Robert Korol

McMaster University | McMaster · Department of Civil Engineering

Research into the post-buckling behavior of columns has typically been undertaken to establish safe design standards for compressive resistance rather than to evaluate the potential energy dissipation capacity under conditions of collapse. However, extreme events, such as very hot fires or acts of terrorism may require structural engineers to ascer...

The purpose of the paper is to investigate the extent to which present-day design of steel framed buildings is susceptible to total collapse when subjected to extreme fire events. We select a 50 storey structure in which 2 and 4 adjacent storeys located at different above-ground heights are, in separate scenarios engulfed in raging fires. A total o...

On September 11, 2001, the world witnessed the total collapse of three large steel-framed high-rises. Since then, scientists and engineers have been working to understand why and how these unprecedented structural failures occurred.

Although the events of that tragic day happened 14 years ago, there remain nagging questions of why the 47 storey WTC 7 steel framed structure collapsed, when it was NOT hit by an airplane. We will review the official rationale of how the collapse events started, and why, in our opinion, the explanation is judged to be wrong. Then, we will proceed...

This paper experimentally investigates the energy absorption potential of two types of concrete floors, namely, normal density concrete and structural low-density concrete, containing secondary (shrinkage and temperature) reinforcements. The test program considered the following secondary reinforcements: 1) traditional welded-wire steel mesh, 2) st...

This paper investigates the energy dissipation potential of axially loaded columns and evaluates the use of a plastic hinge model for analysis of hi-rise building column collapse under extreme loading conditions. The experimental program considered seven axially loaded H-shaped extruded aluminum structural section columns having slenderness ratios...

This paper investigates the energy absorption potential offered by light weight concrete (LWC) floors, perhaps when a building is poised to collapse from some extreme loading event. It is assumed here that the failure of LWC structural floor slabs would likely result in both break-up and pulverization of the concrete. To estimate the extent to whic...

Until recently, the progression and time of collapse of structures has not been a prima ry objective of the structural engineering profession. However, such events are likely to be of ma jor interest in high rise building situations where a fire-initiated failure takes place, or where a controlled demolition is to be im plemented. The paper attempt...

A series of tests on W-shaped beam-to-column connections subjected to quasi-static cyclic loading was conducted to assess their ductility and energy dissipation capabilities. The specimens represent beams in ductile moment resisting frames undergoing alternating lateral loads. The aim of this study was to assess and compare the rotation capacity an...

Extended end-plate connections have been widely used in moment-resisting steel frames with W-shape columns, due to their sufficient stiffness and moment capacity. In addition, such connections are easy to install and permit good quality control. Extended end-plate connections can also be employed in moment-resisting frames with hollow structural se...

Ultra-twist blind fasteners were developed for connecting tube members where access for installation is from one side of the connection only. They offer many advantages, including strengths and sizes comparable to A325 bolts, potential use in tension as well as in moment-resisting connections, and ease of installation. Reliability-based analyses ar...

A research program was undertaken to study the shear-lag phenomenon for slotted hollow structural section (HSS) tension members having gusset plates welded at the ends, a commonly employed detail in braced frame construction. The purpose of this study was to establish whether the shear-lag reduction factor indeed involves only the weld length to we...

This paper presents the results attained in an extensive research programme on Vierendeel joints in hollow structural sections (HSS). A total of 29 specimens comprised of five distinct connection types were tested and their strength and stiffness properties were recorded.As most of the joints tested behaved in a semi-rigid manner, a stiffness metho...

A theoretical analysis has been undertaken for unequal width T-joints, haunch-reinforced, in square hollow structural sections (HSS). The unreinforced joint is merely a special case. The theory was based on a finite difference solution to the elastic chord flange plate equation and predicts the branch-to-chord joint stiffnesses under both bending a...

A new concept utilizing double-chord square hollow sections in welded K-joints of Warren trusses is described. The experimental results of 29 tests are reported, including four connection types: standard, channel, bolted, and back-to-back. The latter type comprised gapped, overlapped, and gapped with connecting stiffener plates.The results indicate...

An ultimate strength theory is developed for double chord rectangular hollow section (RHS) K-joints that accounts for both perfectly plastic and strain hardening material characteristics. The parameters that are investigated are chord depth–width ratio, eccentricity, chord preloading, and diagonal–chord angle. Interaction curves are presented that...

