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When employing the strut-and-tie modelling (STM) method in the conceptual design of reinforced concrete structures, a suitable strut-and-tie (ST) model indicating load transfer mechanisms first needs to be identified. Topology optimization (TO) methods have frequently been used for this purpose. However, although TO methods employing either a ground-structure or a continuum-based TO approach can be used, the performance and effectiveness of these two methods have not been systematically investigated and compared. To obtain a better understanding of the characteristics of both methods, a systematic comparison procedure is proposed to investigate the generation process and the resulting ST designs. Three aspects, relating to structural performance, economic issues, and method applicability are considered in the comparison, with six metrics formulated to quantify these aspects. Based on investigation of designs for three reinforced concrete elements incorporating typical discontinuity regions (two 2D cases and a 3D case), the performance of the two methods is assessed. It is found that both methods result in safe and efficient ST designs, with comparable structural performance, while some differences in terms of computation time and usability are observed. • Quantitative evaluation of strut-and-tie model performance based on six metrics. • Systematic comparison of two different methods for strut-and-tie model generation. • Investigation of the influence of input parameters on generated strut-and-tie models. [ABSTRACT FROM AUTHOR]

• A framework is proposed to design a gridshell serving as the falsework for a concrete shell. Numerical optimization is used to fit the gridshell to a predetermined target surface under the wet concrete loading, taking practical constraints into account. • All sensitivities to perform gradient-based optimization are derived analytically and validated using finite-differences. • The resulting design tool is used to design a small-scale gridshell serving as the falsework for a concrete shell. The gridshell has been constructed and tested to demonstrate the feasibility of the suggested falsework system and the effectiveness of the proposed design approach. Shell structures are material efficient structures capable of covering large spans with minimum weight. If concrete is used as the building material for the shell, it must be initially supported by a formwork. These generally rigid formworks, and their supporting falsework structure, are time and material consuming to construct. Recently, researchers have recommended the use of elastic gridshells as falsework system. Unfortunately, the design of such a system is complicated by large deformations of the bending elements. Moreover, since gridshells are inherently flexible, significant displacements generally occur when applying the wet concrete. To overcome these difficulties, this paper presents a design tool to effectively design a gridshell serving as the falsework for a concrete shell. The gridshell is assumed to be constructed from an initially flat grid of straight slender rods, using cables with adjustable lengths to brace the erected gridshell. An optimization algorithm is proposed that fits the shape of the gridshell under the wet concrete loading to a given target shape by manipulating the lengths of the bracing cables. Meanwhile, the optimization algorithm reduces the construction effort by minimizing the number of cables, and the diameter of the grid rods. Moreover, feasibility of the design is ensured by constraining the axial force in the cables and limiting the displacements under increased loading. A gradient-based optimization scheme is adopted, and an implicit dynamic relaxation approach previously developed specifically for the simulation of bending-active structures is used to solve the nonlinear equilibrium equations. Nonlinear effects such as buckling of the grid rods are taken into account by using co-rotational beam elements. The resulting design tool is applied for the design of a scale model, demonstrating the feasibility of the suggested falsework system. The optimized design fits the target better, uses less cables, and is more resistant to additional loading compared to designs from existing design approaches. Comparisons between the numerical and physical models show deviations of up to around 2% of the larger span for the design load and smaller deviations for smaller loads, with differences attributed to small model scaling effects. [ABSTRACT FROM AUTHOR]

Highlights • Proposal of efficient construction method for RC shells using tile-vaulted formwork. • Presentation of design and structural analysis method for such 2D composite structures. • Validation of limit-analysis method through experimental research. • Application of method to shape and material optimisation. Abstract Tile vaults are traditional, unreinforced masonry structures made of thin bricks (tiles), mortar and fast-setting cement or gypsum. They can be constructed without the need for a formwork, except at the boundaries, making them inherently economic. Tile vaults have historically provided a solution for the efficient construction of vaulted structures. Today, they can be used as permanent formwork for concrete shells, allowing for a significant reduction of the construction cost and waste produced, due to the possibility of reducing or even eliminating the need for traditional formwork. The concrete can be poured directly onto a tile-vaulted formwork to form a composite structure. This paper presents a technique for the construction of single-curvature shells consisting of a composite structure combining tile vaulting and reinforced concrete. A method for the design of these composite vaults and the assessment of their strength and stability against external loading is also presented. This method is based on limit analysis but takes into account the reinforcement's contribution to the composite cross-section's bending capacity. The equilibrium method is implemented computationally to provide fast results for the user. It provides graphical and intuitive results and opens the possibility for the future extension to fully three-dimensional problems. The design and structural analysis method is called Extended Limit Analysis for Reinforced Masonry (ELARM). Both the proposed construction technique and the computational method have been validated through experimental research. The feasibility of the building technique has been validated by the construction of two full-scale prototypes. In addition, the prototypes have been load-tested to failure to compare the results with those predicted by ELARM. [ABSTRACT FROM AUTHOR]

• Strength and failure mechanism of CFS channels with web openings are investigated under shear loads. • Experimentally validated FE models are developed to study the effects of key design variables. • Shear strength and ductility of the elements are significantly affected by the size of openings and web slenderness. • A practical design equation is developed for the shear strength of CFS members with square and circular web openings. • Efficiency of the proposed eqaution is demonsterated compared to AISI and other existing methods in literature. Cold-formed steel (CFS) members are increasingly used as the main loading-bearing elements in modern construction practice, due to the advantages such as high strength-to-weight ratio, and ease of transportation and assembly. Often, web openings are cut out of CFS elements to allow for services, plumbing, heating and electrical systems, which may result in considerable reductions in their shear strength. This study aims to investigate the behaviour and design of CFS channel members with web openings under shear loads. To this end, detailed Finite Element (FE) models of CFS back-to-back channel members were developed featuring material non-linearity and geometric imperfections, and validated against the results of experimental tests. The validated FE models were then employed to carry out a comprehensive parametric study to investigate the effects of opening size and shape (square and circular web openings), as well as cross-sectional web slenderness on the strength, stiffness, failure mechanism, and ductility of CFS elements under shear forces. The results demonstrated that the shear strength of the CFS members can be significantly affected, up to 88 % and 30 %, by the size of openings and web slenderness, respectively. It was also found that while the ductility ratio of the CFS elements can be improved by increasing the opening size, elements with lower web slenderness showed less ductile behaviour. Based on the results of the parametric study, a practical design equation was developed for the shear strength of CFS members with web openings, and the predictions were compared with those determined by the AISI and other existing methods. Finally, a reliability analysis was performed within the framework of the European design standard. [ABSTRACT FROM AUTHOR]

Circular hollow sections (CHS) are widely used in a range of structural engineering applications. Their design is covered by all major design codes, which currently use elastic, perfectly-plastic material models and cross-section classification to determine cross-secti\on compressive and flexural resistances. Experimental data for stocky sections show that this can result in overly conservative estimates of cross-section capacity. The continuous strength method (CSM) has been developed to reflect better the observed behaviour of structural sections of different metallic materials. The method is deformation based and allows for the rational exploitation of strain hardening. In this paper, the CSM is extended to cover the design of non-slender and slender structural steel, stainless steel and aluminium CHS, underpinned by and validated against 342 stub column and bending test results. Comparisons with the test results show that, overall, the CSM on average offers more accurate and less scattered predictions of axial and flexural capacities than existing design methods. [ABSTRACT FROM AUTHOR]