This paper presents a method for detection and estimation of structural damage on the basis of modal parameters of a damaged structure using imperialist competitive algorithm. The imperialist competitive algorithm was developed over the last few years in an attempt to overcome inherent limitations of traditional optimize method. In this research, imperialist competitive algorithm has been employed due to its favorable performance in detection of structural damages. The performance of the proposed method has been verified through using a benchmark problem provided by the IASC-ASCE Task Group on Structural Health Monitoring and a number of numerical examples. By way of comparison between location and amount of damage obtained from the proposed method and simulation model, it was concluded that the method is sensitive to the location and amount of damage. The results clearly revealed the superiority of the presented method in comparison with energy index method.

SUMMARY High statistics of damages in modern structures (buildings structured based on new codes) exposed to near‐fault earthquake illustrates the necessity of more studies on this kind of earthquake effects on the structures. A specification of near‐fault earthquakes is the directivity effects. Existing records of near‐fault quakes containing directivity effects including records of Iran and abroad were modified and used for linear time history analysis of three steel moment frames (5, 8 and 12 story frames), and the results were compared with nonlinear time history analysis and pushover analysis of far‐fault quakes in this paper. The results showed that these records (near fault) motivate high modes of the structure, and especially for the 12‐story structure, high response was detected, but none of these results made the frames collapse. By comparing nonlinear dynamic analysis (time history) with nonlinear static analysis (pushover), it was concluded that various lateral load patterns in pushover cannot cover the time history result needs. Load distribution pattern based on the first vibration mode covers these demands in the lower floors, but in higher floors, this method is not applicable. Copyright © 2012 John Wiley & Sons, Ltd.

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Saline soils usually cannot satisfy the requirements of engineering projects because of their inappropriate geotechnical properties. For this reason, they have always been known as one of the problematic soils worldwide. Moreover, the lack of access to normal water has intensified the use of saline water resources such as seawater in many construction and mining projects. Although cement stabilization is frequently used to improve the engineering properties of saline soils, Portland cement’s usage as a binder is constrained by its negative consequences, particularly on the environment. In this line, the effects of NaCl on the microstructural and mechanical properties of alkali-activated volcanic ash/slag-stabilized sandy soil were investigated in this study. Moreover, the effects of binder type, slag replacement, curing time, curing condition, and NaCl content on the mechanical strength of stabilized soils were examined. In addition, microstructural analyses, including XRD, FTIR, and SEM–EDS mapping tests, were performed to understand the physical and chemical interaction of chloride ions and alkali-activated cements. The results show that alkali-activated slag can be a sustainable alternative to Portland cement for soil stabilization projects in saline environments. The increase in sodium chloride (NaCl) content up to 1 wt.% caused the strength development up to 244% in specimens with 50 and 100 wt.% slag, and adding more NaCl had no significant effect on the strength in all curing conditions. Microstructural investigations showed that the replacement of volcanic ash with slag resulted in the formation of C-S-H and C-A-S-H gels that reduced the porosity of the samples and increased mechanical strength. Furthermore, surface adsorption and chemical encapsulation mechanisms co-occurred in stabilized soil samples containing slag and volcanic ash.

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