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This article focuses on creating an algorithm for the calculation of bending stiffness of an arbitrary polygonal cross section, including the first derivatives of this stiffness with respect to all the input variables. The coordinates of vertices of the cross section are also among these input variables. The algorithm is in principle based on dividing the cross section into trapezoids, calculating zero, first and second moment of area of these trapezoids, including partial derivatives with respect to all the input variables, and then compiling all these partial results into a final output. A DLL library based on this algorithm is then used in an optimization solver based on a reduced‑gradient method. This solver is put into practice to optimize the given cross section characteristics according to prescribed criteria.

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The main aim of this study was to assess the suitability of different existing test setups for the mechanical characterization of a dimpled interface obtained by casting concrete against dimpled high-density polyethylene (HDPE) membrane. Even though this type of interface roughening is widely used, especially for monolithic connections between precast elements, to the best of the authors' knowledge there is no research providing any data regarding its roughness parameters, tension, and shear strength, nor its failure modes. To this end, a two-fold objective was established for this research: (a) to identify and analyze, from a technical standpoint, the available test configurations for characterizing the mechanical performance of interfaces, and (b) to perform an extensive experimental program devoted to characterizing the mechanical performance of a dimpled HDPE membrane-cast concrete interface. The suitability of each test for reproducing the expected stress state and the actual resistance mechanism was analyzed. Moreover, a comparison between tension and shear tests, including its main advantages and disadvantaged are also presented.

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