Terms Of Structure Weight Research Articles

Performance-based design optimization of steel moment frames using capacity controlled search algorithm: a comparison with force-based design approach

The capacity controlled search (CCS) method, which is a recently developed design-driven search algorithm, is implemented for performance-based design optimization (PBDO) of steel moment frames. It is shown that the CCS method is very suitable for PBDO problems since it can locate the optimum solution using a reasonable computational effort unlike metaheuristic search approaches, which often require thousands of structural analyses before converging to a near-optimum solution. Considering the fact that performance-based design (PBD) is a recently emerging design methodology, its comparison with the traditional force-based design (FBD) approach is also carried out extensively in this study. Accordingly, the optimum designs of the investigated steel frames produced according to both design methodologies using the CCS method are compared in terms of structural weight and seismic performance. Unlike most of the previous studies, not only inter-story drifts but also hinge rotation limits are considered as seismic performance criterion during PBDO process of steel moment frames. The numerical applications are presented using three ordinary moment resisting steel frames. It is shown that although the FBD methodology usually leads to heavier designs with respect to the PBD methodology, the optimum designs produced according to the former might fail to satisfy seismic performance requirements.

The effect of joint stiffness on optimization design strategies for gridshells: The role of rigid, semi-rigid and hinged joints

Structural optimization techniques are becoming popular and effective approaches for the design of constructions, able to support architects and structural designers in the complex process of searching competitive solutions, usually in terms of structural weight, cost and accounting for specific structural/functional requirements. In case of gridshells, the structural weight is strictly related to the susceptibility of the structure to global buckling, which is often the governing design criterion. The susceptibility to global buckling is mainly due to the global stiffness of the structures, primarily related to the stiffness of the joints, to the boundary conditions, and to the presence of imperfections. In this context, the paper presents design strategies based on optimization techniques that specifically take into accounts the presence of semi-rigid, rigid and hinged joints in order to guarantee light solutions safe from global buckling phenomena. In particular, two approaches are proposed: the joint stiffness approach, which considers the gridshell composed by semi-rigid joints, all characterized by the same rotational stiffness, and the rigid/hinged approach, which considers the gridshell composed by most hinged joints, and by a low number of rigid joints arranged in optimal positions. The approaches have been applied to a case study characterized by different boundary conditions, different rise-to-span ratios and also considering both perfect and imperfect shapes. The results of the proposed optimization processes highlight the beneficial effect of a finite value of the rotational stiffness of the joints in the susceptibility of the gridshell to global buckling phenomena, leading to light structural solutions.

A Structural Grammar Approach for the Generative Design of Diagrid-Like Structures

An innovative generative design strategy, based on shape grammar, is proposed for the minimum-weight design of diagrid tall buildings. By considering the building as a three-dimensional vertical cantilever beam with a tubular section under horizontal load, it is evident that bending and shear stiffness demands vary along the width and elevation of the building. Further, while the structural design of tall buildings is usually governed by stiffness, the predominant design criterion for diagrids could be the local strength demand, especially for low slenderness values, thanks to the inherent rigidity of the triangular pattern. Starting from these considerations, in this paper, a generative design strategy is proposed, able to find diagrid patterns that accommodate the differentiated stiffness demand along width/elevation and satisfy the predominant design criterion, stiffness or strength. The design strategy is applied to tall building models characterised by different slenderness values. The comparison to diagrid patterns analysed in previous literature works in terms of structural weight and performance parameters highlights the effectiveness of the design strategy and the efficiency of the generated patterns.

A new swift algorithm for bi-objective optimum design of steel moment frames

In this paper, a new algorithm is proposed to multi-objective optimum seismic design of steel moment frames. This algorithm is based on the uniform damage (also known as uniform deformation) theory and so-called multi-objective uniform damage optimization (MUDO). MUDO is a swift algorithm formulated according to a bi-objective approach. Structural weight and maximum interstory drift ratio (IDR) are treated as two conflicting objectives representing economy and safety measures, respectively, and they are minimized simultaneously subject to a set of design constraints. To achieve the optimal Pareto front, MUDO tries to create a uniform distribution of story drifts in the structure and bring it to a target value that gradually varies from the low (minimum damage) to high (maximum damage). In this way, the algorithm obtains a set of optimal solutions in terms of structural weight at different damage levels, which is the Pareto front. To demonstrate the efficiency and robustness of the proposed algorithm, its results for 3-, 6- and 9-story steel moment frames are compared with those of two well-known multi-objective optimization algorithms, NSGA-II and MOPSO. Results indicate that MUDO can achieve better optimal solutions set in a much less computational time than the other two methods.