The carrying capacity of square hollow structural section T-joints stiffened by a rectangular flange plate is investigated for both branch bending moment and punching shear. The ultimate moment or load is determined from the simple yield line method of which one of three failure modes is applicable depending on the plate length. A large number of c...

The results of a series of five large scale experiments on Warren trusses comprised of square HSS and utilizing the concept of a double chord are presented. The trusses were simply supported and loaded at their top chord panel points, thus simulating gravity loading. It was found that the bolted type, the back-to-back with overlap configuration, an...

Predictions from a previously developed analytical model that takes into account plastic hinging action and includes the effects of axial load and moment interaction are compared with the results of tests on double chord RHS trusses. The model incorporates a shear spring mechanism that is applicable to gap joints of HSS trusses. Load–displacement c...

The degree of geometrical imperfections existing in the plate panels of six in situ steel box girder bridges located throughout Canada is reported. The purpose of a continuing investigation is to establish the extent to which strength and performance of Canadian box girders in multispan bridges are sensitive to imperfections. The 95% fractiles obta...

A plastic failure model that is based on the yield line theory of plates is developed to provide a means for predicting the plastic strength of double chord RHS K-joints with separated chords. The model accounts for both localized bending of the chord face and shearing of its inner and outer walls in the gap between the mated diagonals.The results...

An investigation to determine the magnitude of geometric imperfections induced during the fabrication of welded steel box girders is reported for nine highway bridges constructed in Canada. Measurement data were collected to compare the significance of dead load on initial imperfections obtained following fabrication. Existing bridges were found to...

As part of a major study, an experimental box girder having nominally identical cantilever sections was constructed to model the geometry of a pier girder of the Hunt Club–Rideau Bridge structure in Ottawa. The one-fourth scale model did not, however, replicate the varying depth of the prototype. The objective was to determine whether a deliberate...

Conical steel vessels, having an upper cylindrical section and supported by a reinforced concrete shaft, are becoming widely used for water containment in elevated tanks. However, the current codes of practice for water structures in North America do not include any rational method for designing such vessels. In this study, a simple and rational de...

Conical steel tanks having cylindrical upper section caps are widely used as containment vessels for elevated water tower structures. The work presented in this paper was motivated by the collapse of an elevated conical shaped water tower structure in Fredericton, Canada, in December 1990 and also by the fact that the current standards for water st...

The aim of this investigation is to study the effect of different imperfection shapes on the inelastic stability of liquid-filled conical tanks and to determine the critical imperfection shape that would lead to the minimum inelastic limit load. The study is carried out numerically using a self-developed shell element used to simulate a number of c...

Conical steel shells are widely used as water containments for elevated tanks. However, the current codes for design of water structures do not specify any procedure for handling the seismic design of such structures. In this paper, a numerical model is developed for studying the stability of liquid-filled conical tanks subjected to seismic loading...

In this paper, the numerical model developed in the previous paper is used to study the seismic performance of elevated liquid-filled steel conical tanks. A number of conical tanks which are classified as tall or broad tanks according to the ratio of the tank radius to its height are considered. The consistent shell element is used to model the tan...

The work presented in this paper was motivated by the collapse of an elevated conical shaped water tower structure in Fredericton, Canada, in December of 1990. It is analytically based and involves nonlinear stability analysis of liquid-filled conical steel vessels possessing geometric imperfections and residual stresses. A finite-element formulati...

The superior performance of the consistent shell element in the small deflection range has encouraged the authors to extend the formulation to large displacement static and dynamic analyses. The nonlinear extension is based on a total Lagrangian approach. A detailed derivation of the non-linear extension is based on a total Lagrangian approach. A d...

Typical extended end-plate connections used in moment resisting steel frames with Hollow Structural Section (HSS) columns will generally exhibit a certain degree c f flexibility. The actual response of such frames cannot be realistically assessed, unless the connection flexibility is incorporated in the analysis. This requires the development of mo...

This paper initially reviews some of the concepts used in damage assessment; simple damage parameters such as the ductility ratio and realistic mathematical models that reflect the deterioration of steel beams as a consequence of maximum response and dissipated energy are then discussed. Damage models are then presented that use the maximum respons...

