned with the seismic retrofit of multi-storey buildings by installing isolation devices at various levels along their height. The design of an effective retrofit solution of this type requires the selection of the appropriate number of isolation levels to introduce in a building, the elevations at which to place these isolation levels and the properties of each of the isolators to install. The task of identifying configurations of isolators vertically distributed over the height of a building that yield favourable structural behaviour is handled in the present paper with a specially developed optimization procedure, which can automatically and effectively explore the huge set of potential retrofit solutions formed by all possible combinations of isolator numbers, locations and properties. Specifically, a genetic algorithm is implemented to detect the isolation configuration that minimizes the maximum floor acceleration of the building under retrofit, subject to constraints ensuring that maximum allowable values for interstorey drifts, base displacements and overall isolation cost are not exceeded. A 6-storey building is used to test the presented optimization procedure, while several recorded strong earthquake motions are considered, which are applied either individually or in sets to the building in the framework of time-history analyses. The numerical results obtained demonstrate the validity and effectiveness of the optimization procedure, which manages to identify feasible isolation configurations for all test cases examined. Of particular importance is the ability of the optimization procedure to provide valid retrofit solutions for buildings with narrow seismic gaps subjected to very strong earthquakes, in which configurations employing only base isolation usually prove to be ineffective.

The cost of satisfying design requirements on progressive collapse resistance – Investigation based on structural optimisation

This work is concerned with the explicit treatment of progressive collapse resistance within the structural design process. Progressive collapse resistance is associated with the damage tolerance of a structural system and controls the ability of the system to sustain local damage by absorbing the potential of triggering system collapse and suffering disproportionally large consequences. This work focuses on the design of elastoplastic steel frames. The measure of progressive collapse resistance employed is expressed as a ratio comparing the limit loads obtained with elastoplastic analyses of the intact structure and of an artificially damaged structure (‘damage’ is caused by the notional removal of a column from the intact structure). This measure is used to incorporate a constraint on progressive collapse resistance into a structural design optimisation formulation, which – in its classical form – takes only standard design code constraints into account and aims at minimising the structural cost. The developed optimisation approach is capable of producing cost-effective structural designs with acceptable system damage tolerance. By enforcing the satisfaction of the additional design requirement on progressive collapse resistance, structural cost is inevitably increased due to the need for extra material. This increase is quantitatively explored with the presented structural design optimisation approach.

A study of the mechanical behaviour of adobe masonry

Adobe buildings are encountered in almost every region of the world and constitute a significant feature of the international cultural heritage. However, the behaviour of adobe materials and earth masonry has not yet been adequately investigated. This study aims to examine the mechanical properties of mud bricks from Cyprus and the structural response of adobe masonry. Experimental results obtained from the compressive and flexural strength testing of local adobes are presented and analyzed. In addition, the outcomes derived from the implementation of compression tests on adobe assemblages are discussed. Furthermore, the response of earth masonry to cycles of compressive loadingunloading is examined through numerical simulation. Finally, critical issues to be addressed by future research are identified.

A Stress-Test of Alternative Formulations and Algorithmic Configurations for the Binary Combinatorial Optimization of Bridges Rehabilitation Selection

Optimal surface transport asset management is a major concern with multiple economic and operational implications developed in various infrastructure areas. Although relevant ‘mature’ analytical frameworks have been proposed and developed, the problem setup and the algorithmic choices are still issues requiring thorough and detailed investigation. In this chapter, an optimal budget allocation framework is developed and stress-tested for the optimal scheduling of a bridges upgrading program. A suitable test case is developed for performing in-depth analysis that takes into consideration the most important features involved in such scheduling problems, while alternative formulations are also presented and discussed. The proposed frameworks are applied on a real large-scale dataset from the highway system of US, able to provide an adequate test-bed for investigating the optimal upgrade problem. The paper aims in the investigation of the effects that alterations of the problem setup, but also the effects that algorithmic configurations are introducing, when addressing real-world applications. The binary/selection problem is handled with a suitably coded Branch-and-Bound (BaB) algorithm, which is regarded as a robust and fast heuristic for such optimization problems. BaB is tested in alternative standard and extreme configurations, offering insights on its performance. Interestingly enough, although the continuous relaxation introduced by the BaB enables fast convergence, the NP-hard problem’s nature should be cautiously taken into consideration. The results are discussed in order to provide insights of applying the proposed framework in realistic infrastructure upgrading schemes.

The singular function boundary integral method for an elastic plane stress wedge beam problem with a point boundary singularity

The singular function boundary integral method (SFBIM) is applied for the numerical solution of a 2-D Laplace model problem of a perfectly elastic wedge beam under plane stress conditions. The beam has a point boundary singularity, it includes a curved boundary part and is subjected to non-trivial distributed external loading. The implemented solution method converges for this special model problem extremely fast. The numerical estimates attained for the leading singular coefficients of the local asymptotic expansion and the stress and strain fields are highly accurate, as verified by comparison with the available analytical solution.

Subdomain cluster generation for domain decomposition methods using graph partitioning optimization

Balancing and dual domain decomposition methods (DDMs) comprise a family of efficient high performance solution approaches for a large number of problems in computational mechanics. Such DDMs are used in practice on parallel computing environments with the number of generated subdomains being generally larger than the number of available processors. This paper presents an effective heuristic technique for organizing the subdomains into subdomain clusters, in order to assign each cluster to a processor. This task is handled by the proposed approach as a graph partitioning optimization problem using the publicly available software METIS. The objective of the optimization process is to minimize the communication requirements of the DDMs under the constraint of producing balanced processor workloads. This constraint optimization procedure for treating the subdomain cluster generation task leads to increased computational efficiencies for balancing and dual DDMs.

Using Monte Carlo Simulation to Treat Physical Uncertainties in Structural Reliability

This chapter is concerned with the estimation of the reliability of structures in view of physical uncertainties encountered due to the inherent variability in structural properties and loads. In this respect, methods based on the traditional Monte Carlo simulation method are employed to deal with probabilistically modeled uncertainties. Hence, suitable variance reduction techniques and efficient computational procedures are presented, in order to alleviate the high processing demands associated with Monte Carlo computations and make the overall reliability estimation process more tractable in practice. The focus of this chapter is on statistically high-dimensional problems, which involve large numbers of random variables. The merits of some of the techniques and algorithms described are demonstrated with two application examples.

Generation of Balanced Subdomain Clusters with Minimum Interface for Distributed Domain Decomposition Applications

Balancing and dual Domain Decomposition Methods (DDMs) are used in practice on parallel computing environments with the number of generated subdomains being generally larger than the number of available processors. The present study describes partitioning concepts used to: (a) generate subdomains for such DDMs and (b) organize these subdomains into subdomain clusters, in order to assign each cluster to a processor. The discussion concerns distributed computing environments with dedicated homogeneous processors, as well as with heterogeneous and/or non-dedicated processors. The FETI method is used to obtain numerical results demonstrating the merits of the described partitioning algorithms.