Metal intensity of structural roof slab under different supporting conditions

The article presents and solves the problem of finding the design of minimum weight structural slab roof for given steel class, element cross-section type, and loading conditions. Structural roof slabs are widely used for large-span public and industrial buildings and allow a wide variety of structural and architectural forms. At the same time, the placement of supports was changed. In total, 10 options for the supports placement for the 36×36 m structural slab and 6 options for the topology were considered. After applying the load, structure’s strain-stress distribution was determined numerically, a cross-section was selected and its weight was calculated. Then, different options of support were compared in terms of structure weight. In fact, the article solved optimization problem by optimality criterion of metal intensity, restrictions in the form of overall dimensions, topology and strength conditions.

Design comparison of conventional steel structure with pre - engineered structure

The pre-engineered buildings are the steel buildings which are predesigned and prefabricated. For pre-engineered structure the member size is provided as per the requirement at the location and hence the members are tapered in nature. The study is on the design of the pre-engineered structure and its comparison with conventional structure. The objective of the study is to analyze and design a structure as a conventional steel structure and Pre-engineered structure and to compare the design of the structure in terms of structure weight. The use of cold-formed steel sections as secondary members reduces the self-weight of the pre-engineered structure. It was expected that the pre-engineered buildings will be more economical than conventional structure.

Effect of thermal protection system size on aerothermoelastic stability of the hypersonic panel

The design optimization of Thermal Protection System (TPS) for airbreathing hypersonic vehicles is typically carried to resolve aerodynamic heating concerns. The target is achieved through material selection and structural configuration so that the resultant TPS is light weight and provides sufficient insulation. However, in this investigation, aerothermoelastic stability is also incorporated into TPS size design. A simplified arrangement consisting of an underlying panel and TPS with a thermal radiation coating and an insulation layer is investigated. The two-way fluid-thermal-structure coupling scheme includes mutual interaction between panel deformation and aerodynamic heat flux. The coupling aerothermoelastic model is first verified by comparing with the seminar work by Culler. Subsequently, the fluid parameter studies in terms of transitional location and radiation emissivity are then conducted on the verified model. A parametric study is conducted such that seven TPS size cases with various layers thickness are selected and compared in terms of structural weight and onset of flutter. Finally, the aerothermoelastic stability regions manifested by Flat, Buckled, Chaos and Quasi-periodic features pertaining to Mach number, flight height and TPS size are mapped out. The results indicate that TPS size can alter the panel aerothermoelastic stability boundaries in an obvious way. A new finding is that the TPS size in the pioneering work by Culler is not the best design either for a higher flutter boundary or for a lighter weight. In contrast, Case2 and Case7 in this study are better choice due to the delay in onset of flutter with lighter weight. This study necessitates aerothermoelastic analysis in TPS optimization design for the airbreathing hypersonic vehicles.

Collapse-performance-aided design optimization of steel concentrically braced frames

This study focuses on collapse-performance-aided optimization of steel concentrically braced frame (SCBF) structures optimized in the framework of performance-based design. The proposed methodology in this paper consists of three steps. The first step involves tackling the problem of seismic performance-based size and topology optimization of SCBFs. In the second step, incremental dynamic analysis (IDA) is performed to generate IDA and fragility curves for all the obtained optimal designs. Subsequently, their collapse margin ratios are calculated. In the last step, the SCBFs with fixed and optimal placement of bracings are compared in terms of structural weight and seismic collapse capacity. The efficiency of the proposed methodology is illustrated by presenting three numerical examples of 5-, 10-, and 15-story SCBFs with fixed and optimal topology of braces. The results demonstrate that the topologically optimal SCBFs not only have the least structural weight, but also they are of considerable collapse safety in comparison to optimal SCBFs with fixed topology of braces.

A constraint satisfaction problem algorithm for large-scale multi-panel composite structures

This paper proposes a constraint satisfaction problem algorithm based on implicit decision trees and dynamic programming for the design of multiple composite panels subjected to a set of blending rules and external forces. This decision tree is built incrementally on the ‘fly’, adding plies from a particular set, and does not require any guiding laminate or stacking sequence table for blending purposes. The upper bound algorithm complexity is provided in this work. The technique is applied to the design of a well-known composite multi-panel problem addressed in previous studies; the novel procedure exhibits high-quality solutions (in terms of structure weight) and low computational cost (in terms of laminate evaluations). The novel algorithm scalability is also checked showing that the node tree expansion is independent of the number of panels to be designed. This algorithm could therefore be a suitable choice for large-scale multi-panel design problems.