An approach which allows for the prediction of the initiation of local buckling in the design of W-shaped beams under steep moment gradient, is presented in this paper. The method described represents a refined moment-rotation model that includes the effects of strain hardening. This same approach helps define more accurately the slenderness limits...

The behaviour of moment-resisting steel frames under various types of loads is dependent on the type of beam-to-column connections and their flexibilities. The extended end-plate connection is a practical field bolted moment connection that can be adopted in moment-resisting steel frames with hollow structural steel (HSS) columns, by using high str...

The results of a series of ten W-shaped test specimens subjected to monotonic, quasi-static cyclic loading and fatigue type of loading in the form of constant amplitude tests are presented. The objectives were to assess and compare the rotation capacity and energy absorption of monotonically and cyclically loaded beams, and for the latter specimens...

The concept of sustainable development has been widely discussed in a number of forums throughout the world. Recent developments, such as the creation of the World Engineering Partnership for Sustainable Development, will greatly aid in advancing the underlying concept beyond the conceptual stage through to the development of practical approaches t...

During a severe earthquake, steel moment resisting frames are expected to experience significant inelastic deformation in their members and joints. This behaviour is dependent upon several design parameters such as member sizes, frame's overstrength, member deformation capacities and the detailing of components. In this study, the influence of such...

Structural frames designed or proportioned to resist seismic forces must possess adequate ductility to redistribute internal forces or have needed energy absorbing capability. This paper addresses the interaction effects of a steel member's plate slenderness values and its lateral slenderness on rotation capacity. It is shown that members with slen...

Connecting a W-shape beam to a hollow steel section (HSS) column using conventional bolts is difficult due to a lack of access inside the hollow section column to tighten the nut. Field welding the connection remains the common practice. The objective of this work is to propose a bolted moment connection for rectangular hollow steel columns using h...

This paper proposes the analytical models that are capable of predicting the yield strength of T-joints comprised of hollow square sections (HSS), utilizing the concept of double-chord under both direct compression and direct tension forces. Plastic failure mechanisms are suggested and the yield line theory is employed to estimate joints' yield str...

An analytical study was conducted to investigate the effect of joint flexibility, in particular extended end-plate joints, on the response of moment resisting frames. Eight storey frames having extended end-plate joints and with joints detailed according to different design criteria, were analysed for different earthquake records using a step-by-st...

Four tests are performed to investigate the cyclic behavior of beam-to-column subassemblages utilizing bolted extended end-plate joints. The tests are conducted by applying a constant axial load to the column while subjecting the beam to cyclic controlled displacement program. The overall behavior of the subassemblages is examined. In addition, the...

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This paper presents the results of an analytical study conducted to investigate the effects of extended end-plate joint deformation on the static and dynamic characteristics of moment resisting frames. eight-storey and twenty-storey frames designed with extended end-plate beam-to-column joints were analyzed when subjected to different earthquake re...

Testing of seven full-scale extended end plate beam to-column connections under cyclic loading was undertaken. A detailed analysis of the connections and that of their individual elements is presented. The performance of the connections is evaluated in terms of strength, stiffness and energy dissipation. Observations are reported in the context of...

The results of five tests on bolted end-plate beam-to-column connections are described. The specimens were subjected to cyclic loading simulating earthquake effects on a steel moment-resisting frame. The objective of the work is to determine the behaviour of this type of connection under cyclic loading well into the inelastic range and to ascertain...

A finite element elastic-plastic model for separated double chord gap K-joints of steel rectangular hollow sections (RHS), is presented. The model treats a single chord member as composed of a plate representing the inner web and a channel depicting the top and bottom flanges and the outer web, respectively. Triangular and rectangular flat shell el...

An elastic-strain hardening material characteristic is used with the finite element method to model the behavior of Vierendeel trusses that consist of flexible branch-to-chord connections. Both chord and branch members are presumed to be rectangular hollow sections (RHS) of unequal width. Analyses have been undertaken on truss configurations consis...

The importance of primary and secondary stresses on the strength of statically loaded triangulated trusses having rigid joints is reviewed. Support is given to the contention that accurate modelling of material properties and member end conditions is justified both for predicting overall failure loads and for assessing the sequencing through which...

