Search

Structural retrofits to buildings can be implemented to increase the protection level to occupants from potential terrorist bombing attacks. Retrofit strategies discussed in this paper can be categorized into three groups: (i) strengthening concepts, (ii) shielding concepts, and (iii) concepts to control hazardous debris. Strengthening concepts such as span reduction and increasing member sections are considered in this paper for three common construction systems including steel, concrete, and masonry. Shielding concepts are intended to prevent structural members from being fully loaded by blast forces and range from local area applications to entire building coverage. Examples of shielding concepts include a new section of wall that shields a vulnerable portion of the building or a new structure built over an entire building. Examples of concepts to control hazardous debris include arresting or deflecting failed cladding away from critical areas with “catch systems” or internal shield systems. This paper is intended to discuss typical building retrofit strategies for primary structural members (load bearing) and secondary structural members (nonload bearing) through strengthening, shielding, or controlling hazardous debris. [ABSTRACT FROM AUTHOR]

Externally bonded fibre-reinforced-polymer (FRP) laminates and fabrics have been successfully used for strengthening damaged or deficient concrete members, whereas internal FRP reinforcements are becoming an efficient alternative to steel reinforcement, particularly in corrosive environments. Despite the enormous progress that has been observed in the last decade, further research is still required to consolidate recent developments and expand the scope of application of FRPs for structural uses. Nonlinear finite element analysis combined with laboratory testing constitutes an efficient approach for pursuing this objective. The scope of this paper is to illustrate, through a selection of a wide variety of typical applications, the contribution of a refined three-dimensional (3-D) constitutive model for investigating the nonlinear response of concrete structures reinforced with internal and external FRPs. The analyses are carried out using a general and portable constitutive concrete model implemented as a user-defined subroutine at Gauss integration point level in commercial finite element software. The constitutive law follows a 3-D hypoelastic approach that models the nonlinear behaviour of concrete using a scalar damage parameter that accounts for the anisotropic behaviour of partially confined concrete and the inelastic volume expansion upon reaching the peak strength. In tension, the model adopts a macroscopic approach that is directly integrated into the concrete law. It simulates implicitly the reinforcing bar – concrete interaction using tension-stiffening factors modified according to the nature of reinforcement that vary as a function of the member strain. The applications include results of well-known test series published in the literature on beams with external and internal FRP reinforcement, slabs with internal reinforcements, bond failure analysis of external FRP, and the effect of confinement on the behaviour in compression of circular and square elements. The paper demonstrates the ability of the concrete model to correctly simulate the behaviour of structural elements reinforced with FRPs at service load level and reproduce failure mechanisms and loads that are consistent with the experimental observations. [ABSTRACT FROM AUTHOR]

This paper presents partial results of a research program under way at Laval University for which the main goal is to introduce the behaviour of steel connections into commercial structural analysis software. The objective of this paper is to derive analytical characterization equations for three commonly used steel column base connections. The procedure to derive these equations is based on a curve standardization theory that requires a number of experimental results in the form of moment–rotation curves that characterize the behaviour of column base connections. Because of a lack of available experimental results, data were obtained from finite element models. The design of a simple steel structure introducing the semi-rigid behaviour of column bases is presented as an example. It shows that consideration of the semi-rigidity of column base connections increases the accuracy of the analysis results and leads to a decrease in structure weight and deformation. [ABSTRACT FROM AUTHOR]

It is well-known that the lateral-torsional buckling capacity of a wide-flange beam is lower when transverse loads between brace points are applied to the top flange instead of at the shear centre. Although top-flange loading is commonplace, the load height effect can often be neglected due to lateral restraint provided by the loading mechanism itself; however, there are several common cases for which it must be considered in design. This paper provides the research background to the current provisions in CSA Standard S16 to account for the load height effect and proposes an effective length method that expands on these provisions to reduce their conservatism, while maintaining a simplicity appropriate for use in design. Employing a large and diverse database of steel shapes, the proposed method is compared with a comprehensive variety of other design approaches and available numerical and experimental data. [ABSTRACT FROM AUTHOR]

Single-storey braced steel frame buildings (SSBSFs) are currently the most widely used commercial structures, which include strip malls, power centres, warehouses, small and medium-sized industrial plants. The lateral seismic or wind forces acting on such low-rise structures are usually transferred from a metal roof-deck diaphragm to a system of vertical bracing members. Because these flexible roof diaphragms have a considerable effect on the dynamic response of SSBSFs during an earthquake, they also play an important role in the evaluation of the fundamental vibration period, a key parameter in determining the magnitude of the design seismic forces. It is therefore of utmost importance to reliably predict the fundamental period of SSBSFs. This paper presents the results of a four-year field measurement research project on the dynamic behaviour of SSBSFs. The goal of the project was to create a reliable database for the dynamic characteristics of SSBSFs (periods, mode shapes, and damping) and to find a relationship between them and the geometric parameters (height and plan dimensions). The field tests are described, along with the selected buildings and experimental setup. The measured fundamental periods are then compared to the National building code of Canada (NBCC) empirical equations. A statistical analysis of the data, based on different regression models, yielded new proposed building geometric parameters to be used in simple equations for the prediction of the fundamental period of SSBSFs. [ABSTRACT FROM AUTHOR]

