STR-969: SEISMIC DESIGN PROCEDURE FOR STEEL MULTI-TIERED CONCENTRICALLY BRACED FRAMES BEYOND CSA S16 LIMIT

Steel Multi-Tiered Braced Frames (MT-BFs) generally represents a more practical and cost-effective solution in tall single storey steel buildings such as airplane hangars, recreational buildings or convention centers. Special seismic design requirements including column design for in-plane and out-of-plane flexural demands have been introduced for MT-BFs in the Canadian steel design standard CSA S16. In the current CSA S16, MT-BFs are also limited to three and five tiers, respectively, for Type MD (moderately ductile) and Type LD (limited ductility) braced frame categories. In this paper, a 4-tiered Type MD braced frame, exceeding the 3-tier height limit, is designed with explicit consideration of the propagation of brace tension yielding along the frame height. The design is also performed neglecting the flexural demands in the columns. The seismic response of both frames is investigated though nonlinear dynamic analysis. In-plane flexural bending demands on MT-BF columns can be properly predicted by the proposed design and inelastic deformations can properly distribute along the frame height when yielding is triggered in more than one tier. Column buckling occurred when bending moments were omitted in design

Seismic Response and Design of Steel Multi-Tiered Concentrically Braced Frames

RÉSUMÉ Les contreventements concentriques en treillis à multiples segments (CCMS) sont des contreventements constitués de diagonales formant deux ou plusieurs panneaux qui sont superposés sur la hauteur du contreventement. Les CCMS sont couramment utilisés en Amérique du Nord afin d’offrir une résistance latérale pour les bâtiments d’un seul étage de grande hauteur,comme les bâtiments industriels, les installations sportives, les centres de congrès ou les hangars d'avion. Dans ces structures, la configuration CCMS est préférable puisque l'utilisation de diagonales de contreventement simples partant des fondations jusqu’au niveau du toit n’est plus pratique. Dans les CCMS, la longueur et la taille des diagonales sont réduites de manière significative, ce qui est favorable pour rencontrer les limites d'élancement prescrites dans les normes parasismiques. De plus, les colonnes peuvent être considérées comme contreventées latéralement dans le plan du cadre à niveau intermédiaire entre deux panneaux, ce qui contribue également à réduire la taille des poteaux et la quantité requise d'acier. Les colonnes de gravité adjacentes qui sont situées dans le même plan qu’un CCMS peuvent aussi être considérées comme contreventées latéralement en ajoutant des membrures horizontales aux niveaux intermédiaires entre les panneaux. Dans les CCMS, les colonnes sont en général des sections en W orientées de telle sorte que la flexion hors-plan se produise selon l’axe fort de la colonne, permettant ainsi à la colonne de résister au flambement hors plan sur toute la hauteur du cadre.----------ABSTRACT Steel multi-tiered braced frames (MT-BFs) are commonly used in North America to provide lateral resistance for tall single storey buildings such as industrial buildings, sport facilities, convention centers, or airplane hangars. In these structures, MT-BF configuration is preferable, as the use of single bracing members extending from the foundation to the roof level is no longer practical. MT-BFs consist of tall steel braced frames built with multiple bracing panels stacked over the height of the frame. In MT-BFs, brace lengths and sizes are reduced significantly, which is favourable to satisfy the slenderness limits specified in the seismic provisions. Additionally, the columns can be considered as laterally braced in the plane of the frame at every tier point, which also contributes to reducing the steel tonnage. Adjacent gravity columns located along MT-BF lines can similarly be laterally braced by adding horizontal struts at tier levels. In MTBFs, columns are typically I-shaped members oriented such that strong axis bending develops outofplane, so the column can resist out-of-plane buckling over the full building height

Marine macro-algae as a bio-indicator of heavy metal pollution in the marine environments, Persian Gulf

357-363The northern parts of the Persian Gulf are more affected by pollutants because of their low depth, limited rotation, salinity, and high temperature. The anthropogenic and non-anthropogenic contaminations caused by organic and inorganic pollutants in aquatic ecosystems will eventually lead to increase pollution in water, sediments, and aquatic organisms. It seems that, algae are the most suitable indicator for soluble heavy metals (HMs) in both active and passive states. Samplings were carried out on a monthly basis in four different stations in Bushehr Province, northwest of the Persian Gulf from March 2016 to March 2017. ICP-mass spectrometry was used to determine Pb, Cu, Cd, As, Cr, Zn, Al, Mn, Co, V, Ni, Mg, S, Fe, and Ca concentrations in some macroalgae. In this study Padina gymnospora (brown algae) and Hypnea hamulosa (red algae) had the highest absorption, while the Cladophoropsis membranacea (green algae) showed the least absorption in all the sampling areas

Comparison of Seismic Design Requirements for Steel Moment Resisting Frames with Emphasis on Stability of Columns in North America, New Zealand, and Europe