A finite element elasto-plastic analysis of a twin shear beam model, developed to shed light on the behavior of separated double chord gap joints of rectangular hollow sections (RHS), is presented. The model treats a single beam member as composed of a plate simulating its inner web and a channel representing top and bottom flanges and the outer we...

In many applications for which planar tubular steel trusses are considered appropriate, chords consisting of double rectangular hollow sections (RHS) have several advantages over their single-chord counterparts. For unequal-width K- and T-type connections gapped between branch members, it is shown that the double-chord. configuration has frequently...

Elasto-plastic response of T-joints consisting of double chord, rectangular hollow sections (RHS) has been modelled by treating the chord's mated flanges as thin plates supported by coupled springs that simulate the action of the side walls and bottom flanges. Two loading conditions, namely, branch axial force and branch bending are analyzed. The f...

Not infrequently, a column segment within the a storey of a structural frame must be laterally displaced to accommodate the requirements of the users of a building. The ensuing beam-to-staggered column connection is the subject of this paper.Results are reported of an experimental programme of such connections consisting of square hollow section co...

There is a paucity of published work on the behavior of Vierendeel girders in the open literature; however, a considerable amount of effort has focussed on the strength and stiffness of T-joints, particularly involving rectangular hollow sections,(RHS) (Wardenier, 1982). This section is particularly well suited for Vierendeel applications since its...

A unified approach to inelastic finite element modelling of single and back-to-back, double chord rectangular hollow section (RHS) T-joints, shown in Figure 1, is presented in this paper. Switching from one type of T-joint to the other simply requires modifications of the boundary conditions. See Korol et al. (1977), Patel et al. (1973) and Korol a...

An analytical method is proposed and a computer program developed to analyze double chord trusses comprised of rectangular hollow sections. Three types of local yield mechanisms are incorporated: (1) Plastic hinge formation; (2) member yielding due to plastic load limit; and (3) yielding of shear springs that model the connections. The analysis is...

A linear elastic T-joint comprised of double chord RHS has been modelled by treating the mated flanges as thin plates supported by coupled linear springs thus simulating the action of the side walls and connecting bottom flanges. A rigid rectangular inclusion is presumed for the branch member. Two loading conditions are analyzed—branch member axial...

The finite element method is used to model the behavior of rectangular hollow section T-joints beyond the elastic limit, and is applied to determine their ultimate and working strengths. Punching shear and rotational stiffnesses under branch axial force and bending moment have also been calculated. The unreinforced and haunch type joints were analy...

The results of a series of 11 tests on single and two span circular hollow tubular beams are used to compare with inelastic bending and axial compression theories of buckling. Predictions of critical strain from both analyses exceed the values obtained from the experimental results, the bending critical stress being somewhat higher than that for ax...

A theoretical treatment of the buckling of moderately thick circular tubes subjected to pure bending is undertaken. Predictions are made to define ranges for D/t (diameter to thickness) within plastic design, compact, and noncompact categories. Nonlinear material behavior is modelled by Ramberg-Osgood idealization of the stress-strain relationship,...

A series of tests on beams of hollow structural sections is conducted to determine their adequacy in plastic design. A minimum plastic rotation requirement of law times the elastic limit rotation prior to unloading below the fully plastic moment is used to separate sections into categories of plastic and allowable stress design. Local buckling caus...

The effect of cold-bending wide sheet to a circular profile to form a component such as a light-gauge structural member is considered. The residual stresses created by this process followed by spring-back are known to influence subsequent behaviour of such a load-bearing member. A four-element model is described to portray the essential nature of a...

Conical steel vessels are commonly used as water containment for elevated tanks. One of the phenomena associated with the seismic response of liquid-filled tanks is the sloshing motion occurring at the top free surface. In this paper, a mathematical model is developed to predict the liquid sloshing frequencies and corresponding mode shapes of liqui...

Until recently, the progression and time of collapse of structures has not been a primary objective of the structural engineering profession. However, such events are likely to be of major interest in high rise building situations where a fire-initiated failure takes place, or where a controlled demolition is to be implemented. The paper attempts t...