Numerical simulation study on structural behavior of Tensairity domes with annular airbags

Tensairity dome is a lightweight spatial structure composed of struts stabilized by cables and airbags inflated by low pressurized air. Two forms of Tensairity domes with annular airbags, stiffened with central cables or webs placed between the upper and lower chords, were proposed based on the Tensairity concept. The zero-stress state, the initial state and the loaded state were successively simulated to investigate the static behavior of the structures, respectively. The results indicate that both two forms of structure have good static performance and the internal pressure in the airbag at about 1000–4000Pa can ensure the stabilizing role of the inflated airbag. The investigation reveals the subtle interplay between the internal pressure and external loads in the load state, and the tremendous effect of temperature change on overall structure is predicted. The comparisons also show the benefits of webs in the structure for all load cases. Finally, the results show the attractive advantages of Tensairity dome in comparison with conventional structures in terms of structure weight and overall stiffness.

Optimal Topologies for Steel Frames with Ordinary Chevron and X-Braces: The Effect on Total Structural Cost

Today, steel structures with simple frames and concentric steel bracings (both crossed and chevron type) are extensively used in different countries, as well as in Iran. Apart from the seismic performance of each structural system, construction cost plays a significant role in system selection by designers. In an attempt to optimize structural costs, this study aims at examining the number of floors, span length, soil conditions, and brace type. In this study the impact of these factors on structural costs are evaluated. Since parking areas are the most important architectural requirement, therefore specified span widths accommodating two, three, and four vehicles are selected for the models. To this end, regular building models with different span (5.6, 7.5, and 11.2m) are selected according to such architectural considerations. Following structural analysis and design, total structural costs are estimated according to the latest national cost list issued by the Management and Planning Organization of Iran (published in 2014). The results are obtained and reported for different models through graphs and tables. The outcomes are evaluated and compared. Finally, the optimal topologies in terms of structure weight and total cost are determined, along with introducing the most effective factor among span length, story number, brace type, and soil type.

Theory of Plastic Mechanism Control: State-of-The-Art

In this paper, the state-of-the-art regarding the “Theory of Plastic Mechanism Control” (TPMC) is presented. TPMC is aimed at the design of structures assuring a collapse mechanism of global type. The theory has been developed in the nineties with reference to moment-resisting steel frames (MRFs) and progressively extended to all the main structural typologies commonly adopted as seismic-resistant structural systems. In particular, the outcome of the theory is the sum of the plastic moments of the columns required, at each storey, to prevent undesired failure modes, i.e. partial mechanisms and soft-storey mechanisms. The theory is used to provide the design conditions to be satisfied, in the form of a set of inequalities where the unknowns are constituted by the column plastic moments. Even though the set of inequalities was originally solved by means of an algorithm requiring an iterative procedure, now, thanks to new advances, a “closed form solution” has been developed. This result is very important, because the practical application of TPMC can now be carried out even with very simple hand calculations. In order to show the simplicity of the new procedure, numerical applications are herein presented in detail with reference to Moment Resisting Frames (MRFs) and dual systems both composed by Moment Resisting Frames and Eccentrically Braces Frames (MRF-EBFs) with inverted Y scheme and composed by Moment Resisting Frames and Concentrically Braced Frames (MRF-CBFs) with X-braced scheme and V-braced scheme. Finally, the pattern of yielding obtained is validated by means of both push-over analyses and incremental dynamic analyses. A comparison in terms of structural weight of the designed structures is also presented and the corresponding seismic performances are discussed.

MECHANICALLY COUPLED BUOYANT FLAPS: THEORY AND EXPERIMENT

A system composed of two buoyant flaps hinged at the sea floor and coupled with weighted mooring lines is modeled analytically and experimentally. The system behavior is described theoretically utilizing an eigenseries representation of linear wave theory in the vicinity of the breakwater. The structure dynamics are modeled in terms of structure weight, inertia, buoyancy, damping, mooring line tension and the wave pressure field. The mechanically coupled system provides shelter by reflecting incident waves and by attenuating wave energy through structural and viscous damping. The structure can be tuned to minimize wave transmission within a particular frequency range by changing the flap spacing and adjusting the mass and equilibrium position of the mooring line weights. The theory is validated with experimental results for models fabricated from inflatable, parallel-tube membranes. Buoyancy and inertia are changed by filling tubes with air and/or water. Single and double flaps are examined with and without mooring lines. Incident, reflected, and transmitted waves are measured as well as flap motion. Theoretical results are corroborated by the experiments and the importance of including damping in the model is demonstrated.