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Ant colony optimization algorithms (ACOs) have been basically introduced to discrete variable problems and applied to different research domains in several engineering fields. Meanwhile, abundant studies have been already involved to adapt different ant models to continuous search spaces. Assessments indicate competitive performance of ACOs on discrete or continuous domains. Therefore, as potent optimization algorithms, it is encouraging to involve ant models to mixed-variable domains which simultaneously tackle discrete and continuous variables. This paper introduces four ant-based methods to solve mixed-variable problems. Each method is based upon superlative ant algorithms in discrete and/or continuous domains. Proposed methods’ performances are then tested on a set of three mathematical functions and also a water main design problem in engineering field, which are elaborately subject to linear and non-linear constraints. All proposed methods perform rather satisfactorily on considered problems and it is suggested to further extend the application of methods to other engineering studies.

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Offshore pipelines are an effective tool for transportation of oil and gas which are usually assembled by the use of girth welds. Since flaws may naturally exist at such welds, fracture assessment of girth welded offshore pipelines is substantial. Current fracture assessment procedures like BS 7910 consider identical material properties for the weld and the base metals. However the strength difference between weld and base materials has significant effect on fracture assessment results. This effect is magnified greatly for pipelines which are operated in deep waters and are subjected to large plastic loads. In this paper 3D nonlinear elastic-plastic finite element analyses using the ABAQUS software are performed in order to investigate the effect of weld mismatching at various crack geometries on fracture assessment of pipeline’s girth weld. It is noteworthy that such a quantitative study on the effect of weld mismatching condition at different crack geometries on ECA analysis has not been performed so far. Based on simulation performed, a new optimized formula is proposed for fracture analysis of girth welded pipeline with surface cracks considering the effect of weld mismatching conditions at plastic strains. The results show that comparison of proposed formula results with those available experimental data reveals a great agreement. Furthermore, it is observed that the effect of strength difference between the base and the weld materials is insignificant for short cracks whereas mismatching plays a more dominating role in long cracks. Also, with increasing the crack heights the effect of weld mismatching raises meaningfully. In addition, ECA analysis results with and without weld mismatching effect are compared.

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In the current study two methods are evaluated for predicting the compressive strength of concrete containing metakaolin. Adaptive neuro-fuzzy inference system (ANFIS) model and stepwise regression (SR) model are developed as a reliable modeling method for simulating and predicting the compressive strength of concrete containing metakaolin at the different ages. The required data in training and testing state obtained from a reliable data base. Then, a comparison has been made between proposed ANFIS model and SR model to have an idea about the predictive power of these methods.

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The lateral-torsional buckling (LTB) strength of cellular steel girders that were subjected to web distortion was rarely examined. Since no formulation has been presented for predicting the capacity of such beams, in the current paper an extensive numerical investigation containing 660 specimens was modeled using finite element analysis (FEA) to consider the ultimate lateral-distortional buckling (LDB) strength of such members. Then, a reliable algorithm based on the artificial neural networks (ANNs) was developed and the most accurate model was chosen to derive an efficient formula to evaluate the LDB capacity of steel cellular beams. The input and target data required in the ANN models were provided using the ANN analyzes. An attempt was made to include the proposed formula in all the variables affecting the LDB of cellular steel beams. In the next step, the validity of the proposed formula was proved by several statistical criteria, and also the most influential input variable was discussed. eventually, a comparison study was executed between the results provided by the ANN-based equation and the AS4100, EC3, and AISC codes. It was revealed that the presented equation is accurate enough and can be used by practical engineers.