Abstract
In this study, a new structural bracing system named \'Hat Knee Bracing\' (HKB) is presented. In this structural system, a special form of diagonal braces, which is connected to the knee elements instead of beam-column joints, is investigated. The diagonal elements provide lateral stiffness during moderate earthquakes. However the knee elements, which is a fuse-like component, is designed to have one plastic joint in the knee elements for dissipation of the energy caused by strong earthquake. First, a suitable shape for brace and knee elements is proposed through elastic studying of the system and several practical parameters are established. Afterward, by developing applicable and highly accurate models in Drain-2DX, the inelastic behavior of the system is carefully considered. In addition, with inelastic study of the new bracing system and comparison with the prevalent Knee Bracing Frame system (KBF model) in nonlinear static and dynamic analysis, the seismic behavior of the new bracing system is reasonably evaluated.
Key Words
disposal knee brace; moment link; chevron knee brace; hat knee brace; optimal shape; energy dissipation.
Address
Issa JafarRamaji : Department of Civil Engineering, Sharif University of Technology, Tehran, Iran
Massood Mofid : Civil Engineering Department, Center of excellence in structures and earthquake engineering,
Sharif University of Technology, Tehran, Iran
Abstract
For an axially loaded box-shaped member, the width-to-thickness ratio of the plate elements preferably should not be greater than 40 for Q235 steel grades in accordance with the Chinese code GB50017- 2003. However, in practical engineering the plate width-to-thickness ratio is up to 120, much more than the limiting value. In this paper, a 3D nonlinear finite element model is developed that accounts for both geometrical imperfections and residual stresses and the ultimate capacity of welded built-up box columns,
with larger width-to-thickness ratios of 60, 70, 80, and 100, is simulated. At the same time, the interaction
buckling strength of these members is determined using the effective width method recommended in the Chinese code GB50018-2002, Eurocode 3 EN1993-1 and American standard ANSI/AISC 360-10 and the direct strength method developed in recent years. The studies show that the finite element model proposed can simulate the behavior of nonlinear buckling of axially loaded box-shaped members very well. The width-tothickness ratio of the plate elements in welded box section columns can be enlarged up to 100 for Q235 steel
grades. Good agreements are observed between the results obtained from the FEM and direct strength method. The modified direct strength method provides a better estimation of the column strength compared to the direct strength method over the full range of plate width-to-thickness ratio. The Chinese code and Eurocode 3 are overly conservative prediction of column capacity while the American standard provides a better prediction and is slightly conservative for b/t = 60. Therefore, it is suggested that the modified direct strength method should be adopted when revising the Chinese code.
Key Words
width-to-thickness ratio; welded box-shaped section; axially loaded members; ultimate capacity; direct strength method; effective width method; FEM
Address
School of Civil Engineering, Xian University of Architecture and Technology, Xian 710055, PR China
Abstract
Implementation of openings in beams web has been introduced as an innovative method for improving seismic performance of steel moment frames. In this paper, several steel moment frames have been studied in order to evaluate the effect of openings in beams web. The beam sections with web opening have been modeled as a simplified super-element to be used in designing frames and to determine opening configurations. Finite element models of designed frames were generated and nonlinear static pushover analysis was conducted. The efficient location for openings along the beam length was discovered and the effects of beams with web openings on local and global behavioral characteristics of frames were discussed. Base on the results, seismic performance of steel moment frames was improved by creating openings in beams web, in terms of reduction in stress level of frame sensitive areas such as beam to column connections and panel zones.
Key Words
beam web opening, steel moment frame, pushover analysis, finite element method, panel zone
Address
Civil Engineering Department, Amirkabir University of Technology, Tehran, Iran
Abstract
To enhance cable stiffness, this paper proposed a combined application of carbon fiber reinforced polymers (CFRP) and steel materials, resulting in a novel type of hybrid stay cable system especially for the cable-stayed bridges with main span lengths of 1400~2800 m. In this combination, CFRP materials can conserve all their advantages such as light weight and high strength; while steel materials help increase the equivalent stiffness to compensate for the low elastic modulus of CFRP materials. An increase of the equivalent stiffness of the hybrid stay cable system could be further obtained with a reasonable increase of its safety factor. Following this concept, a series of parametric studies for the hybrid stay cable system with the consideration of stiffness and cost were carried out. Three design strategies/criteria, namely, best equivalent stiffness with a given safety factor, highest ratio of equivalent stiffness to material cost with a given safety factor, and best equivalent stiffness under a given cost were proposed from the stiffness and cost viewpoints. Finally, a comprehensive design procedure following the proposed design strategies was suggested. It was shown that the proposed hybrid stay cable system could be a good alternative to the pure CFRP or traditional steel stay cables in the future applications of super long span bridges.
Key Words
hybrid stay cable system; CFRP; steel; stiffness; cost; design strategy; cable-stayed bridge; parametric study
Address
Wen Xiong : Department of Bridge Engineering, School of Transportation, Southeast University, Nanjing 210096, China
C.S. Cai : Department of Civil and Environmental Engineering, Louisiana State University, LA 70803, USA
Rucheng Xiao : Department of Bridge Engineering, Tongji University, Shanghai 200092, China
Yin Zhang : Department of Civil Engineering, Tsinghua University, Beijing 100084, China
Abstract
The paper investigates beam lateral buckling stability according to linear and non-linear models. Closed form solutions for single-symmetric cross sections are first derived according to a non-linear model considering flexural-torsional coupling and pre-buckling deformation effects. The closed form solutions are compared to a beam finite element developed in large torsion. Effects of pre-buckling deflection and gradient moment on beam stability are not well known in the literature. The strength of singly symmetric I-beams under gradient moments is particularly investigated. Beams with T and I cross-sections are considered in the study. It is concluded that pre-buckling deflections effects are important for I-section with large flanges and analytical solutions are possible. For beams with T-sections, lateral buckling resistance depends not only on pre-buckling deflection but also on cross section shape, load distribution and buckling modes. Effects of prebuckling deflections are important only when the largest flange is under compressive stresses and positive gradient moments. For negative gradient moments, all available solutions fail and overestimate the beam strength. Numerical solutions are more powerful. Other load cases are investigated as the stability of continuous beams. Under arbitrary loads, all available solutions fail, and recourse to finite element simulation is more efficient.
Key Words
beam; eigenvalue; finite element; lateral buckling; non-linear; thin-walled beam; open section.
Address
Mohri, F.* and Potier-Ferry, M.:Universite de lorraine, LEM3 UMR CNRS 7239, Ile du Saulcy. 57045 Metz. France
Damil, N.: Laboratoire de Calcul Scientifique en Mecanique, Faculte des Sciences Ben M
Abstract
In this research, mechanical buckling of hybrid functionally graded plates is considered using a
new four variable refined plate theory. Unlike any other theory, the number of unknown functions involved is only four, as against five in case of other shear deformation theories. The theory presented is variationally consistent, does not require shear correction factor, and gives rise to transverse shear stress variation such that the transverse shear stresses vary parabolically across the thickness satisfying shear stress free surface conditions. The plate properties are assumed to be varied through the thickness following a simple power law distribution in terms of volume fraction of material constituents. Governing equations are derived from the principle of minimum total potential energy. The closed-form solution of a simply supported rectangular plate subjected to in-plane loading has been obtained by using the Navier method. The effectiveness of the theories is brought out through illustrative examples.
Key Words
plate theory; buckling analysis; functionally graded materials
Address
Laboratoire des Materiaux et Hydrologie, Universite de Sidi Bel Abbes, Algerie