The seismic design provisions and stability requirements for steel columns used at the first storey of MRFs as specified is Canadian steel design standard (CSA S16), U.S. design provisions for steel buildings (AISC 341 and AISC 360), the New Zealand steel structures standard (NZS 3404), and Eurocodes 3 and 8 (EC3 and EC8) are reviewed. The code provisions are applied to a deep, slender steel I-shaped column to identify possible failure modes. A finite element analysis of the column is performed under cyclic inelastic lateral drift history to validate code predictions. The column was found to fail by out-of-plane instability, after local buckling has developed in the base plastic hinge. This failure mode was not expected from the axial-bending interaction equations available in the design standards except the equation of Eurocode 3. Limits for out-of-plane slenderness in Canadian and European provisions indicate the observed failure mode

Assessing some heavy metals pollutions in sediments of the northern Persian Gulf (Bushehr province)

Background: Land and water pollution by heavy metals is a universal issue. Although the pollution affects all countries, but its range and severity vary hugely. The pollution of the marine environment by heavy metals is a worldwide problem. Marine sediments can be sensitive indicators for monitoring contaminants in aquatic environments. Methods: The concentration of 10 elements (As, Cd, Cr, Cu, Al, Fe, Ni, Pb, Sb, and Zn) was determined in the sediments of four shoreline stations including Imam Hassan port, Ameri port, Bushehr port, and Nayband Bay at the west Persian Gulf from March to December 2017. The elements were measured by inductively coupled plasma mass spectrometry (ICP-MS). Data were analyzed using SPSS version 16. Results: The contamination of the sediments was assessed based on the geoaccumulation index (Igeo) and enrichment factor (EF). Spearman correlation matrix was calculated between all the trace metals and major elements as well as corresponding sampling regions. Statistically significant inter-elemental correlations (e.g., Cr-Fe, Cr-Al, Cr-Ni, Cr-Zn, and Cr-Cu) were found between some metals. High EF levels for Fe, Al, and Pb suggest that metals in the sediments of the northern Persian Gulf could have originated from anthropogenic sources. Conclusion: The contamination pattern of sediments is affected by factors such as sedimentation patterns, physical and chemical properties of the sediments. For example, sediments with fine-grained and high surface area-to-volume ratio can act as good absorbents for many pollutants. Keywords: Heavy metals, Geologic sediment, Persian Gulf, Busheh

Multi-Directional Structural Component Hybrid Testing System for the Assessment of the Seismic Response of Steel I-Shaped Columns

The Multi-Directional Hybrid Testing System (MDHTS) at Polytechnique Montreal is an advanced structural testing system that can be used to study the response of large-scale structural components such as columns, walls, or bridge piers subjected to any combination of displacements and forces along 6 degrees of freedom in static, quasi-static cyclic, pseudo-dynamic, or hybrid tests. This paper describes the main features, components and capacity of the MDHTS used for the seismic testing of steel I-shaped columns. Results of 3D finite element analysis performed to develop the test program and validate the test setup are presented. Three examples of tests on steel columns for concentrically braced frames (CBFs) and moment-resisting frames under seismic and multi-directional cyclic loadings are described. Furthermore, the hybrid simulation system is described and challenges faced when testing specimen exhibiting limited capacity are discussed. The MDTHS is an effective experimental tool to generate reliable data on steel column limit states under inelastic cyclic demands including any combination of local and global geometric instabilities with fixed and flexible boundary conditions

Seismic Design and Response of Steel Multi-Tiered Concentrically Braced Frames in Canada

This article investigates the seismic design and response of steel multi-tiered concentrically braced frames (MT-BFs) in which braces meet at columns between diaphragms. The seismic design provisions of CSA S16-14 are described and illustrated for 3-tiered Type MD (moderately ductile) and 5-tiered Type LD (limited ductile) braced frames. Analysis methods are proposed to evaluate the in-plane flexural demand on columns. The seismic response of the frames is examined through nonlinear response history analysis. As assumed in design, inelastic deformations tend to concentrate in one tier over the frame height, causing non-uniform drift demands and in-plane bending moments in the columns. CSA S16 provisions predicted well the frame in-plane flexural response and result in acceptable ductility demands on the braces. An extended seismic analysis and design approach that accounts for vertical distribution of brace tension yielding along the frame height is proposed for frames that exceed the limits prescribed in CSA S16.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

A Simplified Seismic Design Method for Limited-Ductility Steel Multi-Tiered Concentrically Braced Frames in Moderate Seismic Regions

Steel Multi-Tiered Concentrically Braced Frames (MT-CBFs) represent a bracing configuration where two or more concentric bracing panels are stacked between the ground and roof levels in tall single-storey buildings. A large proportion of MT-CBFs in Canada are located in low-to-moderate seismic regions (Seismic Category 0 – 3) where Limited Ductility CBFs are often preferred in design. Nevertheless, brace tensile yielding may not occur in all tiers of such frames. Additionally, the analysis and design procedure adopted by the 2019 Canadian steel design standard (CSA S16-19) can become tedious in tall frames with multiple panels. In this paper, the seismic behaviour of Limited Ductility MT-CBFs in moderate seismic regions of Canada is examined to propose a simplified design method. A set of 16 prototype MT-CBFs is designed in accordance with CSA S16-19, excluding the design requirements prescribed for MT-CBF columns. Nonlinear dynamic analyses are then performed to examine their seismic response. Finally, an efficient design method is proposed in the framework of CSA S16-19.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author