Effect of the connecting beam stiffness on the bracing limit for reinforced concrete slender columns in single and multi-story frames

The main purpose of this paper is to study analytically the behavior of slender reinforced concrete columns existing in sway and non-sway structures. The studied variables were the stiffness of the beam connected to the slender columns, the stiffness of the bracing columns, and the number of bays and stories in the structure model. The stability of slender columns was studied and the required limits for the lateral bracing were determined using a finite element program to perform buckling analysis, linear analysis, and geometric nonlinear analysis for the different frame structural models. All the results obtained in this study were compared to the available methods included in the different building codes and the methods suggested by other researchers. The results indicated that the minimum value of the bracing limit, required to restrain the slender column against the side-sway, depends on the stiffness of the connecting beams, number of stories, and number of bays. The required bracing limit decreases with increasing the beam stiffness and with increasing the number of bays. However, the required bracing limit increases with the increase of the number of stories in the structure.

Análise Não Linear Geométrica de Treliças Espaciais Associada às Técnicas de Continuação de Comprimento de Arco/ Geometric Nonlinear Analysis of Space Trusses Associated with Arc-Length Path-Following Techniques

Neste artigo, são desenvolvidos algoritmos baseados no método de Newton-Raphson associado às técnicas de Comprimento de Arco Linear, Comprimento de Arco Esférico e Comprimento de Arco Cilíndrico, com o objetivo de validar a equação proposta para o coeficiente de escala. As análises não lineares são efetuadas por meio do método Corrotacional dos Elementos Finitos considerando problemas de treliças espaciais com não linearidade geométrica, cujas trajetórias de equilíbrio apresentam pontos limites de força e deslocamento. Os resultados numéricos versam sobre o tempo de processamento, números totais de passos de carga e iterações acumuladas até a convergência para a solução, além do número médio de iterações por passo de carga. As técnicas de continuação são comparadas e os resultados evidenciam a eficácia do Comprimento de Arco Linear, decorrente da simplicidade da formulação e boa concordância com os resultados observados na literatura, além da não restrição quanto à aplicação em problemas de maior complexidade.

The new buckling curves for cold-formed stainless steel equal-leg angle columns

The design rules for centrically compressed stainless steel equal-leg angle members are not explicitly stated in the current European standard SRPS EN 1993-1-4. This paper summarizes the results of extensive research conducted on this type of structural elements aiming to define recommendations for their design. Based on a systematic experimental investigation, a detailed numerical analysis was performed, and a database of columns' resistances were defined. Material and geometric nonlinear analysis included three key stainless steel alloys, austenitic, ferritic and duplex. The design curves for flexural and flexural-torsional buckling check have been proposed in accordance with European codified procedures.

Feasibility Study of Super-Long Span Bridges Considering Aerostatic Instability by a Two-Stage Geometric Nonlinear Analysis

To meet the need of constructing fixed cross strait links, super-long span bridge with a main span over 2 000[Formula: see text]m is considered as a candidate for their ability to cross deep and wide straits. To this end, some super-long span bridges with proper cable and girder systems were previously proposed and studied. The major design considerations are aimed at adopting new cable material, increasing the entire rigidity of the bridge, stabilizing the dynamic characteristics, strengthening the deck sections, etc. In this paper, a brief review of main cable and girder system is first given of the concepts previously proposed for the design of super-long span bridges. Then some typical examples are studied, focused on various issues related to the design of super-long span bridges, including composite cable, the unstressed length and tension force of the main cable, the stiffness and mass effects of the deck on critical wind speed, and the critical wind speed of various cable systems. The most challenges in super-long span bridges are to solve aerostatic and aerodynamic instability at required design wind speed. In this connection, the wind-induced aerostatic instability of super-long span bridges is studied by a two-stage geometric nonlinear analysis for dead loads and wind loads. The developed program adopted herein for geometric nonlinear analysis was verified and confirmed before. The proposed methods (i.e. composite cable, slotted girder, increasing deck stiffness and mass, cable layout, etc.) obtained for all the examples are in agreement with this study, which indicates applicability of the design approaches presented.

Assessment of the Effect of Wind Load on the Load Capacity of a Single-Layer Bar Dome

The main purpose of the paper was the assessment of the effect of wind load on the load capacity of a single-layer bar dome. Additionally, which numerical method is appropriate for low-rise single-layer bar domes was checked. In order to explain the effect of the height-to-span ratio on the selection of the appropriate calculation model and method of analysis of the bar dome, an example of the known von Mises truss was proposed. Two cases of von Mises truss differing in the height-to-span ratio were considered. For the shallow structure, a significant change in the value of the stiffness matrix determinant and the current stiffness parameter was observed. A similar tendency in the behavior of the structure can be observed on fragments of larger structures, including shallow single-layer steel domes. These problems are described on the basis of the dome, which is located on top of the building housing the restaurant. This structure is subjected to large displacement gradients and the actual configuration is taken into account in analysis. The analysis showed that there is a change in stiffness for these structures, and, therefore, that such structures should be designed according to geometric nonlinear analysis (GNA).

Numerical analysis of torsional tangent rigidity of reinforced concrete waffle slab

This research work deals with the analysis of torsional tangent rigidity of reinforced concrete waffle slabs by comparisons of the numerical analysis with results of experimental tests, with calculations performed using the ATENA program. This program was specially developed for the calculation of reinforced concrete structures, considering the physical and geometric nonlinear analysis using the finite element method. Numerical analysis considered the tensile strength of the concrete and consequently the fracture energy. Numerical situations were tested to obtain the calibration of the numerical analysis with the laboratory tests. After the calibrations, the results were extrapolated to extreme situations to infer tangent torsion rigidity in new situations. It is concluded that, for waffle slabs, near the rupture, the torsional tangent rigidity should be 5% of the torsional tangent rigidity to the initial torsion. In service, considering one third of the total breaking load, the torsional tangent rigidity should be 85% of the torsional tangent rigidity to the initial twist. This great torsional tangent rigidity in service is another parameter that guarantees the structural efficiency of the waffle slabs and can be used in the most diverse applications of structural engineering.