This paper follows the evolution of beam-column design in the Canadian steel construction design standard S16, from simple strength considerations to the current strength and stability interaction equations. Because the design of columns is intrinsically related to the method of analysis, there is also consideration given to the advancement of analyses and stability theory over time, as well as changes in the design environment and tools available to the designer. A brief review of American and European design procedures is also included, and the current practise is examined. The general trend has been toward a more complex model of the beam-column behaviour being adapted into design. As objective design methods replace prescriptive design, there may be a return to earlier standards, where the designer is given more freedom in choosing the design method. While there has been considerable change, there are still aspects of the beam-column behaviour that are not considered in the design standards. This reflects the lack of understanding we have of beam-column behaviour. For example, beam-columns are still considered individually, rather than in the context of the frame of which they are members. This discounts the interaction of members in the frame, a phenomenon that is not yet well understood.
A simple alternative equation for the calculation of the strength of laterally unbraced structural steel beams is presented herein. This equation uses a format similar to the present steel column design curve in the Canadian structural steel design standard, CAN/CSA-S16-09, and is proposed as a replacement for the existing three part curve for beam strength by a one part equation with a continuous derivative. A reliability analysis of the new equation indicates that the equation provides safety levels very close to those of the current formula for classes 1 and 2 rolled sections. It also pro- vides the desired level of safety for welded beams, whereas the current equations tend to over-estimate their strength. The alternative equation also provides adequate safety for class 3 beams. The concept of maximum unbraced length for braced beam design (Lu) is revisited herein and a simple calculation for this length is also proposed.
Tests on full-scale connections between wide flange beams and rectangular hollow section (RHS) columns reveal various modes of failure as a function of connection geometry. Tension and compression moment plates with web clip angles or tension plates and seat angles welded to doubler plate reinforced RHS walls are investigated. Eight failure modes were identified from an experimental program consisting of ten full-scale specimens. Semi-empirical expressions based on assumed stress distributions predict failure modes and corresponding moment capacities reasonably well for various connection configurations. Further analytical parametric studies showed the importance of tension plate and doubler plate dimensions on joint strength and behaviour. Key words: RHS, W-shape, columns, beams, connections, experimental, analytical, design, steel.
In many truss joints consisting of double-angle web members welded to stems of inverted lower chord tee sections, adequate fillet weld lengths may be provided without the need for gusset plates. In such cases where a joint may also be subjected to high combinations of shear and tension, the possibility of overstressing of a tee stem exists. In the investigation of this problem, four analytical techniques, including two proposed herein, and experimental results of 30 full-scale specimen tests, 22 of which were conducted during the investigation presented herein, are presented and evaluated. Analytical and experimental results indicate that the interaction of shear and normal stresses is an important consideration in the design of such joints and that an interaction check is required.Of the many parameters investigated as part of the experimental investigation, the two that most significantly influence the magnitude of tension force that a lower chord can simultaneously carry are the magnitude of applied shear force averaged over the available web shear area and the joint configuration itself. The inclination of a diagonal web member as well as intentional joint eccentricities have little effect on the strength of these joints, although joint ductility appears to be affected by eccentricities.Although all four analytical techniques have similar overall accuracies of prediction, a method based on applying a von Mises criterion at ultimate to determine an equivalent shear area in a tee chord is recommended as being the most suitable. Based on this method, as verified and validated by comparison with extensive experimental results of tests on full-scale specimens, a simplified design curve and associated equations are developed and proposed for design office use. Key words: connection, interaction, shear, tension, welded, truss.
Shallow slides in cohesionless till occurred in several highway fills in the province of Quebec, Canada, following spring thaw and sometimes during rainy autumns. This study has shown that the strength parameters of cohesionless tills can be related to the liquid limit for both drained and undrained conditions. These relationships can be used as input in stability analyses to readily yield design values of stable slopes. Tills with liquid limits between 15% and 25% are all very susceptible to liquefaction flow failures if loosely compacted and saturated. To reduce the risk of shallow slides in the cohesionless till embankments used for highways, a stabilizing coarse-grained fill placed atop of the till embankment appears to be an efficient technique. Design charts of minimum thickness of the stabilizing fill at the base of the till slope were developed using available stability programs and an empirically derived strength of liquefied tills.Key words: cohesionless, till, liquefaction, stability, slope, skin.