The strength of a slender section is governed by local buckling of its elements. The local buckling mode is mainly affected by the width to thickness ratios of elements forming the section and the member slenderness ratio. A nonlinear finite element model was developed in this paper to study the effect of the mentioned factors on the capacity of biaxially loaded slender I-section beam–columns. A group of I sections was selected with varying flange width to flange thickness and web width to web thickness ratios. Different member slenderness ratios were chosen to study the different modes of failure. The results show that the linear interaction equation is safe and provides a good fit to the ultimate capacity of members with intermediate slenderness ratios. It is conservative, however, for short member slenderness ratios. Lastly, compared with the newly developed finite element model, the 1996 edition of the American Iron and Steel Institute specification for cold-formed steel structural members and the European Committee for Standardization Eurocode 3 conservatively predict the capacity of members, especially for large ratios of minor axis to major axis bending. [ABSTRACT FROM AUTHOR]

This paper describes the behaviour of axially loaded short and long square hollow structural section (HSS) columns, strengthened with carbon fibre reinforced polymer (CFRP) sheets. Twenty-seven short-column and five long-column HSS specimens were tested. The effect of CFRP sheet orientation in the longitudinal and transverse directions was studied for short columns. For long columns, CFRP sheets were oriented in the longitudinal direction only. A maximum strength gain of 18% was achieved for short columns with two transverse CFRP layers. For long columns, the maximum strength gain of 23% was achieved with three longitudinal CFRP layers applied on four sides. In all CFRP-strengthened long columns, lateral deflections were reduced. Strength gain in long columns was highly dependent on the column's imperfection. As such, no correlation was established between strength gain and number of CFRP layers. CAN/CSA 16-01 equation was modified to account for CFRP through transformed section analysis so that they could be used to predict the axial-load capacity of long columns. [ABSTRACT FROM AUTHOR]

This paper presents an analytical approach for predicting the length limits of integral bridges built on cohesive soils based on the flexural strength of the abutments and the low cycle fatigue performance of the steel H-piles at the abutments under cyclic thermal loading. First, H-piles that can accommodate large inelastic deformations are determined considering their local buckling instability. Then, a damage model is used to determine the maximum cyclic deformations that such piles can sustain. Next, nonlinear static pushover analyses of typical integral bridges subjected to cyclic thermal variations are conducted to study the effect of various geometric, structural, and geotechnical parameters on their performance. Equations are derived by using the analyses results to determine the maximum length limits of integral bridges built on cohesive soils. It is found that the maximum length limits of integral bridges is affected by the stiffness of the deck, height of the abutment, properties, and orientation of the piles as well as stiffness of the cohesive soils. [ABSTRACT FROM AUTHOR]

This paper describes the seismic behaviour of chevron steel braced frames for 2-, 4-, 8-, and 12-storey steel building structures. Two different design approaches were considered: one that corresponds to current CSA-S16.1 seismic provisions for braced frames with nominal ductility with an R factor of 2.0, and one in which the beams are sized to develop a fraction of the yield tension capacity of the bracing members. In this second approach, an R factor of 3.0 was used for determining the seismic loads and chevron bracing with stronger beams capable of developing 100%, 80%, and 60% of the brace yield load were examined. The results show that current S16.1 provisions for chevron braced frames may lead to systems that are prone to dynamic instability for 4-storey and taller structures. Chevron bracing with stronger beams exhibits a more stable inelastic response and can be used for structures up to 8 storeys in height. For 2- and 4-storey buildings, chevron braced frames with beams designed to develop only 60% of the brace yield resistance can be used. The analyses also show that the force demand in brace connections, beams, and columns as determined from capacity design provisions agree well with that anticipated under strong ground motions.Key words: earthquakes, seismic design, steel, structures, braced frames, bracing members, beams, columns, connections.Cet article décrit le comportement sismique de contreventements en treillis avec diagonales en chevron utilisés dans la charpente d'acier de bâtiments de 2, 4, 8 et 12 étages. Deux approches de conception ont été considérées : l'une qui suit les dispositions actuelles de la norme CSA S16.1 pour les contreventements à ductilité nominale et l'autre où les poutres sont conçues pour résister aux efforts engendrés lorsque l'effort dans la diagonale tendue atteint une fraction de sa limite élastique. Pour la seconde méthode, on a considéré un coefficient R égal à 3,0 pour le calcul des charges sismiques et on a étudié des contreventements dont les poutres pouvaient reprendre des efforts correspondant à un effort dans les diagonales tendues égal à 100%, 80% et 60% de leur limite élastique. Les résultats montrent que les contreventements de 4 étages et plus peuvent subir de grandes déformations latérales et être sujets à une instabilité dynamique lorsque conçus selon la norme S16.1 actuelle. Les contreventements avec poutres pouvant soutenir la plastification des diagonales tendues ont un comportement plus stable et peuvent être utilisés dans des structures jusqu'à 8 étages. Pour des bâtiments de 2 et 4 étages, on peut utiliser des poutres conçues pour un effort dans les diagonales tendues égal à 60% de leur résistance plastique. Les analyses dynamiques démontrent également que les efforts dans les assemblages des diagonales, dans les poutres et dans les poteaux tels, qu'obtenus d'un calcul par capacité, correspondent bien aux efforts que l'on peut anticiper lors d'un séisme important.Mots clés : séismes, conception parasismique, acier, structures, contreventements en treillis, diagonales, poutres, poteaux, assemblages. [ABSTRACT FROM AUTHOR]